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+
9 <refentry id=
"sd_bus_message_append"
10 xmlns:
xi=
"http://www.w3.org/2001/XInclude">
13 <title>sd_bus_message_append
</title>
14 <productname>systemd
</productname>
18 <refentrytitle>sd_bus_message_append
</refentrytitle>
19 <manvolnum>3</manvolnum>
23 <refname>sd_bus_message_append
</refname>
24 <refname>sd_bus_message_appendv
</refname>
26 <refpurpose>Attach fields to a D-Bus message based on a type
32 <funcsynopsisinfo>#include
<systemd/sd-bus.h
></funcsynopsisinfo>
35 <funcdef>int sd_bus_message_append
</funcdef>
36 <paramdef>sd_bus_message *
<parameter>m
</parameter></paramdef>
37 <paramdef>const char *
<parameter>types
</parameter></paramdef>
38 <paramdef>…
</paramdef>
42 <funcdef>int sd_bus_message_appendv
</funcdef>
43 <paramdef>sd_bus_message *
<parameter>m
</parameter></paramdef>
44 <paramdef>const char *
<parameter>types
</parameter></paramdef>
45 <paramdef>va_list
<parameter>ap
</parameter></paramdef>
52 <title>Description
</title>
54 <para>The
<function>sd_bus_message_append()
</function> function
55 appends a sequence of fields to the D-Bus message object
56 <parameter>m
</parameter>. The type string
57 <parameter>types
</parameter> describes the types of the field
58 arguments that follow. For each type specified in the type string,
59 one or more arguments need to be specified, in the same order as
60 declared in the type string.
</para>
62 <para>The type string is composed of the elements shown in the
63 table below. It contains zero or more single
"complete types".
64 Each complete type may be one of the basic types or a fully
65 described container type. A container type may be a structure with
66 the contained types, a variant, an array with its element type, or
67 a dictionary entry with the contained types. The type string is
68 <constant>NUL
</constant>-terminated.
</para>
70 <para>In case of a basic type, one argument of the corresponding
71 type is expected.
</para>
73 <para>A structure is denoted by a sequence of complete types
74 between
<literal>(
</literal> and
<literal>)
</literal>. This
75 sequence cannot be empty — it must contain at least one type.
76 Arguments corresponding to this nested sequence follow the same
77 rules as if they were not nested.
</para>
79 <para>A variant is denoted by
<literal>v
</literal>. Corresponding
80 arguments must begin with a type string denoting a complete type,
81 and following that, arguments corresponding to the specified type.
84 <para>An array is denoted by
<literal>a
</literal> followed by a
85 complete type. Corresponding arguments must begin with the number of
86 entries in the array, followed by the entries themselves,
87 matching the element type of the array.
</para>
89 <para>A dictionary is an array of dictionary entries, denoted by
90 <literal>a
</literal> followed by a pair of complete types between
91 <literal>{
</literal> and
<literal>}
</literal>. The first of those
92 types must be a basic type. Corresponding arguments must begin
93 with the number of dictionary entries, followed by a pair of
94 values for each entry matching the element type of
95 the dictionary entries.
</para>
97 <para>The
<function>sd_bus_message_appendv()
</function> is equivalent to the
98 <function>sd_bus_message_append()
</function>, except that it is called with
99 a
<literal>va_list
</literal> instead of a variable number of arguments. This
100 function does not call the
<function>va_end()
</function> macro. Because it
101 invokes the
<function>va_arg()
</function> macro, the value of
102 <parameter>ap
</parameter> is undefined after the call.
</para>
104 <para>For further details on the D-Bus type system, please consult
106 url=
"http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
107 Specification
</ulink>.
</para>
110 <title>Item type specifiers
</title>
113 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers'])//colspec" />
114 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers']//thead)" />
117 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"xpointer(//table[@id='format-specifiers']//tbody/*)" />
120 <entry><literal>a
</literal></entry>
121 <entry><constant>SD_BUS_TYPE_ARRAY
</constant></entry>
123 <entry>determined by array type and size
</entry>
124 <entry>int, followed by array contents
</entry>
128 <entry><literal>v
</literal></entry>
129 <entry><constant>SD_BUS_TYPE_VARIANT
</constant></entry>
130 <entry>variant
</entry>
131 <entry>determined by the type argument
</entry>
132 <entry>signature string, followed by variant contents
</entry>
136 <entry><literal>(
</literal></entry>
137 <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN
</constant></entry>
138 <entry>array start
</entry>
139 <entry morerows=
"1">determined by the nested types
</entry>
140 <entry morerows=
"1">structure contents
</entry>
143 <entry><literal>)
</literal></entry>
144 <entry><constant>SD_BUS_TYPE_STRUCT_END
</constant></entry>
145 <entry>array end
</entry>
149 <entry><literal>{
</literal></entry>
150 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN
</constant></entry>
151 <entry>dictionary entry start
</entry>
152 <entry morerows=
"1">determined by the nested types
</entry>
153 <entry morerows=
"1">dictionary contents
</entry>
156 <entry><literal>}
</literal></entry>
157 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END
</constant></entry>
158 <entry>dictionary entry end
</entry>
164 <para>For types
"s" and
"g" (unicode string or signature), the pointer may be
165 <constant>NULL
</constant>, which is equivalent to an empty string. See
166 <citerefentry><refentrytitle>sd_bus_message_append_basic
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
167 for the precise interpretation of those and other types.
</para>
172 <title>Types String Grammar
</title>
174 <programlisting>types ::= complete_type*
175 complete_type ::= basic_type | variant | structure | array | dictionary
176 basic_type ::=
"y" |
"n" |
"q" |
"u" |
"i" |
"x" |
"t" |
"d" |
180 structure ::=
"(" complete_type+
")"
181 array ::=
"a" complete_type
182 dictionary ::=
"a" "{" basic_type complete_type
"}"
187 <title>Examples
</title>
189 <para>Append a single basic type (the string
<literal>a string
</literal>):
192 <programlisting>sd_bus_message *m;
194 sd_bus_message_append(m,
"s",
"a string");
</programlisting>
196 <para>Append all types of integers:
</para>
198 <programlisting>uint8_t y =
1;
206 sd_bus_message_append(m,
"ynqiuxtd", y, n, q, i, u, x, t, d);
</programlisting>
208 <para>Append a structure composed of a string and a D-Bus path:
</para>
210 <programlisting>sd_bus_message_append(m,
"(so)",
"a string",
"/a/path");
213 <para>Append an array of UNIX file descriptors:
</para>
215 <programlisting>sd_bus_message_append(m,
"ah",
3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
218 <para>Append a variant, with the real type
"g" (signature),
219 and value
"sdbusisgood":
</para>
221 <programlisting>sd_bus_message_append(m,
"v",
"g",
"sdbusisgood");
</programlisting>
223 <para>Append a dictionary containing the mapping {
1=
>"a",
2=
>"b",
3=
>""}:
226 <programlisting>sd_bus_message_append(m,
"a{is}",
3,
1,
"a",
2,
"b",
3, NULL);
231 <title>Return Value
</title>
233 <para>On success, these functions return
0 or a positive
234 integer. On failure, these functions return a negative
235 errno-style error code.
</para>
238 <xi:include href=
"sd_bus_message_append_basic.xml" xpointer=
"errors" />
240 <xi:include href=
"libsystemd-pkgconfig.xml" />
243 <title>See Also
</title>
246 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
247 <citerefentry><refentrytitle>sd-bus
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
248 <citerefentry><refentrytitle>sd_bus_message_append_basic
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
249 <citerefentry><refentrytitle>sd_bus_message_append_array
</refentrytitle><manvolnum>3</manvolnum></citerefentry>