kamailio/doc/tutorials/serdev/from_parser.xml

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<section id="from_parser" xmlns:xi="http://www.w3.org/2001/XInclude">
    <sectioninfo>
	<revhistory>
	    <revision>
		<revnumber>$Revision$</revnumber>
		<date>$Date$</date>
	    </revision>
	</revhistory>
    </sectioninfo>

    <title>From Header Field Parser</title>
    <para>
	This parser is only a wrapper to the To header field parser. Since
	bodies of both header fields are identical, From parser only calls To
	parser.
    </para>
    <para>
	The wrapper can be found in file <filename>parse_from.c</filename>
	under <filename>parser</filename> subdirectory. There is only one
	function called <function>parse_from_header</function>. The function
	accepts one parameter which is pointer to structure representing the
	From header field to be parsed. The function creates an instance of
	<structname>to_body</structname> structure and initializes it. It then
	calls <function>parse_to</function> function and if everything went OK,
	the pointer to the newly created structure will be put in
	<structfield>parsed</structfield> field of the structure representing
	the parsed header field.
    </para>
    <para>
	The newly created structure will be freed when the whole message is
	being destroyed.  (See To header field parser description for more
	details).
    </para>
    <para>
	From parser <emphasis>must be called explicitly</emphasis> !
    </para>
    <para>
	If the main parser finds a From header field, it will not parse the
	header field body automatically. It is up to you to call the
	<function>parse_from_header</function> when you want to parse a From
	header field body.
    </para>
</section>