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<A NAME="sec:titlepage"></A>
<TABLE CLASS="title">
<TR><TD>
<H1 CLASS="titlemain">Ejabberd 1.1.1 Developers Guide</H1>
<H3 CLASS="titlerest">Alexey Shchepin<BR>
<A HREF="mailto:alexey@sevcom.net"><TT>mailto:alexey@sevcom.net</TT></A><BR>
<A HREF="xmpp:aleksey@jabber.ru"><TT>xmpp:aleksey@jabber.ru</TT></A></H3></TD>
</TR></TABLE><BR>
<BR>
<DIV CLASS="center">
<IMG SRC="logo.png">
<BR>
<BR>
</DIV>
<BLOCKQUOTE CLASS="quotation"><I>I can thoroughly recommend ejabberd for ease of setup &ndash;
Kevin Smith, Current maintainer of the Psi project</I></BLOCKQUOTE>
<!--TOC section Contents-->
<H2 CLASS="section">Contents</H2><!--SEC END -->
<UL CLASS="toc"><LI CLASS="li-toc">
<A HREF="#htoc1">1&nbsp;&nbsp;Introduction</A>
<UL CLASS="toc"><LI CLASS="li-toc">
<A HREF="#htoc2">1.1&nbsp;&nbsp;Key Features</A>
<LI CLASS="li-toc"><A HREF="#htoc3">1.2&nbsp;&nbsp;Additional Features</A>
</UL>
<LI CLASS="li-toc"><A HREF="#htoc4">2&nbsp;&nbsp;How it works</A>
<UL CLASS="toc"><LI CLASS="li-toc">
<A HREF="#htoc5">2.1&nbsp;&nbsp;Router</A>
<LI CLASS="li-toc"><A HREF="#htoc6">2.2&nbsp;&nbsp;Local Router</A>
<LI CLASS="li-toc"><A HREF="#htoc7">2.3&nbsp;&nbsp;Session Manager</A>
<LI CLASS="li-toc"><A HREF="#htoc8">2.4&nbsp;&nbsp;S2S Manager</A>
</UL>
<LI CLASS="li-toc"><A HREF="#htoc9">3&nbsp;&nbsp;XML representation</A>
<LI CLASS="li-toc"><A HREF="#htoc10">4&nbsp;&nbsp;Module <TT>xml</TT></A>
<LI CLASS="li-toc"><A HREF="#htoc11">5&nbsp;&nbsp;Module <TT>xml_stream</TT></A>
<LI CLASS="li-toc"><A HREF="#htoc12">6&nbsp;&nbsp;<TT>ejabberd</TT> modules</A>
<UL CLASS="toc"><LI CLASS="li-toc">
<A HREF="#htoc13">6.1&nbsp;&nbsp;gen_mod behaviour</A>
<LI CLASS="li-toc"><A HREF="#htoc14">6.2&nbsp;&nbsp;Module gen_iq_handler</A>
<LI CLASS="li-toc"><A HREF="#htoc15">6.3&nbsp;&nbsp;Services</A>
</UL>
</UL>
<!--TOC section Introduction-->
<H2 CLASS="section"><A NAME="htoc1">1</A>&nbsp;&nbsp;Introduction</H2><!--SEC END -->
<A NAME="sec:intr"></A>
<TT>ejabberd</TT> is a free (GPL) distributed fault-tolerant Jabber/XMPP server and is mainly written in <A HREF="http://www.erlang.org/">Erlang</A>.<BR>
<BR>
<TT>ejabberd</TT> is designed to be a stable, standards compliant, and feature rich Jabber/XMPP server.<BR>
<BR>
<TT>ejabberd</TT> is suitable for small servers, whether they need to be scalable or not, as well as extremely big servers.<BR>
<BR>
<!--TOC subsection Key Features-->
<H3 CLASS="subsection"><A NAME="htoc2">1.1</A>&nbsp;&nbsp;Key Features</H3><!--SEC END -->
<A NAME="sec:keyfeatures"></A>
<TT>ejabberd</TT> is:
<UL CLASS="itemize"><LI CLASS="li-itemize">
Multiplatform: <TT>ejabberd</TT> runs under Microsoft Windows and Unix derived systems such as Linux, FreeBSD and NetBSD.<BR>
<BR>
<LI CLASS="li-itemize">Distributed: You can run <TT>ejabberd</TT> on a cluster of machines and all of them will serve the same Jabber domain(s). When you need more capacity you can simply add a new cheap node to your cluster. Accordingly, you do not need to buy an expensive high-end machine to support tens of thousands concurrent users.<BR>
<BR>
<LI CLASS="li-itemize">Fault-tolerant: You can deploy an <TT>ejabberd</TT> cluster so that all the information required for a properly working service will be replicated permanently on all nodes. This means that if one of the nodes crashes, the others will continue working without disruption. In addition, nodes also can be added or replaced &#8220;on the fly&#8221;.<BR>
<BR>
<LI CLASS="li-itemize">Administrator Friendly: <TT>ejabberd</TT> is built on top of the Open Source Erlang. As a result you do not need to install an external database, an external web server, amongst others because everything is already included, and ready to run out of the box. Other administrator benefits include:
<UL CLASS="itemize"><LI CLASS="li-itemize">
Comprehensive documentation.
<LI CLASS="li-itemize">Straightforward installers for Linux, Mac OS X, and Windows.
<LI CLASS="li-itemize">Web interface for administration tasks.
<LI CLASS="li-itemize">Shared Roster Groups.
<LI CLASS="li-itemize">Command line administration tool.
<LI CLASS="li-itemize">Can integrate with existing authentication mechanisms.
<LI CLASS="li-itemize">Capability to send announce messages.
</UL><BR>
<BR>
<LI CLASS="li-itemize">Internationalized: <TT>ejabberd</TT> leads in internationalization. Hence it is very well suited in a globalized world. Related features are:
<UL CLASS="itemize"><LI CLASS="li-itemize">
Translated in 11 languages.
<LI CLASS="li-itemize">Support for <A HREF="http://www.ietf.org/rfc/rfc3490.txt">IDNA</A>.
</UL><BR>
<BR>
<LI CLASS="li-itemize">Open Standards: <TT>ejabberd</TT> is the first Open Source Jabber server claiming to fully comply to the XMPP standard.
<UL CLASS="itemize"><LI CLASS="li-itemize">
Fully XMPP compliant
<LI CLASS="li-itemize">XML-based protocol
<LI CLASS="li-itemize"><A HREF="http://ejabberd.jabber.ru/protocols">Many JEPs supported</A>.
</UL></UL>
<!--TOC subsection Additional Features-->
<H3 CLASS="subsection"><A NAME="htoc3">1.2</A>&nbsp;&nbsp;Additional Features</H3><!--SEC END -->
<A NAME="sec:addfeatures"></A>
Besides common Jabber server features, <TT>ejabberd</TT> comes with a wide range of other features:
<UL CLASS="itemize"><LI CLASS="li-itemize">
Modular
<UL CLASS="itemize"><LI CLASS="li-itemize">
Load only the modules you want.
<LI CLASS="li-itemize">Extend <TT>ejabberd</TT> with your own custom modules.
</UL>
<LI CLASS="li-itemize">Security
<UL CLASS="itemize"><LI CLASS="li-itemize">
SASL and STARTTLS for c2s and s2s connections.
<LI CLASS="li-itemize">STARTTLS and Dialback s2s connections.
<LI CLASS="li-itemize">Web interface accessible via HTTPS secure access.
</UL>
<LI CLASS="li-itemize">Databases
<UL CLASS="itemize"><LI CLASS="li-itemize">
Native MySQL support.
<LI CLASS="li-itemize">Native PostgreSQL support.
<LI CLASS="li-itemize">Mnesia.
<LI CLASS="li-itemize">ODBC data storage support.
<LI CLASS="li-itemize">Microsoft SQL Server support (via ODBC).
</UL>
<LI CLASS="li-itemize">Authentication
<UL CLASS="itemize"><LI CLASS="li-itemize">
LDAP and ODBC.
<LI CLASS="li-itemize">External Authentication script.
<LI CLASS="li-itemize">Internal Authentication.
</UL>
<LI CLASS="li-itemize">Others
<UL CLASS="itemize"><LI CLASS="li-itemize">
Compressing XML streams with Stream Compression (<A HREF="http://www.jabber.org/jeps/jep-0138.html">JEP-0138</A>).
<LI CLASS="li-itemize">Interface with networks such as AIM, ICQ and MSN.
<LI CLASS="li-itemize">Statistics via Statistics Gathering (<A HREF="http://www.jabber.org/jeps/jep-0039.html">JEP-0039</A>).
<LI CLASS="li-itemize">IPv6 support both for c2s and s2s connections.
<LI CLASS="li-itemize"><A HREF="http://www.jabber.org/jeps/jep-0045.html">Multi-User Chat</A> module with logging.
<LI CLASS="li-itemize">Users Directory based on users vCards.
<LI CLASS="li-itemize"><A HREF="http://www.jabber.org/jeps/jep-0060.html">Publish-Subscribe</A> component.
<LI CLASS="li-itemize">Support for virtual hosting.
<LI CLASS="li-itemize"><A HREF="http://www.jabber.org/jeps/jep-0025.html">HTTP Polling</A> service.
<LI CLASS="li-itemize">IRC transport.
</UL>
</UL>
<!--TOC section How it works-->
<H2 CLASS="section"><A NAME="htoc4">2</A>&nbsp;&nbsp;How it works</H2><!--SEC END -->
<A NAME="sec:howitworks"></A>
A Jabber domain is served by one or more <TT>ejabberd</TT> nodes. These nodes can
be run on different machines that are connected via a network. They all must
have the ability to connect to port 4369 of all another nodes, and must have
the same magic cookie (see Erlang/OTP documentation, in other words the file
<TT>~ejabberd/.erlang.cookie</TT> must be the same on all nodes). This is
needed because all nodes exchange information about connected users, S2S
connections, registered services, etc...<BR>
<BR>
Each <TT>ejabberd</TT> node have following modules:
<UL CLASS="itemize"><LI CLASS="li-itemize">
router;
<LI CLASS="li-itemize">local router.
<LI CLASS="li-itemize">session manager;
<LI CLASS="li-itemize">S2S manager;
</UL>
<!--TOC subsection Router-->
<H3 CLASS="subsection"><A NAME="htoc5">2.1</A>&nbsp;&nbsp;Router</H3><!--SEC END -->
This module is the main router of Jabber packets on each node. It routes
them based on their destinations domains. It has two tables: local and global
routes. First, domain of packet destination searched in local table, and if it
found, then the packet is routed to appropriate process. If no, then it
searches in global table, and is routed to the appropriate <TT>ejabberd</TT> node or
process. If it does not exists in either tables, then it sent to the S2S
manager.<BR>
<BR>
<!--TOC subsection Local Router-->
<H3 CLASS="subsection"><A NAME="htoc6">2.2</A>&nbsp;&nbsp;Local Router</H3><!--SEC END -->
This module routes packets which have a destination domain equal to this server
name. If destination JID has a non-empty user part, then it routed to the
session manager, else it is processed depending on it's content.<BR>
<BR>
<!--TOC subsection Session Manager-->
<H3 CLASS="subsection"><A NAME="htoc7">2.3</A>&nbsp;&nbsp;Session Manager</H3><!--SEC END -->
This module routes packets to local users. It searches for what user resource
packet must be sended via presence table. If this resource is connected to
this node, it is routed to C2S process, if it connected via another node, then
the packet is sent to session manager on that node.<BR>
<BR>
<!--TOC subsection S2S Manager-->
<H3 CLASS="subsection"><A NAME="htoc8">2.4</A>&nbsp;&nbsp;S2S Manager</H3><!--SEC END -->
This module routes packets to other Jabber servers. First, it checks if an
open S2S connection from the domain of the packet source to the domain of
packet destination already exists. If it is open on another node, then it
routes the packet to S2S manager on that node, if it is open on this node, then
it is routed to the process that serves this connection, and if a connection
does not exist, then it is opened and registered.<BR>
<BR>
<!--TOC section XML representation-->
<H2 CLASS="section"><A NAME="htoc9">3</A>&nbsp;&nbsp;XML representation</H2><!--SEC END -->
<A NAME="sec:xmlrepr"></A>
Each XML stanza is represented as the following tuple:
<PRE CLASS="verbatim">
XMLElement = {xmlelement, Name, Attrs, [ElementOrCDATA]}
Name = string()
Attrs = [Attr]
Attr = {Key, Val}
Key = string()
Val = string()
ElementOrCDATA = XMLElement | CDATA
CDATA = {xmlcdata, string()}
</PRE>E.&nbsp;g. this stanza:
<PRE CLASS="verbatim">
&lt;message to='test@conference.example.org' type='groupchat'&gt;
&lt;body&gt;test&lt;/body&gt;
&lt;/message&gt;
</PRE>is represented as the following structure:
<PRE CLASS="verbatim">
{xmlelement, "message",
[{"to", "test@conference.example.org"},
{"type", "groupchat"}],
[{xmlelement, "body",
[],
[{xmlcdata, "test"}]}]}}
</PRE>
<!--TOC section Module <TT>xml</TT>-->
<H2 CLASS="section"><A NAME="htoc10">4</A>&nbsp;&nbsp;Module <TT>xml</TT></H2><!--SEC END -->
<A NAME="sec:xmlmod"></A>
<DL CLASS="description" COMPACT=compact><DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>element_to_string(El) -&gt; string()</CODE>
<PRE CLASS="verbatim">
El = XMLElement
</PRE>Returns string representation of XML stanza <TT>El</TT>.<BR>
<BR>
<DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>crypt(S) -&gt; string()</CODE>
<PRE CLASS="verbatim">
S = string()
</PRE>Returns string which correspond to <TT>S</TT> with encoded XML special
characters.<BR>
<BR>
<DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>remove_cdata(ECList) -&gt; EList</CODE>
<PRE CLASS="verbatim">
ECList = [ElementOrCDATA]
EList = [XMLElement]
</PRE><TT>EList</TT> is a list of all non-CDATA elements of ECList.<BR>
<BR>
<DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>get_path_s(El, Path) -&gt; Res</CODE>
<PRE CLASS="verbatim">
El = XMLElement
Path = [PathItem]
PathItem = PathElem | PathAttr | PathCDATA
PathElem = {elem, Name}
PathAttr = {attr, Name}
PathCDATA = cdata
Name = string()
Res = string() | XMLElement
</PRE>If <TT>Path</TT> is empty, then returns <TT>El</TT>. Else sequentially
consider elements of <TT>Path</TT>. Each element is one of:
<DL CLASS="description" COMPACT=compact><DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>{elem, Name}</CODE> <TT>Name</TT> is name of subelement of
<TT>El</TT>, if such element exists, then this element considered in
following steps, else returns empty string.
<DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>{attr, Name}</CODE> If <TT>El</TT> have attribute <TT>Name</TT>, then
returns value of this attribute, else returns empty string.
<DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>cdata</CODE> Returns CDATA of <TT>El</TT>.
</DL><BR>
<BR>
<DT CLASS="dt-description"><DD CLASS="dd-description">TODO:
<PRE CLASS="verbatim">
get_cdata/1, get_tag_cdata/1
get_attr/2, get_attr_s/2
get_tag_attr/2, get_tag_attr_s/2
get_subtag/2
</PRE></DL>
<!--TOC section Module <TT>xml_stream</TT>-->
<H2 CLASS="section"><A NAME="htoc11">5</A>&nbsp;&nbsp;Module <TT>xml_stream</TT></H2><!--SEC END -->
<A NAME="sec:xmlstreammod"></A>
<DL CLASS="description" COMPACT=compact><DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>parse_element(Str) -&gt; XMLElement | {error, Err}</CODE>
<PRE CLASS="verbatim">
Str = string()
Err = term()
</PRE>Parses <TT>Str</TT> using XML parser, returns either parsed element or error
tuple.
</DL>
<!--TOC section <TT>ejabberd</TT> modules-->
<H2 CLASS="section"><A NAME="htoc12">6</A>&nbsp;&nbsp;<TT>ejabberd</TT> modules</H2><!--SEC END -->
<A NAME="sec:emods"></A>
<!--TOC subsection gen_mod behaviour-->
<H3 CLASS="subsection"><A NAME="htoc13">6.1</A>&nbsp;&nbsp;gen_mod behaviour</H3><!--SEC END -->
<A NAME="sec:genmod"></A>
TBD<BR>
<BR>
<!--TOC subsection Module gen_iq_handler-->
<H3 CLASS="subsection"><A NAME="htoc14">6.2</A>&nbsp;&nbsp;Module gen_iq_handler</H3><!--SEC END -->
<A NAME="sec:geniqhandl"></A>
The module <CODE>gen_iq_handler</CODE> allows to easily write handlers for IQ packets
of particular XML namespaces that addressed to server or to users bare JIDs.<BR>
<BR>
In this module the following functions are defined:
<DL CLASS="description" COMPACT=compact><DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>add_iq_handler(Component, Host, NS, Module, Function, Type)</CODE>
<PRE CLASS="verbatim">
Component = Module = Function = atom()
Host = NS = string()
Type = no_queue | one_queue | parallel
</PRE>Registers function <CODE>Module:Function</CODE> as handler for IQ packets on
virtual host <CODE>Host</CODE> that contain child of namespace <CODE>NS</CODE> in
<CODE>Component</CODE>. Queueing discipline is <CODE>Type</CODE>. There are at least
two components defined:
<DL CLASS="description" COMPACT=compact><DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>ejabberd_local</CODE> Handles packets that addressed to server JID;
<DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>ejabberd_sm</CODE> Handles packets that addressed to users bare JIDs.
</DL>
<DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>remove_iq_handler(Component, Host, NS)</CODE>
<PRE CLASS="verbatim">
Component = atom()
Host = NS = string()
</PRE>Removes IQ handler on virtual host <CODE>Host</CODE> for namespace <CODE>NS</CODE> from
<CODE>Component</CODE>.
</DL>
Handler function must have the following type:
<DL CLASS="description" COMPACT=compact><DT CLASS="dt-description"><DD CLASS="dd-description"><CODE>Module:Function(From, To, IQ)</CODE>
<PRE CLASS="verbatim">
From = To = jid()
</PRE></DL>
<PRE CLASS="verbatim">
-module(mod_cputime).
-behaviour(gen_mod).
-export([start/2,
stop/1,
process_local_iq/3]).
-include("ejabberd.hrl").
-include("jlib.hrl").
-define(NS_CPUTIME, "ejabberd:cputime").
start(Host, Opts) -&gt;
IQDisc = gen_mod:get_opt(iqdisc, Opts, one_queue),
gen_iq_handler:add_iq_handler(ejabberd_local, Host, ?NS_CPUTIME,
?MODULE, process_local_iq, IQDisc).
stop(Host) -&gt;
gen_iq_handler:remove_iq_handler(ejabberd_local, Host, ?NS_CPUTIME).
process_local_iq(From, To, {iq, ID, Type, XMLNS, SubEl}) -&gt;
case Type of
set -&gt;
{iq, ID, error, XMLNS,
[SubEl, ?ERR_NOT_ALLOWED]};
get -&gt;
CPUTime = element(1, erlang:statistics(runtime))/1000,
SCPUTime = lists:flatten(io_lib:format("~.3f", CPUTime)),
{iq, ID, result, XMLNS,
[{xmlelement, "query",
[{"xmlns", ?NS_CPUTIME}],
[{xmlelement, "cputime", [], [{xmlcdata, SCPUTime}]}]}]}
end.
</PRE>
<!--TOC subsection Services-->
<H3 CLASS="subsection"><A NAME="htoc15">6.3</A>&nbsp;&nbsp;Services</H3><!--SEC END -->
<A NAME="sec:services"></A>
TBD<BR>
<BR>
TODO: use <CODE>proc_lib</CODE>
<PRE CLASS="verbatim">
-module(mod_echo).
-behaviour(gen_mod).
-export([start/2, init/1, stop/1]).
-include("ejabberd.hrl").
-include("jlib.hrl").
start(Host, Opts) -&gt;
MyHost = gen_mod:get_opt(host, Opts, "echo." ++ Host),
register(gen_mod:get_module_proc(Host, ?PROCNAME),
spawn(?MODULE, init, [MyHost])).
init(Host) -&gt;
ejabberd_router:register_local_route(Host),
loop(Host).
loop(Host) -&gt;
receive
{route, From, To, Packet} -&gt;
ejabberd_router:route(To, From, Packet),
loop(Host);
stop -&gt;
ejabberd_router:unregister_route(Host),
ok;
_ -&gt;
loop(Host)
end.
stop(Host) -&gt;
Proc = gen_mod:get_module_proc(Host, ?PROCNAME),
Proc ! stop,
{wait, Proc}.
</PRE>
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