Server cannot set status after HTTP headers have been sent IIS7 5

Question

Sometimes I get exception in my production environment         Process information          Process ID  3832     Process name  w3wp exe    Account name  NT AUTHORITY NETWORK SERVICE        Exception information         Exception type  System Web HttpException      Exception message  Server cannot set status after HTTP headers have been sent         Request information         Request URL  http   www myulr pl logon     Request path   logon     User host address  10 11 9 1       User  user001     Is authenticated  True      Authentication Type  Forms      Thread account name  NT AUTHORITY NETWORK SERVICE         Thread information         Thread ID  10      Thread account name  NT AUTHORITY NETWORK SERVICE      Is impersonating  False          Stack trace  at System Web HttpResponse set StatusCode Int32 value  at   System Web HttpResponseWrapper set StatusCode Int32 value  at   System Web Mvc HandleErrorAttribute OnException ExceptionContext filterContext  at   System Web Mvc ControllerActionInvoker InvokeExceptionFilters ControllerContext controllerContext  IList 1  filters  Exception exception  at   System Web Mvc ControllerActionInvoker InvokeAction ControllerContext controllerContext  String actionName  at System Web Mvc Controller ExecuteCore   at   System Web Mvc MvcHandler  lt  gt c  DisplayClass8  lt BeginProcessRequest gt b  4   at   System Web Mvc Async AsyncResultWrapper  lt  gt c  DisplayClass1  lt MakeVoidDelegate gt b  0   at   System Web Mvc Async AsyncResultWrapper  lt  gt c  DisplayClass8 1   lt BeginSynchronous gt b  7 IAsyncResult    at   System Web Mvc Async AsyncResultWrapper WrappedAsyncResult 1  End   at    System Web Mvc MvcHandler EndProcessRequest IAsyncResult asyncResult  at   System Web HttpApplication CallHandlerExecutionStep System Web HttpApplication IExecutionStep Execute   at   System Web HttpApplication ExecuteStep IExecutionStep step  Boolean amp  ompletedSynchronously     I didn t noticed this error on my test environment what should I check   I am using ASP NET MVC 2  Release Candidate 2

User · Answer

The HTTP server doesn t send the response header back to the client until you either specify an error or else you start sending data  If you start sending data back to the client  then the server has to send the response head  which contains the status code  first  Once the header has been sent  you can no longer put a status code in the header  obviously   Here s the usual problem   You start up the page  and send some initial tags  i e   lt head gt    The server then sends those tags to the client  after first sending the HTTP response header with an assumed SUCCESS status  Now you start working on the meat of the page and discover a problem  You can not send an error at this point because the response header  which would contain the error status  has already been sent   The solution is this   Before you generate any content at all  check if there are going to be any errors   Only then  when you have assured that there will be no problems  can you then start sending content  like the  tag   In your case  it seems like you have a login page that processes a POST request from a form  You probably throw out some initial HTML  then check if the username and password are valid  Instead  you should authenticate the user password first  before you generate any HTML at all

User · Answer

You are actually trying to redirect a page which has some response to throw  So first you keep the information you have throw in a buffer using response buffer    true in beginning of the page and then flush it when required using response flush this error will get fixed

User · Answer

I had the same issue with setting StatusCode and then Response End in HandleUnauthorizedRequest method of AuthorizeAttribute  var ctx   filterContext HttpContext  ctx Response StatusCode    int HttpStatusCode Forbidden  ctx Response End      If you are using  NET 4 5   add this line before Response StatusCode  filterContext HttpContext Response SuppressFormsAuthenticationRedirect   true    If you are using  NET 4 0  try SuppressFormsAuthenticationRedirectModule

User · Answer

If someone still having this problem Try to use instead of ovverriding   public void OnActionExecuting ActionExecutingContext context                try                        if   HttpContext Current User Identity IsAuthenticated                                if   HttpContext Current Response IsRequestBeingRedirected                                         context Result   new RedirectToRouteResult                  new RouteValueDictionary       controller    Login        action    Index                                                           catch  Exception ex                           new RouteValueDictionary      controller    Login        action    Index

User · Answer

We were getting the same error - so this may be useful to some   For us the cause was super simple  An interface change confused an end user and they were pressing the back button in the browser at a  bad  time after a form submission  sure we should probably have used a PRG pattern  but we didn t    We fixed the issue and the user is no longer pressing the back button  Problem solved

User · Answer

I remember the part from this exception    Cannot modify header information - headers already sent by  occurring in PHP  It occurred when the headers were already sent in the redirection phase and any other output was generated e g    echo  hello   header  Location http   stackoverflow com     Pardon me and do correct me if I am wrong but I am still learning MS Technologies and I was trying to help

User · Answer

How about checking this before doing the redirect   if   Response IsRequestBeingRedirected         do the redirect

User · Answer

I ll broadly agree with Vagrant on the cause    your action was executing  writing markup to response stream the stream was unbuffered forcing the response headers to get written before the markup writing could begin  Your view encountered a runtime error Exception handler kicks in trying to set the status code to something else non-200 Fails because the headers have already been sent     Where I disagree with Vagrant is the  cause no errors in binding  remedy - you could still encounter runtime errors in View binding e g  null reference exceptions   A better solution for this is to ensure that Response BufferOutput   true  before any bytes are sent to the Response stream   e g  in your controller action or On Begin Request in application  This enables server transfers  cookies headers to be set etc  right the way up to naturally ending response  or calling end flush     Of course also check that buffer isn t being flushed set to false further down in the stack too   MSDN Reference  HttpResponse BufferOutput

User · Answer

Just to add to the responses above  I had this same issue when i first started using ASP Net MVC and i was doing a Response Redirect during a controller action   Response Redirect   blah   true     Instead of returning a Response Redirect action i should have been returning a RedirectAction   return Redirect   blah

User · Answer

I apologize  but I m adding my 2 cents to the thread just in case anyone has the same problem    I used Forms Authentication in my MVC app But some controller-actions were  anonymous  i e  allowed to non-authenticated users Sometimes in those actions I would still want users to be redirected to the login form under some condition to do that - I have this in my action method  return new HttpStatusCodeResult 401  - and ASP NET is super nice to detect this  and it redirects the user to the login page  Magic  right  It even has the proper ReturnUrl parameter etc    But you see where I m getting here  I return 401  And ASP NET redirects the user  Which is essentially returns 302  One status code is replaced with another   And some IIS servers  just some   throw this exception  Some don t  - I don t have it on my test serevr  only on my production server  ain t it always the case right o O   I know my answer is essentially repeating what s already said here  but sometimes it s just hard to figure out where this overwriting happens exactly

[asp.net-mvc] Server cannot set status after HTTP headers have been sent IIS7.5

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