add option to specify available encodings

[gfemec]

closes #25

[hex7c0]

+1

[Fishrock123]

Correct me if I'm wrong, but I think it always needs to have the identity fallback.

[hex7c0]

right
if you want disable deflate algorithm, you should use ['gzip', 'identity']

[dougwilson]

Right. I'm not sure if the interface should make the user include identity

[hex7c0]

before force identity, people should check the presence of their algorithms inside this module

worst case? ciao like a new superpowerful algorithm :)
['ciao', 'identity'] as option
ab -v 4 -H "Accept-Encoding: ciao" -c 1 -n 1 127.0.0.1:3000/with_compression

LOG: header received:
HTTP/1.1 200 OK
Content-Type: text/plain
Vary: Accept-Encoding
Content-Encoding: ciao
Date: Mon, 26 Jan 2015 18:59:20 GMT
Connection: close

sent with deflate algorithm https://github.com/expressjs/compression/blob/master/index.js#L172

[dougwilson]

@hex7c0 , right, that is another case that needs to be fixed and why this PR hasn't been merged just yet :)

[bjohansebas]

The way forward for this functionality would be as described in #25 (comment), which would bring breaking changes, so we need to wait for a future major release to launch it.

[bjohansebas]

I'd say we want to follow the model described in this comment, rather than making it dynamic.

So I’ll most likely close this PR, but I’d like to hear your thoughts before doing so.