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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_bus_message_open_container"
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_bus_message_open_container</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_bus_message_open_container</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_bus_message_open_container</refname>
+ <refname>sd_bus_message_close_container</refname>
+ <refname>sd_bus_message_enter_container</refname>
+ <refname>sd_bus_message_exit_container</refname>
+
+ <refpurpose>Create and move between containers in D-Bus messages</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int sd_bus_message_open_container</funcdef>
+ <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
+ <paramdef>char <parameter>type</parameter></paramdef>
+ <paramdef>const char *<parameter>contents</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int sd_bus_message_close_container</funcdef>
+ <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int sd_bus_message_enter_container</funcdef>
+ <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
+ <paramdef>char <parameter>type</parameter></paramdef>
+ <paramdef>const char *<parameter>contents</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int sd_bus_message_exit_container</funcdef>
+ <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_bus_message_open_container()</function> appends a new container to the message
+ <parameter>m</parameter>. After opening a new container, it can be filled with content using
+ <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ and similar functions. Containers behave like a stack. To nest containers inside each other, call
+ <function>sd_bus_message_open_container()</function> multiple times without calling
+ <function>sd_bus_message_close_container()</function> in between. Each container will be nested inside the
+ previous container. <parameter>type</parameter> represents the container type and should be one of
+ <literal>r</literal>, <literal>a</literal>, <literal>v</literal> or <literal>e</literal> as described in
+ <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+ Instead of literals, the corresponding constants <constant>SD_BUS_TYPE_STRUCT</constant>,
+ <constant>SD_BUS_TYPE_ARRAY</constant>, <constant>SD_BUS_TYPE_VARIANT</constant> or
+ <constant>SD_BUS_TYPE_DICT_ENTRY</constant> can also be used. <parameter>contents</parameter> describes
+ the type of the container's elements and should be a D-Bus type string following the rules described in
+ <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+ </para>
+
+ <para><function>sd_bus_message_close_container()</function> closes the last container opened with
+ <function>sd_bus_message_open_container()</function>. On success, the write pointer of the message
+ <parameter>m</parameter> is positioned after the closed container in its parent container or in
+ <parameter>m</parameter> itself if there is no parent container.</para>
+
+ <para><function>sd_bus_message_enter_container()</function> enters the next container of the message
+ <parameter>m</parameter> for reading. It behaves mostly the same as
+ <function>sd_bus_message_open_container()</function>. Entering a container allows reading its contents
+ with
+ <citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ and similar functions. <parameter>type</parameter> and <parameter>contents</parameter> are the same as in
+ <function>sd_bus_message_open_container()</function>.</para>
+
+ <para><function>sd_bus_message_exit_container()</function> exits the scope of the last container entered
+ with <function>sd_bus_message_enter_container()</function>. It behaves mostly the same as
+ <function>sd_bus_message_close_container()</function>. Note that
+ <function>sd_bus_message_exit_container()</function> may only be called after iterating through all
+ members of the container, i.e. reading or skipping them. Use
+ <citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ to skip over felds of a container in order to be able to exit the container with
+ <function>sd_bus_message_exit_container()</function> without reading all members.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>On success, these functions return a non-negative integer.
+ <function>sd_bus_message_open_container()</function> and <function>sd_bus_message_close_container()</function>
+ return 0.
+ <function>sd_bus_message_enter_container()</function> returns 1 if it successfully opened a new container, and 0 if
+ that was not possible because the end of the currently open container or message was reached.
+ <function>sd_bus_message_exit_container()</function> returns 1 on success.
+ On failure, all of these functions return a negative errno-style error code.</para>
+
+ <refsect2>
+ <title>Errors</title>
+
+ <para>Returned errors may indicate the following problems:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><constant>-EINVAL</constant></term>
+
+ <listitem><para><parameter>m</parameter> or <parameter>contents</parameter> are
+ <constant>NULL</constant> or <parameter>type</parameter> is invalid.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-EPERM</constant></term>
+
+ <listitem><para>The message <parameter>m</parameter> is already sealed.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ESTALE</constant></term>
+
+ <listitem><para>The message <parameter>m</parameter> is in an invalid state.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ENOMEM</constant></term>
+
+ <listitem><para>Memory allocation failed.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-EBUSY</constant></term>
+
+ <listitem><para><function>sd_bus_message_exit_container()</function> was called but there are
+ unread members left in the container.</para></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
+ </refsect1>
+
+ <xi:include href="libsystemd-pkgconfig.xml" />
+
+ <refsect1>
+ <title>Examples</title>
+
+ <example>
+ <title>Append an array of strings to a message</title>
+
+ <programlisting><xi:include href="sd-bus-container-append.c" parse="text" /></programlisting>
+ </example>
+
+ <example>
+ <title>Read an array of strings from a message</title>
+
+ <programlisting><xi:include href="sd-bus-container-read.c" parse="text" /></programlisting>
+ </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_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
+ </para>
+ </refsect1>
+
+</refentry>