Server cannot append header after HTTP headers have been sent uploading files

Question

I get this exception intermittently in my asp.net mvc 5 c# web application:

Server cannot append header after HTTP headers have been sent.

It just happens uploading images to S3 method (Web Api Controller).

The presendrequestheaders in Global.asax

protected void Application_PreSendRequestHeaders(object sender, EventArgs e)
        {
            HttpApplication app = sender as HttpApplication;
            if (app != null &&
                app.Context != null)
            {
                app.Context.Response.Headers.Remove("Server");
            }
        }

The method that trigger the error:

    [HttpPost]
    [Route("UploadImageJSON")]
    public IHttpActionResult UploadImageJSON(HttpRequestMessage request)
    {
        var httpRequest = HttpContext.Current.Request;

        // Check if files are available
        if (httpRequest.Files.Count != 1) return BadRequest();

        var postedFile = httpRequest.Files[0];

        var contentType = postedFile.ContentType;
        if (!contentType.Contains("image"))
        {
            return StatusCode(HttpStatusCode.NotAcceptable);
        }




        var keyUploadFiles = Constants.UrlS3Amazon +
                             S3.UploadToS3WithStream(postedFile.InputStream, contentType);


        return Json(JsonConvert.SerializeObject(keyUploadFiles));


    }

EDIT: More information... I have my Web App hosted in Elastic BeanStalk with a load balancer, the load balancer has installed a SSL Certificate, and the connection between the load balancer and the EC2 instances are in ports 80. Maybe it could be helpful.

The Elmah log:

System.Web.HttpException (0x80004005): Server cannot append header after HTTP headers have been sent. at System.Web.HttpHeaderCollection.SetHeader(String name, String value, Boolean replace) at Microsoft.Owin.Host.SystemWeb.CallHeaders.AspNetResponseHeaders.Set(String key, String[] values) at Microsoft.Owin.Infrastructure.OwinHelpers.AppendHeaderUnmodified(IDictionary2 headers, String key, String[] values) at Microsoft.Owin.ResponseCookieCollection.Append(String key, String value, CookieOptions options) at Microsoft.Owin.Security.Cookies.CookieAuthenticationHandler.<ApplyResponseGrantAsync>d__b.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.Owin.Security.Infrastructure.AuthenticationHandler.<ApplyResponseCoreAsync>d__8.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.Owin.Security.Infrastructure.AuthenticationHandler.<TeardownAsync>d__5.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.Owin.Security.Infrastructure.AuthenticationMiddleware1.d__0.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.AspNet.Identity.Owin.IdentityFactoryMiddleware2.<Invoke>d__0.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.AspNet.Identity.Owin.IdentityFactoryMiddleware2.d__0.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.AspNet.Identity.Owin.IdentityFactoryMiddleware`2.d__0.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.Owin.Mapping.MapMiddleware.d__0.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.EndFinalWork(IAsyncResult ar) at System.Web.HttpApplication.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Thanks!!

It arrived each time you upload an image with your method ? Because you said at beginning that is an intermittent issue ... — D4rkTiger
Do you have any http modules that the response is passing through? — hivie7510
Your stack trace shows the code passes through Microsoft.Owin.Security.Infrastructure.AuthenticationMiddleware and Microsoft.Owin.Security.Cookies.CookieAuthenticationHandler. How is your authentication flow set up? — MarioDS
Good question. I'm seeing a similar, intermittent error that AFAICT has nothing to do with any of my code, but has the same stack replete with Microsoft.Owin.Security and Microsoft.AspNet.Identity.Owin method calls. In my case "how is the flow set up?" is "how it came out of the AspNet.Identity box." — fortboise
It seems like the exception is occurring in your UploadToS3WithStream method so you need to show the code for that method. — SeanN

Petar Minev Petar Minev · Accepted Answer · 2016-07-11T04:54:32

have you tried with removing app.Context.Response.Headers.Remove("Server"); i think there is this is the issue?

Server cannot append header after HTTP headers have been sent uploading files

1 Answers