Call conn.RemoteAddr() before entering the datachannelHandler goroutine.

This is a workaround for the hang described at
https://bugs.torproject.org/18628#comment:8

1 files changed, 8 insertions, 4 deletions

diff --git a/proxy-go/snowflake.go b/proxy-go/snowflake.go
index 4e46ee4..133bc0e 100644
--- a/proxy-go/snowflake.go
+++ b/proxy-go/snowflake.go
@@ -202,15 +202,19 @@ func CopyLoopTimeout(c1 net.Conn, c2 net.Conn, timeout time.Duration) {
 	wg.Wait()
 }
 
-func datachannelHandler(conn *webRTCConn) {
+// We pass conn.RemoteAddr() as an additional parameter, rather than calling
+// conn.RemoteAddr() inside this function, as a workaround for a hang that
+// otherwise occurs inside of conn.pc.RemoteDescription() (called by
+// RemoteAddr). https://bugs.torproject.org/18628#comment:8
+func datachannelHandler(conn *webRTCConn, remoteAddr net.Addr) {
 	defer conn.Close()
 	defer retToken()
 
 	// Retrieve client IP address
-	if conn.RemoteAddr() != nil && conn.RemoteAddr().String() != "" {
+	if remoteAddr != nil && remoteAddr.String() != "" {
 		// Encode client IP address in relay URL
 		q := opt.relayURL.Query()
-		clientIP := conn.RemoteAddr().String()
+		clientIP := remoteAddr.String()
 		q.Set("client_ip", clientIP)
 		opt.relayURL.RawQuery = q.Encode()
 	} else {
@@ -271,7 +275,7 @@ func makePeerConnectionFromOffer(sdp *webrtc.SessionDescription, config *webrtc.
 		}
 
 		conn := &webRTCConn{pc: pc, dc: dc, pr: pr}
-		go datachannelHandler(conn)
+		go datachannelHandler(conn, conn.RemoteAddr())
 	}
 
 	err = pc.SetRemoteDescription(sdp)