Merge pull request #9490 from keszybz/document-sd_message_read

Document sd_bus_message_read

man/rules/meson.build

@@ -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',

man/sd_bus_error.xml

@@ -100,7 +100,7 @@
         <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
         <paramdef>int <parameter>error</parameter></paramdef>
         <paramdef>const char *<parameter>format</parameter></paramdef>
-        <paramdef>va_list ap</paramdef>
+        <paramdef>va_list <parameter>ap</parameter></paramdef>
       </funcprototype>
 
       <funcprototype>

man/sd_bus_message_append.xml

@@ -94,13 +94,12 @@
     values for each entry matching the element type of
     the dictionary entries.</para>
 
-    <para>The <function>sd_bus_message_appendv()</function> is equivalent to
+    <para>The <function>sd_bus_message_appendv()</function> is equivalent to the
-    the function <function>sd_bus_message_append()</function>,
+    <function>sd_bus_message_append()</function>, except that it is called with
-    except that it is called with a <literal>va_list</literal> instead of
+    a <literal>va_list</literal> instead of a variable number of arguments. This
-    a variable number of arguments. This function does not call the
+    function does not call the <function>va_end()</function> macro. Because it
-    <function>va_end()</function> macro. Because it invokes the
+    invokes the <function>va_arg()</function> macro, the value of
-    <function>va_arg()</function> macro, the value of ap
+    <parameter>ap</parameter> is undefined after the call.</para>
-    is undefined after the call.</para>
 
     <para>For further details on the D-Bus type system, please consult
     the <ulink

man/sd_bus_message_append_basic.xml

@@ -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>

man/sd_bus_message_read.xml

@@ -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>

man/sd_bus_message_read_basic.xml

@@ -52,18 +52,130 @@
     </para>
 
     <para>
-      If <parameter>p</parameter> is not NULL, it should contain a pointer to an
+      If <parameter>p</parameter> is not <constant>NULL</constant>, it should contain
-      appropriate object. For example, if <parameter>type</parameter> is
+      a pointer to an appropriate object. For example, if <parameter>type</parameter>
-      <constant>'y'</constant>, the object passed in <parameter>p</parameter>
+      is <constant>'y'</constant>, the object passed in <parameter>p</parameter>
-      should have type <code>uint8_t *</code>. If <parameter>type</parameter>
+      should have type <code>uint8_t *</code>. If <parameter>type</parameter> is
-      is <constant>'s'</constant>, the object passed in <parameter>p</parameter>
+      <constant>'s'</constant>, the object passed in <parameter>p</parameter> should
-      should have type <code>const char **</code>. Note that, if the basic type
+      have type <code>const char **</code>. Note that, if the basic type is a pointer
-      is a pointer (e.g., <code>const char *</code> in the case of a string),
+      (e.g., <code>const char *</code> in the case of a string), the pointer is only
-      the pointer is only borrowed and the contents must be copied if they are
+      borrowed and the contents must be copied if they are to be used after the end
-      to be used after the end of the messages lifetime. Similarly, during the
+      of the messages lifetime. Similarly, during the lifetime of such a pointer, the
-      lifetime of such a pointer, the message must not be modified.
+      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>