# YAZ User's Guide and Reference

Sebastian Hammer
Adam Dickmeiss
Mike Taylor
Heikki Levanto
Dennis Schafroth
Jakub Skoczen
&version;
©right-year; Index Data

This document is the programmer's guide and reference to the &yaz; package version &version;. &yaz; is a compact toolkit that provides access to the Z39.50 and SRU/Solr protocols, as well as a set of higher-level tools for implementing the server and client roles, respectively. The documentation can be used on its own, or as a reference when looking at the example applications provided with the package.

## Introduction

&yaz; is a C/C++ library for information retrieval applications using the Z39.50/SRU/Solr protocols for information retrieval.

Properties of &yaz;:

- Complete Z39.50 version 3 support. Amendments and Z39.50-2002 revision is supported.

- Supports SRU GET/POST/SOAP version 1.1, 1.2 and 2.0 (over HTTP and HTTPS).

- Includes BER encoders/decoders for the ISO ILL protocol.

- Supports Apache Solr Web Service version 1.4.x (client side only)

- Supports the following transports: BER over TCP/IP (RFC1729), BER over Unix local socket, and HTTP 1.1.

- Secure Socket Layer support using GnuTLS. If enabled, &yaz; uses HTTPS transport (for SOAP) or "Secure BER" (for Z39.50).

- Offers ZOOM C API implementing Z39.50, SRU and Solr Web Service.

- The &yaz; library offers a set of useful utilities related to the protocols, such as MARC (ISO2709) parser, CCL (ISO8777) parser, CQL parser, memory management routines, character set conversion.

- Portable code. &yaz; compiles out-of-the box on most Unixes and on Windows using Microsoft Visual C++.

- Fast operation. The C based BER encoders/decoders as well as the server component of &yaz; is very fast.

- Liberal license that allows for commercial use of &yaz;.

### Reading this Manual

Most implementors only need to read a fraction of the material in this manual, so a quick walk-through of the chapters is in order.

- contains installation instructions for &yaz;. You don't need to read this if you expect to download &yaz; binaries. However, the chapter contains information about how to make your application link with &yaz;.

- describes the ZOOM API of &yaz;. This is definitely worth reading if you wish to develop a Z39.50/SRU client.

- describes the generic front-end server and explains how to develop server Z39.50/SRU applications for &yaz;. Obviously worth reading if you're to develop a server.

- describes how to use the &yaz; Z39.50 client. If you're a developer and wish to test your server or a server from another party, you might find this chapter useful.

- documents the most commonly used Z39.50 C data structures offered by the &yaz; API. Client developers using ZOOM and non-Z39.50 implementors may skip this.

- describes how SRU and SOAP is used in &yaz;. Only if you're developing SRU applications this section is a must.

- contains sections for the various tools offered by &yaz;. Scan through the material quickly and see what's relevant to you! SRU implementors might find the CQL section particularly useful.

- goes through the details of the ODR module which is the work horse that encodes and decodes BER packages. Implementors using ZOOM only, do not need to read this. Most other Z39.50 implementors only need to read the first two sections ( and ).

- describes the network layer module COMSTACK. Implementors using ZOOM or the generic front-end server may skip this. Others, presumably, handling client/server communication on their own should read this.

### The API

The &yaz; toolkit offers several different levels of access to the ISO23950/Z39.50, ILL and SRU protocols. The level that you need to use depends on your requirements, and the role (server or client) that you want to implement. If you're developing a client application you should consider the ZOOM API. It is, by far, the easiest way to develop clients in C. Server implementors should consider the generic front-end server. None of those high-level APIs support the whole protocol, but they do include most facilities used in existing Z39.50 applications.

If you're using 'exotic' functionality (meaning anything not included in the high-level APIs), developing non-standard extensions to Z39.50 or you're going to develop an ILL application, you'll have to learn the lower level APIs of &yaz;.

The YAZ toolkit modules are shown in figure .

YAZ layers

There are four layers.

- A client or server application (or both). This layer includes ZOOM and the generic front-end server.

- The second layer provides a C representation of the protocol units (packages) for Z39.50 ASN.1, ILL ASN.1, SRU.

- The third layer encodes and decodes protocol data units to simple packages (buffer with certain length). The &odr; module encodes and decodes BER whereas the HTTP modules encodes and decodes HTTP requests/responses.

- The lowest layer is &comstack; which exchanges the encoded packages with a peer process over a network.

The &asn; module represents the ASN.1 definition of the Z39.50 protocol. It establishes a set of type and structure definitions, with one structure for each of the top-level PDUs, and one structure or type for each of the contained ASN.1 types. For primitive types, or other types that are defined by the ASN.1 standard itself (such as the EXTERNAL type), the C representation is provided by the &odr; (Open Data Representation) subsystem.

&odr; is a basic mechanism for representing an ASN.1 type in the C programming language, and for implementing BER encoders and decoders for values of that type. The types defined in the &asn; module generally have the prefix `Z_`, and a suffix corresponding to the name of the type in the ASN.1 specification of the protocol (generally Z39.50-1995). In the case of base types (those originating in the ASN.1 standard itself), the prefix `Odr_` is sometimes seen. Either way, look for the actual definition in either `z-core.h` (for the types from the protocol), `odr.h` (for the primitive ASN.1 types). The &asn; library also provides functions (which are, in turn, defined using &odr; primitives) for encoding and decoding data values. Their general form is int `z_xxx` ODR o Z_xxx **p int optional const char *name (note the lower-case "z" in the function name)

If you are using the premade definitions of the &asn; module, and you are not adding a new protocol of your own, the only parts of &odr; that you need to worry about are documented in .

When you have created a BER-encoded buffer, you can use the &comstack; subsystem to transmit (or receive) data over the network. The &comstack; module provides simple functions for establishing a connection (passively or actively, depending on the role of your application), and for exchanging BER-encoded PDUs over that connection. When you create a connection endpoint, you need to specify what transport to use (TCP/IP, SSL or UNIX sockets). For the remainder of the connection's lifetime, you don't have to worry about the underlying transport protocol at all - the &comstack; will ensure that the correct mechanism is used.

We call the combined interfaces to &odr;, &asn;, and &comstack; the service level API. It's the API that most closely models the Z39.50 service/protocol definition, and it provides unlimited access to all fields and facilities of the protocol definitions.

The reason that the &yaz; service-level API is a conglomerate of the APIs from three different sub-modules is twofold. First, we wanted to allow the user a choice of different options for each major task. For instance, if you don't like the protocol API provided by &odr;/&asn;, you can use SNACC or BERUtils instead, and still have the benefits of the transparent transport approach of the &comstack; module. Secondly, we realize that you may have to fit the toolkit into an existing event-processing structure, in a way that is incompatible with the &comstack; interface or some other part of &yaz;.

## Compilation and Installation

### Introduction

The latest version of the software will generally be found at:

We have tried our best to keep the software portable, and on many platforms, you should be able to compile everything with little or no changes.

The software is regularly tested on Debian GNU/Linux, CentOS, Ubuntu Linux, FreeBSD (i386), MAC OSX, Windows 10.

Some versions have be known to work on Windows XP, Solaris, HP/UX, DEC Unix, NetBSD, OpenBSD, IBM AIX, Data General DG/UX (with some CFLAGS tinkering), SGI/IRIX, DDE Supermax, Apple Macintosh (using the Codewarrior programming environment and the GUSI socket libraries), IBM AS/400 .

If you move the software to other platforms, we'd be grateful if you'd let us know about it. If you run into difficulties, we will try to help if we can, and if you solve the problems, we would be happy to include your fixes in the next release. So far, we have mostly avoided `#ifdefs` for individual platforms, and we'd like to keep it that way as far as it makes sense.

Use GitHub Discussions for questions and discussions about &yaz;. General questions and problems can be directed to .

### UNIX/macOS

We provide Debian GNU/Linux (i386 and amd64), Ubuntu (i386 and amd64) and CentOS (amd64 only) packages for &yaz;. You should be able to create packages for other CPUs by building them from the source package.

YAZ is also part of several packages repositories. Some of them are

- Solaris CSW:

- Solaris:

- FreeBSD:

- Debian:

- Ubuntu:

- NetBSD:

#### Compiling from source on Unix

You can choose to compile YAZ from official tar releases from or clone it via GitHub .

If you wish to use character set conversion facilities in &yaz; or if you are compiling &yaz; for use with Zebra, it is a good idea to ensure that the iconv library is installed. Some Unixes today already have it - if not, we suggest GNU libiconv.

YAZ 3.0.16 and later includes a wrapper for the ICU (International Components for Unicode). In order to use this, the developer version of the ICU library must be available. ICU support is recommended for applications such as Pazpar2 and Zebra.

The libxslt, libxml2 libraries are required if &yaz; is to support SRU/Solr. These libraries are very portable and should compile out-of-the box on virtually all Unix platforms. It is available in binary forms for Linux and others.

The GNU tools Autoconf, Automake and Libtool are used to generate Makefiles and configure &yaz; for the system. You do not need these tools unless you're using the Git version of &yaz;.

The CQL parser for &yaz; is built using GNU Bison. This tool is only needed if you're using the Git version of &yaz;.

&yaz; includes a tiny ASN.1 compiler. This compiler is written in Tcl. But as for Bison you do not need it unless you're using Git version of &yaz; or you're using the compiler to build your own codecs for private ASN.1.

If you are checking out from Git, run:

          ./buildconf.sh

This will create the `configure` script and Makefiles.

The next step is always:

         ./configure

The configure script attempts to use use the C compiler specified by the `CC` environment variable. If not set, GNU C will be used if it is available. The `CFLAGS` environment variable holds options to be passed to the C compiler. If you're using Bourne-compatible shell, you may pass something like this to use a particular C compiler with optimization enabled:

         CC=/opt/ccs/bin/cc CFLAGS=-O ./configure

To customize &yaz;, the configure script also accepts a set of options. The most important are:

`--prefix`=prefix

  Specifies installation prefix for &yaz;. This is only needed if you run `make install` later to perform a "system" installation. The prefix is `/usr/local` if not specified.

`--enable-tcpd`

  The front end server will be built using Wietse's TCP wrapper library. It allows you to allow/deny clients depending on IP number. The TCP wrapper library is often used in GNU/Linux and BSD distributions. See hosts_access 5 and tcpd 8 .

`--enable-threads`

  &yaz; will be built using POSIX threads. Specifically, `_REENTRANT` will be defined during compilation.

`--disable-shared`

  The make process will not create shared libraries (also known as shared objects `.so`). By default, shared libraries are created - equivalent to `--enable-shared`.

`--disable-shared`

  The make process will not create static libraries (`.a`). By default, static libraries are created - equivalent to `--enable-static`.

`--with-iconv`[=prefix]

  Compile &yaz; with iconv library in directory prefix. By default configure will search for iconv on the system. Use this option if it doesn't find iconv. Alternatively, `--without-iconv`, can be used to force &yaz; not to use iconv.

`--with-xslt`[=prefix]

  Compile &yaz; with libxslt in directory prefix. Use this option if you want XSLT and XML support. By default, configure will search for libxslt on the system. Use this option if libxslt is not found automatically. Alternatively, `--without-xslt`, can be used to force &yaz; not to use libxslt.

`--with-xml2`[=prefix]

  Compile &yaz; with libxml2 in directory prefix. Use this option if you want &yaz; to use XML and support SRU/Solr. By default, configure will search for libxml2 on the system. Use this option if libxml2 is not found automatically. Alternatively, `--without-xml2`, can be used to force &yaz; not to use libxml2.

  Note that option `--with-xslt` also enables libxml2.

`--with-gnutls`[=prefix]

  &yaz; will be linked with the GNU TLS libraries and an SSL COMSTACK will be provided. By default configure enables SSL support for YAZ if the GNU TLS development libraries are found on the system.

`--with-icu`[=prefix]

  &yaz; will be linked the ICU library in the prefix if given. If prefix is not given, the libraries exposed by the script icu-config will be used if found.

`--with-memcached`

  &yaz; will be linked with libMemcached to allow for result-set caching for ZOOM. The prefix can not be given. Note that 0.40 of libmemcached is required.

`--with-redis`

  &yaz; will be linked with the hiredis C library to allow for result-set caching for ZOOM on a redis server. The prefix can not be given.

When configured, build the software by typing:

          make

The following files are generated by the make process:

`src/libyaz.la`

  Main &yaz; library. This is no ordinary library. It's a Libtool archive. By default, &yaz; creates a static library in `lib/.libs/libyaz.a`.

`src/libyaz_server.la`

  Generic Frontend server. This is an add-on for libyaz.la. Code in this library uses POSIX threads functions - if POSIX threads are available on the platform.

`src/libyaz_icu.la`

  Functions that wrap the ICU library.

`ztest/yaz-ztest`

  Test Z39.50 server.

`client/yaz-client`

  Z39.50 client for testing the protocol. See chapter YAZ client for more information.

`util/yaz-config`

  A Bourne-shell script, generated by configure, that specifies how external applications should compile - and link with &yaz;.

`util/yaz-asncomp`

  The ASN.1 compiler for &yaz;. Requires the Tcl Shell, tclsh, in `PATH` to operate.

`util/yaz-iconv`

  This program converts data in one character set to another. This command exercises the YAZ character set conversion API.

`util/yaz-marcdump`

  This program parses ISO2709 encoded MARC records and prints them in line-format or XML.

`util/yaz-icu`

  This program exposes the ICU wrapper library if that is enabled for YAZ. Only if ICU is available this program is useful.

`util/yaz-url`

  This program is a simple HTTP page fetcher ala wget or curl.

`zoom/zoomsh`

  A simple shell implemented on top of the ZOOM functions. The shell is a command line application that allows you to enter simple commands to perform ZOOM operations.

`zoom/zoomtst1`, `zoom/zoomtst2`, ..

  Several small applications that demonstrate the ZOOM API.

If you wish to install &yaz; in system directories `/usr/local/bin`, `/usr/local/lib` .. etc, you can type:

         make install

You probably need to have root access in order to perform this. You must specify the `--prefix` option for configure if you wish to install &yaz; in other directories than the default `/usr/local/`.

If you wish to perform an un-installation of &yaz;, use:

         make uninstall

This will only work if you haven't reconfigured &yaz; (and therefore changed installation prefix). Note that uninstall will not remove directories created by make install, e.g. `/usr/local/include/yaz`.

#### Compiling from source on macOS

Install Apple's Xcode Command Line Tools (XCLT) package from Apple Developer which provides necessary tools for building C/C++ programs on macOS. You can also try to install it from the command line with:

             xcode-select --install

Out of the box, XCLT is sufficient for compiling basic &yaz; from the source distribution tarball with XML support as it includes libxml2 and libxslt development headers.

For ICU support, you can fetch Apple's source distribution from GitHub:

             git clone https://github.com/apple-oss-distributions/ICU.git

and compile &yaz; with:

             export ICU_CPPFLAGS="-DYAZ_HAVE_ICU=1 -I../../ICU/icu/icu4c/source/common -I../../ICU/icu/icu4c/source/i18n"
             export ICU_LIBS=" -licucore"
             ./configure
             make

For SSL support, &yaz; requires GnuTLS and cannot be compiled with LibreSSL/OpenSSL shipped with macOS (see below).

If you are compiling &yaz; from a Git checkout, at the time of writing XCLT includes GNU Bison v2.3 which is too old to generate &yaz; sources. You can use e.g. Homebrew to install a more recent version:

             brew install bison

After installation make sure to put it on the path:

             export PATH="/opt/homebrew/opt/bison/bin:$PATH"

Note: XCLT 15.4 fails to make `gm4` available as `m4` which can cause a silent Bison failure, one way to fix it is:

             sudo ln -s /Library/Developer/CommandLineTools/usr/bin/gm4 \
               /Library/Developer/CommandLineTools/usr/bin/m4

Additionally, you will need to install DocBook stylesheets to generate documentation:

             brew install docbook docbook-xsl

per the caveats section (`brew info docbook`), for the compilation to find them, add:

             export XML_CATALOG_FILES="/opt/homebrew/etc/xml/catalog"

To compile &yaz; with SSL support, install GnuTLS with:

             brew install gnutls

Homebrew makes GnuTLS discoverable by pkg-config, so no additional flags are needed when configuring &yaz;. You may also want to compile &yaz; with Homebrew's ICU:

             brew install icu4c

but make sure to add compiler flags before the configure stage, per the caveats section (`brew info icu4c`):

             export LDFLAGS="-L/opt/homebrew/opt/icu4c/lib"
             export CPPFLAGS="-I/opt/homebrew/opt/icu4c/include"
             export PKG_CONFIG_PATH="/opt/homebrew/opt/icu4c/lib/pkgconfig"

Additionally, if you want to compile &yaz; with a more recent version of libxml2 and libxslt, you can install them with Homebrew:

             brew install libxml2 libxslt

and, again, make sure to add compiler flags, per the caveats section (`brew info libxml2`):

             export PATH="/opt/homebrew/opt/bison/bin:\
             /opt/homebrew/opt/libxml2/bin:\
             /opt/homebrew/opt/libxslt/bin:\
             $PATH"
             export LDFLAGS="-L/opt/homebrew/opt/libxml2/lib \
             -L/opt/homebrew/opt/libxslt/lib \
             -L/opt/homebrew/opt/icu4c/lib"
             export CPPFLAGS="-I/opt/homebrew/opt/libxml2/include \
             -I/opt/homebrew/opt/libxslt/include \
             -I/opt/homebrew/opt/icu4c/include"
             export PKG_CONFIG_PATH="/opt/homebrew/opt/libxml2/lib/pkgconfig:\
             /opt/homebrew/opt/libxslt/lib/pkgconfig:\
             /opt/homebrew/opt/icu4c/lib/pkgconfig"

Then configure and conpile with:

             ./configure
             make

#### How to make apps using YAZ on UNIX

This section describes how to compile - and link your own applications using the &yaz; toolkit. If you're used to Makefiles this shouldn't be hard. As for other libraries you have used before, you need to set a proper include path for your C/C++ compiler and specify the location of &yaz; libraries. You can do it by hand, but generally we suggest you use the `yaz-config` that is generated by `configure`. This is especially important if you're using the threaded version of &yaz; which require you to pass more options to your linker/compiler.

The `yaz-config` script accepts command line options that makes the `yaz-config` script print options that you should use in your make process. The most important ones are: `--cflags`, `--libs` which prints C compiler flags, and linker flags respectively.

A small and complete `Makefile` for a C application consisting of one source file, `myprog.c`, may look like this:

          YAZCONFIG=/usr/local/bin/yaz-config
          CFLAGS=`$(YAZCONFIG) --cflags`
          LIBS=`$(YAZCONFIG) --libs`
          myprog: myprog.o
             $(CC) $(CFLAGS) -o myprog myprog.o $(LIBS)

The CFLAGS variable consists of a C compiler directive that will set the include path to the parent directory of `yaz`. That is, if &yaz; header files were installed in `/usr/local/include/yaz`, then include path is set to `/usr/local/include`. Therefore, in your applications you should use

          #include <yaz/proto.h>

and not

          #include <proto.h>

For Libtool users, the `yaz-config` script provides a different variant of option `--libs`, called `--lalibs` that returns the name of the Libtool archive(s) for &yaz; rather than the ordinary ones.

For applications using the threaded version of &yaz;, specify `threads` after the other options. When `threads` is given, more flags and linker flags will be printed by `yaz-config`. If our previous example was using threads, you'd have to modify the lines that set `CFLAGS` and `LIBS` as follows:

          CFLAGS=`$(YAZCONFIG) --cflags threads`
          LIBS=`$(YAZCONFIG) --libs threads`

There is no need specify POSIX thread libraries in your Makefile. The `LIBS` variable includes that as well.

### Windows

The easiest way to install YAZ on Windows is by downloading an installer from Index Data's Windows support area . The installer comes with source too - in case you wish to compile YAZ with different compiler options, etc.

#### Compiling from Source on Windows

&yaz; is shipped with "makefiles" for the NMAKE tool that comes with Microsoft Visual Studio. It has been tested with Microsoft Visual Studio 2019 and 2022.

Start a command prompt and switch the sub directory `WIN` where the file `makefile` is located. Customize the installation by editing the `makefile` file (for example by using notepad). The following summarizes the most important settings in that file:

`DEBUG`

  If set to 1, the software is compiled with debugging libraries (code generation is multi-threaded debug DLL). If set to 0, the software is compiled with release libraries (code generation is multi-threaded DLL).

`HAVE_TCL`, `TCL`

  If `HAVE_TCL` is set to 1, nmake will use the ASN.1 compiler (Tcl based). You must set `TCL` to the full path of the Tcl interpreter. A Windows version of Tcl is part of Git for Windows.

  If you do not have Tcl installed, set `HAVE_TCL` to 0.

`HAVE_BISON`, `BISON`

  If GNU Bison is present, you might set `HAVE_BISON` to 1 and specify the Bison executable in `BISON`. Bison is only required if you use the Git version of YAZ or if you modify the grammar for CQL (`cql.y`).

  A Windows version of GNU Bison can be fetched from here: Index Data's Windows support area .

`HAVE_ICONV`, `ICONV_DIR`

  If `HAVE_ICONV` is set to 1, YAZ is compiled with iconv support. In this configuration, set `ICONV_DIR` to the iconv source directory.

`HAVE_LIBXML2`, `LIBXML2_DIR`

  If `HAVE_LIBXML2` is set to 1, YAZ is compiled with SRU support. In this configuration, set `LIBXML2_DIR` to the libxml2 source directory.

  You can get pre-compiled Libxml2+Libxslt DLLs and headers from here. Should you with to compile those libraries yourself, refer to to

`HAVE_LIBXSLT`, `LIBXSLT_DIR`

  If `HAVE_LIBXSLT` is set to 1, YAZ is compiled with XSLT support. In this configuration, set `LIBXSLT_DIR` to the libxslt source directory.

  libxslt depends on libxml2.

`HAVE_ICU`, `ICU_DIR`

  If `HAVE_ICU` is set to 1, YAZ is compiled with ICU support. In this configuration, set `ICU_DIR` to the ICU source directory.

  Pre-compiled ICU libraries for various versions of Visual Studio can be found here or from Index Data's Windows support site.

When satisfied with the settings in the makefile, type

          nmake

If the `nmake` command is not found on your system you probably haven't defined the environment variables required to use that tool. To fix that, find and run the batch file `vcvarsall.bat`. You need to run it from within the command prompt or set the environment variables "globally"; otherwise it doesn't work.

If you wish to recompile &yaz; - for example if you modify settings in the `makefile` you can delete object files, etc by running.

          nmake clean

The following files are generated upon successful compilation:

`bin/yaz&soversion;.dll` / `bin/yaz&soversion;d.dll`

  &yaz; Release/Debug DLL.

`lib/yaz&soversion;.lib` / `lib/yaz&soversion;d.lib`

  Import library for `yaz&soversion;.dll` / `yaz&soversion;d.dll`.

`bin/yaz_cond&soversion;.dll` / `bin/yaz_cond&soversion;d.dll`

  Release/Debug DLL for condition variable utilities (condvar.c).

`lib/yaz_cond&soversion;.lib` / `lib/yaz_cond&soversion;d.lib`

  Import library for `yaz_cond&soversion;.dll` / `yaz_cond&soversion;d.dll`.

`bin/yaz_icu&soversion;.dll` / `bin/yaz_icu&soversion;d.dll`

  Release/Debug DLL for the ICU wrapper utility. Only build if HAVE_ICU is 1.

`lib/yaz_icu&soversion;.lib` / `lib/yaz_icu&soversion;d.lib`

  Import library for `yaz_icu&soversion;.dll` / `yaz_icu&soversion;d.dll`.

`bin/yaz-ztest.exe`

  Z39.50 multi-threaded test/example server. It's a WIN32 console application.

`bin/yaz-client.exe`

  &yaz; Z39.50 client application. It's a WIN32 console application. See chapter YAZ client for more information.

`bin/yaz-icu.exe`

  This program exposes the ICU wrapper library if that is enabled for YAZ. Only if ICU is available this program is built.

`bin/zoomsh.exe`

  Simple console application implemented on top of the ZOOM functions. The application is a command line shell that allows you to enter simple commands to perform ZOOM operations.

`bin/zoomtst1.exe`, `bin/zoomtst2.exe`, ..

  Several small applications that demonstrate the ZOOM API.

#### How to make apps using YAZ on Windows

This section will go though the process of linking your Windows applications with &yaz;.

Some people are confused by the fact that we use the nmake tool to build &yaz;. They think they have to do that too - in order to make their Windows applications work with &yaz;. The good news is that you don't have to. You can use the integrated environment of Visual Studio if desired for your own application.

When setting up a project or Makefile you have to set the following:

include path

  Set it to the `include` directory of &yaz;.

import library `yaz&soversion;.lib`

  You must link with this library. It's located in the sub directory `lib` of &yaz;. If you want to link with the debug version of &yaz;, you must link against `yaz&soversion;d.lib` instead.

dynamic link library `yaz&soversion;.dll`

  This DLL must be in your execution path when you invoke your application. Specifically, you should distribute this DLL with your application.

#### Compiling Libxml2 and Libxslt on windows

Download libxml2 and Libxslt source and unpack it. In the example below we install Libxml2 2.9.2 and Libxslt 1.1.28 for 32-bit, so we use the destination directories libxml2.2.9.2.win32 and libxslt-1.1.28.win32 to reflect both version and architecture.

          cd win32
          cscript configure.js prefix=c:\libxml2-2.9.2.win32 iconv=no
          nmake
          nmake install

There's an error in `configure.js` for Libxml2 2.9.2. Line 17 should be assigned to `configure.ac` rather than `configure.in`.

For Libxslt it is similar. We must ensure that compilation of Libxslt links against the already installed libxml2.

          cd win32
          cscript configure.js prefix=c:\libxslt-1.1.28.win32 iconv=no \
              lib=c:\libxml2-2.9.2.win32\lib \
    	  include=c:\libxml2-2.9.2.win32\include\libxml2
          nmake
          nmake install

## ZOOM

&zoom; is an acronym for 'Z39.50 Object-Orientation Model' and is an initiative started by Mike Taylor (Mike is from the UK, which explains the peculiar name of the model). The goal of &zoom; is to provide a common Z39.50 client API not bound to a particular programming language or toolkit.

From YAZ version 2.1.12, SRU is supported. You can make SRU ZOOM connections by specifying scheme `http://` for the hostname for a connection. The dialect of SRU used is specified by the value of the connection's `sru` option, which may be SRU over HTTP GET (`get`), SRU over HTTP POST (`post`), (SRU over SOAP) (`soap`) or `solr` (Solr Web Service). Using the facility for embedding options in target strings, a connection can be forced to use SRU rather the SRW (the default) by prefixing the target string with `sru=get,`, like this: `sru=get,http://sru.miketaylor.org.uk:80/sru.pl`

Solr protocol support was added to YAZ in version 4.1.0, as a dialect of a SRU protocol, since both are HTTP based protocols.

The lack of a simple Z39.50 client API for &yaz; has become more and more apparent over time. So when the first &zoom; specification became available, an implementation for &yaz; was quickly developed. For the first time, it is now as easy (or easier!) to develop clients as it is to develop servers with &yaz;. This chapter describes the &zoom; C binding. Before going further, please reconsider whether C is the right programming language for the job. There are other language bindings available for &yaz;, and still more are in active development. See the ZOOM web-site for more information.

In order to fully understand this chapter you should read and try the example programs `zoomtst1.c`, `zoomtst2.c`, .. in the `zoom` directory.

The C language misses features found in object oriented languages such as C++, Java, etc. For example, you'll have to manually, destroy all objects you create, even though you may think of them as temporary. Most objects have a `_create` - and a `_destroy` variant. All objects are in fact pointers to internal stuff, but you don't see that because of typedefs. All destroy methods should gracefully ignore a `NULL` pointer.

In each of the sections below you'll find a sub section called protocol behavior, that describes how the API maps to the Z39.50 protocol.

### Connections

The Connection object is a session with a target.

        #include <yaz/zoom.h>

        ZOOM_connection ZOOM_connection_new(const char *host, int portnum);

        ZOOM_connection ZOOM_connection_create(ZOOM_options options);

        void ZOOM_connection_connect(ZOOM_connection c, const char *host,
                                     int portnum);
        void ZOOM_connection_destroy(ZOOM_connection c);

Connection objects are created with either function `ZOOM_connection_new` or `ZOOM_connection_create`. The former creates and automatically attempts to establish a network connection with the target. The latter doesn't establish a connection immediately, thus allowing you to specify options before establishing network connection using the function `ZOOM_connection_connect`. If the port number, `portnum`, is zero, the `host` is consulted for a port specification. If no port is given, 210 is used. A colon denotes the beginning of a port number in the host string. If the host string includes a slash, the following part specifies a database for the connection.

You can prefix the host with a scheme followed by colon. The default scheme is `tcp` (Z39.50 protocol). The scheme `http` selects SRU/SOAP over HTTP by default, but can be changed with option sru.

You can prefix the scheme-qualified host-string with one or more comma-separated `key=value` sequences, each of which represents an option to be set into the connection structure before the protocol-level connection is forged and the initialization handshake takes place. This facility can be used to provide authentication credentials, as in host-strings such as: `user=admin,password=halfAm4n,tcp:localhost:8017/db`

Connection objects should be destroyed using the function `ZOOM_connection_destroy`.

        void ZOOM_connection_option_set(ZOOM_connection c,
                                        const char *key, const char *val);

        void ZOOM_connection_option_setl(ZOOM_connection c,
                                         const char *key,
                                         const char *val, int len);

        const char *ZOOM_connection_option_get(ZOOM_connection c,
                                               const char *key);
        const char *ZOOM_connection_option_getl(ZOOM_connection c,
                                                const char *key,
                                                int *lenp);

The functions `ZOOM_connection_option_set` and `ZOOM_connection_option_setl` allows you to set an option given by key to the value value for the connection. For `ZOOM_connection_option_set`, the value is assumed to be a 0-terminated string. Function `ZOOM_connection_option_setl` specifies a value of a certain size (len).

Functions `ZOOM_connection_option_get` and `ZOOM_connection_option_getl` returns the value for an option given by key.

ZOOM Connection Options

Option | Description | Default
--- | --- | ---
implementationName | Name of your client | none
user | Authentication user name | none
group | Authentication group name | none
password | Authentication password. | none
authenticationMode | How authentication is encoded. | basic
host | Target host. This setting is "read-only". It's automatically set internally when connecting to a target. | none
proxy | Proxy host. If set, the logical host is encoded in the otherInfo area of the Z39.50 Init PDU with OID 1.2.840.10003.10.1000.81.1. | none
clientIP | Client IP. If set, is encoded in the otherInfo area of a Z39.50 PDU with OID 1.2.840.10003.10.1000.81.3. Holds the original IP addresses of a client. Is used if ZOOM is used in a gateway of some sort. | none
timeout | Idle timeout which specifies how long ZOOM will wait for network I/O before giving up. Thus, the actual waiting time might be longer than this value if the target makes a chunked response and the time between each chunk arrive is less this value. For the connect+init, this is the time ZOOM will wait until receiving first byte from Init response. | 30
async | If true (1) the connection operates in asynchronous operation which means that all calls are non-blocking except `ZOOM_event`. | 0
maximumRecordSize | Maximum size of single record. | 1 MB
preferredMessageSize | Maximum size of multiple records. | 1 MB
lang | Language for negotiation. | none
charset | Character set for negotiation. | none
rpnCharset | Client-side character conversion for RPN queries and scan terms. The input terms are converted from UTF-8 to the character set of rpnCharset. | none (no conversion)
serverImplementationId | Implementation ID of server. (The old targetImplementationId option is also supported for the benefit of old applications.) | none
targetImplementationName | Implementation Name of server. (The old targetImplementationName option is also supported for the benefit of old applications.) | none
serverImplementationVersion | Implementation Version of server. (The old targetImplementationVersion option is also supported for the benefit of old applications.) | none
databaseName | One or more database names separated by character plus (`+`), which is to be used by subsequent search requests on this Connection. | Default
piggyback | True (1) if piggyback should be used in searches; false (0) if not. | 1
smallSetUpperBound | If hits is less than or equal to this value, then target will return all records using small element set name | 0
largeSetLowerBound | If hits is greater than this value, the target will return no records. | 1
mediumSetPresentNumber | This value represents the number of records to be returned as part of a search when hits is less than or equal to large set lower bound and if hits is greater than small set upper bound. | 0
smallSetElementSetName | The element set name to be used for small result sets. | none
mediumSetElementSetName | The element set name to be used for medium-sized result sets. | none
init_opt_search, init_opt_present, init_opt_delSet, etc. | After a successful Init, these options may be interrogated to discover whether the server claims to support the specified operations. | none
sru | SRU/Solr transport type. Must be either `soap`, `get`, `post`, or `solr`. | `soap` if scheme is already `http`; ignored otherwise
sru_version | SRU/SRW version. Should be `1.1`, or `1.2`. This is, prior to connect, the version to offer (highest version). And following connect (in fact first operation), holds the negotiated version with the server (same or lower version). | 1.2
extraArgs | Extra arguments for SRU/Solr URLs. The value must be URL encoded already. |
facets | Requested or recommended facets may be given before a search is sent. The value of this setting is described in For inspection of the facets returned, refer to the functions described in . | none
apdulog | If set to a true value such as "1", a log of low-level protocol packets is emitted on standard error stream. This can be very useful for debugging. | 0
saveAPDU | If set to a true value such as "1", a log of low-level protocol packets is saved. The log can be retrieved by reading option APDU. Setting saveAPDU always has the side effect of resetting the currently saved log. This setting is write-only. If read, NULL will be returned. It is only recognized in `ZOOM_connection_option_set`. | 0
APDU | Returns the log of protocol packets. Will be empty if logging is not enabled (see saveAPDU above). This setting is read-only. It is only recognized if used in call to `ZOOM_connection_option_get` or `ZOOM_connection_option_getl`. |
memcached | If given and non-empty, libMemcached will be configured for the connection. This option is inspected by ZOOM when a connection is established. If the `memcached` option is given and YAZ is compiled without libMemcached support, an internal diagnostic (10018) will be thrown. libMemcached support is available for YAZ 5.0.13 or later. If this option is supplied for an earlier version of YAZ, it is ignored. The value of this option is a list options - each is of the form `--name=value`. Option `--server=`host[:port] specifies a memcached server. It may be repeated for multiple memcached servers. Option `--expire=`seconds sets expiry time in seconds for how long result sets are to be cached. | none
redis | If given and non-empty, a redis context will be created for the connection. This option is inspected by ZOOM when a connection is established. If the `redis` option is given and YAZ is compiled without redis support, an internal diagnostic (10018) will be thrown. redis support is available for YAZ 5.2.0 or later. If this option is supplied for an earlier version of YAZ, it is ignored. The value of this option is a set of options, similar to that of the memcached setting. At this stage only --server=host[:port] and --expire=seconds are supported. | none

If either option `lang` or `charset` is set, then Character Set and Language Negotiation is in effect.

         int ZOOM_connection_error(ZOOM_connection c, const char **cp,
                                   const char **addinfo);
         int ZOOM_connection_error_x(ZOOM_connection c, const char **cp,
                                     const char **addinfo, const char **dset);

Function `ZOOM_connection_error` checks for errors for the last operation(s) performed. The function returns zero if no errors occurred; non-zero otherwise indicating the error. Pointers cp and addinfo holds messages for the error and additional-info if passed as non-`NULL`. Function `ZOOM_connection_error_x` is an extended version of `ZOOM_connection_error` that is capable of returning name of diagnostic set in dset.

#### Z39.50 Protocol behavior

The calls `ZOOM_connection_new` and `ZOOM_connection_connect` establishes a TCP/IP connection and sends an Initialize Request to the target if possible. In addition, the calls wait for an Initialize Response from the target and the result is inspected (OK or rejected).

If `proxy` is set then the client will establish a TCP/IP connection with the peer as specified by the `proxy` host and the hostname as part of the connect calls will be set as part of the Initialize Request. The proxy server will then "forward" the PDUs transparently to the target behind the proxy.

For the authentication parameters, if option `user` is set and both options `group` and `pass` are unset, then Open style authentication is used (Version 2/3) in which case the username is usually followed by a slash, then by a password. If either `group` or `pass` is set then idPass authentication (Version 3 only) is used. If none of the options are set, no authentication parameters are set as part of the Initialize Request (obviously).

When option `async` is 1, it really means that all network operations are postponed (and queued) until the function `ZOOM_event` is invoked. When doing so it doesn't make sense to check for errors after `ZOOM_connection_new` is called since that operation "connecting - and init" is still incomplete and the API cannot tell the outcome (yet).

#### SRU/Solr Protocol behavior

The HTTP based protocols (SRU, SRW, Solr) do not feature an Inititialize Request, so the connection phase merely establishes a TCP/IP connection with the HTTP server.

Most of the ZOOM connection options do not affect SRU/Solr and they are ignored. However, future versions of &yaz; might honor `implementationName` and put that as part of User-Agent header for HTTP requests.

The `charset` is used in the Content-Type header of HTTP requests.

Setting `authentcationMode` specifies how authentication parameters are encoded for HTTP. The default is "`basic`" where `user` and `password` are encoded by using HTTP basic authentication.

If `authentcationMode` is "`url`", then user and password are encoded in the URL by parameters `x-username` and `x-password` as given by the SRU standard.

### Queries

Query objects represents queries.

         ZOOM_query ZOOM_query_create(void);

         void ZOOM_query_destroy(ZOOM_query q);

         int ZOOM_query_prefix(ZOOM_query q, const char *str);

         int ZOOM_query_cql(ZOOM_query s, const char *str);

         int ZOOM_query_sortby(ZOOM_query q, const char *criteria);

         int ZOOM_query_sortby2(ZOOM_query q, const char *strategy,
                                const char *criteria);

Create query objects using `ZOOM_query_create` and destroy them by calling `ZOOM_query_destroy`. RPN-queries can be specified in PQF notation by using the function `ZOOM_query_prefix`. The `ZOOM_query_cql` specifies a CQL query to be sent to the server/target. More query types will be added in future versions of &yaz;, such as CCL to RPN-mapping, native CCL query, etc. In addition to a search, a sort criteria may be set. Function `ZOOM_query_sortby` enables Z39.50 sorting and it takes sort criteria using the same string notation as yaz-client's sort command.

`ZOOM_query_sortby2` is similar to `ZOOM_query_sortby` but allows a strategy for sorting. The reason for the strategy parameter is that some protocols offer multiple ways of performing sorting. For example, Z39.50 has the standard sort, which is performed after search on an existing result set. It's also possible to use CQL in Z39.50 as the query type and use CQL's SORTBY keyword. Finally, Index Data's Zebra server also allows sorting to be specified as part of RPN (Type 7).

ZOOM sort strategy

Name | Description
--- | ---
z39.50 | Z39.50 resultset sort
type7 | Sorting embedded in RPN(Type-7)
cql | CQL SORTBY
sru11 | SRU sortKeys parameter
solr | Solr sort
embed | type7 for Z39.50, cql for SRU, solr for Solr protocol

### Result sets

The result set object is a container for records returned from a target.

         ZOOM_resultset ZOOM_connection_search(ZOOM_connection, ZOOM_query q);

         ZOOM_resultset ZOOM_connection_search_pqf(ZOOM_connection c,
                                                   const char *q);
         void ZOOM_resultset_destroy(ZOOM_resultset r);

Function `ZOOM_connection_search` creates a result set, given a connection and query. Destroy a result set by calling `ZOOM_resultset_destroy`. Simple clients using PQF only, may use the function `ZOOM_connection_search_pqf` in which case creating query objects is not necessary.

         void ZOOM_resultset_option_set(ZOOM_resultset r,
                                        const char *key, const char *val);

         const char *ZOOM_resultset_option_get(ZOOM_resultset r, const char *key);

         size_t ZOOM_resultset_size(ZOOM_resultset r);

Functions `ZOOM_resultset_options_set` and `ZOOM_resultset_get` sets and gets an option for a result set similar to `ZOOM_connection_option_get` and `ZOOM_connection_option_set`.

The number of hits, also called result-count, is returned by function `ZOOM_resultset_size`.

ZOOM Result set Options

Option | Description | Default
--- | --- | ---
start | Offset of first record to be retrieved from target. First record has offset 0 unlike the protocol specifications where first record has position 1. This option affects ZOOM_resultset_search and ZOOM_resultset_search_pqf and must be set before any of these functions are invoked. If a range of records must be fetched manually after search, function ZOOM_resultset_records should be used. | 0
count | Number of records to be retrieved. This option affects ZOOM_resultset_search and ZOOM_resultset_search_pqf and must be set before any of these functions are invoked. | 0
presentChunk | The number of records to be requested from the server in each chunk (present request). The value 0 means to request all the records in a single chunk. (The old `step` option is also supported for the benefit of old applications.) | 0
elementSetName | Element-Set name of records. Most targets should honor element set name `B` and `F` for brief and full respectively. | none
preferredRecordSyntax | Preferred Syntax, such as `USMARC`, `SUTRS`, etc. | none
schema | Schema for retrieval, such as `Gils-schema`, `Geo-schema`, etc. | none
setname | Name of Result Set (Result Set ID). If this option isn't set, the ZOOM module will automatically allocate a result set name. | default
rpnCharset | Character set for RPN terms. If this is set, ZOOM C will assume that the ZOOM application is running UTF-8. Terms in RPN queries are then converted to the rpnCharset. If this is unset, ZOOM C will not assume any encoding of RPN terms and no conversion is performed. | none

For servers that support Search Info report, the following options may be read using `ZOOM_resultset_get`. This detailed information is read after a successful search has completed.

This information is a list of of items, where each item is information about a term or subquery. All items in the list are prefixed by `SearchResult.` no where no presents the item number (0=first, 1=second). Read `searchresult.size` to determine the number of items.

Search Info Report Options

Option | Description
--- | ---
searchresult.size | number of search result entries. This option is non-existent if no entries are returned by the server.
searchresult.no.id | sub query ID
searchresult.no.count | result count for item (number of hits)
searchresult.no.subquery.term | subquery term
searchresult.no.interpretation.term | interpretation term
searchresult.no.recommendation.term | recommendation term

#### Z39.50 Result-set Sort

         void ZOOM_resultset_sort(ZOOM_resultset r,
                                  const char *sort_type, const char *sort_spec);

         int ZOOM_resultset_sort1(ZOOM_resultset r,
                                  const char *sort_type, const char *sort_spec);

`ZOOM_resultset_sort` and `ZOOM_resultset_sort1` both sort an existing result-set. The sort_type parameter is not used. Set it to "yaz". The sort_spec is same notation as ZOOM_query_sortby and identical to that offered by yaz-client's sort command.

These functions only work for Z39.50. Use the more generic utility `ZOOM_query_sortby2` for other protocols (and even Z39.50).

#### Z39.50 Protocol behavior

The creation of a result set involves at least a SearchRequest - SearchResponse protocol handshake. Following that, if a sort criteria was specified as part of the query, a SortRequest - SortResponse handshake takes place. Note that it is necessary to perform sorting before any retrieval takes place, so no records will be returned from the target as part of the SearchResponse because these would be unsorted. Hence, piggyback is disabled when sort criteria are set. Following Search - and a possible sort - Retrieval takes place - as one or more Present Requests/Response pairs being transferred.

The API allows for two different modes for retrieval. A high level mode which is somewhat more powerful and a low level one. The low level is enabled when searching on a Connection object for which the settings `smallSetUpperBound`, `mediumSetPresentNumber` and `largeSetLowerBound` are set. The low level mode thus allows you to precisely set how records are returned as part of a search response as offered by the Z39.50 protocol. Since the client may be retrieving records as part of the search response, this mode doesn't work well if sorting is used.

The high-level mode allows you to fetch a range of records from the result set with a given start offset. When you use this mode the client will automatically use piggyback if that is possible with the target, and perform one or more present requests as needed. Even if the target returns fewer records as part of a present response because of a record size limit, etc. the client will repeat sending present requests. As an example, if option `start` is 0 (default) and `count` is 4, and `piggyback` is 1 (default) and no sorting criteria is specified, then the client will attempt to retrieve the 4 records as part the search response (using piggyback). On the other hand, if either `start` is positive or if a sorting criteria is set, or if `piggyback` is 0, then the client will not perform piggyback but send Present Requests instead.

If either of the options `mediumSetElementSetName` and `smallSetElementSetName` are unset, the value of option `elementSetName` is used for piggyback searches. This means that for the high-level mode you only have to specify one elementSetName option rather than three.

#### SRU Protocol behavior

Current version of &yaz; does not take advantage of a result set id returned by the SRU server. Future versions might do, however. Since the ZOOM driver does not save result set IDs, any present (retrieval) is transformed to a SRU SearchRetrieveRequest with same query but, possibly, different offsets.

Option `schema` specifies SRU schema for retrieval. However, options `elementSetName` and `preferredRecordSyntax` are ignored.

Options `start` and `count` are supported by SRU. The remaining options `piggyback`, `smallSetUpperBound`, `largeSetLowerBound`, `mediumSetPresentNumber`, `mediumSetElementSetName`, `smallSetElementSetName` are unsupported.

SRU supports CQL queries, not PQF. If PQF is used, however, the PQF query is transferred anyway using non-standard element `pQuery` in SRU SearchRetrieveRequest.

Solr queries need to be done in Solr query format.

Unfortunately, SRU and Solr do not define a database setting. Hence, `databaseName` is unsupported and ignored. However, the path part in host parameter for functions `ZOOM_connecton_new` and `ZOOM_connection_connect` acts as a database (at least for the &yaz; SRU server).

### Records

A record object is a retrieval record on the client side - created from result sets.

         void ZOOM_resultset_records(ZOOM_resultset r,
                                     ZOOM_record *recs,
                                     size_t start, size_t count);
         ZOOM_record ZOOM_resultset_record(ZOOM_resultset s, size_t pos);

         const char *ZOOM_record_get(ZOOM_record rec, const char *type,
                                     size_t *len);

         int ZOOM_record_error(ZOOM_record rec, const char **msg,
                               const char **addinfo, const char **diagset);

         ZOOM_record ZOOM_record_clone(ZOOM_record rec);

         void ZOOM_record_destroy(ZOOM_record rec);

References to temporary records are returned by functions `ZOOM_resultset_records` or `ZOOM_resultset_record`.

If a persistent reference to a record is desired `ZOOM_record_clone` should be used. It returns a record reference that should be destroyed by a call to `ZOOM_record_destroy`.

A single record is returned by function `ZOOM_resultset_record` that takes a position as argument. First record has position zero. If no record could be obtained `NULL` is returned.

Error information for a record can be checked with `ZOOM_record_error` which returns non-zero (error code) if record is in error, called Surrogate Diagnostics in Z39.50.

Function `ZOOM_resultset_records` retrieves a number of records from a result set. Parameter `start` and `count` specifies the range of records to be returned. Upon completion, the array `recs[0], ..recs[count-1]` holds record objects for the records. The array of records `recs` should be allocated prior the call `ZOOM_resultset_records`. Note that for those records that couldn't be retrieved from the target, `recs[ ..]` is set to `NULL`.

In order to extract information about a single record, `ZOOM_record_get` is provided. The function returns a pointer to certain record information. The nature (type) of the pointer depends on the parameter, type.

The type is a string of the format:

format[;charset=from[/opacfrom][,to]][;format=v][;base64=xpath]

If `charset` is given, then from specifies the character set of the record in its original form (as returned by the server), to specifies the output (returned) character set encoding. If to is omitted, then UTF-8 is assumed. If charset is not given, then no character set conversion takes place. OPAC records may be returned in a different set from the bibliographic MARC record. If this is this the case, opacfrom should be set to the character set of the OPAC record part.

The `format` is generic but can only be used to specify XML indentation when the value v is 1 (`format=1`).

The `base64` allows a full record to be extracted from base64-encoded string in an XML document.

Specifying the OPAC record character set requires YAZ 4.1.5 or later.

Specifying the base64 parameter requires YAZ 4.2.35 or later.

The format argument controls whether record data should be XML pretty-printed (post process operation). It is enabled only if format value v is `1` and the record content is XML well-formed.

In addition, for certain types, the length `len` passed will be set to the size in bytes of the returned information.

The following are the supported values for form.

`database`

  The Database of the record is returned as a C null-terminated string. Return type `const char *`.

`syntax`

  The transfer syntax of the record is returned as a C null-terminated string containing the symbolic name of the record syntax, e.g. `Usmarc`. Return type is `const char *`.

`schema`

  The schema of the record is returned as a C null-terminated string. Return type is `const char *`.

`render`

  The record is returned in a display friendly format. Upon completion, buffer is returned (type `const char *`) and length is stored in `*len`.

`raw`

  The record is returned in the internal YAZ specific format. For GRS-1, Explain, and others, the raw data is returned as type `Z_External *` which is just the type for the member `retrievalRecord` in type `NamePlusRecord`. For SUTRS and octet aligned record (including all MARCs) the octet buffer is returned and the length of the buffer.

`xml`

  The record is returned in XML if possible. SRU, Solr and Z39.50 records with transfer syntax XML are returned verbatim. MARC records are returned in MARCXML (converted from ISO2709 to MARCXML by YAZ). OPAC records are also converted to XML and the bibliographic record is converted to MARCXML (when possible). GRS-1 records are not supported for this form. Upon completion, the XML buffer is returned (type `const char *`) and length is stored in `*len`.

`opac`

  OPAC information for record is returned in XML if an OPAC record is present at the position given. If no OPAC record is present, a NULL pointer is returned.

`txml`

  The record is returned in TurboMARC if possible. SRU and Z39.50 records with transfer syntax XML are returned verbatim. MARC records are returned in TurboMARC (converted from ISO2709 to TurboMARC by YAZ). Upon completion, the XML buffer is returned (type `const char *`) and length is stored in `*len`.

`json`

  Like xml, but MARC records are converted to MARC-in-JSON.

Most MARC21 records uses the MARC-8 character set encoding. An application that wishes to display in Latin-1 would use

         render; charset=marc8,iso-8859-1

#### Z39.50 Protocol behavior

The functions `ZOOM_resultset_record` and `ZOOM_resultset_records` inspects the client-side record cache. Records not found in cache are fetched using Present. The functions may block (and perform network I/O) - even though option `async` is 1, because they return records objects. (And there's no way to return records objects without retrieving them!)

There is a trick, however, in the usage of function `ZOOM_resultset_records` that allows for delayed retrieval (and makes it non-blocking). By using a null pointer for recs you're indicating you're not interested in getting records objects now.

#### SRU/Solr Protocol behavior

The ZOOM driver for SRU/Solr treats records returned by a SRU/Solr server as if they where Z39.50 records with transfer syntax XML and no element set name or database name.

### ZOOM Facets

Facets are only supported for a few Z39.50 targets. It is a relatively new non-standard Z39.50 extension (see facets.asn in the YAZ source). However, facets are usually supported for Solr and SRU 2.0 targets.

Facets may be specified by the facets option before a search is sent. See for the notation. For inspection of the returned facets, the following functions are available:

        ZOOM_facet_field *ZOOM_resultset_facets(ZOOM_resultset r);

        size_t ZOOM_resultset_facets_size(ZOOM_resultset r);

        ZOOM_facet_field ZOOM_resultset_get_facet_field(ZOOM_resultset r,
                                                        const char *facet_name);

        ZOOM_facet_field ZOOM_resultset_get_facet_field_by_index(ZOOM_resultset r,
                                                                 int pos);

        const char *ZOOM_facet_field_name(ZOOM_facet_field facet_field);

        size_t ZOOM_facet_field_term_count(ZOOM_facet_field facet_field);

        const char *ZOOM_facet_field_get_term(ZOOM_facet_field facet_field,
                                              size_t idx, int *freq);

References to temporary structures are returned by all functions. They are only valid as long the Result set is valid.

All facet fields may be returned by a call to `ZOOM_resultset_facets`. The length of the array is given by `ZOOM_resultset_facets_size`. The array is zero-based and the last entry will be at `ZOOM_resultset_facets_size(result_set)`-1.

Facet fields can also be fetched via its name using `ZOOM_resultset_get_facet_field`. Or by its index (starting from 0) by a call to `ZOOM_resultset_get_facet_field_by_index`. Both of these functions return NULL if name is not found or index is out of bounds.

Function `ZOOM_facet_field_name` gets the request facet name from a returned facet field.

Function `ZOOM_facet_field_get_term` returns the idx'th term and term count for a facet field. Idx must between 0 and `ZOOM_facet_field_term_count`-1, otherwise the returned reference will be `NULL`. On a valid idx, the value of the freq reference will be the term count. The `freq` parameter must be valid pointer to integer.

### Scan

This section describes an interface for Scan. Scan is not an official part of the ZOOM model yet. The result of a scan operation is the `ZOOM_scanset` which is a set of terms returned by a target.

The Scan interface is supported for both Z39.50, SRU and Solr.

        ZOOM_scanset ZOOM_connection_scan(ZOOM_connection c,
                                          const char *startpqf);

        ZOOM_scanset ZOOM_connection_scan1(ZOOM_connection c,
                                           ZOOM_query q);

        size_t ZOOM_scanset_size(ZOOM_scanset scan);

        const char *ZOOM_scanset_term(ZOOM_scanset scan, size_t pos,
                                      size_t *occ, size_t *len);

        const char *ZOOM_scanset_display_term(ZOOM_scanset scan, size_t pos,
                                              size_t *occ, size_t *len);

        void ZOOM_scanset_destroy(ZOOM_scanset scan);

        const char *ZOOM_scanset_option_get(ZOOM_scanset scan,
                                            const char *key);

        void ZOOM_scanset_option_set(ZOOM_scanset scan, const char *key,
                                     const char *val);

The scan set is created by function `ZOOM_connection_scan` which performs a scan operation on the connection using the specified startpqf. If the operation was successful, the size of the scan set can be retrieved by a call to `ZOOM_scanset_size`. Like result sets, the items are numbered 0..size-1. To obtain information about a particular scan term, call function `ZOOM_scanset_term`. This function takes a scan set offset `pos` and returns a pointer to a raw term or `NULL` if non-present. If present, the `occ` and `len` are set to the number of occurrences and the length of the actual term respectively. `ZOOM_scanset_display_term` is similar to `ZOOM_scanset_term` except that it returns the display term rather than the raw term. In a few cases, the term is different from display term. Always use the display term for display and the raw term for subsequent scan operations (to get more terms, next scan result, etc).

A scan set may be freed by a call to function `ZOOM_scanset_destroy`. Functions `ZOOM_scanset_option_get` and `ZOOM_scanset_option_set` retrieves and sets an option respectively.

The startpqf is a subset of PQF, namely the Attributes+Term part. Multiple `@attr` can be used. For example to scan in title (complete) phrases:

         @attr 1=4 @attr 6=2 "science o"

The `ZOOM_connecton_scan1` is a newer and more generic alternative to `ZOOM_connection_scan` which allows to use both CQL and PQF for Scan.

ZOOM Scan Set Options

Option | Description | Default
--- | --- | ---
number | Number of Scan Terms requested in next scan. After scan it holds the actual number of terms returned. | 20
position | Preferred Position of term in response in next scan; actual position after completion of scan. | 1
stepSize | Step Size | 0
scanStatus | An integer indicating the Scan Status of last scan. | 0
rpnCharset | Character set for RPN terms. If this is set, ZOOM C will assume that the ZOOM application is running UTF-8. Terms in RPN queries are then converted to the rpnCharset. If this is unset, ZOOM C will not assume any encoding of RPN terms and no conversion is performed. | none

### Extended Services

ZOOM offers an interface to a subset of the Z39.50 extended services as well as a few privately defined ones:

- Z39.50 Item Order (ILL). See .

- Record Update. This allows a client to insert, modify or delete records. See .

- Database Create. This a non-standard feature. Allows a client to create a database. See .

- Database Drop. This a non-standard feature. Allows a client to delete/drop a database. See .

- Commit operation. This a non-standard feature. Allows a client to commit operations. See .

To create an extended service operation, a `ZOOM_package` must be created. The operation is a five step operation. The package is created, package is configured by means of options, the package is sent, result is inspected (by means of options), the package is destroyed.

        ZOOM_package ZOOM_connection_package(ZOOM_connection c,
                                             ZOOM_options options);

        const char *ZOOM_package_option_get(ZOOM_package p,
                                            const char *key);
        void ZOOM_package_option_set(ZOOM_package p, const char *key,
                                     const char *val);
        void ZOOM_package_send(ZOOM_package p, const char *type);

        void ZOOM_package_destroy(ZOOM_package p);

The `ZOOM_connection_package` creates a package for the connection given using the options specified.

Functions `ZOOM_package_option_get` and `ZOOM_package_option_set` gets and sets options.

`ZOOM_package_send` sends the package the via connection specified in `ZOOM_connection_package`. The type specifies the actual extended service package type to be sent.

Extended Service Type

Type | Description
--- | ---
itemorder | Item Order
update | Record Update
create | Database Create
drop | Database Drop
commit | Commit Operation

Extended Service Common Options

Option | Description | Default
--- | --- | ---
package-name | Extended Service Request package name. Must be specified as part of a request. | none
user-id | User ID of Extended Service Package. Is a request option. | none
function | Function of package - one of `create`, `delete`, `modify`. Is a request option. | `create`
waitAction | Wait action for package. Possible values: `wait`, `waitIfPossible`, `dontWait` or `dontReturnPackage`. | `waitIfPossible`
operationStatus | Read after response. One of: done, accepted or failure. Inspect with `ZOOM_pacakage_option_get`. | none
targetReference | Target Reference. This is part of the response as returned by the target. Read it after a successful operation. Inspect with `ZOOM_pacakage_option_get`. | none
taskStatus | Read after response: One of: pending, active, complete, aborted. | none
esError | Read after response: is set to diagnostic code for response. | none
esAddinfo | Read after response: is set to additional info for response. | none

#### Item Order

For Item Order, `type` must be set to `itemorder` in `ZOOM_package_send`.

Item Order Options

Option | Description | Default
--- | --- | ---
contact-name | ILL contact name | none
contact-phone | ILL contact phone | none
contact-email | ILL contact email | none
itemorder-setname | Name of result set for record | default
itemorder-item | Position for item (record) requested. An integer | 1

There are two variants of item order: ILL-variant and XML document variant. In order to use the XML variant the setting `doc` must hold the XML item order document. If that setting is unset, the ILL-variant is used.

ILL Request Options

Option
protocol-version-num
transaction-id,initial-requester-id,person-or-institution-symbol,person
transaction-id,initial-requester-id,person-or-institution-symbol,institution
transaction-id,initial-requester-id,name-of-person-or-institution,name-of-person
transaction-id,initial-requester-id,name-of-person-or-institution,name-of-institution
transaction-id,transaction-group-qualifier
transaction-id,transaction-qualifier
transaction-id,sub-transaction-qualifier
service-date-time,this,date
service-date-time,this,time
service-date-time,original,date
service-date-time,original,time
requester-id,person-or-institution-symbol,person
requester-id,person-or-institution-symbol,institution
requester-id,name-of-person-or-institution,name-of-person
requester-id,name-of-person-or-institution,name-of-institution
responder-id,person-or-institution-symbol,person
responder-id,person-or-institution-symbol,institution
responder-id,name-of-person-or-institution,name-of-person
responder-id,name-of-person-or-institution,name-of-institution
transaction-type
delivery-address,postal-address,name-of-person-or-institution,name-of-person
delivery-address,postal-address,name-of-person-or-institution,name-of-institution
delivery-address,postal-address,extended-postal-delivery-address
delivery-address,postal-address,street-and-number
delivery-address,postal-address,post-office-box
delivery-address,postal-address,city
delivery-address,postal-address,region
delivery-address,postal-address,country
delivery-address,postal-address,postal-code
delivery-address,electronic-address,telecom-service-identifier
delivery-address,electronic-address,telecom-service-addreess
billing-address,postal-address,name-of-person-or-institution,name-of-person
billing-address,postal-address,name-of-person-or-institution,name-of-institution
billing-address,postal-address,extended-postal-delivery-address
billing-address,postal-address,street-and-number
billing-address,postal-address,post-office-box
billing-address,postal-address,city
billing-address,postal-address,region
billing-address,postal-address,country
billing-address,postal-address,postal-code
billing-address,electronic-address,telecom-service-identifier
billing-address,electronic-address,telecom-service-addreess
ill-service-type
requester-optional-messages,can-send-RECEIVED
requester-optional-messages,can-send-RETURNED
requester-optional-messages,requester-SHIPPED
requester-optional-messages,requester-CHECKED-IN
search-type,level-of-service
search-type,need-before-date
search-type,expiry-date
search-type,expiry-flag
place-on-hold
client-id,client-name
client-id,client-status
client-id,client-identifier
item-id,item-type
item-id,call-number
item-id,author
item-id,title
item-id,sub-title
item-id,sponsoring-body
item-id,place-of-publication
item-id,publisher
item-id,series-title-number
item-id,volume-issue
item-id,edition
item-id,publication-date
item-id,publication-date-of-component
item-id,author-of-article
item-id,title-of-article
item-id,pagination
item-id,ISBN
item-id,ISSN
item-id,additional-no-letters
item-id,verification-reference-source
copyright-complicance
retry-flag
forward-flag
requester-note
forward-note

#### Record Update

For Record Update, `type` must be set to `update` in `ZOOM_package_send`.

Record Update Options

Option | Description | Default
--- | --- | ---
action | The update action. One of `specialUpdate`, `recordInsert`, `recordReplace`, `recordDelete`, `elementUpdate`. | `specialUpdate (recordInsert for updateVersion=1 which does not support specialUpdate)`
recordIdOpaque | Opaque Record ID | none
recordIdNumber | Record ID number | none
recordIdString | Record ID string | none
record | The record itself | none
recordOpaque | Specifies an opaque record which is encoded as an ASN.1 ANY type with the OID as given by option `syntax` (see below). Option `recordOpaque` is an alternative to record - and `record` option (above) is ignored if recordOpaque is set. This option is only available in YAZ 3.0.35 and later, and is meant to facilitate Updates with servers from OCLC. | none
syntax | The record syntax (transfer syntax). Is a string that is a known record syntax. | no syntax
databaseName | Database from connection object | Default
correlationInfo.note | Correlation Info Note (string) | none
correlationInfo.id | Correlation Info ID (integer) | none
elementSetName | Element Set for Record | none
updateVersion | Record Update version which holds one of the values 1, 2 or 3. Each version has a distinct OID: 1.2.840.10003.9.5 (first version) , 1.2.840.10003.9.5.1 (second version) and 1.2.840.10003.9.5.1.1 (third and newest version). | 3

#### Database Create

For Database Create, `type` must be set to `create` in `ZOOM_package_send`.

Database Create Options

Option | Description | Default
--- | --- | ---
databaseName | Database from connection object | Default

#### Database Drop

For Database Drop, `type` must be set to `drop` in `ZOOM_package_send`.

Database Drop Options

Option | Description | Default
--- | --- | ---
databaseName | Database from connection object | Default

#### Commit Operation

For Commit, `type` must be set to `commit` in `ZOOM_package_send`.

#### Protocol behavior

All the extended services are Z39.50-only.

The database create, drop, and commit services are privately defined operations. Refer to `esadmin.asn` in YAZ for the ASN.1 definitions.

### Options

Most &zoom; objects provide a way to specify options to change behavior. From an implementation point of view, a set of options is just like an associative array / hash.

         ZOOM_options ZOOM_options_create(void);

         ZOOM_options ZOOM_options_create_with_parent(ZOOM_options parent);

         void ZOOM_options_destroy(ZOOM_options opt);

         const char *ZOOM_options_get(ZOOM_options opt, const char *name);

         void ZOOM_options_set(ZOOM_options opt, const char *name,
                               const char *v);

         typedef const char *(*ZOOM_options_callback)
                                (void *handle, const char *name);

         ZOOM_options_callback
                 ZOOM_options_set_callback(ZOOM_options opt,
                                           ZOOM_options_callback c,
                                           void *handle);

### Query conversions

        int ZOOM_query_cql2rpn(ZOOM_query s, const char *cql_str,
                               ZOOM_connection conn);

        int ZOOM_query_ccl2rpn(ZOOM_query s, const char *ccl_str,
                               const char *config,
                               int *ccl_error, const char **error_string,
                               int *error_pos);

`ZOOM_query_cql2rpn` translates the CQL string, client-side, into RPN which may be passed to the server. This is useful for servers that don't themselves support CQL, for which `ZOOM_query_cql` is useless. 'conn' is used only as a place to stash diagnostics if compilation fails; if this information is not needed, a null pointer may be used. The CQL conversion is driven by option `cqlfile` from connection conn. This specifies a conversion file (e.g. pqf.properties) which must be present.

`ZOOM_query_ccl2rpn` translates the CCL string, client-side, into RPN which may be passed to the server. The conversion is driven by the specification given by `config`. Upon completion 0 is returned on success; -1 is returned on failure. On failure `error_string` and `error_pos` hold the error message and position of first error in original CCL string.

### Events

If you're developing non-blocking applications, you have to deal with events.

        int ZOOM_event(int no, ZOOM_connection *cs);

The `ZOOM_event` executes pending events for a number of connections. Supply the number of connections in `no` and an array of connections in `cs` (`cs[0] ... cs[no-1]`). A pending event could be sending a search, receiving a response, etc. When an event has occurred for one of the connections, this function returns a positive integer `n` denoting that an event occurred for connection `cs[n-1]`. When no events are pending for the connections, a value of zero is returned. To ensure that all outstanding requests are performed, call this function repeatedly until zero is returned.

If `ZOOM_event` returns, and returns non-zero, the last event that occurred can be expected.

        int ZOOM_connection_last_event(ZOOM_connection cs);

`ZOOM_connection_last_event` returns an event type (integer) for the last event.

ZOOM Event IDs

Event | Description
--- | ---
ZOOM_EVENT_NONE | No event has occurred
ZOOM_EVENT_CONNECT | TCP/IP connect has initiated
ZOOM_EVENT_SEND_DATA | Data has been transmitted (sending)
ZOOM_EVENT_RECV_DATA | Data has been received
ZOOM_EVENT_TIMEOUT | Timeout
ZOOM_EVENT_UNKNOWN | Unknown event
ZOOM_EVENT_SEND_APDU | An APDU has been transmitted (sending)
ZOOM_EVENT_RECV_APDU | An APDU has been received
ZOOM_EVENT_RECV_RECORD | A result-set record has been received
ZOOM_EVENT_RECV_SEARCH | A search result has been received

## Generic server

### Introduction

If you aren't into documentation, a good way to learn how the back end interface works is to look at the `backend.h` file. Then, look at the small dummy-server in `ztest/ztest.c`. The `backend.h` file also makes a good reference, once you've chewed your way through the prose of this file.

If you have a database system that you would like to make available by means of Z39.50 or SRU, &yaz; basically offers two options. You can use the APIs provided by the &asn;, &odr;, and &comstack; modules to create and decode PDUs, and exchange them with a client. Using this low-level interface gives you access to all fields and options of the protocol, and you can construct your server as close to your existing database as you like. It is also a fairly involved process, requiring you to set up an event-handling mechanism, protocol state machine, etc. To simplify server implementation, we have implemented a compact and simple, but reasonably full-functioned server-frontend that will handle most of the protocol mechanics, while leaving you to concentrate on your database interface.

The backend interface was designed in anticipation of a specific integration task, while still attempting to achieve some degree of generality. We realize fully that there are points where the interface can be improved significantly. If you have specific functions or parameters that you think could be useful, send us a mail (or better, sign on to the mailing list referred to in the top-level README file). We will try to fit good suggestions into future releases, to the extent that it can be done without requiring too many structural changes in existing applications.

The &yaz; server does not support XCQL.

### The Database Frontend

We refer to this software as a generic database frontend. Your database system is the backend database, and the interface between the two is called the backend API. The backend API consists of a small number of function handlers and structure definitions. You are required to provide the `main()` routine for the server (which can be quite simple), as well as a set of handlers to match each of the prototypes. The interface functions that you write can use any mechanism you like to communicate with your database system: You might link the whole thing together with your database application and access it by function calls; you might use IPC to talk to a database server somewhere; or you might link with third-party software that handles the communication for you (like a commercial database client library). At any rate, the handlers will perform the tasks of:

- Initialization.

- Searching.

- Fetching records.

- Scanning the database index (optional - if you wish to implement SCAN).

- Extended Services (optional).

- Result-Set Delete (optional).

- Result-Set Sort (optional).

- Return Explain for SRU (optional).

(more functions will be added in time to support as much of Z39.50-1995 as possible).

### The Backend API

The header file that you need to use the interface are in the `include/yaz` directory. It's called `backend.h`. It will include other files from the `include/yaz` directory, so you'll probably want to use the -I option of your compiler to tell it where to find the files. When you run `make` in the top-level &yaz; directory, everything you need to create your server is to link with the `lib/libyaz.la` library.

### Your main() Routine

As mentioned, your `main()` routine can be quite brief. If you want to initialize global parameters, or read global configuration tables, this is the place to do it. At the end of the routine, you should call the function

    int statserv_main(int argc, char **argv,
                      bend_initresult *(*bend_init)(bend_initrequest *r),
                      void (*bend_close)(void *handle));

The third and fourth arguments are pointers to handlers. Handler `bend_init` is called whenever the server receives an Initialize Request, so it serves as a Z39.50 session initializer. The `bend_close` handler is called when the session is closed.

`statserv_main` will establish listening sockets according to the parameters given. When connection requests are received, the event handler will typically `fork()` and create a sub-process to handle a new connection. Alternatively the server may be setup to create threads for each connection. If you do use global variables and forking, you should be aware, then, that these cannot be shared between associations, unless you explicitly disable forking by command line parameters.

The server provides a mechanism for controlling some of its behavior without using command-line options. The function

        statserv_options_block *statserv_getcontrol(void);

will return a pointer to a `struct statserv_options_block` describing the current default settings of the server. The structure contains these elements:

`int dynamic`

  A boolean value, which determines whether the server will fork on each incoming request (TRUE), or not (FALSE). Default is TRUE. This flag is only read by UNIX-based servers (WIN32-based servers do not fork).

`int threads`

  A boolean value, which determines whether the server will create a thread on each incoming request (TRUE), or not (FALSE). Default is FALSE. This flag is only read by UNIX-based servers that offer POSIX Threads support. WIN32-based servers always operate in threaded mode.

`int inetd`

  A boolean value, which determines whether the server will operate under a UNIX INET daemon (inetd). Default is FALSE.

`char logfile[ODR_MAXNAME+1]`

  File for diagnostic output ("": stderr).

`char apdufile[ODR_MAXNAME+1]`

  Name of file for logging incoming and outgoing APDUs ("": don't log APDUs, "-": `stderr`).

`char default_listen[1024]`

  Same form as the command-line specification of listener address. "": no default listener address. Default is to listen at "tcp:@:9999". You can only specify one default listener address in this fashion.

`enum oid_proto default_proto;`

  Either `PROTO_Z3950` or `PROTO_SR`. Default is `PROTO_Z39_50`.

`int idle_timeout;`

  Maximum session idle-time, in minutes. Zero indicates no (infinite) timeout. Default is 15 minutes.

`int maxrecordsize;`

  Maximum permissible record (message) size. Default is 64 MB. This amount of memory will only be allocated if a client requests a very large amount of records in one operation (or a big record). Set it to a lower number if you are worried about resource consumption on your host system.

`char configname[ODR_MAXNAME+1]`

  Passed to the backend when a new connection is received.

`char setuid[ODR_MAXNAME+1]`

  Set user id to the user specified, after binding the listener addresses.

`void (*bend_start)(struct statserv_options_block *p)`

  Pointer to function which is called after the command line options have been parsed - but before the server starts listening. For forked UNIX servers, this handler is called in the mother process; for threaded servers, this handler is called in the main thread. The default value of this pointer is NULL in which case it isn't invoked by the frontend server. When the server operates as an NT service, this handler is called whenever the service is started.

`void (*bend_stop)(struct statserv_options_block *p)`

  Pointer to function which is called whenever the server has stopped listening for incoming connections. This function pointer has a default value of NULL in which case it isn't called. When the server operates as an NT service, this handler is called whenever the service is stopped.

`void *handle`

  User defined pointer (default value NULL). This is a per-server handle that can be used to specify "user-data". Do not confuse this with the session-handle as returned by bend_init.

The pointer returned by `statserv_getcontrol` points to a static area. You are allowed to change the contents of the structure, but the changes will not take effect until you call

    void statserv_setcontrol(statserv_options_block *block);

You should generally update this structure before calling `statserv_main()`.

### The Backend Functions

For each service of the protocol, the backend interface declares one or two functions. You are required to provide implementations of the functions representing the services that you wish to implement.

#### Init

    bend_initresult (*bend_init)(bend_initrequest *r);

This handler is called once for each new connection request, after a new process/thread has been created, and an Initialize Request has been received from the client. The pointer to the `bend_init` handler is passed in the call to `statserv_start`.

This handler is also called when operating in SRU mode - when a connection has been made (even though SRU does not offer this service).

Unlike previous versions of YAZ, the `bend_init` also serves as a handler that defines the Z39.50 services that the backend intends to support. Pointers to all service handlers, including search - and fetch must be specified here in this handler.

The request - and result structures are defined as

    typedef struct bend_initrequest
    {
        /** \brief user/name/password to be read */
        Z_IdAuthentication *auth;
        /** \brief encoding stream (for results) */
        ODR stream;
        /** \brief printing stream */
        ODR print;
        /** \brief decoding stream (use stream for results) */
        ODR decode;
        /** \brief reference ID */
        Z_ReferenceId *referenceId;
        /** \brief peer address of client */
        char *peer_name;

        /** \brief character set and language negotiation

        see include/yaz/z-charneg.h
        */
        Z_CharSetandLanguageNegotiation *charneg_request;

        /** \brief character negotiation response */
        Z_External *charneg_response;

        /** \brief character set (encoding) for query terms

        This is NULL by default. It should be set to the native character
        set that the backend assumes for query terms */
        char *query_charset;

        /** \brief whether query_charset also applies to records

        Is 0 (No) by default. Set to 1 (yes) if records is in the same
        character set as queries. If in doubt, use 0 (No).
        */
        int records_in_same_charset;

        char *implementation_id;
        char *implementation_name;
        char *implementation_version;

        /** \brief Z39.50 sort handler */
        int (*bend_sort)(void *handle, bend_sort_rr *rr);
        /** \brief SRU/Z39.50 search handler */
        int (*bend_search)(void *handle, bend_search_rr *rr);
        /** \brief SRU/Z39.50 fetch handler */
        int (*bend_fetch)(void *handle, bend_fetch_rr *rr);
        /** \brief SRU/Z39.50 present handler */
        int (*bend_present)(void *handle, bend_present_rr *rr);
        /** \brief Z39.50 extended services handler */
        int (*bend_esrequest) (void *handle, bend_esrequest_rr *rr);
        /** \brief Z39.50 delete result set handler */
        int (*bend_delete)(void *handle, bend_delete_rr *rr);
        /** \brief Z39.50 scan handler */
        int (*bend_scan)(void *handle, bend_scan_rr *rr);
        /** \brief Z39.50 segment facility handler */
        int (*bend_segment)(void *handle, bend_segment_rr *rr);
        /** \brief SRU explain handler */
        int (*bend_explain)(void *handle, bend_explain_rr *rr);
        /** \brief SRU scan handler */
        int (*bend_srw_scan)(void *handle, bend_scan_rr *rr);
        /** \brief SRU record update handler */
        int (*bend_srw_update)(void *handle, bend_update_rr *rr);

        /** \brief whether named result sets are supported (0=disable, 1=enable) */
        int named_result_sets;
    } bend_initrequest;

    typedef struct bend_initresult
    {
        int errcode;               /* 0==OK */
        char *errstring;           /* system error string or NULL */
        void *handle;              /* private handle to the backend module */
    } bend_initresult;

In general, the server frontend expects that the `bend_*result` pointer that you return is valid at least until the next call to a `bend_* function`. This applies to all of the functions described herein. The parameter structure passed to you in the call belongs to the server frontend, and you should not make assumptions about its contents after the current function call has completed. In other words, if you want to retain any of the contents of a request structure, you should copy them.

The `errcode` should be zero if the initialization of the backend went well. Any other value will be interpreted as an error. The `errstring` isn't used in the current version, but one option would be to stick it in the initResponse as a VisibleString. The `handle` is the most important parameter. It should be set to some value that uniquely identifies the current session to the backend implementation. It is used by the frontend server in any future calls to a backend function. The typical use is to set it to point to a dynamically allocated state structure that is private to your backend module.

The `auth` member holds the authentication information part of the Z39.50 Initialize Request. Interpret this if your server requires authentication.

The members `peer_name`, `implementation_id`, `implementation_name` and `implementation_version` holds DNS of client, ID of implementor, name of client (Z39.50) implementation - and version.

The `bend_` - members are set to NULL when `bend_init` is called. Modify the pointers by setting them to point to backend functions.

#### Search and Retrieve

We now describe the handlers that are required to support search - and retrieve. You must support two functions - one for search - and one for fetch (retrieval of one record). If desirable you can provide a third handler which is called when a present request is received which allows you to optimize retrieval of multiple-records.

    int (*bend_search) (void *handle, bend_search_rr *rr);

    typedef struct {
        char *setname;             /* name to give to this set */
        int replace_set;           /* replace set, if it already exists */
        int num_bases;             /* number of databases in list */
        char **basenames;          /* databases to search */
        Z_ReferenceId *referenceId;/* reference ID */
        Z_Query *query;            /* query structure */
        ODR stream;                /* encode stream */
        ODR decode;                /* decode stream */
        ODR print;                 /* print stream */

        bend_request request;
        bend_association association;
        int *fd;
        int hits;                  /* number of hits */
        int errcode;               /* 0==OK */
        char *errstring;           /* system error string or NULL */
        Z_OtherInformation *search_info; /* additional search info */
        char *srw_sortKeys;        /* holds SRU/SRW sortKeys info */
        char *srw_setname;         /* holds SRU/SRW generated resultsetID */
        int *srw_setnameIdleTime;  /* holds SRU/SRW life-time */
        int estimated_hit_count;   /* if hit count is estimated */
        int partial_resultset;     /* if result set is partial */
    } bend_search_rr;

The `bend_search` handler is a fairly close approximation of a protocol Z39.50 Search Request - and Response PDUs. The `setname` is the resultSetName from the protocol. You are required to establish a mapping between the set name and whatever your backend database likes to use. Similarly, the `replace_set` is a boolean value corresponding to the resultSetIndicator field in the protocol. `num_bases/basenames` is a length of/array of character pointers to the database names provided by the client. The `query` is the full query structure as defined in the protocol ASN.1 specification. It can be either of the possible query types, and it's up to you to determine if you can handle the provided query type. Rather than reproduce the C interface here, we'll refer you to the structure definitions in the file `include/yaz/z-core.h`. If you want to look at the attributeSetId OID of the RPN query, you can either match it against your own internal tables, or you can use the OID tools.

The structure contains a number of hits, and an `errcode/errstring` pair. If an error occurs during the search, or if you're unhappy with the request, you should set the errcode to a value from the BIB-1 diagnostic set. The value will then be returned to the user in a nonsurrogate diagnostic record in the response. The `errstring`, if provided, will go in the addinfo field. Look at the protocol definition for the defined error codes, and the suggested uses of the addinfo field.

The `bend_search` handler is also called when the frontend server receives a SRU SearchRetrieveRequest. For SRU, a CQL query is usually provided by the client. The CQL query is available as part of `Z_Query` structure (note that CQL is now part of Z39.50 via an external). To support CQL in existing implementations that only do Type-1, we refer to the CQL-to-PQF tool described here.

To maintain backwards compatibility, the frontend server of yaz always assume that error codes are BIB-1 diagnostics. For SRU operation, a Bib-1 diagnostic code is mapped to SRU diagnostic.

    int (*bend_fetch) (void *handle, bend_fetch_rr *rr);

    typedef struct bend_fetch_rr {
        char *setname;             /* set name */
        int number;                /* record number */
        Z_ReferenceId *referenceId;/* reference ID */
        Odr_oid *request_format;   /* format, transfer syntax (OID) */
        Z_RecordComposition *comp; /* Formatting instructions */
        ODR stream;                /* encoding stream - memory source if req */
        ODR print;                 /* printing stream */

        char *basename;            /* name of database that provided record */
        int len;                   /* length of record or -1 if structured */
        char *record;              /* record */
        int last_in_set;           /* is it?  */
        Odr_oid *output_format;    /* response format/syntax (OID) */
        int errcode;               /* 0==success */
        char *errstring;           /* system error string or NULL */
        int surrogate_flag;        /* surrogate diagnostic */
        char *schema;              /* string record schema input/output */
    } bend_fetch_rr;

The frontend server calls the `bend_fetch` handler when it needs database records to fulfill a Z39.50 Search Request, a Z39.50 Present Request or a SRU SearchRetrieveRequest. The `setname` is simply the name of the result set that holds the reference to the desired record. The `number` is the offset into the set (with 1 being the first record in the set). The `format` field is the record format requested by the client (See ). A value of NULL for `format` indicates that the client did not request a specific format. The `stream` argument is an &odr; stream which should be used for allocating space for structured data records. The stream will be reset when all records have been assembled, and the response package has been transmitted. For unstructured data, the backend is responsible for maintaining a static or dynamic buffer for the record between calls.

If a SRU SearchRetrieveRequest is received by the frontend server, the `referenceId` is NULL and the `format` (transfer syntax) is the OID for XML. The schema for SRU is stored in both the `Z_RecordComposition` structure and `schema` (simple string).

In the structure, the `basename` is the name of the database that holds the record. `len` is the length of the record returned, in bytes, and `record` is a pointer to the record. `last_in_set` should be nonzero only if the record returned is the last one in the given result set. `errcode` and `errstring`, if given, will be interpreted as a global error pertaining to the set, and will be returned in a non-surrogate-diagnostic. If you wish to return the error as a surrogate-diagnostic (local error) you can do this by setting `surrogate_flag` to 1 also.

If the `len` field has the value -1, then `record` is assumed to point to a constructed data type. The `format` field will be used to determine which encoder should be used to serialize the data.

If your backend generates structured records, it should use `odr_malloc()` on the provided stream for allocating data: This allows the frontend server to keep track of the record sizes.

The `format` field is mapped to an object identifier in the direct reference of the resulting EXTERNAL representation of the record.

The current version of &yaz; only supports the direct reference mode.

    int (*bend_present) (void *handle, bend_present_rr *rr);

    typedef struct {
        char *setname;             /* set name */
        int start;
        int number;                /* record number */
        Odr_oid *format;           /* format, transfer syntax (OID) */
        Z_ReferenceId *referenceId;/* reference ID */
        Z_RecordComposition *comp; /* Formatting instructions */
        ODR stream;                /* encoding stream - memory source if required */
        ODR print;                 /* printing stream */
        bend_request request;
        bend_association association;

        int hits;                  /* number of hits */
        int errcode;               /* 0==OK */
        char *errstring;           /* system error string or NULL */
    } bend_present_rr;

The `bend_present` handler is called when the server receives a Z39.50 Present Request. The `setname`, `start` and `number` is the name of the result set - start position - and number of records to be retrieved respectively. `format` and `comp` is the preferred transfer syntax and element specifications of the present request.

Note that this is handler serves as a supplement for `bend_fetch` and need not to be defined in order to support search - and retrieve.

#### Delete

For back-ends that supports delete of a result set, only one handler must be defined.

    int (*bend_delete)(void *handle, bend_delete_rr *rr);

    typedef struct bend_delete_rr {
        int function;
        int num_setnames;
        char **setnames;
        Z_ReferenceId *referenceId;
        int delete_status;      /* status for the whole operation */
        int *statuses;          /* status each set - indexed as setnames */
        ODR stream;
        ODR print;
    } bend_delete_rr;

The delete set function definition is rather primitive, mostly because we have had no practical need for it as of yet. If someone wants to provide a full delete service, we'd be happy to add the extra parameters that are required. Are there clients out there that will actually delete sets they no longer need?

#### Scan

For servers that wish to offer the scan service one handler must be defined.

    int (*bend_scan)(void *handle, bend_scan_rr *rr);

    typedef enum {
        BEND_SCAN_SUCCESS,  /* ok */
        BEND_SCAN_PARTIAL   /* not all entries could be found */
    } bend_scan_status;

    typedef struct bend_scan_rr {
        int num_bases;      /* number of elements in databaselist */
        char **basenames;   /* databases to search */
        Odr_oid *attributeset;
        Z_ReferenceId *referenceId; /* reference ID */
        Z_AttributesPlusTerm *term;
        ODR stream;         /* encoding stream - memory source if required */
        ODR print;          /* printing stream */

        int *step_size;     /* step size */
        int term_position;  /* desired index of term in result list/returned */
        int num_entries;    /* number of entries requested/returned */

        /* scan term entries. The called handler does not have
           to allocate this. Size of entries is num_entries (see above) */
        struct scan_entry *entries;
        bend_scan_status status;
        int errcode;
        char *errstring;
        char *scanClause;   /* CQL scan clause */
        char *setname;      /* Scan in result set (NULL if omitted) */
    } bend_scan_rr;

This backend server handles both Z39.50 scan and SRU scan. In order for a handler to distinguish between SRU (CQL) scan Z39.50 Scan, it must check for a non-NULL value of `scanClause`.

If designed today, it would be a choice using a union or similar, but that would break binary compatibility with existing servers.

### Application Invocation

The finished application has the following invocation syntax (by way of `statserv_main()`):

&gfs-synopsis;

The options are: &gfs-options;

A listener specification consists of a transport mode followed by a colon (:) followed by a listener address. The transport mode is either `tcp`, `unix:` or `ssl`.

For TCP and SSL, an address has the form

        hostname | IP-number [: portnumber]

The port number defaults to 210 (standard Z39.50 port).

For UNIX, the address is the filename of socket.

For TCP/IP and SSL, the special hostnames `@`, maps to `IN6ADDR_ANY_INIT` with IPV4 binding as well (bindv6only=0), The special hostname `@4` binds to `INADDR_ANY` (IPV4 only listener). The special hostname `@6` binds to `IN6ADDR_ANY_INIT` with bindv6only=1 (IPV6 only listener).

Running the GFS on Unix

Assuming the server application appname is started as root, the following will make it listen on port 210. The server will change identity to `nobody` and write its log to `/var/log/app.log`.

          application -l /var/log/app.log -u nobody tcp:@:210

The server will accept Z39.50 requests and offer SRU service on port 210.

Setting up Apache as SRU Frontend

If you use Apache as your public web server and want to offer HTTP port 80 access to the YAZ server on 210, you can use the `ProxyPass` directive. If you have virtual host `srw.mydomain` you can use the following directives in Apache's httpd.conf:

          <VirtualHost *>
           ErrorLog /home/srw/logs/error_log
           TransferLog /home/srw/logs/access_log
           ProxyPass / http://srw.mydomain:210/
          </VirtualHost>

The above is for the Apache 1.3 series.

Running a server with local access only

A server that is only being accessed from the local host should listen on UNIX file socket rather than an Internet socket. To listen on `/tmp/mysocket` start the server as follows:

          application unix:/tmp/mysocket

### GFS Configuration and Virtual Hosts

&gfs-virtual;

## The Z39.50 ASN.1 Module

### Introduction

The &asn; module provides you with a set of C struct definitions for the various PDUs of the Z39.50 protocol, as well as for the complex types appearing within the PDUs. For the primitive data types, the C representation often takes the form of an ordinary C language type, such as `Odr_int` which is equivalent to an integral C integer. For ASN.1 constructs that have no direct representation in C, such as general octet strings and bit strings, the &odr; module (see section The ODR Module) provides auxiliary definitions.

The &asn; module is located in sub directory `z39.50`. There you'll find C files that implement encoders and decoders for the Z39.50 types. You'll also find the protocol definitions: `z3950v3.asn`, `esupdate.asn`, and others.

### Preparing PDUs

A structure representing a complex ASN.1 type doesn't in itself contain the members of that type. Instead, the structure contains pointers to the members of the type. This is necessary, in part, to allow a mechanism for specifying which of the optional structure (SEQUENCE) members are present, and which are not. It follows that you will need to somehow provide space for the individual members of the structure, and set the pointers to refer to the members.

The conversion routines don't care how you allocate and maintain your C structures - they just follow the pointers that you provide. Depending on the complexity of your application, and your personal taste, there are at least three different approaches that you may take when you allocate the structures.

You can use static or automatic local variables in the function that prepares the PDU. This is a simple approach, and it provides the most efficient form of memory management. While it works well for flat PDUs like the InitRequest, it will generally not be sufficient for say, the generation of an arbitrarily complex RPN query structure.

You can individually create the structure and its members using the `malloc(2)` function. If you want to ensure that the data is freed when it is no longer needed, you will have to define a function that individually releases each member of a structure before freeing the structure itself.

You can use the `odr_malloc()` function (see for details). When you use `odr_malloc()`, you can release all of the allocated data in a single operation, independent of any pointers and relations between the data. The `odr_malloc()` function is based on a "nibble-memory" scheme, in which large portions of memory are allocated, and then gradually handed out with each call to `odr_malloc()`. The next time you call `odr_reset()`, all of the memory allocated since the last call is recycled for future use (actually, it is placed on a free-list).

You can combine all of the methods described here. This will often be the most practical approach. For instance, you might use `odr_malloc()` to allocate an entire structure and some of its elements, while you leave other elements pointing to global or per-session default variables.

The &asn; module provides an important aid in creating new PDUs. For each of the PDU types (say, `Z_InitRequest`), a function is provided that allocates and initializes an instance of that PDU type for you. In the case of the InitRequest, the function is simply named `zget_InitRequest()`, and it sets up reasonable default value for all of the mandatory members. The optional members are generally initialized to null pointers. This last aspect is very important: it ensures that if the PDU definitions are extended after you finish your implementation (to accommodate new versions of the protocol, say), you won't get into trouble with uninitialized pointers in your structures. The functions use `odr_malloc()` to allocate the PDUs and its members, so you can free everything again with a single call to `odr_reset()`. We strongly recommend that you use the `zget_*` functions whenever you are preparing a PDU (in a C++ API, the `zget_` functions would probably be promoted to constructors for the individual types).

The prototype for the individual PDU types generally look like this:

        Z_<type> *zget_<type>(ODR o);

e.g.:

        Z_InitRequest *zget_InitRequest(ODR o);

The &odr; handle should generally be your encoding stream, but it needn't be.

As well as the individual PDU functions, a function `zget_APDU()` is provided, which allocates a top-level Z-APDU of the type requested:

        Z_APDU *zget_APDU(ODR o, int which);

The `which` parameter is (of course) the discriminator belonging to the `Z_APDU` `CHOICE` type. All of the interface described here is provided by the &asn; module, and you access it through the `proto.h` header file.

### EXTERNAL Data

In order to achieve extensibility and adaptability to different application domains, the new version of the protocol defines many structures outside of the main ASN.1 specification, referencing them through ASN.1 EXTERNAL constructs. To simplify the construction and access to the externally referenced data, the &asn; module defines a specialized version of the EXTERNAL construct, called `Z_External`.It is defined thus:

    typedef struct Z_External
    {
        Odr_oid *direct_reference;
        int *indirect_reference;
        char *descriptor;
        enum
        {
            /* Generic types */
            Z_External_single = 0,
            Z_External_octet,
            Z_External_arbitrary,

            /* Specific types */
            Z_External_SUTRS,
            Z_External_explainRecord,
            Z_External_resourceReport1,
            Z_External_resourceReport2

        ...

        } which;
        union
        {
            /* Generic types */
            Odr_any *single_ASN1_type;
            Odr_oct *octet_aligned;
            Odr_bitmask *arbitrary;

            /* Specific types */
            Z_SUTRS *sutrs;
            Z_ExplainRecord *explainRecord;
            Z_ResourceReport1 *resourceReport1;
            Z_ResourceReport2 *resourceReport2;

            ...

        } u;
    } Z_External;

When decoding, the &asn; module will attempt to determine which syntax describes the data by looking at the reference fields (currently only the direct-reference). For ASN.1 structured data, you need only consult the `which` field to determine the type of data. You can the access the data directly through the union. When constructing data for encoding, you set the union pointer to point to the data, and set the `which` field accordingly. Remember also to set the direct (or indirect) reference to the correct OID for the data type. For non-ASN.1 data such as MARC records, use the `octet_aligned` arm of the union.

Some servers return ASN.1 structured data values (e.g. database records) as BER-encoded records placed in the `octet-aligned` branch of the EXTERNAL CHOICE. The ASN-module will not automatically decode these records. To help you decode the records in the application, the function

       Z_ext_typeent *z_ext_gettypebyref(const oid *oid);

can be used to retrieve information about the known, external data types. The function returns a pointer to a static area, or NULL, if no match for the given direct reference is found. The `Z_ext_typeent` is defined as:

    typedef struct Z_ext_typeent
    {
        int oid[OID_SIZE]; /* the direct-reference OID. */
        int what;          /* discriminator value for the external CHOICE */
        Odr_fun fun;       /* decoder function */
    } Z_ext_typeent;

The `what` member contains the `Z_External` union discriminator value for the given type: For the SUTRS record syntax, the value would be `Z_External_sutrs`. The `fun` member contains a pointer to the function which encodes/decodes the given type. Again, for the SUTRS record syntax, the value of `fun` would be `z_SUTRS` (a function pointer).

If you receive an EXTERNAL which contains an octet-string value that you suspect of being an ASN.1-structured data value, you can use `z_ext_gettypebyref` to look for the provided direct-reference. If the return value is different from NULL, you can use the provided function to decode the BER string (see ).

If you want to send EXTERNALs containing ASN.1-structured values in the octet-aligned branch of the CHOICE, this is possible too. However, on the encoding phase, it requires a somewhat involved juggling around of the various buffers involved.

If you need to add new, externally defined data types, you must update the struct above, in the source file `prt-ext.h`, as well as the encoder/decoder in the file `prt-ext.c`. When changing the latter, remember to update both the `arm` array and the list `type_table`, which drives the CHOICE biasing that is necessary to tell the different, structured types apart on decoding.

Eventually, the EXTERNAL processing will most likely automatically insert the correct OIDs or indirect-refs. First, however, we need to determine how application-context management (specifically the presentation-context-list) should fit into the various modules.

### PDU Contents Table

We include, for reference, a listing of the fields of each top-level PDU, as well as their default settings.

Default settings for PDU Initialize Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
protocolVersion | Odr_bitmask | Empty bitmask
options | Odr_bitmask | Empty bitmask
preferredMessageSize | Odr_int | 30*1024
maximumRecordSize | Odr_int | 30*1024
idAuthentication | Z_IdAuthentication | NULL
implementationId | char* | "81"
implementationName | char* | "YAZ"
implementationVersion | char* | YAZ_VERSION
userInformationField | Z_UserInformation | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for PDU Initialize Response

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
protocolVersion | Odr_bitmask | Empty bitmask
options | Odr_bitmask | Empty bitmask
preferredMessageSize | Odr_int | 30*1024
maximumRecordSize | Odr_int | 30*1024
result | Odr_bool | TRUE
implementationId | char* | "id)"
implementationName | char* | "YAZ"
implementationVersion | char* | YAZ_VERSION
userInformationField | Z_UserInformation | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for PDU Search Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
smallSetUpperBound | Odr_int | 0
largeSetLowerBound | Odr_int | 1
mediumSetPresentNumber | Odr_int | 0
replaceIndicator | Odr_bool | TRUE
resultSetName | char * | "default"
num_databaseNames | Odr_int | 0
databaseNames | char ** | NULL
smallSetElementSetNames | Z_ElementSetNames | NULL
mediumSetElementSetNames | Z_ElementSetNames | NULL
preferredRecordSyntax | Odr_oid | NULL
query | Z_Query | NULL
additionalSearchInfo | Z_OtherInformation | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for PDU Search Response

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
resultCount | Odr_int | 0
numberOfRecordsReturned | Odr_int | 0
nextResultSetPosition | Odr_int | 0
searchStatus | Odr_bool | TRUE
resultSetStatus | Odr_int | NULL
presentStatus | Odr_int | NULL
records | Z_Records | NULL
additionalSearchInfo | Z_OtherInformation | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for PDU Present Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
resultSetId | char* | "default"
resultSetStartPoint | Odr_int | 1
numberOfRecordsRequested | Odr_int | 10
num_ranges | Odr_int | 0
additionalRanges | Z_Range | NULL
recordComposition | Z_RecordComposition | NULL
preferredRecordSyntax | Odr_oid | NULL
maxSegmentCount | Odr_int | NULL
maxRecordSize | Odr_int | NULL
maxSegmentSize | Odr_int | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for PDU Present Response

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
numberOfRecordsReturned | Odr_int | 0
nextResultSetPosition | Odr_int | 0
presentStatus | Odr_int | Z_PresentStatus_success
records | Z_Records | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Delete Result Set Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
deleteFunction | Odr_int | Z_DeleteResultSetRequest_list
num_ids | Odr_int | 0
resultSetList | char** | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Delete Result Set Response

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
deleteOperationStatus | Odr_int | Z_DeleteStatus_success
num_statuses | Odr_int | 0
deleteListStatuses | Z_ListStatus** | NULL
numberNotDeleted | Odr_int | NULL
num_bulkStatuses | Odr_int | 0
bulkStatuses | Z_ListStatus | NULL
deleteMessage | char* | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Scan Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
num_databaseNames | Odr_int | 0
databaseNames | char** | NULL
attributeSet | Odr_oid | NULL
termListAndStartPoint | Z_AttributesPlus... | NULL
stepSize | Odr_int | NULL
numberOfTermsRequested | Odr_int | 20
preferredPositionInResponse | Odr_int | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Scan Response

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
stepSize | Odr_int | NULL
scanStatus | Odr_int | Z_Scan_success
numberOfEntriesReturned | Odr_int | 0
positionOfTerm | Odr_int | NULL
entries | Z_ListEntries | NULL
attributeSet | Odr_oid | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Trigger Resource Control Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
requestedAction | Odr_int | Z_TriggerResourceCtrl_resou..
prefResourceReportFormat | Odr_oid | NULL
resultSetWanted | Odr_bool | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Resource Control Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
suspendedFlag | Odr_bool | NULL
resourceReport | Z_External | NULL
partialResultsAvailable | Odr_int | NULL
responseRequired | Odr_bool | FALSE
triggeredRequestFlag | Odr_bool | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Resource Control Response

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
continueFlag | bool_t | TRUE
resultSetWanted | bool_t | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Access Control Request

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
which | enum | Z_AccessRequest_simpleForm;
u | union | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Access Control Response

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
which | enum | Z_AccessResponse_simpleForm
u | union | NULL
diagnostic | Z_DiagRec | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Segment

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
numberOfRecordsReturned | Odr_int | value=0
num_segmentRecords | Odr_int | 0
segmentRecords | Z_NamePlusRecord | NULL
otherInfo | Z_OtherInformation | NULL

Default settings for Close

Field | Type | Default Value
--- | --- | ---
referenceId | Z_ReferenceId | NULL
closeReason | Odr_int | Z_Close_finished
diagnosticInformation | char* | NULL
resourceReportFormat | Odr_oid | NULL
resourceFormat | Z_External | NULL
otherInfo | Z_OtherInformation | NULL

## SOAP and SRU

### Introduction

&yaz; uses a very simple implementation of SOAP that only (currently) supports what is sufficient to offer SRU SOAP functionality. The implementation uses the tree API of libxml2 to encode and decode SOAP packages.

Like the Z39.50 ASN.1 module, the &yaz; SRU implementation uses simple C structs to represent SOAP packages as well as HTTP packages.

### HTTP

&yaz; only offers HTTP as transport carrier for SOAP, but it is relatively easy to change that.

The following definition of `Z_GDU` (Generic Data Unit) allows for both HTTP and Z39.50 in one packet.

    #include <yaz/zgdu.h>

    #define Z_GDU_Z3950         1
    #define Z_GDU_HTTP_Request  2
    #define Z_GDU_HTTP_Response 3
    typedef struct {
      int which;
      union {
        Z_APDU *z3950;
        Z_HTTP_Request *HTTP_Request;
        Z_HTTP_Response *HTTP_Response;
      } u;
    } Z_GDU ;

The corresponding Z_GDU encoder/decoder is `z_GDU`. The `z3950` is any of the known BER encoded Z39.50 APDUs. `HTTP_Request` and `HTTP_Response` is the HTTP Request and Response respectively.

### SOAP Packages

Every SOAP package in &yaz; is represented as follows:

    #include <yaz/soap.h>

    typedef struct {
        char *fault_code;
        char *fault_string;
        char *details;
    } Z_SOAP_Fault;

    typedef struct {
        int no;
        char *ns;
        void *p;
    } Z_SOAP_Generic;

    #define Z_SOAP_fault 1
    #define Z_SOAP_generic 2
    #define Z_SOAP_error 3
    typedef struct {
        int which;
        union {
            Z_SOAP_Fault   *fault;
            Z_SOAP_Generic *generic;
            Z_SOAP_Fault   *soap_error;
        } u;
        const char *ns;
    } Z_SOAP;

The `fault` and `soap_error` arms both represent a SOAP fault - struct `Z_SOAP_Fault`. Any other generic (valid) package is represented by `Z_SOAP_Generic`.

The `ns` as part of `Z_SOAP` is the namespace for SOAP itself and reflects the SOAP version. For version 1.1 it is `http://schemas.xmlsoap.org/soap/envelope/`, for version 1.2 it is `http://www.w3.org/2001/06/soap-envelope`.

    int z_soap_codec(ODR o, Z_SOAP **pp,
                     char **content_buf, int *content_len,
                     Z_SOAP_Handler *handlers);

The `content_buf` and `content_len` is XML buffer and length of buffer respectively.

The `handlers` is a list of SOAP codec handlers - one handler for each service namespace. For SRU SOAP, the namespace would be `http://www.loc.gov/zing/srw/v1.0/`.

When decoding, the `z_soap_codec` inspects the XML content and tries to match one of the services namespaces of the supplied handlers. If there is a match. a handler function is invoked which decodes that particular SOAP package. If successful, the returned `Z_SOAP` package will be of type `Z_SOAP_Generic`. Member `no` is set the offset of the handler that matched; `ns` is set to namespace of the matching handler; the void pointer `p` is set to the C data structure associated with the handler.

When a NULL namespace is met (member `ns` below), that specifies end-of-list.

Each handler is defined as follows:

    typedef struct {
        char *ns;
        void *client_data;
        Z_SOAP_fun f;
    } Z_SOAP_Handler;

The `ns` is the namespace of the service associated with handler `f`. The `client_data` is user-defined data which is passed to the handler.

The prototype for a SOAP service handler is:

    int handler(ODR o, void * ptr, void **handler_data,
                void *client_data, const char *ns);

The o specifies the mode (decode/encode) as usual. The second argument, ptr, is a libxml2 tree node pointer (`xmlNodePtr`) and is a pointer to the `Body` element of the SOAP package. The handler_data is an opaque pointer to C definitions associated with the SOAP service. The client_data is the pointer which was set as part of the `Z_SOAP_handler`. Finally, ns is the service namespace.

### SRU

SRU SOAP is just one implementation of a SOAP handler as described in the previous section. The encoder/decoder handler for SRU is defined as follows:

    #include <yaz/srw.h>

    int yaz_srw_codec(ODR o, void * pptr,
                      Z_SRW_GDU **handler_data,
                      void *client_data, const char *ns);

Here, `Z_SRW_GDU` is either searchRetrieveRequest or a searchRetrieveResponse.

The xQuery and xSortKeys are not handled yet by the SRW implementation of &yaz;. Explain is also missing. Future versions of &yaz; will include these features.

The definition of searchRetrieveRequest is:

    typedef struct {

    #define Z_SRW_query_type_cql  1
    #define Z_SRW_query_type_xcql 2
    #define Z_SRW_query_type_pqf  3
        int query_type;
        union {
            char *cql;
            char *xcql;
            char *pqf;
        } query;

    #define Z_SRW_sort_type_none 1
    #define Z_SRW_sort_type_sort 2
    #define Z_SRW_sort_type_xSort 3
        int sort_type;
        union {
            char *none;
            char *sortKeys;
            char *xSortKeys;
        } sort;
        int  *startRecord;
        int  *maximumRecords;
        char *recordSchema;
        char *recordPacking;
        char *database;
    } Z_SRW_searchRetrieveRequest;

Please observe that data of type xsd:string is represented as a char pointer (`char *`). A null pointer means that the element is absent. Data of type xsd:integer is represented as a pointer to an int (`int *`). Again, a null pointer is used for absent elements.

The SearchRetrieveResponse has the following definition.

    typedef struct {
        int * numberOfRecords;
        char * resultSetId;
        int * resultSetIdleTime;

        Z_SRW_record *records;
        int num_records;

        Z_SRW_diagnostic *diagnostics;
        int num_diagnostics;
        int *nextRecordPosition;
    } Z_SRW_searchRetrieveResponse;

The `num_records` and `num_diagnostics` is number of returned records and diagnostics respectively, and also correspond to the "size of" arrays `records` and `diagnostics`.

A retrieval record is defined as follows:

    typedef struct {
        char *recordSchema;
        char *recordData_buf;
        int recordData_len;
        int *recordPosition;
    } Z_SRW_record;

The record data is defined as a buffer of some length so that data can be of any type. SRW 1.0 currently doesn't allow for this (only XML), but future versions might do.

And, a diagnostic as:

    typedef struct {
        int  *code;
        char *details;
    } Z_SRW_diagnostic;

## Supporting Tools

In support of the service API - primarily the ASN module, which provides the programmatic interface to the Z39.50 APDUs, &yaz; contains a collection of tools that support the development of applications.

### Query Syntax Parsers

Since the type-1 (RPN) query structure has no direct, useful string representation, every origin application needs to provide some form of mapping from a local query notation or representation to a Z_RPNQuery structure. Some programmers will prefer to construct the query manually, perhaps using `odr_malloc()` to simplify memory management. The &yaz; distribution includes three separate, query-generating tools that may be of use to you.

#### Prefix Query Format

Since RPN or reverse polish notation is really just a fancy way of describing a suffix notation format (operator follows operands), it would seem that the confusion is total when we now introduce a prefix notation for RPN. The reason is one of simple laziness - it's somewhat simpler to interpret a prefix format, and this utility was designed for maximum simplicity, to provide a baseline representation for use in simple test applications and scripting environments (like Tcl). The demonstration client included with YAZ uses the PQF.

The PQF has been adopted by other parties developing Z39.50 software. It is often referred to as Prefix Query Notation - PQN.

The PQF is defined by the pquery module in the YAZ library. There are two sets of functions that have similar behavior. First set operates on a PQF parser handle, second set doesn't. First set of functions are more flexible than the second set. Second set is obsolete and is only provided to ensure backwards compatibility.

First set of functions all operate on a PQF parser handle:

         #include <yaz/pquery.h>

         YAZ_PQF_Parser yaz_pqf_create(void);

         void yaz_pqf_destroy(YAZ_PQF_Parser p);

         Z_RPNQuery *yaz_pqf_parse(YAZ_PQF_Parser p, ODR o, const char *qbuf);

         Z_AttributesPlusTerm *yaz_pqf_scan(YAZ_PQF_Parser p, ODR o,
                              Odr_oid **attributeSetId, const char *qbuf);

         int yaz_pqf_error(YAZ_PQF_Parser p, const char **msg, size_t *off);

A PQF parser is created and destructed by functions `yaz_pqf_create` and `yaz_pqf_destroy` respectively. Function `yaz_pqf_parse` parses the query given by string `qbuf`. If parsing was successful, a Z39.50 RPN Query is returned which is created using ODR stream `o`. If parsing failed, a NULL pointer is returned. Function `yaz_pqf_scan` takes a scan query in `qbuf`. If parsing was successful, the function returns attributes plus term pointer and modifies `attributeSetId` to hold attribute set for the scan request - both allocated using ODR stream `o`. If parsing failed, yaz_pqf_scan returns a NULL pointer. Error information for bad queries can be obtained by a call to `yaz_pqf_error` which returns an error code and modifies `*msg` to point to an error description, and modifies `*off` to the offset within the last query where parsing failed.

The second set of functions are declared as follows:

         #include <yaz/pquery.h>

         Z_RPNQuery *p_query_rpn(ODR o, oid_proto proto, const char *qbuf);

         Z_AttributesPlusTerm *p_query_scan(ODR o, oid_proto proto,
                                 Odr_oid **attributeSetP, const char *qbuf);

         int p_query_attset(const char *arg);

The function `p_query_rpn()` takes as arguments an &odr; stream (see section The ODR Module) to provide a memory source (the structure created is released on the next call to `odr_reset()` on the stream), a protocol identifier (one of the constants PROTO_Z3950 and PROTO_SR), an attribute set reference, and finally a null-terminated string holding the query string.

If the parse went well, `p_query_rpn()` returns a pointer to a `Z_RPNQuery` structure which can be placed directly into a `Z_SearchRequest`. If parsing failed, due to syntax error, a NULL pointer is returned.

The `p_query_attset` specifies which attribute set to use if the query doesn't specify one by the `@attrset` operator. The `p_query_attset` returns 0 if the argument is a valid attribute set specifier; otherwise the function returns -1.

The grammar of the PQF is as follows:

         query ::= top-set query-struct.

         top-set ::= [ '@attrset' string ]

         query-struct ::= attr-spec | simple | complex | '@term' term-type query

         attr-spec ::= '@attr' [ string ] string query-struct

         complex ::= operator query-struct query-struct.

         operator ::= '@and' | '@or' | '@not' | '@prox' proximity.

         simple ::= result-set | term.

         result-set ::= '@set' string.

         term ::= string.

         proximity ::= exclusion distance ordered relation which-code unit-code.

         exclusion ::= '1' | '0' | 'void'.

         distance ::= integer.

         ordered ::= '1' | '0'.

         relation ::= integer.

         which-code ::= 'known' | 'private' | integer.

         unit-code ::= integer.

         term-type ::= 'general' | 'numeric' | 'string' | 'oid' | 'datetime' | 'null'.

You will note that the syntax above is a fairly faithful representation of RPN, except for the Attribute, which has been moved a step away from the term, allowing you to associate one or more attributes with an entire query structure. The parser will automatically apply the given attributes to each term as required.

The @attr operator is followed by an attribute specification (`attr-spec` above). The specification consists of an optional attribute set, an attribute type-value pair and a sub-query. The attribute type-value pair is packed in one string: an attribute type, an equals sign, and an attribute value, like this: `@attr 1=1003`. The type is always an integer, but the value may be either an integer or a string (if it doesn't start with a digit character). A string attribute-value is encoded as a Type-1 "complex" attribute with the list of values containing the single string specified, and including no semantic indicators.

Version 3 of the Z39.50 specification defines various encoding of terms. Use `@term` type string, where type is one of: `general`, `numeric` or `string` (for InternationalString). If no term type has been given, the `general` form is used. This is the only encoding allowed in both versions 2 and 3 of the Z39.50 standard.

##### Using Proximity Operators with PQF

This is an advanced topic, describing how to construct queries that make very specific requirements on the relative location of their operands. You may wish to skip this section and go straight to the example PQF queries.

Most Z39.50 servers do not support proximity searching, or support only a small subset of the full functionality that can be expressed using the PQF proximity operator. Be aware that the ability to express a query in PQF is no guarantee that any given server will be able to execute it.

The proximity operator `@prox` is a special and more restrictive version of the conjunction operator `@and`. Its semantics are described in section 3.7.2 (Proximity) of Z39.50 the standard itself, which can be read on-line at

In PQF, the proximity operation is represented by a sequence of the form

           @prox exclusion distance ordered relation which-code unit-code

in which the meanings of the parameters are as described in the standard, and they can take the following values:

- exclusion

  0 = false (i.e. the proximity condition specified by the remaining parameters must be satisfied) or 1 = true (the proximity condition specified by the remaining parameters must not be satisfied).

- distance

  An integer specifying the difference between the locations of the operands: e.g. two adjacent words would have distance=1 since their locations differ by one unit.

- ordered

  1 = ordered (the operands must occur in the order the query specifies them) or 0 = unordered (they may appear in either order).

- relation

  Recognised values are 1 (lessThan), 2 (lessThanOrEqual), 3 (equal), 4 (greaterThanOrEqual), 5 (greaterThan) and 6 (notEqual).

- which-code

  `known` or `k` (the unit-code parameter is taken from the well-known list of alternatives described below) or `private` or `p` (the unit-code parameter has semantics specific to an out-of-band agreement such as a profile).

- unit-code

  If the which-code parameter is `known` then the recognised values are 1 (character), 2 (word), 3 (sentence), 4 (paragraph), 5 (section), 6 (chapter), 7 (document), 8 (element), 9 (subelement), 10 (elementType) and 11 (byte). If which-code is `private` then the acceptable values are determined by the profile.

(The numeric values of the relation and well-known unit-code parameters are taken straight from the ASN.1 of the proximity structure in the standard.)

##### PQF queries

PQF queries using simple terms

    	dylan

    	"bob dylan"

PQF boolean operators

    	@or "dylan" "zimmerman"

    	@and @or dylan zimmerman when

    	@and when @or dylan zimmerman

PQF references to result sets

    	@set Result-1

    	@and @set seta @set setb

Attributes for terms

    	@attr 1=4 computer

    	@attr 1=4 @attr 4=1 "self portrait"

    	@attrset exp1 @attr 1=1 CategoryList

    	@attr gils 1=2008 Copenhagen

    	@attr 1=/book/title computer

PQF Proximity queries

    	@prox 0 3 1 2 k 2 dylan zimmerman

Here the parameters 0, 3, 1, 2, k and 2 represent exclusion, distance, ordered, relation, which-code and unit-code, in that order. So:

- exclusion = 0: the proximity condition must hold

- distance = 3: the terms must be three units apart

- ordered = 1: they must occur in the order they are specified

- relation = 2: lessThanOrEqual (to the distance of 3 units)

- which-code is "known", so the standard unit-codes are used

- unit-code = 2: word.

So the whole proximity query means that the words `dylan` and `zimmerman` must both occur in the record, in that order, differing in position by three or fewer words (i.e. with two or fewer words between them.) The query would find "Bob Dylan, aka. Robert Zimmerman", but not "Bob Dylan, born as Robert Zimmerman" since the distance in this case is four.

PQF specification of search term type

    	@term string "a UTF-8 string, maybe?"

PQF mixed queries

    	@or @and bob dylan @set Result-1

    	@attr 4=1 @and @attr 1=1 "bob dylan" @attr 1=4 "slow train coming"

    	@and @attr 2=4 @attr gils 1=2038 -114 @attr 2=2 @attr gils 1=2039 -109

The last of these examples is a spatial search: in the GILS attribute set, access point 2038 indicates West Bounding Coordinate and 2030 indicates East Bounding Coordinate, so the query is for areas extending from -114 degrees longitude to no more than -109 degrees longitude.

#### CCL

Not all users enjoy typing in prefix query structures and numerical attribute values, even in a minimalistic test client. In the library world, the more intuitive Common Command Language - CCL (ISO 8777) has enjoyed some popularity - especially before the widespread availability of graphical interfaces. It is still useful in applications where you for some reason or other need to provide a symbolic language for expressing boolean query structures.

##### CCL Syntax

The CCL parser obeys the following grammar for the FIND argument. The syntax is annotated using lines prefixed by `--`.

          CCL-Find ::= CCL-Find Op Elements
                    | Elements.

          Op ::= "and" | "or" | "not"
          -- The above means that Elements are separated by boolean operators.

          Elements ::= '(' CCL-Find ')'
                    | Set
                    | Terms
                    | Qualifiers Relation Terms
                    | Qualifiers Relation '(' CCL-Find ')'
                    | Qualifiers '=' string '-' string
          -- Elements is either a recursive definition, a result set reference, a
          -- list of terms, qualifiers followed by terms, qualifiers followed
          -- by a recursive definition or qualifiers in a range (lower - upper).

          Set ::= 'set' = string
          -- Reference to a result set

          Terms ::= Terms Prox Term
                 | Term
          -- Proximity of terms.

          Term ::= Term string
                | string
          -- This basically means that a term may include a blank

          Qualifiers ::= Qualifiers ',' string
                      | string
          -- Qualifiers is a list of strings separated by comma

          Relation ::= '=' | '>=' | '<=' | '<>' | '>' | '<'
          -- Relational operators. This really doesn't follow the ISO8777
          -- standard.

          Prox ::= '%' | '!'
          -- Proximity operator

CCL queries

The following queries are all valid:

           dylan

           "bob dylan"

           dylan or zimmerman

           set=1

           (dylan and bob) or set=1

           righttrunc?

           "notrunc?"

           singlechar#mask

Assuming that the qualifiers `ti` and `au` and `date` are defined, we may use:

           ti=self portrait

           au=(bob dylan and slow train coming)

           date>1980 and (ti=((self portrait)))

##### CCL Qualifiers

Qualifiers are used to direct the search to a particular searchable index, such as title (ti) and author indexes (au). The CCL standard itself doesn't specify a particular set of qualifiers, but it does suggest a few short-hand notations. You can customize the CCL parser to support a particular set of qualifiers to reflect the current target profile. Traditionally, a qualifier would map to a particular use-attribute within the BIB-1 attribute set. It is also possible to set other attributes, such as the structure attribute.

A CCL profile is a set of predefined CCL qualifiers that may be read from a file or set in the CCL API. The YAZ client reads its CCL qualifiers from a file named `default.bib`. There are four types of lines in a CCL profile: qualifier specification, qualifier alias, comments and directives.

###### Qualifier specification

A qualifier specification is of the form:

qualifier-name [attributeset`,`]type`=`val [attributeset`,`]type`=`val ...

where qualifier-name is the name of the qualifier to be used (e.g. `ti`), type is attribute type in the attribute set (Bib-1 is used if no attribute set is given) and val is attribute value. The type can be specified as an integer, or as a single-letter: `u` for use, `r` for relation, `p` for position, `s` for structure,`t` for truncation, or `c` for completeness. The attributes for the special qualifier name `term` are used when no CCL qualifier is given in a query.

Common Bib-1 attributes

Type | Description
--- | ---
`u=`value | Use attribute (1). Common use attributes are 1 Personal-name, 4 Title, 7 ISBN, 8 ISSN, 30 Date, 62 Subject, 1003 Author, 1016 Any. Specify value as an integer.
`r=`value | Relation attribute (2). Common values are 1 <, 2 <=, 3 =, 4 >=, 5 >, 6 <>, 100 phonetic, 101 stem, 102 relevance, 103 always matches.
`p=`value | Position attribute (3). Values: 1 first in field, 2 first in any subfield, 3 any position in field.
`s=`value | Structure attribute (4). Values: 1 phrase, 2 word, 3 key, 4 year, 5 date, 6 word list, 100 date (un), 101 name (norm), 102 name (un), 103 structure, 104 urx, 105 free-form-text, 106 document-text, 107 local-number, 108 string, 109 numeric string.
`t=`value | Truncation attribute (5). Values: 1 right, 2 left, 3 left and right, 100 none, 101 process #, 102 regular-1, 103 regular-2, 104 CCL.
`c=`value | Completeness attribute (6). Values: 1 incomplete subfield, 2 complete subfield, 3 complete field.

Refer to or the complete list of Bib-1 attributes

It is also possible to specify non-numeric attribute values, which are used in combination with certain types. The special combinations are:

Special attribute combos

Name | Description
--- | ---
`s=pw` | The structure is set to either word or phrase depending on the number of tokens in a term (phrase-word).
`s=al` | Each token in the term is ANDed (and-list). This does not set the structure at all.
`s=ol` | Each token in the term is ORed (or-list). This does not set the structure at all.
`s=ag` | Tokens that appears as phrases (with blank in them) gets structure phrase attached (4=1). Tokens that appear to be words gets structure word attached (4=2). Phrases and words are ANDed. This is a variant of s=al and s=pw, with the main difference that words are not split (with operator AND) but instead kept in one RPN token. This facility appeared in YAZ 4.2.38.
`s=sl` | Tokens are split into sub-phrases of all combinations - in order. This facility appeared in YAZ 5.14.0.
`r=o` | Allows ranges and the operators greater-than, less-than, ... equals. This sets Bib-1 relation attribute accordingly (relation ordered). A query construct is only treated as a range if dash is used and that is surrounded by white-space. So `-1980` is treated as term `"-1980"` not `<= 1980`. If `- 1980` is used, however, that is treated as a range.
`r=r` | Similar to `r=o` but assumes that terms are non-negative (not prefixed with `-`). Thus, a dash will always be treated as a range. The construct `1980-1990` is treated as a range with `r=r` but as a single term `"1980-1990"` with `r=o`. The special attribute `r=r` is available in YAZ 2.0.24 or later.
`r=omiteq` | This will omit relation=equals (@attr 2=3) when r=o / r=r is used. This is useful for servers that somehow break when an explicit relation=equals is used. Omitting the relation is usually safe because "equals" is the default behavior. This tweak was added in YAZ version 5.1.2.
`t=l` | Allows term to be left-truncated. If term is of the form `?x`, the resulting Type-1 term is `x` and truncation is left.
`t=r` | Allows term to be right-truncated. If term is of the form `x?`, the resulting Type-1 term is `x` and truncation is right.
`t=n` | If term is does not include `?`, the truncation attribute is set to none (100).
`t=b` | Allows term to be both left-and-right truncated. If term is of the form `?x?`, the resulting term is `x` and truncation is set to both left and right.
`t=x` | Allows masking anywhere in a term, thus fully supporting # (mask one character) and ? (zero or more of any). If masking is used, truncation is set to 102 (regexp-1 in term) and the term is converted accordingly to a regular expression.
`t=z` | Allows masking anywhere in a term, thus fully supporting # (mask one character) and ? (zero or more of any). If masking is used, truncation is set to 104 (Z39.58 in term) and the term is converted accordingly to Z39.58 masking term - actually the same truncation as CCL itself.

CCL profile

Consider the following definition:

    	ti       u=4 s=1
    	au       u=1 s=1
    	term     s=105
    	ranked   r=102
    	date     u=30 r=o

`ti` and `au` both set structure attribute to phrase (s=1). `ti` sets the use-attribute to 4. `au` sets the use-attribute to 1. When no qualifiers are used in the query, the structure-attribute is set to free-form-text (105) (rule for `term`). The `date` sets the relation attribute to the relation used in the CCL query and sets the use attribute to 30 (Bib-1 Date).

You can combine attributes. To Search for "ranked title" you can do

    	 ti,ranked=knuth computer

which will set relation=ranked, use=title, structure=phrase.

Query

    	 date > 1980

is a valid query. But

    	 ti > 1980

is invalid.

###### Qualifier alias

A qualifier alias is of the form:

q q1 q2 ..

which declares q to be an alias for q1, q2... such that the CCL query q=x is equivalent to q1=x or q2=x or ....

###### Comments

Lines with white space or lines that begin with character `#` are treated as comments.

###### Directives

Directive specifications takes the form

`@`directive value

CCL directives

Name | Description | Default
--- | --- | ---
truncation | Truncation character | `?`
mask | Masking character. Requires YAZ 4.2.58 or later | `#`
field | Specifies how multiple fields are to be combined. There are two modes: `or`: multiple qualifier fields are ORed, `merge`: attributes for the qualifier fields are merged and assigned to one term. | `merge`
case | Specifies if CCL operators and qualifiers should be compared with case sensitivity or not. Specify 1 for case sensitive; 0 for case insensitive. | `1`
and | Specifies token for CCL operator AND. | `and`
or | Specifies token for CCL operator OR. | `or`
not | Specifies token for CCL operator NOT. | `not`
set | Specifies token for CCL operator SET. | `set`

##### CCL API

All public definitions can be found in the header file `ccl.h`. A profile identifier is of type `CCL_bibset`. A profile must be created with the call to the function `ccl_qual_mk` which returns a profile handle of type `CCL_bibset`.

To read a file containing qualifier definitions the function `ccl_qual_file` may be convenient. This function takes an already opened `FILE` handle pointer as argument along with a `CCL_bibset` handle.

To parse a simple string with a FIND query use the function

    struct ccl_rpn_node *ccl_find_str(CCL_bibset bibset, const char *str,
                                      int *error, int *pos);

which takes the CCL profile (`bibset`) and query (`str`) as input. Upon successful completion the RPN tree is returned. If an error occurs, such as a syntax error, the integer pointed to by `error` holds the error code and `pos` holds the offset inside query string in which the parsing failed.

An English representation of the error may be obtained by calling the `ccl_err_msg` function. The error codes are listed in `ccl.h`.

To convert the CCL RPN tree (type `struct ccl_rpn_node *`) to the Z_RPNQuery of YAZ the function `ccl_rpn_query` must be used. This function which is part of YAZ is implemented in `yaz-ccl.c`. After calling this function the CCL RPN tree is probably no longer needed. The `ccl_rpn_delete` destroys the CCL RPN tree.

A CCL profile may be destroyed by calling the `ccl_qual_rm` function.

The token names for the CCL operators may be changed by setting the globals (all type `char *`) `ccl_token_and`, `ccl_token_or`, `ccl_token_not` and `ccl_token_set`. An operator may have aliases, i.e. there may be more than one name for the operator. To do this, separate each alias with a space character.

#### CQL

CQL - Common Query Language - was defined for the SRU protocol. In many ways CQL has a similar syntax to CCL. The objective of CQL is different. Where CCL aims to be an end-user language, CQL is the protocol query language for SRU.

If you are new to CQL, read the Gentle Introduction.

The CQL parser in &yaz; provides the following:

- It parses and validates a CQL query.

- It generates a C structure that allows you to convert a CQL query to some other query language, such as SQL.

- The parser converts a valid CQL query to PQF, thus providing a way to use CQL for both SRU servers and Z39.50 targets at the same time.

- The parser converts CQL to XCQL. XCQL is an XML representation of CQL. XCQL is part of the SRU specification. However, since SRU supports CQL only, we don't expect XCQL to be widely used. Furthermore, CQL has the advantage over XCQL that it is easy to read.

##### CQL parsing

A CQL parser is represented by the `CQL_parser` handle. Its contents should be considered &yaz; internal (private).

    #include <yaz/cql.h>

    typedef struct cql_parser *CQL_parser;

    CQL_parser cql_parser_create(void);
    void cql_parser_destroy(CQL_parser cp);

A parser is created by `cql_parser_create` and is destroyed by `cql_parser_destroy`.

To parse a CQL query string, the following function is provided:

    int cql_parser_string(CQL_parser cp, const char *str);

A CQL query is parsed by the `cql_parser_string` which takes a query str. If the query was valid (no syntax errors), then zero is returned; otherwise -1 is returned to indicate a syntax error.

    int cql_parser_stream(CQL_parser cp,
                          int (*getbyte)(void *client_data),
                          void (*ungetbyte)(int b, void *client_data),
                          void *client_data);

    int cql_parser_stdio(CQL_parser cp, FILE *f);

The functions `cql_parser_stream` and `cql_parser_stdio` parse a CQL query - just like `cql_parser_string`. The only difference is that the CQL query can be fed to the parser in different ways. The `cql_parser_stream` uses a generic byte stream as input. The `cql_parser_stdio` uses a `FILE` handle which is opened for reading.

##### CQL tree

If the query string is valid, the CQL parser generates a tree representing the structure of the CQL query.

    struct cql_node *cql_parser_result(CQL_parser cp);

`cql_parser_result` returns a pointer to the root node of the resulting tree.

Each node in a CQL tree is represented by a `struct cql_node`. It is defined as follows:

    #define CQL_NODE_ST 1
    #define CQL_NODE_BOOL 2
    #define CQL_NODE_SORT 3
    struct cql_node {
        int which;
        union {
            struct {
                char *index;
    	    char *index_uri;
                char *term;
                char *relation;
    	    char *relation_uri;
                struct cql_node *modifiers;
            } st;
            struct {
                char *value;
                struct cql_node *left;
                struct cql_node *right;
                struct cql_node *modifiers;
            } boolean;
            struct {
                char *index;
                struct cql_node *next;
                struct cql_node *modifiers;
                struct cql_node *search;
            } sort;
        } u;
    };

There are three node types: search term (ST), boolean (BOOL) and sortby (SORT). A modifier is treated as a search term too.

The search term node has five members:

- `index`: index for search term. If an index is unspecified for a search term, `index` will be NULL.

- `index_uri`: index URI for search term or NULL if none could be resolved for the index.

- `term`: the search term itself.

- `relation`: relation for search term.

- `relation_uri`: relation URI for search term.

- `modifiers`: relation modifiers for search term. The `modifiers` list itself of cql_nodes each of type `ST`.

The boolean node represents `and`, `or`, `not` + proximity.

- `left` and `right`: left - and right operand respectively.

- `modifiers`: proximity arguments.

The sort node represents both the SORTBY clause.

##### CQL to PQF conversion

Conversion to PQF (and Z39.50 RPN) is tricky by the fact that the resulting RPN depends on the Z39.50 target capabilities (combinations of supported attributes). In addition, the CQL and SRU operates on index prefixes (URI or strings), whereas the RPN uses Object Identifiers for attribute sets.

The CQL library of &yaz; defines a `cql_transform_t` handle. It represents a particular mapping between CQL and RPN. This handle is created and destroyed by the functions:

    cql_transform_t cql_transform_create(void);
    int cql_transform_define_fname(cql_transform_t *ct, const char *fname);
    int cql_transform_define_FILE(cql_trasnform_t *ct, FILE *f);
    void cql_transform_close(cql_transform_t ct);

The first method constructs a handle. The second and third functon extends the configuration by reading from a file or an open FILE handle. The transform handle is destroyed by `cql_transform_close` in which case no further reference of the handle is allowed.

There are also two methods which creates and reads configuration from a file combined:

    cql_transform_t cql_transform_open_FILE (FILE *f);
    cql_transform_t cql_transform_open_fname(const char *fname);

When a `cql_transform_t` handle has been created you can convert to RPN.

    int cql_transform_buf(cql_transform_t ct,
                          struct cql_node *cn, char *out, int max);

This function converts the CQL tree `cn` using handle `ct`. For the resulting PQF, you supply a buffer `out` which must be able to hold at at least `max` characters.

If conversion failed, `cql_transform_buf` returns a non-zero SRU error code; otherwise zero is returned (conversion successful). The meanings of the numeric error codes are listed in the SRU specification somewhere (no direct link anymore).

If conversion fails, more information can be obtained by calling

    int cql_transform_error(cql_transform_t ct, char **addinfop);

This function returns the most recently returned numeric error-code and sets the string-pointer at `*addinfop` to point to a string containing additional information about the error that occurred: for example, if the error code is 15 ("Illegal or unsupported context set"), the additional information is the name of the requested context set that was not recognised.

The SRU error-codes may be translated into brief human-readable error messages using

    const char *cql_strerror(int code);

If you wish to be able to produce a PQF result in a different way, there are two alternatives.

    void cql_transform_pr(cql_transform_t ct,
                          struct cql_node *cn,
                          void (*pr)(const char *buf, void *client_data),
                          void *client_data);

    int cql_transform_FILE(cql_transform_t ct,
                           struct cql_node *cn, FILE *f);

The former function produces output to a user-defined output stream. The latter writes the result to an already open `FILE`.

##### Specification of CQL to RPN mappings

The file supplied to functions `cql_transform_open_FILE`, `cql_transform_open_fname` follows a structure found in many Unix utilities. It consists of mapping specifications - one per line. Lines starting with `#` are ignored (comments).

Each line is of the form

           CQL pattern =   RPN equivalent

An RPN pattern is a simple attribute list. Each attribute pair takes the form:

           [set] type=value

The attribute set is optional. The type is the attribute type, value the attribute value.

The character `*` (asterisk) has special meaning when used in the RPN pattern. Each occurrence of `*` is substituted with the CQL matching name (index, relation, qualifier etc). This facility can be used to copy a CQL name verbatim to the RPN result.

The following CQL patterns are recognized:

`index.` set`.`name

  This pattern is invoked when a CQL index, such as dc.title is converted. set and name are the context set and index name respectively. Typically, the RPN specifies an equivalent use attribute.

  For terms not bound by an index, the pattern `index.cql.serverChoice` is used. Here, the prefix `cql` is defined as `http://www.loc.gov/zing/cql/cql-indexes/v1.0/`. If this pattern is not defined, the mapping will fail.

  The pattern, `index.` set`.*` is used when no other index pattern is matched.

`qualifier.` set`.`name (DEPRECATED)

  For backwards compatibility, this is recognised as a synonym of `index.` set`.`name

`relation.` relation

  This pattern specifies how a CQL relation is mapped to RPN. The pattern is name of relation operator. Since `=` is used as separator between CQL pattern and RPN, CQL relations including `=` cannot be used directly. To avoid a conflict, the names `ge`, `eq`, `le`, must be used for CQL operators, greater-than-or-equal, equal, less-than-or-equal respectively. The RPN pattern is supposed to include a relation attribute.

  For terms not bound by a relation, the pattern `relation.scr` is used. If the pattern is not defined, the mapping will fail.

  The special pattern, `relation.*` is used when no other relation pattern is matched.

`relationModifier.` mod

  This pattern specifies how a CQL relation modifier is mapped to RPN. The RPN pattern is usually a relation attribute.

`structure.` type

  This pattern specifies how a CQL structure is mapped to RPN. Note that this CQL pattern is somewhat similar to CQL pattern `relation`. The type is a CQL relation.

  The pattern, `structure.*` is used when no other structure pattern is matched. Usually, the RPN equivalent specifies a structure attribute.

`position.` type

  This pattern specifies how the anchor (position) of CQL is mapped to RPN. The type is one of `first`, `any`, `last`, `firstAndLast`.

  The pattern, `position.*` is used when no other position pattern is matched.

`set.` prefix

  This specification defines a CQL context set for a given prefix. The value on the right hand side is the URI for the set - not RPN. All prefixes used in index patterns must be defined this way.

`set`

  This specification defines a default CQL context set for index names. The value on the right hand side is the URI for the set.

CQL to RPN mapping file

This simple file defines two context sets, three indexes and three relations, a position pattern and a default structure.

           set.cql  = http://www.loc.gov/zing/cql/context-sets/cql/v1.1/
           set.dc   = http://www.loc.gov/zing/cql/dc-indexes/v1.0/

           index.cql.serverChoice = 1=1016
           index.dc.title         = 1=4
           index.dc.subject       = 1=21

           relation.<             = 2=1
           relation.eq            = 2=3
           relation.scr           = 2=3

           position.any           = 3=3 6=1

           structure.*            = 4=1

With the mappings above, the CQL query

            computer

is converted to the PQF:

            @attr 1=1016 @attr 2=3 @attr 4=1 @attr 3=3 @attr 6=1 "computer"

by rules `index.cql.serverChoice`, `relation.scr`, `structure.*`, `position.any`.

CQL query

            computer^

is rejected, since `position.right` is undefined.

CQL query

            >my = "http://www.loc.gov/zing/cql/dc-indexes/v1.0/" my.title = x

is converted to

            @attr 1=4 @attr 2=3 @attr 4=1 @attr 3=3 @attr 6=1 "x"

CQL to RPN string attributes

In this example we allow any index to be passed to RPN as a use attribute.

           # Identifiers for prefixes used in this file. (index.*)
           set.cql  = info:srw/cql-context-set/1/cql-v1.1
           set.rpn  = http://bogus/rpn
           set      = http://bogus/rpn

           # The default index when none is specified by the query
           index.cql.serverChoice     = 1=any

           index.rpn.*                = 1=*
           relation.eq                = 2=3
           structure.*                = 4=1
           position.any               = 3=3

The `http://bogus/rpn` context set is also the default so we can make queries such as

            title = a

which is converted to

            @attr 2=3 @attr 4=1 @attr 3=3 @attr 1=title "a"

CQL to RPN using Bath Profile

The file `etc/pqf.properties` has mappings from the Bath Profile and Dublin Core to RPN. If YAZ is installed as a package it's usually located in `/usr/share/yaz/etc` and part of the development package, such as `libyaz-dev`.

##### CQL to XCQL conversion

Conversion from CQL to XCQL is trivial and does not require a mapping to be defined. There are three functions to choose from depending on the way you wish to store the resulting output (XML buffer containing XCQL).

    int cql_to_xml_buf(struct cql_node *cn, char *out, int max);
    void cql_to_xml(struct cql_node *cn,
                    void (*pr)(const char *buf, void *client_data),
                    void *client_data);
    void cql_to_xml_stdio(struct cql_node *cn, FILE *f);

Function `cql_to_xml_buf` converts to XCQL and stores the result in a user-supplied buffer of a given max size.

`cql_to_xml` writes the result in a user-defined output stream. `cql_to_xml_stdio` writes to a a file.

##### PQF to CQL conversion

Conversion from PQF to CQL is offered by the two functions shown below. The former uses a generic stream for result. The latter puts result in a WRBUF (string container).

    #include <yaz/rpn2cql.h>

    int cql_transform_rpn2cql_stream(cql_transform_t ct,
                                     void (*pr)(const char *buf, void *client_data),
                                     void *client_data,
                                     Z_RPNQuery *q);

    int cql_transform_rpn2cql_wrbuf(cql_transform_t ct,
                                    WRBUF w,
                                    Z_RPNQuery *q);

The configuration is the same as used in CQL to PQF conversions.

### Object Identifiers

The basic YAZ representation of an OID is an array of integers, terminated with the value -1. This integer is of type `Odr_oid`.

Fundamental OID operations and the type `Odr_oid` are defined in `yaz/oid_util.h`.

An OID can either be declared as a automatic variable or it can be allocated using the memory utilities or ODR/NMEM. It's guaranteed that an OID can fit in `OID_SIZE` integers.

Create OID on stack

We can create an OID for the Bib-1 attribute set with:

          Odr_oid bib1[OID_SIZE];
          bib1[0] = 1;
          bib1[1] = 2;
          bib1[2] = 840;
          bib1[3] = 10003;
          bib1[4] = 3;
          bib1[5] = 1;
          bib1[6] = -1;

And OID may also be filled from a string-based representation using dots (.). This is achieved by the function

         int oid_dotstring_to_oid(const char *name, Odr_oid *oid);

This functions returns 0 if name could be converted; -1 otherwise.

Using oid_oiddotstring_to_oid

We can fill the Bib-1 attribute set OID more easily with:

          Odr_oid bib1[OID_SIZE];
          oid_oiddotstring_to_oid("1.2.840.10003.3.1", bib1);

We can also allocate an OID dynamically on an ODR stream with:

        Odr_oid *odr_getoidbystr(ODR o, const char *str);

This creates an OID from a string-based representation using dots. This function take an &odr; stream as parameter. This stream is used to allocate memory for the data elements, which is released on a subsequent call to `odr_reset()` on that stream.

Using odr_getoidbystr

We can create an OID for the Bib-1 attribute set with:

          Odr_oid *bib1 = odr_getoidbystr(odr, "1.2.840.10003.3.1");

The function

         char *oid_oid_to_dotstring(const Odr_oid *oid, char *oidbuf)

does the reverse of `oid_oiddotstring_to_oid`. It converts an OID to the string-based representation using dots. The supplied char buffer `oidbuf` holds the resulting string and must be at least `OID_STR_MAX` in size.

OIDs can be copied with `oid_oidcpy` which takes two OID lists as arguments. Alternatively, an OID copy can be allocated on an ODR stream with:

         Odr_oid *odr_oiddup(ODR odr, const Odr_oid *o);

OIDs can be compared with `oid_oidcmp` which returns zero if the two OIDs provided are identical; non-zero otherwise.

#### OID database

From YAZ version 3 and later, the oident system has been replaced by an OID database. OID database is a misnomer .. the old odient system was also a database.

The OID database is really just a map between named Object Identifiers (string) and their OID raw equivalents. Most operations either convert from string to OID or other way around.

Unfortunately, whenever we supply a string we must also specify the OID class. The class is necessary because some strings correspond to multiple OIDs. An example of such a string is `Bib-1` which may either be an attribute-set or a diagnostic-set.

Applications using the YAZ database should include `yaz/oid_db.h`.

A YAZ database handle is of type `yaz_oid_db_t`. Actually that's a pointer. You need not deal with that. YAZ has a built-in database which can be considered "constant" for most purposes. We can get hold of that by using function `yaz_oid_std`.

All functions with prefix `yaz_string_to_oid` converts from class + string to OID. We have variants of this operation due to different memory allocation strategies.

All functions with prefix `yaz_oid_to_string` converts from OID to string + class.

Create OID with YAZ DB

We can create an OID for the Bib-1 attribute set on the ODR stream odr with:

            Odr_oid *bib1 =
    	yaz_string_to_oid_odr(yaz_oid_std(), CLASS_ATTSET, "Bib-1", odr);

This is more complex than using `odr_getoidbystr`. You would only use `yaz_string_to_oid_odr` when the string (here Bib-1) is supplied by a user or configuration.

#### Standard OIDs

All the object identifiers in the standard OID database as returned by `yaz_oid_std` can be referenced directly in a program as a constant OID. Each constant OID is prefixed with `yaz_oid_` - followed by OID class (lowercase) - then by OID name (normalized and lowercase).

See for list of all object identifiers built into YAZ. These are declared in `yaz/oid_std.h` but are included by `yaz/oid_db.h` as well.

Use a built-in OID

We can allocate our own OID filled with the constant OID for Bib-1 with:

           Odr_oid *bib1 = odr_oiddup(o, yaz_oid_attset_bib1);

### Nibble Memory

Sometimes when you need to allocate and construct a large, interconnected complex of structures, it can be a bit of a pain to release the associated memory again. For the structures describing the Z39.50 PDUs and related structures, it is convenient to use the memory-management system of the &odr; subsystem (see ). However, in some circumstances where you might otherwise benefit from using a simple nibble-memory management system, it may be impractical to use `odr_malloc()` and `odr_reset()`. For this purpose, the memory manager which also supports the &odr; streams is made available in the NMEM module. The external interface to this module is given in the `nmem.h` file.

The following prototypes are given:

        NMEM nmem_create(void);
        void nmem_destroy(NMEM n);
        void *nmem_malloc(NMEM n, size_t size);
        void nmem_reset(NMEM n);
        size_t nmem_total(NMEM n);
        void nmem_init(void);
        void nmem_exit(void);

The `nmem_create()` function returns a pointer to a memory control handle, which can be released again by `nmem_destroy()` when no longer needed. The function `nmem_malloc()` allocates a block of memory of the requested size. A call to `nmem_reset()` or `nmem_destroy()` will release all memory allocated on the handle since it was created (or since the last call to `nmem_reset()`. The function `nmem_total()` returns the number of bytes currently allocated on the handle.

The nibble-memory pool is shared amongst threads. POSIX mutexes and WIN32 Critical sections are introduced to keep the module thread safe. Function `nmem_init()` initializes the nibble-memory library and it is called automatically the first time the `YAZ.DLL` is loaded. &yaz; uses function `DllMain` to achieve this. You should not call `nmem_init` or `nmem_exit` unless you're absolute sure what you're doing. Note that in previous &yaz; versions you'd have to call `nmem_init` yourself.

### Log

&yaz; has evolved a fairly complex log system which should be useful both for debugging &yaz; itself, debugging applications that use &yaz;, and for production use of those applications.

The log functions are declared in header `yaz/log.h` and implemented in `src/log.c`. Due to name clash with syslog and some math utilities the logging interface has been modified as of YAZ 2.0.29. The obsolete interface is still available in header file `yaz/log.h`. The key points of the interface are:

        void yaz_log(int level, const char *fmt, ...)
        void yaz_log_init(int level, const char *prefix, const char *name);
        void yaz_log_init_file(const char *fname);
        void yaz_log_init_level(int level);
        void yaz_log_init_prefix(const char *prefix);
        void yaz_log_time_format(const char *fmt);
        void yaz_log_init_max_size(int mx);

        int yaz_log_mask_str(const char *str);
        int yaz_log_module_level(const char *name);

The reason for the whole log module is the `yaz_log` function. It takes a bitmask indicating the log levels, a `printf`-like format string, and a variable number of arguments to log.

The `log level` is a bit mask, that says on which level(s) the log entry should be made, and optionally set some behaviour of the logging. In the most simple cases, it can be one of `YLOG_FATAL, YLOG_DEBUG, YLOG_WARN, YLOG_LOG`. Those can be combined with bits that modify the way the log entry is written:`YLOG_ERRNO, YLOG_NOTIME, YLOG_FLUSH`. Most of the rest of the bits are deprecated, and should not be used. Use the dynamic log levels instead.

Applications that use &yaz;, should not use the LOG_LOG for ordinary messages, but should make use of the dynamic loglevel system. This consists of two parts, defining the loglevel and checking it.

To define the log levels, the (main) program should pass a string to `yaz_log_mask_str` to define which log levels are to be logged. This string should be a comma-separated list of log level names, and can contain both hard-coded names and dynamic ones. The log level calculation starts with `YLOG_DEFAULT_LEVEL` and adds a bit for each word it meets, unless the word starts with a '-', in which case it clears the bit. If the string `'none'` is found, all bits are cleared. Typically this string comes from the command-line, often identified by `-v`. The `yaz_log_mask_str` returns a log level that should be passed to `yaz_log_init_level` for it to take effect.

Each module should check what log bits should be used, by calling `yaz_log_module_level` with a suitable name for the module. The name is cleared of a preceding path and an extension, if any, so it is quite possible to use `__FILE__` for it. If the name has been passed to `yaz_log_mask_str`, the routine returns a non-zero bitmask, which should then be used in consequent calls to yaz_log. (It can also be tested, so as to avoid unnecessary calls to yaz_log, in time-critical places, or when the log entry would take time to construct.)

Yaz uses the following dynamic log levels: `server, session, request, requestdetail` for the server functionality. `zoom` for the zoom client API. `ztest` for the simple test server. `malloc, nmem, odr, eventl` for internal debugging of yaz itself. Of course, any program using yaz is welcome to define as many new ones as it needs.

By default the log is written to stderr, but this can be changed by a call to `yaz_log_init_file` or `yaz_log_init`. If the log is directed to a file, the file size is checked at every write, and if it exceeds the limit given in `yaz_log_init_max_size`, the log is rotated. The rotation keeps one old version (with a `.1` appended to the name). The size defaults to 1GB. Setting it to zero will disable the rotation feature.

        A typical yaz-log looks like this
      13:23:14-23/11 yaz-ztest(1) [session] Starting session from tcp:127.0.0.1 (pid=30968)
      13:23:14-23/11 yaz-ztest(1) [request] Init from 'YAZ' (81) (ver 2.0.28) OK
      13:23:17-23/11 yaz-ztest(1) [request] Search Z: @attrset Bib-1 foo  OK:7 hits
      13:23:22-23/11 yaz-ztest(1) [request] Present: [1] 2+2  OK 2 records returned
      13:24:13-23/11 yaz-ztest(1) [request] Close OK

The log entries start with a time stamp. This can be omitted by setting the `YLOG_NOTIME` bit in the loglevel. This way automatic tests can be hoped to produce identical log files, that are easy to diff. The format of the time stamp can be set with `yaz_log_time_format`, which takes a format string just like `strftime`.

Next in a log line comes the prefix, often the name of the program. For yaz-based servers, it can also contain the session number. Then comes one or more logbits in square brackets, depending on the logging level set by `yaz_log_init_level` and the loglevel passed to `yaz_log_init_level`. Finally comes the format string and additional values passed to `yaz_log`

The log level `YLOG_LOGLVL`, enabled by the string `loglevel`, will log all the log-level affecting operations. This can come in handy if you need to know what other log levels would be useful. Grep the logfile for `[loglevel]`.

The log system is almost independent of the rest of &yaz;, the only important dependence is of `nmem`, and that only for using the semaphore definition there.

The dynamic log levels and log rotation were introduced in &yaz; 2.0.28. At the same time, the log bit names were changed from `LOG_something` to `YLOG_something`, to avoid collision with `syslog.h`.

### MARC

YAZ provides a fast utility for working with MARC records. Early versions of the MARC utility only allowed decoding of ISO2709. Today the utility may both encode - and decode to a variety of formats.

        #include <yaz/marcdisp.h>

        /* create handler */
        yaz_marc_t yaz_marc_create(void);
        /* destroy */
        void yaz_marc_destroy(yaz_marc_t mt);

        /* set XML mode YAZ_MARC_LINE, YAZ_MARC_SIMPLEXML, ... */
        void yaz_marc_xml(yaz_marc_t mt, int xmlmode);
        #define YAZ_MARC_LINE      0
        #define YAZ_MARC_SIMPLEXML 1
        #define YAZ_MARC_OAIMARC   2
        #define YAZ_MARC_MARCXML   3
        #define YAZ_MARC_ISO2709   4
        #define YAZ_MARC_XCHANGE   5
        #define YAZ_MARC_CHECK     6
        #define YAZ_MARC_TURBOMARC 7
        #define YAZ_MARC_JSON      8

        /* supply iconv handle for character set conversion .. */
        void yaz_marc_iconv(yaz_marc_t mt, yaz_iconv_t cd);

        /* set debug level, 0=none, 1=more, 2=even more, .. */
        void yaz_marc_debug(yaz_marc_t mt, int level);

        /* decode MARC in buf of size bsize. Returns >0 on success; <=0 on failure.
        On success, result in *result with size *rsize. */
        int yaz_marc_decode_buf(yaz_marc_t mt, const char *buf, int bsize,
                                const char **result, size_t *rsize);

        /* decode MARC in buf of size bsize. Returns >0 on success; <=0 on failure.
           On success, result in WRBUF */
        int yaz_marc_decode_wrbuf(yaz_marc_t mt, const char *buf,
                                  int bsize, WRBUF wrbuf);

The synopsis is just a basic subset of all functionality. Refer to the actual header file `marcdisp.h` for details.

A MARC conversion handle must be created by using `yaz_marc_create` and destroyed by calling `yaz_marc_destroy`.

All other functions operate on a `yaz_marc_t` handle. The output is specified by a call to `yaz_marc_xml`. The `xmlmode` must be one of

YAZ_MARC_LINE

  A simple line-by-line format suitable for display but not recommended for further (machine) processing.

YAZ_MARC_MARCXML

  MARCXML.

YAZ_MARC_ISO2709

  ISO2709 (sometimes just referred to as "MARC").

YAZ_MARC_XCHANGE

  MarcXchange.

YAZ_MARC_CHECK

  Pseudo format for validation only. Does not generate any real output except diagnostics.

YAZ_MARC_TURBOMARC

  XML format with same semantics as MARCXML but more compact and geared towards fast processing with XSLT. Refer to for more information.

YAZ_MARC_JSON

  MARC-in-JSON format.

The actual conversion functions are `yaz_marc_decode_buf` and `yaz_marc_decode_wrbuf` which decodes and encodes a MARC record. The former function operates on simple buffers, and stores the resulting record in a WRBUF handle (WRBUF is a simple string type).

Display of MARC record

The following program snippet illustrates how the MARC API may be used to convert a MARC record to the line-by-line format:

          void print_marc(const char *marc_buf, int marc_buf_size)
          {
             char *result;      /* for result buf */
             size_t result_len;    /* for size of result */
             yaz_marc_t mt = yaz_marc_create();
             yaz_marc_xml(mt, YAZ_MARC_LINE);
             yaz_marc_decode_buf(mt, marc_buf, marc_buf_size,
                                 &result, &result_len);
             fwrite(result, result_len, 1, stdout);
             yaz_marc_destroy(mt);  /* note that result is now freed... */
          }

#### TurboMARC

TurboMARC is yet another XML encoding of a MARC record. The format was designed for fast processing with XSLT.

Applications like Pazpar2 uses XSLT to convert an XML encoded MARC record to an internal representation. This conversion mostly checks the tag of a MARC field to determine the basic rules in the conversion. This check is costly when that tag is encoded as an attribute in MARCXML. By having the tag value as the element instead, makes processing many times faster (at least for Libxslt).

TurboMARC is encoded as follows:

- Record elements is part of namespace "`http://www.indexdata.com/turbomarc`".

- A record is enclosed in element `r`.

- A collection of records is enclosed in element `collection`.

- The leader is encoded as element `l` with the leader content as its (text) value.

- A control field is encoded as element `c` concatenated with the tag value of the control field if the tag value matches the regular expression `[a-zA-Z0-9]*`. If the tag value does not match the regular expression `[a-zA-Z0-9]*` the control field is encoded as element `c` and attribute `code` will hold the tag value. This rule ensures that in the rare cases where a tag value might result in a non-well-formed XML, then YAZ will encode it as a coded attribute (as in MARCXML).

  The control field content is the text value of this element. Indicators are encoded as attribute names `i1`, `i2`, etc. and corresponding values for each indicator.

- A data field is encoded as element `d` concatenated with the tag value of the data field or using the attribute `code` as described in the rules for control fields. The children of the data field element are subfield elements. Each subfield element is encoded as `s` concatenated with the sub field code. The text of the subfield element is the contents of the subfield. Indicators are encoded as attributes for the data field element, similar to the encoding for control fields.

### Retrieval Facility

YAZ version 2.1.20 or later includes a Retrieval facility tool which allows a SRU/Z39.50 to describe itself and perform record conversions. The idea is the following:

- An SRU/Z39.50 client sends a retrieval request which includes a combination of the following parameters: syntax (format), schema (or element set name).

- The retrieval facility is invoked with parameters in a server/proxy. The retrieval facility matches the parameters a set of "supported" retrieval types. If there is no match, the retrieval signals an error (syntax and / or schema not supported).

- For a successful match, the backend is invoked with the same or altered retrieval parameters (syntax, schema). If a record is received from the backend, it is converted to the frontend name / syntax.

- The resulting record is sent back the client and tagged with the frontend syntax / schema.

The Retrieval facility is driven by an XML configuration. The configuration is neither Z39.50 ZeeRex or SRU ZeeRex. But it should be easy to generate both of them from the XML configuration. (Unfortunately the two versions of ZeeRex differ substantially in this regard.)

#### Retrieval XML format

All elements should be covered by namespace `http://indexdata.com/yaz` . The root element node must be `retrievalinfo`.

The `retrievalinfo` must include one or more `retrieval` elements. Each `retrieval` defines specific combination of syntax, name and identifier supported by this retrieval service.

The `retrieval` element may include any of the following attributes:

`syntax` (REQUIRED)

  Defines the record syntax. Possible values is any of the names defined in YAZ' OID database or a raw OID in (n.n ... n).

`name` (OPTIONAL)

  Defines the name of the retrieval format. This can be any string. For SRU, the value is equivalent to schema (short-hand); for Z39.50 it's equivalent to simple element set name. For YAZ 3.0.24 and later this name may be specified as a glob expression with operators `*` and `?`.

`identifier` (OPTIONAL)

  Defines the URI schema name of the retrieval format. This can be any string. For SRU, the value is equivalent to URI schema. For Z39.50, there is no equivalent.

The `retrieval` may include one `backend` element. If a `backend` element is given, it specifies how the records are retrieved by some backend and how the records are converted from the backend to the "frontend".

The attributes, `name` and `syntax` may be specified for the `backend` element. The semantics of these attributes is equivalent to those for the `retrieval`. However, these values are passed to the "backend".

The `backend` element may include one or more conversion instructions (as children elements). The supported conversions are:

`marc`

  The `marc` element specifies a conversion to - and from ISO2709 encoded MARC and &acro.marcxml;/MarcXchange. The following attributes may be specified:

  `inputformat` (REQUIRED)

    Format of input. Supported values are `marc` (for ISO2709), `xml` (MARCXML/MarcXchange) and `json` (MARC-in-JSON).

  `outputformat` (REQUIRED)

    Format of output. Supported values are `line` (MARC line format); `marcxml` (for MARCXML), `marc` (ISO2709), `turbomarc`, `marcxchange` (for MarcXchange), or `json` (MARC-in-JSON ).

  `inputcharset` (OPTIONAL)

    Encoding of input. For XML input formats, this need not be given, but for ISO2709 based input formats, this should be set to the encoding used. For MARC21 records, a common inputcharset value would be `marc-8`.

    If inputformat is `marc` and inputcharset is `marc-8`, then effective inputcharset is UTF-8 if leader position has value 'a' (MARC21 rule).

  `outputcharset` (OPTIONAL)

    Encoding of output. If outputformat is XML based, it is strongly recommended to use `utf-8`.

  `leaderspec` (OPTIONAL)

    Specifies a modification to the leader for the resulting output record. The leaderspec is a comma separated list of pos=value pairs, where pos is an integer offset (0 - 23) for leader. Value is either a quoted string or an integer (character value in decimal). For example, to set leader at offset 9 to a, use `9='a'`. This has same effect as `-l` for .

`select`

  The `select` selects one or more text nodes and decodes them as XML. The following attributes may be specified:

  `path` (REQUIRED)

    X-Path expression for selecting text nodes.

  This conversion is available in YAZ 5.8.0 and later.

`solrmarc`

  The `solrmarc` decodes solrmarc records. It assumes that the input is pure solrmarc text (no escaping) and will convert all sequences of the form #XX; to a single character of the hexadecimal value as given by XX. The output, presumably, is a valid ISO2709 buffer.

  This conversion is available in YAZ 5.0.21 and later.

`xslt`

  The `xslt` element specifies a conversion via &acro.xslt;. The following attributes may be specified:

  `stylesheet` (REQUIRED)

    Stylesheet file.

  In addition, the element can be configured as follows:

  `param` (OPTIONAL)

    A `param` tag configures a parameter to be passed to the &acro.xslt; stylesheet. Multiple `param` tags may be defined.

`rdf-lookup`

  The `rdf-lookup` element looks up BIBFRAME elements in some suitable service, for example http://id.loc.gov/authorities/names and replaces the URIs for specified elements with URIs it finds at that service. Its configuration consists of

  `debug` (OPTIONAL)

    Attribute to the `rdf-lookup` tag to enable debug output. A value of "1" makes the filter to add a XML comment next to each key it tried to look up, showing the URL, the result, and timing. This is useful for debugging the configuration. The default is not to add any comments.

  `timeout` (OPTIONAL)

    Attribute of the `rdf-lookup` tag which defines timeout in seconds for the HTTP based rdf-lookup.

  `namespace` (OPTIONAL)

    A `namespace` tag declares a namespace to be used in the `xpath` below. The tag requires two attributes: `prefix` and `href`.

  `lookup` (REQUIRED)

    A section that defines one tag to be looked up, for example an author.The `xpath` attribute (REQUIRED) specifies the path to the element(s).

  `key` (REQUIRED)

    A tag withing the `lookup` tag specifies the value to be used in the lookup, for example a name or an ID. It is a relative Xpath starting from the tag specified in the `lookup`.

  `server` (OPTIONAL)

    Specifies the URL for server to use for the lookup. A `%s` is replaced by the key value to be looked up. If not specified, defaults to the same as the previous `lookup` section, or lacking one, to . The `method` attribute can be used to specify the HTTP method to be used in this lookup. The default is GET, and the useful alternative is HEAD.

  See the example below.

  This conversion is available in YAZ 5.19.0 and later.

#### Retrieval Facility Examples

MARC21 backend

A typical way to use the retrieval facility is to enable XML for servers that only supports ISO2709 encoded MARC21 records.

         <retrievalinfo>
           <retrieval syntax="usmarc" name="F"/>
           <retrieval syntax="usmarc" name="B"/>
           <retrieval syntax="xml" name="marcxml"
    		  identifier="info:srw/schema/1/marcxml-v1.1">
             <backend syntax="usmarc" name="F">
    	   <marc inputformat="marc" outputformat="marcxml"
    		 inputcharset="marc-8"/>
    	 </backend>
           </retrieval>
           <retrieval syntax="xml" name="dc">
             <backend syntax="usmarc" name="F">
    	   <marc inputformat="marc" outputformat="marcxml"
    		 inputcharset="marc-8"/>
               <xslt stylesheet="MARC21slim2DC.xsl"/>
    	 </backend>
           </retrieval>
         </retrievalinfo>

This means that our frontend supports:

- MARC21 F(ull) records.

- MARC21 B(rief) records.

- MARCXML records.

- Dublin core records.

MARCXML backend

SRW/SRU and Solr backends return records in XML. If they return MARCXML or MarcXchange, the retrieval module can convert those into ISO2709 formats, most commonly USMARC (AKA MARC21). In this example, the backend returns MARCXML for schema="marcxml".

         <retrievalinfo>
           <retrieval syntax="usmarc">
             <backend syntax="xml" name="marcxml">
    	   <marc inputformat="xml" outputformat="marc"
    		 outputcharset="marc-8"/>
    	 </backend>
           </retrieval>
           <retrieval syntax="xml" name="marcxml"
    		  identifier="info:srw/schema/1/marcxml-v1.1"/>
           <retrieval syntax="xml" name="dc">
             <backend syntax="xml" name="marcxml">
               <xslt stylesheet="MARC21slim2DC.xsl"/>
    	 </backend>
           </retrieval>
         </retrievalinfo>

This means that our frontend supports:

- MARC21 records (any element set name) in MARC-8 encoding.

- MARCXML records for element-set=marcxml

- Dublin core records for element-set=dc.

RDF-lookup backend

This is a minimal example of the `backend` configuration for the rdf-lookup. It could well be used with some heavy xslt transforms that make BIBFRAME records out of MarxXml.

            <backend syntax="xml" name="rdf-lookup">
              <rdf-lookup debug="1" timeout="10">
                <namespace prefix="bf" href="http://id.loc.gov/ontologies/bibframe/" />
                <namespace prefix="bflc" href="http://id.loc.gov/ontologies/bibframe/lc-extensions/"/>
                <lookup xpath="//bf:contribution/bf:Contribution/bf:agent/bf:Agent">
                  <key field="bflc:name00MatchKey"/>
                  <key field="bflc:name01MatchKey"/>
                  <key field="bflc:name11MatchKey"/>
                  <server url="http://id.loc.gov/authorities/names/label/%s" method="HEAD"/>
                </lookup>
              </rdf-lookup>
            </backend>

The `debug=1` attribute tells the filter to add XML comments to the key nodes that indicate what lookup it tried to do, how it went, and how long it took.

The namespace prefix `bf:` is defined in the `namespace` tags. These namespaces are used in the xpath expressions in the lookup sections.

The `lookup` tag specifies one tag to be looked up. The `xpath` attribute defines which node to modify. It may make use of the `namespace` definitions above.

The `server` tag gives the URL to be used for the lookup. A `%s` in the string will get replaced by the key value. If there is no `server` tag, the one from the preceding `lookup` section is used, and if there is no previous section, the id.loc.gov address is used as a default. The default is to make a GET request, this example uses HEAD

#### API

It should be easy to use the retrieval systems from applications. Refer to the headers `yaz/retrieval.h` and `yaz/record_conv.h`.

### Sorting

This chapter describes sorting and how it is supported in YAZ. Sorting applies to a result-set. The Z39.50 sorting facility takes one or more input result-sets and one result-set as output. The most simple case is that the input-set is the same as the output-set.

Z39.50 sorting has a separate APDU (service) that is, thus, performed following a search (two phases).

In SRU/Solr, however, the model is different. Here, sorting is specified during the search operation. Note, however, that SRU might perform sort as separate search, by referring to an existing result-set in the query (result-set reference).

#### Using the Z39.50 sort service

yaz-client and the ZOOM API support the Z39.50 sort facility. In any case the sort sequence or sort criteria is using a string notation. This notation is a one-line notation suitable for being manually entered or generated, and allows for easy logging (one liner). For the ZOOM API, the sort is specified in the call to ZOOM_query_sortby function. For yaz-client the sort is performed and specified using the sort and sort+ commands. For description of the sort criteria notation refer to the sort command in the yaz-client manual.

The ZOOM API might choose one of several sort strategies for sorting. Refer to .

#### Type-7 sort

Type-7 sort is an extension to the Bib-1 based RPN query where the sort specification is embedded as an Attribute-Plus-Term.

The objectives for introducing Type-7 sorting is that it allows a client to perform sorting even if it does not implement/support Z39.50 sort. Virtually all Z39.50 client software supports RPN queries. It also may improve performance because the sort criteria is specified along with the search query.

The sort is triggered by the presence of type 7, and the value of type 7 specifies the sortRelation . The value for type 7 is 1 for ascending and 2 for descending. For the sortElement only the generic part is handled. If generic sortKey is of type sortField, then attribute type 1 is present and the value is sortField (InternationalString). If generic sortKey is of type sortAttributes, then the attributes in the list are used. Generic sortKey of type elementSpec is not supported.

The term in the sorting Attribute-Plus-Term combo should hold an integer. The value is 0 for primary sorting criteria, 1 for second criteria, etc.

### Facets

YAZ supports facets in the Solr, SRU 2.0 and Z39.50 protocols.

Like Type-1/RPN, YAZ supports a string notation for specifying facets. This notataion maps straight to facets.asn. The notation is parsed by function `yaz_pqf_parse_facet_list` defined in header `yaz/pquery.h`.

For ZOOM C the facets are specified by option "facets". For yaz-client, the 'facets' command is used.

The grammar of this specification is as follows:

       facet-spec ::= facet-list

       facet-list ::= facet-list ',' attr-spec | attr-spec

       attr-spec ::= attr-spec '@attr' string | '@attr' string

The notation is inspired by PQF. The string following '@attr' must not include blanks and is of the form type`=`value, where type is an integer and value is a string or an integer.

There is no formal facets attribute set (it is not given in the protocol by the facets, although it could). The following types apply:

Facet attributes

Type | Description
--- | ---
1 | Field-name. This is often a string, e.g. "Author", "Year", etc.
2 | Sort order. Value should be an integer. Value 0: count descending (frequency). Value 1: alpha ascending.
3 | Number of terms requested.
4 | Start offset (starting from 1)

## The ODR Module

### Introduction

&odr; is the BER-encoding/decoding subsystem of &yaz;. Care has been taken to isolate &odr; from the rest of the package - specifically from the transport interface. &odr; may be used in any context where basic ASN.1/BER representations are used.

If you are only interested in writing a Z39.50 implementation based on the PDUs that are already provided with &yaz;, you only need to concern yourself with the section on managing ODR streams (). Only if you need to implement ASN.1 beyond that which has been provided, should you worry about the second half of the documentation (). If you use one of the higher-level interfaces, you can skip this section entirely.

This is important, so we'll repeat it for emphasis: You do not need to read to implement Z39.50 with &yaz;.

If you need a part of the protocol that isn't already in &yaz;, you should contact the authors before going to work on it yourself: We might already be working on it. Conversely, if you implement a useful part of the protocol before us, we'd be happy to include it in a future release.

### Using ODR

#### ODR Streams

Conceptually, the ODR stream is the source of encoded data in the decoding mode; when encoding, it is the receptacle for the encoded data. Before you can use an ODR stream it must be allocated. This is done with the function

         ODR odr_createmem(int direction);

The `odr_createmem()` function takes as argument one of three manifest constants: `ODR_ENCODE`, `ODR_DECODE`, or `ODR_PRINT`. An &odr; stream can be in only one mode - it is not possible to change its mode once it's selected. Typically, your program will allocate at least two ODR streams - one for decoding, and one for encoding.

When you're done with the stream, you can use

         void odr_destroy(ODR o);

to release the resources allocated for the stream.

#### Memory Management

Two forms of memory management take place in the &odr; system. The first one, which has to do with allocating little bits of memory (sometimes quite large bits of memory, actually) when a protocol package is decoded, and turned into a complex of interlinked structures. This section deals with this system, and how you can use it for your own purposes. The next section deals with the memory management which is required when encoding data - to make sure that a large enough buffer is available to hold the fully encoded PDU.

The &odr; module has its own memory management system, which is used whenever memory is required. Specifically, it is used to allocate space for data when decoding incoming PDUs. You can use the memory system for your own purposes, by using the function

         void *odr_malloc(ODR o, size_t size);

You can't use the normal `free(2)` routine to free memory allocated by this function, and &odr; doesn't provide a parallel function. Instead, you can call

         void odr_reset(ODR o);

when you are done with the memory: Everything allocated since the last call to `odr_reset()` is released. The `odr_reset()` call is also required to clear up an error condition on a stream.

The function

         size_t odr_total(ODR o);

returns the number of bytes allocated on the stream since the last call to `odr_reset()`.

The memory subsystem of &odr; is fairly efficient at allocating and releasing little bits of memory. Rather than managing the individual, small bits of space, the system maintains a free-list of larger chunks of memory, which are handed out in small bits. This scheme is generally known as a nibble-memory system. It is very useful for maintaining short-lived constructions such as protocol PDUs.

If you want to retain a bit of memory beyond the next call to `odr_reset()`, you can use the function

         ODR_MEM odr_extract_mem(ODR o);

This function will give you control of the memory recently allocated on the ODR stream. The memory will live (past calls to `odr_reset()`), until you call the function

         void odr_release_mem(ODR_MEM p);

The opaque `ODR_MEM` handle has no other purpose than referencing the memory block for you until you want to release it.

You can use `odr_extract_mem()` repeatedly between allocating data, to retain individual control of separate chunks of data.

#### Encoding and Decoding Data

When encoding data, the ODR stream will write the encoded octet string in an internal buffer. To retrieve the data, use the function

         char *odr_getbuf(ODR o, int *len, int *size);

The integer pointed to by len is set to the length of the encoded data, and a pointer to that data is returned. `*size` is set to the size of the buffer (unless `size` is null, signaling that you are not interested in the size). The next call to a primitive function using the same &odr; stream will overwrite the data, unless a different buffer has been supplied using the call

         void odr_setbuf(ODR o, char *buf, int len, int can_grow);

which sets the encoding (or decoding) buffer used by `o` to `buf`, using the length `len`. Before a call to an encoding function, you can use `odr_setbuf()` to provide the stream with an encoding buffer of sufficient size (length). The `can_grow` parameter tells the encoding &odr; stream whether it is allowed to use `realloc(2)` to increase the size of the buffer when necessary. The default condition of a new encoding stream is equivalent to the results of calling

         odr_setbuf(stream, 0, 0, 1);

In this case, the stream will allocate and reallocate memory as necessary. The stream reallocates memory by repeatedly doubling the size of the buffer - the result is that the buffer will typically reach its maximum, working size with only a small number of reallocation operations. The memory is freed by the stream when the latter is destroyed, unless it was assigned by the user with the `can_grow` parameter set to zero (in this case, you are expected to retain control of the memory yourself).

To assume full control of an encoded buffer, you must first call `odr_getbuf()` to fetch the buffer and its length. Next, you should call `odr_setbuf()` to provide a different buffer (or a null pointer) to the stream. In the simplest case, you will reuse the same buffer over and over again, and you will just need to call `odr_getbuf()` after each encoding operation to get the length and address of the buffer. Note that the stream may reallocate the buffer during an encoding operation, so it is necessary to retrieve the correct address after each encoding operation.

It is important to realize that the ODR stream will not release this memory when you call `odr_reset()`: It will merely update its internal pointers to prepare for the encoding of a new data value. When the stream is released by the `odr_destroy()` function, the memory given to it by `odr_setbuf` will be released only if the `can_grow` parameter to `odr_setbuf()` was nonzero. The `can_grow` parameter, in other words, is a way of signaling who is to own the buffer, you or the ODR stream. If you never call `odr_setbuf()` on your encoding stream, which is typically the case, the buffer allocated by the stream will belong to the stream by default.

When you wish to decode data, you should first call `odr_setbuf()`, to tell the decoding stream where to find the encoded data, and how long the buffer is (the `can_grow` parameter is ignored by a decoding stream). After this, you can call the function corresponding to the data you wish to decode (e.g. `odr_integer()` odr `z_APDU()`).

Encoding and decoding functions

          int odr_integer(ODR o, Odr_int **p, int optional, const char *name);

          int z_APDU(ODR o, Z_APDU **p, int optional, const char *name);

If the data is absent (or doesn't match the tag corresponding to the type), the return value will be either 0 or 1 depending on the `optional` flag. If `optional` is 0 and the data is absent, an error flag will be raised in the stream, and you'll need to call `odr_reset()` before you can use the stream again. If `optional` is nonzero, the pointer pointed to/ by `p` will be set to the null value, and the function will return 1. The `name` argument is used to pretty-print the tag in question. It may be set to `NULL` if pretty-printing is not desired.

If the data value is found where it's expected, the pointer pointed to by the `p` argument will be set to point to the decoded type. The space for the type will be allocated and owned by the &odr; stream, and it will live until you call `odr_reset()` on the stream. You cannot use `free(2)` to release the memory. You can decode several data elements (by repeated calls to `odr_setbuf()` and your decoding function), and new memory will be allocated each time. When you do call `odr_reset()`, everything decoded since the last call to `odr_reset()` will be released.

Encoding and decoding of an integer

The use of the double indirection can be a little confusing at first (its purpose will become clear later on, hopefully), so an example is in order. We'll encode an integer value, and immediately decode it again using a different stream. A useless, but informative operation.

    void do_nothing_useful(Odr_int value)
    {
        ODR encode, decode;
        Odr_int *valp, *resvalp;
        char *bufferp;
        int len;

        /* allocate streams */
        if (!(encode = odr_createmem(ODR_ENCODE)))
            return;
        if (!(decode = odr_createmem(ODR_DECODE)))
            return;

        valp = &value;
        if (odr_integer(encode, &valp, 0, 0) == 0)
        {
            printf("encoding went bad\n");
            return;
        }
        bufferp = odr_getbuf(encode, &len, 0);
        printf("length of encoded data is %d\n", len);

        /* now let's decode the thing again */
        odr_setbuf(decode, bufferp, len, 0);
        if (odr_integer(decode, &resvalp, 0, 0) == 0)
        {
            printf("decoding went bad\n");
            return;
        }
        /* ODR_INT_PRINTF format for printf (such as %d) */
        printf("the value is " ODR_INT_PRINTF "\n", *resvalp);

        /* clean up */
        odr_destroy(encode);
        odr_destroy(decode);
    }

This looks like a lot of work, offhand. In practice, the &odr; streams will typically be allocated once, in the beginning of your program (or at the beginning of a new network session), and the encoding and decoding will only take place in a few, isolated places in your program, so the overhead is quite manageable.

#### Printing

When an ODR stream is created of type `ODR_PRINT` the ODR module will print the contents of a PDU in a readable format. By default output is written to the `stderr` stream. This behavior can be changed, however, by calling the function

          odr_setprint(ODR o, FILE *file);

before encoders or decoders are being invoked. It is also possible to direct the output to a buffer (or indeed another file), by using the more generic mechanism:

          void odr_set_stream(ODR o, void *handle,
                             void (*stream_write)(ODR o, void *handle, int type,
                                                  const char *buf, int len),
                             void (*stream_close)(void *handle));

Here the user provides an opaque handle and two handlers, stream_write for writing, and stream_close which is supposed to close/free resources associated with handle. The stream_close handler is optional and if NULL for the function is provided, it will not be invoked. The stream_write takes the ODR handle as parameter, the user-defined handle, a type `ODR_OCTETSTRING`, `ODR_VISIBLESTRING` which indicates the type of contents being written.

Another utility useful for diagnostics (error handling) or as part of the printing facilities is:

          const char **odr_get_element_path(ODR o);

which returns a list of current elements that ODR deals with at the moment. For the returned array, say `ar`, then `ar[0]` is the top level element, `ar[n]` is the last. The last element has the property that `ar[n+1] == NULL`.

Element Path for record

For a database record part of a PresentResponse the array returned by `odr_get_element` is `presentResponse`, `databaseOrSurDiagnostics`, `?`, `record`, `?`, `databaseRecord` . The question mark appears due to unnamed constructions.

#### Diagnostics

The encoding/decoding functions all return 0 when an error occurs. Until you call `odr_reset()`, you cannot use the stream again, and any function called will immediately return 0.

To provide information to the programmer or administrator, the function

         void odr_perror(ODR o, char *message);

is provided, which prints the `message` argument to `stderr` along with an error message from the stream.

You can also use the function

         int odr_geterror(ODR o);

to get the current error number from the screen. The number will be one of these constants:

ODR Error codes

code | Description
--- | ---
OMEMORY | Memory allocation failed.
OSYSERR | A system- or library call has failed. The standard diagnostic variable `errno` should be examined to determine the actual error.
OSPACE | No more space for encoding. This will only occur when the user has explicitly provided a buffer for an encoding stream without allowing the system to allocate more space.
OREQUIRED | This is a common protocol error; A required data element was missing during encoding or decoding.
OUNEXPECTED | An unexpected data element was found during decoding.
OOTHER | Other error. This is typically an indication of misuse of the &odr; system by the programmer, and also that the diagnostic system isn't as good as it should be, yet.

The character string array

         char *odr_errlist[]

can be indexed by the error code to obtain a human-readable representation of the problem.

#### Summary and Synopsis

         #include <yaz/odr.h>

         ODR odr_createmem(int direction);

         void odr_destroy(ODR o);

         void odr_reset(ODR o);

         char *odr_getbuf(ODR o, int *len, int *size);

         void odr_setbuf(ODR o, char *buf, int len, int can_grow);

         void *odr_malloc(ODR o, int size);

         NMEM odr_extract_mem(ODR o);

         int odr_geterror(ODR o);

         void odr_perror(ODR o, const char *message);

         extern char *odr_errlist[];

### Programming with ODR

The API of &odr; is designed to reflect the structure of ASN.1, rather than BER itself. Future releases may be able to represent data in other external forms.

There is an ASN.1 tutorial available at this site. This site also has standards for ASN.1 (X.680) and BER (X.690) online.

The ODR interface is based loosely on that of the Sun Microsystems XDR routines. Specifically, each function which corresponds to an ASN.1 primitive type has a dual function. Depending on the settings of the ODR stream which is supplied as a parameter, the function may be used either to encode or decode data. The functions that can be built using these primitive functions, to represent more complex data types, share this quality. The result is that you only have to enter the definition for a type once - and you have the functionality of encoding, decoding (and pretty-printing) all in one unit. The resulting C source code is quite compact, and is a pretty straightforward representation of the source ASN.1 specification.

In many cases, the model of the XDR functions works quite well in this role. In others, it is less elegant. Most of the hassle comes from the optional SEQUENCE members which don't exist in XDR.

#### The Primitive ASN.1 Types

ASN.1 defines a number of primitive types (many of which correspond roughly to primitive types in structured programming languages, such as C).

##### INTEGER

The &odr; function for encoding or decoding (or printing) the ASN.1 INTEGER type looks like this:

          int odr_integer(ODR o, Odr_int **p, int optional, const char *name);

The `Odr_int` is just a simple integer.

This form is typical of the primitive &odr; functions. They are named after the type of data that they encode or decode. They take an &odr; stream, an indirect reference to the type in question, and an `optional` flag (corresponding to the OPTIONAL keyword of ASN.1) as parameters. They all return an integer value of either one or zero. When you use the primitive functions to construct encoders for complex types of your own, you should follow this model as well. This ensures that your new types can be reused as elements in yet more complex types.

The `o` parameter should obviously refer to a properly initialized &odr; stream of the right type (encoding/decoding/printing) for the operation that you wish to perform.

When encoding or printing, the function first looks at `* p`. If `* p` (the pointer pointed to by `p`) is a null pointer, this is taken to mean that the data element is absent. If the `optional` parameter is nonzero, the function will return one (signifying success) without any further processing. If the `optional` is zero, an internal error flag is set in the &odr; stream, and the function will return 0. No further operations can be carried out on the stream without a call to the function `odr_reset()`.

If `*p` is not a null pointer, it is expected to point to an instance of the data type. The data will be subjected to the encoding rules, and the result will be placed in the buffer held by the &odr; stream.

The other ASN.1 primitives have similar functions that operate in similar manners:

##### BOOLEAN

    int odr_bool(ODR o, Odr_bool **p, int optional, const char *name);

##### REAL

Not defined.

##### NULL

    int odr_null(ODR o, Odr_null **p, int optional, const char *name);

In this case, the value of **p is not important. If `*p` is different from the null pointer, the null value is present, otherwise it's absent.

##### OCTET STRING

    typedef struct odr_oct
    {
        unsigned char *buf;
        int len;
    } Odr_oct;

    int odr_octetstring(ODR o, Odr_oct **p, int optional,
                        const char *name);

The `buf` field should point to the character array that holds the octetstring. The `len` field holds the actual length. The character array need not be null-terminated.

To make things a little easier, an alternative is given for string types that are not expected to contain embedded NULL characters (e.g. VisibleString):

          int odr_cstring(ODR o, char **p, int optional, const char *name);

which encodes or decodes between OCTETSTRING representations and null-terminated C strings.

Functions are provided for the derived string types, e.g.:

    int odr_visiblestring(ODR o, char **p, int optional,
                          const char *name);

##### BIT STRING

    int odr_bitstring(ODR o, Odr_bitmask **p, int optional,
                      const char *name);

The opaque type `Odr_bitmask` is only suitable for holding relatively brief bit strings, e.g. for options fields, etc. The constant `ODR_BITMASK_SIZE` multiplied by 8 gives the maximum possible number of bits.

A set of macros are provided for manipulating the `Odr_bitmask` type:

    void ODR_MASK_ZERO(Odr_bitmask *b);

    void ODR_MASK_SET(Odr_bitmask *b, int bitno);

    void ODR_MASK_CLEAR(Odr_bitmask *b, int bitno);

    int ODR_MASK_GET(Odr_bitmask *b, int bitno);

The functions are modeled after the manipulation functions that accompany the `fd_set` type used by the `select(2)` call. `ODR_MASK_ZERO` should always be called first on a new bitmask, to initialize the bits to zero.

##### OBJECT IDENTIFIER

    int odr_oid(ODR o, Odr_oid **p, int optional, const char *name);

The C OID representation is simply an array of integers, terminated by the value -1 (the `Odr_oid` type is synonymous with the `short` type). We suggest that you use the OID database module (see ) to handle object identifiers in your application.

#### Tagging Primitive Types

The simplest way of tagging a type is to use the `odr_implicit_tag()` or `odr_explicit_tag()` macros:

    int odr_implicit_tag(ODR o, Odr_fun fun, int class, int tag,
                         int optional, const char *name);

    int odr_explicit_tag(ODR o, Odr_fun fun, int class, int tag,
                         int optional, const char *name);

To create a type derived from the integer type by implicit tagging, you might write:

         MyInt ::= [210] IMPLICIT INTEGER

In the &odr; system, this would be written like:

    int myInt(ODR o, Odr_int **p, int optional, const char *name)
    {
        return odr_implicit_tag(o, odr_integer, p,
    			    ODR_CONTEXT, 210, optional, name);
    }

The function `myInt()` can then be used like any of the primitive functions provided by &odr;. Note that the behavior of `odr_explicit_tag()` and `odr_implicit_tag()` macros act exactly the same as the functions they are applied to - they respond to error conditions, etc, in the same manner - they simply have three extra parameters. The class parameter may take one of the values: `ODR_CONTEXT`, `ODR_PRIVATE`, `ODR_UNIVERSAL`, or `/ODR_APPLICATION`.

#### Constructed Types

Constructed types are created by combining primitive types. The &odr; system only implements the SEQUENCE and SEQUENCE OF constructions (although adding the rest of the container types should be simple enough, if the need arises).

For implementing SEQUENCEs, the functions

    int odr_sequence_begin(ODR o, void *p, int size, const char *name);
    int odr_sequence_end(ODR o);

are provided.

The `odr_sequence_begin()` function should be called in the beginning of a function that implements a SEQUENCE type. Its parameters are the &odr; stream, a pointer (to a pointer to the type you're implementing), and the `size` of the type (typically a C structure). On encoding, it returns 1 if `* p` is a null pointer. The `size` parameter is ignored. On decoding, it returns 1 if the type is found in the data stream. `size` bytes of memory are allocated, and `*p` is set to point to this space. The `odr_sequence_end()` is called at the end of the complex function. Assume that a type is defined like this:

    MySequence ::= SEQUENCE {
         intval INTEGER,
         boolval BOOLEAN OPTIONAL
    }

The corresponding &odr; encoder/decoder function and the associated data structures could be written like this:

    typedef struct MySequence
    {
        Odr_int *intval;
        Odr_bool *boolval;
    } MySequence;

    int mySequence(ODR o, MySequence **p, int optional, const char *name)
    {
        if (odr_sequence_begin(o, p, sizeof(**p), name) == 0)
            return optional && odr_ok(o);
        return
            odr_integer(o, &(*p)->intval, 0, "intval") &&
            odr_bool(o, &(*p)->boolval, 1, "boolval") &&
            odr_sequence_end(o);
    }

Note the 1 in the call to `odr_bool()`, to mark that the sequence member is optional. If either of the member types had been tagged, the macros `odr_implicit_tag()` or `odr_explicit_tag()` could have been used. The new function can be used exactly like the standard functions provided with &odr;. It will encode, decode or pretty-print a data value of the `MySequence` type. We like to name types with an initial capital, as done in ASN.1 definitions, and to name the corresponding function with the first character of the name in lower case. You could, of course, name your structures, types, and functions any way you please - as long as you're consistent, and your code is easily readable. `odr_ok` is just that - a predicate that returns the state of the stream. It is used to ensure that the behavior of the new type is compatible with the interface of the primitive types.

#### Tagging Constructed Types

See for information on how to tag the primitive types, as well as types that are already defined.

##### Implicit Tagging

Assume the type above had been defined as

    MySequence ::= [10] IMPLICIT SEQUENCE {
          intval INTEGER,
          boolval BOOLEAN OPTIONAL
    }

You would implement this in &odr; by calling the function

    int odr_implicit_settag(ODR o, int class, int tag);

which overrides the tag of the type immediately following it. The macro `odr_implicit_tag()` works by calling `odr_implicit_settag()` immediately before calling the function pointer argument. Your type function could look like this:

    int mySequence(ODR o, MySequence **p, int optional, const char *name)
    {
        if (odr_implicit_settag(o, ODR_CONTEXT, 10) == 0 ||
            odr_sequence_begin(o, p, sizeof(**p), name) == 0)
            return optional && odr_ok(o);
        return
            odr_integer(o, &(*p)->intval, 0, "intval") &&
            odr_bool(o, &(*p)->boolval, 1, "boolval") &&
            odr_sequence_end(o);
    }

The definition of the structure `MySequence` would be the same.

##### Explicit Tagging

Explicit tagging of constructed types is a little more complicated, since you are in effect adding a level of construction to the data.

Assume the definition:

    MySequence ::= [10] IMPLICIT SEQUENCE {
       intval INTEGER,
       boolval BOOLEAN OPTIONAL
    }

Since the new type has an extra level of construction, two new functions are needed to encapsulate the base type:

    int odr_constructed_begin(ODR o, void *p, int class, int tag,
                              const char *name);

    int odr_constructed_end(ODR o);

Assume that the IMPLICIT in the type definition above were replaced with EXPLICIT (or that the IMPLICIT keyword was simply deleted, which would be equivalent). The structure definition would look the same, but the function would look like this:

    int mySequence(ODR o, MySequence **p, int optional, const char *name)
    {
        if (odr_constructed_begin(o, p, ODR_CONTEXT, 10, name) == 0)
            return optional && odr_ok(o);
        if (o->direction == ODR_DECODE)
            *p = odr_malloc(o, sizeof(**p));
        if (odr_sequence_begin(o, p, sizeof(**p), 0) == 0)
        {
            *p = 0; /* this is almost certainly a protocol error */
            return 0;
        }
        return
            odr_integer(o, &(*p)->intval, 0, "intval") &&
            odr_bool(o, &(*p)->boolval, 1, "boolval") &&
            odr_sequence_end(o) &&
            odr_constructed_end(o);
    }

Notice that the interface here gets kind of nasty. The reason is simple: Explicitly tagged, constructed types are fairly rare in the protocols that we care about, so the aesthetic annoyance (not to mention the dangers of a cluttered interface) is less than the time that would be required to develop a better interface. Nevertheless, it is far from satisfying, and it's a point that will be worked on in the future. One option for you would be to simply apply the `odr_explicit_tag()` macro to the first function, and not have to worry about `odr_constructed_*` yourself. Incidentally, as you might have guessed, the `odr_sequence_` functions are themselves implemented using the `/odr_constructed_` functions.

#### SEQUENCE OF

To handle sequences (arrays) of a specific type, the function

    int odr_sequence_of(ODR o, int (*fun)(ODR o, void *p, int optional),
                        void *p, int *num, const char *name);

The `fun` parameter is a pointer to the decoder/encoder function of the type. `p` is a pointer to an array of pointers to your type. `num` is the number of elements in the array.

Assume a type

    MyArray ::= SEQUENCE OF INTEGER

The C representation might be

    typedef struct MyArray
    {
        int num_elements;
        Odr_int **elements;
    } MyArray;

And the function might look like

    int myArray(ODR o, MyArray **p, int optional, const char *name)
    {
        if (o->direction == ODR_DECODE)
            *p = odr_malloc(o, sizeof(**p));
        if (odr_sequence_of(o, odr_integer, &(*p)->elements,
            &(*p)->num_elements, name))
            return 1;
        *p = 0;
            return optional && odr_ok(o);
    }

#### CHOICE Types

The choice type is used fairly often in some ASN.1 definitions, so some work has gone into streamlining its interface.

CHOICE types are handled by the function:

    int odr_choice(ODR o, Odr_arm arm[], void *p, void *whichp,
                   const char *name);

The `arm` array is used to describe each of the possible types that the CHOICE type may assume. Internally in your application, the CHOICE type is represented as a discriminated union. That is, a C union accompanied by an integer (or enum) identifying the active 'arm' of the union. `whichp` is a pointer to the union discriminator. When encoding, it is examined to determine the current type. When decoding, it is set to reference the type that was found in the input stream.

The Odr_arm type is defined thus:

    typedef struct odr_arm
    {
        int tagmode;
        int class;
        int tag;
        int which;
        Odr_fun fun;
        char *name;
    } Odr_arm;

The interpretation of the fields are:

tagmode

  Either `ODR_IMPLICIT`, `ODR_EXPLICIT`, or `ODR_NONE` (-1) to mark no tagging.

which

  The value of the discriminator that corresponds to this CHOICE element. Typically, it will be a #defined constant, or an enum member.

fun

  A pointer to a function that implements the type of the CHOICE member. It may be either a standard &odr; type or a type defined by yourself.

name

  Name of tag.

A handy way to prepare the array for use by the `odr_choice()` function is to define it as a static, initialized array in the beginning of your decoding/encoding function. Assume the type definition:

    MyChoice ::= CHOICE {
        untagged INTEGER,
        tagged   [99] IMPLICIT INTEGER,
        other    BOOLEAN
    }

Your C type might look like

    typedef struct MyChoice
    {
        enum
        {
            MyChoice_untagged,
            MyChoice_tagged,
            MyChoice_other
        } which;
        union
        {
            Odr_int *untagged;
            Odr_int *tagged;
            Odr_bool *other;
        } u;
    };

And your function could look like this:

    int myChoice(ODR o, MyChoice **p, int optional, const char *name)
    {
        static Odr_arm arm[] =
        {
          {-1, -1, -1, MyChoice_untagged, odr_integer, "untagged"},
          {ODR_IMPLICIT, ODR_CONTEXT, 99, MyChoice_tagged, odr_integer,
          "tagged"},
          {-1, -1, -1, MyChoice_other, odr_boolean, "other"},
          {-1, -1, -1, -1, 0}
        };

        if (o->direction == ODR_DECODE)
            *p = odr_malloc(o, sizeof(**p);
        else if (!*p)
            return optional && odr_ok(o);

        if (odr_choice(o, arm, &(*p)->u, &(*p)->which), name)
            return 1;
        *p = 0;
            return optional && odr_ok(o);
    }

In some cases (say, a non-optional choice which is a member of a sequence), you can "embed" the union and its discriminator in the structure belonging to the enclosing type, and you won't need to fiddle with memory allocation to create a separate structure to wrap the discriminator and union.

The corresponding function is somewhat nicer in the Sun XDR interface. Most of the complexity of this interface comes from the possibility of declaring sequence elements (including CHOICEs) optional.

The ASN.1 specifications naturally require that each member of a CHOICE have a distinct tag, so they can be told apart on decoding. Sometimes it can be useful to define a CHOICE that has multiple types that share the same tag. You'll need some other mechanism, perhaps keyed to the context of the CHOICE type. In effect, we would like to introduce a level of context-sensitiveness to our ASN.1 specification. When encoding an internal representation, we have no problem, as long as each CHOICE member has a distinct discriminator value. For decoding, we need a way to tell the choice function to look for a specific arm of the table. The function

    void odr_choice_bias(ODR o, int what);

provides this functionality. When called, it leaves a notice for the next call to `odr_choice()` to be called on the decoding stream `o`, that only the `arm` entry with a `which` field equal to `what` should be tried.

The most important application (perhaps the only one, really) is in the definition of application-specific EXTERNAL encoders/decoders which will automatically decode an ANY member given the direct or indirect reference.

### Debugging

The protocol modules are suffering somewhat from a lack of diagnostic tools at the moment. Specifically ways to pretty-print PDUs that aren't recognized by the system. We'll include something to this end in a not-too-distant release. In the meantime, what we do when we get packages we don't understand is to compile the ODR module with `ODR_DEBUG` defined. This causes the module to dump tracing information as it processes data units. With this output and the protocol specification (Z39.50), it is generally fairly easy to see what goes wrong.

## The COMSTACK Module

### Synopsis (blocking mode)

        COMSTACK stack;
        char *buf = 0;
        int size = 0, length_incoming;
        char server_address_str[] = "localhost:9999";
        void *server_address_ip;
        int status;

        char *protocol_package = "GET / HTTP/1.0\r\n\r\n";
        int protocol_package_length = strlen(protocol_package);

        stack = cs_create(tcpip_type, 1, PROTO_HTTP);
        if (!stack) {
            perror("cs_create");  /* use perror() here since we have no stack yet */
            return -1;
        }

        server_address_ip = cs_straddr(stack, server_address_str);
        if (!server_address_ip) {
            fprintf(stderr, "cs_straddr: address could not be resolved\n");
            return -1;
        }

        status = cs_connect(stack, server_address_ip);
        if (status) {
            fprintf(stderr, "cs_connect: %s\n", cs_strerror(stack));
            return -1;
        }

        status = cs_rcvconnect(stack);
        if (status) {
            fprintf(stderr, "cs_rcvconnect: %s\n", cs_strerror(stack));
            return -1;
        }

        status = cs_put(stack, protocol_package, protocol_package_length);
        if (status) {
            fprintf(stderr, "cs_put: %s\n", cs_strerror(stack));
            return -1;
        }

        /* Now get a response */
        length_incoming = cs_get(stack, &buf, &size);
        if (!length_incoming) {
            fprintf(stderr, "Connection closed\n");
            return -1;
        } else if (length_incoming < 0) {
            fprintf(stderr, "cs_get: %s\n", cs_strerror(stack));
            return -1;
        }

        /* Print result */
        fwrite(buf, length_incoming, 1, stdout);

        /* clean up */
        cs_close(stack);
        if (buf)
            xfree(buf);
        return 0;

### Introduction

The &comstack; subsystem provides a transparent interface to different types of transport stacks for the exchange of BER-encoded data and HTTP packets. At present, the RFC1729 method (BER over TCP/IP), local UNIX socket and an experimental SSL stack are supported, but others may be added in time. The philosophy of the module is to provide a simple interface by hiding unused options and facilities of the underlying libraries. This is always done at the risk of losing generality, and it may prove that the interface will need extension later on.

There hasn't been interest in the XTImOSI stack for some years. Therefore, it is no longer supported.

The interface is implemented in such a fashion that only the sub-layers constructed to the transport methods that you wish to use in your application are linked in.

You will note that even though simplicity was a goal in the design, the interface is still orders of magnitudes more complex than the transport systems found in many other packages. One reason is that the interface needs to support the somewhat different requirements of the different lower-layer communications stacks; another important reason is that the interface seeks to provide a more or less industrial-strength approach to asynchronous event-handling. When no function is allowed to block, things get more complex - particularly on the server side. We urge you to have a look at the demonstration client and server provided with the package. They are meant to be easily readable and instructive, while still being at least moderately useful.

### Common Functions

#### Managing Endpoints

         COMSTACK cs_create(CS_TYPE type, int blocking, int protocol);

Creates an instance of the protocol stack - a communications endpoint. The `type` parameter determines the mode of communication. At present the following values are supported:

`tcpip_type`

  TCP/IP (BER over TCP/IP or HTTP over TCP/IP)

`ssl_type`

  Secure Socket Layer (SSL). This COMSTACK is experimental and is not fully implemented. If HTTP is used, this effectively is HTTPS.

`unix_type`

  Unix socket (unix only). Local Transfer via file socket. See unix 7.

The `cs_create` function returns a null-pointer if a system error occurs. The `blocking` parameter should be '1' if you wish the association to operate in blocking mode, and '0' otherwise. The `protocol` field should be `PROTO_Z3950` or `PROTO_HTTP`. Protocol `PROTO_SR` is no longer supported.

         void cs_close(COMSTACK handle);

Closes the connection (as elegantly as the lower layers will permit), and releases the resources pointed to by the `handle` parameter. The `handle` should not be referenced again after this call.

We really need a soft disconnect, don't we?

#### Data Exchange

         int cs_put(COMSTACK handle, char *buf, int len);

Sends `buf` down the wire. In blocking mode, this function will return only when a full buffer has been written, or an error has occurred. In nonblocking mode, it's possible that the function will be unable to send the full buffer at once, which will be indicated by a return value of 1. The function will keep track of the number of octets already written; you should call it repeatedly with the same values of `buf` and `len`, until the buffer has been transmitted. When a full buffer has been sent, the function will return 0 for success. The return value -1 indicates an error condition (see below).

         int cs_get(COMSTACK handle, char **buf, int *size);

Receives a PDU or HTTP Response from the peer. Returns the number of bytes read. In nonblocking mode, it is possible that not all of the packet can be read at once. In this case, the function returns 1. To simplify the interface, the function is responsible for managing the size of the buffer. It will be reallocated if necessary to contain large packages, and will sometimes be moved around internally by the subsystem when partial packages are read. Before calling `cs_get` for the first time, the buffer can be initialized to the null pointer, and the length should also be set to 0 (cs_get will perform a `malloc(2)` on the buffer for you). When a full buffer has been read, the size of the package is returned (which will always be greater than 1). The return value -1 indicates an error condition.

See also the `cs_more()` function below.

         int cs_more(COMSTACK handle);

The `cs_more()` function should be used in conjunction with `cs_get` and `select(2)`. The `cs_get()` function will sometimes (notably in the TCP/IP mode) read more than a single protocol package off the network. When this happens, the extra package is stored by the subsystem. After calling `cs_get()`, and before waiting for more input, You should always call `cs_more()` to check if there's a full protocol package already read. If `cs_more()` returns 1, `cs_get()` can be used to immediately fetch the new package. For the mOSI subsystem, the function should always return 0, but if you want your stuff to be protocol independent, you should use it.

The `cs_more()` function is required because the RFC1729-method does not provide a way of separating individual PDUs, short of partially decoding the BER. Some other implementations will carefully nibble at the packet by calling `read(2)` several times. This was felt to be too inefficient (or at least clumsy) - hence the call for this extra function.

         int cs_look(COMSTACK handle);

This function is useful when you're operating in nonblocking mode. Call it when `select(2)` tells you there's something happening on the line. It returns one of the following values:

CS_NONE

  No event is pending. The data found on the line was not a complete package.

CS_CONNECT

  A response to your connect request has been received. Call `cs_rcvconnect` to process the event and to finalize the connection establishment.

CS_DISCON

  The other side has closed the connection (or maybe sent a disconnect request - but do we care? Maybe later). Call `cs_close` to close your end of the association as well.

CS_LISTEN

  A connect request has been received. Call `cs_listen` to process the event.

CS_DATA

  There's data to be found on the line. Call `cs_get` to get it.

You should be aware that even if `cs_look()` tells you that there's an event event pending, the corresponding function may still return and tell you there was nothing to be found. This means that only part of a package was available for reading. The same event will show up again, when more data has arrived.

         int cs_fileno(COMSTACK h);

returns the file descriptor of the association. Use this when file-level operations on the endpoint are required (`select(2)` operations, specifically).

### Client Side

        int cs_connect(COMSTACK handle, void *address);

Initiate a connection with the target at `address` (more on addresses below). The function will return 0 on success, and 1 if the operation does not complete immediately (this will only happen on a nonblocking endpoint). In this case, use `cs_rcvconnect` to complete the operation, when `select(2)` or `poll(2)` reports input pending on the association.

        int cs_rcvconnect(COMSTACK handle);

Complete a connect operation initiated by `cs_connect()`. It will return 0 on success; 1 if the operation has not yet completed (in this case, call the function again later); -1 if an error has occurred.

### Server Side

To establish a server under the inetd server, you can use

        COMSTACK cs_createbysocket(int socket, CS_TYPE type, int blocking,
                                   int protocol);

The `socket` parameter is an established socket (when your application is invoked from inetd, the socket will typically be 0. The following parameters are identical to the ones for `cs_create`.

        int cs_bind(COMSTACK handle, void *address, int mode)

Binds a local address to the endpoint. Read about addresses below. The `mode` parameter should be either `CS_CLIENT` or `CS_SERVER`.

        int cs_listen(COMSTACK handle, char *addr, int *addrlen);

Call this to process incoming events on an endpoint that has been bound in listening mode. It will return 0 to indicate that the connect request has been received, 1 to signal a partial reception, and -1 to indicate an error condition.

        COMSTACK cs_accept(COMSTACK handle);

This finalizes the server-side association establishment, after cs_listen has completed successfully. It returns a new connection endpoint, which represents the new association. The application will typically wish to fork off a process to handle the association at this point, and continue listen for new connections on the old `handle`.

You can use the call

        const char *cs_addrstr(COMSTACK);

on an established connection to retrieve the host-name of the remote host.

You may need to use this function with some care if your name server service is slow or unreliable.

### Addresses

The low-level format of the addresses are different depending on the mode of communication you have chosen. A function is provided by each of the lower layers to map a user-friendly string-form address to the binary form required by the lower layers.

        void *cs_straddr(COMSTACK handle, const char *str);

The format for TCP/IP and SSL addresses is:

        <host> [ ':' <portnum> ]

The `hostname` can be either a domain name or an IP address. The port number, if omitted, defaults to 210.

For TCP/IP and SSL, the special hostnames `@`, maps to `IN6ADDR_ANY_INIT` with IPV4 binding as well (bindv6only=0), The special hostname `@4` binds to `INADDR_ANY` (IPV4 only listener). The special hostname `@6` binds to `IN6ADDR_ANY_INIT` with bindv6only=1 (IPV6 only listener).

For UNIX sockets, the format of an address is the socket filename.

When a connection has been established, you can use

        const char *cs_addrstr(COMSTACK h);

to retrieve the host name of the peer system. The function returns a pointer to a static area, which is overwritten on the next call to the function.

A fairly recent addition to the &comstack; module is the utility function

        COMSTACK cs_create_host (const char *str, int blocking, void **vp);

which is just a wrapper for `cs_create` and `cs_straddr`. The str is similar to that described for `cs_straddr` but with a prefix denoting the &comstack; type. Prefixes supported are `tcp:` and `unix:` and `ssl:` for TCP/IP and UNIX and SSL respectively. If no prefix is given, then TCP/IP is used. The blocking is passed to function `cs_create`. The third parameter vp is a pointer to &comstack; stack type specific values. Parameter vp is reserved for future use. Set it to `NULL`.

### SSL

         void *cs_get_ssl(COMSTACK cs);

Returns the SSL handle, `SSL *` for comstack. If comstack is not of type SSL, then NULL is returned.

         int cs_set_ssl_ctx(COMSTACK cs, void *ctx);

Sets SSL context for comstack. The parameter is expected to be of type `SSL_CTX *`. This function should be called just after comstack has been created (before connect, bind, etc). This function returns 1 for success; 0 for failure.

         int cs_set_ssl_certificate_file(COMSTACK cs, const char *fname);

Sets SSL certificate for comstack as a PEM file. This function returns 1 for success; 0 for failure.

         int cs_get_ssl_peer_certificate_x509(COMSTACK cs, char **buf, int *len);

This function returns the peer certificate. If successful, `*buf` and `*len` holds X509 buffer and length respectively. Buffer should be freed with `xfree`. This function returns 1 for success; 0 for failure.

### Diagnostics

All functions return -1 if an error occurs. Typically, the functions will return 0 on success, but the data exchange functions (`cs_get`, `cs_put`, `cs_more`) follow special rules. Consult their descriptions.

The error code for the COMSTACK can be retrieved using C macro `cs_errno` which will return one of the error codes `CSYSERR`, `CSOUTSTATE`, `CSNODATA`, ...

        int cs_errno(COMSTACK handle);

You can the textual representation of the error code by using `cs_errmsg`, which works like `strerror(3)`.

        const char *cs_errmsg(int n);

It is also possible to get straight to the textual representation without the error code, by using `cs_strerror`.

        const char *cs_strerror(COMSTACK h);

### Summary and Synopsis

        #include <yaz/comstack.h>

        #include <yaz/tcpip.h>  /* this is for TCP/IP and SSL support */
        #include <yaz/unix.h>   /* this is for UNIX socket support */

        COMSTACK cs_create(CS_TYPE type, int blocking, int protocol);

        COMSTACK cs_createbysocket(int s, CS_TYPE type, int blocking,
                                   int protocol);
        COMSTACK cs_create_host(const char *str, int blocking,
                                void **vp);

        int cs_bind(COMSTACK handle, int mode);

        int cs_connect(COMSTACK handle, void *address);

        int cs_rcvconnect(COMSTACK handle);

        int cs_listen(COMSTACK handle);

        COMSTACK cs_accept(COMSTACK handle);

        int cs_put(COMSTACK handle, char *buf, int len);

        int cs_get(COMSTACK handle, char **buf, int *size);

        int cs_more(COMSTACK handle);

        void cs_close(COMSTACK handle);

        int cs_look(COMSTACK handle);

        void *cs_straddr(COMSTACK handle, const char *str);

        const char *cs_addrstr(COMSTACK h);

## Future Directions

We have a new and better version of the front-end server on the drawing board. Resources and external commitments will govern when we'll be able to do something real with it. Features should include greater flexibility, greater support for access/resource control, and easy support for Explain (possibly with Zebra as an extra database engine).

&yaz; is a BER toolkit and as such should support all protocols out there based on that. We'd like to see running ILL applications. It shouldn't be that hard. Another thing that would be interesting is LDAP. Maybe a generic framework for doing IR using both LDAP and Z39.50 transparently.

The SOAP implementation is incomplete. In the future we hope to add more features to it. Perhaps make a WSDL/XML Schema compiler. The authors of libxml2 are already working on XML Schema and RELAX NG compilers so this may not be too hard.

It would be neat to have a proper module mechanism for the Generic Frontend Server so that backend would be dynamically loaded (as shared objects / DLLs).

Other than that, &yaz; generally moves in the directions which appear to make the most people happy (including ourselves, as prime users of the software). If there's something you'd like to see in here, then drop us a note and let's see what we can come up with.

## Reference

The material in this chapter is drawn directly from the individual manual entries.

&manref;

## List of Object Identifiers

These is a list of object identifiers that are built into YAZ.

&std-oid-table;

## Bib-1 diagnostics

List of Bib-1 diagnostics that are known to YAZ.

&bib1-diag-table;

## SRU diagnostics

List of SRU diagnostics that are known to YAZ.

&srw-diag-table;

## License

### Index Data Copyright

Copyright © ©right-year; Index Data.

All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

- Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

- Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

- Neither the name of Index Data nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY INDEX DATA ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL INDEX DATA BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

## About Index Data

Index Data is a consulting and software-development enterprise that specializes in library and information management systems. Our interests and expertise span a broad range of related fields, and one of our primary, long-term objectives is the development of a powerful information management system with open network interfaces and hyper-media capabilities.

We make this software available free of charge, on a fairly unrestrictive license; as a service to the networking community, and to further the development of quality software for open network communication.

We'll be happy to answer questions about the software, and about ourselves in general.

The Hacker's Jargon File has the following to say about the use of the prefix "YA" in the name of a software product.

Yet Another. adj. 1. Of your own work: A humorous allusion often used in titles to acknowledge that the topic is not original, though the content is. As in "Yet Another AI Group" or "Yet Another Simulated Annealing Algorithm". 2. Of others' work: Describes something of which there are already far too many.

## Credits

This appendix lists individuals that have contributed in the development of &yaz;. Some have contributed with code, while others have provided bug fixes or suggestions. If we're missing somebody, of if you, for whatever reason, don't like to be listed here, let us know.

- Gary Anderson

- Dimitrios Andreadis

- Morten Bøgeskov

- Rocco Carbone

- Matthew Carey

- Hans van Dalen

- Irina Dijour

- Larry E. Dixson

- Hans van den Dool

- Mads Bondo Dydensborg

- Franck Falcoz

- Kevin Gamiel

- Morten Garkier Hendriksen

- Morten Holmqvist

- Ian Ibbotson

- Shigeru Ishida

- Heiko Jansen

- David Johnson

- Oleg Kolobov

- Giannis Kosmas

- Kang-Jin Lee

- Pieter Van Lierop

- Stefan Lohrum

- Ronald van der Meer

- Thomas W. Place

- Peter Popovics

- Jacob Chr. Poulsen

- Ko van der Sloot

- Mike Taylor

- Rustam T. Usmanov

- Charles Woodfield

- Tom André Øverland

- Hugh McMaster

- Guillaume Jactat