[tor-commits] [snowflake/master] Make WebRTCPeer.preparePeerConnection block.

[dcf at torproject.org]

commit 81d14ad33a21ac487cefb2912a32a72a7cc8ee39
Author: David Fifield <david at bamsoftware.com>
Date:   Thu Apr 23 20:13:16 2020 -0600

    Make WebRTCPeer.preparePeerConnection block.
    
    Formerly, preparePeerConnection set up a callback that sent into a
    channel, and exchangeSDP waited until it could receive from the channel.
    We can move the channel entirely into preparePeerConnection (having it
    not return until the callback has been called) and that way remove some
    shared state.
---
 client/lib/webrtc.go | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/client/lib/webrtc.go b/client/lib/webrtc.go
index e4ac8e0..d489096 100644
--- a/client/lib/webrtc.go
+++ b/client/lib/webrtc.go
@@ -24,11 +24,10 @@ type WebRTCPeer struct {
 	transport *webrtc.DataChannel
 	broker    *BrokerChannel
 
-	offerChannel chan *webrtc.SessionDescription
-	recvPipe     *io.PipeReader
-	writePipe    *io.PipeWriter
-	lastReceive  time.Time
-	buffer       bytes.Buffer
+	recvPipe    *io.PipeReader
+	writePipe   *io.PipeWriter
+	lastReceive time.Time
+	buffer      bytes.Buffer
 
 	closed bool
 
@@ -51,7 +50,6 @@ func NewWebRTCPeer(config *webrtc.Configuration,
 	}
 	connection.config = config
 	connection.broker = broker
-	connection.offerChannel = make(chan *webrtc.SessionDescription, 1)
 
 	// Override with something that's not NullLogger to have real logging.
 	connection.BytesLogger = &BytesNullLogger{}
@@ -153,11 +151,12 @@ func (c *WebRTCPeer) preparePeerConnection() error {
 		return err
 	}
 	// Prepare PeerConnection callbacks.
+	offerChannel := make(chan struct{})
 	// Allow candidates to accumulate until ICEGatheringStateComplete.
 	pc.OnICECandidate(func(candidate *webrtc.ICECandidate) {
 		if candidate == nil {
 			log.Printf("WebRTC: Done gathering candidates")
-			c.offerChannel <- pc.LocalDescription()
+			close(offerChannel)
 		} else {
 			log.Printf("WebRTC: Got ICE candidate: %s", candidate.String())
 		}
@@ -180,6 +179,7 @@ func (c *WebRTCPeer) preparePeerConnection() error {
 	}
 	log.Println("WebRTC: Set local description")
 
+	<-offerChannel // Wait for ICE candidate gathering to complete.
 	log.Println("WebRTC: PeerConnection created.")
 	return nil
 }
@@ -254,10 +254,9 @@ func (c *WebRTCPeer) establishDataChannel() error {
 	return nil
 }
 
-// exchangeSDP blocks until an SDP offer is available, sends it to the Broker,
-// then awaits the SDP answer.
+// exchangeSDP sends the local SDP offer to the Broker and awaits the SDP
+// answer.
 func (c *WebRTCPeer) exchangeSDP() error {
-	<-c.offerChannel
 	// Keep trying the same offer until a valid answer arrives.
 	var answer *webrtc.SessionDescription
 	for {
@@ -282,9 +281,6 @@ func (c *WebRTCPeer) exchangeSDP() error {
 
 // Close all channels and transports
 func (c *WebRTCPeer) cleanup() {
-	if nil != c.offerChannel {
-		close(c.offerChannel)
-	}
 	// Close this side of the SOCKS pipe.
 	if nil != c.writePipe {
 		c.writePipe.Close()