improve voice chat security by implementing join validation

LarpixVoice/Requests.cs

@@ -18,7 +18,6 @@ public class Requests
 
         string roomId = context.Request.Query["room"].ToString();
         string userIdStr = context.Request.Query["userId"].ToString();
-        string secret = context.Request.Query["secret"].ToString();
 
         if (string.IsNullOrEmpty(roomId) || !ulong.TryParse(userIdStr, out ulong clientId))
         {
@@ -27,6 +26,56 @@ public class Requests
         }
 
         using var webSocket = await context.WebSockets.AcceptWebSocketAsync();
+
+        // --- Ticket handshake: first frame must be "<publicId>.<iv>.<ct>".
+        // Unauthenticated connections never touch the room roster; the blob is
+        // validated by the main server, which consumes it atomically.
+        // Tiny buffer: unauthenticated clients cannot pin large allocations. ---
+        var authBuffer = ArrayPool<byte>.Shared.Rent(2048);
+        string ticket;
+        using (var authCts = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
+        {
+            WebSocketReceiveResult firstFrame;
+            try
+            {
+                firstFrame = await webSocket.ReceiveAsync(new ArraySegment<byte>(authBuffer), authCts.Token);
+            }
+            catch (OperationCanceledException)
+            {
+                Console.WriteLine($"Voice ws: ticket timeout, room={roomId}");
+                await SafeClose(webSocket, "Ticket timeout");
+                return;
+            }
+            catch (WebSocketException)
+            {
+                return;
+            }
+
+            if (firstFrame.MessageType != WebSocketMessageType.Text || !firstFrame.EndOfMessage || firstFrame.Count == 0)
+            {
+                await SafeClose(webSocket, "Invalid ticket");
+                return;
+            }
+            ticket = System.Text.Encoding.UTF8.GetString(authBuffer, 0, firstFrame.Count);
+        }
+        ArrayPool<byte>.Shared.Return(authBuffer);
+
+        string[] ticketParts = ticket.Split('.');
+        bool frameShapeOk = ticketParts.Length == 3
+            && ticketParts[0].Length > 0 && ticketParts[0].Length <= 64
+            && ticketParts[1].Length == 16
+            && ticketParts[2].Length > 0 && ticketParts[2].Length <= 128;
+
+        Console.WriteLine($"Voice ws: validating {ticketParts[0][..Math.Min(8, ticketParts[0].Length)]} room={roomId}");
+        if (!frameShapeOk ||
+            !await Utils.AuthorizeConnection(ticketParts[0], ticketParts[1], ticketParts[2], roomId, clientId))
+        {
+            Console.WriteLine($"Voice ws: invalid ticket, room={roomId}");
+            await SafeClose(webSocket, "Invalid ticket");
+            return;
+        }
+
+        Session currentSession = null;
         var roomClients = Rooms.GetOrAdd(roomId, _ => new ConcurrentDictionary<ulong, Session>());
 
         if (roomClients.TryGetValue(clientId, out var oldSession) && oldSession.Socket.State == WebSocketState.Open)
@@ -40,7 +89,7 @@ public class Requests
             }
         }
 
-        var currentSession = new Session(webSocket);
+        currentSession = new Session(webSocket);
         roomClients[clientId] = currentSession;
 
         _ = Task.Run(async () =>
@@ -53,7 +102,7 @@ public class Requests
                     {
                         await currentSession.Socket.SendAsync(new ArraySegment<byte>(packet.Buffer, 0, packet.Length),
                             WebSocketMessageType.Binary, true, CancellationToken.None);
-                        
+
                         Interlocked.Add(ref TotalBytesSent, (ulong)packet.Length);
                     }
                 }
@@ -67,6 +116,7 @@ public class Requests
             }
         });
 
+        // Big buffer only for authenticated media traffic.
         var receiveBuffer = ArrayPool<byte>.Shared.Rent(1024 * 1024);
         try
         {
@@ -80,10 +130,10 @@ public class Requests
                     result = await webSocket.ReceiveAsync(
                         new ArraySegment<byte>(receiveBuffer, totalBytes, receiveBuffer.Length - totalBytes),
                         CancellationToken.None);
-                    
+
                     totalBytes += result.Count;
                     Interlocked.Add(ref TotalBytesReceived, (ulong)result.Count);
-                    
+
                 } while (!result.EndOfMessage);
 
                 if (result.MessageType == WebSocketMessageType.Close) break;
@@ -121,4 +171,16 @@ public class Requests
             if (roomClients.IsEmpty) Rooms.TryRemove(roomId, out _);
         }
     }
+
+    private static async Task SafeClose(WebSocket socket, string reason)
+    {
+        try
+        {
+            if (socket.State == WebSocketState.Open)
+                await socket.CloseAsync(WebSocketCloseStatus.NormalClosure, reason, CancellationToken.None);
+        }
+        catch
+        {
+        }
+    }
 }