@@ -62,17 +62,19 @@ func newWithClientOrServer(servers []webrtc.ICEServer, client bool, opts *ConnOp
6262 return nil , xerrors .Errorf ("create peer connection: %w" , err )
6363 }
6464 conn := & Conn {
65- pingChannelID : 1 ,
66- pingEchoChannelID : 2 ,
67- opts : opts ,
68- rtc : rtc ,
69- offerrer : client ,
70- closed : make (chan struct {}),
71- dcOpenChannel : make (chan * webrtc.DataChannel ),
72- dcDisconnectChannel : make (chan struct {}),
73- dcFailedChannel : make (chan struct {}),
74- localCandidateChannel : make (chan webrtc.ICECandidateInit ),
75- pendingCandidates : make ([]webrtc.ICECandidateInit , 0 ),
65+ pingChannelID : 1 ,
66+ pingEchoChannelID : 2 ,
67+ opts : opts ,
68+ rtc : rtc ,
69+ offerrer : client ,
70+ closed : make (chan struct {}),
71+ dcOpenChannel : make (chan * webrtc.DataChannel ),
72+ dcDisconnectChannel : make (chan struct {}),
73+ dcFailedChannel : make (chan struct {}),
74+ // This channel needs to be bufferred otherwise slow consumers
75+ // of this will cause a connection failure.
76+ localCandidateChannel : make (chan webrtc.ICECandidateInit , 16 ),
77+ pendingRemoteCandidates : make ([]webrtc.ICECandidateInit , 0 ),
7678 localSessionDescriptionChannel : make (chan webrtc.SessionDescription ),
7779 remoteSessionDescriptionChannel : make (chan webrtc.SessionDescription ),
7880 }
@@ -120,7 +122,7 @@ type Conn struct {
120122 localSessionDescriptionChannel chan webrtc.SessionDescription
121123 remoteSessionDescriptionChannel chan webrtc.SessionDescription
122124
123- pendingCandidates []webrtc.ICECandidateInit
125+ pendingRemoteCandidates []webrtc.ICECandidateInit
124126 pendingCandidatesMutex sync.Mutex
125127 pendingCandidatesFlushed bool
126128
@@ -142,14 +144,6 @@ func (c *Conn) init() error {
142144 if iceCandidate == nil {
143145 return
144146 }
145- c .pendingCandidatesMutex .Lock ()
146- defer c .pendingCandidatesMutex .Unlock ()
147-
148- if ! c .pendingCandidatesFlushed {
149- c .opts .Logger .Debug (context .Background (), "adding local candidate to buffer" )
150- c .pendingCandidates = append (c .pendingCandidates , iceCandidate .ToJSON ())
151- return
152- }
153147 c .opts .Logger .Debug (context .Background (), "adding local candidate" )
154148 select {
155149 case <- c .closed :
@@ -262,6 +256,7 @@ func (c *Conn) negotiate() {
262256 _ = c .CloseWithError (xerrors .Errorf ("create offer: %w" , err ))
263257 return
264258 }
259+ c .opts .Logger .Debug (context .Background (), "setting local description" )
265260 err = c .rtc .SetLocalDescription (offer )
266261 if err != nil {
267262 _ = c .CloseWithError (xerrors .Errorf ("set local description: %w" , err ))
@@ -281,25 +276,20 @@ func (c *Conn) negotiate() {
281276 case remoteDescription = <- c .remoteSessionDescriptionChannel :
282277 }
283278
279+ c .opts .Logger .Debug (context .Background (), "setting remote description" )
284280 err := c .rtc .SetRemoteDescription (remoteDescription )
285281 if err != nil {
286- c .pendingCandidatesMutex .Unlock ()
287282 _ = c .CloseWithError (xerrors .Errorf ("set remote description (closed %v): %w" , c .isClosed (), err ))
288283 return
289284 }
290285
291- if c .offerrer {
292- // ICE candidates reset when an offer/answer is set for the first
293- // time. If candidates flush before this point, a connection could fail.
294- c .flushPendingCandidates ()
295- }
296-
297286 if ! c .offerrer {
298287 answer , err := c .rtc .CreateAnswer (& webrtc.AnswerOptions {})
299288 if err != nil {
300289 _ = c .CloseWithError (xerrors .Errorf ("create answer: %w" , err ))
301290 return
302291 }
292+ c .opts .Logger .Debug (context .Background (), "setting local description" )
303293 err = c .rtc .SetLocalDescription (answer )
304294 if err != nil {
305295 _ = c .CloseWithError (xerrors .Errorf ("set local description: %w" , err ))
@@ -313,28 +303,23 @@ func (c *Conn) negotiate() {
313303 return
314304 case c .localSessionDescriptionChannel <- answer :
315305 }
316-
317- // Wait until the local description is set to flush candidates.
318- c .flushPendingCandidates ()
319306 }
320- }
321307
322- // flushPendingCandidates writes all local candidates to the candidate send channel .
323- // The localCandidateChannel is expected to be serviced, otherwise this could block.
324- func ( c * Conn ) flushPendingCandidates () {
308+ // The ICE transport resets when the remote description is updated .
309+ // Adding ICE candidates before this point causes a failed connection,
310+ // because the candidate would be lost.
325311 c .pendingCandidatesMutex .Lock ()
326312 defer c .pendingCandidatesMutex .Unlock ()
327- for _ , pendingCandidate := range c .pendingCandidates {
328- c .opts .Logger .Debug (context .Background (), "flushing local candidate" )
329- select {
330- case <- c .closed :
313+ for _ , pendingCandidate := range c .pendingRemoteCandidates {
314+ c .opts .Logger .Debug (context .Background (), "flushing remote candidate" )
315+ err := c .rtc .AddICECandidate (pendingCandidate )
316+ if err != nil {
317+ _ = c .CloseWithError (xerrors .Errorf ("flush pending candidates: %w" , err ))
331318 return
332- case c .localCandidateChannel <- pendingCandidate :
333319 }
334320 }
335- c .pendingCandidates = make ([]webrtc.ICECandidateInit , 0 )
336321 c .pendingCandidatesFlushed = true
337- c .opts .Logger .Debug (context .Background (), "flushed candidates" )
322+ c .opts .Logger .Debug (context .Background (), "flushed remote candidates" )
338323}
339324
340325// LocalCandidate returns a channel that emits when a local candidate
@@ -345,6 +330,13 @@ func (c *Conn) LocalCandidate() <-chan webrtc.ICECandidateInit {
345330
346331// AddRemoteCandidate adds a remote candidate to the RTC connection.
347332func (c * Conn ) AddRemoteCandidate (i webrtc.ICECandidateInit ) error {
333+ c .pendingCandidatesMutex .Lock ()
334+ defer c .pendingCandidatesMutex .Unlock ()
335+ if ! c .pendingCandidatesFlushed {
336+ c .opts .Logger .Debug (context .Background (), "adding remote candidate to buffer" )
337+ c .pendingRemoteCandidates = append (c .pendingRemoteCandidates , i )
338+ return nil
339+ }
348340 c .opts .Logger .Debug (context .Background (), "adding remote candidate" )
349341 return c .rtc .AddICECandidate (i )
350342}
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