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<refentry id="sd_bus_add_match">
<refentryinfo>
<title>sd_bus_add_match</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_add_match</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_add_match</refname>
<refname>sd_bus_add_match_async</refname>
<refname>sd_bus_match_signal</refname>
<refname>sd_bus_match_signal_async</refname>
<refpurpose>Add a match rule for incoming message dispatching</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>typedef int (*<function>sd_bus_message_handler_t</function>)</funcdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
<paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_add_match</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
<paramdef>const char *<parameter>match</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_add_match_async</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
<paramdef>const char *<parameter>match</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_match_signal</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
<paramdef>const char *<parameter>sender</parameter></paramdef>
<paramdef>const char *<parameter>path</parameter></paramdef>
<paramdef>const char *<parameter>interface</parameter></paramdef>
<paramdef>const char *<parameter>member</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_match_signal_async</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
<paramdef>const char *<parameter>sender</parameter></paramdef>
<paramdef>const char *<parameter>path</parameter></paramdef>
<paramdef>const char *<parameter>interface</parameter></paramdef>
<paramdef>const char *<parameter>member</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>install_callback</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_bus_add_match()</function> installs a match rule for messages received on the specified bus
connection object <parameter>bus</parameter>. The syntax of the match rule expression passed in
<parameter>match</parameter> is described in the <ulink
url="https://dbus.freedesktop.org/doc/dbus-specification.html">D-Bus Specification</ulink>. The specified handler
function <parameter>callback</parameter> is called for eaching incoming message matching the specified expression,
the <parameter>userdata</parameter> parameter is passed as-is to the callback function. The match is installed
synchronously when connected to a bus broker, i.e. the call sends a control message requested the match to be added
to the broker and waits until the broker confirms the match has been installed successfully.</para>
<para><function>sd_bus_add_match_async()</function> operates very similar to
<function>sd_bus_match_signal()</function>, however it installs the match asynchronously, in a non-blocking
fashion: a request is sent to the broker, but the call does not wait for a response. The
<parameter>install_callback</parameter> function is called when the response is later received, with the response
message from the broker as parameter. If this function is specified as <constant>NULL</constant> a default
implementation is used that terminates the bus connection should installing the match fail.</para>
<para><function>sd_bus_match_signal()</function> is very similar to <function>sd_bus_add_match()</function>, but
only matches signals, and instead of a match expression accepts four parameters: <parameter>sender</parameter> (the
service name of the sender), <parameter>path</parameter> (the object path of the emitting object),
<parameter>interface</parameter> (the interface the signal belongs to), <parameter>member</parameter> (the signal
name), from which the match string is internally generated. Optionally, these parameters may be specified as
<constant>NULL</constant> in which case the relevant field of incoming signals is not tested.</para>
<para><function>sd_bus_match_signal_async()</function> combines the signal matching logic of
<function>sd_bus_match_signal()</function> with the asynchronous behaviour of
<function>sd_bus_add_match_async()</function>.</para>
<para>On success, and if non-<constant>NULL</constant>, the <parameter>slot</parameter> return parameter will be
set to a slot object that may be used as a reference to the installed match, and may be utilized to remove it again
at a later time with
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If specified
as <constant>NULL</constant> the lifetime of the match is bound to the lifetime of the bus object itself, and the
match is generally not removed independently. See
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
details.</para>
<para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
on it. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call
<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry> to create a
new reference.</para>
<para>If an error occurs during the callback invocation, the callback should return a negative error number
(optionally, a more precise error may be returned in <parameter>ret_error</parameter>, as well). If it wants other
callbacks that match the same rule to be called, it should return 0. Otherwise it should return a positive integer.
</para>
<para>If the <parameter>bus</parameter> refers to a direct connection (i.e. not a bus connection, as set with
<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>) the
match is only installed on the client side, and the synchronous and asynchronous functions operate the same.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>
On success, <function>sd_bus_add_match()</function> and the other calls return 0 or a positive integer. On
failure, they return a negative errno-style error code.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para><function>sd_bus_add_match()</function> and the other functions described here are available as a shared
library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>