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zlib browser support penetration

Medium Priority
Last Modified: 2013-11-19
I understand that if I compress my content at the server level before sending it through the Internet to a browser my webpage should load faster.

What kind of support is there for this from web browsers?  Are there any notable browsers that do NOT support zlib compression?
Could you help me find a chart/table/matrix that shows which browsers support zlib compression and which ones don't?

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So, the thing is the following, if you compress you data in the gzip format using zlib, then really all common browsers support this since a very long time, I don't have a table now, but you can use that with no care.... if you want to use any other compressing algorithm ( I actually never looked into the zlib, so I don't know in detail what/if other compressions are possible) than support might vary....

Is that enough as an answer?

Cheers, Jörg

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Top Expert 2009
To elaborate a bit on the previous comment, there are notable browsers that do not support zlib compression, but they are quite rare. Most notably:

  1. Netscape 3.0 only supports the deflate algorithm, Since Netscape Communicator 4.06 gzip compression is supported.
  2. Internet Explorer 5.5 has a bug that may give some problems, it is explained here and can be worked around from the server side: http://support.microsoft.com/kb/313712 (there's a hotfix to solve the problem).
  3. Internet Explorer 6.0 has a bug also, which can also be worked around from the server side. The SP1 of IE6 will remedy this bug. It is explained here: http://support.microsoft.com/kb/312496
  4. Opera before version 5.12 does not support gzip
  5. Many users report problems with Konqeror and gzip, but the browser should support it. A workaround from the serverside is mentioned here: http://www.codeproject.com/KB/aspnet/HttpCompressionQnD.aspx
  6. Recent versions of Safari support gzip, not sure when it started, but there's mention of bugs when you gzip the javascript (.js) files. One such report was here: http://forums.macrumors.com/showthread.php?t=527062
  7. If you use Apache, there's a lib that fixes this automatically from the serverside: CompressClientFixup.
If you want to test it with a not mentioned browser, you can try this page that serves several pages in several compression types: http://carsten.codimi.de/gzip.yaws/

Some of the information above is summarized here: http://www.http-compression.com/. The rest came from several links, news groups etc.

All in all you can pretty safely turn compression on. Many websites have it on by default without much problems. Using content negotiation you may want to switch it of for older browsers or for buggy browsers (see above).

-- Abel --
Top Expert 2009
Ah, forgot two things:

Netscape (as the info on one of the links above shows) kept having serious bugs with gzip until version 6.02 came out. Firefox has supported gzip from the very start (version 1.0).

Browsers that do not support gzip will not send the header Accept-Encoding: gzip. If it is not send, you should not gzip your content. IIS 6/7 and Apache 2+ do that correctly. But, as you can now see, some browsers do send that header but have some bugs still.
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