Merge pull request #2121 from vitorpamplona/claude/fix-webrtc-answer-state-SaXhI

Handle WebRTC offer glare in call renegotiation

amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/CallController.kt

@@ -539,11 +539,37 @@ class CallController(
         Log.d(TAG) { "Renegotiation offer from ${peerPubKey.take(8)}, sdpLength=${sdpOffer.length}" }
 
         scope.launch {
-            ps.session.setRemoteDescription(SessionDescription(SessionDescription.Type.OFFER, sdpOffer))
-            ps.session.createAnswer { sdp ->
-                scope.launch {
-                    callManager.sendRenegotiationAnswer(sdp.description, peerPubKey)
+            val signalingState = ps.session.getSignalingState()
+
+            if (signalingState == PeerConnection.SignalingState.HAVE_LOCAL_OFFER) {
+                // Glare: both sides sent offers simultaneously.
+                // Use pubkey comparison as tiebreaker — higher pubkey wins.
+                val myPubKey = signerProvider().pubKey
+                if (myPubKey > peerPubKey) {
+                    Log.d(TAG) { "Glare with ${peerPubKey.take(8)}: I win (my offer takes priority), ignoring remote offer" }
+                    return@launch
                 }
+                Log.d(TAG) { "Glare with ${peerPubKey.take(8)}: I lose, rolling back my offer" }
+                ps.session.rollback {
+                    scope.launch {
+                        applyRenegotiationOffer(ps, peerPubKey, sdpOffer)
+                    }
+                }
+            } else {
+                applyRenegotiationOffer(ps, peerPubKey, sdpOffer)
+            }
+        }
+    }
+
+    private fun applyRenegotiationOffer(
+        ps: PeerSessionState,
+        peerPubKey: HexKey,
+        sdpOffer: String,
+    ) {
+        ps.session.setRemoteDescription(SessionDescription(SessionDescription.Type.OFFER, sdpOffer))
+        ps.session.createAnswer { sdp ->
+            scope.launch {
+                callManager.sendRenegotiationAnswer(sdp.description, peerPubKey)
             }
         }
     }

amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/WebRtcCallSession.kt

@@ -257,6 +257,32 @@ class WebRtcCallSession(
 
     fun getSignalingState(): PeerConnection.SignalingState? = peerConnection?.signalingState()
 
+    /**
+     * Rolls back a local offer so an incoming remote offer can be accepted
+     * (WebRTC offe glare handling).
+     */
+    fun rollback(onDone: () -> Unit) {
+        val rollbackSdp = SessionDescription(SessionDescription.Type.ROLLBACK, "")
+        peerConnection?.setLocalDescription(
+            object : SdpObserver {
+                override fun onCreateSuccess(sdp: SessionDescription?) {}
+
+                override fun onCreateFailure(error: String?) {}
+
+                override fun onSetSuccess() {
+                    Log.d(TAG) { "Rollback SUCCESS" }
+                    onDone()
+                }
+
+                override fun onSetFailure(error: String?) {
+                    Log.e(TAG, "Rollback FAILED: $error")
+                    error?.let { onError("Rollback failed: $it") }
+                }
+            },
+            rollbackSdp,
+        )
+    }
+
     fun dispose() {
         peerConnection?.close()
         peerConnection?.dispose()