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diff --git a/man/sd_bus_message_read.xml b/man/sd_bus_message_read.xml new file mode 100644 index 0000000..65497aa --- /dev/null +++ b/man/sd_bus_message_read.xml @@ -0,0 +1,284 @@ +<?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-or-later --> + +<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> + <refname>sd_bus_message_peek_type</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>const 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>const char *<parameter>types</parameter></paramdef> + <paramdef>va_list <parameter>ap</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef>int <function>sd_bus_message_peek_type</function></funcdef> + <paramdef>sd_bus_message *<parameter>m</parameter></paramdef> + <paramdef>char *<parameter>type</parameter></paramdef> + <paramdef>const char **<parameter>contents</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 <type>int8_t</type> for a <literal>y</literal> in the type string, a pointer to + <type>int32_t</type> for an <literal>i</literal>, a pointer to <type>const char*</type> for an + <literal>s</literal>, ...) which are set based on the values in the message. As an exception, in case of + 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., <type>const char *</type> 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 message's lifetime. If the type is + <literal>h</literal> (UNIX file descriptor), the descriptor is not duplicated by this call and the + returned descriptor remains in possession of the message object, and needs to be duplicated by the caller + in order to keep an open reference to it after the message object is freed.</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><type>int</type>, 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> + + <para><function>sd_bus_message_peek_type()</function> determines the type of the next element in + <parameter>m</parameter> to be read by <function>sd_bus_message_read()</function> or similar functions. + On success, the type is stored in <parameter>type</parameter>, if it is not <constant>NULL</constant>. + If the type is a container type, the type of its elements is stored in <parameter>contents</parameter>, + if it is not <constant>NULL</constant>. If this function successfully determines the type of the next + element in <parameter>m</parameter>, it returns a positive integer. If there are no more elements to be + read, it returns zero.</para> + </refsect1> + + <refsect1> + <title>Return Value</title> + + <para>On success, these functions return a non-negative integer. On failure, they return a negative + errno-style error code.</para> + + <refsect2 id='errors'> + <title>Errors</title> + + <para>Returned errors may indicate the following problems:</para> + + <variablelist> + <xi:include href="sd_bus_message_read_basic.xml" xpointer="errors-einval"/> + <xi:include href="sd_bus_message_read_basic.xml" xpointer="errors-enxio"/> + <xi:include href="sd_bus_message_read_basic.xml" xpointer="errors-ebadmsg"/> + <varlistentry> + <term><constant>-EBUSY</constant></term> + + <listitem><para>When reading from a container, this error will be returned if unread elements + are left in the container.</para> + + <xi:include href="version-info.xml" xpointer="v251"/></listitem> + </varlistentry> + </variablelist> + </refsect2> + </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 a boolean value:</para> + + <programlisting>sd_bus_message *m; +int x; /* Do not use C99 'bool' type here, it's typically smaller + in memory and would cause memory corruption */ + +sd_bus_message_read(m, "b", &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> + + <para>Read a single file descriptor, and duplicate it in order to keep it open after the message is + freed.</para> + + <programlisting>sd_bus_message *m; +int fd, fd_copy; + +sd_bus_message_read(m, "h", &fd); +fd_copy = fcntl(fd, FD_DUPFD_CLOEXEC, 3);</programlisting> + </refsect1> + + <refsect1> + <title>History</title> + <para><function>sd_bus_message_read()</function> and + <function>sd_bus_message_readv()</function> were added in version 240.</para> + <para><function>sd_bus_message_peek_type()</function> was added in version 246.</para> + </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>, + <citerefentry><refentrytitle>sd_bus_message_enter_container</refentrytitle><manvolnum>3</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |