Fix minio compatibility. Do not append empty Transfer-Encoding header.

[andreikop]

I don't know why Transfer-Encoding: is appended, but it seems like the header is silently ignored by curl.
However when S3 auth v4 is used, this header is included to a list of signed headers and breaks authorization. At list for minio.
This PR together with #50 allows to use libs3 with minio server implementation.

My master branch contains both this PR and #50 and works with minio

[bji]

Thank you!

[bosim]

It seems to break AWS S3.
Got ErrorNotImplemented
A header you provided implies functionality that is not implemented
Header: Transfer-Encoding

[bji]

OK thanks.

[bji]

Sorry so bosim, you're saying that having Transfer-Encoding breaks functionality? So this change that I merged removed Transfer-Encoding, therefore I think you are saying that this change should be kept, and not reverted, correct?

[bosim]

Removing Transfer-Encoding gives the error I mentioned above, so basically this commit breaks AWS compatibility. I can connect fine to miniio using PR #50 with the Transfer-Encoding present (just tried).

[bji]

OK thanks for the clarification I will revert the change.

[bji]

I have reverted the change. I have to admit that I don't really actively develop libs3 anymore and am not even doing basic checks when I merge the pull requests, just trusting that the requester has done due diligence. I do look at the code to make sure that it looks sane and that I can't easily detect any attempts to put backdoors or security violations in.

I think that andreikop's change may or may not be necessary after I merge in the v4 authentication pull requests, which I have not done because they are much more significant and I feel like I have to do much more due diligence with them, which I haven't found the time/energy for yet.

[andreikop]

@bosim, which libcurl version do you use?
Could you provide dumps of:

• succesfull request without the fix to Amazon S3
• succesfull request without the fix to minio with V4 auth
• failed request to Amazon S3
  It is easier to record dumps with Wireshark, than press right button, chose Follow -> TCP stream and copy-paste the text

[bosim]

@andreikop The machine I used for testing was openSUSE LEAP 42.2, i.e. libcurl version 7.37.0-13.1

I will try to provide the dumps tomorrow.

[bosim]

@andreikop Could you maybe test #50 with the recent version of miniio to see if stuff works out for you?

[andreikop]

@bosim, at first I tried to use #50, than added this patch because libs3 sends wrong authorization.
My master contains #50 + my patch