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