Close sessions for lost WebSockets to prevent zombie SyncPlay groups (#17079)

Close sessions for lost WebSockets to prevent zombie SyncPlay groups

Emby.Server.Implementations/Session/SessionWebSocketListener.cs

@@ -246,8 +246,21 @@ namespace Emby.Server.Implementations.Session
                     _logger.LogInformation("Lost {0} WebSockets.", lost.Count);
                     foreach (var webSocket in lost)
                     {
-                        // TODO: handle session relative to the lost webSocket
                         RemoveWebSocket(webSocket);
+
+                        // The connection stopped answering keep-alives, so a close frame will
+                        // never arrive and the pending receive loop would hang forever, keeping
+                        // the session (and e.g. its SyncPlay group membership) alive. Disposing
+                        // the connection aborts the receive loop, which raises Closed and lets
+                        // the session end normally.
+                        try
+                        {
+                            webSocket.Dispose();
+                        }
+                        catch (Exception exception)
+                        {
+                            _logger.LogWarning(exception, "Error disposing lost WebSocket from {RemoteEndPoint}.", webSocket.RemoteEndPoint);
+                        }
                     }
                 }
             }