Add KeepAliveMode and SupportedWebSocketSubProtocols options

src/Transports.AspNetCore/GraphQLHttpMiddleware.cs

@@ -1007,7 +1007,7 @@ protected virtual Task WriteJsonResponseAsync<TResult>(HttpContext context, Http
     /// <summary>
     /// Gets a list of WebSocket sub-protocols supported.
     /// </summary>
-    protected virtual IEnumerable<string> SupportedWebSocketSubProtocols => _supportedSubProtocols;
+    protected virtual IEnumerable<string> SupportedWebSocketSubProtocols => _options.WebSockets.SupportedWebSocketSubProtocols;
 
     /// <summary>
     /// Creates an <see cref="IWebSocketConnection"/>, a WebSocket message pump.

src/Transports.AspNetCore/WebSockets/BaseSubscriptionServer.cs

@@ -259,10 +259,33 @@ protected virtual Task OnNotAuthorizedPolicyAsync(OperationMessage message, Auth
     /// <br/><br/>
     /// Otherwise, the connection is acknowledged via <see cref="OnConnectionAcknowledgeAsync(OperationMessage)"/>,
     /// <see cref="TryInitialize"/> is called to indicate that this WebSocket connection is ready to accept requests,
-    /// and keep-alive messages are sent via <see cref="OnSendKeepAliveAsync"/> if configured to do so.
-    /// Keep-alive messages are only sent if no messages have been sent over the WebSockets connection for the
-    /// length of time configured in <see cref="GraphQLWebSocketOptions.KeepAliveTimeout"/>.
+    /// and <see cref="OnSendKeepAliveAsync"/> is called to start sending keep-alive messages if configured to do so.
     /// </summary>
+    protected virtual async Task OnConnectionInitAsync(OperationMessage message)
+    {
+        if (!await AuthorizeAsync(message))
+        {
+            return;
+        }
+        await OnConnectionAcknowledgeAsync(message);
+        if (TryInitialize() == false)
+            return;
+
+        _ = OnKeepAliveLoopAsync();
+    }
+
+    /// <summary>
+    /// Executes when the client is attempting to initialize the connection.
+    /// <br/><br/>
+    /// By default, this first checks <see cref="AuthorizeAsync(OperationMessage)"/> to validate that the
+    /// request has passed authentication.  If validation fails, the connection is closed with an Access
+    /// Denied message.
+    /// <br/><br/>
+    /// Otherwise, the connection is acknowledged via <see cref="OnConnectionAcknowledgeAsync(OperationMessage)"/>,
+    /// <see cref="TryInitialize"/> is called to indicate that this WebSocket connection is ready to accept requests,
+    /// and <see cref="OnSendKeepAliveAsync"/> is called to start sending keep-alive messages if configured to do so.
+    /// </summary>
+    [Obsolete($"Please use the {nameof(OnConnectionInitAsync)}(message) and {nameof(OnKeepAliveLoopAsync)} methods instead. This method will be removed in a future version of this library.")]
     protected virtual async Task OnConnectionInitAsync(OperationMessage message, bool smartKeepAlive)
     {
         if (!await AuthorizeAsync(message))
@@ -277,12 +300,49 @@ protected virtual async Task OnConnectionInitAsync(OperationMessage message, boo
         if (keepAliveTimeout > TimeSpan.Zero)
         {
             if (smartKeepAlive)
-                _ = StartSmartKeepAliveLoopAsync();
+                _ = OnKeepAliveLoopAsync(keepAliveTimeout, KeepAliveMode.Timeout);
             else
-                _ = StartKeepAliveLoopAsync();
+                _ = OnKeepAliveLoopAsync(keepAliveTimeout, KeepAliveMode.Interval);
+        }
+    }
+
+    /// <summary>
+    /// Starts sending keep-alive messages if configured to do so. Inspects the configured
+    /// <see cref="GraphQLWebSocketOptions"/> and passes control to <see cref="OnKeepAliveLoopAsync(TimeSpan, KeepAliveMode)"/>
+    /// if keep-alive messages are enabled.
+    /// </summary>
+    protected virtual Task OnKeepAliveLoopAsync()
+    {
+        return OnKeepAliveLoopAsync(
+            _options.KeepAliveTimeout ?? DefaultKeepAliveTimeout,
+            _options.KeepAliveMode);
+    }
+
+    /// <summary>
+    /// Sends keep-alive messages according to the specified timeout period and method.
+    /// See <see cref="KeepAliveMode"/> for implementation details for each supported mode.
+    /// </summary>
+    protected virtual async Task OnKeepAliveLoopAsync(TimeSpan keepAliveTimeout, KeepAliveMode keepAliveMode)
+    {
+        if (keepAliveTimeout <= TimeSpan.Zero)
+            return;
+
+        switch (keepAliveMode)
+        {
+            case KeepAliveMode.Default:
+            case KeepAliveMode.Timeout:
+                await StartSmartKeepAliveLoopAsync();
+                break;
+            case KeepAliveMode.Interval:
+                await StartDumbKeepAliveLoopAsync();
+                break;
+            case KeepAliveMode.TimeoutWithPayload:
+                throw new NotImplementedException($"{nameof(KeepAliveMode.TimeoutWithPayload)} is not implemented within the {nameof(BaseSubscriptionServer)} class.");
+            default:
+                throw new ArgumentOutOfRangeException(nameof(keepAliveMode));
         }
 
-        async Task StartKeepAliveLoopAsync()
+        async Task StartDumbKeepAliveLoopAsync()
         {
             while (!CancellationToken.IsCancellationRequested)
             {

src/Transports.AspNetCore/WebSockets/GraphQLWebSocketOptions.cs

@@ -25,6 +25,12 @@ public class GraphQLWebSocketOptions
     /// </summary>
     public TimeSpan? KeepAliveTimeout { get; set; }
 
+    /// <summary>
+    /// Gets or sets the keep-alive mode used for websocket subscriptions.
+    /// This property is only applicable when using the GraphQLWs protocol.
+    /// </summary>
+    public KeepAliveMode KeepAliveMode { get; set; } = KeepAliveMode.Default;
+
     /// <summary>
     /// The amount of time to wait to attempt a graceful teardown of the WebSockets protocol.
     /// A value of <see langword="null"/> indicates the default value defined by the implementation.
@@ -42,4 +48,17 @@ public class GraphQLWebSocketOptions
     /// Disconnects a subscription from the client in the event of any GraphQL errors during a subscription.  The default value is <see langword="false"/>.
     /// </summary>
     public bool DisconnectAfterAnyError { get; set; }
+
+    /// <summary>
+    /// The list of supported WebSocket sub-protocols.
+    /// Defaults to <see cref="GraphQLWs.SubscriptionServer.SubProtocol"/> and <see cref="SubscriptionsTransportWs.SubscriptionServer.SubProtocol"/>.
+    /// Adding other sub-protocols require the <see cref="GraphQLHttpMiddleware.CreateMessageProcessor(IWebSocketConnection, string)"/> method
+    /// to be overridden to handle the new sub-protocol.
+    /// </summary>
+    /// <remarks>
+    /// When the <see cref="KeepAliveMode"/> is set to <see cref="KeepAliveMode.TimeoutWithPayload"/>, you may wish to remove
+    /// <see cref="SubscriptionsTransportWs.SubscriptionServer.SubProtocol"/> from this list to prevent clients from using
+    /// protocols which do not support the <see cref="KeepAliveMode.TimeoutWithPayload"/> keep-alive mode.
+    /// </remarks>
+    public List<string> SupportedWebSocketSubProtocols { get; set; } = [GraphQLWs.SubscriptionServer.SubProtocol, SubscriptionsTransportWs.SubscriptionServer.SubProtocol];
 }

src/Transports.AspNetCore/WebSockets/GraphQLWs/PingPayload.cs

@@ -0,0 +1,12 @@
+namespace GraphQL.Server.Transports.AspNetCore.WebSockets.GraphQLWs;
+
+/// <summary>
+/// The payload of the ping message.
+/// </summary>
+public class PingPayload
+{
+    /// <summary>
+    /// The unique identifier of the ping message.
+    /// </summary>
+    public string? id { get; set; }
+}

src/Transports.AspNetCore/WebSockets/GraphQLWs/SubscriptionServer.cs

@@ -4,6 +4,11 @@ namespace GraphQL.Server.Transports.AspNetCore.WebSockets.GraphQLWs;
 public class SubscriptionServer : BaseSubscriptionServer
 {
     private readonly IWebSocketAuthenticationService? _authenticationService;
+    private readonly IGraphQLSerializer _serializer;
+    private readonly GraphQLWebSocketOptions _options;
+    private DateTime _lastPongReceivedUtc;
+    private string? _lastPingId;
+    private readonly object _lastPingLock = new();
 
     /// <summary>
     /// The WebSocket sub-protocol used for this protocol.
@@ -67,6 +72,8 @@ public SubscriptionServer(
         UserContextBuilder = userContextBuilder ?? throw new ArgumentNullException(nameof(userContextBuilder));
         Serializer = serializer ?? throw new ArgumentNullException(nameof(serializer));
         _authenticationService = authenticationService;
+        _serializer = serializer;
+        _options = options;
     }
 
     /// <inheritdoc/>
@@ -90,7 +97,9 @@ public override async Task OnMessageReceivedAsync(OperationMessage message)
             }
             else
             {
+#pragma warning disable CS0618 // Type or member is obsolete
                 await OnConnectionInitAsync(message, true);
+#pragma warning restore CS0618 // Type or member is obsolete
             }
             return;
         }
@@ -113,6 +122,69 @@ public override async Task OnMessageReceivedAsync(OperationMessage message)
         }
     }
 
+    /// <inheritdoc/>
+    [Obsolete($"Please use the {nameof(OnConnectionInitAsync)} and {nameof(OnKeepAliveLoopAsync)} methods instead. This method will be removed in a future version of this library.")]
+    protected override Task OnConnectionInitAsync(OperationMessage message, bool smartKeepAlive)
+    {
+        if (smartKeepAlive)
+            return base.OnConnectionInitAsync(message);
+        else
+            return base.OnConnectionInitAsync(message, smartKeepAlive);
+    }
+
+    /// <inheritdoc/>
+    protected override Task OnKeepAliveLoopAsync(TimeSpan keepAliveTimeout, KeepAliveMode keepAliveMode)
+    {
+        if (keepAliveMode == KeepAliveMode.TimeoutWithPayload)
+        {
+            if (keepAliveTimeout <= TimeSpan.Zero)
+                return Task.CompletedTask;
+            return SecureKeepAliveLoopAsync(keepAliveTimeout, keepAliveTimeout);
+        }
+        return base.OnKeepAliveLoopAsync(keepAliveTimeout, keepAliveMode);
+
+        // pingInterval is the time since the last pong was received before sending a new ping
+        // pongInterval is the time to wait for a pong after a ping was sent before forcibly closing the connection
+        async Task SecureKeepAliveLoopAsync(TimeSpan pingInterval, TimeSpan pongInterval)
+        {
+            lock (_lastPingLock)
+                _lastPongReceivedUtc = DateTime.UtcNow;
+            while (!CancellationToken.IsCancellationRequested)
+            {
+                // Wait for the next ping interval
+                TimeSpan interval;
+                var now = DateTime.UtcNow;
+                DateTime lastPongReceivedUtc;
+                lock (_lastPingLock)
+                {
+                    lastPongReceivedUtc = _lastPongReceivedUtc;
+                }
+                var nextPing = _lastPongReceivedUtc.Add(pingInterval);
+                interval = nextPing.Subtract(now);
+                if (interval > TimeSpan.Zero) // could easily be zero or less, if pongInterval is equal or greater than pingInterval
+                    await Task.Delay(interval, CancellationToken);
+
+                // Send a new ping message
+                await OnSendKeepAliveAsync();
+
+                // Wait for the pong response
+                await Task.Delay(pongInterval, CancellationToken);
+                bool abort;
+                lock (_lastPingLock)
+                {
+                    abort = _lastPongReceivedUtc == lastPongReceivedUtc;
+                }
+                if (abort)
+                {
+                    // Forcibly close the connection if the client has not responded to the keep-alive message.
+                    // Do not send a close message to the client or wait for a response.
+                    Connection.HttpContext.Abort();
+                    return;
+                }
+            }
+        }
+    }
+
     /// <summary>
     /// Pong is a required response to a ping, and also a unidirectional keep-alive packet,
     /// whereas ping is a bidirectional keep-alive packet.
@@ -129,11 +201,46 @@ protected virtual Task OnPingAsync(OperationMessage message)
     /// Executes when a pong message is received.
     /// </summary>
     protected virtual Task OnPongAsync(OperationMessage message)
-        => Task.CompletedTask;
+    {
+        if (_options.KeepAliveMode == KeepAliveMode.TimeoutWithPayload)
+        {
+            try
+            {
+                var pingId = _serializer.ReadNode<PingPayload>(message.Payload)?.id;
+                lock (_lastPingLock)
+                {
+                    if (_lastPingId == pingId)
+                        _lastPongReceivedUtc = DateTime.UtcNow;
+                }
+            }
+            catch { } // ignore deserialization errors in case the pong message does not match the expected format
+        }
+        return Task.CompletedTask;
+    }
 
     /// <inheritdoc/>
     protected override Task OnSendKeepAliveAsync()
-        => Connection.SendMessageAsync(_pongMessage);
+    {
+        if (_options.KeepAliveMode == KeepAliveMode.TimeoutWithPayload)
+        {
+            var lastPingId = Guid.NewGuid().ToString("N");
+            lock (_lastPingLock)
+            {
+                _lastPingId = lastPingId;
+            }
+            return Connection.SendMessageAsync(
+                new()
+                {
+                    Type = MessageType.Ping,
+                    Payload = new PingPayload { id = lastPingId }
+                }
+            );
+        }
+        else
+        {
+            return Connection.SendMessageAsync(_pongMessage);
+        }
+    }
 
     private static readonly OperationMessage _connectionAckMessage = new() { Type = MessageType.ConnectionAck };
     /// <inheritdoc/>

src/Transports.AspNetCore/WebSockets/KeepAliveMode.cs

@@ -0,0 +1,36 @@
+namespace GraphQL.Server.Transports.AspNetCore.WebSockets;
+
+/// <summary>
+/// Specifies the mode of keep-alive behavior.
+/// </summary>
+public enum KeepAliveMode
+{
+    /// <summary>
+    /// Same as <see cref="Timeout"/>: Sends a unidirectional keep-alive message when no message has been received within the specified timeout period.
+    /// </summary>
+    Default = 0,
+
+    /// <summary>
+    /// Sends a unidirectional keep-alive message when no message has been received within the specified timeout period.
+    /// </summary>
+    Timeout = 1,
+
+    /// <summary>
+    /// Sends a unidirectional keep-alive message at a fixed interval, regardless of message activity.
+    /// </summary>
+    Interval = 2,
+
+    /// <summary>
+    /// Sends a Ping message with a payload after the specified timeout from the last received Pong,
+    /// and waits for a corresponding Pong response. Requires that the client reflects the payload
+    /// in the response. Forcibly disconnects the client if the client does not respond with a Pong
+    /// message within the specified timeout. This means that a dead connection will be closed after
+    /// a maximum of double the <see cref="GraphQLWebSocketOptions.KeepAliveTimeout"/> period.
+    /// </summary>
+    /// <remarks>
+    /// This mode is particularly useful when backpressure causes subscription messages to be delayed
+    /// due to a slow or unresponsive client connection. The server can detect that the client is not
+    /// processing messages in a timely manner and disconnect the client to free up resources.
+    /// </remarks>
+    TimeoutWithPayload = 3,
+}

src/Transports.AspNetCore/WebSockets/SubscriptionsTransportWs/SubscriptionServer.cs

@@ -85,7 +85,9 @@ public override async Task OnMessageReceivedAsync(OperationMessage message)
             }
             else
             {
+#pragma warning disable CS0618 // Type or member is obsolete
                 await OnConnectionInitAsync(message, false);
+#pragma warning restore CS0618 // Type or member is obsolete
             }
             return;
         }
@@ -108,6 +110,26 @@ public override async Task OnMessageReceivedAsync(OperationMessage message)
         }
     }
 
+    /// <inheritdoc/>
+    [Obsolete($"Please use the {nameof(OnConnectionInitAsync)} and {nameof(OnKeepAliveLoopAsync)} methods instead. This method will be removed in a future version of this library.")]
+    protected override Task OnConnectionInitAsync(OperationMessage message, bool smartKeepAlive)
+    {
+        if (!smartKeepAlive)
+            return base.OnConnectionInitAsync(message);
+        else
+            return base.OnConnectionInitAsync(message, smartKeepAlive);
+    }
+
+    /// <inheritdoc/>
+    /// <remarks>
+    /// This implementation overrides <see cref="GraphQLWebSocketOptions.KeepAliveMode"/> to <see cref="KeepAliveMode.Interval"/>
+    /// as this protocol does not support the other modes. Override this method to support your own implementation.
+    /// </remarks>
+    protected override Task OnKeepAliveLoopAsync(TimeSpan keepAliveTimeout, KeepAliveMode keepAliveMode)
+        => base.OnKeepAliveLoopAsync(
+            keepAliveTimeout,
+            KeepAliveMode.Interval);
+
     private static readonly OperationMessage _keepAliveMessage = new() { Type = MessageType.GQL_CONNECTION_KEEP_ALIVE };
     /// <inheritdoc/>
     protected override Task OnSendKeepAliveAsync()