<?xml version='1.0'?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> <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 <systemd/sd-bus.h></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>History</title> <para><function>sd_bus_message_new_method_call()</function> and <function>sd_bus_message_new_method_return()</function> were added in version 246.</para> </refsect1> <refsect1> <title>See Also</title> <para><simplelist type="inline"> <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> <member><citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> <member><citerefentry><refentrytitle>sd_bus_call</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> <member><citerefentry><refentrytitle>sd_bus_call_method</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> <member><citerefentry><refentrytitle>sd_bus_path_encode</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> </simplelist></para> </refsect1> </refentry>