HTTP compression in IIS 6.0 causing problems with certain users

Ok, I think we've figured it out...

On the client side, Squid 2.5 and earlier doesn't understand "Transfer-encoding: chunked", so it delivers each chunk as the entire client request. Since it's only 1 chunk of the entire compressed request, it's invalid data and can't be read by the browser. (Not sure if this is an issue with other proxies)

On the server side, IIS always sends chunked encoding for Dynamic Compression (since IIS doesn't cache application responses, it has to compress each response on the fly, hence the chunked encoding).

The only way we can think of to fix this is to completely disable compression for HTTP 1.0 clients and only compress for HTTP 1.1 responses. The drawback is that anyone behind a proxy that sends 1.0 requests won't get compressed data and the site will load 0.5 - 1 second slower for those users.

Changes made in the metabase.xml file:

<IIsCompressionSchemes            Location ="/LM/W3SVC/Filters/Compression/Parameters"
...
HcDoOnDemandCompression="TRUE"
HcNoCompressionForHttp10="TRUE"
...
</IIsCompressionSchemes>

If anyone has a better solution, please let me know!

If this is reproducible then I would start by examining the response headers sent to the client to ensure that there is a 1.0 proxy somewhere in the request/response stream as indicated in the Via: response header. If not, then chances are you're barking up the wrong tree. Proxies must insert this header and the protocol they use in both directions of the request/response stream.