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• 05-23-2006, 3:29 PM

  goinoutwest Joined on 05-23-2006, 7:19 PM Posts 4

  Response.Flush breaks IIS's "Custom Errors" Reply Contact [Yes, I know I'm complaining about ancient technology] After using Response.Flush, any errors encountered will not "trigger" IIS's configured "Custom Error" page.  I can't find any mention of this on MSDN. I find it frustrating that there are several articles that suggest using Response.Flush for all kinds of performance improvements on slow pages.  The articles always fail to mention this crippling "side-effect" of using it. Does anyone know why it fails?  Where's the KB article?

• 05-23-2006, 6:02 PM

  In reply to

  bills Joined on 02-03-2006, 5:33 PM Redmond, WA Posts 433	Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact Hi - could you post some sample code that reproduces the issue? thanks- bill ~~~~~~~~~~~~~~~~~~~~~~~~ Bill Staples Product Unit Manager, IIS blog: http://blogs.iis.net/bills

• 05-23-2006, 6:44 PM

  In reply to

  goinoutwest Joined on 05-23-2006, 7:19 PM Posts 4

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact Yeah, here's some repro instructions: 1) Configure a "Custom Error" using IIS mgr for the 500;100 error.  Choose a File or URL and point to the page you'd like to have as your error message. 2) Create a Test.asp page, and make the contents the following: <%@ Language=VBScript %> <% ' TURN ON BUFFERING Response.Buffer = TRUE ' FLUSH THE CONTENT AND HEADERS TO THE CLIENT ' Response.Flush() ' CAUSE AN ERROR This_Function_Does_Not_Exist() %> 3) Browse to the page and observe that your selected error page appears before you.  Finally, UNcomment the "Response.Flush()" line of code.  Reload page in your browser.  Your "error handling" page is not invoked. Thanks for taking a look!

• 06-01-2006, 9:56 AM

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  wwwcoder Joined on 03-13-2003, 7:58 AM Girard, PA Posts 4

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact From my understanding of ASP, when you execute a flush you're basically sending the content of the processed  page to the Web browser. The HTTP headers have already been written and sent to the browser once you send the Response.Flush. Basically you shut off of the Buffer and sent out the response. Since the headers have already been sent to the browser you can longer issue a 500 http response code, and call your custom page. This isn't an error, it is just how HTTP works. WWWCoder.com Redmond Gadgets My Weblog

• 06-05-2006, 10:01 PM

  In reply to

  goinoutwest Joined on 05-23-2006, 7:19 PM Posts 4

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact You are correct, that after Response.Flush has been called the headers are sent to the client.  So, it is therefore impossible to change that 200OK into a 500 response code.  I have no issues with that. However, there seems to be no reason that the "Custom Error" page could not be invoked at the time of the error.  Often times, developers used code in the "Custom Error" page to alert them that an error had occurred on their web site.  If they use Response.Flush before the error occurs their alerting/logging mechanism will not be triggered. The only alternative (when using Response.Flush on a page) is to use the horrible OnError ResumeNext style error trapping.

• 06-13-2006, 9:02 PM

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  anilr Joined on 05-23-2006, 10:13 PM Redmond, WA Posts 2,343

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact goinoutwest: However, there seems to be no reason that the "Custom Error" page could not be invoked at the time of the error.  Often times, developers used code in the "Custom Error" page to alert them that an error had occurred on their web site.  If they use Response.Flush before the error occurs their alerting/logging mechanism will not be triggered.   The custom-error feature was not designed to logging/alerting when an error occurs but for sending a customized error message to the client - as it is too late to send a customized error message to the client at this point, no custom-error page is invoked. Anil Ruia Senior Software Design Engineer IIS Core Server

• 06-13-2006, 9:44 PM

  In reply to

  goinoutwest Joined on 05-23-2006, 7:19 PM Posts 4

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact anilr: The custom-error feature was not designed to logging/alerting when an error occurs but for sending a customized error message to the client I believe you are incorrect.  The custom-error feature was designed for both.  See this Microsoft article: http://www.microsoft.com/technet/prodtechnol/windows2000serv/technologies/iis/tips/custerr.mspx Just so we're clear, here is a relevant quote from the article: "The examples mentioned in this article are simplified to demonstrate the Custom Error feature for 404 errors. They can be easily extended to handle most other HTTP errors and modified to take immediate action, like sending administrative alerts."

• 06-26-2006, 6:36 PM

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  anilr Joined on 05-23-2006, 10:13 PM Redmond, WA Posts 2,343

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact Regardless of what that document says, that is not how custom-error behaved on any IIS version - it does not even get invoked in many cases when the error status is set before the response is flushed to the client - write an aspx page which generates a 404 response and no custom-error will be invoked for it. On IIS7, you may be able to write a module (native or managed) which registers for Log/EndOfRequest) notification and does any logging/administrative alert on failed requests.   Anil Ruia Senior Software Design Engineer IIS Core Server

• 09-14-2006, 3:37 PM

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  renniquer Joined on 09-14-2006, 7:22 PM Posts 1

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact I've experienced the same error, and here's the workaround I came up with: 1. Right after you call Response.Flush(), add this line of code: HttpContext.Current.Items["responseFlushed"] = true; 2. In Global.asax, add the following to Application_Error: if (Convert.ToBoolean(HttpContext.Current.Items["responseFlushed"])) {     HttpContext.Current.Server.Transfer("CustomErrorPage.htm"); } That should do it. You can add additional code to get your actual customErrors settings from web.config using System.Web.Configuration instead of hard coding the custom error page file path. You might also want to make sure Server isn't null. Note that you should use HttpContext.Current.Items and NOT HttpContext.Current.Session, as the Items collection will reset itself on each request, resetting Items["responseFlushed"] to false in the process.

• 10-10-2006, 5:42 PM

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  legacycoder Joined on 10-10-2006, 5:41 PM Posts 1

  Re: Response.Flush breaks IIS's "Custom Errors" Reply Contact Goinoutwest, have you been able to resolve this issue?  We're having the exact same problem...  goinoutwest: anilr: The custom-error feature was not designed to logging/alerting when an error occurs but for sending a customized error message to the client I believe you are incorrect.  The custom-error feature was designed for both.  See this Microsoft article: http://www.microsoft.com/technet/prodtechnol/windows2000serv/technologies/iis/tips/custerr.mspx Just so we're clear, here is a relevant quote from the article: "The examples mentioned in this article are simplified to demonstrate the Custom Error feature for 404 errors. They can be easily extended to handle most other HTTP errors and modified to take immediate action, like sending administrative alerts."