`mod_deflate` is returning `Content-Encoding: gzip`. Is that normal?

Question

mod_deflate is configured on my Apache 2.2 web server. But my response headers are showing gzip as the Content-Encoding instead of deflate:

HTTP/1.1 200 OK
Date: Mon, 26 Sep 2011 22:26:11 GMT
Server: Apache
Last-Modified: Mon, 26 Sep 2011 11:32:54 GMT
Accept-Ranges: bytes
X-Powered-By: Servlet/2.5 JSP/2.1
Vary: Accept-Encoding,User-Agent
Content-Encoding: gzip
Age: 36
Content-Length: 144338
Keep-Alive: timeout=15
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8

Notice this line:

Content-Encoding: gzip

Is this normal?

Answer 1

Yes, that's normal.

If you read the Apache 2.2 mod_deflate docs, gzip is all over them. That's the compression and decompression scheme that mod_deflate uses (via the zlib library).

Answer 2

"gzip" is nothing but DEFLATE with a CRC-32 checksum and some header / footer info. What you see is just what the module is doing.