man/sd_bus_message_append.xml

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