Proxy silently ignored without `http:`

[gurgeous]

Basic Info

• Faraday Version: 1.4.1
• Ruby Version: 2.7

Issue description

Proxy silently ignored without http:. For example, if you set proxy to something:1234 it will be silently ignored. The correct proxy setting would be http://something:1234. This is an important issue because it's undocumented, difficult to debug, and can have serious consequences for crawling projects.

I propose either:

1. In ProxyOptions.from, reject strings that lack a scheme.
   or
2. In ProxyOptions.from, default to http:// for strings that lack a scheme.

Let me know if you agree with one of these options and I'l put together a PR. Thanks!

Steps to reproduce

> Faraday::ProxyOptions.from("something:1234").host
# => nil

> Faraday::ProxyOptions.from("http://something:1234").host
# => "something"

[iMacTia]

Thanks @gurgeous option 2 sounds good to me, but I have to admit I'm no expert on proxies... are we sure there's no use case where one might want to omit the protocol?

We pass the string as is to URI for parsing. something:1234 is a valid URI, although that will populate the scheme and opaque properties. It seems like a use case for mailto and similar links, which I guess would not apply to proxies.

[gurgeous]

I am not an expert either... as far as I know the only use cases are http(s) and socks? Not sure if socks is even supported yet. I'll put together a simple PR and we can see if anyone complains.

[iMacTia]

Sounds good, thanks!
I don't think we support SOCKS atm, but I remember there was some work on that in the past

[olleolleolle]

@iMacTia Reading that work, made me realize that "assume it's an HTTP proxy" is a pretty good assumption.