fix: Close peer negotiate mutex if we haven't negotiated (#1774)

Closes #1706 and #1644.

peer/channel.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"net"
 	"sync"
+	"time"
 
 	"github.com/pion/datachannel"
 	"github.com/pion/webrtc/v3"
@@ -244,6 +245,14 @@ func (c *Channel) Write(bytes []byte) (n int, err error) {
 	if c.dc.BufferedAmount()+uint64(len(bytes)) >= maxBufferedAmount {
 		<-c.sendMore
 	}
+
+	// There's an obvious race-condition here. This is an edge-case, as
+	// most-frequently data won't be pooled so synchronously, but is
+	// definitely possible.
+	//
+	// See: https://github.com/pion/sctp/issues/181
+	time.Sleep(time.Microsecond)
+
 	return c.rwc.Write(bytes)
 }
 

peer/conn.go

@@ -73,6 +73,7 @@ func newWithClientOrServer(servers []webrtc.ICEServer, client bool, opts *ConnOp
 		dcFailedChannel:                 make(chan struct{}),
 		localCandidateChannel:           make(chan webrtc.ICECandidateInit),
 		localSessionDescriptionChannel:  make(chan webrtc.SessionDescription, 1),
+		negotiated:                      make(chan struct{}),
 		remoteSessionDescriptionChannel: make(chan webrtc.SessionDescription, 1),
 		settingEngine:                   opts.SettingEngine,
 	}
@@ -124,8 +125,7 @@ type Conn struct {
 	localSessionDescriptionChannel  chan webrtc.SessionDescription
 	remoteSessionDescriptionChannel chan webrtc.SessionDescription
 
-	negotiateMutex sync.Mutex
-	hasNegotiated  bool
+	negotiated chan struct{}
 
 	loggerValue   atomic.Value
 	settingEngine webrtc.SettingEngine
@@ -152,9 +152,6 @@ func (c *Conn) logger() slog.Logger {
 }
 
 func (c *Conn) init() error {
-	// The negotiation needed callback can take a little bit to execute!
-	c.negotiateMutex.Lock()
-
 	c.rtc.OnNegotiationNeeded(c.negotiate)
 	c.rtc.OnICEConnectionStateChange(func(iceConnectionState webrtc.ICEConnectionState) {
 		c.closedICEMutex.Lock()
@@ -290,11 +287,13 @@ func (c *Conn) negotiate() {
 	c.logger().Debug(context.Background(), "negotiating")
 	// ICE candidates cannot be added until SessionDescriptions have been
 	// exchanged between peers.
-	if c.hasNegotiated {
-		c.negotiateMutex.Lock()
-	}
-	c.hasNegotiated = true
-	defer c.negotiateMutex.Unlock()
+	defer func() {
+		select {
+		case <-c.negotiated:
+		default:
+			close(c.negotiated)
+		}
+	}()
 
 	if c.offerer {
 		offer, err := c.rtc.CreateOffer(&webrtc.OfferOptions{})
@@ -368,8 +367,10 @@ func (c *Conn) AddRemoteCandidate(i webrtc.ICECandidateInit) {
 	// This must occur in a goroutine to allow the SessionDescriptions
 	// to be exchanged first.
 	go func() {
-		c.negotiateMutex.Lock()
-		defer c.negotiateMutex.Unlock()
+		select {
+		case <-c.closed:
+		case <-c.negotiated:
+		}
 		if c.isClosed() {
 			return
 		}

peer/conn_test.go

@@ -59,9 +59,7 @@ func TestMain(m *testing.M) {
 }
 
 func TestConn(t *testing.T) {
-	t.Skip("known flake -- https://github.com/coder/coder/issues/1644")
 	t.Parallel()
-
 	t.Run("Ping", func(t *testing.T) {
 		t.Parallel()
 		client, server, _ := createPair(t)