Extend client API with custom HTTP requests

[mat007]

- What I did

I made the client underlying HTTP client accessible, useful for instance for docker/cli#1034

- How I did it

Added a HTTPClient() accessor to the Client interface.

- A picture of a cute animal (not mandatory but encouraged)

[cpuguy83]

I don't really see the context of why this would be needed in the mentioned issue.

Also would it be better to add a method to get the HTTP client rather than having the API client itself perform the request? It seems weird to have the API client just do any random request.

[mat007]

I don't really see the context of why this would be needed in the mentioned issue.

It might be a bit hard to follow with much of the context being lost due to the many rebases.
Basically this was suggested by @vdemeester to be able to rewrite docker/cli@0bf781e into docker/cli@05bbb2e

Also would it be better to add a method to get the HTTP client rather than having the API client itself perform the request? It seems weird to have the API client just do any random request.

I really don't have enough experience with the design of moby and docker/CLI to answer that.
However the initial need was indeed a way to get access to the underlying HTTP client in order to use its configuration (mainly credentials), so I'd be happy with a good old GetHTTPClient().
@vdemeester any though on this?

[vdemeester]

@mat007 yeah having a exported method to get the client's http client would work too 👼

[cpuguy83]

Or something to read the credentials. Is this just the tlsconfig? We could provide a copy of the tlsconfig easily enough.

[mat007]

@cpuguy83 I changed the PR to now expose a HTTPClient getter instead.

[cpuguy83]

Should this make a copy of the client?

[mat007]

OK, I changed that. Still returning a pointer though as http.Client functions take a pointer as receptor and it's more convenient to directly get a pointer there.

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[cpuguy83]

LGTM

[thaJeztah]

LGTM