NYCPHP Meetup

[nycphp-talk] form posts, back button, IE page expired

Chris Shiflett shiflett at php.net
Mon Aug 18 16:35:04 EDT 2003


--- Brian Pang <bpang at bpang.com> wrote:
> How do you guys/gals deal with the IE Page Expired page which is
> generated if you use the back button to return to a page which had
> form POST information in it originally?

To answer your immediate question, you can do either of the following:

1. Allow caching
2. Use an intermediate URL for processing

To explain why browsers seem to behave differently, read on...

If you will look at section 13.13 of RFC 2616
(http://www.ietf.org/rfc/rfc2616.txt), you will see the following statement:

"In particular history mechanisms SHOULD NOT try to show a semantically
transparent view of the current state of a resource. Rather, a history
mechanism is meant to show exactly what the user saw at the time when the
resource was retrieved."

It sounds like whether you allow caching should make no difference, right? The
back button (history mechanism) should not ask the user to repost data, because
it should be displaying exactly what it did before. This is how lynx works, if
you're familiar with using it.

In most cases, your PHP applications are going to send a Cache-Control header
that includes the no-store directive (unless you are controlling your headers
more specifically than most developers). In section 14.9.2, the no-store
directive of the Cache-Control header is explained:

"If sent in a request, a cache MUST NOT store any part of either this request
or any response to it. If sent in a response, a cache MUST NOT store any part
of either this response or the request that elicited it."

Thus, depending on how your interpret these statements, it seems quite likely
that you might come to very different conclusions about how to implement a
history mechanism. This might account for the discrepancies in implementation.

Hope that helps.

Chris

=====
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