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">
6 This file is part of systemd.
8 Copyright 2014 Zbigniew Jędrzejewski-Szmek
10 systemd is free software; you can redistribute it and/or modify it
11 under the terms of the GNU Lesser General Public License as published by
12 the Free Software Foundation; either version 2.1 of the License, or
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24 <refentry id="sd_bus_message_append"
25 xmlns:xi="http://www.w3.org/2001/XInclude">
28 <title>sd_bus_message_append</title>
29 <productname>systemd</productname>
33 <contrib>A monkey with a typewriter</contrib>
34 <firstname>Zbigniew</firstname>
35 <surname>Jędrzejewski-Szmek</surname>
36 <email>zbyszek@in.waw.pl</email>
42 <refentrytitle>sd_bus_message_append</refentrytitle>
43 <manvolnum>3</manvolnum>
47 <refname>sd_bus_message_append</refname>
48 <refname>sd_bus_message_appendv</refname>
50 <refpurpose>Attach fields to a D-Bus message based on a type
56 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
59 <funcdef>int sd_bus_message_append</funcdef>
60 <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
61 <paramdef>const char *<parameter>types</parameter></paramdef>
62 <paramdef>…</paramdef>
66 <funcdef>int sd_bus_message_appendv</funcdef>
67 <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
68 <paramdef>const char *<parameter>types</parameter></paramdef>
69 <paramdef>va_list <parameter>ap</parameter></paramdef>
76 <title>Description</title>
78 <para>The <function>sd_bus_message_append()</function> function
79 appends a sequence of fields to the D-Bus message object
80 <parameter>m</parameter>. The type string
81 <parameter>types</parameter> describes the types of the field
82 arguments that follow. For each type specified in the type string,
83 one or more arguments need to be specified, in the same order as
84 declared in the type string.</para>
86 <para>The type string is composed of the elements shown in the
87 table below. It contains zero or more single "complete types".
88 Each complete type may be one of the basic types or a fully
89 described container type. A container type may be a structure with
90 the contained types, a variant, an array with its element type, or
91 a dictionary entry with the contained types. The type string is
92 <constant>NUL</constant>-terminated.</para>
94 <para>In case of a basic type, one argument of the corresponding
95 type is expected.</para>
97 <para>A structure is denoted by a sequence of complete types
98 between <literal>(</literal> and <literal>)</literal>. This
99 sequence cannot be empty — it must contain at least one type.
100 Arguments corresponding to this nested sequence follow the same
101 rules as if they were not nested.</para>
103 <para>A variant is denoted by <literal>v</literal>. Corresponding
104 arguments must begin with a type string denoting a complete type,
105 and following that, arguments corresponding to the specified type.
108 <para>An array is denoted by <literal>a</literal> followed by a
109 complete type. Corresponding arguments must begin with the number of
110 entries in the array, followed by the entries themselves,
111 matching the element type of the array.</para>
113 <para>A dictionary is an array of dictionary entries, denoted by
114 <literal>a</literal> followed by a pair of complete types between
115 <literal>{</literal> and <literal>}</literal>. The first of those
116 types must be a basic type. Corresponding arguments must begin
117 with the number of dictionary entries, followed by a pair of
118 values for each entry matching the element type of
119 the dictionary entries.</para>
121 <para>The <function>sd_bus_message_appendv()</function> is equivalent to
122 the function <function>sd_bus_message_append()</function>,
123 except that it is called with a <literal>va_list</literal> instead of
124 a variable number of arguments. This function does not call the
125 <function>va_end()</function> macro. Because it invokes the
126 <function>va_arg()</function> macro, the value of ap
127 is undefined after the call.</para>
129 <para>For further details on the D-Bus type system, please consult
131 url="http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
132 Specification</ulink>.</para>
135 <title>Item type specifiers</title>
138 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers'])//colspec" />
139 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//thead)" />
142 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />
145 <entry><literal>a</literal></entry>
146 <entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>
148 <entry>determined by array type and size</entry>
149 <entry>int, followed by array contents</entry>
153 <entry><literal>v</literal></entry>
154 <entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>
155 <entry>variant</entry>
156 <entry>determined by the type argument</entry>
157 <entry>signature string, followed by variant contents</entry>
161 <entry><literal>(</literal></entry>
162 <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>
163 <entry>array start</entry>
164 <entry morerows="1">determined by the nested types</entry>
165 <entry morerows="1">structure contents</entry>
168 <entry><literal>)</literal></entry>
169 <entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>
170 <entry>array end</entry>
174 <entry><literal>{</literal></entry>
175 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>
176 <entry>dictionary entry start</entry>
177 <entry morerows="1">determined by the nested types</entry>
178 <entry morerows="1">dictionary contents</entry>
181 <entry><literal>}</literal></entry>
182 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>
183 <entry>dictionary entry end</entry>
189 <para>For types "s" and "g" (unicode string or signature), the pointer may be
190 <constant>NULL</constant>, which is equivalent to an empty string. See
191 <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>
192 for the precise interpretation of those and other types.</para>
197 <title>Types String Grammar</title>
199 <programlisting>types ::= complete_type*
200 complete_type ::= basic_type | variant | structure | array | dictionary
201 basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" |
205 structure ::= "(" complete_type+ ")"
206 array ::= "a" complete_type
207 dictionary ::= "a" "{" basic_type complete_type "}"
212 <title>Examples</title>
214 <para>Append a single basic type (the string <literal>a string</literal>):
217 <programlisting>sd_bus_message *m;
219 sd_bus_message_append(m, "s", "a string");</programlisting>
221 <para>Append all types of integers:</para>
223 <programlisting>uint8_t y = 1;
231 sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);</programlisting>
233 <para>Append a structure composed of a string and a D-Bus path:</para>
235 <programlisting>sd_bus_message_append(m, "(so)", "a string", "/a/path");
238 <para>Append an array of UNIX file descriptors:</para>
240 <programlisting>sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
243 <para>Append a variant, with the real type "g" (signature),
244 and value "sdbusisgood":</para>
246 <programlisting>sd_bus_message_append(m, "v", "g", "sdbusisgood");</programlisting>
248 <para>Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:
251 <programlisting>sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);
256 <title>Return Value</title>
258 <para>On success, these functions return 0 or a positive
259 integer. On failure, these functions return a negative
260 errno-style error code.</para>
263 <xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
268 <para><function>sd_bus_open_user()</function> and other functions
269 described here are available as a shared library, which can be
270 compiled and linked to with the
271 <constant>libelogind-bus</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
276 <title>See Also</title>
279 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
280 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
281 <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
282 <citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry>