man/sd_bus_message_open_container.xml

   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>