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 Copyright 2014 Zbigniew Jędrzejewski-Szmek
11 <refentry id=
"sd_bus_message_append"
12 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
15 <title>sd_bus_message_append
</title>
16 <productname>systemd
</productname>
20 <contrib>A monkey with a typewriter
</contrib>
21 <firstname>Zbigniew
</firstname>
22 <surname>Jędrzejewski-Szmek
</surname>
23 <email>zbyszek@in.waw.pl
</email>
29 <refentrytitle>sd_bus_message_append
</refentrytitle>
30 <manvolnum>3</manvolnum>
34 <refname>sd_bus_message_append
</refname>
35 <refname>sd_bus_message_appendv
</refname>
37 <refpurpose>Attach fields to a D-Bus message based on a type
43 <funcsynopsisinfo>#include
<systemd/sd-bus.h
></funcsynopsisinfo>
46 <funcdef>int sd_bus_message_append
</funcdef>
47 <paramdef>sd_bus_message *
<parameter>m
</parameter></paramdef>
48 <paramdef>const char *
<parameter>types
</parameter></paramdef>
49 <paramdef>…
</paramdef>
53 <funcdef>int sd_bus_message_appendv
</funcdef>
54 <paramdef>sd_bus_message *
<parameter>m
</parameter></paramdef>
55 <paramdef>const char *
<parameter>types
</parameter></paramdef>
56 <paramdef>va_list
<parameter>ap
</parameter></paramdef>
63 <title>Description
</title>
65 <para>The
<function>sd_bus_message_append()
</function> function
66 appends a sequence of fields to the D-Bus message object
67 <parameter>m
</parameter>. The type string
68 <parameter>types
</parameter> describes the types of the field
69 arguments that follow. For each type specified in the type string,
70 one or more arguments need to be specified, in the same order as
71 declared in the type string.
</para>
73 <para>The type string is composed of the elements shown in the
74 table below. It contains zero or more single
"complete types".
75 Each complete type may be one of the basic types or a fully
76 described container type. A container type may be a structure with
77 the contained types, a variant, an array with its element type, or
78 a dictionary entry with the contained types. The type string is
79 <constant>NUL
</constant>-terminated.
</para>
81 <para>In case of a basic type, one argument of the corresponding
82 type is expected.
</para>
84 <para>A structure is denoted by a sequence of complete types
85 between
<literal>(
</literal> and
<literal>)
</literal>. This
86 sequence cannot be empty — it must contain at least one type.
87 Arguments corresponding to this nested sequence follow the same
88 rules as if they were not nested.
</para>
90 <para>A variant is denoted by
<literal>v
</literal>. Corresponding
91 arguments must begin with a type string denoting a complete type,
92 and following that, arguments corresponding to the specified type.
95 <para>An array is denoted by
<literal>a
</literal> followed by a
96 complete type. Corresponding arguments must begin with the number of
97 entries in the array, followed by the entries themselves,
98 matching the element type of the array.
</para>
100 <para>A dictionary is an array of dictionary entries, denoted by
101 <literal>a
</literal> followed by a pair of complete types between
102 <literal>{
</literal> and
<literal>}
</literal>. The first of those
103 types must be a basic type. Corresponding arguments must begin
104 with the number of dictionary entries, followed by a pair of
105 values for each entry matching the element type of
106 the dictionary entries.
</para>
108 <para>The
<function>sd_bus_message_appendv()
</function> is equivalent to
109 the function
<function>sd_bus_message_append()
</function>,
110 except that it is called with a
<literal>va_list
</literal> instead of
111 a variable number of arguments. This function does not call the
112 <function>va_end()
</function> macro. Because it invokes the
113 <function>va_arg()
</function> macro, the value of ap
114 is undefined after the call.
</para>
116 <para>For further details on the D-Bus type system, please consult
118 url=
"http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
119 Specification
</ulink>.
</para>
122 <title>Item type specifiers
</title>
125 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers'])//colspec" />
126 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers']//thead)" />
129 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers']//tbody/*)" />
132 <entry><literal>a
</literal></entry>
133 <entry><constant>SD_BUS_TYPE_ARRAY
</constant></entry>
135 <entry>determined by array type and size
</entry>
136 <entry>int, followed by array contents
</entry>
140 <entry><literal>v
</literal></entry>
141 <entry><constant>SD_BUS_TYPE_VARIANT
</constant></entry>
142 <entry>variant
</entry>
143 <entry>determined by the type argument
</entry>
144 <entry>signature string, followed by variant contents
</entry>
148 <entry><literal>(
</literal></entry>
149 <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN
</constant></entry>
150 <entry>array start
</entry>
151 <entry morerows=
"1">determined by the nested types
</entry>
152 <entry morerows=
"1">structure contents
</entry>
155 <entry><literal>)
</literal></entry>
156 <entry><constant>SD_BUS_TYPE_STRUCT_END
</constant></entry>
157 <entry>array end
</entry>
161 <entry><literal>{
</literal></entry>
162 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN
</constant></entry>
163 <entry>dictionary entry start
</entry>
164 <entry morerows=
"1">determined by the nested types
</entry>
165 <entry morerows=
"1">dictionary contents
</entry>
168 <entry><literal>}
</literal></entry>
169 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END
</constant></entry>
170 <entry>dictionary entry end
</entry>
176 <para>For types
"s" and
"g" (unicode string or signature), the pointer may be
177 <constant>NULL
</constant>, which is equivalent to an empty string. See
178 <citerefentry><refentrytitle>sd_bus_message_append_basic
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
179 for the precise interpretation of those and other types.
</para>
184 <title>Types String Grammar
</title>
186 <programlisting>types ::= complete_type*
187 complete_type ::= basic_type | variant | structure | array | dictionary
188 basic_type ::=
"y" |
"n" |
"q" |
"u" |
"i" |
"x" |
"t" |
"d" |
192 structure ::=
"(" complete_type+
")"
193 array ::=
"a" complete_type
194 dictionary ::=
"a" "{" basic_type complete_type
"}"
199 <title>Examples
</title>
201 <para>Append a single basic type (the string
<literal>a string
</literal>):
204 <programlisting>sd_bus_message *m;
206 sd_bus_message_append(m,
"s",
"a string");
</programlisting>
208 <para>Append all types of integers:
</para>
210 <programlisting>uint8_t y =
1;
218 sd_bus_message_append(m,
"ynqiuxtd", y, n, q, i, u, x, t, d);
</programlisting>
220 <para>Append a structure composed of a string and a D-Bus path:
</para>
222 <programlisting>sd_bus_message_append(m,
"(so)",
"a string",
"/a/path");
225 <para>Append an array of UNIX file descriptors:
</para>
227 <programlisting>sd_bus_message_append(m,
"ah",
3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
230 <para>Append a variant, with the real type
"g" (signature),
231 and value
"sdbusisgood":
</para>
233 <programlisting>sd_bus_message_append(m,
"v",
"g",
"sdbusisgood");
</programlisting>
235 <para>Append a dictionary containing the mapping {
1=
>"a",
2=
>"b",
3=
>""}:
238 <programlisting>sd_bus_message_append(m,
"a{is}",
3,
1,
"a",
2,
"b",
3, NULL);
243 <title>Return Value
</title>
245 <para>On success, these functions return
0 or a positive
246 integer. On failure, these functions return a negative
247 errno-style error code.
</para>
250 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"errors" />
252 <xi:include href=
"libsystemd-pkgconfig.xml" />
255 <title>See Also
</title>
258 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
259 <citerefentry><refentrytitle>sd-bus
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
260 <citerefentry><refentrytitle>sd_bus_message_append_basic
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
261 <citerefentry><refentrytitle>sd_bus_message_append_array
</refentrytitle><manvolnum>3</manvolnum></citerefentry>