Add support for authenticated proxies

[mikoim]

This PR allows s3cmd to use an authenticated proxy server.
fix #1128

Changed behavior

• proxy_host accepts username and password (e.g., proxy_host = username:password@hostname)
• s3cmd --configure can handle a credential from environment variable http_proxy or https_proxy (if use_https = True)

TODO

• use_https = True -> Set Proxy-Authenticate header via HTTPConnection.set_tunnel()
• use_https = False -> Need help
• replace split() with urlparse() https://github.com/s3tools/s3cmd/pull/1129/files#diff-a33e8f45f499529c23e3ee67788fb744R237-R238

[fviard]

Thank you for your contribution!
Here are my suggestions for a few improvements:

• don't use encode/decode but, "deunicodise_s" and "unicodise_s" from Utils.
  And so, there will be no need to specify the encoding.
  (as there is no issue to decode ascii with utf-8).

• Instead of creating new config entries for proxy_username, proxy_password, it would be better to reuse the proxy_host entry so, configuration is not changed.
  the id would be to support a syntax like:
  proxy_host = login:pass@myhost
  For that, nothing special to do, just at the time of usage, you have 2 choices:

  • Just detect the @ in proxy_host and split by @ and : to extract login/pass/host.

  • Use urlparse to extract the info.

• For use_https = False, it looks like that there is no nice way to do that, but I'm still thinking about it.

[mikoim]

@fviard Thank you for your advice. For backward-compatibility, proxy_host and proxy_port should be kept, but I guess that the format "login:pass@myhost" is not common. How about introducing new parameter like a proxy_url, which supports "schema://username:password@host:port/"?

[fviard]

It is a detail, but you can probably exchange the imports and have the python3 "from urlib.parse import urlparse" case first as it should now be the default case.

[fviard]

it is probably better to use split('@', 1) to avoid unexpected issues.

[fviard]

Same a previous, split(':', 1)

[fviard]

Thank your for your update and sorry for the long delay of my reply, sadly it was a very busy month :-s

@fviard Thank you for your advice. For backward-compatibility, proxy_host and proxy_port should be kept, but I guess that the format "login:pass@myhost" is not common. How about introducing new parameter like a proxy_url, which supports "schema://username:password@host:port/"?

Your point makes sense, but I'm a little bit reluctant to add a new option because of the confusion that it would induce.
(As I think that s3cmd is already a little bit scary as it has a lot of options)
And we would have still to support the proxy_host/proxy_port option for a long time for backward compatibility.

But something that could be done, I think, is to already accept url with that pattern in proxy_host.
Like, if there is a port in proxy_host, it overrides proxy_port.