Troubleshoot connection errors

This section provides help with errors that can occur when trying to establish a connection to a ASP.NET Core SignalR hub.

Response code 404

When using WebSockets and skipNegotiation = true

WebSocket connection to 'wss://xxx/HubName' failed: Error during WebSocket handshake: Unexpected response code: 404
  • When using multiple servers without sticky sessions, the connection can start on one server and then switch to another server. The other server is not aware of the previous connection.

  • Verify the client is connecting to the correct endpoint. For example, the server is hosted at http://127.0.0.1:5000/hub/myHub and client is trying to connect to http://127.0.0.1:5000/myHub.

  • If the connection uses the ID and takes too long to send a request to the server after the negotiate, the server:

    • Deletes the ID.
    • Returns a 404.

Response code 400 or 503

For the following error:

WebSocket connection to 'wss://xxx/HubName' failed: Error during WebSocket handshake: Unexpected response code: 400

Error: Failed to start the connection: Error: There was an error with the transport.

This error is usually caused by a client using only the WebSockets transport but the WebSockets protocol is not enabled on the server.

Response code 307

When using WebSockets and skipNegotiation = true

WebSocket connection to 'ws://xxx/HubName' failed: Error during WebSocket handshake: Unexpected response code: 307

This error can also happen during the negotiate request.

Common cause:

  • App is configured to enforce HTTPS by calling UseHttpsRedirection in Startup, or enforces HTTPS via URL rewrite rule.

Possible solution:

  • Change the URL on the client side from "http" to "https". .withUrl("https://xxx/HubName")

Response code 405

Http status code 405 - Method Not Allowed

  • The app doesn't have CORS enabled

Response code 0

Http status code 0 - Usually a CORS issue, no status code is given

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:5000/default/negotiate?negotiateVersion=1. (Reason: CORS header 'Access-Control-Allow-Origin' missing).
  • Add the expected origins to .WithOrigins(...)
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:5000/default/negotiate?negotiateVersion=1. (Reason: expected 'true' in CORS header 'Access-Control-Allow-Credentials').
  • Add .AllowCredentials() to your CORS policy. Cannot use .AllowAnyOrigin() or .WithOrigins("*") with this option

Response code 413

Http status code 413 - Payload Too Large

This is often caused by having an access token that is over 4k.

  • If using the Azure SignalR Service, reduce the token size by customizing the claims being sent through the Service with:
.AddAzureSignalR(options =>
{
    options.ClaimsProvider = context => context.User.Claims;
});

Transient network failures

Transient network failures may close the SignalR connection. The server may interpret the closed connection as a graceful client disconnect. To get more info on why a client disconnected in those cases gather logs from the client and server.