man/sd_bus_message_append.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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<refentry id="sd_bus_message_append" conditional="ENABLE_KDBUS"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_bus_message_append</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>A monkey with a typewriter</contrib>
        <firstname>Zbigniew</firstname>
        <surname>Jędrzejewski-Szmek</surname>
        <email>zbyszek@in.waw.pl</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_message_append</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_message_append</refname>

    <refpurpose>Attach parts of message based on a format string</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int sd_bus_message_append</funcdef>
        <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
        <paramdef>const char *<parameter>types</parameter></paramdef>
        <paramdef>...</paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>The <function>sd_bus_message_append</function> function appends
    a sequence of items to message <parameter>m</parameter>. The
    format string <parameter>types</parameter> describes the types of
    arguments that follow.</para>

    <para>The format string is composed of the elements shown in the
    table below. It contains zero or more single "complete types".
    Each complete type may be one of the basic types or a fully
    described container type. A container type may be a structure, a
    variant type code, an array with its element type, or a dictionary
    with its entry type. The format string is
    <constant>NUL</constant>-terminated.</para>

    <para>In case of a basic type, one argument of the corresponding
    type is expected.</para>

    <para>A structure is denoted by a sequence of complete types
    between <literal>(</literal> and <literal>)</literal>. This
    sequence cannot be empty — it must contain at least one type.
    Arguments corresponding to this nested sequence follow the same
    rules as if they were not nested.</para>

    <para>A variant is denoted by <literal>v</literal>. Correspoding
    arguments must include a format string denoting a complete type,
    and following that, arguments corresponding to the specified type.
    </para>

    <para>An array is denoted by <literal>a</literal> followed by a
    complete type. Corresponding arguments must include the size of
    the array, and then repeated this number of times, arguments
    corresponding to the nested type.</para>

    <para>A dictionary is an array of dictionary entries, denoted by
    <literal>a</literal> followed by a pair of complete types between
    <literal>{</literal> and <literal>}</literal>. The first of those
    types must be a basic type. Corresponding arguments must include
    the size of the dictionary, and then repeated this number of
    times, arguments corresponding to each of the two nested
    types.</para>

    <table>
      <title>Item format specifiers</title>

      <tgroup cols='4'>
        <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers'])//colspec" />
        <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//thead)" />

        <tbody>
          <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />

          <row>
            <entry><literal>a</literal></entry>
            <entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>
            <entry>array</entry>
            <entry>determined by array type and size</entry>
          </row>

          <row>
            <entry><literal>v</literal></entry>
            <entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>
            <entry>variant</entry>
            <entry>determined by the type argument</entry>
          </row>

          <row>
            <entry><literal>(</literal></entry>
            <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>
            <entry>array start</entry>
            <entry morerows="1">determined by the nested types</entry>
          </row>
          <row>
            <entry><literal>)</literal></entry>
            <entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>
            <entry>array end</entry>
          </row>

          <row>
            <entry><literal>{</literal></entry>
            <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>
            <entry>dictionary entry start</entry>
            <entry morerows="1">determined by the nested types</entry>
          </row>
          <row>
            <entry><literal>}</literal></entry>
            <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>
            <entry>dictionary entry end</entry>
          </row>
       </tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    <title>Types string grammar</title>

    <programlisting>types ::= complete_type*
complete_type ::= basic_type | variant | structure | array | dictionary
basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" |
               "b" | "h" |
               "s" | "o" | "g"
variant ::= "v"
structure ::= "(" complete_type+ ")"
array ::= "a" complete_type
dictionary ::= "a" "{" basic_type complete_type "}"
</programlisting>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <para>Append a single basic type (the string <literal>a string</literal>):
    </para>

    <programlisting>sd_bus_message *m;
...
sd_bus_message_append(m, "s", "a string");</programlisting>

    <para>Append all types of integers:</para>

    <programlisting>uint8_t y = 1;
int16_t n = 2;
uint16_t q = 3;
int32_t i = 4;
uint32_t u = 5;
int32_t x = 6;
uint32_t t = 7;
double d = 8.0;
sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);</programlisting>

     <para>Append a structure composed of string and a D-Bus path:</para>

     <programlisting>sd_bus_message_append(m, "(so)", "a string", "/a/path");
</programlisting>

     <para>Append an array of UNIX file descriptors:</para>

     <programlisting>sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
</programlisting>

     <para>Append a variant, with the real type "g" (signature),
     and value "sdbusisgood":</para>

     <programlisting>sd_bus_message_append(m, "v", "g", "sdbusisgood");</programlisting>

     <para>Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:
     </para>

     <programlisting>sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);
     </programlisting>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On success, this call returns 0 or a positive
    integer. On failure, this call returns a negative
    errno-style error code.</para>
  </refsect1>

  <xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />

  <refsect1>
    <title>Notes</title>

    <para><function>sd_bus_open_user()</function> and other functions
    described here are available as a shared library, which can be
    compiled and linked to with the
    <constant>libsystemd-bus</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    file.</para>
  </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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>