“Content-Encoding: gzip” is stripped by proxy?

Posted on by wooway

When you send an HTTP request through a proxy, and the web site returns an HTTP header like this:

HTTP/1.1 200 OK
…
Content-Encoding: gzip
…

There is a chance that line “Content-Encoding: gzip” could be stripped by the proxy.  Here is some research I did if the proxy server is Microsoft ISA Server 2006.

1) There is an article in the official blog: http://blogs.technet.com/b/isablog/archive/2009/10/25/error-500-not-supported-while-browsing-internet-through-isa-server-2006.aspx

2) Solutions for different senarios:

A) Forward proxy: http://support.microsoft.com/?id=927263

B) Reverse proxy: http://msdn.microsoft.com/en-us/library/ms826283

3) Some background info, not really relevant though: http://technet.microsoft.com/en-us/library/bb794746.aspx

4) Extended readings:

A) http://www.carbonwind.net/blog/post/Forefront-TMG-2010-RC-Malware-Inspection-and-NIS-a-few-HTTP-compression-security-considerations-for-outbound-HTTP-connections.aspx

B) http://blogs.technet.com/b/isablog/archive/2009/03/04/how-to-allow-http-301-through-isa-server-2006.aspx

5) Similar topic on ISA Server 2004 SP2:

A) Symptom: http://linuxminded.xs4all.nl/?target=writings.plc&writing=workaround-ms-isa2004-sp2-gzip-issue

B) Solution: http://support.microsoft.com/?id=916106

C) Background Info: http://technet.microsoft.com/en-us/library/cc302594.aspx

D) Extended reading: http://forums.isaserver.org/m_220016100/tm.htm