net/portmapper: log upnp information

This logs some basic statistics for UPnP, so that tailscale can better understand what routers
are being used and how to connect to them.

Signed-off-by: julianknodt <julianknodt@gmail.com>

net/portmapper/portmapper.go

@@ -714,7 +714,10 @@ func (c *Client) Probe(ctx context.Context) (res ProbeResult, err error) {
 				res.UPnP = true
 				c.mu.Lock()
 				c.uPnPSawTime = time.Now()
+				if c.uPnPMeta != meta {
+					c.logf("UPnP meta changed: %+v", meta)
 					c.uPnPMeta = meta
+				}
 				c.mu.Unlock()
 			}
 		case c.pxpPort(): // same value for PMP and PCP

net/portmapper/upnp.go

@@ -311,6 +311,11 @@ func (c *Client) getUPnPPortMapping(
 
 type uPnPDiscoResponse struct {
 	Location string
+	// Server describes what version the UPnP is, such as MiniUPnPd/2.x.x
+	Server string
+	// USN is the serial number of the device, which also contains
+	// what kind of UPnP service is being offered, i.e. InternetGatewayDevice:2
+	USN string
 }
 
 // parseUPnPDiscoResponse parses a UPnP HTTP-over-UDP discovery response.
@@ -321,5 +326,7 @@ func parseUPnPDiscoResponse(body []byte) (uPnPDiscoResponse, error) {
 		return r, err
 	}
 	r.Location = res.Header.Get("Location")
+	r.Server = res.Header.Get("Server")
+	r.USN = res.Header.Get("Usn")
 	return r, nil
 }

net/portmapper/upnp_test.go

@@ -43,9 +43,13 @@ func TestParseUPnPDiscoResponse(t *testing.T) {
 	}{
 		{"google", googleWifiUPnPDisco, uPnPDiscoResponse{
 			Location: "http://192.168.86.1:5000/rootDesc.xml",
+			Server:   "Linux/5.4.0-1034-gcp UPnP/1.1 MiniUPnPd/1.9",
+			USN:      "uuid:a9708184-a6c0-413a-bbac-11bcf7e30ece::urn:schemas-upnp-org:device:InternetGatewayDevice:2",
 		}},
 		{"pfsense", pfSenseUPnPDisco, uPnPDiscoResponse{
 			Location: "http://192.168.1.1:2189/rootDesc.xml",
+			Server:   "FreeBSD/12.2-STABLE UPnP/1.1 MiniUPnPd/2.2.1",
+			USN:      "uuid:bee7052b-49e8-3597-b545-55a1e38ac11::urn:schemas-upnp-org:device:InternetGatewayDevice:1",
 		}},
 	}
 	for _, tt := range tests {