ASP.NET Core SignalR configuration

This article covers ASP.NET Core SignalR configuration.

For Blazor SignalR guidance, which adds to or supersedes the guidance in this article, see ASP.NET Core Blazor SignalR guidance.

JSON/MessagePack serialization options

ASP.NET Core SignalR supports two protocols for encoding messages: JSON and MessagePack. Each protocol has serialization configuration options.

JSON serialization can be configured on the server using the AddJsonProtocol extension method. AddJsonProtocol can be added after AddSignalR in Startup.ConfigureServices. The AddJsonProtocol method takes a delegate that receives an options object. The PayloadSerializerOptions property on that object is a System.Text.Json JsonSerializerOptions object that can be used to configure serialization of arguments and return values. For more information, see the System.Text.Json documentation.

For example, to configure the serializer to not change the casing of property names, rather than the default camel case names, use the following code in Program.cs:

builder.Services.AddSignalR()
    .AddJsonProtocol(options => {
        options.PayloadSerializerOptions.PropertyNamingPolicy = null;
    });

In the .NET client, the same AddJsonProtocol extension method exists on HubConnectionBuilder. The Microsoft.Extensions.DependencyInjection namespace must be imported to resolve the extension method:

// At the top of the file:
using Microsoft.Extensions.DependencyInjection;

// When constructing your connection:
var connection = new HubConnectionBuilder()
    .AddJsonProtocol(options => {
        options.PayloadSerializerOptions.PropertyNamingPolicy = null;
    })
    .Build();

Note

It's not possible to configure JSON serialization in the JavaScript client at this time.

Switch to Newtonsoft.Json

If you need features of Newtonsoft.Json that aren't supported in System.Text.Json, see Switch to Newtonsoft.Json.

MessagePack serialization options

MessagePack serialization can be configured by providing a delegate to the AddMessagePackProtocol call. See MessagePack in SignalR for more details.

Note

It's not possible to configure MessagePack serialization in the JavaScript client at this time.

Configure server options

The following table describes options for configuring SignalR hubs:

Option	Default Value	Description
ClientTimeoutInterval	30 seconds	The server considers the client disconnected if it hasn't received a message (including keep-alive) in this interval. It could take longer than this timeout interval for the client to be marked disconnected due to how this is implemented. The recommended value is double the KeepAliveInterval value.
HandshakeTimeout	15 seconds	If the client doesn't send an initial handshake message within this time interval, the connection is closed. This is an advanced setting that should only be modified if handshake timeout errors are occurring due to severe network latency. For more detail on the handshake process, see the SignalR Hub Protocol Specification.
KeepAliveInterval	15 seconds	If the server hasn't sent a message within this interval, a ping message is sent automatically to keep the connection open. When changing KeepAliveInterval, change the ServerTimeout or serverTimeoutInMilliseconds setting on the client. The recommended ServerTimeout or serverTimeoutInMilliseconds value is double the KeepAliveInterval value.
SupportedProtocols	All installed protocols	Protocols supported by this hub. By default, all protocols registered on the server are allowed. Protocols can be removed from this list to disable specific protocols for individual hubs.
EnableDetailedErrors	false	If true, detailed exception messages are returned to clients when an exception is thrown in a Hub method. The default is false because these exception messages can contain sensitive information.
StreamBufferCapacity	10	The maximum number of items that can be buffered for client upload streams. If this limit is reached, the processing of invocations is blocked until the server processes stream items.
MaximumReceiveMessageSize	32 KB	Maximum size of a single incoming hub message. Increasing the value might increase the risk of Denial of service (DoS) attacks.
MaximumParallelInvocationsPerClient	1	The maximum number of hub methods that each client can call in parallel before queueing.
DisableImplicitFromServicesParameters	false	Hub method arguments are resolved from DI if possible.

Options can be configured for all hubs by providing an options delegate to the AddSignalR call in Program.cs.

 builder.Services.AddSignalR(hubOptions =>
 {
     hubOptions.EnableDetailedErrors = true;
     hubOptions.KeepAliveInterval = TimeSpan.FromMinutes(1);
 });

Options for a single hub override the global options provided in AddSignalR and can be configured using AddHubOptions:

builder.Services.AddSignalR().AddHubOptions<ChatHub>(options =>
{
    options.EnableDetailedErrors = true;
});

Advanced HTTP configuration options

Use HttpConnectionDispatcherOptions to configure advanced settings related to transports and memory buffer management. These options are configured by passing a delegate to MapHub in Program.cs.

using Microsoft.AspNetCore.Http.Connections;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRazorPages();
builder.Services.AddSignalR();

var app = builder.Build();

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapRazorPages();
app.MapHub<ChatHub>("/chathub", options =>
{
    options.Transports =
        HttpTransportType.WebSockets |
        HttpTransportType.LongPolling;
}
);
app.Run();

The following table describes options for configuring ASP.NET Core SignalR's advanced HTTP options:

Option	Default Value	Description
ApplicationMaxBufferSize	64 KB	The maximum number of bytes received from the client that the server buffers before applying backpressure. Increasing this value allows the server to receive larger messages faster without applying backpressure, but can increase memory consumption.
TransportMaxBufferSize	64 KB	The maximum number of bytes sent by the app that the server buffers before observing backpressure. Increasing this value allows the server to buffer larger messages faster without awaiting backpressure, but can increase memory consumption.
AuthorizationData	Data automatically gathered from the Authorize attributes applied to the Hub class.	A list of IAuthorizeData objects used to determine if a client is authorized to connect to the hub.
Transports	All Transports are enabled.	A bit flags enum of HttpTransportType values that can restrict the transports a client can use to connect.
LongPolling	See below.	Additional options specific to the Long Polling transport.
WebSockets	See below.	Additional options specific to the WebSockets transport.
MinimumProtocolVersion	0	Specify the minimum version of the negotiate protocol. This is used to limit clients to newer versions.
CloseOnAuthenticationExpiration	false	Set this option to enable authentication expiration tracking, which will close connections when a token expires.

The Long Polling transport has additional options that can be configured using the LongPolling property:

Option	Default Value	Description
PollTimeout	90 seconds	The maximum amount of time the server waits for a message to send to the client before terminating a single poll request. Decreasing this value causes the client to issue new poll requests more frequently.

The WebSocket transport has additional options that can be configured using the WebSockets property:

Option	Default Value	Description
CloseTimeout	5 seconds	After the server closes, if the client fails to close within this time interval, the connection is terminated.
SubProtocolSelector	null	A delegate that can be used to set the Sec-WebSocket-Protocol header to a custom value. The delegate receives the values requested by the client as input and is expected to return the desired value.

Configure client options

Client options can be configured on the HubConnectionBuilder type (available in the .NET and JavaScript clients). It's also available in the Java client, but the HttpHubConnectionBuilder subclass is what contains the builder configuration options, as well as on the HubConnection itself.

Configure logging

Logging is configured in the .NET Client using the ConfigureLogging method. Logging providers and filters can be registered in the same way as they are on the server. See the Logging in ASP.NET Core documentation for more information.

Note

In order to register Logging providers, you must install the necessary packages. See the Built-in logging providers section of the docs for a full list.

For example, to enable Console logging, install the Microsoft.Extensions.Logging.Console NuGet package. Call the AddConsole extension method:

var connection = new HubConnectionBuilder()
    .WithUrl("https://example.com/chathub")
    .ConfigureLogging(logging => {
        logging.SetMinimumLevel(LogLevel.Information);
        logging.AddConsole();
    })
    .Build();

In the JavaScript client, a similar configureLogging method exists. Provide a LogLevel value indicating the minimum level of log messages to produce. Logs are written to the browser console window.

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub")
    .configureLogging(signalR.LogLevel.Information)
    .build();

Instead of a LogLevel value, you can also provide a string value representing a log level name. This is useful when configuring SignalR logging in environments where you don't have access to the LogLevel constants.

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub")
    .configureLogging("warn")
    .build();

The following table lists the available log levels. The value you provide to configureLogging sets the minimum log level that will be logged. Messages logged at this level, or the levels listed after it in the table, will be logged.

String	LogLevel
trace	LogLevel.Trace
debug	LogLevel.Debug
info or information	LogLevel.Information
warn or warning	LogLevel.Warning
error	LogLevel.Error
critical	LogLevel.Critical
none	LogLevel.None

Note

To disable logging entirely, specify signalR.LogLevel.None in the configureLogging method.

For more information on logging, see the SignalR Diagnostics documentation.

The SignalR Java client uses the SLF4J library for logging. It's a high-level logging API that allows users of the library to choose their own specific logging implementation by bringing in a specific logging dependency. The following code snippet shows how to use java.util.logging with the SignalR Java client.

implementation 'org.slf4j:slf4j-jdk14:1.7.25'

If you don't configure logging in your dependencies, SLF4J loads a default no-operation logger with the following warning message:

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

This can safely be ignored.

Configure allowed transports

The transports used by SignalR can be configured in the WithUrl call (withUrl in JavaScript). A bitwise-OR of the values of HttpTransportType can be used to restrict the client to only use the specified transports. All transports are enabled by default.

For example, to disable the Server-Sent Events transport, but allow WebSockets and Long Polling connections:

var connection = new HubConnectionBuilder()
    .WithUrl("https://example.com/chathub", HttpTransportType.WebSockets | HttpTransportType.LongPolling)
    .Build();

In the JavaScript client, transports are configured by setting the transport field on the options object provided to withUrl:

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub", { transport: signalR.HttpTransportType.WebSockets | signalR.HttpTransportType.LongPolling })
    .build();

In this version of the Java client WebSockets is the only available transport.

In the Java client, the transport is selected with the withTransport method on the HttpHubConnectionBuilder. The Java client defaults to using the WebSockets transport.

HubConnection hubConnection = HubConnectionBuilder.create("https://example.com/chathub")
    .withTransport(TransportEnum.WEBSOCKETS)
    .build();

Note

The SignalR Java client doesn't support transport fallback yet.

Configure bearer authentication

To provide authentication data along with SignalR requests, use the AccessTokenProvider option (accessTokenFactory in JavaScript) to specify a function that returns the desired access token. In the .NET Client, this access token is passed in as an HTTP "Bearer Authentication" token (Using the Authorization header with a type of Bearer). In the JavaScript client, the access token is used as a Bearer token, except in a few cases where browser APIs restrict the ability to apply headers (specifically, in Server-Sent Events and WebSockets requests). In these cases, the access token is provided as a query string value access_token.

In the .NET client, the AccessTokenProvider option can be specified using the options delegate in WithUrl:

var connection = new HubConnectionBuilder()
    .WithUrl("https://example.com/chathub", options => {
        options.AccessTokenProvider = async () => {
            // Get and return the access token.
        };
    })
    .Build();

In the JavaScript client, the access token is configured by setting the accessTokenFactory field on the options object in withUrl:

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub", {
        accessTokenFactory: () => {
            // Get and return the access token.
            // This function can return a JavaScript Promise if asynchronous
            // logic is required to retrieve the access token.
        }
    })
    .build();

In the SignalR Java client, you can configure a bearer token to use for authentication by providing an access token factory to the HttpHubConnectionBuilder. Use withAccessTokenFactory to provide an RxJava Single<String>. With a call to Single.defer, you can write logic to produce access tokens for your client.

HubConnection hubConnection = HubConnectionBuilder.create("https://example.com/chathub")
    .withAccessTokenProvider(Single.defer(() -> {
        // Your logic here.
        return Single.just("An Access Token");
    })).build();

Configure timeout and keep-alive options

Additional options for configuring timeout and keep-alive behavior:

.NET

Option	Default value	Description
WithServerTimeout	30 seconds (30,000 milliseconds)	Timeout for server activity and is set directly on HubConnectionBuilder. If the server hasn't sent a message in this interval, the client considers the server disconnected and triggers the Closed event (onclose in JavaScript). This value must be large enough for a ping message to be sent from the server and received by the client within the timeout interval. The recommended value is a number at least double the server's keep-alive interval (WithKeepAliveInterval) value to allow time for pings to arrive.
HandshakeTimeout	15 seconds	Timeout for initial server handshake and is available on the HubConnection object itself. If the server doesn't send a handshake response in this interval, the client cancels the handshake and triggers the Closed event (onclose in JavaScript). This is an advanced setting that should only be modified if handshake timeout errors are occurring due to severe network latency. For more detail on the handshake process, see the SignalR Hub Protocol Specification.
WithKeepAliveInterval	15 seconds	Determines the interval at which the client sends ping messages and is set directly on HubConnectionBuilder. This setting allows the server to detect hard disconnects, such as when a client unplugs their computer from the network. Sending any message from the client resets the timer to the start of the interval. If the client hasn't sent a message in the ClientTimeoutInterval set on the server, the server considers the client disconnected.

In the .NET Client, timeout values are specified as TimeSpan values.

The following example shows values that are double the default values:

var builder = new HubConnectionBuilder()
    .WithUrl(Navigation.ToAbsoluteUri("/chathub"))
    .WithServerTimeout(TimeSpan.FromSeconds(60))
    .WithKeepAliveInterval(TimeSpan.FromSeconds(30))
    .Build();

builder.On<string, string>("ReceiveMessage", (user, message) => ...

await builder.StartAsync();

JavaScript

Option	Default value	Description
withServerTimeout	30 seconds (30,000 milliseconds)	Timeout for server activity and is set directly on HubConnectionBuilder. If the server hasn't sent a message in this interval, the client considers the server disconnected and triggers the onclose event. This setting allows the server to detect hard disconnects, such as when a client unplugs their computer from the network. This value must be large enough for a ping message to be sent from the server and received by the client within the timeout interval. The recommended value is a number at least double the server's keep-alive interval (withKeepAliveInterval) value to allow time for pings to arrive.
withKeepAliveInterval	15 seconds (15,000 milliseconds)	Determines the interval at which the client sends ping messages and is set directly on HubConnectionBuilder. This setting allows the server to detect hard disconnects, such as when a client unplugs their computer from the network. Sending any message from the client resets the timer to the start of the interval. If the client hasn't sent a message in the ClientTimeoutInterval set on the server, the server considers the client disconnected. The ping occurs at most as often as the server pings. If the server pings every five seconds, assigning a value lower than 5000 (5 seconds) pings every five seconds. The default value is 15 seconds. The keep-alive interval should be less than or equal to half the value assigned to the server timeout (withServerTimeout).

The following example shows values that are double the default values:

var connection = new signalR.HubConnectionBuilder()
  .withUrl("/chatHub")
  .withServerTimeout(60000)
  .withKeepAliveInterval(30000)
  .build();

Java

Option	Default value	Description
getServerTimeout / setServerTimeout	30 seconds (30,000 milliseconds)	Timeout for server activity. If the server hasn't sent a message in this interval, the client considers the server disconnected and triggers the onClose event. This value must be large enough for a ping message to be sent from the server and received by the client within the timeout interval. The recommended value is a number at least double the server's KeepAliveInterval value to allow time for pings to arrive.
withHandshakeResponseTimeout	15 seconds	Timeout for initial server handshake. If the server doesn't send a handshake response in this interval, the client cancels the handshake and triggers the onClose event. This is an advanced setting that should only be modified if handshake timeout errors are occurring due to severe network latency. For more detail on the Handshake process, see the SignalR Hub Protocol Specification.
getKeepAliveInterval / setKeepAliveInterval	15 seconds (15,000 milliseconds)	Determines the interval at which the client sends ping messages. Sending any message from the client resets the timer to the start of the interval. If the client hasn't sent a message in the ClientTimeoutInterval set on the server, the server considers the client disconnected.

Configure stateful reconnect

SignalR stateful reconnect reduces the perceived downtime of clients that have a temporary disconnect in their network connection, such as when switching network connections or a short temporary loss in access.

Stateful reconnect achieves this by:

• Temporarily buffering data on the server and client.
• Acknowledging messages received (ACK-ing) by both the server and client.
• Recognizing when a connection is up and replaying messages that might have been sent while the connection was down.

Stateful reconnect is available in ASP.NET Core 8.0 and later.

Opt in to stateful reconnect at both the server hub endpoint and the client:

• Update the server hub endpoint configuration to enable the AllowStatefulReconnects option:

  app.MapHub<MyHub>("/hubName", options =>
  {
      options.AllowStatefulReconnects = true;
  });
  

  Optionally, the maximum buffer size in bytes allowed by the server can be set globally or for a specific hub with the StatefulReconnectBufferSize option:

  The StatefulReconnectBufferSize option set globally:

  builder.AddSignalR(o => o.StatefulReconnectBufferSize = 1000);
  

  The StatefulReconnectBufferSize option set for a specific hub:

  builder.AddSignalR().AddHubOptions<MyHub>(o => o.StatefulReconnectBufferSize = 1000);
  

  The StatefulReconnectBufferSize option is optional with a default of 100,000 bytes.

• Update JavaScript or TypeScript client code to enable the withStatefulReconnect option:

  const builder = new signalR.HubConnectionBuilder()
    .withUrl("/hubname")
    .withStatefulReconnect({ bufferSize: 1000 });  // Optional, defaults to 100,000
  const connection = builder.build();
  

  The bufferSize option is optional with a default of 100,000 bytes.

• Update .NET client code to enable the WithStatefulReconnect option:

    var builder = new HubConnectionBuilder()
        .WithUrl("<hub url>")
        .WithStatefulReconnect();
    builder.Services.Configure<HubConnectionOptions>(o => o.StatefulReconnectBufferSize = 1000);
    var hubConnection = builder.Build();
  

  The StatefulReconnectBufferSize option is optional with a default of 100,000 bytes.

Configure additional options

Additional options can be configured in the WithUrl (withUrl in JavaScript) method on HubConnectionBuilder or on the various configuration APIs on the HttpHubConnectionBuilder in the Java client:

.NET

.NET Option	Default value	Description
AccessTokenProvider	null	A function returning a string that is provided as a Bearer authentication token in HTTP requests.
SkipNegotiation	false	Set this to true to skip the negotiation step. Only supported when the WebSockets transport is the only enabled transport. This setting can't be enabled when using the Azure SignalR Service.
ClientCertificates	Empty	A collection of TLS certificates to send to authenticate requests.
Cookies	Empty	A collection of HTTP cookies to send with every HTTP request.
Credentials	Empty	Credentials to send with every HTTP request.
CloseTimeout	5 seconds	WebSockets only. The maximum amount of time the client waits after closing for the server to acknowledge the close request. If the server doesn't acknowledge the close within this time, the client disconnects.
Headers	Empty	A Map of additional HTTP headers to send with every HTTP request.
HttpMessageHandlerFactory	null	A delegate that can be used to configure or replace the HttpMessageHandler used to send HTTP requests. Not used for WebSocket connections. This delegate must return a non-null value, and it receives the default value as a parameter. Either modify settings on that default value and return it, or return a new HttpMessageHandler instance. When replacing the handler make sure to copy the settings you want to keep from the provided handler, otherwise, the configured options (such as Cookies and Headers) won't apply to the new handler.
Proxy	null	An HTTP proxy to use when sending HTTP requests.
UseDefaultCredentials	false	Set this boolean to send the default credentials for HTTP and WebSockets requests. This enables the use of Windows authentication.
WebSocketConfiguration	null	A delegate that can be used to configure additional WebSocket options. Receives an instance of ClientWebSocketOptions that can be used to configure the options.
ApplicationMaxBufferSize	1 MB	The maximum number of bytes received from the server that the client buffers before applying backpressure. Increasing this value allows the client to receive larger messages faster without applying backpressure, but can increase memory consumption.
TransportMaxBufferSize	1 MB	The maximum number of bytes sent by the user application that the client buffers before observing backpressure. Increasing this value allows the client to buffer larger messages faster without awaiting backpressure, but can increase memory consumption.

JavaScript

JavaScript Option	Default Value	Description
accessTokenFactory	null	A function returning a string that is provided as a Bearer authentication token in HTTP requests.
transport	null	An HttpTransportType value specifying the transport to use for the connection.
headers	null	Dictionary of headers sent with every HTTP request. Sending headers in the browser doesn't work for WebSockets or the ServerSentEvents stream.
logMessageContent	null	Set to true to log the bytes/chars of messages sent and received by the client.
skipNegotiation	false	Set this to true to skip the negotiation step. Only supported when the WebSockets transport is the only enabled transport. This setting can't be enabled when using the Azure SignalR Service.
withCredentials	true	Specifies whether credentials will be sent with the CORS request. Azure App Service uses cookies for sticky sessions and needs this option enabled to work correctly. For more info on CORS with SignalR, see Security considerations in ASP.NET Core SignalR.
timeout	100,000	Timeout in milliseconds to apply to HTTP requests. This doesn't apply to Long Polling poll requests, EventSource, or WebSockets.

Java

Java Option	Default Value	Description
withAccessTokenProvider	null	A function returning a string that is provided as a Bearer authentication token in HTTP requests.
shouldSkipNegotiate	false	Set this to true to skip the negotiation step. Only supported when the WebSockets transport is the only enabled transport. This setting can't be enabled when using the Azure SignalR Service.
withHeader withHeaders	Empty	A Map of additional HTTP headers to send with every HTTP request.

In the .NET Client, these options can be modified by the options delegate provided to WithUrl:

var connection = new HubConnectionBuilder()
    .WithUrl("https://example.com/chathub", options => {
        options.Headers["Foo"] = "Bar";
        options.SkipNegotiation = true;
        options.Transports = HttpTransportType.WebSockets;
        options.Cookies.Add(new Cookie(/* ... */);
        options.ClientCertificates.Add(/* ... */);
    })
    .Build();

In the JavaScript Client, these options can be provided in a JavaScript object provided to withUrl:

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub", {
        // "Foo: Bar" will not be sent with WebSockets or Server-Sent Events requests
        headers: { "Foo": "Bar" },
        transport: signalR.HttpTransportType.LongPolling 
    })
    .build();

In the Java client, these options can be configured with the methods on the HttpHubConnectionBuilder returned from the HubConnectionBuilder.create("HUB URL")

HubConnection hubConnection = HubConnectionBuilder.create("https://example.com/chathub")
        .withHeader("Foo", "Bar")
        .shouldSkipNegotiate(true)
        .withHandshakeResponseTimeout(30*1000)
        .build();

Additional resources

• Get started with ASP.NET Core SignalR
• Use hubs in ASP.NET Core SignalR
• ASP.NET Core SignalR JavaScript client
• ASP.NET Core SignalR .NET Client
• Use MessagePack Hub Protocol in SignalR for ASP.NET Core
• ASP.NET Core SignalR supported platforms