feat: enable custom transports in configs

[fortuna]

This PR makes the config parser configurable. This way people can extend it with new protocols. For example, one may add an "Intra" wrapper, or a "V2Ray" wrapper, or a "Psiphon" wrapper that is configured with a separate file. Here is a hypothetical example:

go run myproxy -transport 'smart|ss://$SECRET@$HOST:$PORT' -smart_config 'config.json'

Or:

go run myproxy -transport 'smart:///usr/home/config.json|ss://$SECRET@$HOST:$PORT'

This will help @amircybersec, who wanted to add v2ray to his app and still reuse our config.

[fortuna]

Any thoughts?

[amircybersec]

This is super cool! so basically to define a new wrapper (for example vless), I need to do something like this in my code:

configParser := config.NewDefaultConfigParser()
configParser.RegisterStreamDialerWrapper("vless", wrapStreamDialerWithVLESS)

and implement wrapStreamDialerWithVLESS.

I think there are other places in the SDK where config is used and it needs to get updated. I will double check and add them to the PR.

I can also update doc.go to show some examples for this.

[jyyi1]

Code LGTM, please update the PR title to "refactor: make configs dynamically configurable".

For your example in the PR description, I'd prefer to include the config file name in the URL:

go run myproxy -transport 'smart:///usr/home/config.json|ss://$SECRET@$HOST:$PORT'

[jyyi1]

Maybe we can have another NewEmptyConfigParser()? This can be used by OutlineCLI (NewEmptyConfigParser().RegisterShadowsocksDialerWrappers()), because it only expects the ss:// config.

[amircybersec]

@jyyi1 I also think having NewEmptyConfigParser() is useful in general but in the case of Outline CLI why do we want to limit the config to ss:// only? I am working on a sock5-over-tls server that I believe would be useful to folks who are using Outline CLI.

https://github.com/amircybersec/socks5-over-tls

This way CLI users can also use fragmentation and packet split capability of the Outline SDK.

[jyyi1]

That sounds good to me, we don't have to limit the config type of Outline CLI, we can enable other VPN protocols (such as socks5 or maybe vmess) if we support them. Now we only have ss.

[amircybersec]

@jyyi1 BTW, since ConfigParser type is exported, one could just do p := new(ConfigParser) to create an empty config parser instead of NewEmptyConfigParser() but the explicit method can help too.

[fortuna]

Yeah, the zero struct is valid and can be used.

[amircybersec]

@fortuna I added a section at the end of the doc file on creating a custom config. Everything else looks good to me.

[amircybersec]

All looks good to me; I added a section to doc.go with explanation on how to define and register a new config.

[fortuna]

@jyyi1 I added your example, but this is a feature in the sense of new functionality, not a refactor.