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23 <div class="titlepage"><div><div><h2 class="title">
24 <a name="server-tutorial"></a>Writing a UPnP Service</h2></div></div></div>
25 <div class="simplesect">
26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
27 <a name="id2897295"></a>Introduction</h2></div></div></div>
29 This chapter explains how to implement a UPnP service using GUPnP. For
30 this example we will create a virtual UPnP-enabled light bulb.
33 Before any code can be written, the device and services that it implement
34 need to be described in XML. Although this can be frustrating, if you are
35 implementing a standardised service (see <a class="ulink" href="http://upnp.org/standardizeddcps/" target="_top">http://upnp.org/standardizeddcps/</a> for the list of standard devices
36 and services) then the service description is already written for you and
37 the device description is trivial. UPnP has standardised <a class="ulink" href="http://upnp.org/standardizeddcps/lighting.asp" target="_top">Lighting
38 Controls</a>, so we'll be using the device and service types defined
42 <div class="simplesect">
43 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
44 <a name="id2900786"></a>Defining the Device</h2></div></div></div>
46 The first step is to write the <em class="firstterm">device description</em>
47 file. This is a short XML document which describes the device and what
48 services it provides (for more details see the <a class="ulink" href="http://upnp.org/specs/arch/UPnP-DeviceArchitecture-v1.0.pdf" target="_top">UPnP
49 Device Architecture</a> specification, section 2.1). We'll be using
50 the <code class="literal">BinaryLight1</code> device type, but if none of the
51 existing device types are suitable a custom device type can be created.
53 <pre class="programlisting"><?xml version="1.0" encoding="utf-8"?>
54 <root xmlns="urn:schemas-upnp-org:device-1-0">
56 <major>1</major>
57 <minor>0</minor>
61 <deviceType>urn:schemas-upnp-org:device:BinaryLight:1</deviceType>
62 <friendlyName>Kitchen Lights</friendlyName>
63 <manufacturer>OpenedHand</manufacturer>
64 <modelName>Virtual Light</modelName>
65 <UDN>uuid:cc93d8e6-6b8b-4f60-87ca-228c36b5b0e8</UDN>
69 <serviceType>urn:schemas-upnp-org:service:SwitchPower:1</serviceType>
70 <serviceId>urn:upnp-org:serviceId:SwitchPower:1</serviceId>
71 <SCPDURL>/SwitchPower1.xml</SCPDURL>
72 <controlURL>/SwitchPower/Control</controlURL>
73 <eventSubURL>/SwitchPower/Event</eventSubURL>
80 The <code class="sgmltag-element">specVersion</code> tag defines what version of the UPnP
81 Device Architecture the document conforms to. At the time of writing the
85 Next there is the root <code class="sgmltag-element">device</code> tag. This contains
86 metadata about the device, lists the services it provides and any
87 sub-devices present (there are none in this example). The
88 <code class="sgmltag-element">deviceType</code> tag specifies the type of the device.
91 Next we have <code class="sgmltag-element">friendlyName</code>,
92 <code class="sgmltag-element">manufacturer</code> and <code class="sgmltag-element">modelName</code>. The
93 friendly name is a human-readable name for the device, the manufacturer
94 and model name are self-explanatory.
97 Next there is the UDN, or <em class="firstterm">Unique Device Name</em>. This
98 is an identifier which is unique for each device but persistent for each
99 particular device. Although it has to start with <code class="literal">uuid:</code>
100 note that it doesn't have to be an UUID. There are several alternatives
101 here: for example it could be computed at built-time if the software will
102 only be used on a single machine, or it could be calculated using the
103 device's serial number or MAC address.
106 Finally we have the <code class="sgmltag-element">serviceList</code> which describes the
107 services this device provides. Each service has a service type (again
108 there are types defined for standardised services or you can create your
109 own), service identifier, and three URLs. As a service type we're using
110 the standard <code class="literal">SwitchPower1</code> service. The
111 <code class="sgmltag-element">SCPDURL</code> field specifies where the <em class="firstterm">Service
112 Control Protocol Document</em> can be found, this describes the
113 service in more detail and will be covered next. Finally there are the
114 control and event URLs, which need to be unique on the device and will be
118 <div class="simplesect">
119 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
120 <a name="id2913595"></a>Defining Services</h2></div></div></div>
122 Becase we are using a standard service we can use the service description
123 from the specification. This is the <code class="literal">SwitchPower1</code>
124 service description file:
126 <pre class="programlisting"><?xml version="1.0" encoding="utf-8"?>
127 <scpd xmlns="urn:schemas-upnp-org:service-1-0">
129 <major>1</major>
130 <minor>0</minor>
134 <name>SetTarget</name>
137 <name>NewTargetValue</name>
138 <relatedStateVariable>Target</relatedStateVariable>
139 <direction>in</direction>
141 </argumentList>
144 <name>GetTarget</name>
147 <name>RetTargetValue</name>
148 <relatedStateVariable>Target</relatedStateVariable>
149 <direction>out</direction>
151 </argumentList>
154 <name>GetStatus</name>
157 <name>ResultStatus</name>
158 <relatedStateVariable>Status</relatedStateVariable>
159 <direction>out</direction>
161 </argumentList>
164 <serviceStateTable>
165 <stateVariable sendEvents="no">
166 <name>Target</name>
167 <dataType>boolean</dataType>
168 <defaultValue>0</defaultValue>
169 </stateVariable>
170 <stateVariable sendEvents="yes">
171 <name>Status</name>
172 <dataType>boolean</dataType>
173 <defaultValue>0</defaultValue>
174 </stateVariable>
175 </serviceStateTable>
179 Again, the <code class="sgmltag-element">specVersion</code> tag defines the UPnP version
180 that is being used. The rest of the document consists of an
181 <code class="sgmltag-element">actionList</code> defining the <a class="glossterm" href="glossary.html#action"><em class="glossterm">actions</em></a> available and a
182 <code class="sgmltag-element">serviceStateTable</code> defining the <a class="glossterm" href="glossary.html#state-variable"><em class="glossterm">state variables</em></a>.
185 Every <code class="sgmltag-element">action</code> has a <code class="sgmltag-element">name</code> and a list
186 of <code class="sgmltag-element">argument</code>s. Arguments also have a name, a direction
187 (<code class="literal">in</code> or <code class="literal">out</code> for input or output
188 arguments) and a related state variable. The state variable is used to
189 determine the type of the argument, and as such is a required element.
190 This can lead to the creation of otherwise unused state variables to
191 define the type for an argument (the <code class="literal">WANIPConnection</code>
192 service is a good example of this), thanks to the legacy behind UPnP.
195 <code class="sgmltag-element">stateVariable</code>s need to specify their
196 <code class="sgmltag-element">name</code> and <code class="sgmltag-element">dataType</code>. State variables
197 by default send notifications when they change, to specify that a variable
198 doesn't do this set the <code class="sgmltag-element">sendEvents</code> attribute to
199 <code class="literal">no</code>. Finally there are optional
200 <code class="sgmltag-element">defaultValue</code>, <code class="sgmltag-element">allowedValueList</code> and
201 <code class="sgmltag-element">allowedValueRange</code> elements which specify what the
202 default and valid values for the variable.
205 For the full specification of the service definition file, including a
206 complete list of valid <code class="sgmltag-element">dataType</code>s, see section 2.3 of
207 the <a class="ulink" href="http://upnp.org/specs/arch/UPnP-DeviceArchitecture-v1.0.pdf" target="_top">UPnP
208 Device Architecture</a>.
211 <div class="simplesect">
212 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
213 <a name="id2909172"></a>Implementing the Device</h2></div></div></div>
215 Before starting to implement the device, some boilerplate code is needed
216 to initialise GUPnP. GLib types and threading needs to be initialised,
217 and then a GUPnP context can be created using gupnp_context_new().
219 <pre class="programlisting">GUPnPContext *context;
220 /* Initialize required subsystems */
221 g_thread_init (NULL);
223 /* Create the GUPnP context with default host and port */
224 context = gupnp_context_new (NULL, NULL, 0, NULL);</pre>
226 UPnP uses HTTP to provide the device and service description files, so
227 next we tell GUPnP to publish them. This is done with
228 gupnp_context_host_path() which takes a local filename to send when a
229 certain server path is requested.
231 <pre class="programlisting">gupnp_context_host_path (context, "BinaryLight1.xml", "/BinaryLight1.xml");
232 gupnp_context_host_path (context, "SwitchPower1.xml", "/SwitchPower1.xml");</pre>
234 Next the root device can be created.
236 <pre class="programlisting">GUPnPRootDevice *dev;
237 /* Create the root device object */
238 dev = gupnp_root_device_new (context, "/BinaryLight1.xml");
239 /* Activate the root device, so that it announces itself */
240 gupnp_root_device_set_available (dev, TRUE);</pre>
242 GUPnP scans the device description and any service description files it
243 refers to, so if the main loop was entered now the device and service
244 would be available on the network, albeit with no functionality. The
245 remaining task is to implement the services.
248 <div class="simplesect">
249 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
250 <a name="id2851217"></a>Implementing a Service</h2></div></div></div>
252 To implement a service we first fetch the #GUPnPService from the root
253 device using gupnp_device_info_get_service() (#GUPnPRootDevice is a
254 subclass of #GUPnPDevice, which implements #GUPnPDeviceInfo). This
255 returns a #GUPnPServiceInfo which again is an interface, implemented by
256 #GUPnPService (on the server) and #GUPnPServiceProxy (on the client).
258 <pre class="programlisting">GUPnPServiceInfo *service;
259 service = gupnp_device_info_get_service
260 (GUPNP_DEVICE_INFO (dev), "urn:schemas-upnp-org:service:SwitchPower:1");</pre>
262 #GUPnPService handles interacting with the network itself, leaving the
263 implementation of the service itself to signal handlers that we need to
264 connect. There are two signals: #GUPnPService::action-invoked and
265 #GUPnPService::query-variable. #GUPnPService::action-invoked is emitted
266 when a client invokes an action: the handler is passed a
267 #GUPnPServiceAction object that identifies which action was invoked, and
268 is used to return values using gupnp_service_action_set().
269 #GUPnPService::query-variable is emitted for evented variables when a
270 control point subscribes to the service (to announce the initial value),
271 or whenever a client queries the value of a state variable (note that this
272 is now deprecated behaviour for UPnP control points): the handler is
273 passed the variable name and a #GValue which should be set to the current
274 value of the variable.
277 There are two approaches that clients can take to handle these signals.
278 They can either connect a single handler to #GUPnPService::action-invoked
279 or #GUPnPService::query-variable and examine the arguments to decide what
280 action to take. Alternatively, handlers can be targetted at specific
281 actions or variables by using the <em class="firstterm">signal detail</em>
282 when connecting. For example, this causes
283 <code class="function">on_get_status_action</code> to be called when the
284 <code class="function">GetStatus</code> action is invoked:
286 <pre class="programlisting">static void on_get_status_action (GUPnPService *service, GUPnPServiceAction *action, gpointer user_data);
288 g_signal_connect (service, "action-invoked::GetStatus", G_CALLBACK (on_get_status_action), NULL);</pre>
290 The implementation of action handlers is quite simple. The handler is
291 passed a #GUPnPServiceAction object which represents the in-progress
292 action. If required it can be queried using
293 gupnp_service_action_get_name() to identify the action (this isn't
294 required if detailed signals were connected). Any
295 <em class="firstterm">in</em> arguments can be retrieving using
296 gupnp_service_action_get(), and then return values can be set using
297 gupnp_service_action_set(). Once the action has been performed, either
298 gupnp_service_action_return() or gupnp_service_action_return_error()
299 should be called to either return successfully or return an error code.
300 If any evented state variables were modified during the action then a
301 notification should be emitted using gupnp_service_notify(). This is an
302 example implementation of <code class="function">GetStatus</code> and
303 <code class="function">SetTarget</code>:
305 <pre class="programlisting">static gboolean status;
308 get_status_cb (GUPnPService *service, GUPnPServiceAction *action, gpointer user_data)
310 gupnp_service_action_set (action,
311 "ResultStatus", G_TYPE_BOOLEAN, status,
313 gupnp_service_action_return (action);
317 set_target_cb (GUPnPService *service, GUPnPServiceAction *action, gpointer user_data)
319 gupnp_service_action_get (action,
320 "NewTargetValue", G_TYPE_BOOLEAN, &status,
322 gupnp_service_action_return (action);
323 gupnp_service_notify (service, "Status", G_TYPE_STRING, status, NULL);
326 g_signal_connect (service, "action-invoked::GetStatus", G_CALLBACK (get_status_cb), NULL);
327 g_signal_connect (service, "action-invoked::SetTarget", G_CALLBACK (set_target_cb), NULL);</pre>
329 State variable query handlers are called with the name of the variable and
330 a #GValue. This value should be initialized with the relevant type and
331 then set to the current value. Again signal detail can be used to connect
332 handlers to specific state variable callbacks.
334 <pre class="programlisting">static gboolean status;
337 query_status_cb (GUPnPService *service, char *variable, GValue *value, gpointer user_data)
339 g_value_init (value, G_TYPE_BOOLEAN);
340 g_value_set_boolean (value, status);
343 g_signal_connect (service, "query-variable::Status", G_CALLBACK (query_status_cb), NULL);</pre>
345 The service is now fully implemented. To complete it, enter a GLib main
346 loop and wait for a client to connect. The complete source code for this
347 example is available as <code class="filename">examples/light-server.c</code> in
351 For services which have many actions and variables there is a convenience
352 method gupnp_service_signals_autoconnect() which will automatically
353 connect specially named handlers to signals. See the documentation for
354 full details on how it works.
357 <div class="simplesect">
358 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
359 <a name="id2919384"></a>Generating Service-specific Wrappers</h2></div></div></div>
361 Using service-specific wrappers can simplify the implementation of a service.
362 Wrappers can be generated with <a class="xref" href="gupnp-binding-tool.html" title="gupnp-binding-tool"><span class="refentrytitle">gupnp-binding-tool</span>(1)</a>
363 using the option <code class="literal">--mode server</code>.
366 In the following examples the wrapper has been created with <code class="literal">--mode server --prefix switch</code>.
368 <pre class="programlisting">static gboolean status;
371 get_status_cb (GUPnPService *service,
372 GUPnPServiceAction *action,
375 switch_get_status_action_set (action, status);
377 gupnp_service_action_return (action);
381 set_target_cb (GUPnPService *service,
382 GUPnPServiceAction *action,
385 switch_set_target_action_get (action, &status);
386 switch_status_variable_notify (service, status);
388 gupnp_service_action_return (action);
393 switch_get_status_action_connect (service, G_CALLBACK(get_status_cb), NULL);
394 switch_set_target_action_connect (service, G_CALLBACK(set_target_cb), NULL);</pre>
396 Note how many possible problem situations that were run-time errors are
397 actually compile-time errors when wrappers are used: Action names,
398 argument names and argument types are easier to get correct (and available
399 in editor autocompletion).
402 State variable query handlers are implemented in a similar manner, but
403 they are even simpler as the return value of the handler is the state
406 <pre class="programlisting">static gboolean
407 query_status_cb (GUPnPService *service,
415 switch_status_query_connect (service, query_status_cb, NULL);</pre>
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