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<title>The TpSvc* interfaces: telepathy-glib API Reference Manual</title>
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<h2><span class="refentrytitle">
The TpSvc* interfaces
</span></h2>
<p>The TpSvc* interfaces — How to export Telepathy objects</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
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<p>
The GInterfaces whose names start with TpSvc are generated automatically
from the Telepathy specification, and can be used to make it easier
to export methods and signals onto D-Bus. By implementing these
GInterfaces you can avoid needing to generate any "glue" using the
dbus-glib tools - this is all done internally inside telepathy-glib.
</p>
<p>
The media session interface makes a convenient example
because it only has two methods (Error() and Ready())
and one signal (NewStreamHandler), and media session handlers
aren't expected to implement any other interfaces.
</p>
<p>
The first thing to do is pre-declare the interface init function,
and define the type you'll be using, declaring it to implement the
media stream handler interface:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
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<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">static void</span> <span class="function">stream_handler_iface_init</span> <span class="gtkdoc opt">(</span>gpointer<span class="gtkdoc opt">,</span> gpointer<span class="gtkdoc opt">);</span>
<span class="function">G_DEFINE_TYPE_WITH_CODE</span><span class="gtkdoc opt">(</span>GabbleMediaStream<span class="gtkdoc opt">,</span>
gabble_media_stream<span class="gtkdoc opt">,</span>
G_TYPE_OBJECT<span class="gtkdoc opt">,</span>
<span class="function">G_IMPLEMENT_INTERFACE</span> <span class="gtkdoc opt">(</span>TP_TYPE_SVC_MEDIA_STREAM_HANDLER<span class="gtkdoc opt">,</span>
stream_handler_iface_init<span class="gtkdoc opt">)</span>
<span class="gtkdoc opt">)</span></pre></td>
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</tbody>
</table>
</div>
<p>
Here we're using a subclass of G_TYPE_OBJECT. You can of course subclass
any type.
</p>
<p>
If you're implementing more than one interface on the same object,
define more than one init function, and call G_IMPLEMENT_INTERFACE
more than once. The interface init functions can even be extern
if you want to separate off chunks of functionality into a different
.c file. For instance, here's GabbleConnection:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="comment">/* in header files */</span>
<span class="gtkdoc kwb">void</span> <span class="function">conn_aliasing_iface_init</span> <span class="gtkdoc opt">(</span>gpointer<span class="gtkdoc opt">,</span> gpointer<span class="gtkdoc opt">);</span>
<span class="gtkdoc kwb">void</span> <span class="function">conn_avatars_iface_init</span> <span class="gtkdoc opt">(</span>gpointer<span class="gtkdoc opt">,</span> gpointer<span class="gtkdoc opt">);</span>
<span class="gtkdoc kwb">void</span> <span class="function">conn_presence_iface_init</span> <span class="gtkdoc opt">(</span>gpointer<span class="gtkdoc opt">,</span> gpointer<span class="gtkdoc opt">);</span>
<span class="comment">/* in gabble-connection.c */</span>
<span class="gtkdoc kwb">static void</span> <span class="function">conn_iface_init</span> <span class="gtkdoc opt">(</span>gpointer<span class="gtkdoc opt">,</span> gpointer<span class="gtkdoc opt">);</span>
<span class="gtkdoc kwb">static void</span> <span class="function">capabilities_iface_init</span> <span class="gtkdoc opt">(</span>gpointer<span class="gtkdoc opt">,</span> gpointer<span class="gtkdoc opt">);</span>
<span class="function">G_DEFINE_TYPE_WITH_CODE</span><span class="gtkdoc opt">(</span>GabbleConnection<span class="gtkdoc opt">,</span>
gabble_connection<span class="gtkdoc opt">,</span>
TP_TYPE_BASE_CONNECTION<span class="gtkdoc opt">,</span>
<span class="function">G_IMPLEMENT_INTERFACE</span> <span class="gtkdoc opt">(</span>TP_TYPE_SVC_CONNECTION<span class="gtkdoc opt">,</span>
conn_iface_init<span class="gtkdoc opt">);</span>
<span class="function">G_IMPLEMENT_INTERFACE</span> <span class="gtkdoc opt">(</span>TP_TYPE_SVC_CONNECTION_INTERFACE_ALIASING<span class="gtkdoc opt">,</span>
conn_aliasing_iface_init<span class="gtkdoc opt">);</span>
<span class="function">G_IMPLEMENT_INTERFACE</span> <span class="gtkdoc opt">(</span>TP_TYPE_SVC_CONNECTION_INTERFACE_AVATARS<span class="gtkdoc opt">,</span>
conn_avatars_iface_init<span class="gtkdoc opt">);</span>
<span class="function">G_IMPLEMENT_INTERFACE</span> <span class="gtkdoc opt">(</span>TP_TYPE_SVC_CONNECTION_INTERFACE_CAPABILITIES<span class="gtkdoc opt">,</span>
capabilities_init<span class="gtkdoc opt">);</span>
<span class="function">G_IMPLEMENT_INTERFACE</span> <span class="gtkdoc opt">(</span>TP_TYPE_SVC_CONNECTION_INTERFACE_PRESENCE<span class="gtkdoc opt">,</span>
conn_presence_iface_init<span class="gtkdoc opt">);</span>
<span class="gtkdoc opt">)</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
The _class_init, _init etc. functions are just like normal, so I
won't describe them here. One thing to note, though, is that for
signals which are defined by the GInterface, you do not need to do
anything in the _class_init - the GInterface has already set the
signal up for you.
</p>
<p>
For each exported D-Bus method, there's a typedef ending with _impl
giving the signature you should use for your method implementation.
For example, here's the signature for the Error method on the
media session handler interface:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
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<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">void</span> <span class="gtkdoc opt">(*</span>tp_svc_media_session_handler_error_impl<span class="gtkdoc opt">)</span>
<span class="gtkdoc opt">(</span>TpSvcMediaSessionHandler <span class="gtkdoc opt">*</span>self<span class="gtkdoc opt">,</span> guint errno<span class="gtkdoc opt">,</span> <span class="gtkdoc kwb">const char</span> <span class="gtkdoc opt">*</span>message<span class="gtkdoc opt">,</span>
DBusGMethodInvocation <span class="gtkdoc opt">*</span>context<span class="gtkdoc opt">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
and here's the beginning of the corresponding implementation:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
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<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">static void</span>
<span class="function">gabble_media_session_error</span> <span class="gtkdoc opt">(</span>TpSvcMediaSessionHandler <span class="gtkdoc opt">*</span>iface<span class="gtkdoc opt">,</span>
guint errno<span class="gtkdoc opt">,</span>
<span class="gtkdoc kwb">const char</span> <span class="gtkdoc opt">*</span>message<span class="gtkdoc opt">,</span>
DBusGMethodInvocation <span class="gtkdoc opt">*</span>context<span class="gtkdoc opt">)</span>
<span class="gtkdoc opt">{</span>
GabbleMediaSession <span class="gtkdoc opt">*</span>self <span class="gtkdoc opt">=</span> <span class="function">GABBLE_MEDIA_SESSION</span> <span class="gtkdoc opt">(</span>iface<span class="gtkdoc opt">);</span>
<span class="comment">/* do stuff with self here */</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
All service methods in telepathy-glib are asynchronous - you can of
course implement them synchronously if you like, but you have to return
the result or error to D-Bus by calling a callback rather than by
returning from a function.
</p>
<p>
The method implementation's last parameter is a DBusGMethodInvocation.
To send the reply, you must either call dbus_g_method_return_error
(for a failure), dbus_g_method_return (for a successful return),
or an inline function whose name contains "_return_from_" provided by
the TpSvc interface. For example, for Error there's an inline function
tp_svc_media_session_handler_return_from_error(). These inline functions
are just a simple wrapper around dbus_g_method_return() to make it
type-safe - it's recommended that you use them where possible.
</p>
<p>
For instance, Error doesn't return anything, so
tp_svc_media_session_handler_return_from_error() doesn't take any
parameters apart from the DBusGMethodInvocation:
</p>
<div class="informalexample">
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<tbody>
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<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">static void</span>
<span class="function">gabble_media_session_error</span> <span class="gtkdoc opt">(</span>TpSvcMediaSessionHandler <span class="gtkdoc opt">*</span>iface<span class="gtkdoc opt">,</span>
guint errno<span class="gtkdoc opt">,</span>
<span class="gtkdoc kwb">const char</span> <span class="gtkdoc opt">*</span>message<span class="gtkdoc opt">,</span>
DBusGMethodInvocation <span class="gtkdoc opt">*</span>context<span class="gtkdoc opt">)</span>
<span class="gtkdoc opt">{</span>
GabbleMediaSession <span class="gtkdoc opt">*</span>self <span class="gtkdoc opt">=</span> <span class="function">GABBLE_MEDIA_SESSION</span> <span class="gtkdoc opt">(</span>iface<span class="gtkdoc opt">);</span>
<span class="comment">/* do stuff with self here */</span>
<span class="function"><a href="telepathy-glib-svc-media-interfaces.html#tp-svc-media-session-handler-return-from-error">tp_svc_media_session_handler_return_from_error</a></span> <span class="gtkdoc opt">(</span>context<span class="gtkdoc opt">);</span>
<span class="gtkdoc opt">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
As for signals, they're named as dictated by dbus-glib. This normally
gives you a sensible lower-case name - for instance NewStreamHandler
is mapped to "new-stream-handler".
</p>
<p>
To emit a signal, the generated code contains another convenience
function whose name contains _emit_. This is prototyped to take
the correct arguments for the signal, and emits it efficiently:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="function"><a href="telepathy-glib-svc-media-interfaces.html#tp-svc-media-session-handler-emit-new-stream-handler">tp_svc_media_session_handler_emit_new_stream_handler</a></span> <span class="gtkdoc opt">(</span>session<span class="gtkdoc opt">,</span>
object_path<span class="gtkdoc opt">,</span> id<span class="gtkdoc opt">,</span> media_type<span class="gtkdoc opt">,</span> TP_MEDIA_STREAM_DIRECTION_BIDIRECTIONAL<span class="gtkdoc opt">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
Finally, the interface init function needs to be written. Normally
you'd set the fields of a vtable to be pointers to your method
implementations. However, we couldn't do this in telepathy-glib
because that would mean breaking the ABI every time we added methods
to an interface. Instead, you call functions, with pointers to your
method implementations as a parameter:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">static void</span>
<span class="function">session_handler_iface_init</span> <span class="gtkdoc opt">(</span>gpointer g_iface<span class="gtkdoc opt">,</span> gpointer iface_data<span class="gtkdoc opt">)</span>
<span class="gtkdoc opt">{</span>
TpSvcMediaSessionHandlerClass <span class="gtkdoc opt">*</span>klass <span class="gtkdoc opt">=</span>
<span class="gtkdoc opt">(</span>TpSvcMediaSessionHandlerClass <span class="gtkdoc opt">*)</span>g_iface<span class="gtkdoc opt">;</span>
<span class="function"><a href="telepathy-glib-svc-media-interfaces.html#tp-svc-media-session-handler-implement-error">tp_svc_media_session_handler_implement_error</a></span> <span class="gtkdoc opt">(</span>klass<span class="gtkdoc opt">,</span>
gabble_media_session_error<span class="gtkdoc opt">);</span>
<span class="function"><a href="telepathy-glib-svc-media-interfaces.html#tp-svc-media-session-handler-implement-ready">tp_svc_media_session_handler_implement_ready</a></span> <span class="gtkdoc opt">(</span>klass<span class="gtkdoc opt">,</span>
gabble_media_session_ready<span class="gtkdoc opt">);</span>
<span class="gtkdoc opt">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
This is obviously quite repetitive if there are a lot of methods, so
the convention I've used in telepathy-glib, Gabble and
telepathy-sofiasip is to define a temporary macro called IMPLEMENT:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
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<td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">static void</span>
<span class="function">session_handler_iface_init</span> <span class="gtkdoc opt">(</span>gpointer g_iface<span class="gtkdoc opt">,</span> gpointer iface_data<span class="gtkdoc opt">)</span>
<span class="gtkdoc opt">{</span>
TpSvcMediaSessionHandlerClass <span class="gtkdoc opt">*</span>klass <span class="gtkdoc opt">=</span>
<span class="gtkdoc opt">(</span>TpSvcMediaSessionHandlerClass <span class="gtkdoc opt">*)</span>g_iface<span class="gtkdoc opt">;</span>
<span class="gtkdoc ppc">#define IMPLEMENT(x) tp_svc_media_session_handler_implement_##x (\</span>
<span class="gtkdoc ppc"> klass, gabble_media_session_##x)</span>
<span class="function">IMPLEMENT</span><span class="gtkdoc opt">(</span>error<span class="gtkdoc opt">);</span>
<span class="function">IMPLEMENT</span><span class="gtkdoc opt">(</span>ready<span class="gtkdoc opt">);</span>
<span class="gtkdoc ppc">#undef IMPLEMENT</span>
<span class="gtkdoc opt">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
If you're implementing many interfaces, just write many similar
interface init functions.
</p>
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