From c3050b9e430a61653ceb008d9859a6d47d65e8d3 Mon Sep 17 00:00:00 2001
From: Maxim Dolgolyov <maxim.dolgolyov@gmail.com>
Date: Wed, 15 Apr 2026 13:28:38 +0300
Subject: [PATCH] =?UTF-8?q?fix:=20WebRTC=20audio=20=E2=80=94=20glare=20han?=
 =?UTF-8?q?dling=20(Perfect=20Negotiation)=20+=20autoplay=20+=20signalingS?=
 =?UTF-8?q?tate=20guard?=
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---
 frontend/js/classroom-rtc.js | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/frontend/js/classroom-rtc.js b/frontend/js/classroom-rtc.js
index cddbe2d..7023615 100644
--- a/frontend/js/classroom-rtc.js
+++ b/frontend/js/classroom-rtc.js
@@ -193,6 +193,18 @@ class ClassroomRTC {
 
   async _handleOffer(fromUid, payload) {
     const peer = this._getOrCreate(fromUid);
+
+    // Perfect Negotiation: resolve offer collision (both peers sending offers simultaneously).
+    // Polite peer (higher uid) yields — rolls back its own offer and handles the incoming one.
+    // Impolite peer (lower uid) ignores the collision offer and waits for the answer to its own.
+    const polite = this._uid > fromUid;
+    const collision = peer.pc.signalingState !== 'stable' || peer.negotiating;
+    if (collision) {
+      if (!polite) return;
+      // Polite: explicit rollback for older browsers; modern Chrome handles it implicitly
+      await peer.pc.setLocalDescription({ type: 'rollback' }).catch(() => {});
+    }
+
     await peer.pc.setRemoteDescription({ type: 'offer', sdp: payload.sdp });
     peer.remoteSet = true;
     await this._flushCandidates(peer);
@@ -277,7 +289,7 @@ class ClassroomRTC {
 
     /* Renegotiation: fires when tracks are added/removed (e.g. screen share) */
     pc.onnegotiationneeded = async () => {
-      if (peer.negotiating || !peer.remoteSet) return;
+      if (peer.negotiating || !peer.remoteSet || pc.signalingState !== 'stable') return;
       peer.negotiating = true;
       try {
         const offer = await pc.createOffer();
@@ -299,6 +311,7 @@ class ClassroomRTC {
           document.body.appendChild(peer.audioEl);
         }
         peer.audioEl.srcObject = stream;
+        peer.audioEl.play().catch(() => {});
         this._startVAD(uid, stream);
       } else if (track.kind === 'video') {
         if (this._onScreen) this._onScreen(stream);