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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd_bus_message_get_cookie" conditional="ENABLE_KDBUS">

<refentryinfo>

<title>sd_bus_message_get_cookie</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sd_bus_message_get_cookie</refentrytitle>

<manvolnum>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd_bus_message_get_cookie</refname>

<refname>sd_bus_message_get_reply_cookie</refname>

<refpurpose>Returns the transaction cookie of a message</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

<funcprototype>

<funcdef>int <function>sd_bus_message_get_cookie</function></funcdef>

<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>

<paramdef>uint64_t *<parameter>cookie</parameter></paramdef>

</funcprototype>

<funcprototype>

<funcdef>int <function>sd_bus_message_get_reply_cookie</function></funcdef>

<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>

<paramdef>uint64_t *<parameter>cookie</parameter></paramdef>

</funcprototype>

</funcsynopsis>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><function>sd_bus_message_get_cookie()</function> returns the

transaction cookie of a message. The cookie uniquely identifies a

message within each bus peer, but is not globally unique. It is

assigned when a message is sent.</para>

<para><function>sd_bus_message_get_reply_cookie()</function>

returns the transaction cookie of the message the specified

message is a response to. When a reply message is generated for a

method call message, its cookie is copied over into this field.

Note that while every message that is transferred is identified by

a cookie, only response messages carry a reply cookie

field.</para>

<para>Both functions take a message object as first parameter and

a place to store the 64-bit cookie in.</para>

</refsect1>

<refsect1>

<title>Return Value</title>

<para>On success, these calls return 0 or a positive integer. On

failure, these calls return a negative errno-style error

code.</para>

<para>On success, the cookie/reply cookie is returned in the

specified 64-bit unsigned integer variable.</para>

</refsect1>

<refsect1>

<title>Errors</title>

<para>Returned errors may indicate the following problems:</para>

<variablelist>

<varlistentry>

<term><constant>-EINVAL</constant></term>

<listitem><para>A specified parameter

is invalid.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-ENODATA</constant></term>

<listitem><para>No cookie has been assigned to this message.

This either indicates that the message has not been sent yet

and hence has no cookie assigned, or that the message is not a

method response message and hence carries a reply cookie

field.</para></listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Notes</title>

<para>The <function>sd_bus_message_get_cookie()</function> and

<function>sd_bus_message_get_reply_cookie()</function> interfaces

are available as a shared library, which can be compiled and

linked to with the

<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

file.</para>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>