<?xml version='1.0'?> <!--*-nxml-*--> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/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>History</title> <para><function>sd_bus_message_get_cookie()</function> and <function>sd_bus_message_get_reply_cookie()</function> were added in version 209.</para> </refsect1> <refsect1> <title>See Also</title> <para><simplelist type="inline"> <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> <member><citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> <member><citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> </simplelist></para> </refsect1> </refentry>