systemd/man/sd_bus_message_open_container.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<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 over 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>

          <xi:include href="version-info.xml" xpointer="v246"/></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EBADMSG</constant></term>

          <listitem><para>Message <parameter>m</parameter> has invalid structure.</para>

          <xi:include href="version-info.xml" xpointer="v254"/></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENXIO</constant></term>

          <listitem><para>Message <parameter>m</parameter> does not have a container of type
          <parameter>type</parameter> at the current position, or the contents do not match
          <parameter>contents</parameter>.</para>

          <xi:include href="version-info.xml" xpointer="v254"/></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EPERM</constant></term>

          <listitem><para>The message <parameter>m</parameter> is already sealed.</para>

          <xi:include href="version-info.xml" xpointer="v246"/></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ESTALE</constant></term>

          <listitem><para>The message <parameter>m</parameter> is in an invalid state.</para>

          <xi:include href="version-info.xml" xpointer="v246"/></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ENOMEM</constant></term>

          <listitem><para>Memory allocation failed.</para>

          <xi:include href="version-info.xml" xpointer="v246"/></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>

          <xi:include href="version-info.xml" xpointer="v247"/></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><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_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink></member>
    </simplelist></para>
  </refsect1>

</refentry>