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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_bus_message_get_cookie"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_message_get_cookie</title>
<productname>systemd</productname>
</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 <systemd/sd-bus.h></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, they 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>
<refsect2>
<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>
</refsect2>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<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>
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