man/sd_bus_message_append_basic.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   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_basic">
  14
  15   <refentryinfo>
  16     <title>sd_bus_message_append_basic</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>A monkey with a typewriter</contrib>
  22         <firstname>Zbigniew</firstname>
  23         <surname>Jędrzejewski-Szmek</surname>
  24         <email>zbyszek@in.waw.pl</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_bus_message_append_basic</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_bus_message_append_basic</refname>
  36
  37     <refpurpose>Attach a single field to a message</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <funcsynopsis>
  42       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  43
  44       <funcprototype>
  45         <funcdef>int sd_bus_message_append_basic</funcdef>
  46         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  47         <paramdef>char <parameter>type</parameter></paramdef>
  48         <paramdef>const void *<parameter>p</parameter></paramdef>
  49       </funcprototype>
  50     </funcsynopsis>
  51   </refsynopsisdiv>
  52
  53   <refsect1>
  54     <title>Description</title>
  55
  56     <para><function>sd_bus_message_append_basic()</function> appends a
  57     single field to the message <parameter>m</parameter>. The
  58     parameter <parameter>type</parameter> determines how the pointer
  59     <parameter>p</parameter> is interpreted.
  60     <parameter>type</parameter> must be one of the basic types as
  61     defined by the <ulink
  62     url="http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types">Basic
  63     Types</ulink> section of the D-Bus specification, and listed in
  64     the table below.
  65     </para>
  66
  67     <table id='format-specifiers'>
  68       <title>Item type specifiers</title>
  69
  70       <tgroup cols='5'>
  71         <colspec colname='specifier' />
  72         <colspec colname='constant' />
  73         <colspec colname='description' />
  74         <colspec colname='size' />
  75         <colspec colname='ctype' />
  76         <thead>
  77           <row>
  78             <entry>Specifier</entry>
  79             <entry>Constant</entry>
  80             <entry>Description</entry>
  81             <entry>Size</entry>
  82             <entry>Expected C Type</entry>
  83           </row>
  84         </thead>
  85         <tbody>
  86           <row>
  87             <entry><literal>y</literal></entry>
  88             <entry><constant>SD_BUS_TYPE_BYTE</constant></entry>
  89             <entry>unsigned integer</entry>
  90             <entry>1 byte</entry>
  91             <entry>uint8_t</entry>
  92           </row>
  93
  94           <row>
  95             <entry><literal>b</literal></entry>
  96             <entry><constant>SD_BUS_TYPE_BOOLEAN</constant></entry>
  97             <entry>boolean</entry>
  98             <entry>4 bytes</entry>
  99             <entry>int</entry>
 100           </row>
 101
 102           <row>
 103             <entry><literal>n</literal></entry>
 104             <entry><constant>SD_BUS_TYPE_INT16</constant></entry>
 105             <entry>signed integer</entry>
 106             <entry>2 bytes</entry>
 107             <entry>int16_t</entry>
 108           </row>
 109
 110           <row>
 111             <entry><literal>q</literal></entry>
 112             <entry><constant>SD_BUS_TYPE_UINT16</constant></entry>
 113             <entry>unsigned integer</entry>
 114             <entry>2 bytes</entry>
 115             <entry>uint16_t</entry>
 116           </row>
 117
 118           <row>
 119             <entry><literal>i</literal></entry>
 120             <entry><constant>SD_BUS_TYPE_INT32</constant></entry>
 121             <entry>signed integer</entry>
 122             <entry>4 bytes</entry>
 123             <entry>int32_t</entry>
 124           </row>
 125
 126           <row>
 127             <entry><literal>u</literal></entry>
 128             <entry><constant>SD_BUS_TYPE_UINT32</constant></entry>
 129             <entry>unsigned integer</entry>
 130             <entry>4 bytes</entry>
 131             <entry>uint32_t</entry>
 132           </row>
 133
 134           <row>
 135             <entry><literal>x</literal></entry>
 136             <entry><constant>SD_BUS_TYPE_INT64</constant></entry>
 137             <entry>signed integer</entry>
 138             <entry>8 bytes</entry>
 139             <entry>int64_t</entry>
 140           </row>
 141
 142           <row>
 143             <entry><literal>t</literal></entry>
 144             <entry><constant>SD_BUS_TYPE_UINT64</constant></entry>
 145             <entry>unsigned integer</entry>
 146             <entry>8 bytes</entry>
 147             <entry>uint64_t</entry>
 148           </row>
 149
 150           <row>
 151             <entry><literal>d</literal></entry>
 152             <entry><constant>SD_BUS_TYPE_DOUBLE</constant></entry>
 153             <entry>floating-point</entry>
 154             <entry>8 bytes</entry>
 155             <entry>double</entry>
 156           </row>
 157
 158           <row>
 159             <entry><literal>s</literal></entry>
 160             <entry><constant>SD_BUS_TYPE_STRING</constant></entry>
 161             <entry>Unicode string</entry>
 162             <entry>variable</entry>
 163             <entry>char[]</entry>
 164           </row>
 165
 166           <row>
 167             <entry><literal>o</literal></entry>
 168             <entry><constant>SD_BUS_TYPE_OBJECT_PATH</constant></entry>
 169             <entry>object path</entry>
 170             <entry>variable</entry>
 171             <entry>char[]</entry>
 172           </row>
 173
 174           <row>
 175             <entry><literal>g</literal></entry>
 176             <entry><constant>SD_BUS_TYPE_SIGNATURE</constant></entry>
 177             <entry>signature</entry>
 178             <entry>variable</entry>
 179             <entry>char[]</entry>
 180           </row>
 181
 182           <row>
 183             <entry><literal>h</literal></entry>
 184             <entry><constant>SD_BUS_TYPE_UNIX_FD</constant></entry>
 185             <entry>UNIX file descriptor</entry>
 186             <entry>4 bytes</entry>
 187             <entry>int</entry>
 188           </row>
 189        </tbody>
 190       </tgroup>
 191     </table>
 192
 193     <para>The value of the parameter is copied into a memory area held
 194     by the message object, stays in the possession of the caller and
 195     may hence be freely changed after this call without affecting the
 196     bus message it has been added to. If <parameter>type</parameter>
 197     is <literal>h</literal> (UNIX file descriptor), the descriptor is
 198     duplicated by this call and the passed descriptor stays in
 199     possession of the caller.</para>
 200
 201     <para>For types <literal>s</literal>, <literal>o</literal>, and
 202     <literal>g</literal>, the parameter <parameter>p</parameter> is
 203     interpreted as a pointer to a <constant>NUL</constant>-terminated
 204     character sequence. As a special case, a <constant>NULL</constant>
 205     pointer is interpreted as an empty string. The string should be
 206     valid Unicode string encoded as UTF-8. In case of the two latter
 207     types, the additional requirements for a D-Bus object path or
 208     type signature should be satisfied. Those requirements should be
 209     verified by the recipient of the message.
 210     </para>
 211   </refsect1>
 212
 213   <refsect1>
 214     <title>Return Value</title>
 215
 216     <para>On success, this call returns 0 or a positive integer. On
 217     failure, it returns a negative errno-style error code.</para>
 218   </refsect1>
 219
 220   <refsect1 id='errors'>
 221     <title>Errors</title>
 222
 223     <para>Returned errors may indicate the following problems:</para>
 224
 225     <variablelist>
 226
 227       <varlistentry>
 228         <term><constant>-EINVAL</constant></term>
 229
 230         <listitem><para>Specified parameter is invalid.
 231         </para></listitem>
 232       </varlistentry>
 233
 234       <varlistentry>
 235         <term><constant>-EPERM</constant></term>
 236
 237         <listitem><para>Message has been sealed.
 238         </para></listitem>
 239       </varlistentry>
 240
 241       <varlistentry>
 242         <term><constant>-ESTALE</constant></term>
 243
 244         <listitem><para>Message is in invalid state.
 245         </para></listitem>
 246       </varlistentry>
 247
 248       <varlistentry>
 249         <term><constant>-ENXIO</constant></term>
 250
 251         <listitem><para>Message cannot be appended to.
 252         </para></listitem>
 253       </varlistentry>
 254
 255       <varlistentry>
 256         <term><constant>-ENOMEM</constant></term>
 257
 258         <listitem><para>Memory allocation failed.</para></listitem>
 259       </varlistentry>
 260     </variablelist>
 261   </refsect1>
 262
 263   <refsect1>
 264     <title>Notes</title>
 265
 266     <para>The <function>sd_bus_append_basic()</function> function
 267     described here is available as a shared library, which can be
 268     compiled and linked to with the
 269     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 270     file.</para>
 271   </refsect1>
 272
 273   <refsect1>
 274     <title>See Also</title>
 275
 276     <para>
 277       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 278       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 279       <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 280       <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
 281     </para>
 282   </refsect1>
 283
 284 </refentry>