man: describe functions for appending to messages

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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+This file is part of systemd.
+
+Copyright 2014 Zbigniew Jędrzejewski-Szmek
+
+systemd is free software; you can redistribute it and/or modify it
+under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+systemd is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<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>Function <function>sd_bus_message_append</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>