OnStarting cannot be set because the response has already started.

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I’m trying to recreate a feature from a legacy api that supported jsonp as a middleware in .net 7. What I have written appears to work fine when I initiate the request from the chrome browser but when using a node http client kestrel throws an invalidoperationexcpetion.

Expected Behavior

No matter the client, the middleware should modify the response without error.

Steps To Reproduce

i’ve registered this middleware at a few different spots in the pipeline and it doesn’t seem to matter.

#nullable enable
using System.IO;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace api.quirks;

public class JsonpMiddleware {
    private readonly RequestDelegate _next;

    public JsonpMiddleware(RequestDelegate next) {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context) {
        var version = context.GetRequestedApiVersion()!;

        if (version > ApiVersion.Default) {
            await _next(context);

            return;
        }

        if (!context.Request.Query.TryGetValue("callback", out var callback)) {
            await _next(context);

            return;
        }

        if (!context.Response.HasStarted) {
            context.Response.OnStarting(() => {
                context.Response.ContentType = "text/javascript; charset=utf-8";

                return Task.CompletedTask;
            });
        }

        await context.Response.WriteAsync($"/**/ typeof {callback} === 'function' && {callback} (");
        await _next(context); // this is the line that throws
        await context.Response.WriteAsync(");");
        await context.Response.Body.FlushAsync();

        return;
    }
}

Exceptions (if any)

[ERR 10:31:42] (Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware) An unhandled exception has occurred while executing the request. 
System.InvalidOperationException: OnStarting 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.OnStarting(Func`2 callback, Object state)
   at Microsoft.AspNetCore.Mvc.ReportApiVersionsAttribute.OnActionExecuting(ActionExecutingContext context)
   at Microsoft.AspNetCore.Mvc.Filters.ActionFilterAttribute.OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at CorrelationId.CorrelationIdMiddleware.Invoke(HttpContext context, ICorrelationContextFactory correlationContextFactory)
   at api.quirks.JsonpMiddleware.InvokeAsync(HttpContext context) in .../JsonpMiddleware.cs:line 40
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
[WRN 10:31:42] (Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware) The response has already started, the error page middleware will not be executed. 

.NET Version

7.0.202

Anything else?

No response