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
   9 <refentry id="sd_bus_message_get_cookie"
  10           xmlns:xi="http://www.w3.org/2001/XInclude">
  11
  12   <refentryinfo>
  13     <title>sd_bus_message_get_cookie</title>
  14     <productname>systemd</productname>
  15   </refentryinfo>
  16
  17   <refmeta>
  18     <refentrytitle>sd_bus_message_get_cookie</refentrytitle>
  19     <manvolnum>3</manvolnum>
  20   </refmeta>
  21
  22   <refnamediv>
  23     <refname>sd_bus_message_get_cookie</refname>
  24     <refname>sd_bus_message_get_reply_cookie</refname>
  25     <refpurpose>Returns the transaction cookie of a message</refpurpose>
  26   </refnamediv>
  27
  28   <refsynopsisdiv>
  29     <funcsynopsis>
  30       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  31
  32       <funcprototype>
  33         <funcdef>int <function>sd_bus_message_get_cookie</function></funcdef>
  34         <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
  35         <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
  36       </funcprototype>
  37
  38       <funcprototype>
  39         <funcdef>int <function>sd_bus_message_get_reply_cookie</function></funcdef>
  40         <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
  41         <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
  42       </funcprototype>
  43     </funcsynopsis>
  44   </refsynopsisdiv>
  45
  46   <refsect1>
  47     <title>Description</title>
  48
  49     <para><function>sd_bus_message_get_cookie()</function> returns the
  50     transaction cookie of a message. The cookie uniquely identifies a
  51     message within each bus peer, but is not globally unique. It is
  52     assigned when a message is sent.</para>
  53
  54     <para><function>sd_bus_message_get_reply_cookie()</function>
  55     returns the transaction cookie of the message the specified
  56     message is a response to. When a reply message is generated for a
  57     method call message, its cookie is copied over into this field.
  58     Note that while every message that is transferred is identified by
  59     a cookie, only response messages carry a reply cookie
  60     field.</para>
  61
  62     <para>Both functions take a message object as first parameter and
  63     a place to store the 64-bit cookie in.</para>
  64   </refsect1>
  65
  66   <refsect1>
  67     <title>Return Value</title>
  68
  69     <para>On success, these calls return 0 or a positive integer. On
  70     failure, these calls return a negative errno-style error
  71     code.</para>
  72
  73     <para>On success, the cookie/reply cookie is returned in the
  74     specified 64-bit unsigned integer variable.</para>
  75   </refsect1>
  76
  77   <refsect1>
  78     <title>Errors</title>
  79
  80     <para>Returned errors may indicate the following problems:</para>
  81
  82     <variablelist>
  83       <varlistentry>
  84         <term><constant>-EINVAL</constant></term>
  85
  86         <listitem><para>A specified parameter
  87         is invalid.</para></listitem>
  88       </varlistentry>
  89
  90       <varlistentry>
  91         <term><constant>-ENODATA</constant></term>
  92
  93         <listitem><para>No cookie has been assigned to this message.
  94         This either indicates that the message has not been sent yet
  95         and hence has no cookie assigned, or that the message is not a
  96         method response message and hence carries a reply cookie
  97         field.</para></listitem>
  98       </varlistentry>
  99     </variablelist>
 100   </refsect1>
 101
 102   <xi:include href="libsystemd-pkgconfig.xml" />
 103
 104   <refsect1>
 105     <title>See Also</title>
 106
 107     <para>
 108       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 109       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 110       <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 111     </para>
 112   </refsect1>
 113
 114 </refentry>