ISA 2004: Web Publishing disabling HTTP Compression

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Date: Tue, 21 Sep 2004 16:16:01 -0400

I'm using ISA 2004 and publishing internal web servers using Web Publishing.
I have enabled HTTP Compression (IIS6) on these sites, and everything works
if I access the server internally (directly).

However, external clients that go through ISA are not getting HTTP
Compression.

I did some experiments and this is what I found out:

I created a test page on my internal server that dumps the headers. If I
access the site internally, I see this header:

    Accept-Encoding: gzip, deflate

And all is well.

However, if I access it from an external site, the header is no longer
there.

I then created a simple Web Filter and installed it on the ISA Server. This
filter simply logs the Accept-Encoding header during the PREPROC_HEADERS
notification. The logs show that the Accept-Encoding header is present.

Therefore, somewhere between the time my filter executes and ISA dispactches
the request to my web server, the Accept-Encoding header is stripped. I
understand that HTTP Filtering of the response body and HTTP compression
don't mix. However, I have disabled every Web Filter (except the one I
added) and I'm still seeing this problem.

Is this normal behavior?

Am I going to have to implement HTTP Compression in my filter and not use
the one built in to IIS 6?

Oddly, I found this quote on Microsoft site:
http://www.microsoft.com/technet/prodtechnol/isa/2004/plan/httpfiltering.mspx

      Q. Can I cache compressed content?
      A. In a Web publishing scenario, ISA Server allows the traversal of
compressed responses from the Web server to the client, if the client sends
an Accept-Encoding header indicating that it will accept compressed content.
However, compressed content will not be cached. Note that ISA Server does
not support traversal of compression responses in a forward proxy scenario,
and does not support inspection of compressed response bodies in any
direction.

So it appears that this is supposed to work. What am I missing here?

BTW: I disabled HTTP Caching, and it is still not working.

Michael

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