Redo protocol for proxy--broker messages

Switch to containing all communication between the proxy and the broker
in the HTTP response body. This will make things easier if we ever use
something other than HTTP communicate between different actors in the
snowflake system.

Other changes to the protocol are as follows:
- requests are accompanied by a version number so the broker can be
backwards compatable if desired in the future
- all responses are 200 OK unless the request was badly formatted

broker/broker.go

@@ -21,6 +21,7 @@ import (
 	"syscall"
 	"time"
 
+	"git.torproject.org/pluggable-transports/snowflake.git/common/messages"
 	"git.torproject.org/pluggable-transports/snowflake.git/common/safelog"
 	"golang.org/x/crypto/acme/autocert"
 )
@@ -151,15 +152,16 @@ func (ctx *BrokerContext) AddSnowflake(id string) *Snowflake {
 For snowflake proxies to request a client from the Broker.
 */
 func proxyPolls(ctx *BrokerContext, w http.ResponseWriter, r *http.Request) {
-	id := r.Header.Get("X-Session-ID")
 	body, err := ioutil.ReadAll(http.MaxBytesReader(w, r.Body, readLimit))
-	if nil != err {
+	if err != nil {
 		log.Println("Invalid data.")
 		w.WriteHeader(http.StatusBadRequest)
 		return
 	}
-	if string(body) != id {
-		log.Println("Mismatched IDs!")
+
+	sid, err := messages.DecodePollRequest(body)
+	if err != nil {
+		log.Println("Invalid data.")
 		w.WriteHeader(http.StatusBadRequest)
 		return
 	}
@@ -173,14 +175,26 @@ func proxyPolls(ctx *BrokerContext, w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Wait for a client to avail an offer to the snowflake, or timeout if nil.
-	offer := ctx.RequestOffer(id)
+	offer := ctx.RequestOffer(sid)
+	var b []byte
 	if nil == offer {
 		ctx.metrics.proxyIdleCount++
-		w.WriteHeader(http.StatusGatewayTimeout)
+
+		b, err = messages.EncodePollResponse("", false)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		w.Write(b)
+		return
+	}
+	b, err = messages.EncodePollResponse(string(offer), true)
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
 		return
 	}
-	log.Println("Passing client offer to snowflake.")
-	if _, err := w.Write(offer); err != nil {
+	if _, err := w.Write(b); err != nil {
 		log.Printf("proxyPolls unable to write offer with error: %v", err)
 	}
 }
@@ -235,22 +249,40 @@ an offer from proxyHandler to respond with an answer in an HTTP POST,
 which the broker will pass back to the original client.
 */
 func proxyAnswers(ctx *BrokerContext, w http.ResponseWriter, r *http.Request) {
-	id := r.Header.Get("X-Session-ID")
+
+	body, err := ioutil.ReadAll(http.MaxBytesReader(w, r.Body, readLimit))
+	if nil != err || nil == body || len(body) <= 0 {
+		log.Println("Invalid data.")
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	answer, id, err := messages.DecodeAnswerRequest(body)
+	if err != nil || answer == "" {
+		log.Println("Invalid data.")
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	var success = true
 	snowflake, ok := ctx.idToSnowflake[id]
 	if !ok || nil == snowflake {
 		// The snowflake took too long to respond with an answer, so its client
 		// disappeared / the snowflake is no longer recognized by the Broker.
-		w.WriteHeader(http.StatusGone)
-		return
+		success = false
 	}
-	body, err := ioutil.ReadAll(http.MaxBytesReader(w, r.Body, readLimit))
-	if nil != err || nil == body || len(body) <= 0 {
-		log.Println("Invalid data.")
-		w.WriteHeader(http.StatusBadRequest)
+	b, err := messages.EncodeAnswerResponse(success)
+	if err != nil {
+		log.Printf("Error encoding answer: %s", err.Error())
+		w.WriteHeader(http.StatusInternalServerError)
 		return
 	}
+	w.Write(b)
+
+	if success {
+		snowflake.answerChannel <- []byte(answer)
+	}
 
-	snowflake.answerChannel <- body
 }
 
 func debugHandler(ctx *BrokerContext, w http.ResponseWriter, r *http.Request) {

broker/snowflake-broker_test.go

@@ -113,9 +113,8 @@ func TestBroker(t *testing.T) {
 		Convey("Responds to proxy polls...", func() {
 			done := make(chan bool)
 			w := httptest.NewRecorder()
-			data := bytes.NewReader([]byte("test"))
+			data := bytes.NewReader([]byte(`{"Sid":"ymbcCMto7KHNGYlp","Version":"1.0"}`))
 			r, err := http.NewRequest("POST", "snowflake.broker/proxy", data)
-			r.Header.Set("X-Session-ID", "test")
 			So(err, ShouldBeNil)
 
 			Convey("with a client offer if available.", func() {
@@ -125,57 +124,59 @@ func TestBroker(t *testing.T) {
 				}(ctx)
 				// Pass a fake client offer to this proxy
 				p := <-ctx.proxyPolls
-				So(p.id, ShouldEqual, "test")
+				So(p.id, ShouldEqual, "ymbcCMto7KHNGYlp")
 				p.offerChannel <- []byte("fake offer")
 				<-done
 				So(w.Code, ShouldEqual, http.StatusOK)
-				So(w.Body.String(), ShouldEqual, "fake offer")
+				So(w.Body.String(), ShouldEqual, `{"Status":"client match","Offer":"fake offer"}`)
 			})
 
-			Convey("times out when no client offer is available.", func() {
+			Convey("return empty 200 OK when no client offer is available.", func() {
 				go func(ctx *BrokerContext) {
 					proxyPolls(ctx, w, r)
 					done <- true
 				}(ctx)
 				p := <-ctx.proxyPolls
-				So(p.id, ShouldEqual, "test")
+				So(p.id, ShouldEqual, "ymbcCMto7KHNGYlp")
 				// nil means timeout
 				p.offerChannel <- nil
 				<-done
-				So(w.Body.String(), ShouldEqual, "")
-				So(w.Code, ShouldEqual, http.StatusGatewayTimeout)
+				So(w.Body.String(), ShouldEqual, `{"Status":"no match","Offer":""}`)
+				So(w.Code, ShouldEqual, http.StatusOK)
 			})
 		})
 
 		Convey("Responds to proxy answers...", func() {
 			s := ctx.AddSnowflake("test")
 			w := httptest.NewRecorder()
-			data := bytes.NewReader([]byte("fake answer"))
+			data := bytes.NewReader([]byte(`{"Version":"1.0","Sid":"test","Answer":"test"}`))
 
 			Convey("by passing to the client if valid.", func() {
 				r, err := http.NewRequest("POST", "snowflake.broker/answer", data)
 				So(err, ShouldBeNil)
-				r.Header.Set("X-Session-ID", "test")
 				go func(ctx *BrokerContext) {
 					proxyAnswers(ctx, w, r)
 				}(ctx)
 				answer := <-s.answerChannel
 				So(w.Code, ShouldEqual, http.StatusOK)
-				So(answer, ShouldResemble, []byte("fake answer"))
+				So(answer, ShouldResemble, []byte("test"))
 			})
 
-			Convey("with error if the proxy is not recognized", func() {
-				r, err := http.NewRequest("POST", "snowflake.broker/answer", nil)
+			Convey("with client gone status if the proxy is not recognized", func() {
+				data = bytes.NewReader([]byte(`{"Version":"1.0","Sid":"invalid","Answer":"test"}`))
+				r, err := http.NewRequest("POST", "snowflake.broker/answer", data)
 				So(err, ShouldBeNil)
-				r.Header.Set("X-Session-ID", "invalid")
 				proxyAnswers(ctx, w, r)
-				So(w.Code, ShouldEqual, http.StatusGone)
+				So(w.Code, ShouldEqual, http.StatusOK)
+				b, err := ioutil.ReadAll(w.Body)
+				So(err, ShouldBeNil)
+				So(b, ShouldResemble, []byte(`{"Status":"client gone"}`))
+
 			})
 
 			Convey("with error if the proxy gives invalid answer", func() {
 				data := bytes.NewReader(nil)
 				r, err := http.NewRequest("POST", "snowflake.broker/answer", data)
-				r.Header.Set("X-Session-ID", "test")
 				So(err, ShouldBeNil)
 				proxyAnswers(ctx, w, r)
 				So(w.Code, ShouldEqual, http.StatusBadRequest)
@@ -184,7 +185,6 @@ func TestBroker(t *testing.T) {
 			Convey("with error if the proxy writes too much data", func() {
 				data := bytes.NewReader(make([]byte, 100001))
 				r, err := http.NewRequest("POST", "snowflake.broker/answer", data)
-				r.Header.Set("X-Session-ID", "test")
 				So(err, ShouldBeNil)
 				proxyAnswers(ctx, w, r)
 				So(w.Code, ShouldEqual, http.StatusBadRequest)
@@ -199,11 +199,10 @@ func TestBroker(t *testing.T) {
 		ctx := NewBrokerContext(NullLogger())
 
 		// Proxy polls with its ID first...
-		dataP := bytes.NewReader([]byte("test"))
+		dataP := bytes.NewReader([]byte(`{"Sid":"ymbcCMto7KHNGYlp","Version":"1.0"}`))
 		wP := httptest.NewRecorder()
 		rP, err := http.NewRequest("POST", "snowflake.broker/proxy", dataP)
 		So(err, ShouldBeNil)
-		rP.Header.Set("X-Session-ID", "test")
 		go func() {
 			proxyPolls(ctx, wP, rP)
 			polled <- true
@@ -211,13 +210,13 @@ func TestBroker(t *testing.T) {
 
 		// Manually do the Broker goroutine action here for full control.
 		p := <-ctx.proxyPolls
-		So(p.id, ShouldEqual, "test")
+		So(p.id, ShouldEqual, "ymbcCMto7KHNGYlp")
 		s := ctx.AddSnowflake(p.id)
 		go func() {
 			offer := <-s.offerChannel
 			p.offerChannel <- offer
 		}()
-		So(ctx.idToSnowflake["test"], ShouldNotBeNil)
+		So(ctx.idToSnowflake["ymbcCMto7KHNGYlp"], ShouldNotBeNil)
 
 		// Client request blocks until proxy answer arrives.
 		dataC := bytes.NewReader([]byte("fake offer"))
@@ -231,20 +230,19 @@ func TestBroker(t *testing.T) {
 
 		<-polled
 		So(wP.Code, ShouldEqual, http.StatusOK)
-		So(wP.Body.String(), ShouldResemble, "fake offer")
-		So(ctx.idToSnowflake["test"], ShouldNotBeNil)
+		So(wP.Body.String(), ShouldResemble, `{"Status":"client match","Offer":"fake offer"}`)
+		So(ctx.idToSnowflake["ymbcCMto7KHNGYlp"], ShouldNotBeNil)
 		// Follow up with the answer request afterwards
 		wA := httptest.NewRecorder()
-		dataA := bytes.NewReader([]byte("fake answer"))
-		rA, err := http.NewRequest("POST", "snowflake.broker/proxy", dataA)
+		dataA := bytes.NewReader([]byte(`{"Version":"1.0","Sid":"ymbcCMto7KHNGYlp","Answer":"test"}`))
+		rA, err := http.NewRequest("POST", "snowflake.broker/answer", dataA)
 		So(err, ShouldBeNil)
-		rA.Header.Set("X-Session-ID", "test")
 		proxyAnswers(ctx, wA, rA)
 		So(wA.Code, ShouldEqual, http.StatusOK)
 
 		<-done
 		So(wC.Code, ShouldEqual, http.StatusOK)
-		So(wC.Body.String(), ShouldEqual, "fake answer")
+		So(wC.Body.String(), ShouldEqual, "test")
 	})
 }
 
@@ -408,7 +406,7 @@ func TestMetrics(t *testing.T) {
 		//Test addition of proxy polls
 		Convey("for proxy polls", func() {
 			w := httptest.NewRecorder()
-			data := bytes.NewReader([]byte("test"))
+			data := bytes.NewReader([]byte("{\"Sid\":\"ymbcCMto7KHNGYlp\",\"Version\":\"1.0\"}"))
 			r, err := http.NewRequest("POST", "snowflake.broker/proxy", data)
 			r.Header.Set("X-Session-ID", "test")
 			r.RemoteAddr = "129.97.208.23:8888" //CA geoip
@@ -492,7 +490,7 @@ func TestMetrics(t *testing.T) {
 		//Test unique ip
 		Convey("proxy counts by unique ip", func() {
 			w := httptest.NewRecorder()
-			data := bytes.NewReader([]byte("test"))
+			data := bytes.NewReader([]byte(`{"Sid":"ymbcCMto7KHNGYlp","Version":"1.0"}`))
 			r, err := http.NewRequest("POST", "snowflake.broker/proxy", data)
 			r.Header.Set("X-Session-ID", "test")
 			r.RemoteAddr = "129.97.208.23:8888" //CA geoip
@@ -505,7 +503,7 @@ func TestMetrics(t *testing.T) {
 			p.offerChannel <- nil
 			<-done
 
-			data = bytes.NewReader([]byte("test"))
+			data = bytes.NewReader([]byte(`{"Sid":"ymbcCMto7KHNGYlp","Version":"1.0"}`))
 			r, err = http.NewRequest("POST", "snowflake.broker/proxy", data)
 			if err != nil {
 				log.Printf("unable to get NewRequest with error: %v", err)

common/messages/proxy.go

+//Package for communication with the snowflake broker
+
+//import "git.torproject.org/pluggable-transports/snowflake.git/common/messages"
+package messages
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+const version = "1.0"
+
+/* Version 1.0 specification:
+
+== ProxyPollRequest ==
+{
+  Sid: [generated session id of proxy]
+  Version: 1.0
+}
+
+== ProxyPollResponse ==
+1) If a client is matched:
+HTTP 200 OK
+{
+  Status: "client match",
+  {
+    type: offer,
+    sdp: [WebRTC SDP]
+  }
+}
+
+2) If a client is not matched:
+HTTP 200 OK
+
+{
+    Status: "no proxies"
+}
+
+3) If the request is malformed:
+HTTP 400 BadRequest
+
+== ProxyAnswerRequest ==
+{
+  Sid: [generated session id of proxy]
+  Version: 1.0
+  Answer:
+  {
+    type: answer
+    sdp: [WebRTC SDP]
+  }
+}
+
+== ProxyAnswerResponse ==
+1) If the client retrieved the answer:
+HTTP 200 OK
+
+{
+  Status: "success"
+}
+
+2) If the client left:
+HTTP 200 OK
+
+{
+  Status: "client gone"
+}
+
+3) If the request is malformed:
+HTTP 400 BadRequest
+
+*/
+
+type ProxyPollRequest struct {
+	Sid     string
+	Version string
+}
+
+func EncodePollRequest(sid string) ([]byte, error) {
+	return json.Marshal(ProxyPollRequest{
+		Sid:     sid,
+		Version: version,
+	})
+}
+
+// Decodes a poll message from a snowflake proxy and returns the
+// sid of the proxy on success and an error if it failed
+func DecodePollRequest(data []byte) (string, error) {
+	var message ProxyPollRequest
+
+	err := json.Unmarshal(data, &message)
+	if err != nil {
+		return "", err
+	}
+	if message.Version != "1.0" {
+		return "", fmt.Errorf("using unknown version")
+	}
+
+	// Version 1.0 requires an Sid
+	if message.Sid == "" {
+		return "", fmt.Errorf("no supplied session id")
+	}
+
+	return message.Sid, nil
+}
+
+type ProxyPollResponse struct {
+	Status string
+	Offer  string
+}
+
+func EncodePollResponse(offer string, success bool) ([]byte, error) {
+	if success {
+		return json.Marshal(ProxyPollResponse{
+			Status: "client match",
+			Offer:  offer,
+		})
+
+	}
+	return json.Marshal(ProxyPollResponse{
+		Status: "no match",
+	})
+}
+
+// Decodes a poll response from the broker and returns an offer
+// If there is a client match, the returned offer string will be non-empty
+func DecodePollResponse(data []byte) (string, error) {
+	var message ProxyPollResponse
+
+	err := json.Unmarshal(data, &message)
+	if err != nil {
+		return "", err
+	}
+	if message.Status == "" {
+		return "", fmt.Errorf("received invalid data")
+	}
+
+	if message.Status == "client match" {
+		if message.Offer == "" {
+			return "", fmt.Errorf("no supplied offer")
+		}
+	} else {
+		message.Offer = ""
+	}
+
+	return message.Offer, nil
+}
+
+type ProxyAnswerRequest struct {
+	Version string
+	Sid     string
+	Answer  string
+}
+
+func EncodeAnswerRequest(answer string, sid string) ([]byte, error) {
+	return json.Marshal(ProxyAnswerRequest{
+		Version: "1.0",
+		Sid:     sid,
+		Answer:  answer,
+	})
+}
+
+// Returns the sdp answer and proxy sid
+func DecodeAnswerRequest(data []byte) (string, string, error) {
+	var message ProxyAnswerRequest
+
+	err := json.Unmarshal(data, &message)
+	if err != nil {
+		return "", "", err
+	}
+	if message.Version != "1.0" {
+		return "", "", fmt.Errorf("using unknown version")
+	}
+
+	if message.Sid == "" || message.Answer == "" {
+		return "", "", fmt.Errorf("no supplied sid or answer")
+	}
+
+	return message.Answer, message.Sid, nil
+}
+
+type ProxyAnswerResponse struct {
+	Status string
+}
+
+func EncodeAnswerResponse(success bool) ([]byte, error) {
+	if success {
+		return json.Marshal(ProxyAnswerResponse{
+			Status: "success",
+		})
+
+	}
+	return json.Marshal(ProxyAnswerResponse{
+		Status: "client gone",
+	})
+}
+
+func DecodeAnswerResponse(data []byte) (bool, error) {
+	var message ProxyAnswerResponse
+	var success bool
+
+	err := json.Unmarshal(data, &message)
+	if err != nil {
+		return success, err
+	}
+	if message.Status == "" {
+		return success, fmt.Errorf("received invalid data")
+	}
+
+	if message.Status == "success" {
+		success = true
+	}
+
+	return success, nil
+}

common/messages/proxy_test.go

+package messages
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestDecodeProxyPollRequest(t *testing.T) {
+	Convey("Context", t, func() {
+		for _, test := range []struct {
+			sid  string
+			data string
+			err  error
+		}{
+			{
+				//Version 1.0 proxy message
+				"ymbcCMto7KHNGYlp",
+				`{"Sid":"ymbcCMto7KHNGYlp","Version":"1.0"}`,
+				nil,
+			},
+			{
+				//Version 0.X proxy message:
+				"",
+				"ymbcCMto7KHNGYlp",
+				&json.SyntaxError{},
+			},
+			{
+				"",
+				`{"Sid":"ymbcCMto7KHNGYlp"}`,
+				fmt.Errorf(""),
+			},
+			{
+				"",
+				"{}",
+				fmt.Errorf(""),
+			},
+			{
+				"",
+				`{"Version":"1.0"}`,
+				fmt.Errorf(""),
+			},
+			{
+				"",
+				`{"Version":"2.0"}`,
+				fmt.Errorf(""),
+			},
+		} {
+			sid, err := DecodePollRequest([]byte(test.data))
+			So(sid, ShouldResemble, test.sid)
+			So(err, ShouldHaveSameTypeAs, test.err)
+		}
+
+	})
+}
+
+func TestEncodeProxyPollRequests(t *testing.T) {
+	Convey("Context", t, func() {
+		b, err := EncodePollRequest("ymbcCMto7KHNGYlp")
+		So(err, ShouldEqual, nil)
+		sid, err := DecodePollRequest(b)
+		So(sid, ShouldEqual, "ymbcCMto7KHNGYlp")
+		So(err, ShouldEqual, nil)
+	})
+}
+
+func TestDecodeProxyAnswerRequest(t *testing.T) {
+	Convey("Context", t, func() {
+		for _, test := range []struct {
+			answer string
+			sid    string
+			data   string
+			err    error
+		}{
+			{
+				"test",
+				"test",
+				`{"Version":"1.0","Sid":"test","Answer":"test"}`,
+				nil,
+			},
+			{
+				"",
+				"",
+				`{"type":"offer","sdp":"v=0\r\no=- 4358805017720277108 2 IN IP4 [scrubbed]\r\ns=-\r\nt=0 0\r\na=group:BUNDLE data\r\na=msid-semantic: WMS\r\nm=application 56688 DTLS/SCTP 5000\r\nc=IN IP4 [scrubbed]\r\na=candidate:3769337065 1 udp 2122260223 [scrubbed] 56688 typ host generation 0 network-id 1 network-cost 50\r\na=candidate:2921887769 1 tcp 1518280447 [scrubbed] 35441 typ host tcptype passive generation 0 network-id 1 network-cost 50\r\na=ice-ufrag:aMAZ\r\na=ice-pwd:jcHb08Jjgrazp2dzjdrvPPvV\r\na=ice-options:trickle\r\na=fingerprint:sha-256 C8:88:EE:B9:E7:02:2E:21:37:ED:7A:D1:EB:2B:A3:15:A2:3B:5B:1C:3D:D4:D5:1F:06:CF:52:40:03:F8:DD:66\r\na=setup:actpass\r\na=mid:data\r\na=sctpmap:5000 webrtc-datachannel 1024\r\n"}`,
+				fmt.Errorf(""),
+			},
+			{
+				"",
+				"",
+				`{"Version":"1.0","Answer":"test"}`,
+				fmt.Errorf(""),
+			},
+			{
+				"",
+				"",
+				`{"Version":"1.0","Sid":"test"}`,
+				fmt.Errorf(""),
+			},
+		} {
+			answer, sid, err := DecodeAnswerRequest([]byte(test.data))
+			So(answer, ShouldResemble, test.answer)
+			So(sid, ShouldResemble, test.sid)
+			So(err, ShouldHaveSameTypeAs, test.err)
+		}
+
+	})
+}
+
+func TestEncodeProxyAnswerRequest(t *testing.T) {
+	Convey("Context", t, func() {
+		b, err := EncodeAnswerRequest("test answer", "test sid")
+		So(err, ShouldEqual, nil)
+		answer, sid, err := DecodeAnswerRequest(b)
+		So(answer, ShouldEqual, "test answer")
+		So(sid, ShouldEqual, "test sid")
+		So(err, ShouldEqual, nil)
+	})
+}
+
+func TestDecodeProxyAnswerResponse(t *testing.T) {
+	Convey("Context", t, func() {
+		for _, test := range []struct {
+			success bool
+			data    string
+			err     error
+		}{
+			{
+				true,
+				`{"Status":"success"}`,
+				nil,
+			},
+			{
+				false,
+				`{"Status":"client gone"}`,
+				nil,
+			},
+			{
+				false,
+				`{"Test":"test"}`,
+				fmt.Errorf(""),
+			},
+		} {
+			success, err := DecodeAnswerResponse([]byte(test.data))
+			So(success, ShouldResemble, test.success)
+			So(err, ShouldHaveSameTypeAs, test.err)
+		}
+
+	})
+}
+
+func TestEncodeProxyAnswerResponse(t *testing.T) {
+	Convey("Context", t, func() {
+		b, err := EncodeAnswerResponse(true)
+		So(err, ShouldEqual, nil)
+		success, err := DecodeAnswerResponse(b)
+		So(success, ShouldEqual, true)
+		So(err, ShouldEqual, nil)
+	})
+}

proxy-go/snowflake.go

@@ -19,6 +19,7 @@ import (
 	"sync"
 	"time"
 
+	"git.torproject.org/pluggable-transports/snowflake.git/common/messages"
 	"git.torproject.org/pluggable-transports/snowflake.git/common/safelog"
 	"github.com/pion/webrtc"
 	"golang.org/x/net/websocket"
@@ -168,7 +169,12 @@ func pollOffer(sid string) *webrtc.SessionDescription {
 			timeOfNextPoll = now
 		}
 
-		req, _ := http.NewRequest("POST", broker.String(), bytes.NewBuffer([]byte(sid)))
+		b, err := messages.EncodePollRequest(sid)
+		if err != nil {
+			log.Printf("Error encoding poll message: %s", err.Error())
+			return nil
+		}
+		req, _ := http.NewRequest("POST", broker.String(), bytes.NewBuffer(b))
 		req.Header.Set("X-Session-ID", sid)
 		resp, err := client.Do(req)
 		if err != nil {
@@ -182,7 +188,16 @@ func pollOffer(sid string) *webrtc.SessionDescription {
 				if err != nil {
 					log.Printf("error reading broker response: %s", err)
 				} else {
-					return deserializeSessionDescription(string(body))
+
+					offer, err := messages.DecodePollResponse(body)
+					if err != nil {
+						log.Printf("error reading broker response: %s", err.Error())
+						log.Printf("body: %s", body)
+						return nil
+					}
+					if offer != "" {
+						return deserializeSessionDescription(offer)
+					}
 				}
 			}
 		}
@@ -191,9 +206,12 @@ func pollOffer(sid string) *webrtc.SessionDescription {
 
 func sendAnswer(sid string, pc *webrtc.PeerConnection) error {
 	broker := brokerURL.ResolveReference(&url.URL{Path: "answer"})
-	body := bytes.NewBuffer([]byte(serializeSessionDescription(pc.LocalDescription())))
-	req, _ := http.NewRequest("POST", broker.String(), body)
-	req.Header.Set("X-Session-ID", sid)
+	answer := string([]byte(serializeSessionDescription(pc.LocalDescription())))
+	b, err := messages.EncodeAnswerRequest(answer, sid)
+	if err != nil {
+		return err
+	}
+	req, _ := http.NewRequest("POST", broker.String(), bytes.NewBuffer(b))
 	resp, err := client.Do(req)
 	if err != nil {
 		return err
@@ -201,6 +219,19 @@ func sendAnswer(sid string, pc *webrtc.PeerConnection) error {
 	if resp.StatusCode != http.StatusOK {
 		return fmt.Errorf("broker returned %d", resp.StatusCode)
 	}
+
+	body, err := limitedRead(resp.Body, readLimit)
+	if err != nil {
+		return fmt.Errorf("error reading broker response: %s", err)
+	}
+	success, err := messages.DecodeAnswerResponse(body)
+	if err != nil {
+		return err
+	}
+	if !success {
+		return fmt.Errorf("broker returned client timeout")
+	}
+
 	return nil
 }
 

translation @ bbf11bb0

-Subproject commit 120578ec9dbf0975fc9ac573130282f628b9747a
+Subproject commit bbf11bb0c9f1aca4f6b18c6505645f85e2fa1986