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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 <systemd/sd-bus.h></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 fields 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>
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