defer Close your gzip handler will prevent panics from writing http headers about gziphandler

[jameshartig]

@azr Looks like d3d7d67 fixed your POC. Now when Close() is called, gw == nil which causes it to immediately return.

If you write anything inside of CatchPanic it won't be gzip'd but that's expected since its wrapping withGz. So this can be closed.

[adammck]

Ouch! That's a nasty bug. Thank you very much for reporting it, and especially for including a POC. The solution isn't immediately obvious to me, but so long as we call Reset before attempting to re-use the gzip writers (which we do), I see no harm in simply not calling Close when a panic occurs. Perhaps we should (partially) revert #8?

[azr]

Sorry I was totally wrong for you :)

[azr]

Whoops I actually found a way to reproduce: https://play.golang.org/p/zDqhbl4Nnn

log outputs : 2016/08/22 17:24:16 http: multiple response.WriteHeader calls

$ curl -H "Accept-Encoding: gzip" -i localhost:8000
HTTP/1.1 200 OK
Content-Encoding: gzip
Vary: Accept-Encoding
Date: Mon, 22 Aug 2016 15:24:18 GMT
Content-Length: 23
Content-Type: application/x-gzip

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[elithrar]

You could also just call Reset explicitly instead of Close (as a
precaution).

On Mon, Aug 22, 2016 at 8:46 AM Adam Mckaig [email protected]
wrote:

Ouch! That's a nasty bug. Thank you very much for reporting it, and
especially for including a POC. The solution isn't immediately obvious to
me, but so long as we call Reset before attempting to re-use the gzip
writers (which we do), I see no harm in simply not calling Close when a
panic occurs. Perhaps we should (partially) revert #8
#8?

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[adammck]

We already call Reset immediately after grabbing a gzw from the pool, so I think omitting the Close should be okay.

[azr]

Hey, you're welcome :)