-<!-- $Id: book.xml,v 1.1 2006-03-16 12:03:39 adam Exp $ -->
+<?xml version="1.0" standalone="no"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1//EN"
+ "http://www.oasis-open.org/docbook/xml/4.1/docbookx.dtd"
+[
+ <!ENTITY local SYSTEM "local.ent">
+ <!ENTITY manref SYSTEM "manref.xml">
+ <!ENTITY progref SYSTEM "progref.xml">
+ <!ENTITY % common SYSTEM "common/common.ent">
+ %common;
+ <!-- Next line allows imagedata/@format="PDF" and is taken from
+ http://lists.oasis-open.org/archives/docbook/200303/msg00163.html
+ -->
+ <!ENTITY % local.notation.class "| PDF">
+ <!-- Next line is necessary for some XML parsers, for reasons I
+ don't understand. I got this from
+ http://lists.oasis-open.org/archives/docbook/200303/msg00180.html
+ -->
+ <!NOTATION PDF SYSTEM "PDF">
+]>
+<!-- $Id: book.xml,v 1.41 2006-10-12 11:34:07 marc Exp $ -->
+<book id="metaproxy">
<bookinfo>
- <title>Metaproxy - User's Guide and Reference</title>
- <author>
- <firstname>Mike</firstname><surname>Taylor</surname>
- </author>
- <copyright>
- <year>2006</year>
- <holder>Index Data</holder>
- </copyright>
- <abstract>
- <simpara>
- ###
- Metaproxy is ... in need of description :-)
- </simpara>
- </abstract>
+ <title>Metaproxy - User's Guide and Reference</title>
+ <author>
+ <firstname>Adam</firstname><surname>Dickmeiss</surname>
+ </author>
+ <author>
+ <firstname>Marc</firstname><surname>Cromme</surname>
+ </author>
+ <author>
+ <firstname>Mike</firstname><surname>Taylor</surname>
+ </author>
+ <copyright>
+ <year>2006</year>
+ <holder>Index Data ApS</holder>
+ </copyright>
+ <abstract>
+ <simpara>
+ Metaproxy is a universal router, proxy and encapsulated
+ metasearcher for information retrieval protocols. It accepts,
+ processes, interprets and redirects requests from IR clients using
+ standard protocols such as
+ <ulink url="&url.z39.50;">ANSI/NISO Z39.50</ulink>
+ (and in the future <ulink url="&url.sru;">SRU</ulink>
+ and <ulink url="&url.srw;">SRW</ulink>), as
+ well as functioning as a limited
+ <ulink url="&url.http;">HTTP</ulink> server.
+ Metaproxy is configured by an XML file which
+ specifies how the software should function in terms of routes that
+ the request packets can take through the proxy, each step on a
+ route being an instantiation of a filter. Filters come in many
+ types, one for each operation: accepting Z39.50 packets, logging,
+ query transformation, multiplexing, etc. Further filter-types can
+ be added as loadable modules to extend Metaproxy functionality,
+ using the filter API.
+ </simpara>
+ <simpara>
+ Metaproxy is <emphasis>not</emphasis> open-source software, but
+ may be freely downloaded, unpacked, inspected, built and run for
+ evaluation purposes. Deployment requires a separate, commercial,
+ license.
+ </simpara>
+ <simpara>
+ <inlinemediaobject>
+ <imageobject>
+ <imagedata fileref="common/id.png" format="PNG"/>
+ </imageobject>
+ <imageobject>
+ <imagedata fileref="common/id.eps" format="EPS"/>
+ </imageobject>
+ </inlinemediaobject>
+ </simpara>
+ </abstract>
</bookinfo>
-
-
<chapter id="introduction">
- <title>Introduction</title>
-
-
- <section>
- <title>Overview</title>
- <para>
- <ulink url="http://indexdata.dk/metaproxy/">Metaproxy</ulink>
- is ..
- </para>
+ <title>Introduction</title>
+
+
<para>
- ### We should probably consider saying a little more by way of
- introduction.
+ <ulink url="&url.metaproxy;">Metaproxy</ulink>
+ is a standalone program that acts as a universal router, proxy and
+ encapsulated metasearcher for information retrieval protocols such
+ as <ulink url="&url.z39.50;">Z39.50</ulink>, and in the future
+ <ulink url="&url.sru;">SRU</ulink> and <ulink url="&url.srw;">SRW</ulink>.
+ To clients, it acts as a server of these protocols: it can be searched,
+ records can be retrieved from it, etc.
+ To servers, it acts as a client: it searches in them,
+ retrieves records from them, etc. it satisfies its clients'
+ requests by transforming them, multiplexing them, forwarding them
+ on to zero or more servers, merging the results, transforming
+ them, and delivering them back to the client. In addition, it
+ acts as a simple <ulink url="&url.http;">HTTP</ulink> server; support
+ for further protocols can be added in a modular fashion, through the
+ creation of new filters.
</para>
- </section>
- </chapter>
-
-
-
- <chapter id="filters">
- <title>Filters</title>
-
-
- <section>
- <title>Introductory notes</title>
+ <screen>
+ Anything goes in!
+ Anything goes out!
+ Fish, bananas, cold pyjamas,
+ Mutton, beef and trout!
+ - attributed to Cole Porter.
+ </screen>
<para>
- It's useful to think of Metaproxy as an interpreter providing a small
- number of primitives and operations, but operating on a very
- complex data type, namely the ``package''.
+ Metaproxy is a more capable alternative to
+ <ulink url="&url.yazproxy;">YAZ Proxy</ulink>,
+ being more powerful, flexible, configurable and extensible. Among
+ its many advantages over the older, more pedestrian work are
+ support for multiplexing (encapsulated metasearching), routing by
+ database name, authentication and authorisation and serving local
+ files via HTTP. Equally significant, its modular architecture
+ facilitites the creation of pluggable modules implementing further
+ functionality.
</para>
<para>
- A package represents a Z39.50 or SRW/U request (whether for Init,
- Search, Scan, etc.) together with information about where it came
- from. Packages are created by front-end filters such as
- <literal>frontend_net</literal> (see below), which reads them from
- the network; other front-end filters are possible. They then pass
- along a route consisting of a sequence of filters, each of which
- transforms the package and may also have side-effects such as
- generating logging. Eventually, the route will yield a response,
- which is sent back to the origin.
+ This manual will describe how to install Metaproxy
+ before giving an overview of its architecture, then discussing the
+ key concept of a filter in some depth and giving an overview of
+ the various filter types, then discussing the configuration file
+ format. After this come several optional chapters which may be
+ freely skipped: a detailed discussion of virtual databases and
+ multi-database searching, some notes on writing extensions
+ (additional filter types) and a high-level description of the
+ source code. Finally comes the reference guide, which contains
+ instructions for invoking the <command>metaproxy</command>
+ program, and detailed information on each type of filter,
+ including examples.
</para>
+ </chapter>
+
+ <chapter id="license">
+ <title>The Metaproxy License</title>
+ <orderedlist numeration="arabic">
+ <listitem>
+ <para>
+ You are allowed to download this software for evaluation purposes.
+ You can unpack it, build it, run it, see how it works and how it fits
+ your needs, all at zero cost.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ You may NOT deploy the software. For the purposes of this license,
+ deployment means running it for any purpose other than evaluation,
+ whether or not you or anyone else makes a profit from doing so. If
+ you wish to deploy the software, you must first contact Index Data and
+ arrange to purchase a DEPLOYMENT LICENCE. If you are unsure
+ whether or not your proposed use of the software constitutes
+ deployment, email us at <literal>info@indexdata.com</literal>
+ for clarification.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ You may modify your copy of the software (fix bugs, add features)
+ if you need to. We encourage you to send your changes back to us for
+ integration into the master copy, but you are not obliged to do so. You
+ may NOT pass your changes on to any other party.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ There is NO WARRANTY for this software, to the extent permitted by
+ applicable law. We provide the software ``as is'' without warranty of
+ any kind, either expressed or implied, including, but not limited to, the
+ implied warranties of MERCHANTABILITY and FITNESS FOR A
+ PARTICULAR PURPOSE. The entire risk as to the quality and
+ performance of the software is with you. Should the software prove
+ defective, you assume the cost of all necessary servicing, repair or
+ correction. In no event unless required by applicable law will we be
+ liable to you for damages, arising out of the use of the software,
+ including but not limited to loss of data or data being rendered
+ inaccurate.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ All rights to the software are reserved by Index Data except where
+ this license explicitly says otherwise.
+ </para>
+ </listitem>
+ </orderedlist>
+ </chapter>
+
+ <chapter id="installation">
+ <title>Installation</title>
<para>
- There are many kinds of filter: some that are defined statically
- as part of Metaproxy, and other that may be provided by third parties
- and dynamically loaded. They all conform to the same simple API
- of essentially two methods: <function>configure()</function> is
- called at startup time, and is passed a DOM tree representing that
- part of the configuration file that pertains to this filter
- instance: it is expected to walk that tree extracting relevant
- information; and <function>process()</function> is called every
- time the filter has to processes a package.
+ Metaproxy depends on the following tools/libraries:
+ <variablelist>
+ <varlistentry><term><ulink url="&url.yazplusplus;">YAZ++</ulink></term>
+ <listitem>
+ <para>
+ This is a C++ library based on <ulink url="&url.yaz;">YAZ</ulink>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry><term><ulink url="&url.libxslt;">Libxslt</ulink></term>
+ <listitem>
+ <para>This is an XSLT processor - based on
+ <ulink url="&url.libxml2;">Libxml2</ulink>. Both Libxml2 and
+ Libxslt must be installed with the development components
+ (header files, etc.) as well as the run-time libraries.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry><term><ulink url="&url.boost;">Boost</ulink></term>
+ <listitem>
+ <para>
+ The popular C++ library. Initial versions of Metaproxy
+ was built with 1.33.0. Version 1.33.1 works too.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
</para>
<para>
- While all filters provide the same API, there are different modes
- of functionality. Some filters are sources: they create
- packages
- (<literal>frontend_net</literal>);
- others are sinks: they consume packages and return a result
- (<literal>z3950_client</literal>,
- <literal>backend_test</literal>,
- <literal>http_file</literal>);
- the others are true filters, that read, process and pass on the
- packages they are fed
- (<literal>auth_simple</literal>,
- <literal>log</literal>,
- <literal>multi</literal>,
- <literal>session_shared</literal>,
- <literal>template</literal>,
- <literal>virt_db</literal>).
+ In order to compile Metaproxy a modern C++ compiler is
+ required. Boost, in particular, requires the C++ compiler
+ to facilitate the newest features. Refer to Boost
+ <ulink url="&url.boost.compilers.status;">Compiler Status</ulink>
+ for more information.
</para>
- </section>
-
-
- <section>
- <title>Individual filters</title>
<para>
- The filters are here named by the string that is used as the
- <literal>type</literal> attribute of a
- <literal><filter></literal> element in the configuration
- file to request them, with the name of the class that implements
- them in parentheses.
+ We have succesfully built Metaproxy using the compilers
+ <ulink url="&url.gcc;">GCC</ulink> version 4.0 and
+ <ulink url="&url.vstudio;">Microsoft Visual Studio</ulink> 2003/2005.
</para>
- <section>
- <title><literal>auth_simple</literal>
- (mp::filter::AuthSimple)</title>
- <para>
- Simple authentication and authorisation. The configuration
- specifies the name of a file that is the user register, which
- lists <varname>username</varname>:<varname>password</varname>
- pairs, one per line, colon separated. When a session begins, it
- is rejected unless username and passsword are supplied, and match
- a pair in the register.
- </para>
+ <section id="installation.unix">
+ <title>Installation on Unix (from Source)</title>
<para>
- ### discuss authorisation phase
+ Here is a quick step-by-step guide on how to compile all the
+ tools that Metaproxy uses. Only few systems have none of the required
+ tools binary packages. If, for example, Libxml2/libxslt are already
+ installed as development packages use those (and omit compilation).
</para>
- </section>
-
- <section>
- <title><literal>backend_test</literal>
- (mp::filter::Backend_test)</title>
+
<para>
- A sink that provides dummy responses in the manner of the
- <literal>yaz-ztest</literal> Z39.50 server. This is useful only
- for testing.
+ Libxml2/libxslt:
</para>
- </section>
-
- <section>
- <title><literal>frontend_net</literal>
- (mp::filter::FrontendNet)</title>
+ <screen>
+ gunzip -c libxml2-version.tar.gz|tar xf -
+ cd libxml2-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
+ <screen>
+ gunzip -c libxslt-version.tar.gz|tar xf -
+ cd libxslt-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
<para>
- A source that accepts Z39.50 and SRW connections from a port
- specified in the configuration, reads protocol units, and
- feeds them into the next filter, eventually returning the
- result to the origin.
+ YAZ/YAZ++:
</para>
- </section>
-
- <section>
- <title><literal>http_file</literal>
- (mp::filter::HttpFile)</title>
+ <screen>
+ gunzip -c yaz-version.tar.gz|tar xf -
+ cd yaz-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
+ <screen>
+ gunzip -c yazpp-version.tar.gz|tar xf -
+ cd yazpp-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
<para>
- A sink that returns the contents of files from the local
- filesystem in response to HTTP requests. (Yes, Virginia, this
- does mean that Metaproxy is also a Web-server in its spare time. So
- far it does not contain either an email-reader or a Lisp
- interpreter, but that day is surely coming.)
+ Boost:
</para>
- </section>
-
- <section>
- <title><literal>log</literal>
- (mp::filter::Log)</title>
+ <screen>
+ gunzip -c boost-version.tar.gz|tar xf -
+ cd boost-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
<para>
- Writes logging information to standard output, and passes on
- the package unchanged.
+ Metaproxy:
</para>
+ <screen>
+ gunzip -c metaproxy-version.tar.gz|tar xf -
+ cd metaproxy-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
</section>
- <section>
- <title><literal>multi</literal>
- (mp::filter::Multi)</title>
+ <section id="installation.debian">
+ <title>Installation on Debian GNU/Linux</title>
<para>
- Performs multicast searching. See the extended discussion of
- multi-database searching below.
+ All dependencies for Metaproxy are available as
+ <ulink url="&url.debian;">Debian</ulink>
+ packages for the sarge (stable in 2005) and etch (testing in 2005)
+ distributions.
</para>
- </section>
-
- <section>
- <title><literal>session_shared</literal>
- (mp::filter::SessionShared)</title>
<para>
- When this is finished, it will implement global sharing of
- result sets (i.e. between threads and therefore between
- clients), but it's not yet done.
+ The procedures for Debian based systems, such as
+ <ulink url="&url.ubuntu;">Ubuntu</ulink> is probably similar
</para>
- </section>
-
- <section>
- <title><literal>template</literal>
- (mp::filter::Template)</title>
<para>
- Does nothing at all, merely passing the packet on. (Maybe it
- should be called <literal>nop</literal> or
- <literal>passthrough</literal>?) This exists not to be used, but
- to be copied - to become the skeleton of new filters as they are
- written.
+ There is currently no official Debian package for YAZ++.
+ And the Debian package for YAZ is probably too old.
+ Update the <filename>/etc/apt/sources.list</filename>
+ to include the Index Data repository.
+ See YAZ' <ulink url="&url.yaz.download.debian;">Download Debian</ulink>
+ for more information.
</para>
- </section>
-
- <section>
- <title><literal>virt_db</literal>
- (mp::filter::Virt_db)</title>
+ <screen>
+ apt-get install libxslt1-dev
+ apt-get install libyazpp-dev
+ apt-get install libboost-dev
+ apt-get install libboost-thread-dev
+ apt-get install libboost-date-time-dev
+ apt-get install libboost-program-options-dev
+ apt-get install libboost-test-dev
+ </screen>
<para>
- Performs virtual database selection. See the extended discussion
- of virtual databases below.
+ With these packages installed, the usual configure + make
+ procedure can be used for Metaproxy as outlined in
+ <xref linkend="installation.unix"/>.
</para>
</section>
- <section>
- <title><literal>z3950_client</literal>
- (mp::filter::Z3950Client)</title>
+ <section id="installation.windows">
+ <title>Installation on Windows</title>
<para>
- Performs Z39.50 searching and retrieval by proxying the
- packages that are passed to it. Init requests are sent to the
- address specified in the <literal>VAL_PROXY</literal> otherInfo
- attached to the request: this may have been specified by client,
- or generated by a <literal>virt_db</literal> filter earlier in
- the route. Subsequent requests are sent to the same address,
- which is remembered at Init time in a Session object.
+ Metaproxy can be compiled with Microsoft
+ <ulink url="&url.vstudio;">Visual Studio</ulink>.
+ Version 2003 (C 7.1) and 2005 (C 8.0) is known to work.
</para>
- </section>
- </section>
+ <section id="installation.windows.boost">
+ <title>Boost</title>
+ <para>
+ Get Boost from its <ulink url="&url.boost;">home page</ulink>.
+ You also need Boost Jam (an alternative to make).
+ That's also available from the Boost home page.
+ The files to be downloaded are called something like:
+ <filename>boost_1_33-1.exe</filename>
+ and
+ <filename>boost-jam-3.1.12-1-ntx86.zip</filename>.
+ Unpack Boost Jam first. Put <filename>bjam.exe</filename>
+ in your system path. Make a command prompt and ensure
+ it can be found automatically. If not check the PATH.
+ The Boost .exe is a self-extracting exe with
+ complete source for Boost. Compile that source with
+ Boost Jam (An alternative to Make).
+ The compilation takes a while.
+ For Visual Studio 2003, use
+ <screen>
+ bjam "-sTOOLS=vc-7_1"
+ </screen>
+ Here <literal>vc-7_1</literal> refers to a "Toolset" (compiler system).
+ For Visual Studio 2005, use
+ <screen>
+ bjam "-sTOOLS=vc-8_0"
+ </screen>
+ To install the libraries in a common place, use
+ <screen>
+ bjam "-sTOOLS=vc-7_1" install
+ </screen>
+ (or vc-8_0 for VS 2005).
+ </para>
+ <para>
+ By default, the Boost build process installs the resulting
+ libraries + header files in
+ <literal>\boost\lib</literal>, <literal>\boost\include</literal>.
+ </para>
+ <para>
+ For more informatation about installing Boost refer to the
+ <ulink url="&url.boost.getting.started;">getting started</ulink>
+ pages.
+ </para>
+ </section>
+
+ <section id="installation.windows.libxslt">
+ <title>Libxslt</title>
+ <para>
+ <ulink url="&url.libxslt;">Libxslt</ulink> can be downloaded
+ for Windows from
+ <ulink url="&url.libxml2.download.win32;">here</ulink>.
+ </para>
+ <para>
+ Libxslt has other dependencies, but thes can all be downloaded
+ from the same site. Get the following:
+ iconv, zlib, libxml2, libxslt.
+ </para>
+ </section>
+
+ <section id="installation.windows.yaz">
+ <title>YAZ</title>
+ <para>
+ <ulink url="&url.yaz;">YAZ</ulink> can be downloaded
+ for Windows from
+ <ulink url="&url.yaz.download.win32;">here</ulink>.
+ </para>
+ </section>
+
+ <section id="installation.windows.yazplusplus">
+ <title>YAZ++</title>
+ <para>
+ Get <ulink url="&url.yazplusplus;">YAZ++</ulink> as well.
+ Version 1.0 or later is required. For now get it from
+ Index Data's
+ <ulink url="&url.snapshot.download;">Snapshot area</ulink>.
+ </para>
+ <para>
+ YAZ++ includes NMAKE makefiles, similar to those found in the
+ YAZ package.
+ </para>
+ </section>
+
+ <section id="installation.windows.metaproxy">
+ <title>Metaproxy</title>
+ <para>
+ Metaproxy is shipped with NMAKE makfiles as well - similar
+ to those found in the YAZ++/YAZ packages. Adjust this Makefile
+ to point to the proper locations of Boost, Libxslt, Libxml2,
+ zlib, iconv, yaz and yazpp.
+ </para>
+
+ <variablelist>
+ <varlistentry><term><literal>DEBUG</literal></term>
+ <listitem><para>
+ 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).
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>BOOST</literal></term>
+ <listitem>
+ <para>
+ Boost install location
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>BOOST_VERSION</literal></term>
+ <listitem>
+ <para>
+ Boost version (replace . with _).
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>BOOST_TOOLSET</literal></term>
+ <listitem>
+ <para>
+ Boost toolset.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>LIBXSLT_DIR</literal>,
+ <literal>LIBXML2_DIR</literal> ..</term>
+ <listitem>
+ <para>
+ Specify the locations of Libxslt, libiconv, libxml2 and
+ libxslt.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ <para>
+ After succesful compilation you'll find
+ <literal>metaproxy.exe</literal> in the
+ <literal>bin</literal> directory.
+ </para>
+ </section>
- <section>
- <title>Future directions</title>
+ </section>
+ </chapter>
+
+ <chapter id="architecture">
+ <title>The Metaproxy Architecture</title>
<para>
- Some other filters that do not yet exist, but which would be
- useful, are briefly described. These may be added in future
- releases.
+ The Metaproxy architecture is based on three concepts:
+ the <emphasis>package</emphasis>,
+ the <emphasis>route</emphasis>
+ and the <emphasis>filter</emphasis>.
</para>
-
<variablelist>
<varlistentry>
- <term><literal>frontend_cli</literal> (source)</term>
+ <term>Packages</term>
<listitem>
<para>
- Command-line interface for generating requests.
+ A package is request or response, encoded in some protocol,
+ issued by a client, making its way through Metaproxy, send to or
+ received from a server, or sent back to the client.
</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><literal>srw2z3950</literal> (filter)</term>
- <listitem>
<para>
- Translate SRW requests into Z39.50 requests.
+ The core of a package is the protocol unit - for example, a
+ Z39.50 Init Request or Search Response, or an SRU searchRetrieve
+ URL or Explain Response. In addition to this core, a package
+ also carries some extra information added and used by Metaproxy
+ itself.
</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><literal>srw_client</literal> (sink)</term>
- <listitem>
<para>
- SRW searching and retrieval.
+ In general, packages are doctored as they pass through
+ Metaproxy. For example, when the proxy performs authentication
+ and authorisation on a Z39.50 Init request, it removes the
+ authentication credentials from the package so that they are not
+ passed onto the back-end server; and when search-response
+ packages are obtained from multiple servers, they are merged
+ into a single unified package that makes its way back to the
+ client.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><literal>sru_client</literal> (sink)</term>
+ <term>Routes</term>
<listitem>
<para>
- SRU searching and retrieval.
+ Packages make their way through routes, which can be thought of
+ as programs that operate on the package data-type. Each
+ incoming package initially makes its way through a default
+ route, but may be switched to a different route based on various
+ considerations. Routes are made up of sequences of filters (see
+ below).
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><literal>opensearch_client</literal> (sink)</term>
+ <term>Filters</term>
<listitem>
<para>
- A9 OpenSearch searching and retrieval.
+ Filters provide the individual instructions within a route, and
+ effect the necessary transformations on packages. A particular
+ configuration of Metaproxy is essentially a set of filters,
+ described by configuration details and arranged in order in one
+ or more routes. There are many kinds of filter - about a dozen
+ at the time of writing with more appearing all the time - each
+ performing a specific function and configured by different
+ information.
+ </para>
+ <para>
+ The word ``filter'' is sometimes used rather loosely, in two
+ different ways: it may be used to mean a particular
+ <emphasis>type</emphasis> of filter, as when we speak of ``the
+ auth_simple filter'' or ``the multi filter''; or it may be used
+ to be a specific <emphasis>instance</emphasis> of a filter
+ within a Metaproxy configuration. For example, a single
+ configuration will often contain multiple instances of the
+ <literal>z3950_client</literal> filter. In
+ operational terms, of these is a separate filter. In practice,
+ context always make it clear which sense of the word ``filter''
+ is being used.
+ </para>
+ <para>
+ Extensibility of Metaproxy is primarily through the creation of
+ plugins that provide new filters. The filter API is small and
+ conceptually simple, but there are many details to master. See
+ the section below on
+ <link linkend="extensions">extensions</link>.
</para>
</listitem>
</varlistentry>
</variablelist>
- </section>
+ <para>
+ Since packages are created and handled by the system itself, and
+ routes are conceptually simple, most of the remainder of this
+ document concentrates on filters. After a brief overview of the
+ filter types follows, along with some thoughts on possible future
+ directions.
+ </para>
</chapter>
- <chapter id="configuration">
- <title>Configuration: the Metaproxy configuration file format</title>
+ <chapter id="filters">
+ <title>Filters</title>
+
+
+ <section>
+ <title>Introductory notes</title>
+ <para>
+ It's useful to think of Metaproxy as an interpreter providing a small
+ number of primitives and operations, but operating on a very
+ complex data type, namely the ``package''.
+ </para>
+ <para>
+ A package represents a Z39.50 or SRU/W request (whether for Init,
+ Search, Scan, etc.) together with information about where it came
+ from. Packages are created by front-end filters such as
+ <literal>frontend_net</literal> (see below), which reads them from
+ the network; other front-end filters are possible. They then pass
+ along a route consisting of a sequence of filters, each of which
+ transforms the package and may also have side-effects such as
+ generating logging. Eventually, the route will yield a response,
+ which is sent back to the origin.
+ </para>
+ <para>
+ There are many kinds of filter: some that are defined statically
+ as part of Metaproxy, and others may be provided by third parties
+ and dynamically loaded. They all conform to the same simple API
+ of essentially two methods: <function>configure()</function> is
+ called at startup time, and is passed an XML DOM tree representing that
+ part of the configuration file that pertains to this filter
+ instance: it is expected to walk that tree extracting relevant
+ information; and <function>process()</function> is called every
+ time the filter has to processes a package.
+ </para>
+ <para>
+ While all filters provide the same API, there are different modes
+ of functionality. Some filters are sources: they create
+ packages
+ (<literal>frontend_net</literal>);
+ others are sinks: they consume packages and return a result
+ (<literal>z3950_client</literal>,
+ <literal>backend_test</literal>,
+ <literal>bounce</literal>,
+ <literal>http_file</literal>);
+ the others are true filters, that read, process and pass on the
+ packages they are fed
+ (<literal>auth_simple</literal>,
+ <literal>log</literal>,
+ <literal>multi</literal>,
+ <literal>query_rewrite</literal>,
+ <literal>record_transform</literal>,
+ <literal>session_shared</literal>,
+ <literal>sru_z3950</literal>,
+ <literal>template</literal>,
+ <literal>virt_db</literal>).
+ </para>
+ </section>
+
+
+ <section id="overview.filter.types">
+ <title>Overview of filter types</title>
+ <para>
+ We now briefly consider each of the types of filter supported by
+ the core Metaproxy binary. This overview is intended to give a
+ flavour of the available functionality; more detailed information
+ about each type of filter is included below in
+ <link linkend="filterref"
+ >the reference guide to Metaproxy filters</link>.
+ </para>
+ <para>
+ The filters are here named by the string that is used as the
+ <literal>type</literal> attribute of a
+ <literal><filter></literal> element in the configuration
+ file to request them, with the name of the class that implements
+ them in parentheses. (The classname is not needed for normal
+ configuration and use of Metaproxy; it is useful only to
+ developers.)
+ </para>
+ <para>
+ The filters are here listed in alphabetical order:
+ </para>
+
+<!--
+### New filters:
- <section>
- <title>Introductory notes</title>
- <para>
- If Metaproxy is an interpreter providing operations on packages, then
- its configuration file can be thought of as a program for that
- interpreter. Configuration is by means of a single file, the name
- of which is supplied as the sole command-line argument to the
- <command>yp2</command> program.
- </para>
- <para>
- The configuration files are written in XML. (But that's just an
- implementation detail - they could just as well have been written
- in YAML or Lisp-like S-expressions, or in a custom syntax.)
- </para>
- <para>
- Since XML has been chosen, an XML schema,
- <filename>config.xsd</filename>, is provided for validating
- configuration files. This file is supplied in the
- <filename>etc</filename> directory of the Metaproxy distribution. It
- can be used by (among other tools) the <command>xmllint</command>
- program supplied as part of the <literal>libxml2</literal>
- distribution:
- </para>
- <screen>
- xmllint --noout --schema etc/config.xsd my-config-file.xml
- </screen>
- <para>
- (A recent version of <literal>libxml2</literal> is required, as
- support for XML Schemas is a relatively recent addition.)
- </para>
- </section>
+New virt_db-alike that does inteligent peer choice, explain merging,
+adds FD&N to explain. Keeps init responses (like "virt_db Classic"),
+makes routing choices based on local explain knowledge. Ref IDDI
+paper.
- <section>
- <title>Overview of XML structure</title>
- <para>
- All elements and attributes are in the namespace
- <ulink url="http://indexdata.dk/yp2/config/1"/>.
- This is most easily achieved by setting the default namespace on
- the top-level element, as here:
- </para>
- <screen>
- <yp2 xmlns="http://indexdata.dk/yp2/config/1">
- </screen>
- <para>
- The top-level element is <yp2>. This contains a
- <start> element, a <filters> element and a
- <routes> element, in that order. <filters> is
- optional; the other two are mandatory. All three are
- non-repeatable.
- </para>
- <para>
- The <start> element is empty, but carries a
- <literal>route</literal> attribute, whose value is the name of
- route at which to start running - analogouse to the name of the
- start production in a formal grammar.
- </para>
- <para>
- If present, <filters> contains zero or more <filter>
- elements; filters carry a <literal>type</literal> attribute and
- contain various elements that provide suitable configuration for
- filters of that type. The filter-specific elements are described
- below. Filters defined in this part of the file must carry an
- <literal>id</literal> attribute so that they can be referenced
- from elsewhere.
- </para>
- <para>
- <routes> contains one or more <route> elements, each
- of which must carry an <literal>id</literal> element. One of the
- routes must have the ID value that was specified as the start
- route in the <start> element's <literal>route</literal>
- attribute. Each route contains zero or more <filter>
- elements. These are of two types. They may be empty, but carry a
- <literal>refid</literal> attribute whose value is the same as the
- <literal>id</literal> of a filter previously defined in the
- <filters> section. Alternatively, a route within a filter
- may omit the <literal>refid</literal> attribute, but contain
- configuration elements similar to those used for filters defined
- in the <filters> section.
- </para>
- </section>
+Filter to convert Explain Classic to ZeeRex.
+CQL2PQF (which needs augmented ZeeRex) - MARC for Talis.
- <section>
- <title>Filter configuration</title>
- <para>
- All <filter> elements have in common that they must carry a
- <literal>type</literal> attribute whose value is one of the
- supported ones, listed in the schema file and discussed below. In
- additional, <filters>s occurring the <filters> section
- must have an <literal>id</literal> attribute, and those occurring
- within a route must have either a <literal>refid</literal>
- attribute referencing a previously defined filter or contain its
- own configuration information.
- </para>
- <para>
- In general, each filter recognises different configuration
- elements within its element, as each filter has different
- functionality. These are as follows:
- </para>
+SRU2Z39.50 (ditto).
- <section>
- <title><literal>auth_simple</literal></title>
- <screen>
- <filter type="auth_simple">
- <userRegister>../etc/example.simple-auth</userRegister>
- </filter>
- </screen>
- </section>
+Figure out what additional information we need in:
+ ZeeRex (check against D3.1)
+ Init request (e.g. loop detection)
+ Query package (e.g. number of hops)
+ Query response (e.g. record source)
- <section>
- <title><literal>backend_test</literal></title>
- <screen>
- <filter type="backend_test"/>
- </screen>
- </section>
+-->
- <section>
- <title><literal>frontend_net</literal></title>
- <screen>
- <filter type="frontend_net">
- <threads>10</threads>
- <port>@:9000</port>
- </filter>
- </screen>
+ <section>
+ <title><literal>auth_simple</literal>
+ (mp::filter::AuthSimple)</title>
+ <para>
+ Simple authentication and authorisation. The configuration
+ specifies the name of a file that is the user register, which
+ lists <varname>username</varname>:<varname>password</varname>
+ pairs, one per line, colon separated. When a session begins, it
+ is rejected unless username and passsword are supplied, and match
+ a pair in the register. The configuration file may also specific
+ the name of another file that is the target register: this lists
+ lists <varname>username</varname>:<varname>dbname</varname>,<varname>dbname</varname>...
+ sets, one per line, with multiple database names separated by
+ commas. When a search is processed, it is rejected unless the
+ database to be searched is one of those listed as available to
+ the user.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>backend_test</literal>
+ (mp::filter::Backend_test)</title>
+ <para>
+ A partial sink that provides dummy responses in the manner of the
+ <literal>yaz-ztest</literal> Z39.50 server. This is useful only
+ for testing. Seriously, you don't need this. Pretend you didn't
+ even read this section.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>bounce</literal>
+ (mp::filter::Bounce)</title>
+ <para>
+ A sink that swallows <emphasis>all packages</emphasis>,
+ and returns them almost unprocessed.
+ It never sends any package of any type further down the row, but
+ sets Z39.50 packages to Z_Close, and HTTP_Request packages to
+ HTTP_Response err code 400 packages, and adds a suitable bounce
+ message.
+ The bounce filter is usually added at end of each filter chain
+ config.xml to prevent infinite hanging of for example HTTP
+ requests packages when only the Z39.50 client partial sink
+ filter is found in the
+ route.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>frontend_net</literal>
+ (mp::filter::FrontendNet)</title>
+ <para>
+ A source that accepts Z39.50 connections from a port
+ specified in the configuration, reads protocol units, and
+ feeds them into the next filter in the route. When the result is
+ revceived, it is returned to the original origin.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>http_file</literal>
+ (mp::filter::HttpFile)</title>
+ <para>
+ A partial sink which swallows only HTTP_Request packages, and
+ returns the contents of files from the local
+ filesystem in response to HTTP requests.
+ It lets Z39.50 packages and all other forthcoming package types
+ pass untouched.
+ (Yes, Virginia, this
+ does mean that Metaproxy is also a Web-server in its spare time. So
+ far it does not contain either an email-reader or a Lisp
+ interpreter, but that day is surely coming.)
+ </para>
+ </section>
+
+ <section>
+ <title><literal>log</literal>
+ (mp::filter::Log)</title>
+ <para>
+ Writes logging information to standard output, and passes on
+ the package unchanged. A log file name can be specified, as well
+ as multiple different logging formats.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>multi</literal>
+ (mp::filter::Multi)</title>
+ <para>
+ Performs multi-database searching.
+ See
+ <link linkend="multidb">the extended discussion</link>
+ of virtual databases and multi-database searching below.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>query_rewrite</literal>
+ (mp::filter::QueryRewrite)</title>
+ <para>
+ Rewrites Z39.50 Type-1 and Type-101 (``RPN'') queries by a
+ three-step process: the query is transliterated from Z39.50
+ packet structures into an XML representation; that XML
+ representation is transformed by an XSLT stylesheet; and the
+ resulting XML is transliterated back into the Z39.50 packet
+ structure.
+ </para>
+ </section>
+
+
+ <section>
+ <title><literal>record_transform</literal>
+ (mp::filter::RecordTransform)</title>
+ <para>
+ This filter acts only on Z3950 present requests, and let all
+ other types of packages and requests pass untouched. It's use is
+ twofold: blocking Z3950 present requests, which the backend
+ server does not understand and can not honour, and transforming
+ the present syntax and elementset name according to the rules
+ specified, to fetch only exisitng record formats, and transform
+ them on the fly to requested record syntaxes.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>session_shared</literal>
+ (mp::filter::SessionShared)</title>
+ <para>
+ When this is finished, it will implement global sharing of
+ result sets (i.e. between threads and therefore between
+ clients), yielding performance improvements especially when
+ incoming requests are from a stateless environment such as a
+ web-server, in which the client process representing a session
+ might be any one of many. However:
+ </para>
+ <warning>
+ <para>
+ This filter is not yet completed.
+ </para>
+ </warning>
+ </section>
+
+ <section>
+ <title><literal>sru_z3950</literal>
+ (mp::filter::SRUtoZ3950)</title>
+ <para>
+ This filter transforms valid
+ SRU/GET or SRU/SOAP requests to Z3950 requests, and wraps the
+ recieved hit counts and XML records into suitable SRU response messages.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>template</literal>
+ (mp::filter::Template)</title>
+ <para>
+ Does nothing at all, merely passing the packet on. (Maybe it
+ should be called <literal>nop</literal> or
+ <literal>passthrough</literal>?) This exists not to be used, but
+ to be copied - to become the skeleton of new filters as they are
+ written. As with <literal>backend_test</literal>, this is not
+ intended for civilians.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>virt_db</literal>
+ (mp::filter::VirtualDB)</title>
+ <para>
+ Performs virtual database selection: based on the name of the
+ database in the search request, a server is selected, and its
+ address added to the request in a <literal>VAL_PROXY</literal>
+ otherInfo packet. It will subsequently be used by a
+ <literal>z3950_client</literal> filter.
+ See
+ <link linkend="multidb">the extended discussion</link>
+ of virtual databases and multi-database searching below.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>z3950_client</literal>
+ (mp::filter::Z3950Client)</title>
+ <para>
+ A partial sink which swallows only Z39.50 packages.
+ It performs Z39.50 searching and retrieval by proxying the
+ packages that are passed to it. Init requests are sent to the
+ address specified in the <literal>VAL_PROXY</literal> otherInfo
+ attached to the request: this may have been specified by client,
+ or generated by a <literal>virt_db</literal> filter earlier in
+ the route. Subsequent requests are sent to the same address,
+ which is remembered at Init time in a Session object.
+ HTTP_Request packages and all other forthcoming package types
+ are passed untouched.
+ </para>
</section>
-
- <section>
- <title><literal>http_file</literal></title>
- <screen>
- <filter type="http_file">
- <mimetypes>/etc/mime.types</mimetypes>
- <area>
- <documentroot>.</documentroot>
- <prefix>/etc</prefix>
- </area>
- </filter>
- </screen>
</section>
+
+
+ <section id="future.directions">
+ <title>Future directions</title>
+ <para>
+ Some other filters that do not yet exist, but which would be
+ useful, are briefly described. These may be added in future
+ releases (or may be created by third parties, as loadable
+ modules).
+ </para>
- <section>
- <title><literal>log</literal></title>
- <screen>
- <filter type="log">
- <message>B</message>
- </filter>
- </screen>
+ <variablelist>
+ <varlistentry>
+ <term><literal>frontend_cli</literal> (source)</term>
+ <listitem>
+ <para>
+ Command-line interface for generating requests.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>frontend_sru</literal> (source)</term>
+ <listitem>
+ <para>
+ Receive SRU (and perhaps SRW) requests.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>sru2z3950</literal> (filter)</term>
+ <listitem>
+ <para>
+ Translate SRU requests into Z39.50 requests.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>sru_client</literal> (sink)</term>
+ <listitem>
+ <para>
+ SRU searching and retrieval.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>srw_client</literal> (sink)</term>
+ <listitem>
+ <para>
+ SRW searching and retrieval.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>opensearch_client</literal> (sink)</term>
+ <listitem>
+ <para>
+ A9 OpenSearch searching and retrieval.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
</section>
-
+ </chapter>
+
+
+
+ <chapter id="configuration">
+ <title>Configuration: the Metaproxy configuration file format</title>
+
+
<section>
- <title><literal>multi</literal></title>
- <screen>
- <filter type="multi"/>
- </screen>
+ <title>Introductory notes</title>
+ <para>
+ If Metaproxy is an interpreter providing operations on packages, then
+ its configuration file can be thought of as a program for that
+ interpreter. Configuration is by means of a single file, the name
+ of which is supplied as the sole command-line argument to the
+ <command>metaproxy</command> program. (See
+ <link linkend="progref">the reference guide</link>
+ below for more information on invoking Metaproxy.)
+ </para>
+ <para>
+ The configuration files are written in XML. (But that's just an
+ implementation detail - they could just as well have been written
+ in YAML or Lisp-like S-expressions, or in a custom syntax.)
+ </para>
</section>
-
- <section>
- <title><literal>session_shared</literal></title>
+
+ <section id="overview.xml.structure">
+ <title>Overview of the config file XML structure</title>
+ <para>
+ All elements and attributes are in the namespace
+ <ulink url="http://indexdata.dk/yp2/config/1"/>.
+ This is most easily achieved by setting the default namespace on
+ the top-level element, as here:
+ </para>
<screen>
- <filter type="session_shared">
- ### Not yet defined
- </filter>
+ <yp2 xmlns="http://indexdata.dk/yp2/config/1">
</screen>
+ <para>
+ The top-level element is <yp2>. This contains a
+ <start> element, a <filters> element and a
+ <routes> element, in that order. <filters> is
+ optional; the other two are mandatory. All three are
+ non-repeatable.
+ </para>
+ <para>
+ The <start> element is empty, but carries a
+ <literal>route</literal> attribute, whose value is the name of
+ route at which to start running - analogous to the name of the
+ start production in a formal grammar.
+ </para>
+ <para>
+ If present, <filters> contains zero or more <filter>
+ elements. Each filter carries a <literal>type</literal> attribute
+ which specifies what kind of filter is being defined
+ (<literal>frontend_net</literal>, <literal>log</literal>, etc.)
+ and contain various elements that provide suitable configuration
+ for a filter of its type. The filter-specific elements are
+ described in
+ <link linkend="filterref">the reference guide below</link>.
+ Filters defined in this part of the file must carry an
+ <literal>id</literal> attribute so that they can be referenced
+ from elsewhere.
+ </para>
+ <para>
+ <routes> contains one or more <route> elements, each
+ of which must carry an <literal>id</literal> element. One of the
+ routes must have the ID value that was specified as the start
+ route in the <start> element's <literal>route</literal>
+ attribute. Each route contains zero or more <filter>
+ elements. These are of two types. They may be empty, but carry a
+ <literal>refid</literal> attribute whose value is the same as the
+ <literal>id</literal> of a filter previously defined in the
+ <filters> section. Alternatively, a route within a filter
+ may omit the <literal>refid</literal> attribute, but contain
+ configuration elements similar to those used for filters defined
+ in the <filters> section. (In other words, each filter in a
+ route may be included either by reference or by physical
+ inclusion.)
+ </para>
</section>
- <section>
- <title><literal>template</literal></title>
- <screen>
- <filter type="template"/>
- </screen>
- </section>
- <section>
- <title><literal>virt_db</literal></title>
+ <section id="example.configuration">
+ <title>An example configuration</title>
+ <para>
+ The following is a small, but complete, Metaproxy configuration
+ file (included in the distribution as
+ <literal>metaproxy/etc/config1.xml</literal>).
+ This file defines a very simple configuration that simply proxies
+ to whatever back-end server the client requests, but logs each
+ request and response. This can be useful for debugging complex
+ client-server dialogues.
+ </para>
+ <screen><![CDATA[<?xml version="1.0"?>
+<yp2 xmlns="http://indexdata.dk/yp2/config/1">
+ <start route="start"/>
+ <filters>
+ <filter id="frontend" type="frontend_net">
+ <port>@:9000</port>
+ </filter>
+ <filter id="backend" type="z3950_client">
+ </filter>
+ </filters>
+ <routes>
+ <route id="start">
+ <filter refid="frontend"/>
+ <filter type="log"/>
+ <filter refid="backend"/>
+ <filter type="bounce"/>
+ </route>
+ </routes>
+</yp2>
+]]></screen>
+ <para>
+ It works by defining a single route, called
+ <literal>start</literal>, which consists of a sequence of four
+ filters. The first and last of these are included by reference:
+ their <literal><filter></literal> elements have
+ <literal>refid</literal> attributes that refer to filters defined
+ within the prior <literal><filters></literal> section. The
+ middle filter is included inline in the route.
+ </para>
+ <para>
+ The four filters in the route are as follows: first, a
+ <literal>frontend_net</literal> filter accepts Z39.50 requests
+ from any host on port 9000; then these requests are passed through
+ a <literal>log</literal> filter that emits a message for each
+ request; they are then fed into a <literal>z3950_client</literal>
+ filter, which forwards all Z39.50 requests to the client-specified
+ back-end Z39.509 server. Those Z39.50 packages are returned by the
+ <literal>z3950_client</literal> filter, with the response data
+ filled by the external Z39.50 server targeted.
+ All non-Z39.50 packages are passed through to the
+ <literal>bounce</literal> filter, which defitely bounces
+ everything, including fish, bananas, cold pyjamas,
+ mutton, beef and trout packages.
+ When the response arrives, it is handed
+ back to the <literal>log</literal> filter, which emits another
+ message; and then to the <literal>frontend_net</literal> filter,
+ which returns the response to the client.
+ </para>
+ </section>
+ <section id="checking.xml.syntax">
+ <title>Config file syntax checking</title>
+ <para>
+ The distribution contains RelaxNG Compact and XML syntax checking
+ files, as well as XML Schema files. These are found in the
+ distribution pathes
<screen>
- <filter type="virt_db">
- <virtual>
- <database>loc</database>
- <target>z3950.loc.gov:7090/voyager</target>
- </virtual>
- <virtual>
- <database>idgils</database>
- <target>indexdata.dk/gils</target>
- </virtual>
- </filter>
+ xml/schema/metaproxy.rnc
+ xml/schema/metaproxy.rng
+ xml/schema/metaproxy.xsd
</screen>
- </section>
-
- <section>
- <title><literal>z3950_client</literal></title>
+ and can be used to verify or debug the XML structure of
+ configuration files. For example, using the utility
+ <filename>xmllint</filename>, syntax checking is done like this:
<screen>
- <filter type="z3950_client">
- <timeout>30</timeout>
- </filter>
+ xmllint --noout --schema xml/schema/metaproxy.xsd etc/config-local.xml
+ xmllint --noout --relaxng xml/schema/metaproxy.rng etc/config-local.xml
</screen>
- </section>
- </section>
+ (A recent version of <literal>libxml2</literal> is required, as
+ support for XML Schemas is a relatively recent addition.)
+ </para>
+ <para>
+ You can of course use any other RelaxNG or XML Schema compliant tool
+ you wish.
+ </para>
+ </section>
</chapter>
<chapter id="multidb">
- <title>Virtual database as multi-database searching</title>
-
-
- <section>
- <title>Introductory notes</title>
- <para>
- Two of Metaproxy's filters are concerned with multiple-database
- operations. Of these, <literal>virt_db</literal> can work alone
- to control the routing of searches to one of a number of servers,
- while <literal>multi</literal> can work with the output of
- <literal>virt_db</literal> to perform multicast searching, merging
- the results into a unified result-set. The interaction between
- these two filters is necessarily complex, reflecting the real
- complexity of multicast searching in a protocol such as Z39.50
- that separates initialisation from searching, with the database to
- search known only during the latter operation.
- </para>
- <para>
- ### Much, much more to say!
- </para>
- </section>
- </chapter>
+ <title>Virtual databases and multi-database searching</title>
-
- <chapter id="classes">
- <title>Classes in the Metaproxy source code</title>
-
-
- <section>
- <title>Introductory notes</title>
- <para>
- <emphasis>Stop! Do not read this!</emphasis>
- You won't enjoy it at all.
- </para>
- <para>
- This chapter contains documentation of the Metaproxy source code, and is
- of interest only to maintainers and developers. If you need to
- change Metaproxy's behaviour or write a new filter, then you will most
- likely find this chapter helpful. Otherwise it's a waste of your
- good time. Seriously: go and watch a film or something.
- <citetitle>This is Spinal Tap</citetitle> is particularly good.
- </para>
- <para>
- Still here? OK, let's continue.
- </para>
- <para>
- In general, classes seem to be named big-endianly, so that
- <literal>FactoryFilter</literal> is not a filter that filters
- factories, but a factory that produces filters; and
- <literal>FactoryStatic</literal> is a factory for the statically
- registered filters (as opposed to those that are dynamically
- loaded).
- </para>
- </section>
-
- <section>
- <title>Individual classes</title>
- <para>
- The classes making up the Metaproxy application are here listed by
- class-name, with the names of the source files that define them in
- parentheses.
- </para>
-
<section>
- <title><literal>mp::FactoryFilter</literal>
- (<filename>factory_filter.cpp</filename>)</title>
- <para>
- A factory class that exists primarily to provide the
- <literal>create()</literal> method, which takes the name of a
- filter class as its argument and returns a new filter of that
- type. To enable this, the factory must first be populated by
- calling <literal>add_creator()</literal> for static filters (this
- is done by the <literal>FactoryStatic</literal> class, see below)
- and <literal>add_creator_dyn()</literal> for filters loaded
- dynamically.
+ <title>Introductory notes</title>
+ <para>
+ Two of Metaproxy's filters are concerned with multiple-database
+ operations. Of these, <literal>virt_db</literal> can work alone
+ to control the routing of searches to one of a number of servers,
+ while <literal>multi</literal> can work together with
+ <literal>virt_db</literal> to perform multi-database searching, merging
+ the results into a unified result-set - ``metasearch in a box''.
</para>
- </section>
-
- <section>
- <title><literal>mp::FactoryStatic</literal>
- (<filename>factory_static.cpp</filename>)</title>
- <para>
- A subclass of <literal>FactoryFilter</literal> which is
- responsible for registering all the statically defined filter
- types. It does this by knowing about all those filters'
- structures, which are listed in its constructor. Merely
- instantiating this class registers all the static classes. It is
- for the benefit of this class that <literal>struct
- yp2_filter_struct</literal> exists, and that all the filter
- classes provide a static object of that type.
+ <para>
+ The interaction between
+ these two filters is necessarily complex: it reflects the real,
+ irreducible complexity of multi-database searching in a protocol such
+ as Z39.50 that separates initialisation from searching, and in
+ which the database to be searched is not known at initialisation
+ time.
</para>
- </section>
-
- <section>
- <title><literal>mp::filter::Base</literal>
- (<filename>filter.cpp</filename>)</title>
- <para>
- The virtual base class of all filters. The filter API is, on the
- surface at least, extremely simple: two methods.
- <literal>configure()</literal> is passed a DOM tree representing
- that part of the configuration file that pertains to this filter
- instance, and is expected to walk that tree extracting relevant
- information. And <literal>process()</literal> processes a
- package (see below). That surface simplicitly is a bit
- misleading, as <literal>process()</literal> needs to know a lot
- about the <literal>Package</literal> class in order to do
- anything useful.
+ <para>
+ It's possible to use these filters without understanding the
+ details of their functioning and the interaction between them; the
+ next two sections of this chapter are ``HOWTO'' guides for doing
+ just that. However, debugging complex configurations will require
+ a deeper understanding, which the last two sections of this
+ chapters attempt to provide.
</para>
</section>
- <section>
- <title><literal>mp::filter::AuthSimple</literal>,
- <literal>Backend_test</literal>, etc.
- (<filename>filter_auth_simple.cpp</filename>,
- <filename>filter_backend_test.cpp</filename>, etc.)</title>
- <para>
- Individual filters. Each of these is implemented by a header and
- a source file, named <filename>filter_*.hpp</filename> and
- <filename>filter_*.cpp</filename> respectively. All the header
- files should be pretty much identical, in that they declare the
- class, including a private <literal>Rep</literal> class and a
- member pointer to it, and the two public methods. The only extra
- information in any filter header is additional private types and
- members (which should really all be in the <literal>Rep</literal>
- anyway) and private methods (which should also remain known only
- to the source file, but C++'s brain-damaged design requires this
- dirty laundry to be exhibited in public. Thanks, Bjarne!)
- </para>
- <para>
- The source file for each filter needs to supply:
- </para>
- <itemizedlist>
- <listitem>
- <para>
- A definition of the private <literal>Rep</literal> class.
- </para>
- </listitem>
- <listitem>
- <para>
- Some boilerplate constructors and destructors.
- </para>
- </listitem>
- <listitem>
- <para>
- A <literal>configure()</literal> method that uses the
- appropriate XML fragment.
- </para>
- </listitem>
- <listitem>
- <para>
- Most important, the <literal>process()</literal> method that
- does all the actual work.
- </para>
- </listitem>
- </itemizedlist>
- </section>
- <section>
- <title><literal>mp::Package</literal>
- (<filename>package.cpp</filename>)</title>
+ <section id="multidb.virt_db">
+ <title>Virtual databases with the <literal>virt_db</literal> filter</title>
<para>
- Represents a package on its way through the series of filters
- that make up a route. This is essentially a Z39.50 or SRU APDU
- together with information about where it came from, which is
- modified as it passes through the various filters.
+ Working alone, the purpose of the
+ <literal>virt_db</literal>
+ filter is to route search requests to one of a selection of
+ back-end databases. In this way, a single Z39.50 endpoint
+ (running Metaproxy) can provide access to several different
+ underlying services, including those that would otherwise be
+ inaccessible due to firewalls. In many useful configurations, the
+ back-end databases are local to the Metaproxy installation, but
+ the software does not enforce this, and any valid Z39.50 servers
+ may be used as back-ends.
</para>
- </section>
-
- <section>
- <title><literal>mp::Pipe</literal>
- (<filename>pipe.cpp</filename>)</title>
<para>
- This class provides a compatibility layer so that we have an IPC
- mechanism that works the same under Unix and Windows. It's not
- particularly exciting.
+ For example, a <literal>virt_db</literal>
+ filter could be set up so that searches in the virtual database
+ ``lc'' are forwarded to the Library of Congress bibliographic
+ catalogue server, and searches in the virtual database ``marc''
+ are forwarded to the toy database of MARC records that Index Data
+ hosts for testing purposes. A <literal>virt_db</literal>
+ configuration to make this switch would look like this:
</para>
- </section>
-
- <section>
- <title><literal>mp::RouterChain</literal>
- (<filename>router_chain.cpp</filename>)</title>
+ <screen><![CDATA[<filter type="virt_db">
+ <virtual>
+ <database>lc</database>
+ <target>z3950.loc.gov:7090/voyager</target>
+ </virtual>
+ <virtual>
+ <database>marc</database>
+ <target>indexdata.dk/marc</target>
+ </virtual>
+</filter>]]></screen>
<para>
- ###
+ As well as being useful in it own right, this filter also provides
+ the foundation for multi-database searching.
</para>
</section>
- <section>
- <title><literal>mp::RouterFleXML</literal>
- (<filename>router_flexml.cpp</filename>)</title>
+
+ <section id="multidb.multi">
+ <title>Multi-database search with the <literal>multi</literal> filter</title>
<para>
- ###
+ To arrange for Metaproxy to broadcast searches to multiple back-end
+ servers, the configuration needs to include two components: a
+ <literal>virt_db</literal>
+ filter that specifies multiple
+ <literal><target></literal>
+ elements, and a subsequent
+ <literal>multi</literal>
+ filter. Here, for example, is a complete configuration that
+ broadcasts searches to both the Library of Congress catalogue and
+ Index Data's tiny testing database of MARC records:
+ </para>
+ <screen><![CDATA[<?xml version="1.0"?>
+<yp2 xmlns="http://indexdata.dk/yp2/config/1">
+ <start route="start"/>
+ <routes>
+ <route id="start">
+ <filter type="frontend_net">
+ <threads>10</threads>
+ <port>@:9000</port>
+ </filter>
+ <filter type="virt_db">
+ <virtual>
+ <database>lc</database>
+ <target>z3950.loc.gov:7090/voyager</target>
+ </virtual>
+ <virtual>
+ <database>marc</database>
+ <target>indexdata.dk/marc</target>
+ </virtual>
+ <virtual>
+ <database>all</database>
+ <target>z3950.loc.gov:7090/voyager</target>
+ <target>indexdata.dk/marc</target>
+ </virtual>
+ </filter>
+ <filter type="multi"/>
+ <filter type="z3950_client">
+ <timeout>30</timeout>
+ </filter>
+ <filter type="bounce"/>
+ </route>
+ </routes>
+</yp2>]]></screen>
+ <para>
+ (Using a
+ <literal>virt_db</literal>
+ filter that specifies multiple
+ <literal><target></literal>
+ elements but without a subsequent
+ <literal>multi</literal>
+ filter yields surprising and undesirable results, as will be
+ described below. Don't do that.)
</para>
- </section>
-
- <section>
- <title><literal>mp::Session</literal>
- (<filename>session.cpp</filename>)</title>
<para>
- ###
+ Metaproxy can be invoked with this configuration as follows:
+ </para>
+ <screen>../src/metaproxy --config config-simple-multi.xml</screen>
+ <para>
+ And thereafter, Z39.50 clients can connect to the running server
+ (on port 9000, as specified in the configuration) and search in
+ any of the databases
+ <literal>lc</literal> (the Library of Congress catalogue),
+ <literal>marc</literal> (Index Data's test database of MARC records)
+ or
+ <literal>all</literal> (both of these). As an example, a session
+ using the YAZ command-line client <literal>yaz-client</literal> is
+ here included (edited for brevity and clarity):
+ </para>
+ <screen><![CDATA[$ yaz-client @:9000
+Connecting...OK.
+Z> base lc
+Z> find computer
+Search was a success.
+Number of hits: 10000, setno 1
+Elapsed: 5.521070
+Z> base marc
+Z> find computer
+Search was a success.
+Number of hits: 10, setno 3
+Elapsed: 0.060187
+Z> base all
+Z> find computer
+Search was a success.
+Number of hits: 10010, setno 4
+Elapsed: 2.237648
+Z> show 1
+[marc]Record type: USmarc
+001 11224466
+003 DLC
+005 00000000000000.0
+008 910710c19910701nju 00010 eng
+010 $a 11224466
+040 $a DLC $c DLC
+050 00 $a 123-xyz
+100 10 $a Jack Collins
+245 10 $a How to program a computer
+260 1 $a Penguin
+263 $a 8710
+300 $a p. cm.
+Elapsed: 0.119612
+Z> show 2
+[VOYAGER]Record type: USmarc
+001 13339105
+005 20041229102447.0
+008 030910s2004 caua 000 0 eng
+035 $a (DLC) 2003112666
+906 $a 7 $b cbc $c orignew $d 4 $e epcn $f 20 $g y-gencatlg
+925 0 $a acquire $b 1 shelf copy $x policy default
+955 $a pc10 2003-09-10 $a pv12 2004-06-23 to SSCD; $h sj05 2004-11-30 $e sj05 2004-11-30 to Shelf.
+010 $a 2003112666
+020 $a 0761542892
+040 $a DLC $c DLC $d DLC
+050 00 $a MLCM 2004/03312 (G)
+245 10 $a 007, everything or nothing : $b Prima's official strategy guide / $c created by Kaizen Media Group.
+246 3 $a Double-O-seven, everything or nothing
+246 30 $a Prima's official strategy guide
+260 $a Roseville, CA : $b Prima Games, $c c2004.
+300 $a 161 p. : $b col. ill. ; $c 28 cm.
+500 $a "Platforms: Nintendo GameCube, Macintosh, PC, PlayStation 2 computer entertainment system, Xbox"--P. [4] of cover.
+650 0 $a Video games.
+710 2 $a Kaizen Media Group.
+856 42 $3 Publisher description $u http://www.loc.gov/catdir/description/random052/2003112666.html
+Elapsed: 0.150623
+Z>
+]]></screen>
+ <para>
+ As can be seen, the first record in the result set is from the
+ Index Data test database, and the second from the Library of
+ Congress database. The result-set continues alternating records
+ round-robin style until the point where one of the databases'
+ records are exhausted.
+ </para>
+ <para>
+ This example uses only two back-end databases; more may be used.
+ There is no limitation imposed on the number of databases that may
+ be metasearched in this way: issues of resource usage and
+ administrative complexity dictate the practical limits.
+ </para>
+ <para>
+ What happens when one of the databases doesn't respond? By default,
+ the entire multi-database search fails, and the appropriate
+ diagnostic is returned to the client. This is usually appropriate
+ during development, when technicians need maximum information, but
+ can be inconvenient in deployment, when users typically don't want
+ to be bothered with problems of this kind and prefer just to get
+ the records from the databases that are available. To obtain this
+ latter behaviour add an empty
+ <literal><hideunavailable></literal>
+ element inside the
+ <literal>multi</literal> filter:
+ </para>
+ <screen><![CDATA[ <filter type="multi">
+ <hideunavailable/>
+ </filter>]]></screen>
+ <para>
+ Under this regime, an error is reported to the client only if
+ <emphasis>all</emphasis> the databases in a multi-database search
+ are unavailable.
</para>
</section>
- <section>
- <title><literal>mp::ThreadPoolSocketObserver</literal>
- (<filename>thread_pool_observer.cpp</filename>)</title>
+
+ <section id="multidb.what">
+ <title>What's going on?</title>
+ <warning>
+ <title>Lark's vomit</title>
+ <para>
+ This section goes into a level of technical detail that is
+ probably not necessary in order to configure and use Metaproxy.
+ It is provided only for those who like to know how things work.
+ You should feel free to skip on to the next section if this one
+ doesn't seem like fun.
+ </para>
+ </warning>
+ <para>
+ Hold on tight - this may get a little hairy.
+ </para>
+ <para>
+ In the general course of things, a Z39.50 Init request may carry
+ with it an otherInfo packet of type <literal>VAL_PROXY</literal>,
+ whose value indicates the address of a Z39.50 server to which the
+ ultimate connection is to be made. (This otherInfo packet is
+ supported by YAZ-based Z39.50 clients and servers, but has not yet
+ been ratified by the Maintenance Agency and so is not widely used
+ in non-Index Data software. We're working on it.)
+ The <literal>VAL_PROXY</literal> packet functions
+ analogously to the absoluteURI-style Request-URI used with the GET
+ method when a web browser asks a proxy to forward its request: see
+ the
+ <ulink url="http://www.w3.org/Protocols/rfc2616/rfc2616-sec5.html#sec5.1.2"
+ >Request-URI</ulink>
+ section of
+ <ulink url="http://www.w3.org/Protocols/rfc2616/rfc2616.html"
+ >the HTTP 1.1 specification</ulink>.
+ </para>
+ <para>
+ Within Metaproxy, Search requests that are part of the same
+ session as an Init request that carries a
+ <literal>VAL_PROXY</literal> otherInfo are also annotated with the
+ same information. The role of the <literal>virt_db</literal>
+ filter is to rewrite this otherInfo packet dependent on the
+ virtual database that the client wants to search.
+ </para>
<para>
- ###
+ When Metaproxy receives a Z39.50 Init request from a client, it
+ doesn't immediately forward that request to the back-end server.
+ Why not? Because it doesn't know <emphasis>which</emphasis>
+ back-end server to forward it to until the client sends a Search
+ request that specifies the database that it wants to search in.
+ Instead, it just treasures the Init request up in its heart; and,
+ later, the first time the client does a search on one of the
+ specified virtual databases, a connection is forged to the
+ appropriate server and the Init request is forwarded to it. If,
+ later in the session, the same client searches in a different
+ virtual database, then a connection is forged to the server that
+ hosts it, and the same cached Init request is forwarded there,
+ too.
</para>
+ <para>
+ All of this clever Init-delaying is done by the
+ <literal>frontend_net</literal> filter. The
+ <literal>virt_db</literal> filter knows nothing about it; in
+ fact, because the Init request that is received from the client
+ doesn't get forwarded until a Search request is received, the
+ <literal>virt_db</literal> filter (and the
+ <literal>z3950_client</literal> filter behind it) doesn't even get
+ invoked at Init time. The <emphasis>only</emphasis> thing that a
+ <literal>virt_db</literal> filter ever does is rewrite the
+ <literal>VAL_PROXY</literal> otherInfo in the requests that pass
+ through it.
+ </para>
+ <para>
+ It is possible for a <literal>virt_db</literal> filter to contain
+ multiple
+ <literal><target></literal>
+ elements. What does this mean? Only that the filter will add
+ multiple <literal>VAL_PROXY</literal> otherInfo packets to the
+ Search requests that pass through it. That's because the virtual
+ DB filter is dumb, and does exactly what it's told - no more, no
+ less.
+ If a Search request with multiple <literal>VAL_PROXY</literal>
+ otherInfo packets reaches a <literal>z3950_client</literal>
+ filter, this is an error. That filter doesn't know how to deal
+ with multiple targets, so it will either just pick one and search
+ in it, or (better) fail with an error message.
+ </para>
+ <para>
+ The <literal>multi</literal> filter comes to the rescue! This is
+ the only filter that knows how to deal with multiple
+ <literal>VAL_PROXY</literal> otherInfo packets, and it does so by
+ making multiple copies of the entire Search request: one for each
+ <literal>VAL_PROXY</literal>. Each of these new copies is then
+ passed down through the remaining filters in the route. (The
+ copies are handled in parallel though the
+ spawning of new threads.) Since the copies each have only one
+ <literal>VAL_PROXY</literal> otherInfo, they can be handled by the
+ <literal>z3950_client</literal> filter, which happily deals with
+ each one individually. When the results of the individual
+ searches come back up to the <literal>multi</literal> filter, it
+ merges them into a single Search response, which is what
+ eventually makes it back to the client.
+ </para>
+ </section>
+
+
+ <section id="multidb.picture">
+ <title>A picture is worth a thousand words (but only five hundred on 64-bit architectures)</title>
+ <simpara>
+ <inlinemediaobject>
+ <imageobject>
+ <imagedata fileref="multi.pdf" format="PDF" scale="50"/>
+ </imageobject>
+ <imageobject>
+ <imagedata fileref="multi.png" format="PNG"/>
+ </imageobject>
+ <textobject>
+ <!-- Fall back if none of the images can be used -->
+ <phrase>
+ [Here there should be a diagram showing the progress of
+ packages through the filters during a simple virtual-database
+ search and a multi-database search, but is seems that your
+ toolchain has not been able to include the diagram in this
+ document. This is because of LaTeX suckage. Time to move to
+ OpenOffice. Yes, really.]
+ </phrase>
+ </textobject>
+<!-- ### This used to work with an older version of DocBook
+ <caption>
+ <para>Caption: progress of packages through filters.</para>
+ </caption>
+-->
+ </inlinemediaobject>
+ </simpara>
</section>
+ </chapter>
+
+
+
+ <chapter id="extensions">
+ <title>Writing extensions for Metaproxy</title>
+ <para>### To be written</para>
+ </chapter>
+
+
+
+
+ <chapter id="classes">
+ <title>Classes in the Metaproxy source code</title>
+
<section>
- <title><literal>mp::util</literal>
- (<filename>util.cpp</filename>)</title>
+ <title>Introductory notes</title>
+ <para>
+ <emphasis>Stop! Do not read this!</emphasis>
+ You won't enjoy it at all. You should just skip ahead to
+ <link linkend="refguide">the reference guide</link>,
+ which tells
+ <!-- The remainder of this paragraph is lifted verbatim from
+ Douglas Adams' _Hitch Hiker's Guide to the Galaxy_, chapter 8 -->
+ you things you really need to know, like the fact that the
+ fabulously beautiful planet Bethselamin is now so worried about
+ the cumulative erosion by ten billion visiting tourists a year
+ that any net imbalance between the amount you eat and the amount
+ you excrete whilst on the planet is surgically removed from your
+ bodyweight when you leave: so every time you go to the lavatory it
+ is vitally important to get a receipt.
+ </para>
+ <para>
+ This chapter contains documentation of the Metaproxy source code, and is
+ of interest only to maintainers and developers. If you need to
+ change Metaproxy's behaviour or write a new filter, then you will most
+ likely find this chapter helpful. Otherwise it's a waste of your
+ good time. Seriously: go and watch a film or something.
+ <citetitle>This is Spinal Tap</citetitle> is particularly good.
+ </para>
+ <para>
+ Still here? OK, let's continue.
+ </para>
<para>
- A namespace of various small utility functions and classes,
- collected together for convenience. Most importantly, includes
- the <literal>mp::util::odr</literal> class, a wrapper for YAZ's
- ODR facilities.
+ In general, classes seem to be named big-endianly, so that
+ <literal>FactoryFilter</literal> is not a filter that filters
+ factories, but a factory that produces filters; and
+ <literal>FactoryStatic</literal> is a factory for the statically
+ registered filters (as opposed to those that are dynamically
+ loaded).
</para>
</section>
- <section>
- <title><literal>mp::xml</literal>
- (<filename>xmlutil.cpp</filename>)</title>
+ <section id="individual.classes">
+ <title>Individual classes</title>
<para>
- A namespace of various XML utility functions and classes,
- collected together for convenience.
+ The classes making up the Metaproxy application are here listed by
+ class-name, with the names of the source files that define them in
+ parentheses.
</para>
+
+ <section>
+ <title><literal>mp::FactoryFilter</literal>
+ (<filename>factory_filter.cpp</filename>)</title>
+ <para>
+ A factory class that exists primarily to provide the
+ <literal>create()</literal> method, which takes the name of a
+ filter class as its argument and returns a new filter of that
+ type. To enable this, the factory must first be populated by
+ calling <literal>add_creator()</literal> for static filters (this
+ is done by the <literal>FactoryStatic</literal> class, see below)
+ and <literal>add_creator_dyn()</literal> for filters loaded
+ dynamically.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::FactoryStatic</literal>
+ (<filename>factory_static.cpp</filename>)</title>
+ <para>
+ A subclass of <literal>FactoryFilter</literal> which is
+ responsible for registering all the statically defined filter
+ types. It does this by knowing about all those filters'
+ structures, which are listed in its constructor. Merely
+ instantiating this class registers all the static classes. It is
+ for the benefit of this class that <literal>struct
+ metaproxy_1_filter_struct</literal> exists, and that all the filter
+ classes provide a static object of that type.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::filter::Base</literal>
+ (<filename>filter.cpp</filename>)</title>
+ <para>
+ The virtual base class of all filters. The filter API is, on the
+ surface at least, extremely simple: two methods.
+ <literal>configure()</literal> is passed an XML DOM tree representing
+ that part of the configuration file that pertains to this filter
+ instance, and is expected to walk that tree extracting relevant
+ information. And <literal>process()</literal> processes a
+ package (see below). That surface simplicitly is a bit
+ misleading, as <literal>process()</literal> needs to know a lot
+ about the <literal>Package</literal> class in order to do
+ anything useful.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::filter::AuthSimple</literal>,
+ <literal>Backend_test</literal>, etc.
+ (<filename>filter_auth_simple.cpp</filename>,
+ <filename>filter_backend_test.cpp</filename>, etc.)</title>
+ <para>
+ Individual filters. Each of these is implemented by a header and
+ a source file, named <filename>filter_*.hpp</filename> and
+ <filename>filter_*.cpp</filename> respectively. All the header
+ files should be pretty much identical, in that they declare the
+ class, including a private <literal>Rep</literal> class and a
+ member pointer to it, and the two public methods. The only extra
+ information in any filter header is additional private types and
+ members (which should really all be in the <literal>Rep</literal>
+ anyway) and private methods (which should also remain known only
+ to the source file, but C++'s brain-damaged design requires this
+ dirty laundry to be exhibited in public. Thanks, Bjarne!)
+ </para>
+ <para>
+ The source file for each filter needs to supply:
+ </para>
+ <itemizedlist>
+ <listitem>
+ <para>
+ A definition of the private <literal>Rep</literal> class.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Some boilerplate constructors and destructors.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ A <literal>configure()</literal> method that uses the
+ appropriate XML fragment.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Most important, the <literal>process()</literal> method that
+ does all the actual work.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </section>
+
+ <section>
+ <title><literal>mp::Package</literal>
+ (<filename>package.cpp</filename>)</title>
+ <para>
+ Represents a package on its way through the series of filters
+ that make up a route. This is essentially a Z39.50 or SRU APDU
+ together with information about where it came from, which is
+ modified as it passes through the various filters.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::Pipe</literal>
+ (<filename>pipe.cpp</filename>)</title>
+ <para>
+ This class provides a compatibility layer so that we have an IPC
+ mechanism that works the same under Unix and Windows. It's not
+ particularly exciting.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::RouterChain</literal>
+ (<filename>router_chain.cpp</filename>)</title>
+ <para>
+ ### to be written
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::RouterFleXML</literal>
+ (<filename>router_flexml.cpp</filename>)</title>
+ <para>
+ ### to be written
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::Session</literal>
+ (<filename>session.cpp</filename>)</title>
+ <para>
+ ### to be written
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::ThreadPoolSocketObserver</literal>
+ (<filename>thread_pool_observer.cpp</filename>)</title>
+ <para>
+ ### to be written
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::util</literal>
+ (<filename>util.cpp</filename>)</title>
+ <para>
+ A namespace of various small utility functions and classes,
+ collected together for convenience. Most importantly, includes
+ the <literal>mp::util::odr</literal> class, a wrapper for YAZ's
+ ODR facilities.
+ </para>
+ </section>
+
+ <section>
+ <title><literal>mp::xml</literal>
+ (<filename>xmlutil.cpp</filename>)</title>
+ <para>
+ A namespace of various XML utility functions and classes,
+ collected together for convenience.
+ </para>
+ </section>
</section>
- </section>
- <section>
- <title>Other Source Files</title>
- <para>
- In addition to the Metaproxy source files that define the classes
- described above, there are a few additional files which are
- briefly described here:
- </para>
- <variablelist>
- <varlistentry>
- <term><literal>metaproxy_prog.cpp</literal></term>
- <listitem>
- <para>
- The main function of the <command>yp2</command> program.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><literal>ex_router_flexml.cpp</literal></term>
- <listitem>
- <para>
- Identical to <literal>metaproxy_prog.cpp</literal>: it's not clear why.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><literal>test_*.cpp</literal></term>
- <listitem>
- <para>
- Unit-tests for various modules.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- <para>
- ### Still to be described:
- <literal>ex_filter_frontend_net.cpp</literal>,
- <literal>filter_dl.cpp</literal>,
- <literal>plainfile.cpp</literal>,
- <literal>tstdl.cpp</literal>.
- </para>
-
-
- <!-- Epilogue -->
- <para>
- --
- </para>
- <screen>
- <!-- This is just a lame way to get some vertical whitespace at
- the end of the document -->
-
-
-
-
- </screen>
- </section>
+ <section id="other.source.files">
+ <title>Other Source Files</title>
+ <para>
+ In addition to the Metaproxy source files that define the classes
+ described above, there are a few additional files which are
+ briefly described here:
+ </para>
+ <variablelist>
+ <varlistentry>
+ <term><literal>metaproxy_prog.cpp</literal></term>
+ <listitem>
+ <para>
+ The main function of the <command>metaproxy</command> program.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>ex_router_flexml.cpp</literal></term>
+ <listitem>
+ <para>
+ Identical to <literal>metaproxy_prog.cpp</literal>: it's not clear why.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>test_*.cpp</literal></term>
+ <listitem>
+ <para>
+ Unit-tests for various modules.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ <para>
+ ### Still to be described:
+ <literal>ex_filter_frontend_net.cpp</literal>,
+ <literal>filter_dl.cpp</literal>,
+ <literal>plainfile.cpp</literal>,
+ <literal>tstdl.cpp</literal>.
+ </para>
+ </section>
</chapter>
-
-<!-- Keep this comment at the end of the file
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-End:
--->
+
+
+
+ <reference id="refguide">
+ <title>Reference guide</title>
+ <para>
+ The material in this chapter is drawn directly from the individual
+ manual entries. In particular, the Metaproxy invocation section is
+ available using <command>man metaproxy</command>, and the section
+ on each individual filter is available using the name of the filter
+ as the argument to the <command>man</command> command.
+ </para>
+ &manref;
+ </reference>
+</book>
+
+ <!-- Keep this comment at the end of the file
+ Local variables:
+ mode: sgml
+ sgml-omittag:t
+ sgml-shorttag:t
+ sgml-minimize-attributes:nil
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+ sgml-parent-document: nil
+ sgml-local-catalogs: nil
+ sgml-namecase-general:t
+ End:
+ -->