man/sd_bus_message_append.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2014 Zbigniew Jędrzejewski-Szmek
  11 -->
  12
  13 <refentry id="sd_bus_message_append"
  14           xmlns:xi="http://www.w3.org/2001/XInclude">
  15
  16   <refentryinfo>
  17     <title>sd_bus_message_append</title>
  18     <productname>systemd</productname>
  19
  20     <authorgroup>
  21       <author>
  22         <contrib>A monkey with a typewriter</contrib>
  23         <firstname>Zbigniew</firstname>
  24         <surname>Jędrzejewski-Szmek</surname>
  25         <email>zbyszek@in.waw.pl</email>
  26       </author>
  27     </authorgroup>
  28   </refentryinfo>
  29
  30   <refmeta>
  31     <refentrytitle>sd_bus_message_append</refentrytitle>
  32     <manvolnum>3</manvolnum>
  33   </refmeta>
  34
  35   <refnamediv>
  36     <refname>sd_bus_message_append</refname>
  37     <refname>sd_bus_message_appendv</refname>
  38
  39     <refpurpose>Attach fields to a D-Bus message based on a type
  40     string</refpurpose>
  41   </refnamediv>
  42
  43   <refsynopsisdiv>
  44     <funcsynopsis>
  45       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  46
  47       <funcprototype>
  48         <funcdef>int sd_bus_message_append</funcdef>
  49         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  50         <paramdef>const char *<parameter>types</parameter></paramdef>
  51         <paramdef>…</paramdef>
  52       </funcprototype>
  53
  54       <funcprototype>
  55           <funcdef>int sd_bus_message_appendv</funcdef>
  56           <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  57           <paramdef>const char *<parameter>types</parameter></paramdef>
  58           <paramdef>va_list <parameter>ap</parameter></paramdef>
  59       </funcprototype>
  60
  61     </funcsynopsis>
  62   </refsynopsisdiv>
  63
  64   <refsect1>
  65     <title>Description</title>
  66
  67     <para>The <function>sd_bus_message_append()</function> function
  68     appends a sequence of fields to the D-Bus message object
  69     <parameter>m</parameter>. The type string
  70     <parameter>types</parameter> describes the types of the field
  71     arguments that follow. For each type specified in the type string,
  72     one or more arguments need to be specified, in the same order as
  73     declared in the type string.</para>
  74
  75     <para>The type string is composed of the elements shown in the
  76     table below. It contains zero or more single "complete types".
  77     Each complete type may be one of the basic types or a fully
  78     described container type. A container type may be a structure with
  79     the contained types, a variant, an array with its element type, or
  80     a dictionary entry with the contained types. The type string is
  81     <constant>NUL</constant>-terminated.</para>
  82
  83     <para>In case of a basic type, one argument of the corresponding
  84     type is expected.</para>
  85
  86     <para>A structure is denoted by a sequence of complete types
  87     between <literal>(</literal> and <literal>)</literal>. This
  88     sequence cannot be empty — it must contain at least one type.
  89     Arguments corresponding to this nested sequence follow the same
  90     rules as if they were not nested.</para>
  91
  92     <para>A variant is denoted by <literal>v</literal>. Corresponding
  93     arguments must begin with a type string denoting a complete type,
  94     and following that, arguments corresponding to the specified type.
  95     </para>
  96
  97     <para>An array is denoted by <literal>a</literal> followed by a
  98     complete type. Corresponding arguments must begin with the number of
  99     entries in the array, followed by the entries themselves,
 100     matching the element type of the array.</para>
 101
 102     <para>A dictionary is an array of dictionary entries, denoted by
 103     <literal>a</literal> followed by a pair of complete types between
 104     <literal>{</literal> and <literal>}</literal>. The first of those
 105     types must be a basic type. Corresponding arguments must begin
 106     with the number of dictionary entries, followed by a pair of
 107     values for each entry matching the element type of
 108     the dictionary entries.</para>
 109
 110     <para>The <function>sd_bus_message_appendv()</function> is equivalent to
 111     the function <function>sd_bus_message_append()</function>,
 112     except that it is called with a <literal>va_list</literal> instead of
 113     a variable number of arguments. This function does not call the
 114     <function>va_end()</function> macro. Because it invokes the
 115     <function>va_arg()</function> macro, the value of ap
 116     is undefined after the call.</para>
 117
 118     <para>For further details on the D-Bus type system, please consult
 119     the <ulink
 120     url="http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
 121     Specification</ulink>.</para>
 122
 123     <table>
 124       <title>Item type specifiers</title>
 125
 126       <tgroup cols='5'>
 127         <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers'])//colspec" />
 128         <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//thead)" />
 129
 130         <tbody>
 131           <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />
 132
 133           <row>
 134             <entry><literal>a</literal></entry>
 135             <entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>
 136             <entry>array</entry>
 137             <entry>determined by array type and size</entry>
 138             <entry>int, followed by array contents</entry>
 139           </row>
 140
 141           <row>
 142             <entry><literal>v</literal></entry>
 143             <entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>
 144             <entry>variant</entry>
 145             <entry>determined by the type argument</entry>
 146             <entry>signature string, followed by variant contents</entry>
 147           </row>
 148
 149           <row>
 150             <entry><literal>(</literal></entry>
 151             <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>
 152             <entry>array start</entry>
 153             <entry morerows="1">determined by the nested types</entry>
 154             <entry morerows="1">structure contents</entry>
 155           </row>
 156           <row>
 157             <entry><literal>)</literal></entry>
 158             <entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>
 159             <entry>array end</entry>
 160           </row>
 161
 162           <row>
 163             <entry><literal>{</literal></entry>
 164             <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>
 165             <entry>dictionary entry start</entry>
 166             <entry morerows="1">determined by the nested types</entry>
 167             <entry morerows="1">dictionary contents</entry>
 168           </row>
 169           <row>
 170             <entry><literal>}</literal></entry>
 171             <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>
 172             <entry>dictionary entry end</entry>
 173           </row>
 174        </tbody>
 175       </tgroup>
 176     </table>
 177
 178     <para>For types "s" and "g" (unicode string or signature), the pointer may be
 179     <constant>NULL</constant>, which is equivalent to an empty string. See
 180     <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 181     for the precise interpretation of those and other types.</para>
 182
 183   </refsect1>
 184
 185   <refsect1>
 186     <title>Types String Grammar</title>
 187
 188     <programlisting>types ::= complete_type*
 189 complete_type ::= basic_type | variant | structure | array | dictionary
 190 basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" |
 191                "b" | "h" |
 192                "s" | "o" | "g"
 193 variant ::= "v"
 194 structure ::= "(" complete_type+ ")"
 195 array ::= "a" complete_type
 196 dictionary ::= "a" "{" basic_type complete_type "}"
 197 </programlisting>
 198   </refsect1>
 199
 200   <refsect1>
 201     <title>Examples</title>
 202
 203     <para>Append a single basic type (the string <literal>a string</literal>):
 204     </para>
 205
 206     <programlisting>sd_bus_message *m;
 207 …
 208 sd_bus_message_append(m, "s", "a string");</programlisting>
 209
 210     <para>Append all types of integers:</para>
 211
 212     <programlisting>uint8_t y = 1;
 213 int16_t n = 2;
 214 uint16_t q = 3;
 215 int32_t i = 4;
 216 uint32_t u = 5;
 217 int32_t x = 6;
 218 uint32_t t = 7;
 219 double d = 8.0;
 220 sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);</programlisting>
 221
 222      <para>Append a structure composed of a string and a D-Bus path:</para>
 223
 224      <programlisting>sd_bus_message_append(m, "(so)", "a string", "/a/path");
 225 </programlisting>
 226
 227      <para>Append an array of UNIX file descriptors:</para>
 228
 229      <programlisting>sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
 230 </programlisting>
 231
 232      <para>Append a variant, with the real type "g" (signature),
 233      and value "sdbusisgood":</para>
 234
 235      <programlisting>sd_bus_message_append(m, "v", "g", "sdbusisgood");</programlisting>
 236
 237      <para>Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:
 238      </para>
 239
 240      <programlisting>sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);
 241      </programlisting>
 242   </refsect1>
 243
 244   <refsect1>
 245     <title>Return Value</title>
 246
 247     <para>On success, these functions return 0 or a positive
 248     integer. On failure, these functions return a negative
 249     errno-style error code.</para>
 250   </refsect1>
 251
 252   <xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
 253
 254   <refsect1>
 255     <title>Notes</title>
 256
 257     <para><function>sd_bus_open_user()</function> and other functions
 258     described here are available as a shared library, which can be
 259     compiled and linked to with the
 260     <constant>libsystemd-bus</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 261     file.</para>
 262   </refsect1>
 263
 264   <refsect1>
 265     <title>See Also</title>
 266
 267     <para>
 268       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 269       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 270       <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 271       <citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 272     </para>
 273   </refsect1>
 274
 275 </refentry>