doc/client-tutorial.xml

   1 <?xml version="1.0"?>
   2 <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
   3
   4 <chapter id="client-tutorial">
   5   <title>Writing a UPnP Client</title>
   6
   7   <simplesect>
   8     <title>Introduction</title>
   9     <para>
  10       This chapter explains how to write an application which fetches the
  11       external IP address from an UPnP-compliant modem.  To do this a
  12       <glossterm>Control Point</glossterm> is created, which searches for
  13       services of the type
  14       <literal>urn:schemas-upnp-org:service:WANIPConnection:1</literal> (part of
  15       the <ulink url="http://upnp.org/standardizeddcps/igd.asp">Internet Gateway
  16       Device</ulink> specification).  As services are discovered
  17       <firstterm>Service Proxy</firstterm> objects are created by GUPnP to allow
  18       interaction with the service, on which we can invoke the action
  19       <function>GetExternalIPAddress</function> to fetch the external IP
  20       address.
  21     </para>
  22   </simplesect>
  23
  24   <simplesect>
  25     <title>Finding Services</title>
  26     <para>
  27       First, we initialize GUPnP and create a control point targeting the
  28       service type.  Then we connect a signal handler so that we are notified
  29       when services we are interested in are found.
  30     </para>
  31     <programlisting>#include &lt;libgupnp/gupnp-control-point.h&gt;
  32
  33 static GMainLoop *main_loop;
  34
  35 static void
  36 service_proxy_available_cb (GUPnPControlPoint *cp,
  37                             GUPnPServiceProxy *proxy,
  38                             gpointer           userdata)
  39 {
  40   /* &hellip; */
  41 }
  42
  43 int
  44 main (int argc, char **argv)
  45 {
  46   GUPnPContext *context;
  47   GUPnPControlPoint *cp;
  48
  49   /* Required initialisation */
  50   g_type_init ();
  51
  52   /* Create a new GUPnP Context.  By here we are using the default GLib main
  53      context, and connecting to the current machine's default IP on an
  54      automatically generated port. */
  55   context = gupnp_context_new (NULL, NULL, 0, NULL);
  56
  57   /* Create a Control Point targeting WAN IP Connection services */
  58   cp = gupnp_control_point_new
  59     (context, "urn:schemas-upnp-org:service:WANIPConnection:1");
  60
  61   /* The service-proxy-available signal is emitted when any services which match
  62      our target are found, so connect to it */
  63   g_signal_connect (cp,
  64                     "service-proxy-available",
  65                     G_CALLBACK (service_proxy_available_cb),
  66                     NULL);
  67
  68   /* Tell the Control Point to start searching */
  69   gssdp_resource_browser_set_active (GSSDP_RESOURCE_BROWSER (cp), TRUE);
  70
  71   /* Enter the main loop. This will start the search and result in callbacks to
  72      service_proxy_available_cb. */
  73   main_loop = g_main_loop_new (NULL, FALSE);
  74   g_main_loop_run (main_loop);
  75
  76   /* Clean up */
  77   g_main_loop_unref (main_loop);
  78   g_object_unref (cp);
  79   g_object_unref (context);
  80
  81   return 0;
  82 }</programlisting>
  83   </simplesect>
  84
  85   <simplesect>
  86     <title>Invoking Actions</title>
  87     <para>
  88       Now we have an application which searches for the service we specified and
  89       calls <function>service_proxy_available_cb</function> for each one it
  90       found.  To get the external IP address we need to invoke the
  91       <literal>GetExternalIPAddress</literal> action.  This action takes no in
  92       arguments, and has a single out argument called "NewExternalIPAddress".
  93       GUPnP has a set of methods to invoke actions (which will be very familiar
  94       to anyone who has used <literal>dbus-glib</literal>) where you pass a
  95       <constant>NULL</constant>-terminated varargs list of (name, GType, value)
  96       tuples for the in arguments, then a <constant>NULL</constant>-terminated
  97       varargs list of (name, GType, return location) tuples for the out
  98       arguments.
  99     </para>
 100     <programlisting>static void
 101 service_proxy_available_cb (GUPnPControlPoint *cp,
 102                             GUPnPServiceProxy *proxy,
 103                             gpointer           userdata)
 104 {
 105   GError *error = NULL;
 106   char *ip = NULL;
 107
 108   gupnp_service_proxy_send_action (proxy,
 109                                    /* Action name and error location */
 110                                    "GetExternalIPAddress", &amp;error,
 111                                    /* IN args */
 112                                    NULL,
 113                                    /* OUT args */
 114                                    "NewExternalIPAddress",
 115                                    G_TYPE_STRING, &amp;ip,
 116                                    NULL);
 117
 118   if (error == NULL) {
 119     g_print ("External IP address is %s\n", ip);
 120     g_free (ip);
 121   } else {
 122     g_printerr ("Error: %s\n", error-&gt;message);
 123     g_error_free (error);
 124   }
 125   g_main_loop_quit (main_loop);
 126 }</programlisting>
 127     <para>
 128       Note that gupnp_service_proxy_send_action() blocks until the service has
 129       replied.  If you need to make non-blocking calls then use
 130       gupnp_service_proxy_begin_action(), which takes a callback that will be
 131       called from the mainloop when the reply is received.
 132     </para>
 133   </simplesect>
 134
 135   <simplesect>
 136     <title>Subscribing to state variable change notifications</title>
 137     <para>
 138       It is possible to get change notifications for the service state variables
 139       that have attribute <literal>sendEvents="yes"</literal>. We'll demonstrate
 140       this by modifying <function>service_proxy_available_cb()</function> and using
 141       gupnp_service_proxy_add_notify() to setup a notification callback:
 142     </para>
 143     <programlisting>static void
 144 external_ip_address_changed (GUPnPServiceProxy *proxy,
 145                              const char        *variable,
 146                              GValue            *value,
 147                              gpointer           userdata)
 148 {
 149   g_print ("External IP address changed: %s\n", g_value_get_string (value));
 150 }
 151
 152 static void
 153 service_proxy_available_cb (GUPnPControlPoint *cp,
 154                             GUPnPServiceProxy *proxy,
 155                             gpointer           userdata)
 156 {
 157   g_print ("Found a WAN IP Connection service\n");
 158
 159   gupnp_service_proxy_set_subscribed (proxy, TRUE);
 160   if (!gupnp_service_proxy_add_notify (proxy,
 161                                        "ExternalIPAddress",
 162                                        G_TYPE_STRING,
 163                                        external_ip_address_changed,
 164                                        NULL)) {
 165     g_printerr ("Failed to add notify");
 166   }
 167 }</programlisting>
 168   </simplesect>
 169
 170   <simplesect>
 171     <title>Generating Wrappers</title>
 172     <para>
 173       Using gupnp_service_proxy_send_action() and gupnp_service_proxy_add_notify ()
 174       can become tedious, because of the requirement to specify the types and deal
 175       with GValues.  An
 176       alternative is to use <xref linkend="gupnp-binding-tool"/>, which
 177       generates wrappers that hide the boilerplate code from you.  Using a
 178       wrapper generated with prefix 'ipconn' would replace
 179       gupnp_service_proxy_send_action() with this code:
 180     </para>
 181     <programlisting>ipconn_get_external_ip_address (proxy, &amp;ip, &amp;error);</programlisting>
 182     <para>
 183       State variable change notifications are friendlier with wrappers as well:
 184     </para>
 185     <programlisting>static void
 186 external_ip_address_changed (GUPnPServiceProxy *proxy,
 187                              const gchar       *external_ip_address,
 188                              gpointer           userdata)
 189 {
 190   g_print ("External IP address changed: '%s'\n", external_ip_address);
 191 }
 192
 193 static void
 194 service_proxy_available_cb (GUPnPControlPoint *cp,
 195                             GUPnPServiceProxy *proxy
 196                             gpointer           userdata)
 197 {
 198   g_print ("Found a WAN IP Connection service\n");
 199
 200   gupnp_service_proxy_set_subscribed (proxy, TRUE);
 201   if (!ipconn_external_ip_address_add_notify (proxy,
 202                                               external_ip_address_changed,
 203                                               NULL)) {
 204     g_printerr ("Failed to add notify");
 205   }
 206 }</programlisting>
 207   </simplesect>
 208 </chapter>