man/sd_bus_message_get_cookie.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2013 Lennart Poettering
  11 -->
  12
  13 <refentry id="sd_bus_message_get_cookie">
  14
  15   <refentryinfo>
  16     <title>sd_bus_message_get_cookie</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_bus_message_get_cookie</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_bus_message_get_cookie</refname>
  36     <refname>sd_bus_message_get_reply_cookie</refname>
  37     <refpurpose>Returns the transaction cookie of a message</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <funcsynopsis>
  42       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  43
  44       <funcprototype>
  45         <funcdef>int <function>sd_bus_message_get_cookie</function></funcdef>
  46         <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
  47         <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
  48       </funcprototype>
  49
  50       <funcprototype>
  51         <funcdef>int <function>sd_bus_message_get_reply_cookie</function></funcdef>
  52         <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
  53         <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
  54       </funcprototype>
  55     </funcsynopsis>
  56   </refsynopsisdiv>
  57
  58   <refsect1>
  59     <title>Description</title>
  60
  61     <para><function>sd_bus_message_get_cookie()</function> returns the
  62     transaction cookie of a message. The cookie uniquely identifies a
  63     message within each bus peer, but is not globally unique. It is
  64     assigned when a message is sent.</para>
  65
  66     <para><function>sd_bus_message_get_reply_cookie()</function>
  67     returns the transaction cookie of the message the specified
  68     message is a response to. When a reply message is generated for a
  69     method call message, its cookie is copied over into this field.
  70     Note that while every message that is transferred is identified by
  71     a cookie, only response messages carry a reply cookie
  72     field.</para>
  73
  74     <para>Both functions take a message object as first parameter and
  75     a place to store the 64-bit cookie in.</para>
  76   </refsect1>
  77
  78   <refsect1>
  79     <title>Return Value</title>
  80
  81     <para>On success, these calls return 0 or a positive integer. On
  82     failure, these calls return a negative errno-style error
  83     code.</para>
  84
  85     <para>On success, the cookie/reply cookie is returned in the
  86     specified 64-bit unsigned integer variable.</para>
  87   </refsect1>
  88
  89   <refsect1>
  90     <title>Errors</title>
  91
  92     <para>Returned errors may indicate the following problems:</para>
  93
  94     <variablelist>
  95       <varlistentry>
  96         <term><constant>-EINVAL</constant></term>
  97
  98         <listitem><para>A specified parameter
  99         is invalid.</para></listitem>
 100       </varlistentry>
 101
 102       <varlistentry>
 103         <term><constant>-ENODATA</constant></term>
 104
 105         <listitem><para>No cookie has been assigned to this message.
 106         This either indicates that the message has not been sent yet
 107         and hence has no cookie assigned, or that the message is not a
 108         method response message and hence carries a reply cookie
 109         field.</para></listitem>
 110       </varlistentry>
 111     </variablelist>
 112   </refsect1>
 113
 114   <refsect1>
 115     <title>Notes</title>
 116
 117     <para>The <function>sd_bus_message_get_cookie()</function> and
 118     <function>sd_bus_message_get_reply_cookie()</function> interfaces
 119     are available as a shared library, which can be compiled and
 120     linked to with the
 121     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 122     file.</para>
 123   </refsect1>
 124
 125   <refsect1>
 126     <title>See Also</title>
 127
 128     <para>
 129       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 130       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 131       <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 132     </para>
 133   </refsect1>
 134
 135 </refentry>