man/sd_bus_add_match.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
   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 2016 Julian Orth
  11 -->
  12
  13 <refentry id="sd_bus_add_match">
  14
  15   <refentryinfo>
  16     <title>sd_bus_add_match</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <firstname>Julian</firstname>
  22         <surname>Orth</surname>
  23         <email>ju.orth@gmail.com</email>
  24       </author>
  25     </authorgroup>
  26   </refentryinfo>
  27
  28   <refmeta>
  29     <refentrytitle>sd_bus_add_match</refentrytitle>
  30     <manvolnum>3</manvolnum>
  31   </refmeta>
  32
  33   <refnamediv>
  34     <refname>sd_bus_add_match</refname>
  35     <refname>sd_bus_add_match_async</refname>
  36     <refname>sd_bus_match_signal</refname>
  37     <refname>sd_bus_match_signal_async</refname>
  38
  39     <refpurpose>Add a match rule for incoming message dispatching</refpurpose>
  40   </refnamediv>
  41
  42   <refsynopsisdiv>
  43     <funcsynopsis>
  44       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  45
  46       <funcprototype>
  47         <funcdef>typedef int (*<function>sd_bus_message_handler_t</function>)</funcdef>
  48         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  49         <paramdef>void *<parameter>userdata</parameter></paramdef>
  50         <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
  51       </funcprototype>
  52
  53       <funcprototype>
  54         <funcdef>int <function>sd_bus_add_match</function></funcdef>
  55         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  56         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  57         <paramdef>const char *<parameter>match</parameter></paramdef>
  58         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  59         <paramdef>void *<parameter>userdata</parameter></paramdef>
  60       </funcprototype>
  61
  62       <funcprototype>
  63         <funcdef>int <function>sd_bus_add_match_async</function></funcdef>
  64         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  65         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  66         <paramdef>const char *<parameter>match</parameter></paramdef>
  67         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  68         <paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
  69         <paramdef>void *<parameter>userdata</parameter></paramdef>
  70       </funcprototype>
  71
  72       <funcprototype>
  73         <funcdef>int <function>sd_bus_match_signal</function></funcdef>
  74         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  75         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  76         <paramdef>const char *<parameter>sender</parameter></paramdef>
  77         <paramdef>const char *<parameter>path</parameter></paramdef>
  78         <paramdef>const char *<parameter>interface</parameter></paramdef>
  79         <paramdef>const char *<parameter>member</parameter></paramdef>
  80         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  81         <paramdef>void *<parameter>userdata</parameter></paramdef>
  82       </funcprototype>
  83
  84       <funcprototype>
  85         <funcdef>int <function>sd_bus_match_signal_async</function></funcdef>
  86         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  87         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  88         <paramdef>const char *<parameter>sender</parameter></paramdef>
  89         <paramdef>const char *<parameter>path</parameter></paramdef>
  90         <paramdef>const char *<parameter>interface</parameter></paramdef>
  91         <paramdef>const char *<parameter>member</parameter></paramdef>
  92         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  93         <paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
  94         <paramdef>void *<parameter>userdata</parameter></paramdef>
  95       </funcprototype>
  96
  97     </funcsynopsis>
  98   </refsynopsisdiv>
  99
 100   <refsect1>
 101     <title>Description</title>
 102
 103     <para><function>sd_bus_add_match()</function> installs a match rule for messages received on the specified bus
 104     connection object <parameter>bus</parameter>. The syntax of the match rule expression passed in
 105     <parameter>match</parameter> is described in the <ulink
 106     url="https://dbus.freedesktop.org/doc/dbus-specification.html">D-Bus Specification</ulink>. The specified handler
 107     function <parameter>callback</parameter> is called for eaching incoming message matching the specified expression,
 108     the <parameter>userdata</parameter> parameter is passed as-is to the callback function. The match is installed
 109     synchronously when connected to a bus broker, i.e. the call sends a control message requested the match to be added
 110     to the broker and waits until the broker confirms the match has been installed successfully.</para>
 111
 112     <para><function>sd_bus_add_match_async()</function> operates very similar to
 113     <function>sd_bus_match_signal()</function>, however it installs the match asynchronously, in a non-blocking
 114     fashion: a request is sent to the broker, but the call does not wait for a response. The
 115     <parameter>install_callback</parameter> function is called when the response is later received, with the response
 116     message from the broker as parameter. If this function is specified as <constant>NULL</constant> a default
 117     implementation is used that terminates the bus connection should installing the match fail.</para>
 118
 119     <para><function>sd_bus_match_signal()</function> is very similar to <function>sd_bus_add_match()</function>, but
 120     only matches signals, and instead of a match expression accepts four parameters: <parameter>sender</parameter> (the
 121     service name of the sender), <parameter>path</parameter> (the object path of the emitting object),
 122     <parameter>interface</parameter> (the interface the signal belongs to), <parameter>member</parameter> (the signal
 123     name), from which the match string is internally generated. Optionally, these parameters may be specified as
 124     <constant>NULL</constant> in which case the relevant field of incoming signals is not tested.</para>
 125
 126     <para><function>sd_bus_match_signal_async()</function> is combines the signal matching logic of
 127     <function>sd_bus_match_signal()</function> with the asynchronous behaviour of
 128     <function>sd_bus_add_match_async()</function>.</para>
 129
 130     <para>On success, and if non-<constant>NULL</constant>, the <parameter>slot</parameter> return parameter will be
 131     set to a slot object that may be used as a reference to the installed match, and may be utilized to remove it again
 132     at a later time with
 133     <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If specified
 134     as <constant>NULL</constant> the lifetime of the match is bound to the lifetime of the bus object itself, and the
 135     match cannot be removed independently.</para>
 136
 137     <para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
 138     not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 139     on it. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call
 140     <citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to create a
 141     new reference.</para>
 142
 143     <para>If an error occurs during the callback invocation, the callback should return a negative error number
 144     (optionally, a more precise error may be returned in <parameter>ret_error</parameter>, as well). If it wants other
 145     callbacks that match the same rule to be called, it should return 0. Otherwise it should return a positive integer.
 146     </para>
 147
 148     <para>If the <parameter>bus</parameter> refers to a direct connection (i.e. not a bus connection, as set with
 149     <citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>) the
 150     match is only installed on the client side, and the synchronous and asynchronous functions operate the same.</para>
 151   </refsect1>
 152
 153   <refsect1>
 154     <title>Return Value</title>
 155
 156     <para>
 157       On success, <function>sd_bus_add_match()</function> and the other calls return 0 or a positive integer. On
 158       failure, they return a negative errno-style error code.
 159     </para>
 160   </refsect1>
 161
 162   <refsect1>
 163     <title>Notes</title>
 164
 165     <para><function>sd_bus_add_match()</function> and the other functions described here are available as a shared
 166     library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
 167     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 168   </refsect1>
 169
 170   <refsect1>
 171     <title>See Also</title>
 172
 173     <para>
 174       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 175       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 176       <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 177       <citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 178       <citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 179     </para>
 180   </refsect1>
 181
 182 </refentry>