glib/docs/reference/gio/gdbus-codegen.xml

<refentry id="gdbus-codegen" lang="en">

<refentryinfo>
  <title>gdbus</title>
  <productname>GIO</productname>
  <authorgroup>
    <author>
      <contrib>Developer</contrib>
      <firstname>David</firstname>
      <surname>Zeuthen</surname>
      <email>zeuthen@gmail.com</email>
    </author>
  </authorgroup>
</refentryinfo>

<refmeta>
  <refentrytitle>gdbus-codegen</refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo class="manual">User Commands</refmiscinfo>
</refmeta>

<refnamediv>
  <refname>gdbus-codegen</refname>
  <refpurpose>D-Bus code and documentation generator</refpurpose>
</refnamediv>

<refsynopsisdiv>
  <cmdsynopsis>
    <command>gdbus-codegen</command>
    <arg><option>-h</option>, <option>--help</option></arg>
    <arg><option>--interface-prefix</option> <replaceable>org.project.Prefix</replaceable></arg>
    <arg><option>--generate-c-code</option> <replaceable>OUTFILES</replaceable></arg>
    <arg><option>--c-namespace</option> <replaceable>YourProject</replaceable></arg>
    <arg><option>--c-generate-object-manager</option></arg>
    <arg><option>--generate-docbook</option> <replaceable>OUTFILES</replaceable></arg>
    <arg><option>--xml-files</option> <replaceable>FILE</replaceable></arg>
    <group choice="plain" rep="repeat">
      <arg>
        <option>--annotate</option>
        <replaceable>ELEMENT</replaceable>
        <replaceable>KEY</replaceable>
        <replaceable>VALUE</replaceable>
      </arg>
    </group>
    <arg choice="plain">FILE</arg>
    <arg>
      <arg choice="plain" rep="repeat">FILE</arg>
    </arg>
  </cmdsynopsis>
</refsynopsisdiv>

<refsect1>
  <title>Description</title>
  <para>
    <command>gdbus-codegen</command> is used to generate code and/or
    documentation for one or more D-Bus interfaces. The tool reads
    <ulink
    url="http://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format">D-Bus
    Introspection XML</ulink> files and generates output files. The
    tool currently supports generating C code (via
    <option>--generate-c-code</option>) and Docbook XML (via
    <option>--generate-docbook</option>).
  </para>
</refsect1>

<refsect1>
  <title>Generating C code</title>
  <para>
    When generating C code, a
    #GInterface<!-- -->-derived type is generated for each D-Bus
    interface. Additionally, for every generated type,
    <type>FooBar</type>, two concrete instantiable types,
    <type>FooBarProxy</type> and <type>FooBarSkeleton</type>, implementing
    said interface are also generated. The former is derived from
    #GDBusProxy and intended for use on the client side
    while the latter is derived from the
    #GDBusInterfaceSkeleton type making it easy to export on a
    #GDBusConnection either directly or via a
    #GDBusObjectManagerServer instance.
  </para>
  <para>
    The name of each generated C type is derived from the D-Bus
    interface name stripped with the prefix given with
    <option>--interface-prefix</option> and with the dots removed and
    initial characters capitalized. For example, for the D-Bus
    interface <literal>com.acme.Coyote</literal> the name used is
    <literal>ComAcmeCoyote</literal>. For the D-Bus interface
    <literal>org.project.Bar.Frobnicator</literal> with
    <option>--interface-prefix</option>
    <literal>org.project.</literal>, the name used is
    <literal>BarFrobnicator</literal>.
  </para>
  <para>
    For methods, signals and properties, if not specified, the name
    defaults to the name of the method, signal or property.
  </para>
  <para>
    Two forms of the name are used - the CamelCase form and the
    lower-case form. The CamelCase form is used for the #GType and
    struct name, while lower-case form is used in function names. The
    lower-case form is calculated by converting from CamelCase to
    lower-case and inserting underscores at word boundaries (using
    certain heuristics).
  </para>
  <para>
    If the value given by the <literal>org.gtk.GDBus.C.Name</literal>
    annotation or the <option>--c-namespace</option> option contains
    an underscore (sometimes called <emphasis>Ugly_Case</emphasis>),
    then the camel-case name is derived by removing all underscores,
    and the lower-case name is derived by lower-casing the
    string. This is useful in some situations where abbreviations are
    used. For example, if the annotation is used on the interface
    <literal>net.MyCorp.MyApp.iSCSITarget</literal> with the value
    <literal>iSCSI_Target</literal> the CamelCase form is
    <literal>iSCSITarget</literal> while the lower-case form is
    <literal>iscsi_target</literal>. If the annotation is used on the
    method <literal>EjectTheiPod</literal> with the value
    <literal>Eject_The_iPod</literal>, the lower-case form is
    <literal>eject_the_ipod</literal>.
  </para>
</refsect1>

<refsect1>
  <title>Generating Docbook documentation</title>
  <para>
    Each generated Docbook XML file (see the
    <option>--generate-docbook</option> option for details) is a <ulink
    url="http://www.docbook.org/tdg/en/html/refentry.html"><literal>RefEntry</literal></ulink>
    article describing the D-Bus interface.
  </para>
</refsect1>

<refsect1>
  <title>Options</title>
  <para>
    The following options are supported:
  </para>
  <variablelist>

    <varlistentry>
      <term><option>-h</option>, <option>--help</option></term>
      <listitem>
        <para>
          Show help and exit.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><option>--xml-files</option> <replaceable>FILE</replaceable></term>
      <listitem>
        <para>
          The D-Bus introspection XML file.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><option>--interface-prefix</option> <replaceable>org.project.Prefix.</replaceable></term>
      <listitem>
        <para>
          A prefix to strip from all D-Bus interface names when
          calculating the typename for the C binding and the Docbook
          <ulink
          url="http://www.docbook.org/tdg/en/html/primary.html">sortas
          attribute</ulink>.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><option>--generate-docbook</option> <replaceable>OUTFILES</replaceable></term>
      <listitem>
        <para>
          Generate Docbook Documentation for each D-Bus interface and
          put it in <filename>OUTFILES-NAME.xml</filename> where
          <literal>NAME</literal> is a place-holder for the interface
          name, e.g. <literal>net.Corp.FooBar</literal> and so on.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><option>--generate-c-code</option> <replaceable>OUTFILES</replaceable></term>
      <listitem>
        <para>
          Generate C code for all D-Bus interfaces and put it in
          <filename>OUTFILES.c</filename> and
          <filename>OUTFILES.h</filename>.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><option>--c-namespace</option> <replaceable>YourProject</replaceable></term>
      <listitem>
        <para>
          The namespace to use for generated C code. This is expected
          to be in <ulink
          url="http://en.wikipedia.org/wiki/CamelCase">CamelCase</ulink>
          or <emphasis>Ugly_Case</emphasis> (see above).
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><option>--c-generate-object-manager</option></term>
      <listitem>
        <para>
          If this option is passed, suitable #GDBusObject,
          #GDBusObjectProxy, #GDBusObjectSkeleton and
          #GDBusObjectManagerClient subclasses are generated.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><option>--annotate</option> <replaceable>ELEMENT</replaceable> <replaceable>KEY</replaceable> <replaceable>VALUE</replaceable></term>
      <listitem>
        <para>
          Used to inject D-Bus annotations into the given XML
          files. It can be used with interfaces, methods, signals,
          properties and arguments in the following way:
        </para>
<informalexample><programlisting><![CDATA[
gdbus-codegen --c-namespace MyApp                           \
  --generate-c-code myapp-generated                         \
  --annotate "org.project.InterfaceName"                    \
    org.gtk.GDBus.C.Name MyFrobnicator                      \
  --annotate "org.project.InterfaceName:Property"           \
    bar bat                                                 \
  --annotate "org.project.InterfaceName.Method()"           \
    org.freedesktop.DBus.Deprecated true                    \
  --annotate "org.project.InterfaceName.Method()[arg_name]" \
    snake hiss                                              \
  --annotate "org.project.InterfaceName::Signal"            \
    cat meow                                                \
  --annotate "org.project.InterfaceName::Signal[arg_name]"  \
    dog wuff                                                \
  myapp-dbus-interfaces.xml
]]></programlisting></informalexample>
        <para>
          Any UTF-8 string can be used for <replaceable>KEY</replaceable> and <replaceable>VALUE</replaceable>.
        </para>
      </listitem>
    </varlistentry>

  </variablelist>
</refsect1>

<refsect1>
  <title>Supported D-Bus Annotations</title>
  <para>
    The following D-Bus annotations are supported by
    <command>gdbus-codegen</command>:
  </para>

  <variablelist>

    <varlistentry>
      <term><literal>org.freedesktop.DBus.Deprecated</literal></term>
      <listitem>
        <para>
          Can be used on any <literal>&lt;interface&gt;</literal>,
          <literal>&lt;method&gt;</literal>,
          <literal>&lt;signal&gt;</literal> and
          <literal>&lt;property&gt;</literal> element to specify that
          the element is deprecated if its value is
          <literal>true</literal>. Note that this annotation is
          defined in the <ulink
          url="http://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format">D-Bus
          specification</ulink> and can only assume the values
          <literal>true</literal> and <literal>false</literal>. In
          particular, you cannot specify the version that the element
          was deprecated in nor any helpful deprecation message. Such
          information should be added to the element documentation
          instead.
        </para>
        <para>
          When generating C code, this annotation is used to add
          #G_GNUC_DEPRECATED to generated functions for the element.
        </para>
        <para>
          When generating Docbook XML, a deprecation warning will
          appear along the documentation for the element.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><literal>org.gtk.GDBus.Since</literal></term>
      <listitem>
        <para>
          Can be used on any <literal>&lt;interface&gt;</literal>,
          <literal>&lt;method&gt;</literal>,
          <literal>&lt;signal&gt;</literal> and
          <literal>&lt;property&gt;</literal> element to specify the
          version (any free-form string but compared using a
          version-aware sort function) the element appeared in.
        </para>
        <para>
          When generating C code, this field is used to ensure
          function pointer order for preserving ABI/API, see <xref
          linkend="gdbus-code-stability"/>.
        </para>
        <para>
          When generating Docbook XML, the value of this tag appears
          in the documentation.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><literal>org.gtk.GDBus.DocString</literal></term>
      <listitem>
        <para>
          A string with Docbook content for documentation. This annotation can
          be used on <literal>&lt;interface&gt;</literal>,
          <literal>&lt;method&gt;</literal>,
          <literal>&lt;signal&gt;</literal>,
          <literal>&lt;property&gt;</literal> and
          <literal>&lt;arg&gt;</literal> elements.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><literal>org.gtk.GDBus.DocString.Short</literal></term>
      <listitem>
        <para>
          A string with Docbook content for short/brief
          documentation. This annotation can only be used on
          <literal>&lt;interface&gt;</literal> elements.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><literal>org.gtk.GDBus.C.Name</literal></term>
      <listitem>
        <para>
          Can be used on any <literal>&lt;interface&gt;</literal>,
          <literal>&lt;method&gt;</literal>,
          <literal>&lt;signal&gt;</literal> and
          <literal>&lt;property&gt;</literal> element to specify the
          name to use when generating C code. The value is expected to
          be in <ulink
          url="http://en.wikipedia.org/wiki/CamelCase">CamelCase</ulink>
          or <emphasis>Ugly_Case</emphasis> (see above).
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><literal>org.gtk.GDBus.C.ForceGVariant</literal></term>
      <listitem>
        <para>
          If set to a non-empty string, a #GVariant instance will
          be used instead of the natural C type. This annotation can
          be used on any <literal>&lt;arg&gt;</literal> and
          <literal>&lt;property&gt;</literal> element.
        </para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><literal>org.gtk.GDBus.C.UnixFD</literal></term>
      <listitem>
        <para>
          If set to a non-empty string, the generated code will
          include parameters to exchange file descriptors using the
          #GUnixFDList type. This annotation can be used on
          <literal>&lt;method&gt;</literal> elements.
        </para>
      </listitem>
    </varlistentry>

  </variablelist>

  <para>
    As an easier alternative to using the
    <literal>org.gtk.GDBus.DocString</literal> annotation, note that
    parser used by <command>gdbus-codegen</command> parses XML
    comments in a way similar to <ulink
    url="http://www.gtk.org/gtk-doc/">gtk-doc</ulink>:
<informalexample><programlisting><![CDATA[
<!--
  net.Corp.Bar:
  @short_description: A short description

  A <emphasis>longer</emphasis> description.

  This is a new paragraph.
-->
<interface name="net.corp.Bar">
  <!--
    FooMethod:
    @greeting: The docs for greeting parameter.
    @response: The docs for response parameter.

    The docs for the actual method.
  -->
  <method name="FooMethod">
    <arg name="greeting" direction="in" type="s"/>
    <arg name="response" direction="out" type="s"/>
  </method>

  <!--
    BarSignal:
    @blah: The docs for blah parameter.
    @boo: The docs for boo parameter.
    @since: 2.30

    The docs for the actual signal.
  -->
  <signal name="BarSignal">
    <arg name="blah" type="s"/>
    <arg name="boo" type="s"/>
  </signal>

  <!-- BazProperty: The docs for the property. -->
  <property name="BazProperty" type="s" access="read"/>
</interface>
]]></programlisting></informalexample>
  </para>
  <para>
    Note that <literal><![CDATA[@since]]></literal> can be used in any inline
    documentation bit (e.g. for interfaces, methods, signals and
    properties) to set the <literal>org.gtk.GDBus.Since</literal>
    annotation. For the <literal>org.gtk.GDBus.DocString</literal>
    annotation (and inline comments), note that substrings of the form
    <literal><![CDATA[#net.Corp.Bar]]></literal>,
    <literal><![CDATA[net.Corp.Bar.FooMethod()]]></literal>,
    <literal><![CDATA[#net.Corp.Bar::BarSignal]]></literal> and
    <literal><![CDATA[#net.Corp.InlineDocs:BazProperty]]></literal> are all
    expanded to links to the respective interface, method, signal and
    property.
    Additionally, substrings starting with <literal>@</literal> and <literal>%</literal> characters are rendered as
    <ulink url="http://www.docbook.org/tdg/en/html/parameter.html">parameter</ulink> and
    <ulink url="http://www.docbook.org/tdg/en/html/constant.html">constant</ulink> respectively.
  </para>
  <para>
    If both XML comments and
    <literal>org.gtk.GDBus.DocString</literal> or
    <literal>org.gtk.GDBus.DocString.Short</literal> annotations are
    present, the latter wins.
  </para>
</refsect1>

<refsect1>
  <title>Example</title>
  <para>
    Consider the following D-Bus Introspection XML.
  </para>
  <informalexample><programlisting><![CDATA[
<node>
  <interface name="net.Corp.MyApp.Frobber">
    <method name="HelloWorld">
      <arg name="greeting" direction="in" type="s"/>
      <arg name="response" direction="out" type="s"/>
    </method>

    <signal name="Notification">
      <arg name="icon_blob" type="ay"/>
      <arg name="height" type="i"/>
      <arg name="messages" type="as"/>
    </signal>

    <property name="Verbose" type="b" access="readwrite"/>
  </interface>
</node>
]]></programlisting>
  </informalexample>
  <para>
    If <command>gdbus-codegen</command> is used on this file like this:
  </para>
<informalexample><programlisting><![CDATA[
gdbus-codegen --generate-c-code myapp-generated       \
              --c-namespace MyApp                     \
              --interface-prefix net.corp.MyApp.      \
              net.Corp.MyApp.Frobber.xml
]]></programlisting></informalexample>
  <para>
    two files called
    <filename>myapp-generated.[ch]</filename> are
    generated. The files provide an abstract
    #GTypeInterface<!-- -->-derived type called
    <type>MyAppFrobber</type> as well as two instantiable types with
    the same name but suffixed with <type>Proxy</type> and
    <type>Skeleton</type>. The generated file, roughly, contains the
    following facilities:
  </para>
<informalexample><programlisting><![CDATA[
/* GType macros for the three generated types */
#define MY_APP_TYPE_FROBBER (my_app_frobber_get_type ())
#define MY_APP_TYPE_FROBBER_SKELETON (my_app_frobber_skeleton_get_type ())
#define MY_APP_TYPE_FROBBER_PROXY (my_app_frobber_proxy_get_type ())

typedef struct _MyAppFrobber MyAppFrobber; /* Dummy typedef */

typedef struct
{
  GTypeInterface parent_iface;

  /* Signal handler for the ::notification signal */
  void (*notification) (MyAppFrobber *proxy,
                        GVariant *icon_blob,
                        gint height,
                        const gchar* const *messages);

  /* Signal handler for the ::handle-hello-world signal */
  gboolean (*handle_hello_world) (MyAppFrobber *proxy,
                                  GDBusMethodInvocation *invocation,
                                  const gchar *greeting);
} MyAppFrobberIface;

/* Asynchronously calls HelloWorld() */
void
my_app_frobber_call_hello_world (MyAppFrobber *proxy,
                                 const gchar *greeting,
                                 GCancellable *cancellable,
                                 GAsyncReadyCallback callback,
                                 gpointer user_data);
gboolean
my_app_frobber_call_hello_world_finish (MyAppFrobber *proxy,
                                        gchar **out_response,
                                        GAsyncResult *res,
                                        GError **error);

/* Synchronously calls HelloWorld(). Blocks calling thread. */
gboolean
my_app_frobber_call_hello_world_sync (MyAppFrobber *proxy,
                                      const gchar *greeting,
                                      gchar **out_response,
                                      GCancellable *cancellable,
                                      GError **error);

/* Completes handling the HelloWorld() method call */
void
my_app_frobber_complete_hello_world (MyAppFrobber *object,
                                     GDBusMethodInvocation *invocation,
                                     const gchar *response);

/* Emits the ::notification signal / Notification() D-Bus signal */
void
my_app_frobber_emit_notification (MyAppFrobber *object,
                                  GVariant *icon_blob,
                                  gint height,
                                  const gchar* const *messages);

/* Gets the :verbose GObject property / Verbose D-Bus property.
 * Does no blocking I/O.
 */
gboolean my_app_frobber_get_verbose (MyAppFrobber *object);

/* Sets the :verbose GObject property / Verbose D-Bus property.
 * Does no blocking I/O.
 */
void my_app_frobber_set_verbose (MyAppFrobber *object,
                                 gboolean      value);

/* Gets the interface info */
GDBusInterfaceInfo *my_app_frobber_interface_info (void);

/* Creates a new skeleton object, ready to be exported */
MyAppFrobber *my_app_frobber_skeleton_new (void);

/* Client-side proxy constructors.
 *
 * Additionally, _new_for_bus(), _new_for_bus_finish() and
 * _new_for_bus_sync() proxy constructors are also generated.
 */
void
my_app_frobber_proxy_new        (GDBusConnection     *connection,
                                 GDBusProxyFlags      flags,
                                 const gchar         *name,
                                 const gchar         *object_path,
                                 GCancellable        *cancellable,
                                 GAsyncReadyCallback  callback,
                                 gpointer             user_data);
MyAppFrobber *
my_app_frobber_proxy_new_finish (GAsyncResult        *res,
                                 GError             **error);
MyAppFrobber *
my_app_frobber_proxy_new_sync   (GDBusConnection     *connection,
                                 GDBusProxyFlags      flags,
                                 const gchar         *name,
                                 const gchar         *object_path,
                                 GCancellable        *cancellable,
                                 GError             **error);
]]></programlisting></informalexample>
  <para>
    Thus, for every D-Bus method, there will be three C functions for
    calling the method, one #GObject signal for handling an incoming
    call and one C function for completing an incoming call. For every
    D-Bus signal, there's one #GObject signal and one C function for
    emitting it. For every D-Bus property, two C functions are
    generated (one setter, one getter) and one #GObject property. The
    following table summarizes the generated facilities and where they
    are applicable:
  </para>
  <informaltable>
    <tgroup cols="3">
      <thead>
        <row>
          <entry></entry>
          <entry>Client</entry>
          <entry>Server</entry>
        </row>
      </thead>
      <tbody>
        <row>
          <entry>Types</entry>
          <entry>Use <type>MyAppFrobberProxy</type></entry>
          <entry>Any type implementing the <type>MyAppFrobber</type> interface</entry>
        </row>
        <row>
          <entry>Methods</entry>
          <entry>Use <function>m_a_f_hello_world()</function> to call.</entry>
          <entry>Receive via the <function>handle_hello_world()</function> signal handler. Complete the call with <function>m_a_f_complete_hello_world()</function></entry>
        </row>
        <row>
          <entry>Signals</entry>
          <entry>Connect to the <function>::notification</function> GObject signal.</entry>
          <entry>Use <function>m_a_f_emit_notification()</function> to emit signal.</entry>
        </row>
        <row>
          <entry>Properties (Reading)</entry>
          <entry>Use <function>m_a_f_get_verbose()</function> or <parameter>:verbose</parameter>.</entry>
          <entry>Implement #GObject<!-- -->'s <function>get_property()</function> vfunc.</entry>
        </row>
        <row>
          <entry>Properties (writing)</entry>
          <entry>Use <function>m_a_f_set_verbose()</function> or <parameter>:verbose</parameter>.</entry>
          <entry>Implement #GObject<!-- -->'s <function>set_property()</function> vfunc.</entry>
        </row>
      </tbody>
    </tgroup>
  </informaltable>

  <refsect2>
    <title>Client-side usage</title>
    <para>
      You can use the generated proxy type with the generated
      constructors:
    </para>
    <informalexample><programlisting><![CDATA[
    MyAppFrobber *proxy;
    GError *error;

    error = NULL;
    proxy = my_app_frobber_proxy_new_for_bus_sync (
                G_BUS_TYPE_SESSION,
                G_DBUS_PROXY_FLAGS_NONE,
                "net.Corp.MyApp",              /* bus name */
                "/net/Corp/MyApp/SomeFrobber", /* object */
                NULL,                          /* GCancellable* */
                &error);
    /* do stuff with proxy */
    g_object_unref (proxy);
]]></programlisting></informalexample>
    <para>
      Instead of using the generic #GDBusProxy facilities, one can use
      the generated methods such as
      <function>my_app_frobber_call_hello_world()</function> to invoke
      the <function>net.Corp.MyApp.Frobber.HelloWorld()</function>
      D-Bus method, connect to the the
      <function>::notification</function> GObject signal to receive
      the <function>net.Corp.MyApp.Frobber::Notication</function>
      D-Bus signal and get/set the
      <parameter>net.Corp.MyApp.Frobber:Verbose</parameter> D-Bus
      Property using either the GObject property
      <parameter>:verbose</parameter> or the
      <function>my_app_get_verbose()</function> and
      <function>my_app_set_verbose()</function> methods. Use the
      standard #GObject::notify signal to listen to property changes.
    </para>
    <para>
      Note that all property access is via #GDBusProxy<!-- -->'s
      property cache so no I/O is ever done when reading properties.
      Also note that setting a property will cause the
      <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-properties">org.freedesktop.DBus.Properties.Set</ulink> method to be
      called on the remote object. This call, however, is asynchronous
      so setting a property won't block. Further, the change is
      delayed and no error checking is possible.
    </para>
  </refsect2>

  <refsect2>
    <title>Server-side usage</title>
    <para>
      The generated <type>MyAppFrobber</type> interface is designed so
      it is easy to implement it in a #GObject
      subclass. For example, to handle
      <function>HelloWorld()</function> method invocations, set the
      vfunc for <function>handle_hello_hello_world()</function> in the
      <type>MyAppFrobberIface</type> structure. Similary, to handle
      the <parameter>net.Corp.MyApp.Frobber:Verbose</parameter>
      property override the <parameter>:verbose</parameter> #GObject
      property from the subclass. To emit a signal, use
      e.g. <function>my_app_emit_signal()</function> or
      g_signal_emit_by_name().
    </para>
    <para>
      Instead of subclassing, it is often easier to use the generated
      <type>MyAppFrobberSkeleton</type> subclass. To handle incoming
      method calls, use <function>g_signal_connect()</function> with
      the <function>::handle-*</function> signals and instead of
      overriding #GObject<!-- -->'s
      <function>get_property()</function> and
      <function>set_property()</function> vfuncs, use
      g_object_get() and
      g_object_set() or the generated property
      getters and setters (the generated class has an internal
      property bag implementation).
    </para>
    <informalexample><programlisting><![CDATA[
static gboolean
on_handle_hello_world (MyAppFrobber           *interface,
                       GDBusMethodInvocation  *invocation,
                       const gchar            *greeting,
                       gpointer                user_data)
{
  if (g_strcmp0 (greeting, "Boo") != 0)
    {
      gchar *response;
      response = g_strdup_printf ("Word! You said `%s'.", greeting);
      my_app_complete_hello_world (interface, invocation, response);
      g_free (response);
    }
  else
    {
      g_dbus_method_invocation_return_error (invocation,
                 MY_APP_ERROR,
                 MY_APP_ERROR_NO_WHINING,
                 "Hey, %s, there will be no whining!",
                 g_dbus_method_invocation_get_sender (invocation));
    }
  return TRUE;
}

  [...]

  interface = my_app_frobber_skeleton_new ();
  my_app_frobber_set_verbose (interface, TRUE);

  g_signal_connect (interface,
                    "handle-hello-world",
                    G_CALLBACK (on_handle_hello_world),
                    some_user_data);

  [...]

  error = NULL;
  if (!g_dbus_interface_skeleton_export (G_DBUS_INTERFACE_SKELETON (interface),
                                         connection,
                                         "/path/of/dbus_object",
                                         &error))
    {
      /* handle error */
    }
]]></programlisting></informalexample>
    <para>
      To facilitate atomic changesets (multiple properties changing at
      the same time), #GObject::notify signals are queued up when
      received. The queue is drained in an idle handler (which is called from the
      <link linkend="g-main-context-push-thread-default">thread-default main loop</link>
      of the thread where the skeleton object was
      contructed) and will cause emissions of the <ulink
      url="http://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-properties">org.freedesktop.DBus.Properties::PropertiesChanged</ulink>
      signal with all the properties that have changed. Use
      g_dbus_interface_skeleton_flush() or
      g_dbus_object_skeleton_flush() to empty the queue
      immediately. Use g_object_freeze_notify() and
      g_object_thaw_notify() for atomic changesets if on a different
      thread.
    </para>
  </refsect2>
</refsect1>

<refsect1>
  <title>C Type Mapping</title>
  <para>
    Scalar types
    (type-strings
    <link linkend="G-VARIANT-TYPE-BOOLEAN:CAPS">'b'</link>,
    <link linkend="G-VARIANT-TYPE-BYTE:CAPS">'y'</link>,
    <link linkend="G-VARIANT-TYPE-INT16:CAPS">'n'</link>,
    <link linkend="G-VARIANT-TYPE-UINT16:CAPS">'q'</link>,
    <link linkend="G-VARIANT-TYPE-INT32:CAPS">'i'</link>,
    <link linkend="G-VARIANT-TYPE-UINT32:CAPS">'u'</link>,
    <link linkend="G-VARIANT-TYPE-INT64:CAPS">'x'</link>,
    <link linkend="G-VARIANT-TYPE-UINT64:CAPS">'t'</link> and
    <link linkend="G-VARIANT-TYPE-DOUBLE:CAPS">'d'</link>)
    ),
    strings (type-strings
    <link linkend="G-VARIANT-TYPE-STRING:CAPS">'s'</link>,
    <link linkend="G-VARIANT-TYPE-BYTESTRING:CAPS">'ay'</link>,
    <link linkend="G-VARIANT-TYPE-OBJECT-PATH:CAPS">'o'</link> and
    <link linkend="G-VARIANT-TYPE-SIGNATURE:CAPS">'g'</link>) and
    arrays of string (type-strings
    <link linkend="G-VARIANT-TYPE-STRING-ARRAY:CAPS">'as'</link>,
    <link linkend="G-VARIANT-TYPE-OBJECT-PATH-ARRAY:CAPS">'ao'</link> and
    <link linkend="G-VARIANT-TYPE-BYTESTRING-ARRAY:CAPS">'aay'</link>)
    are mapped to the natural types,
    e.g. #gboolean, #gdouble, #gint, <link linkend="gchararray">gchar*</link>,
    <link linkend="GStrv">gchar**</link> and
    so on. Everything else is mapped to the #GVariant
    type.
  </para>
  <para>
    This automatic mapping can be turned off by using the annotation
    <literal>org.gtk.GDBus.C.ForceGVariant</literal> - if used then a
    #GVariant is always exchanged instead of the
    corresponding native C type. This annotation may be convenient to
    use when using
    bytestrings (type-string <link linkend="G-VARIANT-TYPE-BYTESTRING:CAPS">'ay'</link>)
    for data that could have embedded NUL bytes.
  </para>
</refsect1>

<refsect1 id="gdbus-code-stability">
  <title>Stability Guarantees</title>
  <para>
    The generated C functions are guaranteed to not change their ABI
    that is, if a method, signal or property does not change its
    signature in the introspection XML, the generated C functions will
    not change its C ABI either. The ABI of the generated instance and
    class structures will be preserved as well.
  </para>
  <para>
    The ABI of the generated #GType<!-- -->s will be preserved only if
    the <literal>org.gtk.GDBus.Since</literal> annotation is used
    judiciously — this is because the VTable for the #GInterface
    relies on functions pointers for signal handlers. Specifically, if
    a D-Bus method, property or signal or is added to a D-Bus
    interface, then ABI of the generated #GInterface type is preserved
    if, and only if, each added method, property signal is annotated
    with they <literal>org.gtk.GDBus.Since</literal> annotation using
    a greater version number than previous versions.
  </para>
  <para>
    The generated C code currently happens to be annotated with <ulink
    url="http://www.gtk.org/gtk-doc/">gtk-doc</ulink> / <ulink
    url="https://wiki.gnome.org/Projects/GObjectIntrospection">GObject
    Introspection</ulink> comments / annotations. The layout and
    contents might change in the future so no guarantees about
    e.g. <literal>SECTION</literal> usage etc. is given.
  </para>
  <para>
    While the generated Docbook for D-Bus interfaces isn't expected to
    change, no guarantees are given at this point.
  </para>
  <para>
    It is important to note that the generated code should not be
    checked into revision control systems, nor it should be included
    in distributed source archives.
  </para>
</refsect1>

<refsect1>
  <title>Bugs</title>
  <para>
    Please send bug reports to either the distribution bug tracker
    or the upstream bug tracker at
    <ulink url="https://bugzilla.gnome.org/enter_bug.cgi?product=glib">https://bugzilla.gnome.org/enter_bug.cgi?product=glib</ulink>.
  </para>
</refsect1>

<refsect1>
  <title>See also</title>
  <para>
    <citerefentry>
      <refentrytitle>gdbus</refentrytitle><manvolnum>1</manvolnum>
    </citerefentry>
  </para>
</refsect1>

</refentry>