Need for terminal middleware

[jerriep]

I had the following code which used to work fine in RC2

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole(LogLevel.Debug);

        app.Use(async (context, next) =>
        {
            await context.Response.WriteAsync("<p>Hello from Middleware 1</p>");

            await next.Invoke();

            await context.Response.WriteAsync("<p>Goodbye from Middleware 1</p>");
        });

        app.Use(async (context, next) =>
        {
            await context.Response.WriteAsync("<p>Hello from Middleware 2</p>");

            await next.Invoke();

            await context.Response.WriteAsync("<p>Goodbye from Middleware 2</p>");
        });
    }
}

But now with 1.0 this does not seem to work anymore. I get the following error:

 Connection id "0HKU1UAM61D6F": An unhandled exception was thrown by the application.
System.InvalidOperationException: Status code cannot be set, response has already started.
   at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame.set_StatusCode(Int32 value)
   at Microsoft.AspNetCore.Builder.Internal.ApplicationBuilder.<>c.<Build>b__16_0(HttpContext context)
   at MiddlewareDeepDive.Startup.<>c.<<Configure>b__1_1>d.MoveNext() in C:\Development\AspnetCasts\MiddlewareDeepDive\02 - Your first middleware pipeline\After\MiddlewareDeepDive\Startup.cs:line 39
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at MiddlewareDeepDive.Startup.<>c.<<Configure>b__1_0>d.MoveNext() in C:\Development\AspnetCasts\MiddlewareDeepDive\02 - Your first middleware pipeline\After\MiddlewareDeepDive\Startup.cs:line 30
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Hosting.Internal.RequestServicesContainerMiddleware.<Invoke>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame`1.<RequestProcessingAsync>d__2.MoveNext()

And also I only get the following output displayed:

Hello from Middleware 1

Hello from Middleware 2

Is this something that has changed in 1.0 RTM? Should the middleware pipeline now always contain terminal middleware at the end on the pipeline?

Edit:
FWIW, here is a video proving that this used to work fine in RC2:
https://www.youtube.com/watch?v=B2WftX-etVo

See from around the 8:20 mark...

[Tratcher]

This was a Kestrel bug that was fixed for RTM: aspnet/KestrelHttpServer#805

There is always a terminal 404 middleware at the end of the pipeline. It's failing because the status code can't be changed after you call write.

As a guideline, it's a bad practice to call next if you have started the response. Middleware should produce a response OR call next.

[jerriep]

Thanks for explanation @Tratcher

[joeaudette]

just fyi, I landed on this issue because I was getting the same exception after upgrading my app to 1.1.

The difference is I was only doing response.writeasync from a controller action not middleware, no exception thrown in my code but after the action method completes kestrel throws this error.

I solved it in my app by changing to return an IActionResult instead of using response.writeasync but it seems weird that you can't do that from a controller action without an error

[Tratcher]

@joeaudette when you were calling WriteAsync directly in your controller what were you returning from the controller? MVCs behavior is highly dependent on what you return.

[joeaudette]

@Tratcher the action method was just async Task with no return type, I was either setting Response.StatusCode or writing a string into the response. it is a method called by ajax to edit or create a blog post and the string I was writing to the response was just the url for the post on success. So my method was completing with no error and only writing string into the response, then kestrel was throwing this error.
The code changes to solve the error led to better code but still thought you should be able to use response.write without an exception happening after, it worked fine in 1.0 so it is something different in 1.1

[Tratcher]

@joeaudette can you share your error and stack trace? I'll ask @ryanbrandenburg to take a look.

[joeaudette]

sure I'm logging to json files and this is what it logged:

{"Id":"f36bee83-bd38-4337-9010-a0117bef37a9","LogDateUtc":"2016-11-30T18:08:06.0950414Z","IpAddress":"127.0.0.1","Culture":"en-US","Url":"/Blog/AjaxPost","ShortUrl":"/Blog/AjaxPost","Thread":"","LogLevel":"Error","Logger":"Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware","Message":"An unhandled exception has occurred while executing the request\r\nSystem.InvalidOperationException: OnStarting cannot be set, response has already started.\r\n   at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame.ThrowResponseAlreadyStartedException(String value)\r\n   at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame.OnStarting(Func`2 callback, Object state)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeNextResourceFilter>d__22.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ResourceExecutedContext context)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeAsync>d__20.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Builder.RouterMiddleware.<Invoke>d__4.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at SaasKit.Multitenancy.Internal.TenantPipelineMiddleware`1.<Invoke>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at SaasKit.Multitenancy.Internal.TenantResolutionMiddleware`1.<Invoke>d__3.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.<Invoke>d__4.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Session.SessionMiddleware.<Invoke>d__9.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at Microsoft.AspNetCore.Session.SessionMiddleware.<Invoke>d__9.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.<Invoke>d__7.MoveNext()","StateJson":"[{\"Key\":\"{OriginalFormat}\",\"Value\":\"An unhandled exception has occurred while executing the request\"}]","EventId":0}

[joeaudette]

if you want to see the diff of what I changed to fix it in my app ie to see more specifically what the method was doing before, it is here: cloudscribe/cloudscribe.SimpleContent@19ead4f

[Tratcher]

Ahh, that's a different error. You're hitting this: aspnet/Mvc#5555

[pravinhabbu4u]

@Tratcher I am facing below issue with Kestrel server in Middleware. I am using "Microsoft.AspNetCore.Server.Kestrel": "1.1.0". Same code works fine on my local machine with IIS Express, however, it fails whenever I deploy it on Windows server 2012. Can I help me with the same?

    public async Task Invoke(HttpContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException(nameof(context));
        }

        if (ShouldRespondToRequest(context.Request))
        {
            await WriteResponseAsync(context.Response).ConfigureAwait(true);
            //await Task.Delay(5000); was trying this to see if issue gets resolved
        }
        //Continue On
        await next.Invoke(context);
        //await next(context).ConfigureAwait(true);

    }

fail: Microsoft.AspNetCore.Server.Kestrel[13]
Connection id "0HL2DV24BLUGV": An unhandled exception was thrown by the application.
System.InvalidOperationException: StatusCode cannot be set, response has already started.
at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame.ThrowResponseAlreadyStartedException(String value)
at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame.set_StatusCode(Int32 value)
at Microsoft.AspNetCore.Builder.Internal.ApplicationBuilder.<>c.b__16_0(HttpContext context)
at GraphQL.Middleware.GraphQLMiddleware.d__4.MoveNext() in C:\Examples\TestGraphQLServer3\src\TestGraphQLServer3\GraphQLMiddleware.cs:line 80
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at GraphQL.Middleware.GraphiQLMiddleware.d__5.MoveNext() in C:\Examples\TestGraphQLServer3\src\TestGraphQLServer3\GraphiQLMiddleware.cs:line 82
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)

[Tratcher]

Return after writeresponseasync, don't call next.

[pravinhabbu4u]

@Tratcher Thanks a ton. It worked like a charm after adding return after adding return in both Middlewares after writeasync

Middleware 1:

        public async Task Invoke(HttpContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            if (ShouldRespondToRequest(context.Request))
            {
                 
                await WriteResponseAsync(context.Response).ConfigureAwait(true);
                return;
            }

            await next.Invoke(context);
        }

Middleware 2:

        public async Task Invoke(HttpContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            if (ShouldRespondToRequest(context.Request))
            {
                var executionResult = await ExecuteAsync(context.Request).ConfigureAwait(true);
                await WriteResponseAsync(context.Response, executionResult).ConfigureAwait(true);
                return;
            }

            await next(context).ConfigureAwait(true);
        }