From 8169c40bb6a52a4823b4185787bf95e7a4bc8186 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Fri, 3 Apr 2026 21:41:49 +0000
Subject: [PATCH] fix: handle WebRTC offer glare during renegotiation

When two peers simultaneously trigger renegotiation (e.g., both enable
video), both create local offers and enter HAVE_LOCAL_OFFER state. When
a remote offer arrives in this state, setRemoteDescription fails with
"Called in wrong state: have-local-offer".

Fix by implementing standard WebRTC glare handling: use pubkey comparison
as a tiebreaker (higher pubkey wins). The losing peer rolls back their
local offer before accepting the remote one.

https://claude.ai/code/session_01XLbnNVx3GDhHrPZKPXfFdD
---
 .../amethyst/service/call/CallController.kt   | 34 ++++++++++++++++---
 .../service/call/WebRtcCallSession.kt         | 26 ++++++++++++++
 2 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/CallController.kt b/amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/CallController.kt
index 8d8eca8e0..0cbb6021b 100644
--- a/amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/CallController.kt
+++ b/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)
             }
         }
     }
diff --git a/amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/WebRtcCallSession.kt b/amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/WebRtcCallSession.kt
index 44745c0ee..3379e2160 100644
--- a/amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/WebRtcCallSession.kt
+++ b/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()