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 SPDX-License-Identifier: LGPL-2.1+
8 This file is part of systemd.
10 Copyright 2014 Zbigniew Jędrzejewski-Szmek
12 systemd is free software; you can redistribute it and/or modify it
13 under the terms of the GNU Lesser General Public License as published by
14 the Free Software Foundation; either version 2.1 of the License, or
15 (at your option) any later version.
17 systemd is distributed in the hope that it will be useful, but
18 WITHOUT ANY WARRANTY; without even the implied warranty of
19 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20 Lesser General Public License for more details.
22 You should have received a copy of the GNU Lesser General Public License
23 along with systemd; If not, see <http://www.gnu.org/licenses/>.
26 <refentry id=
"sd_bus_message_append"
27 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
30 <title>sd_bus_message_append
</title>
31 <productname>systemd
</productname>
35 <contrib>A monkey with a typewriter
</contrib>
36 <firstname>Zbigniew
</firstname>
37 <surname>Jędrzejewski-Szmek
</surname>
38 <email>zbyszek@in.waw.pl
</email>
44 <refentrytitle>sd_bus_message_append
</refentrytitle>
45 <manvolnum>3</manvolnum>
49 <refname>sd_bus_message_append
</refname>
50 <refname>sd_bus_message_appendv
</refname>
52 <refpurpose>Attach fields to a D-Bus message based on a type
58 <funcsynopsisinfo>#include
<systemd/sd-bus.h
></funcsynopsisinfo>
61 <funcdef>int sd_bus_message_append
</funcdef>
62 <paramdef>sd_bus_message *
<parameter>m
</parameter></paramdef>
63 <paramdef>const char *
<parameter>types
</parameter></paramdef>
64 <paramdef>…
</paramdef>
68 <funcdef>int sd_bus_message_appendv
</funcdef>
69 <paramdef>sd_bus_message *
<parameter>m
</parameter></paramdef>
70 <paramdef>const char *
<parameter>types
</parameter></paramdef>
71 <paramdef>va_list
<parameter>ap
</parameter></paramdef>
78 <title>Description
</title>
80 <para>The
<function>sd_bus_message_append()
</function> function
81 appends a sequence of fields to the D-Bus message object
82 <parameter>m
</parameter>. The type string
83 <parameter>types
</parameter> describes the types of the field
84 arguments that follow. For each type specified in the type string,
85 one or more arguments need to be specified, in the same order as
86 declared in the type string.
</para>
88 <para>The type string is composed of the elements shown in the
89 table below. It contains zero or more single
"complete types".
90 Each complete type may be one of the basic types or a fully
91 described container type. A container type may be a structure with
92 the contained types, a variant, an array with its element type, or
93 a dictionary entry with the contained types. The type string is
94 <constant>NUL
</constant>-terminated.
</para>
96 <para>In case of a basic type, one argument of the corresponding
97 type is expected.
</para>
99 <para>A structure is denoted by a sequence of complete types
100 between
<literal>(
</literal> and
<literal>)
</literal>. This
101 sequence cannot be empty — it must contain at least one type.
102 Arguments corresponding to this nested sequence follow the same
103 rules as if they were not nested.
</para>
105 <para>A variant is denoted by
<literal>v
</literal>. Corresponding
106 arguments must begin with a type string denoting a complete type,
107 and following that, arguments corresponding to the specified type.
110 <para>An array is denoted by
<literal>a
</literal> followed by a
111 complete type. Corresponding arguments must begin with the number of
112 entries in the array, followed by the entries themselves,
113 matching the element type of the array.
</para>
115 <para>A dictionary is an array of dictionary entries, denoted by
116 <literal>a
</literal> followed by a pair of complete types between
117 <literal>{
</literal> and
<literal>}
</literal>. The first of those
118 types must be a basic type. Corresponding arguments must begin
119 with the number of dictionary entries, followed by a pair of
120 values for each entry matching the element type of
121 the dictionary entries.
</para>
123 <para>The
<function>sd_bus_message_appendv()
</function> is equivalent to
124 the function
<function>sd_bus_message_append()
</function>,
125 except that it is called with a
<literal>va_list
</literal> instead of
126 a variable number of arguments. This function does not call the
127 <function>va_end()
</function> macro. Because it invokes the
128 <function>va_arg()
</function> macro, the value of ap
129 is undefined after the call.
</para>
131 <para>For further details on the D-Bus type system, please consult
133 url=
"http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
134 Specification
</ulink>.
</para>
137 <title>Item type specifiers
</title>
140 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers'])//colspec" />
141 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers']//thead)" />
144 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers']//tbody/*)" />
147 <entry><literal>a
</literal></entry>
148 <entry><constant>SD_BUS_TYPE_ARRAY
</constant></entry>
150 <entry>determined by array type and size
</entry>
151 <entry>int, followed by array contents
</entry>
155 <entry><literal>v
</literal></entry>
156 <entry><constant>SD_BUS_TYPE_VARIANT
</constant></entry>
157 <entry>variant
</entry>
158 <entry>determined by the type argument
</entry>
159 <entry>signature string, followed by variant contents
</entry>
163 <entry><literal>(
</literal></entry>
164 <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN
</constant></entry>
165 <entry>array start
</entry>
166 <entry morerows=
"1">determined by the nested types
</entry>
167 <entry morerows=
"1">structure contents
</entry>
170 <entry><literal>)
</literal></entry>
171 <entry><constant>SD_BUS_TYPE_STRUCT_END
</constant></entry>
172 <entry>array end
</entry>
176 <entry><literal>{
</literal></entry>
177 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN
</constant></entry>
178 <entry>dictionary entry start
</entry>
179 <entry morerows=
"1">determined by the nested types
</entry>
180 <entry morerows=
"1">dictionary contents
</entry>
183 <entry><literal>}
</literal></entry>
184 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END
</constant></entry>
185 <entry>dictionary entry end
</entry>
191 <para>For types
"s" and
"g" (unicode string or signature), the pointer may be
192 <constant>NULL
</constant>, which is equivalent to an empty string. See
193 <citerefentry><refentrytitle>sd_bus_message_append_basic
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
194 for the precise interpretation of those and other types.
</para>
199 <title>Types String Grammar
</title>
201 <programlisting>types ::= complete_type*
202 complete_type ::= basic_type | variant | structure | array | dictionary
203 basic_type ::=
"y" |
"n" |
"q" |
"u" |
"i" |
"x" |
"t" |
"d" |
207 structure ::=
"(" complete_type+
")"
208 array ::=
"a" complete_type
209 dictionary ::=
"a" "{" basic_type complete_type
"}"
214 <title>Examples
</title>
216 <para>Append a single basic type (the string
<literal>a string
</literal>):
219 <programlisting>sd_bus_message *m;
221 sd_bus_message_append(m,
"s",
"a string");
</programlisting>
223 <para>Append all types of integers:
</para>
225 <programlisting>uint8_t y =
1;
233 sd_bus_message_append(m,
"ynqiuxtd", y, n, q, i, u, x, t, d);
</programlisting>
235 <para>Append a structure composed of a string and a D-Bus path:
</para>
237 <programlisting>sd_bus_message_append(m,
"(so)",
"a string",
"/a/path");
240 <para>Append an array of UNIX file descriptors:
</para>
242 <programlisting>sd_bus_message_append(m,
"ah",
3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
245 <para>Append a variant, with the real type
"g" (signature),
246 and value
"sdbusisgood":
</para>
248 <programlisting>sd_bus_message_append(m,
"v",
"g",
"sdbusisgood");
</programlisting>
250 <para>Append a dictionary containing the mapping {
1=
>"a",
2=
>"b",
3=
>""}:
253 <programlisting>sd_bus_message_append(m,
"a{is}",
3,
1,
"a",
2,
"b",
3, NULL);
258 <title>Return Value
</title>
260 <para>On success, these functions return
0 or a positive
261 integer. On failure, these functions return a negative
262 errno-style error code.
</para>
265 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"errors" />
270 <para><function>sd_bus_open_user()
</function> and other functions
271 described here are available as a shared library, which can be
272 compiled and linked to with the
273 <constant>libsystemd-bus
</constant> <citerefentry project='die-net'
><refentrytitle>pkg-config
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
278 <title>See Also
</title>
281 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
282 <citerefentry><refentrytitle>sd-bus
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
283 <citerefentry><refentrytitle>sd_bus_message_append_basic
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
284 <citerefentry><refentrytitle>sd_bus_message_append_array
</refentrytitle><manvolnum>3</manvolnum></citerefentry>