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 <refentrytitle>sd_bus_message_append</refentrytitle>
21 <manvolnum>3</manvolnum>
25 <refname>sd_bus_message_append</refname>
26 <refname>sd_bus_message_appendv</refname>
28 <refpurpose>Attach fields to a D-Bus message based on a type
34 <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
37 <funcdef>int sd_bus_message_append</funcdef>
38 <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
39 <paramdef>const char *<parameter>types</parameter></paramdef>
40 <paramdef>…</paramdef>
44 <funcdef>int sd_bus_message_appendv</funcdef>
45 <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
46 <paramdef>const char *<parameter>types</parameter></paramdef>
47 <paramdef>va_list <parameter>ap</parameter></paramdef>
54 <title>Description</title>
56 <para>The <function>sd_bus_message_append()</function> function
57 appends a sequence of fields to the D-Bus message object
58 <parameter>m</parameter>. The type string
59 <parameter>types</parameter> describes the types of the field
60 arguments that follow. For each type specified in the type string,
61 one or more arguments need to be specified, in the same order as
62 declared in the type string.</para>
64 <para>The type string is composed of the elements shown in the
65 table below. It contains zero or more single "complete types".
66 Each complete type may be one of the basic types or a fully
67 described container type. A container type may be a structure with
68 the contained types, a variant, an array with its element type, or
69 a dictionary entry with the contained types. The type string is
70 <constant>NUL</constant>-terminated.</para>
72 <para>In case of a basic type, one argument of the corresponding
73 type is expected.</para>
75 <para>A structure is denoted by a sequence of complete types
76 between <literal>(</literal> and <literal>)</literal>. This
77 sequence cannot be empty — it must contain at least one type.
78 Arguments corresponding to this nested sequence follow the same
79 rules as if they were not nested.</para>
81 <para>A variant is denoted by <literal>v</literal>. Corresponding
82 arguments must begin with a type string denoting a complete type,
83 and following that, arguments corresponding to the specified type.
86 <para>An array is denoted by <literal>a</literal> followed by a
87 complete type. Corresponding arguments must begin with the number of
88 entries in the array, followed by the entries themselves,
89 matching the element type of the array.</para>
91 <para>A dictionary is an array of dictionary entries, denoted by
92 <literal>a</literal> followed by a pair of complete types between
93 <literal>{</literal> and <literal>}</literal>. The first of those
94 types must be a basic type. Corresponding arguments must begin
95 with the number of dictionary entries, followed by a pair of
96 values for each entry matching the element type of
97 the dictionary entries.</para>
99 <para>The <function>sd_bus_message_appendv()</function> is equivalent to
100 the function <function>sd_bus_message_append()</function>,
101 except that it is called with a <literal>va_list</literal> instead of
102 a variable number of arguments. This function does not call the
103 <function>va_end()</function> macro. Because it invokes the
104 <function>va_arg()</function> macro, the value of ap
105 is undefined after the call.</para>
107 <para>For further details on the D-Bus type system, please consult
109 url="http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
110 Specification</ulink>.</para>
113 <title>Item type specifiers</title>
116 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers'])//colspec" />
117 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//thead)" />
120 <xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />
123 <entry><literal>a</literal></entry>
124 <entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>
126 <entry>determined by array type and size</entry>
127 <entry>int, followed by array contents</entry>
131 <entry><literal>v</literal></entry>
132 <entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>
133 <entry>variant</entry>
134 <entry>determined by the type argument</entry>
135 <entry>signature string, followed by variant contents</entry>
139 <entry><literal>(</literal></entry>
140 <entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>
141 <entry>array start</entry>
142 <entry morerows="1">determined by the nested types</entry>
143 <entry morerows="1">structure contents</entry>
146 <entry><literal>)</literal></entry>
147 <entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>
148 <entry>array end</entry>
152 <entry><literal>{</literal></entry>
153 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>
154 <entry>dictionary entry start</entry>
155 <entry morerows="1">determined by the nested types</entry>
156 <entry morerows="1">dictionary contents</entry>
159 <entry><literal>}</literal></entry>
160 <entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>
161 <entry>dictionary entry end</entry>
167 <para>For types "s" and "g" (unicode string or signature), the pointer may be
168 <constant>NULL</constant>, which is equivalent to an empty string. See
169 <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>
170 for the precise interpretation of those and other types.</para>
175 <title>Types String Grammar</title>
177 <programlisting>types ::= complete_type*
178 complete_type ::= basic_type | variant | structure | array | dictionary
179 basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" |
183 structure ::= "(" complete_type+ ")"
184 array ::= "a" complete_type
185 dictionary ::= "a" "{" basic_type complete_type "}"
190 <title>Examples</title>
192 <para>Append a single basic type (the string <literal>a string</literal>):
195 <programlisting>sd_bus_message *m;
197 sd_bus_message_append(m, "s", "a string");</programlisting>
199 <para>Append all types of integers:</para>
201 <programlisting>uint8_t y = 1;
209 sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);</programlisting>
211 <para>Append a structure composed of a string and a D-Bus path:</para>
213 <programlisting>sd_bus_message_append(m, "(so)", "a string", "/a/path");
216 <para>Append an array of UNIX file descriptors:</para>
218 <programlisting>sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
221 <para>Append a variant, with the real type "g" (signature),
222 and value "sdbusisgood":</para>
224 <programlisting>sd_bus_message_append(m, "v", "g", "sdbusisgood");</programlisting>
226 <para>Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:
229 <programlisting>sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);
234 <title>Return Value</title>
236 <para>On success, these functions return 0 or a positive
237 integer. On failure, these functions return a negative
238 errno-style error code.</para>
241 <xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
243 <xi:include href="libelogind-pkgconfig.xml" />
246 <title>See Also</title>
249 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
250 <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
251 <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
252 <citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry>