man/sd_bus_message_append.xml

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