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4GuysFromRolla.com : ASP FAQS : The Nature of Things


Question:

When I try to do a Reponse.Redirect, it get an error message about "the HTTP headers are already written..." Why? What can I do?


[Print this FAQ]

Answer: If you get a message similar to this one

Response object error 'ASP 0156 : 80004005'
Header Error
/somePageName.asp, line 9999
The HTTP headers are already written to the client browser. Any HTTP header modifications must be made before writing page content.

then simply believe the message!

The rules of Web servers say that you can not do a Response.Redirect once anything has been written to the browser!

"But I haven't done any Response.Write before this line!"

Ahh, but did you code even the tag <HTML> before the Response.Redirect? That tag sends oodles of stuff to the browser, automatically!

So, what can you do?

Two solutions:

(1) Don't do any Response.Write or put any ordinary HTML code or even put in the <HTML> tag until after the point where you do the (possibly conditional) Response.Redirect.

Most of the time, this is easy to do. For example, if you are validating a username and password, there is no need to output anything to the browser before the point where you discover that one or both of the values is wrong.

But if that doesn't work...

(2) Add the line

<%
Response.Buffer = True
%>

before any possible output on the page! Typically, it should be the first line in the file, barring any <% @ .... %> line you might have.

Then, if your code decides it needs to do a Response.Redirect, simply do this:

<%
Response.Clear
Response.Redirect "http://www.disney.com"
%>


The call to Response.Clear wipes out anything that was sitting in the buffer waiting to be sent to the user, at which point Response.Redirect is much happier.

NOTE: Recent versions of IIS will turn buffering on by default, in which case the Response.Buffer = True is unnecessary, though the call to Response.Clear is still needed. However, it can't hurt to be sure buffering is enabled, so why not drop in that line, just to be safe?


FAQ posted by Bill Wilkinson at 10/25/2000 9:17:40 PM to the The Nature of Things category. This FAQ has been viewed 47,395 times.

Do you have a FAQ you'd like to suggest? Suggestions? Comments? If so, send it in! Also, if you'd like to be a FAQ Admin (creating/editing FAQs), let me know! If you are looking for other FAQs, be sure to check out the 4Guys FAQ and Commonly Asked Messageboard Questions!

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Last computed at 9/17/2007 3:22:00 AM


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