Discovering UPnP devices

Here I present to you a piece of code that does a very basic UPnP discovery of devices on the network. This is normally the starting point for any UPnP control program.

Discovery is an important part of UPnP. It allows devices to be truly "plug 'n' play". It negates the need for the user to ave to configure the network settings on devices before they plug them in. This relies on the network supporting IP address allocation using DHCP, but DHCP is almost universally used in home networks as well as most corporate networks.

One potential problem with DHCP is that it is difficult to know in advance what IP addresses are ging to be assigned to devices. It is possible to configure DHCP to statically map IP addresses to specific devices, but this requires a configuraion step and removes the "plug 'n' play" element. Discovery solves this problem.

The code I present requires the Gnome GUPnP libraries (as well as dependent libraries such as GSSDP). These are readily available on most Linux distributions. You will need the development packages.

The code below is a very primitive control point. When run it will discover all of the UPnP devices on the local network, and then exit. This code is based on the GUPnP example control point which has been extended slightly. There are comments in the code explaining each major part:

//============================================================================
// Name : UPnPDiscovery.cpp
// Author : Majik 
// Version : 2.0 
//============================================================================ 
#include  
static GMainLoop *main_loop; 
/* This is our callback method to terminate the main loop
 * after the timeout has expired */

 static gboolean main_loop_timeout(void *data)
 {
   g_main_loop_quit (main_loop);
   return 0;
 }
 /* This is our callback method to handle new devices
 * which have been discovered. It simply prints the
 * device model and friendly name to to console */
 
 static void device_proxy_available_cb(GUPnPControlPoint *cp, GUPnPDeviceProxy *proxy)
 {
    GUPnPDeviceInfo* gupnp_device_info = GUPNP_DEVICE_INFO(proxy);
    g_print("Device model: %s", gupnp_device_info_get_model_name(gupnp_device_info));
    g_print("\tFriendly name: %s\n", gupnp_device_info_get_friendly_name(gupnp_device_info));
 }
 /*
  * This is the main program */
 
 int main (int argc, char **argv)
 {
    GUPnPContext *context;
    GUPnPControlPoint *cp;
    /* Required initialisation */
    g_thread_init (NULL);
    g_type_init ();
    /* Create a new GUPnP Context. By here we are using the default GLib main context, and connecting to the current machine's default IP on an automatically generated port. */
    context = gupnp_context_new (NULL, NULL, 0, NULL);

    /* Create a Control Point targeting UPnP Root devices */
   
    cp = gupnp_control_point_new(context, "upnp:rootdevice");
   /* The device-proxy-available signal is emitted when any devices which match our target are found, so connect to it */
    g_signal_connect (cp, "device-proxy-available", G_CALLBACK (device_proxy_available_cb), NULL);
   
    /* Tell the Control Point to start searching */
    gssdp_resource_browser_set_active (GSSDP_RESOURCE_BROWSER (cp), TRUE);

    /* Set a timeout of 2 seconds to finish processing */   
    g_timeout_add_seconds (2, main_loop_timeout, NULL);

    /* Enter the main loop. This will start the search and result in callbacks to device_proxy_available_cb. */
    main_loop = g_main_loop_new (NULL, FALSE);
    g_main_loop_run (main_loop);

    /* Clean up */
    g_main_loop_unref (main_loop);
    g_object_unref (cp);
    g_object_unref (context);
    return 0;
 } 

The way this works is using "callbacks", which is a very common technique in UPnP development as well as in other types of asynchronous programming. There are two callback functions:

device_proxy_available_cb - This is called whenever a new device is discovered on the network.
main_loop_timeout - This is called by a timer after a set period. It is used to terminate the program, otherwise it would run forever waiting for new devices to appear on the network

A typical output when this is run is as follows:

Device model: MiniUPnPd Friendly name: WANConnectionDevice
Device model: Sonos ZonePlayer 100 Friendly name: 192.168.0.203 - Sonos ZonePlayer
Device model: Sonos ZonePlayer S5 Friendly name: 192.168.0.204 - Sonos ZonePlayer
Device model: Sonos ZonePlayer S5 Friendly name: 192.168.0.206 - Sonos ZonePlayer
Device model: Sonos WD100 Friendly name: 192.168.0.205 - Sonos Wireless Dock


As you can see, this discovers not only Sonos devices but other UPnP devices on the network. In my case it discovers my UPnP IGD device (my firewall).