Add "allowReconnect" to SignalR CloseMessages (#14908)

src/Components/Server/src/BlazorPack/BlazorPackHubProtocol.cs

@@ -78,7 +78,7 @@ namespace Microsoft.AspNetCore.Components.Server.BlazorPack
                     message = PingMessage.Instance;
                     return true;
                 case HubProtocolConstants.CloseMessageType:
-                    message = CreateCloseMessage(ref reader);
+                    message = CreateCloseMessage(ref reader, itemCount);
                     return true;
                 default:
                     // Future protocol changes can add message types, old clients can ignore them
@@ -196,10 +196,23 @@ namespace Microsoft.AspNetCore.Components.Server.BlazorPack
             return ApplyHeaders(headers, new CancelInvocationMessage(invocationId));
         }
 
-        private static CloseMessage CreateCloseMessage(ref MessagePackReader reader)
+        private static CloseMessage CreateCloseMessage(ref MessagePackReader reader, int itemCount)
         {
             var error = ReadString(ref reader, "error");
-            return new CloseMessage(error);
+            var allowReconnect = false;
+
+            if (itemCount > 2)
+            {
+                allowReconnect = ReadBoolean(ref reader, "allowReconnect");
+            }
+
+            // An empty string is still an error
+            if (error == null && !allowReconnect)
+            {
+                return CloseMessage.Empty;
+            }
+
+            return new CloseMessage(error, allowReconnect);
         }
 
         private static Dictionary<string, string> ReadHeaders(ref MessagePackReader reader)
@@ -515,7 +528,7 @@ namespace Microsoft.AspNetCore.Components.Server.BlazorPack
 
         private void WriteCloseMessage(CloseMessage message, ref MessagePackWriter writer)
         {
-            writer.WriteArrayHeader(2);
+            writer.WriteArrayHeader(3);
             writer.Write(HubProtocolConstants.CloseMessageType);
             if (string.IsNullOrEmpty(message.Error))
             {
@@ -525,6 +538,8 @@ namespace Microsoft.AspNetCore.Components.Server.BlazorPack
             {
                 writer.Write(message.Error);
             }
+
+            writer.Write(message.AllowReconnect);
         }
 
         private void WritePingMessage(PingMessage _, ref MessagePackWriter writer)
@@ -559,6 +574,17 @@ namespace Microsoft.AspNetCore.Components.Server.BlazorPack
             return destination;
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static bool ReadBoolean(ref MessagePackReader reader, string field)
+        {
+            if (reader.End || reader.NextMessagePackType != MessagePackType.Boolean)
+            {
+                ThrowInvalidDataException(field, "Boolean");
+            }
+
+            return reader.ReadBoolean();
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static int ReadInt32(ref MessagePackReader reader, string field)
         {

src/SignalR/clients/csharp/Client.Core/src/HubConnection.cs

@@ -878,7 +878,7 @@ namespace Microsoft.AspNetCore.SignalR.Client
             }
         }
 
-        private async Task<(bool close, Exception exception)> ProcessMessagesAsync(HubMessage message, ConnectionState connectionState, ChannelWriter<InvocationMessage> invocationMessageWriter)
+        private async Task<CloseMessage> ProcessMessagesAsync(HubMessage message, ConnectionState connectionState, ChannelWriter<InvocationMessage> invocationMessageWriter)
         {
             Log.ResettingKeepAliveTimer(_logger);
             connectionState.ResetTimeout();
@@ -911,7 +911,7 @@ namespace Microsoft.AspNetCore.SignalR.Client
                     if (!connectionState.TryGetInvocation(streamItem.InvocationId, out irq))
                     {
                         Log.DroppedStreamMessage(_logger, streamItem.InvocationId);
-                        return (close: false, exception: null);
+                        break;
                     }
                     await DispatchInvocationStreamItemAsync(streamItem, irq);
                     break;
@@ -919,13 +919,12 @@ namespace Microsoft.AspNetCore.SignalR.Client
                     if (string.IsNullOrEmpty(close.Error))
                     {
                         Log.ReceivedClose(_logger);
-                        return (close: true, exception: null);
                     }
                     else
                     {
                         Log.ReceivedCloseWithError(_logger, close.Error);
-                        return (close: true, exception: new HubException($"The server closed the connection with the following error: {close.Error}"));
                     }
+                    return close;
                 case PingMessage _:
                     Log.ReceivedPing(_logger);
                     // timeout is reset above, on receiving any message
@@ -934,7 +933,7 @@ namespace Microsoft.AspNetCore.SignalR.Client
                     throw new InvalidOperationException($"Unexpected message type: {message.GetType().FullName}");
             }
 
-            return (close: false, exception: null);
+            return null;
         }
 
         private async Task DispatchInvocationAsync(InvocationMessage invocation)
@@ -1150,25 +1149,33 @@ namespace Microsoft.AspNetCore.SignalR.Client
                         {
                             Log.ProcessingMessage(_logger, buffer.Length);
 
-                            var close = false;
+                            CloseMessage closeMessage = null;
 
                             while (_protocol.TryParseMessage(ref buffer, connectionState, out var message))
                             {
-                                Exception exception;
-
                                 // We have data, process it
-                                (close, exception) = await ProcessMessagesAsync(message, connectionState, invocationMessageChannel.Writer);
+                                closeMessage = await ProcessMessagesAsync(message, connectionState, invocationMessageChannel.Writer);
-                                if (close)
+
+                                if (closeMessage != null)
                                 {
                                     // Closing because we got a close frame, possibly with an error in it.
-                                    connectionState.CloseException = exception;
+                                    if (closeMessage.Error != null)
-                                    connectionState.Stopping = true;
+                                    {
+                                        connectionState.CloseException = new HubException($"The server closed the connection with the following error: {closeMessage.Error}");
+                                    }
+
+                                    // Stopping being true indicates the client shouldn't try to reconnect even if automatic reconnects are enabled.
+                                    if (!closeMessage.AllowReconnect)
+                                    {
+                                        connectionState.Stopping = true;
+                                    }
+
                                     break;
                                 }
                             }
 
                             // If we're closing stop everything
-                            if (close)
+                            if (closeMessage != null)
                             {
                                 break;
                             }
@@ -1637,6 +1644,8 @@ namespace Microsoft.AspNetCore.SignalR.Client
             public Exception CloseException { get; set; }
             public CancellationToken UploadStreamToken { get; set; }
 
+            // Indicates the connection is stopping AND the client should NOT attempt to reconnect even if automatic reconnects are enabled.
+            // This means either HubConnection.DisposeAsync/StopAsync was called OR a CloseMessage with AllowReconnects set to false was received.
             public bool Stopping
             {
                 get => _stopping;

src/SignalR/clients/csharp/Client/test/UnitTests/HubConnectionTests.Reconnect.cs

@@ -368,6 +368,156 @@ namespace Microsoft.AspNetCore.SignalR.Client.Tests
                 }
             }
 
+            [Fact]
+            public async Task CanBeInducedByCloseMessageWithAllowReconnectSet()
+            {
+                bool ExpectedErrors(WriteContext writeContext)
+                {
+                    return writeContext.LoggerName == typeof(HubConnection).FullName &&
+                           (writeContext.EventId.Name == "ReceivedCloseWithError" ||
+                            writeContext.EventId.Name == "ReconnectingWithError");
+                }
+
+                var failReconnectTcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+                using (StartVerifiableLog(ExpectedErrors))
+                {
+                    var builder = new HubConnectionBuilder().WithLoggerFactory(LoggerFactory).WithUrl("http://example.com");
+                    var testConnectionFactory = default(ReconnectingConnectionFactory);
+       
+                    testConnectionFactory = new ReconnectingConnectionFactory(() => new TestConnection());
+                    builder.Services.AddSingleton<IConnectionFactory>(testConnectionFactory);
+
+                    var retryContexts = new List<RetryContext>();
+                    var mockReconnectPolicy = new Mock<IRetryPolicy>();
+                    mockReconnectPolicy.Setup(p => p.NextRetryDelay(It.IsAny<RetryContext>())).Returns<RetryContext>(context =>
+                    {
+                        retryContexts.Add(context);
+                        return TimeSpan.Zero;
+                    });
+                    builder.WithAutomaticReconnect(mockReconnectPolicy.Object);
+
+                    await using var hubConnection = builder.Build();
+                    var reconnectingCount = 0;
+                    var reconnectedCount = 0;
+                    var reconnectingErrorTcs = new TaskCompletionSource<Exception>(TaskCreationOptions.RunContinuationsAsynchronously);
+                    var reconnectedConnectionIdTcs = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
+                    var closedErrorTcs = new TaskCompletionSource<Exception>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+                    hubConnection.Reconnecting += error =>
+                    {
+                        reconnectingCount++;
+                        reconnectingErrorTcs.SetResult(error);
+                        return Task.CompletedTask;
+                    };
+
+                    hubConnection.Reconnected += connectionId =>
+                    {
+                        reconnectedCount++;
+                        reconnectedConnectionIdTcs.SetResult(connectionId);
+                        return Task.CompletedTask;
+                    };
+
+                    hubConnection.Closed += error =>
+                    {
+                        closedErrorTcs.SetResult(error);
+                        return Task.CompletedTask;
+                    };
+
+                    await hubConnection.StartAsync().OrTimeout();
+
+                    var currentConnection = await testConnectionFactory.GetNextOrCurrentTestConnection();
+                    await currentConnection.ReceiveJsonMessage(new
+                    {
+                        type = HubProtocolConstants.CloseMessageType,
+                        error = "Error!",
+                        allowReconnect = true,
+                    });
+
+                    var reconnectingException = await reconnectingErrorTcs.Task.OrTimeout();
+                    var expectedMessage = "The server closed the connection with the following error: Error!";
+
+                    Assert.Equal(expectedMessage, reconnectingException.Message);
+                    Assert.Single(retryContexts);
+                    Assert.Equal(expectedMessage, retryContexts[0].RetryReason.Message);
+                    Assert.Equal(0, retryContexts[0].PreviousRetryCount);
+                    Assert.Equal(TimeSpan.Zero, retryContexts[0].ElapsedTime);
+
+                    await reconnectedConnectionIdTcs.Task.OrTimeout();
+
+                    await hubConnection.StopAsync().OrTimeout();
+
+                    var closeError = await closedErrorTcs.Task.OrTimeout();
+                    Assert.Null(closeError);
+                    Assert.Equal(1, reconnectingCount);
+                    Assert.Equal(1, reconnectedCount);
+                }
+            }
+
+            [Fact]
+            public async Task CannotBeInducedByCloseMessageWithAllowReconnectOmitted()
+            {
+                bool ExpectedErrors(WriteContext writeContext)
+                {
+                    return writeContext.LoggerName == typeof(HubConnection).FullName &&
+                           (writeContext.EventId.Name == "ReceivedCloseWithError" ||
+                            writeContext.EventId.Name == "ShutdownWithError");
+                }
+
+                var failReconnectTcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+                using (StartVerifiableLog(ExpectedErrors))
+                {
+                    var builder = new HubConnectionBuilder().WithLoggerFactory(LoggerFactory).WithUrl("http://example.com");
+                    var testConnectionFactory = default(ReconnectingConnectionFactory);
+       
+                    testConnectionFactory = new ReconnectingConnectionFactory(() => new TestConnection());
+                    builder.Services.AddSingleton<IConnectionFactory>(testConnectionFactory);
+
+                    var reconnectingCount = 0;
+                    var nextRetryDelayCallCount = 0;
+                    var closedErrorTcs = new TaskCompletionSource<Exception>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+                    var mockReconnectPolicy = new Mock<IRetryPolicy>();
+                    mockReconnectPolicy.Setup(p => p.NextRetryDelay(It.IsAny<RetryContext>())).Returns<RetryContext>(context =>
+                    {
+                        nextRetryDelayCallCount++;
+                        return TimeSpan.Zero;
+                    });
+
+                    builder.WithAutomaticReconnect(mockReconnectPolicy.Object);
+
+                    await using var hubConnection = builder.Build();
+
+                    hubConnection.Reconnecting += error =>
+                    {
+                        reconnectingCount++;
+                        return Task.CompletedTask;
+                    };
+
+                    hubConnection.Closed += error =>
+                    {
+                        closedErrorTcs.SetResult(error);
+                        return Task.CompletedTask;
+                    };
+
+                    await hubConnection.StartAsync().OrTimeout();
+
+                    var currentConnection = await testConnectionFactory.GetNextOrCurrentTestConnection();
+                    await currentConnection.ReceiveJsonMessage(new
+                    {
+                        type = HubProtocolConstants.CloseMessageType,
+                        error = "Error!",
+                    });
+
+                    var closeError = await closedErrorTcs.Task.OrTimeout();
+
+                    Assert.Equal("The server closed the connection with the following error: Error!", closeError.Message);
+                    Assert.Equal(0, nextRetryDelayCallCount);
+                    Assert.Equal(0, reconnectingCount);
+                }
+            }
+
             [Fact]
             public async Task EventsNotFiredIfFirstRetryDelayIsNull()
             {

src/SignalR/clients/ts/signalr-protocol-msgpack/src/MessagePackHubProtocol.ts

@@ -124,6 +124,7 @@ export class MessagePackHubProtocol implements IHubProtocol {
 
         return {
             // Close messages have no headers.
+            allowReconnect: properties.length >= 3 ? properties[2] : undefined,
             error: properties[1],
             type: MessageType.Close,
         } as HubMessage;

src/SignalR/clients/ts/signalr/src/HubConnection.ts

@@ -545,8 +545,18 @@ export class HubConnection {
                     case MessageType.Close:
                         this.logger.log(LogLevel.Information, "Close message received from server.");
 
-                        // We don't want to wait on the stop itself.
+                        const error = message.error ? new Error("Server returned an error on close: " + message.error) : undefined;
-                        this.stopPromise = this.stopInternal(message.error ? new Error("Server returned an error on close: " + message.error) : undefined);
+
+                        if (message.allowReconnect === true) {
+                            // It feels wrong not to await connection.stop() here, but processIncomingData is called as part of an onreceive callback which is not async,
+                            // this is already the behavior for serverTimeout(), and HttpConnection.Stop() should catch and log all possible exceptions.
+
+                            // tslint:disable-next-line:no-floating-promises
+                            this.connection.stop(error);
+                        } else {
+                            // We cannot await stopInternal() here, but subsequent calls to stop() will await this if stopInternal() is still ongoing.
+                            this.stopPromise = this.stopInternal(error);
+                        }
 
                         break;
                     default:

src/SignalR/clients/ts/signalr/src/IHubProtocol.ts

@@ -131,6 +131,9 @@ export interface CloseMessage extends HubMessageBase {
      * If this property is undefined, the connection was closed normally and without error.
      */
     readonly error?: string;
+
+    /** If true, clients with automatic reconnects enabled should attempt to reconnect after receiving the CloseMessage. Otherwise, they should not. */
+    readonly allowReconnect?: boolean;
 }
 
 /** A hub message sent to request that a streaming invocation be canceled. */

src/SignalR/clients/ts/signalr/tests/HubConnection.Reconnect.test.ts

@@ -3,6 +3,7 @@
 
 import { DefaultReconnectPolicy } from "../src/DefaultReconnectPolicy";
 import { HubConnection, HubConnectionState } from "../src/HubConnection";
+import { MessageType } from "../src/IHubProtocol";
 import { RetryContext } from "../src/IRetryPolicy";
 import { JsonHubProtocol } from "../src/JsonHubProtocol";
 
@@ -728,4 +729,60 @@ describe("auto reconnect", () => {
             expect(closeCount).toBe(1);
         });
     });
+
+    it("reconnect on close message if allowReconnect is true and auto reconnect is enabled", async () => {
+        await VerifyLogger.run(async (logger) => {
+            const connection = new TestConnection();
+            const hubConnection = HubConnection.create(connection, logger, new JsonHubProtocol(), new DefaultReconnectPolicy());
+            try {
+                let isReconnecting = false;
+                let reconnectingError: Error | undefined;
+
+                hubConnection.onreconnecting((e) => {
+                    isReconnecting = true;
+                    reconnectingError = e;
+                });
+
+                await hubConnection.start();
+
+                connection.receive({
+                    allowReconnect: true,
+                    error: "Error!",
+                    type: MessageType.Close,
+                });
+
+                expect(isReconnecting).toEqual(true);
+                expect(reconnectingError!.message).toEqual("Server returned an error on close: Error!");
+            } finally {
+                await hubConnection.stop();
+            }
+        });
+    });
+
+    it("stop on close message if allowReconnect is missing and auto reconnect is enabled", async () => {
+        await VerifyLogger.run(async (logger) => {
+            const connection = new TestConnection();
+            const hubConnection = HubConnection.create(connection, logger, new JsonHubProtocol(), new DefaultReconnectPolicy());
+            try {
+                let isClosed = false;
+                let closeError: Error | undefined;
+                hubConnection.onclose((e) => {
+                    isClosed = true;
+                    closeError = e;
+                });
+
+                await hubConnection.start();
+
+                connection.receive({
+                    error: "Error!",
+                    type: MessageType.Close,
+                });
+
+                expect(isClosed).toEqual(true);
+                expect(closeError!.message).toEqual("Server returned an error on close: Error!");
+            } finally {
+                await hubConnection.stop();
+            }
+        });
+    });
 });

src/SignalR/clients/ts/signalr/tests/HubConnection.test.ts

@@ -822,7 +822,9 @@ describe("HubConnection", () => {
 
                     await hubConnection.start();
 
+                    // allowReconnect Should have no effect since auto reconnect is disabled by default.
                     connection.receive({
+                        allowReconnect: true,
                         error: "Error!",
                         type: MessageType.Close,
                     });

src/SignalR/common/Protocols.Json/src/Protocol/JsonHubProtocol.cs

@@ -31,6 +31,8 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
         private static JsonEncodedText TypePropertyNameBytes = JsonEncodedText.Encode(TypePropertyName);
         private const string ErrorPropertyName = "error";
         private static JsonEncodedText ErrorPropertyNameBytes = JsonEncodedText.Encode(ErrorPropertyName);
+        private const string AllowReconnectPropertyName = "allowReconnect";
+        private static JsonEncodedText AllowReconnectPropertyNameBytes = JsonEncodedText.Encode(AllowReconnectPropertyName);
         private const string TargetPropertyName = "target";
         private static JsonEncodedText TargetPropertyNameBytes = JsonEncodedText.Encode(TargetPropertyName);
         private const string ArgumentsPropertyName = "arguments";
@@ -132,6 +134,7 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                 ExceptionDispatchInfo argumentBindingException = null;
                 Dictionary<string, string> headers = null;
                 var completed = false;
+                var allowReconnect = false;
 
                 var reader = new Utf8JsonReader(input, isFinalBlock: true, state: default);
 
@@ -186,6 +189,10 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                             {
                                 error = reader.ReadAsString(ErrorPropertyName);
                             }
+                            else if (reader.ValueTextEquals(AllowReconnectPropertyNameBytes.EncodedUtf8Bytes))
+                            {
+                                allowReconnect = reader.ReadAsBoolean(AllowReconnectPropertyName);
+                            }
                             else if (reader.ValueTextEquals(ResultPropertyNameBytes.EncodedUtf8Bytes))
                             {
                                 hasResult = true;
@@ -372,7 +379,7 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                     case HubProtocolConstants.PingMessageType:
                         return PingMessage.Instance;
                     case HubProtocolConstants.CloseMessageType:
-                        return BindCloseMessage(error);
+                        return BindCloseMessage(error, allowReconnect);
                     case null:
                         throw new InvalidDataException($"Missing required property '{TypePropertyName}'.");
                     default:
@@ -544,6 +551,11 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
             {
                 writer.WriteString(ErrorPropertyNameBytes, message.Error);
             }
+
+            if (message.AllowReconnect)
+            {
+                writer.WriteBoolean(AllowReconnectPropertyNameBytes, true);
+            }
         }
 
         private void WriteArguments(object[] arguments, Utf8JsonWriter writer)
@@ -722,16 +734,15 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
             return arguments ?? Array.Empty<object>();
         }
 
-        private CloseMessage BindCloseMessage(string error)
+        private CloseMessage BindCloseMessage(string error, bool allowReconnect)
         {
             // An empty string is still an error
-            if (error == null)
+            if (error == null && !allowReconnect)
             {
                 return CloseMessage.Empty;
             }
 
-            var message = new CloseMessage(error);
+            return new CloseMessage(error, allowReconnect);
-            return message;
         }
 
         private HubMessage ApplyHeaders(HubMessage message, Dictionary<string, string> headers)

src/SignalR/common/Protocols.MessagePack/src/Protocol/MessagePackHubProtocol.cs

@@ -137,7 +137,7 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                 case HubProtocolConstants.PingMessageType:
                     return PingMessage.Instance;
                 case HubProtocolConstants.CloseMessageType:
-                    return CreateCloseMessage(input, ref startOffset);
+                    return CreateCloseMessage(input, ref startOffset, itemCount);
                 default:
                     // Future protocol changes can add message types, old clients can ignore them
                     return null;
@@ -261,10 +261,23 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
             return ApplyHeaders(headers, new CancelInvocationMessage(invocationId));
         }
 
-        private static CloseMessage CreateCloseMessage(byte[] input, ref int offset)
+        private static CloseMessage CreateCloseMessage(byte[] input, ref int offset, int itemCount)
         {
             var error = ReadString(input, ref offset, "error");
-            return new CloseMessage(error);
+            var allowReconnect = false;
+
+            if (itemCount > 2)
+            {
+                allowReconnect = ReadBoolean(input, ref offset, "allowReconnect");
+            }
+
+            // An empty string is still an error
+            if (error == null && !allowReconnect)
+            {
+                return CloseMessage.Empty;
+            }
+
+            return new CloseMessage(error, allowReconnect);
         }
 
         private static Dictionary<string, string> ReadHeaders(byte[] input, ref int offset)
@@ -533,7 +546,7 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
 
         private void WriteCloseMessage(CloseMessage message, Stream packer)
         {
-            MessagePackBinary.WriteArrayHeader(packer, 2);
+            MessagePackBinary.WriteArrayHeader(packer, 3);
             MessagePackBinary.WriteInt16(packer, HubProtocolConstants.CloseMessageType);
             if (string.IsNullOrEmpty(message.Error))
             {
@@ -543,6 +556,8 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
             {
                 MessagePackBinary.WriteString(packer, message.Error);
             }
+
+            MessagePackBinary.WriteBoolean(packer, message.AllowReconnect);
         }
 
         private void WritePingMessage(PingMessage pingMessage, Stream packer)
@@ -576,6 +591,23 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
             return ReadString(input, ref offset, "invocationId");
         }
 
+        private static bool ReadBoolean(byte[] input, ref int offset, string field)
+        {
+            Exception msgPackException = null;
+            try
+            {
+                var readBool = MessagePackBinary.ReadBoolean(input, offset, out var readSize);
+                offset += readSize;
+                return readBool;
+            }
+            catch (Exception e)
+            {
+                msgPackException = e;
+            }
+
+            throw new InvalidDataException($"Reading '{field}' as Boolean failed.", msgPackException);
+        }
+
         private static int ReadInt32(byte[] input, ref int offset, string field)
         {
             Exception msgPackException = null;

src/SignalR/common/Protocols.NewtonsoftJson/src/Protocol/NewtonsoftJsonHubProtocol.cs

@@ -30,6 +30,7 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
         private const string TargetPropertyName = "target";
         private const string ArgumentsPropertyName = "arguments";
         private const string HeadersPropertyName = "headers";
+        private const string AllowReconnectPropertyName = "allowReconnect";
 
         private static readonly string ProtocolName = "json";
         private static readonly int ProtocolVersion = 1;
@@ -131,6 +132,7 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                 ExceptionDispatchInfo argumentBindingException = null;
                 Dictionary<string, string> headers = null;
                 var completed = false;
+                var allowReconnect = false;
 
                 using (var reader = JsonUtils.CreateJsonTextReader(textReader))
                 {
@@ -187,6 +189,9 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                                     case ErrorPropertyName:
                                         error = JsonUtils.ReadAsString(reader, ErrorPropertyName);
                                         break;
+                                    case AllowReconnectPropertyName:
+                                        allowReconnect = JsonUtils.ReadAsBoolean(reader, AllowReconnectPropertyName);
+                                        break;
                                     case ResultPropertyName:
                                         hasResult = true;
 
@@ -373,7 +378,7 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                     case HubProtocolConstants.PingMessageType:
                         return PingMessage.Instance;
                     case HubProtocolConstants.CloseMessageType:
-                        return BindCloseMessage(error);
+                        return BindCloseMessage(error, allowReconnect);
                     case null:
                         throw new InvalidDataException($"Missing required property '{TypePropertyName}'.");
                     default:
@@ -550,6 +555,12 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
                 writer.WritePropertyName(ErrorPropertyName);
                 writer.WriteValue(message.Error);
             }
+
+            if (message.AllowReconnect)
+            {
+                writer.WritePropertyName(AllowReconnectPropertyName);
+                writer.WriteValue(true);
+            }
         }
 
         private void WriteArguments(object[] arguments, JsonTextWriter writer)
@@ -733,16 +744,15 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
             throw new JsonReaderException("Unexpected end when reading JSON");
         }
 
-        private CloseMessage BindCloseMessage(string error)
+        private CloseMessage BindCloseMessage(string error, bool allowReconnect)
         {
             // An empty string is still an error
-            if (error == null)
+            if (error == null && !allowReconnect)
             {
                 return CloseMessage.Empty;
             }
 
-            var message = new CloseMessage(error);
+            return new CloseMessage(error, allowReconnect);
-            return message;
         }
 
         private object[] BindArguments(JArray args, IReadOnlyList<Type> paramTypes)

src/SignalR/common/Shared/JsonUtils.cs

@@ -114,6 +114,18 @@ namespace Microsoft.AspNetCore.Internal
             }
         }
 
+        public static bool ReadAsBoolean(JsonTextReader reader, string propertyName)
+        {
+            reader.Read();
+
+            if (reader.TokenType != JsonToken.Boolean || reader.Value == null)
+            {
+                throw new InvalidDataException($"Expected '{propertyName}' to be of type {JTokenType.Boolean}.");
+            }
+
+            return Convert.ToBoolean(reader.Value, CultureInfo.InvariantCulture);
+        }
+
         public static int? ReadAsInt32(JsonTextReader reader, string propertyName)
         {
             reader.Read();

src/SignalR/common/Shared/SystemTextJsonExtensions.cs

@@ -57,6 +57,18 @@ namespace Microsoft.AspNetCore.Internal
             }
         }
 
+        public static bool ReadAsBoolean(this ref Utf8JsonReader reader, string propertyName)
+        {
+            reader.Read();
+
+            return reader.TokenType switch
+            {
+                JsonTokenType.False => false,
+                JsonTokenType.True => true,
+                _ => throw new InvalidDataException($"Expected '{propertyName}' to be true or false."),
+            };
+        }
+
         public static string ReadAsString(this ref Utf8JsonReader reader, string propertyName)
         {
             reader.Read();

src/SignalR/common/SignalR.Common/ref/Microsoft.AspNetCore.SignalR.Common.netcoreapp.cs

@@ -31,6 +31,8 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
     {
         public static readonly Microsoft.AspNetCore.SignalR.Protocol.CloseMessage Empty;
         public CloseMessage(string error) { }
+        public CloseMessage(string error, bool allowReconnect) { }
+        public bool AllowReconnect { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
         public string Error { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
     }
     public partial class CompletionMessage : Microsoft.AspNetCore.SignalR.Protocol.HubInvocationMessage

src/SignalR/common/SignalR.Common/ref/Microsoft.AspNetCore.SignalR.Common.netstandard2.0.cs

@@ -31,6 +31,8 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
     {
         public static readonly Microsoft.AspNetCore.SignalR.Protocol.CloseMessage Empty;
         public CloseMessage(string error) { }
+        public CloseMessage(string error, bool allowReconnect) { }
+        public bool AllowReconnect { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
         public string Error { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
     }
     public partial class CompletionMessage : Microsoft.AspNetCore.SignalR.Protocol.HubInvocationMessage

src/SignalR/common/SignalR.Common/src/Protocol/CloseMessage.cs

@@ -12,9 +12,9 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
     public class CloseMessage : HubMessage
     {
         /// <summary>
-        /// An empty close message with no error.
+        /// An empty close message with no error and <see cref="AllowReconnect"/> set to <see langword="false"/>.
         /// </summary>
-        public static readonly CloseMessage Empty = new CloseMessage(null);
+        public static readonly CloseMessage Empty = new CloseMessage(error: null, allowReconnect: false);
 
         /// <summary>
         /// Gets the optional error message.
@@ -22,12 +22,32 @@ namespace Microsoft.AspNetCore.SignalR.Protocol
         public string Error { get; }
 
         /// <summary>
-        /// Initializes a new instance of the <see cref="CloseMessage"/> class with an optional error message.
+        /// If <see langword="false"/>, clients with automatic reconnects enabled should not attempt to automatically reconnect after receiving the <see cref="CloseMessage"/>.
+        /// </summary>
+        public bool AllowReconnect { get; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CloseMessage"/> class with an optional error message and <see cref="AllowReconnect"/> set to <see langword="false"/>.
         /// </summary>
         /// <param name="error">An optional error message.</param>
         public CloseMessage(string error)
+            : this(error, allowReconnect: false)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CloseMessage"/> class with an optional error message and a <see cref="bool"/> indicating whether or not a client with
+        /// automatic reconnects enabled should attempt to reconnect upon receiving the message.
+        /// </summary>
+        /// <param name="error">An optional error message.</param>
+        /// <param name="allowReconnect">
+        /// <see langword="true"/>, if client with automatic reconnects enabled should attempt to reconnect after receiving the <see cref="CloseMessage"/>;
+        /// <see langword="false"/>, if the client should not try to reconnect whether or not automatic reconnects are enabled.
+        /// </param>
+        public CloseMessage(string error, bool allowReconnect)
         {
             Error = error;
+            AllowReconnect = allowReconnect;
         }
     }
 }

src/SignalR/common/SignalR.Common/test/Internal/Protocol/JsonHubProtocolTestsBase.cs

@@ -67,6 +67,8 @@ namespace Microsoft.AspNetCore.SignalR.Common.Tests.Internal.Protocol
             new JsonProtocolTestData("CloseMessage_HasError", new CloseMessage("Error!"), false, true, "{\"type\":7,\"error\":\"Error!\"}"),
             new JsonProtocolTestData("CloseMessage_HasErrorEmptyString", new CloseMessage(""), false, true, "{\"type\":7,\"error\":\"\"}"),
             new JsonProtocolTestData("CloseMessage_HasErrorWithCamelCase", new CloseMessage("Error!"), true, true, "{\"type\":7,\"error\":\"Error!\"}"),
+            new JsonProtocolTestData("CloseMessage_HasAllowReconnect", new CloseMessage(error: null, allowReconnect: true), true, true, "{\"type\":7,\"allowReconnect\":true}"),
+            new JsonProtocolTestData("CloseMessage_HasErrorAndAllowReconnect", new CloseMessage("Error!", allowReconnect: true), true, true, "{\"type\":7,\"error\":\"Error!\",\"allowReconnect\":true}"),
 
         }.ToDictionary(t => t.Name);
 

src/SignalR/common/SignalR.Common/test/Internal/Protocol/MessagePackHubProtocolTestBase.cs

@@ -178,6 +178,24 @@ namespace Microsoft.AspNetCore.SignalR.Common.Tests.Internal.Protocol
                 name: "Ping",
                 message: PingMessage.Instance,
                 binary: "kQY="),
+
+            // Close Messages
+            new ProtocolTestData(
+                name: "CloseMessage",
+                message: CloseMessage.Empty,
+                binary: "kwfAwg=="),
+            new ProtocolTestData(
+                name: "CloseMessage_HasError",
+                message: new CloseMessage("Error!"),
+                binary: "kwemRXJyb3Ihwg=="),
+            new ProtocolTestData(
+                name: "CloseMessage_HasAllowReconnect",
+                message: new CloseMessage(error: null, allowReconnect: true),
+                binary: "kwfAww=="),
+            new ProtocolTestData(
+                name: "CloseMessage_HasErrorAndAllowReconnect",
+                message: new CloseMessage("Error!", allowReconnect: true),
+                binary: "kwemRXJyb3Ihww=="),
         }.ToDictionary(t => t.Name);
 
         [Theory]

src/SignalR/docs/specs/HubProtocol.md

@@ -482,6 +482,7 @@ A `Close` message is a JSON object with the following properties
 
 * `type` - A `Number` with the literal value `7`, indicating that this message is a `Close`.
 * `error` - An optional `String` encoding the error message.
+* `allowReconnect` - An optional `Boolean` indicating to clients with automatic reconnects enabled that they should attempt to reconnect after receiving the message.
 
 Example - A `Close` message without an error
 ```json
@@ -498,6 +499,15 @@ Example - A `Close` message with an error
 }
 ```
 
+Example - A `Close` message with an error that allows automatic client reconnects.
+```json
+{
+    "type": 7,
+    "error": "Connection closed because of an error!",
+    "allowReconnect": true
+}
+```
+
 ### JSON Header Encoding
 
 Message headers are encoded into a JSON object, with string values, that are stored in the `headers` property. For example:
@@ -809,11 +819,12 @@ is decoded as follows:
 `Close` messages have the following structure
 
 ```
-[7, Error]
+[7, Error, AllowReconnect?]
 ```
 
 * `7` - Message Type - `7` indicates this is a `Close` message.
 * `Error` - Error - A `String` encoding the error for the message.
+* `AllowReconnect` - An optional `Boolean` indicating to clients with automatic reconnects enabled that they should attempt to reconnect after receiving the message.
 
 Examples:
 
@@ -833,6 +844,23 @@ is decoded as follows:
 * `0x79` - `y`
 * `0x7a` - `z`
 
+#### Close message that allows automatic client reconnects
+
+The following payload:
+```
+0x93 0x07 0xa3 0x78 0x79 0x7a 0xc3
+```
+
+is decoded as follows:
+
+* `0x93` - 3-element array
+* `0x07` - `7` (Message Type - `Close` message)
+* `0xa3` - string of length 3 (Error)
+* `0x78` - `x`
+* `0x79` - `y`
+* `0x7a` - `z`
+* `0xc3` - `True` (AllowReconnect)
+
 ### MessagePack Headers Encoding
 
 Headers are encoded in MessagePack messages as a Map that immediately follows the type value. The Map can be empty, in which case it is represented by the byte `0x80`. If there are items in the map,

src/SignalR/server/Core/src/HubConnectionContext.cs

@@ -42,6 +42,7 @@ namespace Microsoft.AspNetCore.SignalR
         private ReadOnlyMemory<byte> _cachedPingMessage;
         private bool _clientTimeoutActive;
         private bool _connectionAborted;
+        private volatile bool _allowReconnect = true;
         private int _streamBufferCapacity;
         private long? _maxMessageSize;
 
@@ -106,6 +107,9 @@ namespace Microsoft.AspNetCore.SignalR
         /// </summary>
         public virtual IDictionary<object, object> Items => _connectionContext.Items;
 
+        // Used by HubConnectionHandler to determine whether to set CloseMessage.AllowReconnect.
+        internal bool AllowReconnect => _allowReconnect;
+
         // Used by HubConnectionHandler
         internal PipeReader Input => _connectionContext.Transport.Input;
 
@@ -201,7 +205,7 @@ namespace Microsoft.AspNetCore.SignalR
             {
                 Log.FailedWritingMessage(_logger, ex);
 
-                Abort();
+                AbortAllowReconnect();
 
                 return new ValueTask<FlushResult>(new FlushResult(isCanceled: false, isCompleted: true));
             }
@@ -220,7 +224,7 @@ namespace Microsoft.AspNetCore.SignalR
             {
                 Log.FailedWritingMessage(_logger, ex);
 
-                Abort();
+                AbortAllowReconnect();
 
                 return new ValueTask<FlushResult>(new FlushResult(isCanceled: false, isCompleted: true));
             }
@@ -236,7 +240,7 @@ namespace Microsoft.AspNetCore.SignalR
             {
                 Log.FailedWritingMessage(_logger, ex);
 
-                Abort();
+                AbortAllowReconnect();
             }
             finally
             {
@@ -262,7 +266,7 @@ namespace Microsoft.AspNetCore.SignalR
             catch (Exception ex)
             {
                 Log.FailedWritingMessage(_logger, ex);
-                Abort();
+                AbortAllowReconnect();
             }
             finally
             {
@@ -287,7 +291,7 @@ namespace Microsoft.AspNetCore.SignalR
             catch (Exception ex)
             {
                 Log.FailedWritingMessage(_logger, ex);
-                Abort();
+                AbortAllowReconnect();
             }
             finally
             {
@@ -323,7 +327,7 @@ namespace Microsoft.AspNetCore.SignalR
             catch (Exception ex)
             {
                 Log.FailedWritingMessage(_logger, ex);
-                Abort();
+                AbortAllowReconnect();
             }
             finally
             {
@@ -358,6 +362,12 @@ namespace Microsoft.AspNetCore.SignalR
         /// Aborts the connection.
         /// </summary>
         public virtual void Abort()
+        {
+            _allowReconnect = false;
+            AbortAllowReconnect();
+        }
+
+        private void AbortAllowReconnect()
         {
             _connectionAborted = true;
 
@@ -514,7 +524,7 @@ namespace Microsoft.AspNetCore.SignalR
         // Used by the HubConnectionHandler only
         internal Task AbortAsync()
         {
-            Abort();
+            AbortAllowReconnect();
             return _abortCompletedTcs.Task;
         }
 
@@ -560,7 +570,7 @@ namespace Microsoft.AspNetCore.SignalR
                 if (!_receivedMessageThisInterval)
                 {
                     Log.ClientTimeout(_logger, TimeSpan.FromTicks(_clientTimeoutInterval));
-                    Abort();
+                    AbortAllowReconnect();
                 }
 
                 _receivedMessageThisInterval = false;

src/SignalR/server/Core/src/HubConnectionHandler.cs

@@ -126,7 +126,8 @@ namespace Microsoft.AspNetCore.SignalR
             {
                 Log.ErrorDispatchingHubEvent(_logger, "OnConnectedAsync", ex);
 
-                await SendCloseAsync(connection, ex);
+                // The client shouldn't try to reconnect given an error in OnConnected.
+                await SendCloseAsync(connection, ex, allowReconnect: false);
 
                 // return instead of throw to let close message send successfully
                 return;
@@ -157,7 +158,7 @@ namespace Microsoft.AspNetCore.SignalR
         private async Task HubOnDisconnectedAsync(HubConnectionContext connection, Exception exception)
         {
             // send close message before aborting the connection
-            await SendCloseAsync(connection, exception);
+            await SendCloseAsync(connection, exception, connection.AllowReconnect);
 
             // We wait on abort to complete, this is so that we can guarantee that all callbacks have fired
             // before OnDisconnectedAsync
@@ -176,14 +177,18 @@ namespace Microsoft.AspNetCore.SignalR
             }
         }
 
-        private async Task SendCloseAsync(HubConnectionContext connection, Exception exception)
+        private async Task SendCloseAsync(HubConnectionContext connection, Exception exception, bool allowReconnect)
         {
             var closeMessage = CloseMessage.Empty;
 
             if (exception != null)
             {
                 var errorMessage = ErrorMessageHelper.BuildErrorMessage("Connection closed with an error.", exception, _enableDetailedErrors);
-                closeMessage = new CloseMessage(errorMessage);
+                closeMessage = new CloseMessage(errorMessage, allowReconnect);
+            }
+            else if (allowReconnect)
+            {
+                closeMessage = new CloseMessage(error: null, allowReconnect);
             }
 
             try