man/sd_bus_message_new_method_call.xml

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<refentry id="sd_bus_message_new_method_call"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_bus_message_new_method_call</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_message_new_method_call</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_message_new_method_call</refname>
    <refname>sd_bus_message_new_method_return</refname>

    <refpurpose>Create a method call message</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_bus_message_new_method_call</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
        <paramdef>const char *<parameter>destination</parameter></paramdef>
        <paramdef>const char *<parameter>path</parameter></paramdef>
        <paramdef>const char *<parameter>interface</parameter></paramdef>
        <paramdef>const char *<parameter>member</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_message_new_method_return</function></funcdef>
        <paramdef>sd_bus_message *<parameter>call</parameter></paramdef>
        <paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>The <function>sd_bus_message_new_method_call()</function> function creates a new bus
    message object that encapsulates a D-Bus method call, and returns it in the
    <parameter>m</parameter> output parameter. The call will be made on the destination
    <parameter>destination</parameter>, path <parameter>path</parameter>, on the interface
    <parameter>interface</parameter>, member <parameter>member</parameter>.</para>

    <para>Briefly, the <emphasis>destination</emphasis> is a dot-separated name that identifies a
    service connected to the bus. The <emphasis>path</emphasis> is a slash-separated identifier of
    an object within the destination that resembles a file system path. The meaning of this path is
    defined by the destination. The <emphasis>interface</emphasis> is a dot-separated name that
    resembles a Java interface name that identifies a group of methods and signals supported by the
    object identified by path. Methods and signals are collectively called
    <emphasis>members</emphasis> and are identified by a simple name composed of ASCII letters,
    numbers, and underscores. See the <ulink
    url="https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts">D-Bus Tutorial</ulink> for an
    in-depth explanation.</para>

    <para>The <parameter>destination</parameter> parameter may be <constant>NULL</constant>. The
    <parameter>interface</parameter> parameter may be <constant>NULL</constant>, if the destination
    has only a single member with the given name and there is no ambiguity if the interface name is
    omitted.</para>

    <para>Note that this is a low level interface. See
    <citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for a more convenient way of calling D-Bus methods.</para>

    <para>The <function>sd_bus_message_new_method_return()</function> function creates a new bus
    message object that is a reply to the method call <parameter>call</parameter> and returns it in
    the <parameter>m</parameter> output parameter. The <parameter>call</parameter> parameter must be
    a method call message. The sender of <parameter>call</parameter> is used as the destination.
    </para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On success, these functions return a non-negative integer. On failure, they return a
    negative errno-style error code.</para>

    <refsect2 id='errors'>
      <title>Errors</title>

      <para>Returned errors may indicate the following problems:</para>

      <variablelist>
        <varlistentry>
          <term><constant>-EINVAL</constant></term>

          <listitem><para>The output parameter <parameter>m</parameter> is
          <constant>NULL</constant>.</para>

          <para>The <parameter>destination</parameter> parameter is non-null and is not a valid D-Bus
          service name (<literal>org.somewhere.Something</literal>), the <parameter>path</parameter>
          parameter is not a valid D-Bus path (<literal>/an/object/path</literal>), the
          <parameter>interface</parameter> parameter is non-null and is not a valid D-Bus interface
          name (<literal>an.interface.name</literal>), or the <parameter>member</parameter> parameter
          is not a valid D-Bus member (<literal>Name</literal>).</para>

          <para>The <parameter>call</parameter> parameter is not a method call object.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOTCONN</constant></term>

          <listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or
          the bus is not connected.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOMEM</constant></term>

          <listitem><para>Memory allocation failed.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EPERM</constant></term>

          <listitem>
            <para>The <parameter>call</parameter> parameter is not sealed.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EOPNOTSUPP</constant></term>

          <listitem>
            <para>The <parameter>call</parameter> message does not have a cookie.</para>
          </listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

  <xi:include href="libsystemd-pkgconfig.xml" />

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Make a call to a D-Bus method that takes a single parameter</title>

      <programlisting><xi:include href="print-unit-path.c" parse="text" /></programlisting>
      <para>This defines a minimally useful program that will open a connection to the bus, create a
      message object, send it, wait for the reply, and finally extract and print the answer. It does
      error handling and proper memory management.</para>
    </example>
  </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_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_path_encode</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>