webrtc: fix WHIP/WHEP implementation (#1857) (#1861)

offers and answers are now encoded in SDP in place of JSON; Location
header is set by the server.

This fixes compatibility with GStreamer and whipsink

internal/core/webrtc_http_server.go

@@ -309,6 +309,7 @@ func (s *webRTCHTTPServer) onRequest(ctx *gin.Context) {
 			ctx.Writer.Header().Set("E-Tag", res.sx.secret.String())
 			ctx.Writer.Header().Set("Accept-Patch", "application/trickle-ice-sdpfrag")
 			ctx.Writer.Header()["Link"] = iceServersToLinkHeader(s.parent.genICEServers())
+			ctx.Writer.Header().Set("Location", ctx.Request.URL.String())
 			ctx.Writer.WriteHeader(http.StatusCreated)
 			ctx.Writer.Write(res.answer)
 

internal/core/webrtc_manager_test.go

@@ -2,7 +2,7 @@ package core
 
 import (
 	"bytes"
-	"encoding/json"
+	"io"
 	"net/http"
 	"sync"
 	"testing"
@@ -38,10 +38,7 @@ func whipGetICEServers(t *testing.T, hc *http.Client, ur string) []webrtc.ICESer
 func whipPostOffer(t *testing.T, hc *http.Client, ur string,
 	offer *webrtc.SessionDescription,
 ) (*webrtc.SessionDescription, string) {
-	enc, err := json.Marshal(offer)
-	require.NoError(t, err)
-
-	req, err := http.NewRequest("POST", ur, bytes.NewReader(enc))
+	req, err := http.NewRequest("POST", ur, bytes.NewReader([]byte(offer.SDP)))
 	require.NoError(t, err)
 
 	req.Header.Set("Content-Type", "application/sdp")
@@ -51,22 +48,27 @@ func whipPostOffer(t *testing.T, hc *http.Client, ur string,
 	defer res.Body.Close()
 
 	require.Equal(t, http.StatusCreated, res.StatusCode)
+	require.Equal(t, "application/sdp", res.Header.Get("Content-Type"))
+	require.Equal(t, "application/trickle-ice-sdpfrag", res.Header.Get("Accept-Patch"))
+	require.Equal(t, req.URL.Path, res.Header.Get("Location"))
 
 	link, ok := res.Header["Link"]
 	require.Equal(t, true, ok)
 	servers := linkHeaderToIceServers(link)
 	require.NotEqual(t, 0, len(servers))
 
-	require.Equal(t, "application/sdp", res.Header.Get("Content-Type"))
 	etag := res.Header.Get("E-Tag")
 	require.NotEqual(t, 0, len(etag))
-	require.Equal(t, "application/trickle-ice-sdpfrag", res.Header.Get("Accept-Patch"))
 
-	var answer webrtc.SessionDescription
-	err = json.NewDecoder(res.Body).Decode(&answer)
+	sdp, err := io.ReadAll(res.Body)
 	require.NoError(t, err)
 
-	return &answer, etag
+	answer := &webrtc.SessionDescription{
+		Type: webrtc.SDPTypeAnswer,
+		SDP:  string(sdp),
+	}
+
+	return answer, etag
 }
 
 func whipPostCandidate(t *testing.T, ur string, offer *webrtc.SessionDescription,
@@ -323,10 +325,7 @@ func TestWebRTCReadNotFound(t *testing.T) {
 	offer, err := pc.CreateOffer(nil)
 	require.NoError(t, err)
 
-	enc, err := json.Marshal(offer)
-	require.NoError(t, err)
-
-	req, err := http.NewRequest("POST", "http://localhost:8889/stream/whep", bytes.NewReader(enc))
+	req, err := http.NewRequest("POST", "http://localhost:8889/stream/whep", bytes.NewReader([]byte(offer.SDP)))
 	require.NoError(t, err)
 
 	req.Header.Set("Content-Type", "application/sdp")

internal/core/webrtc_publish_index.html

@@ -232,16 +232,19 @@ class Transmitter {
                     headers: {
                         'Content-Type': 'application/sdp',
                     },
-                    body: JSON.stringify(desc),
+                    body: desc.sdp,
                 })
                     .then((res) => {
                         if (res.status !== 201) {
                             throw new Error('bad status code');
                         }
                         this.eTag = res.headers.get('E-Tag');
-                        return res.json();
+                        return res.text();
                     })
-                    .then((answer) => this.onRemoteDescription(answer))
+                    .then((sdp) => this.onRemoteDescription(new RTCSessionDescription({
+                        type: 'answer',
+                        sdp,
+                    })))
                     .catch((err) => {
                         console.log('error: ' + err);
                         this.scheduleRestart();

internal/core/webrtc_read_index.html

@@ -143,16 +143,19 @@ class WHEPClient {
                     headers: {
                         'Content-Type': 'application/sdp',
                     },
-                    body: JSON.stringify(desc),
+                    body: desc.sdp,
                 })
                     .then((res) => {
                         if (res.status !== 201) {
                             throw new Error('bad status code');
                         }
                         this.eTag = res.headers.get('E-Tag');
-                        return res.json();
+                        return res.text();
                     })
-                    .then((answer) => this.onRemoteDescription(answer))
+                    .then((sdp) => this.onRemoteDescription(new RTCSessionDescription({
+                        type: 'answer',
+                        sdp,
+                    })))
                     .catch((err) => {
                         console.log('error: ' + err);
                         this.scheduleRestart();

internal/core/webrtc_session.go

@@ -3,7 +3,6 @@ package core
 import (
 	"context"
 	"encoding/hex"
-	"encoding/json"
 	"fmt"
 	"net/http"
 	"strconv"
@@ -256,11 +255,6 @@ func (s *webRTCSession) runPublish() (int, error) {
 
 	defer res.path.publisherRemove(pathPublisherRemoveReq{author: s})
 
-	offer, err := s.decodeOffer()
-	if err != nil {
-		return http.StatusBadRequest, err
-	}
-
 	pc, err := newPeerConnection(
 		s.req.videoCodec,
 		s.req.audioCodec,
@@ -297,6 +291,7 @@ func (s *webRTCSession) runPublish() (int, error) {
 		}
 	})
 
+	offer := s.buildOffer()
 	err = pc.SetRemoteDescription(*offer)
 	if err != nil {
 		return http.StatusBadRequest, err
@@ -390,11 +385,6 @@ func (s *webRTCSession) runRead() (int, error) {
 		return http.StatusBadRequest, err
 	}
 
-	offer, err := s.decodeOffer()
-	if err != nil {
-		return http.StatusBadRequest, err
-	}
-
 	pc, err := newPeerConnection(
 		"",
 		"",
@@ -416,6 +406,7 @@ func (s *webRTCSession) runRead() (int, error) {
 		}
 	}
 
+	offer := s.buildOffer()
 	err = pc.SetRemoteDescription(*offer)
 	if err != nil {
 		return http.StatusBadRequest, err
@@ -484,18 +475,11 @@ func (s *webRTCSession) runRead() (int, error) {
 	}
 }
 
-func (s *webRTCSession) decodeOffer() (*webrtc.SessionDescription, error) {
-	var offer webrtc.SessionDescription
-	err := json.Unmarshal(s.req.offer, &offer)
-	if err != nil {
-		return nil, err
-	}
-
-	if offer.Type != webrtc.SDPTypeOffer {
-		return nil, fmt.Errorf("received SDP is not an offer")
+func (s *webRTCSession) buildOffer() *webrtc.SessionDescription {
+	return &webrtc.SessionDescription{
+		Type: webrtc.SDPTypeOffer,
+		SDP:  string(s.req.offer),
 	}
-
-	return &offer, nil
 }
 
 func (s *webRTCSession) waitGatheringDone(pc *peerConnection) error {
@@ -511,15 +495,10 @@ func (s *webRTCSession) waitGatheringDone(pc *peerConnection) error {
 }
 
 func (s *webRTCSession) writeAnswer(answer *webrtc.SessionDescription) error {
-	enc, err := json.Marshal(answer)
-	if err != nil {
-		return err
-	}
-
 	select {
 	case s.req.res <- webRTCSessionNewRes{
 		sx:     s,
-		answer: enc,
+		answer: []byte(answer.SDP),
 	}:
 		s.answerSent = true
 	case <-s.ctx.Done():