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