systemd/man/sd_bus_add_match.xml

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<refentry id="sd_bus_add_match">

  <refentryinfo>
    <title>sd_bus_add_match</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <firstname>Julian</firstname>
        <surname>Orth</surname>
        <email>ju.orth@gmail.com</email>
      </author>
    </authorgroup>
  </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 &lt;systemd/sd-bus.h&gt;</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> is 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 cannot be removed independently.</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>
    </para>
  </refsect1>

</refentry>