man/sd_bus_add_match.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright © 2016 Julian Orth
   9 -->
  10
  11 <refentry id="sd_bus_add_match" xmlns:xi="http://www.w3.org/2001/XInclude">
  12
  13   <refentryinfo>
  14     <title>sd_bus_add_match</title>
  15     <productname>systemd</productname>
  16   </refentryinfo>
  17
  18   <refmeta>
  19     <refentrytitle>sd_bus_add_match</refentrytitle>
  20     <manvolnum>3</manvolnum>
  21   </refmeta>
  22
  23   <refnamediv>
  24     <refname>sd_bus_add_match</refname>
  25     <refname>sd_bus_add_match_async</refname>
  26     <refname>sd_bus_match_signal</refname>
  27     <refname>sd_bus_match_signal_async</refname>
  28
  29     <refpurpose>Add a match rule for incoming message dispatching</refpurpose>
  30   </refnamediv>
  31
  32   <refsynopsisdiv>
  33     <funcsynopsis>
  34       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  35
  36       <funcprototype>
  37         <funcdef>typedef int (*<function>sd_bus_message_handler_t</function>)</funcdef>
  38         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  39         <paramdef>void *<parameter>userdata</parameter></paramdef>
  40         <paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
  41       </funcprototype>
  42
  43       <funcprototype>
  44         <funcdef>int <function>sd_bus_add_match</function></funcdef>
  45         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  46         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  47         <paramdef>const char *<parameter>match</parameter></paramdef>
  48         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  49         <paramdef>void *<parameter>userdata</parameter></paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>int <function>sd_bus_add_match_async</function></funcdef>
  54         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  55         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  56         <paramdef>const char *<parameter>match</parameter></paramdef>
  57         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  58         <paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
  59         <paramdef>void *<parameter>userdata</parameter></paramdef>
  60       </funcprototype>
  61
  62       <funcprototype>
  63         <funcdef>int <function>sd_bus_match_signal</function></funcdef>
  64         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  65         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  66         <paramdef>const char *<parameter>sender</parameter></paramdef>
  67         <paramdef>const char *<parameter>path</parameter></paramdef>
  68         <paramdef>const char *<parameter>interface</parameter></paramdef>
  69         <paramdef>const char *<parameter>member</parameter></paramdef>
  70         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  71         <paramdef>void *<parameter>userdata</parameter></paramdef>
  72       </funcprototype>
  73
  74       <funcprototype>
  75         <funcdef>int <function>sd_bus_match_signal_async</function></funcdef>
  76         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  77         <paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
  78         <paramdef>const char *<parameter>sender</parameter></paramdef>
  79         <paramdef>const char *<parameter>path</parameter></paramdef>
  80         <paramdef>const char *<parameter>interface</parameter></paramdef>
  81         <paramdef>const char *<parameter>member</parameter></paramdef>
  82         <paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
  83         <paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
  84         <paramdef>void *<parameter>userdata</parameter></paramdef>
  85       </funcprototype>
  86
  87     </funcsynopsis>
  88   </refsynopsisdiv>
  89
  90   <refsect1>
  91     <title>Description</title>
  92
  93     <para><function>sd_bus_add_match()</function> installs a match rule for messages received on the specified bus
  94     connection object <parameter>bus</parameter>. The syntax of the match rule expression passed in
  95     <parameter>match</parameter> is described in the <ulink
  96     url="https://dbus.freedesktop.org/doc/dbus-specification.html">D-Bus Specification</ulink>. The specified handler
  97     function <parameter>callback</parameter> is called for eaching incoming message matching the specified expression,
  98     the <parameter>userdata</parameter> parameter is passed as-is to the callback function. The match is installed
  99     synchronously when connected to a bus broker, i.e. the call sends a control message requested the match to be added
 100     to the broker and waits until the broker confirms the match has been installed successfully.</para>
 101
 102     <para><function>sd_bus_add_match_async()</function> operates very similar to
 103     <function>sd_bus_match_signal()</function>, however it installs the match asynchronously, in a non-blocking
 104     fashion: a request is sent to the broker, but the call does not wait for a response. The
 105     <parameter>install_callback</parameter> function is called when the response is later received, with the response
 106     message from the broker as parameter. If this function is specified as <constant>NULL</constant> a default
 107     implementation is used that terminates the bus connection should installing the match fail.</para>
 108
 109     <para><function>sd_bus_match_signal()</function> is very similar to <function>sd_bus_add_match()</function>, but
 110     only matches signals, and instead of a match expression accepts four parameters: <parameter>sender</parameter> (the
 111     service name of the sender), <parameter>path</parameter> (the object path of the emitting object),
 112     <parameter>interface</parameter> (the interface the signal belongs to), <parameter>member</parameter> (the signal
 113     name), from which the match string is internally generated. Optionally, these parameters may be specified as
 114     <constant>NULL</constant> in which case the relevant field of incoming signals is not tested.</para>
 115
 116     <para><function>sd_bus_match_signal_async()</function> combines the signal matching logic of
 117     <function>sd_bus_match_signal()</function> with the asynchronous behaviour of
 118     <function>sd_bus_add_match_async()</function>.</para>
 119
 120     <para>On success, and if non-<constant>NULL</constant>, the <parameter>slot</parameter> return parameter will be
 121     set to a slot object that may be used as a reference to the installed match, and may be utilized to remove it again
 122     at a later time with
 123     <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If specified
 124     as <constant>NULL</constant> the lifetime of the match is bound to the lifetime of the bus object itself, and the
 125     match is generally not removed independently. See
 126     <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
 127     details.</para>
 128
 129     <para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
 130     not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 131     on it. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call
 132     <citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to create a
 133     new reference.</para>
 134
 135     <para>If an error occurs during the callback invocation, the callback should return a negative error number
 136     (optionally, a more precise error may be returned in <parameter>ret_error</parameter>, as well). If it wants other
 137     callbacks that match the same rule to be called, it should return 0. Otherwise it should return a positive integer.
 138     </para>
 139
 140     <para>If the <parameter>bus</parameter> refers to a direct connection (i.e. not a bus connection, as set with
 141     <citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>) the
 142     match is only installed on the client side, and the synchronous and asynchronous functions operate the same.</para>
 143   </refsect1>
 144
 145   <refsect1>
 146     <title>Return Value</title>
 147
 148     <para>
 149       On success, <function>sd_bus_add_match()</function> and the other calls return 0 or a positive integer. On
 150       failure, they return a negative errno-style error code.
 151     </para>
 152   </refsect1>
 153
 154   <refsect1>
 155     <title>Notes</title>
 156
 157     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 158   </refsect1>
 159
 160   <refsect1>
 161     <title>See Also</title>
 162
 163     <para>
 164       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 165       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 166       <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 167       <citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 168       <citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 169       <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 170     </para>
 171   </refsect1>
 172
 173 </refentry>