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        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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<refentry id="sd_bus_message_get_cookie" conditional="ENABLE_KDBUS">

        <refentryinfo>
                <title>sd_bus_message_get_cookie</title>
                <productname>systemd</productname>

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

        <refmeta>
                <refentrytitle>sd_bus_message_get_cookie</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_bus_message_get_cookie</refname>
                <refname>sd_bus_message_get_reply_cookie</refname>
                <refpurpose>Returns the transaction cookie of a message</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

                        <funcprototype>
                                <funcdef>int <function>sd_bus_message_get_cookie</function></funcdef>
                                <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
                                <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_bus_message_get_reply_cookie</function></funcdef>
                                <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
                                <paramdef>uint64_t *<parameter>cookie</parameter></paramdef>
                        </funcprototype>
                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_bus_message_get_cookie()</function> returns
                the transaction cookie of a message. The cookie
                uniquely identifies a message within each bus peer,
                but is not globally unique. It is assigned when a
                message is sent.</para>

                <para><function>sd_bus_message_get_reply_cookie()</function>
                returns the transaction cookie of the message the
                specified message is a response to. When a reply
                message is generated for a method call message, its
                cookie is copied over into this field. Note that while
                every message that is transferred is identified by a
                cookie, only response messages carry a reply cookie
                field.</para>

                <para>Both functions take a message object as first
                parameter and a place to store the 64-bit cookie
                in.</para>
        </refsect1>

        <refsect1>
                <title>Return Value</title>

                <para>On success, these calls return 0 or a positive
                integer. On failure, these calls return a negative
                errno-style error code.</para>

                <para>On success, the cookie/reply cookie is returned
                in the specified 64-bit unsigned integer variable.</para>
        </refsect1>

        <refsect1>
                <title>Errors</title>

                <para>Returned errors may indicate the following problems:</para>

                <variablelist>
                        <varlistentry>
                                <term><constant>-EINVAL</constant></term>

                                <listitem><para>A specified parameter
                                is invalid.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><constant>-ENODATA</constant></term>

                                <listitem><para>No cookie has been
                                assigned to this message. This either
                                indicates that the message has not
                                been sent yet and hence has no cookie
                                assigned, or that the message is not a
                                method response message and hence
                                carries a reply cookie
                                field.</para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The <function>sd_bus_message_get_cookie()</function>
                and <function>sd_bus_message_get_reply_cookie()</function>
                interfaces are available as a shared library, which can
                be compiled and linked to with the
                <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file.</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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>
