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<!-- Module User's Guide -->

<chapter>

	<title>&adminguide;</title>

	<section>
	<title>Overview</title>
	<para>
		This module provides basic HTTP/1.0 server functionality inside
		&kamailio;. SIP and HTTP are very similar protocols, so, practically, the
		SIP parser can easily handle HTTP requests just by adding a fake
		Via header.
	</para>
	<para>
		The <module>xmlrpc</module> module uses the same concept.
		The xHTTP module offers a generic way of handling the <acronym>HTTP</acronym>
		protocol, by calling <emphasis>event_route[xhttp:request]</emphasis>
		in your config. You can check the HTTP URL via the config variable
		<acronym>$hu</acronym>. Note that use of <acronym>$ru</acronym> will
		raise errors since the structure of an HTTP URL is not compatible with
		that of a SIP URI.
	</para>
	</section>

	<section>
	<title>Note on Latency</title>
	<para>
		Because HTTP requests in <emphasis>xhttp</emphasis> are handled
		by the same, finite number of SIP worker processes that operate on
		SIP messages, the same general principles regarding script execution
		speed and throughput should be observed by the writer in
		<emphasis>event_route[xhttp:request]</emphasis> as in any other
		part of the route script.
	</para>
	<para>
		For example, if you initiate a database query in the HTTP request route
		that takes a long time to return rows, the SIP worker process in which
		the request is handled will be blocked for that time and unable to
		process other SIP messages.  In most typical installations, there are
		only a few of these worker processes running.
	</para>
	<para>
		Therefore, it is highly inadvisable to execute particularly slow things in the
		<emphasis>event_route[xhttp:request]</emphasis>, because the request is not
		handled in an asynchronous manner or otherwise peripherally to general
		SIP processing.  SIP worker threads will block, pending the outcome of the
		event route just like any other config script route.
	</para>
	<para>
		This is no more or less true for <emphasis>xhttp</emphasis> than it is for
		any other block of script in any other scenario, and does not warrant any
		extraordinary concern.  It nevertheless bears mention here because some
		processes with embedded HTTP servers have the request processing take place
		"outside" of the main synchronous event sequence, whether by creating
		separate threads or by some other asynchronous handling.  That is not the
		case with <emphasis>xhttp</emphasis>.
	</para>
	</section>

	<section>
	<title>Dependencies</title>
	<section>
		<title>&kamailio; Modules</title>
		<para>
		The following modules must be loaded before this module:
			<itemizedlist>
			<listitem>
			<para>
				<emphasis>sl</emphasis> - stateless reply.
			</para>
			</listitem>
			</itemizedlist>
		</para>
	</section>
	<section>
		<title>&kamailio; Core Settings</title>
		<para>
		SIP requires a Content-Length header for TCP transport. But most HTTP clients do not
		set the content length for normal GET requests. Therefore, the core must be configured
		to allow incoming requests without content length header:
			<itemizedlist>
			<listitem>
			<para>
				<emphasis>tcp_accept_no_cl=yes</emphasis>
			</para>
			</listitem>
			</itemizedlist>
		</para>
	</section>
	<section>
		<title>External Libraries or Applications</title>
		<para>
		The following libraries or applications must be installed before running
		&kamailio; with this module loaded:
			<itemizedlist>
			<listitem>
			<para>
				<emphasis>None</emphasis>
			</para>
			</listitem>
			</itemizedlist>
		</para>
	</section>
	</section>
	<section>
	<title>Parameters</title>
	<section id="xhttp.p.url_skip">
		<title><varname>url_skip</varname> (str)</title>
		<para>
			Regular expression to match the HTTP URL. If there is a match,
			the event route is not executed.
		</para>
		<para>
		<emphasis>
			Default value is null (don't skip).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>url_skip</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("xhttp", "url_skip", "^/RPC2")
...
</programlisting>
		</example>
	</section>
	<section id="xhttp.p.url_match">
		<title><varname>url_match</varname> (str)</title>
		<para>
			Regular expression to match the HTTP URL. If there is no match,
			the event route is not executed. This check is done after
			url_skip, so if both url_skip and url_match would match then
			the event route is not executed (url_skip has higher priority).
		</para>
		<para>
		<emphasis>
			Default value is null (match everything).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>url_match</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("xhttp", "url_match", "^/sip/")
...
</programlisting>
		</example>
	</section>
	<section id="xhttp.p.event_callback">
		<title><varname>event_callback</varname> (str)</title>
		<para>
			The name of the function in the kemi configuration file (embedded
			scripting language such as Lua, Python, ...) to be executed instead
			of event_route[xhttp:request] block.
		</para>
		<para>
			The function has one string parameter with the value "xhttp:request".
		</para>
		<para>
		<emphasis>
			Default value is 'empty' (no function is executed for events).
		</emphasis>
		</para>
		<example>
		<title>Set <varname>event_callback</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("xhttp", "event_callback", "ksr_xhttp_event")
...
-- event callback function implemented in Lua
function ksr_xhttp_event(evname)
	KSR.info("===== xhttp module triggered event: " .. evname .. "\n");
	return 1;
end
...
</programlisting>
	    </example>
	</section>
	</section>

	<section>
	<title>Functions</title>
	<section id="xhttp.f.xhttp_reply">
	    <title>
		<function moreinfo="none">xhttp_reply(code, reason, ctype, body)</function>
	    </title>
	    <para>
		Send back a reply with content-type and body.
	    </para>
		<example>
		<title><function>xhttp_reply</function> usage</title>
		<programlisting format="linespecific">
...
event_route[xhttp:request] {
    xhttp_reply("200", "OK", "text/html",
        "&lt;html&gt;&lt;body&gt;OK - [$si:$sp]&lt;/body&gt;&lt;/html&gt;");
}
...
</programlisting>
	    </example>
	</section>
	</section>

    <section>
    <title>Event Routes</title>
    <section id="xhttp.evr.request">
        <title>
        <function moreinfo="none">xhttp:request</function>
        </title>
        <para>
			The event route is executed when a new HTTP request is received.
        </para>
        <programlisting  format="linespecific">
...
tcp_accept_no_cl=yes
...
loadmodule "sl.so"
loadmodule "xhttp.so
...
event_route[xhttp:request] {
    xhttp_reply("200", "OK", "text/html",
        "&lt;html&gt;&lt;body&gt;OK - [$si:$sp]&lt;/body&gt;&lt;/html&gt;");
}
...
        </programlisting>
	</section>
	</section>
</chapter>