mirror of
https://github.com/systemd/systemd.git
synced 2024-12-22 17:35:35 +03:00
b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
228 lines
8.6 KiB
XML
228 lines
8.6 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
|
|
|
|
<refentry id="sd_bus_message_read"
|
|
xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
|
|
<refentryinfo>
|
|
<title>sd_bus_message_read</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>sd_bus_message_read</refentrytitle>
|
|
<manvolnum>3</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>sd_bus_message_read</refname>
|
|
<refname>sd_bus_message_readv</refname>
|
|
|
|
<refpurpose>Read a sequence of values from a message</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<funcsynopsis>
|
|
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_bus_message_read</function></funcdef>
|
|
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
|
|
<paramdef>char char *<parameter>types</parameter></paramdef>
|
|
<paramdef>...</paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_bus_message_readv</function></funcdef>
|
|
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
|
|
<paramdef>char char *<parameter>types</parameter></paramdef>
|
|
<paramdef>va_list <parameter>ap</parameter></paramdef>
|
|
</funcprototype>
|
|
</funcsynopsis>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para><function>sd_bus_message_read()</function> reads a sequence of fields from
|
|
the D-Bus message object <parameter>m</parameter> and advances the read position
|
|
in the message. The type string <parameter>types</parameter> describes the types
|
|
of items expected in the message and the field arguments that follow. The type
|
|
string may be <constant>NULL</constant> or empty, in which case nothing is
|
|
read.</para>
|
|
|
|
<para>The type string is composed of the elements described in
|
|
<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
i.e. basic and container types. It must contain zero or more single "complete
|
|
types". The type string is <constant>NUL</constant>-terminated.</para>
|
|
|
|
<para>For each type specified in the type string, one or more arguments need to be specified
|
|
after the <parameter>types</parameter> parameter, in the same order. The arguments must be
|
|
pointers to appropriate types (a pointer to <code>int8_t</code> for a <literal>y</literal> in
|
|
the type string, a pointer to <code>int32_t</code> for an <literal>i</literal>, a pointer to
|
|
<code>const char*</code> for an <literal>s</literal>, ...) which are set based on the values in
|
|
the message. As an exception, in case or array and variant types, the first argument is an
|
|
"input" argument that further specifies how the message should be read. See the table below for
|
|
a complete list of allowed arguments and their types. Note that, if the basic type is a pointer
|
|
(e.g., <code>const char *</code> in the case of a string), the argument is a pointer to a
|
|
pointer, and also the pointer value that is written is only borrowed and the contents must be
|
|
copied if they are to be used after the end of the messages lifetime.</para>
|
|
|
|
<para>Each argument may also be <constant>NULL</constant>, in which case the value is read and
|
|
ignored.</para>
|
|
|
|
<table>
|
|
<title>Item type specifiers</title>
|
|
|
|
<tgroup cols='5'>
|
|
<colspec colname='specifier' />
|
|
<colspec colname='constant' />
|
|
<colspec colname='description' />
|
|
<colspec colname='type1' />
|
|
<colspec colname='type2' />
|
|
<thead>
|
|
<row>
|
|
<entry>Specifier</entry>
|
|
<entry>Constant</entry>
|
|
<entry>Description</entry>
|
|
<entry>Type of the first argument</entry>
|
|
<entry>Types of the subsequent arguments, if any</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<xi:include href="sd_bus_message_read_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />
|
|
|
|
<row>
|
|
<entry><literal>a</literal></entry>
|
|
<entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>
|
|
<entry>array</entry>
|
|
<entry>int, which specifies the expected length <parameter>n</parameter> of the array</entry>
|
|
<entry><parameter>n</parameter> sets of arguments appropriate for the array element type</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>v</literal></entry>
|
|
<entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>
|
|
<entry>variant</entry>
|
|
<entry>signature string</entry>
|
|
<entry>arguments appropriate for the types specified by the signature</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>(</literal></entry>
|
|
<entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>
|
|
<entry>array start</entry>
|
|
<entry morerows="1" namest="type1" nameend="type2">arguments appropriate for the structure elements</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>)</literal></entry>
|
|
<entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>
|
|
<entry>array end</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>{</literal></entry>
|
|
<entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>
|
|
<entry>dictionary entry start</entry>
|
|
<entry morerows="1">arguments appropriate for the first type in the pair</entry>
|
|
<entry morerows="1">arguments appropriate for the second type in the pair</entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>}</literal></entry>
|
|
<entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>
|
|
<entry>dictionary entry end</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>If objects of the specified types are not present at the current position
|
|
in the message, an error is returned.
|
|
</para>
|
|
|
|
<para>The <function>sd_bus_message_readv()</function> is equivalent to the
|
|
<function>sd_bus_message_read()</function>, except that it is called with a
|
|
<literal>va_list</literal> instead of a variable number of arguments. This
|
|
function does not call the <function>va_end()</function> macro. Because it
|
|
invokes the <function>va_arg()</function> macro, the value of
|
|
<parameter>ap</parameter> is undefined after the call.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Return Value</title>
|
|
|
|
<para>On success, <function>sd_bus_message_read()</function> and
|
|
<function>sd_bus_message_readv()</function> return 0 or a positive integer. On failure, they return a
|
|
negative errno-style error code.</para>
|
|
|
|
<xi:include href="sd_bus_message_read_basic.xml" xpointer="errors" />
|
|
</refsect1>
|
|
|
|
<xi:include href="libsystemd-pkgconfig.xml" />
|
|
|
|
<refsect1>
|
|
<title>Examples</title>
|
|
|
|
<para>Read a single basic type (a 64-bit integer):
|
|
</para>
|
|
|
|
<programlisting>sd_bus_message *m;
|
|
int64_t x;
|
|
|
|
sd_bus_message_read(m, "x", &x);</programlisting>
|
|
|
|
<para>Read all types of integers:</para>
|
|
|
|
<programlisting>uint8_t y;
|
|
int16_t n;
|
|
uint16_t q;
|
|
int32_t i;
|
|
uint32_t u;
|
|
int32_t x;
|
|
uint32_t t;
|
|
double d;
|
|
|
|
sd_bus_message_read(m, "ynqiuxtd", &y, &n, &q, &i, &u, &x, &t, &d);</programlisting>
|
|
|
|
<para>Read a structure composed of a string and a D-Bus path:</para>
|
|
|
|
<programlisting>const char *s, *p;
|
|
|
|
sd_bus_message_read(m, "(so)", &s, &p);
|
|
</programlisting>
|
|
|
|
<para>Read a variant, with the real type "gt" (signature, unsigned integer):
|
|
</para>
|
|
|
|
<programlisting>const char *s;
|
|
uint64_t *v;
|
|
|
|
sd_bus_message_read(m, "v", "gt", &s, &v);</programlisting>
|
|
|
|
<para>Read a dictionary containing three pairs of type {integer=>string}:
|
|
</para>
|
|
|
|
<programlisting>int i, j, k;
|
|
const char *s, *t, *u;
|
|
|
|
sd_bus_message_read(m, "a{is}", 3, &i, &s, &j, &t, &k, &u);
|
|
</programlisting>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
|
|
<para>
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_bus_message_read_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|