kamailio/doc/tutorials/serdev/via_parser.xml

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<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" 
   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<section id="via_parser" xmlns:xi="http://www.w3.org/2001/XInclude">
    <sectioninfo>
	<revhistory>
	    <revision>
		<revnumber>$Revision$</revnumber>
		<date>$Date$</date>
	    </revision>
	</revhistory>
    </sectioninfo>
    
    <title>Via HF Body Parser</title>
    <para>
	Purpose of this parser is to parse body of Via header field. The parser
	can be found in file <filename>parse_via.c</filename> under
	<filename>parser</filename> subdirectory.
    </para>
    <para>
	Main function is <function>parse_via</function> but there is no need to
	call the function explicitly. Every time the parser finds a Via header
	field, this function will be called automatically. Result of the parser
	is <structname>via_body</structname> structure. Pointer to the
	structure will be stored in <structfield>parsed</structfield> field of
	<structname>hdr_field</structname> structure representing the parsed
	header field.
    </para>
    <para>
	The parser itself is a finite state machine that will parse Via body
	according to the grammar defined in <acronym>RFC3261</acronym> and
	store result in <structname>via_body</structname> structure.
    </para>
    <para>
	The parser gets called automatically from function
	<function>get_hdr_field</function> in file
	<filename>msg_parser.c</filename>. The function first creates and
	initializes an instance of <structname>via_body</structname> structure,
	then calls <function>parse_via</function> function with the structure
	as a parameter and if everything went OK, puts the pointer to the
	structure in <structfield>parsed</structfield> field of
	<structname>hdr_field</structname> structure representing the parsed
	Via header field.
    </para>
    <para>
	The newly created structure will be freed when the message is being
	destroyed, see function <function>clean_hdr_field</function> in file
	<filename>hf.c</filename> for more details.
    </para>
    <para>
	Structure <structname>via_body</structname> is described in
	<xref linkend="via_body"/>.
    </para>
</section>