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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
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<H1 ALIGN=center>Ejabberd Developers Guide</H1>
<H3 ALIGN=center>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>
<H3 ALIGN=center>September 10, 2003</H3><DIV ALIGN=center>
<IMG SRC="logo.png">
</DIV><BR>
<BR>
<!--TOC section Table of Contents-->
<H2>Table of Contents</H2><!--SEC END -->
<UL><LI>
<A HREF="#htoc1">1 Introduction</A>
<UL><LI>
<A HREF="#htoc2">1.1 How it works</A>
<UL><LI>
<A HREF="#htoc3">1.1.1 Router</A>
<LI><A HREF="#htoc4">1.1.2 Local Router</A>
<LI><A HREF="#htoc5">1.1.3 Session Manager</A>
<LI><A HREF="#htoc6">1.1.4 S2S Manager</A>
</UL>
</UL>
<LI><A HREF="#htoc7">2 XML representation</A>
<LI><A HREF="#htoc8">3 Module <TT>xml</TT></A>
<LI><A HREF="#htoc9">4 <TT>ejabberd</TT> modules</A>
<UL><LI>
<A HREF="#htoc10">4.1 <CODE>gen_mod</CODE> behaviour</A>
<LI><A HREF="#htoc11">4.2 Module <CODE>gen_iq_handler</CODE></A>
<LI><A HREF="#htoc12">4.3 Services</A>
</UL>
</UL>
<!--TOC section Introduction-->
<H2><A NAME="htoc1">1</A> Introduction</H2><!--SEC END -->
<A NAME="sec:intro"></A>
<TT>ejabberd</TT> is a Free and Open Source fault-tolerant distributed Jabber
server. It is writen mostly in Erlang.<BR>
<BR>
The main features of <TT>ejabberd</TT> is:
<UL><LI>
Works on most of popular platforms: *nix (tested on Linux and FreeBSD)
and Win32
<LI>Distributed: You can run <TT>ejabberd</TT> on a cluster of machines and all of
them will serve one Jabber domain.
<LI>Fault-tolerance: You can setup an <TT>ejabberd</TT> cluster so that all the
information required for a properly working service will be stored
permanently on more than one node. This means that if one of the nodes
crashes, then the others will continue working without disruption.
You can also add or replace more nodes ``on the fly''.
<LI>Built-in <A HREF="http://www.jabber.org/jeps/jep-0045.html">Multi-User
Chat</A> service
<LI>Built-in IRC transport
<LI>Built-in
<A HREF="http://www.jabber.org/jeps/jep-0060.html">Publish-Subscribe</A>
service
<LI>Built-in Jabber Users Directory service based on users vCards
<LI>Support for
<A HREF="http://www.jabber.org/jeps/jep-0030.html">JEP-0030</A>
(Service Discovery).
<LI>Support for
<A HREF="http://www.jabber.org/jeps/jep-0039.html">JEP-0039</A>
(Statistics Gathering).
<LI>Support for <TT>xml:lang</TT> attribute in many XML elements
</UL>
<!--TOC subsection How it works-->
<H3><A NAME="htoc2">1.1</A> How it works</H3><!--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><LI>
router;
<LI>local router.
<LI>session manager;
<LI>S2S manager;
</UL>
<!--TOC subsubsection Router-->
<H4><A NAME="htoc3">1.1.1</A> Router</H4><!--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 subsubsection Local Router-->
<H4><A NAME="htoc4">1.1.2</A> Local Router</H4><!--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 subsubsection Session Manager-->
<H4><A NAME="htoc5">1.1.3</A> Session Manager</H4><!--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 subsubsection S2S Manager-->
<H4><A NAME="htoc6">1.1.4</A> S2S Manager</H4><!--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><A NAME="htoc7">2</A> XML representation</H2><!--SEC END -->
<A NAME="sec:xmlrepr"></A>
Each XML stanza represented as following tuple:
<PRE>
XMLElement = {xmlelement, Name, Attrs, [ElementOrCDATA]}
Name = string()
Attrs = [Attr]
Attr = {Key, Val}
Key = string()
Val = string()
ElementOrCDATA = XMLElement | CDATA
CDATA = {xmlcdata, string()}
</PRE>E. g. this stanza:
<PRE>
<message to='test@conference.e.localhost' type='groupchat'>
<body>test</body>
</message>
</PRE>represented as following structure:
<PRE>
{xmlelement, "message",
[{"to", "test@conference.e.localhost"},
{"type", "groupchat"}],
[{xmlelement, "body",
[],
[{xmlcdata, "test"}]}]}}
</PRE>
<!--TOC section Module <TT>xml</TT>-->
<H2><A NAME="htoc8">3</A> Module <TT>xml</TT></H2><!--SEC END -->
<A NAME="sec:xmlmod"></A>
<DL COMPACT=compact><DT>
<CODE><B>element_to_string(El) -> string()</B></CODE><DD>
<PRE>
El = XMLElement
</PRE>Returns string representation of XML stanza <TT>El</TT>.<BR>
<BR>
<DT><CODE><B>crypt(S) -> string()</B></CODE><DD>
<PRE>
S = string()
</PRE>Returns string which correspond to <TT>S</TT> with encoded XML special
characters.<BR>
<BR>
<DT><CODE><B>remove_cdata(ECList) -> EList</B></CODE><DD>
<PRE>
ECList = [ElementOrCDATA]
EList = [XMLElement]
</PRE><TT>EList</TT> is a list of all non-CDATA elements of ECList.<BR>
<BR>
<DT><CODE><B>get_path_s(El, Path) -> Res</B></CODE><DD>
<PRE>
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 COMPACT=compact><DT>
<CODE><B>{elem, Name}</B></CODE><DD> <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><CODE><B>{attr, Name}</B></CODE><DD> If <TT>El</TT> have attribute <TT>Name</TT>, then
returns value of this attribute, else returns empty string.
<DT><CODE><B>cdata</B></CODE><DD> Returns CDATA of <TT>El</TT>.
</DL><BR>
<BR>
<DT><B>TODO:</B><DD>
<PRE>
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 <TT>ejabberd</TT> modules-->
<H2><A NAME="htoc9">4</A> <TT>ejabberd</TT> modules</H2><!--SEC END -->
<A NAME="sec:emods"></A>
<!--TOC subsection <CODE>gen_mod</CODE> behaviour-->
<H3><A NAME="htoc10">4.1</A> <CODE>gen_mod</CODE> behaviour</H3><!--SEC END -->
<A NAME="sec:genmod"></A>
TBD<BR>
<BR>
<!--TOC subsection Module <CODE>gen_iq_handler</CODE>-->
<H3><A NAME="htoc11">4.2</A> Module <CODE>gen_iq_handler</CODE></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 COMPACT=compact><DT>
<CODE><B>add_iq_handler(Component, NS, Module, Function, Type)</B></CODE><DD>
<PRE>
Component = Module = Function = atom()
NS = string()
Type = no_queue | one_queue | parallel
</PRE>Registers function <CODE>Module:Function</CODE> as handler for IQ packets 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 COMPACT=compact><DT>
<CODE><B>ejabberd_local</B></CODE><DD> Handles packets that addressed to server JID;
<DT><CODE><B>ejabberd_sm</B></CODE><DD> Handles packets that addressed to users bare JIDs.
</DL>
<DT><CODE><B>remove_iq_handler(Component, NS)</B></CODE><DD>
<PRE>
Component = atom()
NS = string()
</PRE>Removes IQ handler for namespace <CODE>NS</CODE> from <CODE>Component</CODE>.
</DL>
Handler function must have the following type:
<DL COMPACT=compact><DT>
<CODE><B>Module:Function(From, To, IQ)</B></CODE><DD>
<PRE>
From = To = jid()
</PRE></DL>
<PRE>
-module(mod_cputime).
-behaviour(gen_mod).
-export([start/1,
stop/0,
process_local_iq/3]).
-include("ejabberd.hrl").
-include("jlib.hrl").
-define(NS_CPUTIME, "ejabberd:cputime").
start(Opts) ->
IQDisc = gen_mod:get_opt(iqdisc, Opts, one_queue),
gen_iq_handler:add_iq_handler(ejabberd_local, ?NS_CPUTIME,
?MODULE, process_local_iq, IQDisc).
stop() ->
gen_iq_handler:remove_iq_handler(ejabberd_local, ?NS_CPUTIME).
process_local_iq(From, To, {iq, ID, Type, XMLNS, SubEl}) ->
case Type of
set ->
{iq, ID, error, XMLNS,
[SubEl, ?ERR_NOT_ALLOWED]};
get ->
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><A NAME="htoc12">4.3</A> Services</H3><!--SEC END -->
<A NAME="sec:services"></A>
TBD<BR>
<BR>
TODO: use <CODE>proc_lib</CODE>
<PRE>
-module(mod_echo).
-behaviour(gen_mod).
-export([start/1, init/1, stop/0]).
-include("ejabberd.hrl").
-include("jlib.hrl").
start(Opts) ->
Host = gen_mod:get_opt(host, Opts, "echo." ++ ?MYNAME),
register(ejabberd_mod_echo, spawn(?MODULE, init, [Host])).
init(Host) ->
ejabberd_router:register_local_route(Host),
loop(Host).
loop(Host) ->
receive
{route, From, To, Packet} ->
ejabberd_router:route(To, From, Packet),
loop(Host);
stop ->
ejabberd_router:unregister_local_route(Host),
ok;
_ ->
loop(Host)
end.
stop() ->
ejabberd_mod_echo ! stop,
ok.
</PRE>
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