Internet Explorer 8 + Deflate

The gzip and deflate methods aren't the same... they are very close, but there are some subtle differences with the header, so, if you change your content-encoding, you should also change your parameters to the encoding method (specifically, the window size)!

See: http://apcmag.com/improve_your_site_with_http_compression.htm

Probably the other browsers are ignoring your content-encoding specification and doing some automatic recognition, but IE8 is not...

See: http://www.zlib.net/manual.html#deflateInit2

Try to use:

method=Z_DEFLATEDwindowBits=-15  (negative so that the header is suppressed)

And use "gzip" as the content-encoding

I wanted to clarify what I've discovered on this, as I've written my own deflate algorithm, my own HTTP server, and to my dismay IE8 also failed to recognize my deflated content:

HTTP RFC is http://www.faqs.org/ftp/rfc/rfc2616.pdf. Page 17 states both RFC 1950 and RFC 1951 is used when performing a deflate in the HTTP headers. RFC 1950 is simply defining the header and trailer bytes; the deflate algorithm is defined in RFC 1951. When I programmed this to spec, IE8 failed.

When I ignored RFC 1950 and only did RFC 1951, it passed.

I would assume, then, that IE8 isn't following RFC 2616 page 17 correctly, and all of the other browsers are nice enough to accept either format.