Flex applications hanging when using gzip http header / body compression

I just discovered a problem while attempting to use Brian Rinaldi's excellent Illudium PU36 Code Generator on my development server. It would load up but then after entering my Coldfusion administrator password it would just hang. It always used to work so I realised that something must have changed on my server.

Upon monitoring the HTTP requests going to the server I noticed that the first request to /flex2gateway/ on the server was hanging. The response header was received, but then it was waiting for the response body that never seemed to arrive.

After some head scratching I realised that I had implemented gzip http header / body compression on my development server (a filter for the JRun server). As soon as I removed this the code generator started working perfectly.

This is almost 100% a problem that will affect most Flex apps, so it's something to look out for if you have any issues with hangs when trying to use Flex.

Disclaimer: As I have only used one Flex application I have not been able to test the above assertion. If you know of Flex apps that work with the http compression filter I'm using, please let me know.

The compression filter I am using is GZIP2WayFilter by Thomas Bayer. Apart from the issue with Flex this works very well indeed with compression of CFM templates to crazy sizes.