[Web] Failed to complete negotiation with the server: XMLHttpRequest error.

[AmbujaAK]

version : signalr_core: ^1.0.5 code :

final connection = HubConnectionBuilder()
.withUrl(
"$kBaseUrl/serverpush",
HttpConnectionOptions(
logging: (level, message) => print('$level: $message'),
))
.build();

await connection.start();

connection.on('FlutterRecMsgFromHub', (message) {
  print(message.toString());
});

> *Issues :* 
Restarted application in 670ms.
LogLevel.debug: Starting HubConnection.
LogLevel.debug: Starting connection with transfer format 'TransferFormat.text'.
LogLevel.debug: Sending negotiation request: https://p4infrdevsignalrwebapp01.azurewebsites.net/serverpush/negotiate.
LogLevel.error: Failed to complete negotiation with the server: XMLHttpRequest error.
LogLevel.error: Failed to start the connection: XMLHttpRequest error.
LogLevel.debug: HubConnection failed to start successfully because of error '{XMLHttpRequest error..toString}'.
Error: XMLHttpRequest error.
    at Object.createErrorWithStack (http://localhost:63192/dart_sdk.js:4362:12)
    at Object._rethrow (http://localhost:63192/dart_sdk.js:38245:16)
    at async._AsyncCallbackEntry.new.callback (http://localhost:63192/dart_sdk.js:38239:13)
    at Object._microtaskLoop (http://localhost:63192/dart_sdk.js:38071:13)
    at _startMicrotaskLoop (http://localhost:63192/dart_sdk.js:38077:13)
    at http://localhost:63192/dart_sdk.js:33574:9

[AdrianKlm]

I have the same problem. Any information on when it will be fixed?

[Jddl]

            services.AddCors(op =>
            {
                op.AddPolicy("SignalRCors", set =>
                {
                    set.SetIsOriginAllowed(origin => true)
                       .AllowAnyHeader()
                       .AllowAnyMethod()
                       .AllowCredentials();
                });
            });

[laimonas]

@AmbujaAK maybe try to look there https://github.com/jamiewest/signalr_core/issues/24#issuecomment-710113013

[agwanyaseen]

Same issue, these plugin not working on flutter web , Any Idea till when it will going to be fixed?

[milodude]

The XMLHttpRequest error is due to Cors policy issue. I managed to solve it by doing the next steps in a C# application.

1- Define in your startup.cs file a new porperty ie:
readonly string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";

2-At your configure method in the same Startup.cs file add the next line to add Cors services.AddCors(options => { options.AddPolicy(MyAllowSpecificOrigins, policy => { policy.WithOrigins("http://localhost:58944") .AllowAnyHeader() .AllowAnyMethod() .AllowCredentials(); }); }); Where WithOrigins must be filled with the UI host url you are trying to send the message from.

3- Use Cors at your Configure method in the same Startup.cs file app.UseCors(MyAllowSpecificOrigins); app.UseRouting(); It must be defined before UseRouting method.

Please give it a shot and let everyone know if this worked out for you.

[petsve]

Allowing Cors solved it for me too. But the port could change between runs so I made the server code a bit more generic. In .NET you could use the following:

services.AddCors(options => { options.AddPolicy(MyAllowSpecificOrigins, builder => builder.SetIsOriginAllowed(origin => new Uri(origin).IsLoopback) ); });

[Codzaa]

@jamiewest Hi !

I bumped into this same error but I found a different solution that does not involve configuring 'CORS'.

final connection = HubConnectionBuilder() .withUrl( 'http://localhost:9670/hub', HttpConnectionOptions( skipNegotiation: true, transport: HttpTransportType.webSockets, logging: (level, message) => print(message), )) .build();

You can simply set skipNegotiation to true, but when reading the docs on the microsoft site (https://docs.microsoft.com/en-us/javascript/api/%40aspnet/signalr/ihttpconnectionoptions?view=signalr-js-latest#skipnegotiation) , it says that you have to be using Web Sockets for this to work.

By the way what are the downsides to setting skipNegotiation to true, any security issues or something?

Environment Flutter 2.8.0 .Net 5