net/portmapper: fix UPnP probing, work against all ports

Prior to Tailscale 1.12 it detected UPnP on any port.
Starting with Tailscale 1.11.x, it stopped detecting UPnP on all ports.

Then start plumbing its discovered Location header port number to the
code that was assuming port 5000.

Fixes #2109

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/debug.go

@@ -206,6 +206,8 @@ func debugPortmap(ctx context.Context) error {
 	ctx, cancel := context.WithTimeout(ctx, 3*time.Second)
 	defer cancel()
 
+	portmapper.VerboseLogs = true
+
 	done := make(chan bool, 1)
 
 	var c *portmapper.Client

go.mod

@@ -31,7 +31,7 @@ require (
 	github.com/pkg/sftp v1.13.0
 	github.com/tailscale/certstore v0.0.0-20210528134328-066c94b793d3
 	github.com/tailscale/depaware v0.0.0-20201214215404-77d1e9757027
-	github.com/tailscale/goupnp v1.0.1-0.20210710010003-1cf2d718bbb2
+	github.com/tailscale/goupnp v1.0.1-0.20210804011211-c64d0f06ea05
 	github.com/tailscale/hujson v0.0.0-20200924210142-dde312d0d6a2
 	github.com/tcnksm/go-httpstat v0.2.0
 	github.com/toqueteos/webbrowser v1.2.0

go.sum

@@ -581,8 +581,8 @@ github.com/tailscale/certstore v0.0.0-20210528134328-066c94b793d3 h1:fEubocuQkrl
 github.com/tailscale/certstore v0.0.0-20210528134328-066c94b793d3/go.mod h1:2P+hpOwd53e7JMX/L4f3VXkv1G+33ES6IWZSrkIeWNs=
 github.com/tailscale/depaware v0.0.0-20201214215404-77d1e9757027 h1:lK99QQdH3yBWY6aGilF+IRlQIdmhzLrsEmF6JgN+Ryw=
 github.com/tailscale/depaware v0.0.0-20201214215404-77d1e9757027/go.mod h1:p9lPsd+cx33L3H9nNoecRRxPssFKUwwI50I3pZ0yT+8=
-github.com/tailscale/goupnp v1.0.1-0.20210710010003-1cf2d718bbb2 h1:AIJ8AF9O7jBmCwilP0ydwJMIzW5dw48Us8f3hLJhYBY=
-github.com/tailscale/goupnp v1.0.1-0.20210710010003-1cf2d718bbb2/go.mod h1:PdCqy9JzfWMJf1H5UJW2ip33/d4YkoKN0r67yKH1mG8=
+github.com/tailscale/goupnp v1.0.1-0.20210804011211-c64d0f06ea05 h1:4chzWmimtJPxRs2O36yuGRW3f9SYV+bMTTvMBI0EKio=
+github.com/tailscale/goupnp v1.0.1-0.20210804011211-c64d0f06ea05/go.mod h1:PdCqy9JzfWMJf1H5UJW2ip33/d4YkoKN0r67yKH1mG8=
 github.com/tailscale/hujson v0.0.0-20200924210142-dde312d0d6a2 h1:reREUgl2FG+o7YCsrZB8XLjnuKv5hEIWtnOdAbRAXZI=
 github.com/tailscale/hujson v0.0.0-20200924210142-dde312d0d6a2/go.mod h1:STqf+YV0ADdzk4ejtXFsGqDpATP9JoL0OB+hiFQbkdE=
 github.com/tcnksm/go-httpstat v0.2.0 h1:rP7T5e5U2HfmOBmZzGgGZjBQ5/GluWUylujl0tJ04I0=

net/portmapper/disabled_stubs.go

@@ -15,10 +15,6 @@ import (
 
 type upnpClient interface{}
 
-func getUPnPClient(ctx context.Context, gw netaddr.IP) (upnpClient, error) {
-	return nil, nil
-}
-
 func (c *Client) getUPnPPortMapping(
 	ctx context.Context,
 	gw netaddr.IP,

net/portmapper/portmapper.go

@@ -14,9 +14,11 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"net/http"
 	"sync"
 	"time"
 
+	"go4.org/mem"
 	"inet.af/netaddr"
 	"tailscale.com/net/interfaces"
 	"tailscale.com/net/netns"
@@ -62,8 +64,11 @@ type Client struct {
 	pmpPubIPTime time.Time  // time pmpPubIP last verified
 	pmpLastEpoch uint32
 
-	pcpSawTime  time.Time // time we last saw PCP was available
-	uPnPSawTime time.Time // time we last saw UPnP was available
+	pcpSawTime time.Time // time we last saw PCP was available
+
+	uPnPSawTime    time.Time         // time we last saw UPnP was available
+	uPnPMeta       uPnPDiscoResponse // Location header from UPnP UDP discovery response
+	uPnPHTTPClient *http.Client      // nil until needed
 
 	localPort uint16
 
@@ -560,27 +565,9 @@ func (c *Client) Probe(ctx context.Context) (res ProbeResult, err error) {
 	defer cancel()
 	defer closeCloserOnContextDone(ctx, uc)()
 
-	if c.sawUPnPRecently() {
-		res.UPnP = true
-	} else {
-		hasUPnP := make(chan bool, 1)
-		defer func() {
-			res.UPnP = <-hasUPnP
-		}()
-		go func() {
-			client, err := getUPnPClient(ctx, gw)
-			if err == nil && client != nil {
-				hasUPnP <- true
-				c.mu.Lock()
-				c.uPnPSawTime = time.Now()
-				c.mu.Unlock()
-			}
-			close(hasUPnP)
-		}()
-	}
-
 	pcpAddr := netaddr.IPPortFrom(gw, pcpPort).UDPAddr()
 	pmpAddr := netaddr.IPPortFrom(gw, pmpPort).UDPAddr()
+	upnpAddr := netaddr.IPPortFrom(gw, upnpPort).UDPAddr()
 
 	// Don't send probes to services that we recently learned (for
 	// the same gw/myIP) are available. See
@@ -595,11 +582,16 @@ func (c *Client) Probe(ctx context.Context) (res ProbeResult, err error) {
 	} else {
 		uc.WriteTo(pcpAnnounceRequest(myIP), pcpAddr)
 	}
+	if c.sawUPnPRecently() {
+		res.UPnP = true
+	} else {
+		uc.WriteTo(uPnPPacket, upnpAddr)
+	}
 
 	buf := make([]byte, 1500)
 	pcpHeard := false // true when we get any PCP response
 	for {
-		if pcpHeard && res.PMP {
+		if pcpHeard && res.PMP && res.UPnP {
 			// Nothing more to discover.
 			return res, nil
 		}
@@ -612,6 +604,19 @@ func (c *Client) Probe(ctx context.Context) (res ProbeResult, err error) {
 		}
 		port := addr.(*net.UDPAddr).Port
 		switch port {
+		case upnpPort:
+			if mem.Contains(mem.B(buf[:n]), mem.S(":InternetGatewayDevice:")) {
+				meta, err := parseUPnPDiscoResponse(buf[:n])
+				if err != nil {
+					c.logf("unrecognized UPnP discovery response; ignoring")
+				}
+				// log.Printf("UPnP reply %+v, %q", meta, buf[:n])
+				res.UPnP = true
+				c.mu.Lock()
+				c.uPnPSawTime = time.Now()
+				c.uPnPMeta = meta
+				c.mu.Unlock()
+			}
 		case pcpPort: // same as pmpPort
 			if pres, ok := parsePCPResponse(buf[:n]); ok {
 				if pres.OpCode == pcpOpReply|pcpOpAnnounce {
@@ -724,3 +729,13 @@ func parsePCPResponse(b []byte) (res pcpResponse, ok bool) {
 }
 
 var pmpReqExternalAddrPacket = []byte{0, 0} // version 0, opcode 0 = "Public address request"
+
+const (
+	upnpPort = 1900
+)
+
+var uPnPPacket = []byte("M-SEARCH * HTTP/1.1\r\n" +
+	"HOST: 239.255.255.250:1900\r\n" +
+	"ST: ssdp:all\r\n" +
+	"MAN: \"ssdp:discover\"\r\n" +
+	"MX: 2\r\n\r\n")

net/portmapper/upnp.go

@@ -8,17 +8,27 @@
 package portmapper
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"fmt"
+	"log"
 	"math/rand"
+	"net/http"
 	"net/url"
 	"time"
 
+	"github.com/tailscale/goupnp"
 	"github.com/tailscale/goupnp/dcps/internetgateway2"
 	"inet.af/netaddr"
 	"tailscale.com/control/controlknobs"
+	"tailscale.com/net/netns"
 )
 
+// VerboseLogs controls verbose debug logging.
+// It exists for use by "tailscaled debug --portmap".
+var VerboseLogs bool
+
 // References:
 //
 // WANIP Connection v2: http://upnp.org/specs/gw/UPnP-gw-WANIPConnection-v2-Service.pdf
@@ -44,7 +54,8 @@ func (u *upnpMapping) Release(ctx context.Context) {
 }
 
 // upnpClient is an interface over the multiple different clients exported by goupnp,
-// exposing the functions we need for portmapping. They are auto-generated from XML-specs.
+// exposing the functions we need for portmapping. Those clients are auto-generated from XML-specs,
+// which is why they're not very idiomatic.
 type upnpClient interface {
 	AddPortMapping(
 		ctx context.Context,
@@ -77,7 +88,7 @@ type upnpClient interface {
 		// greater than 0. From the spec, it appears if it is set to 0, it will switch to using
 		// 604800 seconds, but not sure why this is desired. The recommended time is 3600 seconds.
 		leaseDurationSec uint32,
-	) (err error)
+	) error
 
 	DeletePortMapping(ctx context.Context, remoteHost string, externalPort uint16, protocol string) error
 	GetExternalIPAddress(ctx context.Context) (externalIPAddress string, err error)
@@ -92,6 +103,8 @@ const tsPortMappingDesc = "tailscale-portmap"
 // behavior of calling AddPortMapping with port = 0 to specify a wildcard port.
 // It returns the new external port (which may not be identical to the external port specified),
 // or an error.
+//
+// TODO(bradfitz): also returned the actual lease duration obtained. and check it regularly.
 func addAnyPortMapping(
 	ctx context.Context,
 	upnp upnpClient,
@@ -130,51 +143,76 @@ func addAnyPortMapping(
 	return externalPort, err
 }
 
-// getUPnPClients gets a client for interfacing with UPnP, ignoring the underlying protocol for
+// getUPnPClient gets a client for interfacing with UPnP, ignoring the underlying protocol for
 // now.
 // Adapted from https://github.com/huin/goupnp/blob/master/GUIDE.md.
-func getUPnPClient(ctx context.Context, gw netaddr.IP) (upnpClient, error) {
+//
+// The gw is the detected gateway.
+//
+// The meta is the most recently parsed UDP discovery packet response
+// from the Internet Gateway Device.
+//
+// The provided ctx is not retained in the returned upnpClient, but
+// its associated HTTP client is (if set via goupnp.WithHTTPClient).
+func getUPnPClient(ctx context.Context, gw netaddr.IP, meta uPnPDiscoResponse) (upnpClient, error) {
 	if controlknobs.DisableUPnP() {
 		return nil, nil
 	}
-	ctx, cancel := context.WithTimeout(ctx, 250*time.Millisecond)
-	defer cancel()
-	// Attempt to connect over the multiple available connection types concurrently,
-	// returning the fastest.
 
-	// TODO(jknodt): this url seems super brittle? maybe discovery is better but this is faster
-	u, err := url.Parse(fmt.Sprintf("http://%s:5000/rootDesc.xml", gw))
+	if meta.Location == "" {
+		return nil, nil
+	}
+
+	if VerboseLogs {
+		log.Printf("fetching %v", meta.Location)
+	}
+	u, err := url.Parse(meta.Location)
 	if err != nil {
 		return nil, err
 	}
 
-	clients := make(chan upnpClient, 3)
-	go func() {
-		var err error
-		ip1Clients, err := internetgateway2.NewWANIPConnection1ClientsByURL(ctx, u)
-		if err == nil && len(ip1Clients) > 0 {
-			clients <- ip1Clients[0]
-		}
-	}()
-	go func() {
-		ip2Clients, err := internetgateway2.NewWANIPConnection2ClientsByURL(ctx, u)
-		if err == nil && len(ip2Clients) > 0 {
-			clients <- ip2Clients[0]
-		}
-	}()
-	go func() {
-		ppp1Clients, err := internetgateway2.NewWANPPPConnection1ClientsByURL(ctx, u)
-		if err == nil && len(ppp1Clients) > 0 {
-			clients <- ppp1Clients[0]
-		}
-	}()
-
-	select {
-	case client := <-clients:
-		return client, nil
-	case <-ctx.Done():
-		return nil, ctx.Err()
+	ipp, err := netaddr.ParseIPPort(u.Host)
+	if err != nil {
+		return nil, fmt.Errorf("unexpected host %q in %q", u.Host, meta.Location)
 	}
+	if ipp.IP() != gw {
+		return nil, fmt.Errorf("UPnP discovered root %q does not match gateway IP %v; ignoring UPnP",
+			meta.Location, gw)
+	}
+
+	ctx, cancel := context.WithTimeout(ctx, 500*time.Millisecond)
+	defer cancel()
+
+	// This part does a network fetch.
+	root, err := goupnp.DeviceByURL(ctx, u)
+	if err != nil {
+		return nil, err
+	}
+
+	// These parts don't do a network fetch.
+	// Pick the best service type available.
+	if cc, _ := internetgateway2.NewWANIPConnection2ClientsFromRootDevice(ctx, root, u); len(cc) > 0 {
+		return cc[0], nil
+	}
+	if cc, _ := internetgateway2.NewWANIPConnection1ClientsFromRootDevice(ctx, root, u); len(cc) > 0 {
+		return cc[0], nil
+	}
+	if cc, _ := internetgateway2.NewWANPPPConnection1ClientsFromRootDevice(ctx, root, u); len(cc) > 0 {
+		return cc[0], nil
+	}
+	return nil, nil
+}
+
+func (c *Client) upnpHTTPClientLocked() *http.Client {
+	if c.uPnPHTTPClient == nil {
+		c.uPnPHTTPClient = &http.Client{
+			Transport: &http.Transport{
+				DialContext:     netns.NewDialer().DialContext,
+				IdleConnTimeout: 2 * time.Second, // LAN is cheap
+			},
+		}
+	}
+	return c.uPnPHTTPClient
 }
 
 // getUPnPPortMapping attempts to create a port-mapping over the UPnP protocol. On success,
@@ -199,11 +237,17 @@ func (c *Client) getUPnPPortMapping(
 	var err error
 	c.mu.Lock()
 	oldMapping, ok := c.mapping.(*upnpMapping)
+	meta := c.uPnPMeta
+	httpClient := c.upnpHTTPClientLocked()
 	c.mu.Unlock()
 	if ok && oldMapping != nil {
 		client = oldMapping.client
 	} else {
-		client, err = getUPnPClient(ctx, gw)
+		ctx := goupnp.WithHTTPClient(ctx, httpClient)
+		client, err = getUPnPClient(ctx, gw, meta)
+		if VerboseLogs {
+			log.Printf("getUPnPClient: %T, %v", client, err)
+		}
 		if err != nil {
 			return netaddr.IPPort{}, false
 		}
@@ -221,11 +265,17 @@ func (c *Client) getUPnPPortMapping(
 		internal.IP().String(),
 		time.Second*pmpMapLifetimeSec,
 	)
+	if VerboseLogs {
+		log.Printf("addAnyPortMapping: %v, %v", newPort, err)
+	}
 	if err != nil {
 		return netaddr.IPPort{}, false
 	}
 	// TODO cache this ip somewhere?
 	extIP, err := client.GetExternalIPAddress(ctx)
+	if VerboseLogs {
+		log.Printf("client.GetExternalIPAddress: %v, %v", extIP, err)
+	}
 	if err != nil {
 		// TODO this doesn't seem right
 		return netaddr.IPPort{}, false
@@ -246,3 +296,18 @@ func (c *Client) getUPnPPortMapping(
 	c.localPort = newPort
 	return upnp.external, true
 }
+
+type uPnPDiscoResponse struct {
+	Location string
+}
+
+// parseUPnPDiscoResponse parses a UPnP HTTP-over-UDP discovery response.
+func parseUPnPDiscoResponse(body []byte) (uPnPDiscoResponse, error) {
+	var r uPnPDiscoResponse
+	res, err := http.ReadResponse(bufio.NewReaderSize(bytes.NewReader(body), 128), nil)
+	if err != nil {
+		return r, err
+	}
+	r.Location = res.Header.Get("Location")
+	return r, nil
+}

net/portmapper/upnp_test.go

@@ -0,0 +1,95 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package portmapper
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"reflect"
+	"testing"
+
+	"inet.af/netaddr"
+)
+
+// Google Wifi
+const (
+	googleWifiUPnPDisco = "HTTP/1.1 200 OK\r\nCACHE-CONTROL: max-age=120\r\nST: urn:schemas-upnp-org:device:InternetGatewayDevice:2\r\nUSN: uuid:a9708184-a6c0-413a-bbac-11bcf7e30ece::urn:schemas-upnp-org:device:InternetGatewayDevice:2\r\nEXT:\r\nSERVER: Linux/5.4.0-1034-gcp UPnP/1.1 MiniUPnPd/1.9\r\nLOCATION: http://192.168.86.1:5000/rootDesc.xml\r\nOPT: \"http://schemas.upnp.org/upnp/1/0/\"; ns=01\r\n01-NLS: 1\r\nBOOTID.UPNP.ORG: 1\r\nCONFIGID.UPNP.ORG: 1337\r\n\r\n"
+
+	googleWifiRootDescXML = `<?xml version="1.0"?>
+<root xmlns="urn:schemas-upnp-org:device-1-0"><specVersion><major>1</major><minor>0</minor></specVersion><device><deviceType>urn:schemas-upnp-org:device:InternetGatewayDevice:2</deviceType><friendlyName>OnHub</friendlyName><manufacturer>Google</manufacturer><manufacturerURL>http://google.com/</manufacturerURL><modelDescription>Wireless Router</modelDescription><modelName>OnHub</modelName><modelNumber>1</modelNumber><modelURL>https://on.google.com/hub/</modelURL><serialNumber>00000000</serialNumber><UDN>uuid:a9708184-a6c0-413a-bbac-11bcf7e30ece</UDN><serviceList><service><serviceType>urn:schemas-upnp-org:service:Layer3Forwarding:1</serviceType><serviceId>urn:upnp-org:serviceId:Layer3Forwarding1</serviceId><controlURL>/ctl/L3F</controlURL><eventSubURL>/evt/L3F</eventSubURL><SCPDURL>/L3F.xml</SCPDURL></service><service><serviceType>urn:schemas-upnp-org:service:DeviceProtection:1</serviceType><serviceId>urn:upnp-org:serviceId:DeviceProtection1</serviceId><controlURL>/ctl/DP</controlURL><eventSubURL>/evt/DP</eventSubURL><SCPDURL>/DP.xml</SCPDURL></service></serviceList><deviceList><device><deviceType>urn:schemas-upnp-org:device:WANDevice:2</deviceType><friendlyName>WANDevice</friendlyName><manufacturer>MiniUPnP</manufacturer><manufacturerURL>http://miniupnp.free.fr/</manufacturerURL><modelDescription>WAN Device</modelDescription><modelName>WAN Device</modelName><modelNumber>20210414</modelNumber><modelURL>http://miniupnp.free.fr/</modelURL><serialNumber>00000000</serialNumber><UDN>uuid:a9708184-a6c0-413a-bbac-11bcf7e30ecf</UDN><UPC>000000000000</UPC><serviceList><service><serviceType>urn:schemas-upnp-org:service:WANCommonInterfaceConfig:1</serviceType><serviceId>urn:upnp-org:serviceId:WANCommonIFC1</serviceId><controlURL>/ctl/CmnIfCfg</controlURL><eventSubURL>/evt/CmnIfCfg</eventSubURL><SCPDURL>/WANCfg.xml</SCPDURL></service></serviceList><deviceList><device><deviceType>urn:schemas-upnp-org:device:WANConnectionDevice:2</deviceType><friendlyName>WANConnectionDevice</friendlyName><manufacturer>MiniUPnP</manufacturer><manufacturerURL>http://miniupnp.free.fr/</manufacturerURL><modelDescription>MiniUPnP daemon</modelDescription><modelName>MiniUPnPd</modelName><modelNumber>20210414</modelNumber><modelURL>http://miniupnp.free.fr/</modelURL><serialNumber>00000000</serialNumber><UDN>uuid:a9708184-a6c0-413a-bbac-11bcf7e30ec0</UDN><UPC>000000000000</UPC><serviceList><service><serviceType>urn:schemas-upnp-org:service:WANIPConnection:2</serviceType><serviceId>urn:upnp-org:serviceId:WANIPConn1</serviceId><controlURL>/ctl/IPConn</controlURL><eventSubURL>/evt/IPConn</eventSubURL><SCPDURL>/WANIPCn.xml</SCPDURL></service></serviceList></device></deviceList></device></deviceList><presentationURL>http://testwifi.here/</presentationURL></device></root>`
+)
+
+// pfSense 2.5.0-RELEASE / FreeBSD 12.2-STABLE
+const (
+	pfSenseUPnPDisco = "HTTP/1.1 200 OK\r\nCACHE-CONTROL: max-age=120\r\nST: urn:schemas-upnp-org:device:InternetGatewayDevice:1\r\nUSN: uuid:bee7052b-49e8-3597-b545-55a1e38ac11::urn:schemas-upnp-org:device:InternetGatewayDevice:1\r\nEXT:\r\nSERVER: FreeBSD/12.2-STABLE UPnP/1.1 MiniUPnPd/2.2.1\r\nLOCATION: http://192.168.1.1:2189/rootDesc.xml\r\nOPT: \"http://schemas.upnp.org/upnp/1/0/\"; ns=01\r\n01-NLS: 1627958564\r\nBOOTID.UPNP.ORG: 1627958564\r\nCONFIGID.UPNP.ORG: 1337\r\n\r\n"
+
+	pfSenseRootDescXML = `<?xml version="1.0"?>
+<root xmlns="urn:schemas-upnp-org:device-1-0" configId="1337"><specVersion><major>1</major><minor>1</minor></specVersion><device><deviceType>urn:schemas-upnp-org:device:InternetGatewayDevice:1</deviceType><friendlyName>FreeBSD router</friendlyName><manufacturer>FreeBSD</manufacturer><manufacturerURL>http://www.freebsd.org/</manufacturerURL><modelDescription>FreeBSD router</modelDescription><modelName>FreeBSD router</modelName><modelNumber>2.5.0-RELEASE</modelNumber><modelURL>http://www.freebsd.org/</modelURL><serialNumber>BEE7052B</serialNumber><UDN>uuid:bee7052b-49e8-3597-b545-55a1e38ac11</UDN><serviceList><service><serviceType>urn:schemas-upnp-org:service:Layer3Forwarding:1</serviceType><serviceId>urn:upnp-org:serviceId:L3Forwarding1</serviceId><SCPDURL>/L3F.xml</SCPDURL><controlURL>/ctl/L3F</controlURL><eventSubURL>/evt/L3F</eventSubURL></service></serviceList><deviceList><device><deviceType>urn:schemas-upnp-org:device:WANDevice:1</deviceType><friendlyName>WANDevice</friendlyName><manufacturer>MiniUPnP</manufacturer><manufacturerURL>http://miniupnp.free.fr/</manufacturerURL><modelDescription>WAN Device</modelDescription><modelName>WAN Device</modelName><modelNumber>20210205</modelNumber><modelURL>http://miniupnp.free.fr/</modelURL><serialNumber>BEE7052B</serialNumber><UDN>uuid:bee7052b-49e8-3597-b545-55a1e38ac12</UDN><UPC>000000000000</UPC><serviceList><service><serviceType>urn:schemas-upnp-org:service:WANCommonInterfaceConfig:1</serviceType><serviceId>urn:upnp-org:serviceId:WANCommonIFC1</serviceId><SCPDURL>/WANCfg.xml</SCPDURL><controlURL>/ctl/CmnIfCfg</controlURL><eventSubURL>/evt/CmnIfCfg</eventSubURL></service></serviceList><deviceList><device><deviceType>urn:schemas-upnp-org:device:WANConnectionDevice:1</deviceType><friendlyName>WANConnectionDevice</friendlyName><manufacturer>MiniUPnP</manufacturer><manufacturerURL>http://miniupnp.free.fr/</manufacturerURL><modelDescription>MiniUPnP daemon</modelDescription><modelName>MiniUPnPd</modelName><modelNumber>20210205</modelNumber><modelURL>http://miniupnp.free.fr/</modelURL><serialNumber>BEE7052B</serialNumber><UDN>uuid:bee7052b-49e8-3597-b545-55a1e38ac13</UDN><UPC>000000000000</UPC><serviceList><service><serviceType>urn:schemas-upnp-org:service:WANIPConnection:1</serviceType><serviceId>urn:upnp-org:serviceId:WANIPConn1</serviceId><SCPDURL>/WANIPCn.xml</SCPDURL><controlURL>/ctl/IPConn</controlURL><eventSubURL>/evt/IPConn</eventSubURL></service></serviceList></device></deviceList></device></deviceList><presentationURL>https://192.168.1.1/</presentationURL></device></root>`
+)
+
+func TestParseUPnPDiscoResponse(t *testing.T) {
+	tests := []struct {
+		name    string
+		headers string
+		want    uPnPDiscoResponse
+	}{
+		{"google", googleWifiUPnPDisco, uPnPDiscoResponse{
+			Location: "http://192.168.86.1:5000/rootDesc.xml",
+		}},
+		{"pfsense", pfSenseUPnPDisco, uPnPDiscoResponse{
+			Location: "http://192.168.1.1:2189/rootDesc.xml",
+		}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := parseUPnPDiscoResponse([]byte(tt.headers))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("unexpected result:\n got: %+v\nwant: %+v\n", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestGetUPnPClient(t *testing.T) {
+	tests := []struct {
+		name    string
+		xmlBody string
+		want    string
+	}{
+		{"google", googleWifiRootDescXML, "*internetgateway2.WANIPConnection2"},
+		{"pfsense", pfSenseRootDescXML, "*internetgateway2.WANIPConnection1"},
+		// TODO(bradfitz): find a PPP one in the wild
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				if r.RequestURI == "/rootDesc.xml" {
+					io.WriteString(w, tt.xmlBody)
+					return
+				}
+				http.NotFound(w, r)
+			}))
+			defer ts.Close()
+			gw, _ := netaddr.FromStdIP(ts.Listener.Addr().(*net.TCPAddr).IP)
+			c, err := getUPnPClient(context.Background(), gw, uPnPDiscoResponse{
+				Location: ts.URL + "/rootDesc.xml",
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			got := fmt.Sprintf("%T", c)
+			if got != tt.want {
+				t.Errorf("got %v; want %v", got, tt.want)
+			}
+		})
+	}
+}