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man: document sd_bus_read(), add more about sd_bus_read_basic()

This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2018-07-03 01:11:11 +02:00
parent c765233c89
commit 50972aac44
4 changed files with 385 additions and 10 deletions
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1
man/rules/meson.build
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@ -209,6 +209,7 @@ manpages = [
'3',
['sd_bus_message_get_realtime_usec', 'sd_bus_message_get_seqnum'],
''],
['sd_bus_message_read', '3', ['sd_bus_message_readv'], ''],
['sd_bus_message_read_basic', '3', [], ''],
['sd_bus_message_set_destination', '3', ['sd_bus_message_set_sender'], ''],
['sd_bus_negotiate_fds',

1
man/sd_bus_message_append_basic.xml
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@ -255,6 +255,7 @@
<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_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
</para>

231
man/sd_bus_message_read.xml Normal file
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@ -0,0 +1,231 @@
<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//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 &lt;systemd/sd-bus.h&gt;</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>
</refsect1>
<xi:include href="sd_bus_message_read_basic.xml" xpointer="errors" />
<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", &amp;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", &amp;y, &amp;n, &amp;q, &amp;i, &amp;u, &amp;x, &amp;t, &amp;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)", &amp;s, &amp;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", &amp;s, &amp;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, &amp;i, &amp;s, &amp;j, &amp;t, &amp;k, &amp;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_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>

162
man/sd_bus_message_read_basic.xml
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@ -52,18 +52,130 @@
</para>
<para>
If <parameter>p</parameter> is not NULL, it should contain a pointer to an
appropriate object. For example, if <parameter>type</parameter> is
<constant>'y'</constant>, the object passed in <parameter>p</parameter>
should have type <code>uint8_t *</code>. If <parameter>type</parameter>
is <constant>'s'</constant>, the object passed in <parameter>p</parameter>
should have type <code>const char **</code>. Note that, if the basic type
is a pointer (e.g., <code>const char *</code> in the case of a string),
the pointer is only borrowed and the contents must be copied if they are
to be used after the end of the messages lifetime. Similarly, during the
lifetime of such a pointer, the message must not be modified.
If <parameter>p</parameter> is not <constant>NULL</constant>, it should contain
a pointer to an appropriate object. For example, if <parameter>type</parameter>
is <constant>'y'</constant>, the object passed in <parameter>p</parameter>
should have type <code>uint8_t *</code>. If <parameter>type</parameter> is
<constant>'s'</constant>, the object passed in <parameter>p</parameter> should
have type <code>const char **</code>. Note that, if the basic type is a pointer
(e.g., <code>const char *</code> in the case of a string), the pointer is only
borrowed and the contents must be copied if they are to be used after the end
of the messages lifetime. Similarly, during the lifetime of such a pointer, the
message must not be modified. See the table below for a complete list of allowed
types.
</para>
<table id='format-specifiers'>
<title>Item type specifiers</title>
<tgroup cols='4'>
<colspec colname='specifier' />
<colspec colname='constant' />
<colspec colname='description' />
<colspec colname='ctype' />
<thead>
<row>
<entry>Specifier</entry>
<entry>Constant</entry>
<entry>Description</entry>
<entry>Expected C Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>y</literal></entry>
<entry><constant>SD_BUS_TYPE_BYTE</constant></entry>
<entry>unsigned integer</entry>
<entry>uint8_t *</entry>
</row>
<row>
<entry><literal>b</literal></entry>
<entry><constant>SD_BUS_TYPE_BOOLEAN</constant></entry>
<entry>boolean</entry>
<entry>int *</entry>
</row>
<row>
<entry><literal>n</literal></entry>
<entry><constant>SD_BUS_TYPE_INT16</constant></entry>
<entry>signed integer</entry>
<entry>int16_t *</entry>
</row>
<row>
<entry><literal>q</literal></entry>
<entry><constant>SD_BUS_TYPE_UINT16</constant></entry>
<entry>unsigned integer</entry>
<entry>uint16_t *</entry>
</row>
<row>
<entry><literal>i</literal></entry>
<entry><constant>SD_BUS_TYPE_INT32</constant></entry>
<entry>signed integer</entry>
<entry>int32_t *</entry>
</row>
<row>
<entry><literal>u</literal></entry>
<entry><constant>SD_BUS_TYPE_UINT32</constant></entry>
<entry>unsigned integer</entry>
<entry>uint32_t *</entry>
</row>
<row>
<entry><literal>x</literal></entry>
<entry><constant>SD_BUS_TYPE_INT64</constant></entry>
<entry>signed integer</entry>
<entry>int64_t *</entry>
</row>
<row>
<entry><literal>t</literal></entry>
<entry><constant>SD_BUS_TYPE_UINT64</constant></entry>
<entry>unsigned integer</entry>
<entry>uint64_t *</entry>
</row>
<row>
<entry><literal>d</literal></entry>
<entry><constant>SD_BUS_TYPE_DOUBLE</constant></entry>
<entry>floating-point</entry>
<entry>double *</entry>
</row>
<row>
<entry><literal>s</literal></entry>
<entry><constant>SD_BUS_TYPE_STRING</constant></entry>
<entry>Unicode string</entry>
<entry>const char **</entry>
</row>
<row>
<entry><literal>o</literal></entry>
<entry><constant>SD_BUS_TYPE_OBJECT_PATH</constant></entry>
<entry>object path</entry>
<entry>const char **</entry>
</row>
<row>
<entry><literal>g</literal></entry>
<entry><constant>SD_BUS_TYPE_SIGNATURE</constant></entry>
<entry>signature</entry>
<entry>const char **</entry>
</row>
<row>
<entry><literal>h</literal></entry>
<entry><constant>SD_BUS_TYPE_UNIX_FD</constant></entry>
<entry>UNIX file descriptor</entry>
<entry>int *</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
If there is no object of the specified type at the current position in the
message, an error is returned.
@ -80,12 +192,42 @@
</para>
</refsect1>
<refsect1 id='errors'>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>Specified type string is invalid or the message parameter is
<constant>NULL</constant>.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENXIO</constant></term>
<listitem><para>The message does not contain the specified type at current
position.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-EBADMSG</constant></term>
<listitem><para>The message cannot be parsed.</para></listitem>
</varlistentry>
</variablelist>
</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_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>