Implement per-stream requests.

README.PROTOCOL

@@ -213,6 +213,16 @@ restart by sending a `renegotiate` message:
 }
 ```
 
+At any time after answering, the client may change the set of streams
+being offered by sending a 'requestStream' request:
+```javascript
+{
+    type: 'answerStream'
+    id: id,
+    request: [audio, video]
+}
+```
+
 ## Closing streams
 
 The offerer may close a stream at any time by sending a `close` message.

rtpconn/rtpconn.go

@@ -149,6 +149,7 @@ type rtpDownConnection struct {
 	remote            conn.Up
 	iceCandidates     []*webrtc.ICECandidateInit
 	negotiationNeeded int
+	requested         []string
 
 	mu     sync.Mutex
 	tracks []*rtpDownTrack
@@ -432,6 +433,7 @@ func (up *rtpUpTrack) hasRtcpFb(tpe, parameter string) bool {
 
 type rtpUpConnection struct {
 	id            string
+	client        group.Client
 	label         string
 	userId        string
 	username      string
@@ -585,7 +587,7 @@ func newUpConn(c group.Client, id string, label string, offer string) (*rtpUpCon
 		}
 	}
 
-	up := &rtpUpConnection{id: id, label: label, pc: pc}
+	up := &rtpUpConnection{id: id, client: c, label: label, pc: pc}
 
 	pc.OnTrack(func(remote *webrtc.TrackRemote, receiver *webrtc.RTPReceiver) {
 		up.mu.Lock()

rtpconn/webclient.go

@@ -141,7 +141,7 @@ type clientMessage struct {
 	SDP              string                   `json:"sdp,omitempty"`
 	Candidate        *webrtc.ICECandidateInit `json:"candidate,omitempty"`
 	Label            string                   `json:"label,omitempty"`
-	Request          map[string][]string      `json:"request,omitempty"`
+	Request          interface{}              `json:"request,omitempty"`
 	RTCConfiguration *webrtc.Configuration    `json:"rtcConfiguration,omitempty"`
 }
 
@@ -638,6 +638,52 @@ func gotICE(c *webClient, candidate *webrtc.ICECandidateInit, id string) error {
 	return conn.addICECandidate(candidate)
 }
 
+var errBadType = errors.New("bad type")
+
+func toStringArray(r interface{}) ([]string, error) {
+	if r == nil {
+		return nil, nil
+	}
+	rr, ok := r.([]interface{})
+	if !ok {
+		return nil, errBadType
+	}
+	if rr == nil {
+		return nil, nil
+	}
+
+	rrr := make([]string, len(rr))
+	for i, s := range rr {
+		rrr[i], ok = s.(string)
+		if !ok {
+			return nil, errBadType
+		}
+	}
+	return rrr, nil
+}
+
+func parseRequested(r interface{}) (map[string][]string, error) {
+	if r == nil {
+		return nil, nil
+	}
+	rr, ok := r.(map[string]interface{})
+	if !ok {
+		return nil, errBadType
+	}
+	if rr == nil {
+		return nil, nil
+	}
+	rrr := make(map[string][]string)
+	for k, v := range rr {
+		vv, err := toStringArray(v)
+		if err != nil {
+			return nil, err
+		}
+		rrr[k] = vv
+	}
+	return rrr, nil
+}
+
 func (c *webClient) setRequested(requested map[string][]string) error {
 	if c.group == nil {
 		return errors.New("attempted to request with no group joined")
@@ -648,6 +694,16 @@ func (c *webClient) setRequested(requested map[string][]string) error {
 	return nil
 }
 
+func (c *webClient) setRequestedStream(down *rtpDownConnection, requested []string) error {
+	var remoteClient group.Client
+	remote, ok := down.remote.(*rtpUpConnection)
+	if ok {
+		remoteClient = remote.client
+	}
+	down.requested = requested
+	return remoteClient.RequestConns(c, c.group, remote.id)
+}
+
 func (c *webClient) RequestConns(target group.Client, g *group.Group, id string) error {
 	return c.action(requestConnsAction{g, target, id})
 }
@@ -659,14 +715,18 @@ func requestConns(target group.Client, g *group.Group, id string) {
 	}
 }
 
-func requestedTracks(c *webClient, up conn.Up, tracks []conn.UpTrack) []conn.UpTrack {
+func requestedTracks(c *webClient, override []string, up conn.Up, tracks []conn.UpTrack) []conn.UpTrack {
-	r, ok := c.requested[up.Label()]
+	r := override
+	if r == nil {
+		var ok bool
+		r, ok = c.requested[up.Label()]
 		if !ok {
 			r, ok = c.requested[""]
 		}
 		if !ok || len(r) == 0 {
 			return nil
 		}
+	}
 
 	var audio, video, videoLow bool
 	for _, s := range r {
@@ -894,8 +954,18 @@ func handleAction(c *webClient, a interface{}) error {
 			return nil
 		}
 		var tracks []conn.UpTrack
+		var override []string
 		if a.conn != nil {
-			tracks = requestedTracks(c, a.conn, a.tracks)
+			var old *rtpDownConnection
+			if a.replace != "" {
+				old = getDownConn(c, a.replace)
+			} else {
+				old = getDownConn(c, a.conn.Id())
+			}
+			if old != nil {
+				override = old.requested
+			}
+			tracks = requestedTracks(c, override, a.conn, a.tracks)
 		}
 
 		if len(tracks) == 0 {
@@ -938,6 +1008,7 @@ func handleAction(c *webClient, a interface{}) error {
 	case requestConnsAction:
 		g := c.group
 		if g == nil || a.group != g {
+			log.Printf("Misdirected pushConns")
 			return nil
 		}
 		for _, u := range c.up {
@@ -1241,7 +1312,21 @@ func handleClientMessage(c *webClient, m clientMessage) error {
 			}
 		}
 	case "request":
-		return c.setRequested(m.Request)
+		requested, err := parseRequested(m.Request)
+		if err != nil {
+			return err
+		}
+		return c.setRequested(requested)
+	case "requestStream":
+		down := getDownConn(c, m.Id)
+		if down == nil {
+			return ErrUnknownId
+		}
+		requested, err := toStringArray(m.Request)
+		if err != nil {
+			return err
+		}
+		c.setRequestedStream(down, requested)
 	case "offer":
 		if m.Id == "" {
 			return errEmptyId

static/protocol.js

@@ -214,7 +214,7 @@ function ServerConnection() {
   * @property {string} [sdp]
   * @property {RTCIceCandidate} [candidate]
   * @property {string} [label]
-  * @property {Object<string,Array<string>>} [request]
+  * @property {Object<string,Array<string>>|Array<string>} [request]
   * @property {Object<string,any>} [rtcConfiguration]
   */
 
@@ -440,11 +440,11 @@ ServerConnection.prototype.leave = function(group) {
 };
 
 /**
- * request sets the list of requested media types.
+ * request sets the list of requested tracks
  *
  * @param {Object<string,Array<string>>} what
- *     - A dictionary that maps labels to a sequence of 'audio' and 'video'.
+ *     - A dictionary that maps labels to a sequence of 'audio', 'video'
- *       An entry with an empty label '' provides the default.
+ *       or 'video-low.  An entry with an empty label '' provides the default.
  */
 ServerConnection.prototype.request = function(what) {
     this.send({
@@ -1219,6 +1219,21 @@ Stream.prototype.restartIce = function () {
     c.negotiate(true);
 };
 
+/**
+ * request sets the list of tracks.  If this is not called, or called with
+ * a null argument, then the default is provided by ServerConnection.request.
+ *
+ * @param {Array<string>} what - a sequence of 'audio', 'video' or 'video-low'.
+ */
+Stream.prototype.request = function(what) {
+    let c = this;
+    c.sc.send({
+        type: 'requestStream',
+        id: c.id,
+        request: what,
+    });
+};
+
 /**
  * updateStats is called periodically, if requested by setStatsInterval,
  * in order to recompute stream statistics and invoke the onstats handler.