Simplify proxy NAT checking logic

proxy/lib/snowflake.go

@@ -60,13 +60,13 @@ const (
 )
 
 const (
-	// NATUnknown represents a NAT type which is unknown.
+	// NATUnknown is set if the proxy cannot connect to probetest.
 	NATUnknown = "unknown"
 
-	// NATRestricted represents a restricted NAT.
+	// NATRestricted is set if the proxy times out when connecting to a symmetric NAT.
 	NATRestricted = "restricted"
 
-	// NATUnrestricted represents an unrestricted NAT.
+	// NATUnrestricted is set if the proxy successfully connects to a symmetric NAT.
 	NATUnrestricted = "unrestricted"
 )
 
@@ -99,6 +99,12 @@ func getCurrentNATType() string {
 	return currentNATType
 }
 
+func setCurrentNATType(newType string) {
+	currentNATTypeAccess.Lock()
+	defer currentNATTypeAccess.Unlock()
+	currentNATType = newType
+}
+
 var (
 	tokens *tokens_t
 	config webrtc.Configuration
@@ -694,9 +700,13 @@ func (sf *SnowflakeProxy) Start() error {
 	}
 	tokens = newTokens(sf.Capacity)
 
-	sf.checkNATType(config, sf.NATProbeURL)
-	currentNATTypeLoaded := getCurrentNATType()
-	sf.EventDispatcher.OnNewSnowflakeEvent(&event.EventOnCurrentNATTypeDetermined{CurNATType: currentNATTypeLoaded})
+	err = sf.checkNATType(config, sf.NATProbeURL)
+	if err != nil {
+		// non-fatal error. Log it and continue
+		log.Printf(err.Error())
+		setCurrentNATType(NATUnknown)
+	}
+	sf.EventDispatcher.OnNewSnowflakeEvent(&event.EventOnCurrentNATTypeDetermined{CurNATType: getCurrentNATType()})
 
 	NatRetestTask := task.Periodic{
 		Interval: sf.NATTypeMeasurementInterval,
@@ -704,6 +714,9 @@ func (sf *SnowflakeProxy) Start() error {
 			sf.checkNATType(config, sf.NATProbeURL)
 			return nil
 		},
+		OnError: func(err error) {
+			log.Printf("Periodic probetest failed: %s, retaining current NAT type: %s", err.Error(), getCurrentNATType())
+		},
 	}
 
 	if sf.NATTypeMeasurementInterval != 0 {
@@ -735,87 +748,64 @@ func (sf *SnowflakeProxy) Stop() {
 // checkNATType use probetest to determine NAT compatability by
 // attempting to connect with a known symmetric NAT. If success,
 // it is considered "unrestricted". If timeout it is considered "restricted"
-func (sf *SnowflakeProxy) checkNATType(config webrtc.Configuration, probeURL string) {
+func (sf *SnowflakeProxy) checkNATType(config webrtc.Configuration, probeURL string) error {
 	probe, err := newSignalingServer(probeURL, false)
 	if err != nil {
-		log.Printf("Error parsing url: %s", err.Error())
+		return fmt.Errorf("Error parsing url: %w", err)
 	}
 
 	dataChan := make(chan struct{})
 	pc, err := sf.makeNewPeerConnection(config, dataChan)
 	if err != nil {
-		log.Printf("error making WebRTC connection: %s", err)
-		return
+		return fmt.Errorf("Error making WebRTC connection: %w", err)
 	}
 
 	offer := pc.LocalDescription()
 	log.Printf("Probetest offer: \n\t%s", strings.ReplaceAll(offer.SDP, "\n", "\n\t"))
 	sdp, err := util.SerializeSessionDescription(offer)
 	if err != nil {
-		log.Printf("Error encoding probe message: %s", err.Error())
-		return
+		return fmt.Errorf("Error encoding probe message: %w", err)
 	}
 
 	// send offer
 	body, err := messages.EncodePollResponse(sdp, true, "")
 	if err != nil {
-		log.Printf("Error encoding probe message: %s", err.Error())
-		return
+		return fmt.Errorf("Error encoding probe message: %w", err)
 	}
 
 	resp, err := probe.Post(probe.url.String(), bytes.NewBuffer(body))
 	if err != nil {
-		log.Printf("error polling probe: %s", err.Error())
-		return
+		return fmt.Errorf("Error polling probe: %w", err)
 	}
 
 	sdp, _, err = messages.DecodeAnswerRequest(resp)
 	if err != nil {
-		log.Printf("Error reading probe response: %s", err.Error())
-		return
+		return fmt.Errorf("Error reading probe response: %w", err)
 	}
 
 	answer, err := util.DeserializeSessionDescription(sdp)
 	if err != nil {
-		log.Printf("Error setting answer: %s", err.Error())
-		return
+		return fmt.Errorf("Error setting answer: %w", err)
 	}
 
 	err = pc.SetRemoteDescription(*answer)
 	if err != nil {
-		log.Printf("Error setting answer: %s", err.Error())
-		return
+		return fmt.Errorf("Error setting answer: %w", err)
 	}
 
-	currentNATTypeLoaded := getCurrentNATType()
+	prevNATType := getCurrentNATType()
 
-	currentNATTypeTestResult := NATUnknown
 	select {
 	case <-dataChan:
-		currentNATTypeTestResult = NATUnrestricted
+		setCurrentNATType(NATUnrestricted)
 	case <-time.After(dataChannelTimeout):
-		currentNATTypeTestResult = NATRestricted
+		setCurrentNATType(NATRestricted)
 	}
 
-	currentNATTypeToStore := NATUnknown
-	switch currentNATTypeLoaded + "->" + currentNATTypeTestResult {
-	case NATUnrestricted + "->" + NATUnknown:
-		currentNATTypeToStore = NATUnrestricted
-
-	case NATRestricted + "->" + NATUnknown:
-		currentNATTypeToStore = NATRestricted
-
-	default:
-		currentNATTypeToStore = currentNATTypeTestResult
-	}
-
-	log.Printf("NAT Type measurement: %v -> %v = %v\n", currentNATTypeLoaded, currentNATTypeTestResult, currentNATTypeToStore)
-
-	currentNATTypeAccess.Lock()
-	currentNATType = currentNATTypeToStore
-	currentNATTypeAccess.Unlock()
+	log.Printf("NAT Type measurement: %v -> %v\n", prevNATType, getCurrentNATType())
 
 	if err := pc.Close(); err != nil {
 		log.Printf("error calling pc.Close: %v", err)
 	}
+	return nil
 }