Update utils.js

[VisualFox]

This fix an issue with zlib: unexpected end of file with node v7.2.1 - Follow the PR: More lenient gzip decompression #2492 request/request#2492 -

[VisualFox]

With a more recent version of Node (7.2.1) Zlib was randomly throwing a "unexpected end of file" exception.

I think this PR summarise well the issue: request/request#2492
I simply ported this PR to iframely/lib/utils.js

My implementation is probably a bit naive (that just a simple copy and paste) but that fixed the issue. Let me know if you want me to re-factor the code differently.

[iparamonau]

Thanks for the PR. We'll need a bit of time to carefully evaluate the issue.

[VisualFox]

You are very welcome and that makes perfect sense to me. Let me know if I can help you.

The first step is probably to be able to reproduce the issue. I was getting these exceptions when testing google map and youtube, but even that was not consistent. I will say only a quarter of the requests were triggering the error. Also I was firing 10 requests in a rows, I am not sure if that was part of the problem, but I was trying to evaluate iframely in a production environment.

My fix is a bit naive too, as it was at the base more a hack to evaluate the issue. It works on my end but there are few different approach we can use.

One of them is to just pass these options:

var zlibOptions = {
flush: zlib.Z_SYNC_FLUSH,
finishFlush: zlib.Z_SYNC_FLUSH
};

to zlib.createUnzip()

I guess I didn't understand why your were using the same createUnzip method for both gzip and deflate mode, and that why I refactored the code this way.

[nleush]

Merged to develop.

[iparamonau]

@VisualFox tested and accepted. Works well. Thanks for heads up!