Check NO_PROXY env to disable proxy settings

[q0w]

Fix #5378

[SpecLad]

This isn't how no_proxy normally works. It's supposed to contain a list of domains for which a proxy is not to be used.

[pfmoore]

Also, doesn't requests pick up the NO_PROXY environment variable automatically? We shouldn't need any explicit code in pip for this. The discussion in #5378 seems pretty confused - I can't see anyone who tried the NO_PROXY environment variable¹ and confirmed it wasn't working.

As far as I can see, the expectation from the issue was for a --no-proxy option to pip that would disable any proxy settings. I'm not entirely sure how it should work, though. Should it just ignore any pip-specific proxy settings like --proxy whether specified via an option, a PIP_PROXY environment variable, or a config file? Should it explicitly remove the HTTP_PROXY, HTTPS_PROXY and NO_PROXY environment variables from the environment? As well, or instead?

Footnotes

1. At least, not correctly. Someone tried setting it to "1", but according to the documentation I can find via Google, it's supposed to be a list of servers which should be accessed without a proxy. ↩

[pfmoore]

We should not use the NO_PROXY environment variable in a non-standard way like this.

[q0w]

To not add a new optional --no-proxy argument, you can use NO_PROXY='*' to disable proxy for all domains, why not?
https://github.com/encode/httpx/blob/36f16234bc47006c7efd1b8d4b363000ab8b2b3d/tests/client/test_proxies.py#L248

[q0w]

I've tested manually NO_PROXY='*' and it works out of box with pip for disabling proxy without this patch.

[pfmoore]

I've tested manually NO_PROXY='*' and it works out of box with pip for disabling proxy without this patch.

So I guess that means there's a solution for #5378 without needing any change to pip?

[q0w]

Yes, it just needs to be documented
but it would not take precedence over --proxy arg

[pfmoore]

https://pip.pypa.io/en/stable/user_guide/#using-a-proxy-server states

by setting the standard environment-variables http_proxy, https_proxy and no_proxy.

I don't think it's up to us to document how those variables work, as they are intended to work the same as in every other application. But I wouldn't object to a brief clarifying statement, nor would I object to a note about how they relate to --proxy. Are you interested in re-purposing this PR for such a documentation change?

[q0w]

Sorry, i am not good at writing docs.

[uranusjr]

Either way I think this PR can be closed?

[q0w]

Or I can reimplement this by adding --noproxy arg for pip. @pfmoore what do you think?

[pfmoore]

Or I can reimplement this by adding --noproxy arg for pip. @pfmoore what do you think?

Given that the NO_PROXY environment variable handles this, I don't see the benefit.