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+
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 <contrib>A monkey with a typewriter</contrib>
19 <firstname>Zbigniew</firstname>
20 <surname>Jędrzejewski-Szmek</surname>
21 <email>zbyszek@in.waw.pl</email>
27 <refentrytitle>sd_bus_message_append</refentrytitle>
28 <manvolnum>3</manvolnum>
32 <refname>sd_bus_message_append</refname>
33 <refname>sd_bus_message_appendv</refname>
35 <refpurpose>Attach fields to a D-Bus message based on a type
41 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
44 <funcdef>int sd_bus_message_append</funcdef>
45 <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
46 <paramdef>const char *<parameter>types</parameter></paramdef>
47 <paramdef>…</paramdef>
51 <funcdef>int sd_bus_message_appendv</funcdef>
52 <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
53 <paramdef>const char *<parameter>types</parameter></paramdef>
54 <paramdef>va_list <parameter>ap</parameter></paramdef>
61 <title>Description</title>
63 <para>The <function>sd_bus_message_append()</function> function
64 appends a sequence of fields to the D-Bus message object
65 <parameter>m</parameter>. The type string
66 <parameter>types</parameter> describes the types of the field
67 arguments that follow. For each type specified in the type string,
68 one or more arguments need to be specified, in the same order as
69 declared in the type string.</para>
71 <para>The type string is composed of the elements shown in the
72 table below. It contains zero or more single "complete types".
73 Each complete type may be one of the basic types or a fully
74 described container type. A container type may be a structure with
75 the contained types, a variant, an array with its element type, or
76 a dictionary entry with the contained types. The type string is
77 <constant>NUL</constant>-terminated.</para>
79 <para>In case of a basic type, one argument of the corresponding
80 type is expected.</para>
82 <para>A structure is denoted by a sequence of complete types
83 between <literal>(</literal> and <literal>)</literal>. This
84 sequence cannot be empty — it must contain at least one type.
85 Arguments corresponding to this nested sequence follow the same
86 rules as if they were not nested.</para>
88 <para>A variant is denoted by <literal>v</literal>. Corresponding
89 arguments must begin with a type string denoting a complete type,
90 and following that, arguments corresponding to the specified type.
93 <para>An array is denoted by <literal>a</literal> followed by a
94 complete type. Corresponding arguments must begin with the number of
95 entries in the array, followed by the entries themselves,
96 matching the element type of the array.</para>
98 <para>A dictionary is an array of dictionary entries, denoted by
99 <literal>a</literal> followed by a pair of complete types between
100 <literal>{</literal> and <literal>}</literal>. The first of those
101 types must be a basic type. Corresponding arguments must begin
102 with the number of dictionary entries, followed by a pair of
103 values for each entry matching the element type of
104 the dictionary entries.</para>
106 <para>The <function>sd_bus_message_appendv()</function> is equivalent to
107 the function <function>sd_bus_message_append()</function>,
108 except that it is called with a <literal>va_list</literal> instead of
109 a variable number of arguments. This function does not call the
110 <function>va_end()</function> macro. Because it invokes the
111 <function>va_arg()</function> macro, the value of ap
112 is undefined after the call.</para>
114 <para>For further details on the D-Bus type system, please consult
116 url="http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
117 Specification</ulink>.</para>
120 <title>Item type specifiers</title>
123 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers'])//colspec" />
124 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//thead)" />
127 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />
130 <entry><literal>a</literal></entry>
131 <entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>
133 <entry>determined by array type and size</entry>
134 <entry>int, followed by array contents</entry>
138 <entry><literal>v</literal></entry>
139 <entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>
140 <entry>variant</entry>
141 <entry>determined by the type argument</entry>
142 <entry>signature string, followed by variant contents</entry>
146 <entry><literal>(</literal></entry>
147 <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>
148 <entry>array start</entry>
149 <entry morerows="1">determined by the nested types</entry>
150 <entry morerows="1">structure contents</entry>
153 <entry><literal>)</literal></entry>
154 <entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>
155 <entry>array end</entry>
159 <entry><literal>{</literal></entry>
160 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>
161 <entry>dictionary entry start</entry>
162 <entry morerows="1">determined by the nested types</entry>
163 <entry morerows="1">dictionary contents</entry>
166 <entry><literal>}</literal></entry>
167 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>
168 <entry>dictionary entry end</entry>
174 <para>For types "s" and "g" (unicode string or signature), the pointer may be
175 <constant>NULL</constant>, which is equivalent to an empty string. See
176 <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>
177 for the precise interpretation of those and other types.</para>
182 <title>Types String Grammar</title>
184 <programlisting>types ::= complete_type*
185 complete_type ::= basic_type | variant | structure | array | dictionary
186 basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" |
190 structure ::= "(" complete_type+ ")"
191 array ::= "a" complete_type
192 dictionary ::= "a" "{" basic_type complete_type "}"
197 <title>Examples</title>
199 <para>Append a single basic type (the string <literal>a string</literal>):
202 <programlisting>sd_bus_message *m;
204 sd_bus_message_append(m, "s", "a string");</programlisting>
206 <para>Append all types of integers:</para>
208 <programlisting>uint8_t y = 1;
216 sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);</programlisting>
218 <para>Append a structure composed of a string and a D-Bus path:</para>
220 <programlisting>sd_bus_message_append(m, "(so)", "a string", "/a/path");
223 <para>Append an array of UNIX file descriptors:</para>
225 <programlisting>sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
228 <para>Append a variant, with the real type "g" (signature),
229 and value "sdbusisgood":</para>
231 <programlisting>sd_bus_message_append(m, "v", "g", "sdbusisgood");</programlisting>
233 <para>Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:
236 <programlisting>sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);
241 <title>Return Value</title>
243 <para>On success, these functions return 0 or a positive
244 integer. On failure, these functions return a negative
245 errno-style error code.</para>
248 <xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
250 <xi:include href="libelogind-pkgconfig.xml" />
253 <title>See Also</title>
256 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
257 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
258 <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
259 <citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry>