javascript xmlhttp error on signalr in asp.net core

问题

In my application 2 projects and mvc client run at port(5002) and web api project run at port (5001). I have implemented signalr in mvc client. Now showing error log in console as below:

and i have also added configuration to my api project for core policy like:

services.AddCors(options =>
{
    options.AddPolicy("signalr",
        builder =>
        {
            builder.WithOrigins("https://localhost:5002")
                   .AllowAnyHeader()
                   .AllowAnyMethod();
        });
});

And now also showing same error. Please suggest.

回答1:

You need to configure your CORS like this:

services.AddCors(options =>
{
    options.AddPolicy("signalr", builder => builder.WithOrigins("https://localhost:5002")
        .AllowAnyHeader()
        .AllowAnyMethod()
        .AllowCredentials()
        .SetIsOriginAllowed((host) => true));
});

The lambda function that you pass to the .SetIsOriginAllowed() method returns true if an origin is allowed, so always returning true allows any origin to send requests to the api. The allow origin access control http header returned when using this method contains the origin that sent the request, not a wildcard, e.g. Access-Control-Allow-Origin: http://localhost:4200.

来源：https://stackoverflow.com/questions/62958384/javascript-xmlhttp-error-on-signalr-in-asp-net-core