1<?xml version='1.0'?>
2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="sd_bus_message_open_container"
7          xmlns:xi="http://www.w3.org/2001/XInclude">
8
9  <refentryinfo>
10    <title>sd_bus_message_open_container</title>
11    <productname>systemd</productname>
12  </refentryinfo>
13
14  <refmeta>
15    <refentrytitle>sd_bus_message_open_container</refentrytitle>
16    <manvolnum>3</manvolnum>
17  </refmeta>
18
19  <refnamediv>
20    <refname>sd_bus_message_open_container</refname>
21    <refname>sd_bus_message_close_container</refname>
22    <refname>sd_bus_message_enter_container</refname>
23    <refname>sd_bus_message_exit_container</refname>
24
25    <refpurpose>Create and move between containers in D-Bus messages</refpurpose>
26  </refnamediv>
27
28  <refsynopsisdiv>
29    <funcsynopsis>
30      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
31
32      <funcprototype>
33        <funcdef>int sd_bus_message_open_container</funcdef>
34        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
35        <paramdef>char <parameter>type</parameter></paramdef>
36        <paramdef>const char *<parameter>contents</parameter></paramdef>
37      </funcprototype>
38
39      <funcprototype>
40        <funcdef>int sd_bus_message_close_container</funcdef>
41        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
42      </funcprototype>
43
44      <funcprototype>
45        <funcdef>int sd_bus_message_enter_container</funcdef>
46        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
47        <paramdef>char <parameter>type</parameter></paramdef>
48        <paramdef>const char *<parameter>contents</parameter></paramdef>
49      </funcprototype>
50
51      <funcprototype>
52        <funcdef>int sd_bus_message_exit_container</funcdef>
53        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
54      </funcprototype>
55    </funcsynopsis>
56  </refsynopsisdiv>
57
58  <refsect1>
59    <title>Description</title>
60
61    <para><function>sd_bus_message_open_container()</function> appends a new container to the message
62    <parameter>m</parameter>. After opening a new container, it can be filled with content using
63    <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>
64    and similar functions. Containers behave like a stack. To nest containers inside each other, call
65    <function>sd_bus_message_open_container()</function> multiple times without calling
66    <function>sd_bus_message_close_container()</function> in between. Each container will be nested inside the
67    previous container. <parameter>type</parameter> represents the container type and should be one of
68    <literal>r</literal>, <literal>a</literal>, <literal>v</literal> or <literal>e</literal> as described in
69    <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
70    Instead of literals, the corresponding constants <constant>SD_BUS_TYPE_STRUCT</constant>,
71    <constant>SD_BUS_TYPE_ARRAY</constant>, <constant>SD_BUS_TYPE_VARIANT</constant> or
72    <constant>SD_BUS_TYPE_DICT_ENTRY</constant> can also be used. <parameter>contents</parameter> describes
73    the type of the container's elements and should be a D-Bus type string following the rules described in
74    <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
75    </para>
76
77    <para><function>sd_bus_message_close_container()</function> closes the last container opened with
78    <function>sd_bus_message_open_container()</function>. On success, the write pointer of the message
79    <parameter>m</parameter> is positioned after the closed container in its parent container or in
80    <parameter>m</parameter> itself if there is no parent container.</para>
81
82    <para><function>sd_bus_message_enter_container()</function> enters the next container of the message
83    <parameter>m</parameter> for reading. It behaves mostly the same as
84    <function>sd_bus_message_open_container()</function>. Entering a container allows reading its contents
85    with
86    <citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>
87    and similar functions. <parameter>type</parameter> and <parameter>contents</parameter> are the same as in
88    <function>sd_bus_message_open_container()</function>.</para>
89
90    <para><function>sd_bus_message_exit_container()</function> exits the scope of the last container entered
91    with <function>sd_bus_message_enter_container()</function>. It behaves mostly the same as
92    <function>sd_bus_message_close_container()</function>. Note that
93    <function>sd_bus_message_exit_container()</function> may only be called after iterating through all
94    members of the container, i.e. reading or skipping them. Use
95    <citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>
96    to skip over felds of a container in order to be able to exit the container with
97    <function>sd_bus_message_exit_container()</function> without reading all members.</para>
98  </refsect1>
99
100  <refsect1>
101    <title>Return Value</title>
102
103    <para>On success, these functions return a non-negative integer.
104    <function>sd_bus_message_open_container()</function> and <function>sd_bus_message_close_container()</function>
105    return 0.
106    <function>sd_bus_message_enter_container()</function> returns 1 if it successfully opened a new container, and 0 if
107    that was not possible because the end of the currently open container or message was reached.
108    <function>sd_bus_message_exit_container()</function> returns 1 on success.
109    On failure, all of these functions return a negative errno-style error code.</para>
110
111    <refsect2>
112      <title>Errors</title>
113
114      <para>Returned errors may indicate the following problems:</para>
115
116      <variablelist>
117        <varlistentry>
118          <term><constant>-EINVAL</constant></term>
119
120          <listitem><para><parameter>m</parameter> or <parameter>contents</parameter> are
121          <constant>NULL</constant> or <parameter>type</parameter> is invalid.</para></listitem>
122        </varlistentry>
123
124        <varlistentry>
125          <term><constant>-EPERM</constant></term>
126
127          <listitem><para>The message <parameter>m</parameter> is already sealed.</para></listitem>
128        </varlistentry>
129
130        <varlistentry>
131          <term><constant>-ESTALE</constant></term>
132
133          <listitem><para>The message <parameter>m</parameter> is in an invalid state.</para></listitem>
134        </varlistentry>
135
136        <varlistentry>
137          <term><constant>-ENOMEM</constant></term>
138
139          <listitem><para>Memory allocation failed.</para></listitem>
140        </varlistentry>
141
142        <varlistentry>
143          <term><constant>-EBUSY</constant></term>
144
145          <listitem><para><function>sd_bus_message_exit_container()</function> was called but there are
146          unread members left in the container.</para></listitem>
147        </varlistentry>
148      </variablelist>
149    </refsect2>
150  </refsect1>
151
152  <xi:include href="libsystemd-pkgconfig.xml" />
153
154  <refsect1>
155    <title>Examples</title>
156
157    <example>
158      <title>Append an array of strings to a message</title>
159
160      <programlisting><xi:include href="sd-bus-container-append.c" parse="text" /></programlisting>
161    </example>
162
163    <example>
164      <title>Read an array of strings from a message</title>
165
166      <programlisting><xi:include href="sd-bus-container-read.c" parse="text" /></programlisting>
167    </example>
168  </refsect1>
169
170  <refsect1>
171    <title>See Also</title>
172
173    <para>
174      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
175      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
176      <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
177      <citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
178      <citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
179      <ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
180    </para>
181  </refsect1>
182
183</refentry>
184