Set explicit User-Agent string when accessing S3

[dmp42]

Using a distinctive UA string containing the registry version + go version would help debugging (distinguish registry queries from other systems accessing the bucket).

That UA string should be set only for the registry, and not for distribution as a library.

cc @RichardScothern

[stevvooe]

@dmp42 So, this should be set in the S3 library?

[BrianBland]

Yeah, I'm trying to see if there's any extensible way to modify the S3 client through the goamz library that would enable a change like this, would have to modify the http Client/Transport found here: https://github.com/AdRoll/goamz/blob/master/s3/s3.go#L1165

[BrianBland]

Read over the v4 auth documentation and only the Host, Content-Type and any x-amz-* headers need to be signed, so changing other headers at the final transport wouldn't break signatures. I'd suggest adding something akin to our client RequestModifier, or at least HeaderModifier (https://github.com/docker/distribution/blob/master/registry/client/transport/transport.go#L11), but interestingly enough the official http.RoundTripper docs suggest that RoundTrip should not modify the request (https://golang.org/pkg/net/http/#RoundTripper)

[stevvooe]

@BrianBland The only way to fix this would probably to refactor goamz to allow injection of an http.Client.

[RichardScothern]

+1. Do it!

On Tue, Jan 19, 2016 at 3:56 PM, Stephen Day notifications@github.com
wrote:

@BrianBland https://github.com/BrianBland The only way to fix this
would probably to refactor goamz to allow injection of an http.Client.

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#1353 (comment)
.

[RichardScothern]

Implemented.