引用 AspNetCoreRateLimit => StatusCode cannot be set because the response has already started.

app.UseIpRateLimiting(); #需要放在前面，否则抓去不准，还有可能会出现下列错误

本次出现这个错误，是因为  .Net Core 跨域

里面的这行：httpContext.Response.StatusCode = 204; 由于StatusCode 先给它设了 204，所以导致 IpRateLimit 报了下图的错误。

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseIpRateLimiting(); #需要放在前面

    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
        app.UseStatusCodePagesWithReExecute("/Home/Error");
    }

    //..............
}

app.UseIpRateLimiting(); #需要放在前面，否则抓去不准，还有可能会出现下列错误

fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HM084E4TPLBN", Request id "0HM084E4TPLBN:00000001": An unhandled exception was thrown by the application.
System.InvalidOperationException: StatusCode cannot be set because the response has already started.
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ThrowResponseAlreadyStartedException(String value)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.set_StatusCode(Int32 value)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.Microsoft.AspNetCore.Http.Features.IHttpResponseFeature.set_StatusCode(Int32 value)
   at Microsoft.AspNetCore.Http.DefaultHttpResponse.set_StatusCode(Int32 value)
   at Microsoft.AspNetCore.Routing.Matching.HttpMethodMatcherPolicy.<>c__DisplayClass15_0.<CreateRejectionEndpoint>b__0(HttpContext context)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.Invoke(HttpContext httpContext)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
   at AspNetCoreRateLimit.RateLimitMiddleware`1.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.HandleException(HttpContext context, ExceptionDispatchInfo edi)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)