Add example of using the library to discover an InternetGatewayDevice.

cmd/discoverigd/discoverigd.go

@@ -0,0 +1,42 @@
+// Serves as a simple example/test of discovering UPnP devices on the local
+// network.
+package main
+
+import (
+	"fmt"
+
+	"github.com/huin/goupnp"
+)
+
+var spaces = "                                     "
+
+type indentLevel int
+
+func (i indentLevel) String() string {
+	return spaces[:i]
+}
+
+func displayDevice(indent indentLevel, device *goupnp.Device) {
+	fmt.Println(indent.String(), device)
+	for _, srv := range device.Services {
+		fmt.Println((indent + 1).String(), srv)
+	}
+	for _, subdev := range device.Devices {
+		displayDevice(indent+1, subdev)
+	}
+}
+
+func main() {
+	if results, err := goupnp.DiscoverDevices(goupnp.DeviceTypeInternetGatewayDevice); err != nil {
+		fmt.Println("Error discovering InternetGatewayDevice with UPnP: ", err)
+	} else {
+		fmt.Printf("Discovered %d InternetGatewayDevices:\n", len(results))
+		for _, maybeRootDevice := range results {
+			if maybeRootDevice.Err != nil {
+				fmt.Println(maybeRootDevice.Err)
+			} else {
+				displayDevice(0, maybeRootDevice.Root.Device)
+			}
+		}
+	}
+}