Stop storing version in ClientPollRequest

This continues to asserts the known version while decoding.  The client
will only ever generate the latest version while encoding and if the
response needs to change, the impetus will be a new feature, set in the
deserialized request, which can be used as a distinguisher.

broker/http.go

@@ -146,9 +146,8 @@ func clientOffers(i *IPC, w http.ResponseWriter, r *http.Request) {
 	if len(body) > 0 && body[0] == '{' {
 		isLegacy = true
 		req := messages.ClientPollRequest{
-			Offer:   string(body),
+			Offer: string(body),
-			NAT:     r.Header.Get("Snowflake-NAT-Type"),
+			NAT:   r.Header.Get("Snowflake-NAT-Type"),
-			Version: messages.ClientVersion1_0,
 		}
 		body, err = req.EncodeClientPollRequest()
 		if err != nil {

broker/ipc.go

@@ -129,15 +129,9 @@ func (i *IPC) ClientOffers(arg messages.Arg, response *[]byte) error {
 		return sendClientResponse(&messages.ClientPollResponse{Error: err.Error()}, response)
 	}
 
-	var offer *ClientOffer
+	offer := &ClientOffer{
-	switch req.Version {
+		natType: req.NAT,
-	case messages.ClientVersion1_0:
+		sdp:     []byte(req.Offer),
-		offer = &ClientOffer{
-			natType: req.NAT,
-			sdp:     []byte(req.Offer),
-		}
-	default:
-		panic("unknown version")
 	}
 
 	// Only hand out known restricted snowflakes to unrestricted clients
@@ -162,13 +156,8 @@ func (i *IPC) ClientOffers(arg messages.Arg, response *[]byte) error {
 			i.ctx.metrics.clientRestrictedDeniedCount++
 		}
 		i.ctx.metrics.lock.Unlock()
-		switch req.Version {
+		resp := &messages.ClientPollResponse{Error: messages.StrNoProxies}
-		case messages.ClientVersion1_0:
+		return sendClientResponse(resp, response)
-			resp := &messages.ClientPollResponse{Error: messages.StrNoProxies}
-			return sendClientResponse(resp, response)
-		default:
-			panic("unknown version")
-		}
 	}
 
 	// Otherwise, find the most available snowflake proxy, and pass the offer to it.
@@ -185,24 +174,14 @@ func (i *IPC) ClientOffers(arg messages.Arg, response *[]byte) error {
 		i.ctx.metrics.clientProxyMatchCount++
 		i.ctx.metrics.promMetrics.ClientPollTotal.With(prometheus.Labels{"nat": offer.natType, "status": "matched"}).Inc()
 		i.ctx.metrics.lock.Unlock()
-		switch req.Version {
+		resp := &messages.ClientPollResponse{Answer: answer}
-		case messages.ClientVersion1_0:
+		err = sendClientResponse(resp, response)
-			resp := &messages.ClientPollResponse{Answer: answer}
-			err = sendClientResponse(resp, response)
-		default:
-			panic("unknown version")
-		}
 		// Initial tracking of elapsed time.
 		i.ctx.metrics.clientRoundtripEstimate = time.Since(startTime) / time.Millisecond
 	case <-time.After(time.Second * ClientTimeout):
 		log.Println("Client: Timed out.")
-		switch req.Version {
+		resp := &messages.ClientPollResponse{Error: messages.StrTimedOut}
-		case messages.ClientVersion1_0:
+		err = sendClientResponse(resp, response)
-			resp := &messages.ClientPollResponse{Error: messages.StrTimedOut}
-			err = sendClientResponse(resp, response)
-		default:
-			panic("unknown version")
-		}
 	}
 
 	i.ctx.snowflakeLock.Lock()

client/lib/rendezvous.go

@@ -116,9 +116,8 @@ func (bc *BrokerChannel) Negotiate(offer *webrtc.SessionDescription) (
 	// Encode the client poll request.
 	bc.lock.Lock()
 	req := &messages.ClientPollRequest{
-		Offer:   offerSDP,
+		Offer: offerSDP,
-		NAT:     bc.natType,
+		NAT:   bc.natType,
-		Version: messages.ClientVersion1_0,
 	}
 	encReq, err := req.EncodeClientPollRequest()
 	bc.lock.Unlock()

client/lib/rendezvous_test.go

@@ -43,9 +43,8 @@ func (t errorTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 // offer.
 func makeEncPollReq(offer string) []byte {
 	encPollReq, err := (&messages.ClientPollRequest{
-		Offer:   offer,
+		Offer: offer,
-		NAT:     nat.NATUnknown,
+		NAT:   nat.NATUnknown,
-		Version: messages.ClientVersion1_0,
 	}).EncodeClientPollRequest()
 	if err != nil {
 		panic(err)

common/messages/client.go

@@ -11,7 +11,7 @@ import (
 	"git.torproject.org/pluggable-transports/snowflake.git/v2/common/nat"
 )
 
-const ClientVersion1_0 = "1.0"
+const ClientVersion = "1.0"
 
 /* Client--Broker protocol v1.x specification:
 
@@ -50,21 +50,17 @@ for the error.
 */
 
 type ClientPollRequest struct {
-	Offer   string `json:"offer"`
+	Offer string `json:"offer"`
-	NAT     string `json:"nat"`
+	NAT   string `json:"nat"`
-	Version string `json:"-"`
 }
 
 // Encodes a poll message from a snowflake client
 func (req *ClientPollRequest) EncodeClientPollRequest() ([]byte, error) {
-	if req.Version != ClientVersion1_0 {
-		return nil, fmt.Errorf("unsupported message version")
-	}
 	body, err := json.Marshal(req)
 	if err != nil {
 		return nil, err
 	}
-	return append([]byte(req.Version+"\n"), body...), nil
+	return append([]byte(ClientVersion+"\n"), body...), nil
 }
 
 // Decodes a poll message from a snowflake client
@@ -78,9 +74,7 @@ func DecodeClientPollRequest(data []byte) (*ClientPollRequest, error) {
 
 	var message ClientPollRequest
 
-	if string(parts[0]) == ClientVersion1_0 {
+	if string(parts[0]) != ClientVersion {
-		message.Version = ClientVersion1_0
-	} else {
 		return nil, fmt.Errorf("unsupported message version")
 	}
 

common/messages/messages_test.go

@@ -327,9 +327,8 @@ func TestDecodeClientPollRequest(t *testing.T) {
 func TestEncodeClientPollRequests(t *testing.T) {
 	Convey("Context", t, func() {
 		req1 := &ClientPollRequest{
-			NAT:     "unknown",
+			NAT:   "unknown",
-			Offer:   "fake",
+			Offer: "fake",
-			Version: ClientVersion1_0,
 		}
 		b, err := req1.EncodeClientPollRequest()
 		So(err, ShouldEqual, nil)