x/net/proxy: doesn't allow custom Dialers

[nathanleclaire]

If desired to use a custom Dialer as the inner, direct Dialer in the proxy package, for instance to use a net.Dialer with a configured timeout, it is not possible to use the convenience wrappers such as DialerFromEnvironment with a customized inner Dialer.

Perhaps https://github.com/golang/net/blob/master/proxy/direct.go#L14 could be changed so that Direct is an instance of type Dialer interface, not a type direct struct, and consequently users could set it however they like? Or, the dialers in PerHost (https://github.com/golang/net/blob/master/proxy/per_host.go#L15) could be exposed for modification after return from a function such as ProxyFromEnvironment.

[dweomer]

@nathanleclaire I think golang/net#38 effectively addresses this issue by implementing checks for a DialContext receiver and using it if available. I realize that this is almost 4 years old now but if you could verify that would be helpful.

[gopherbot]

Change https://golang.org/cl/168921 mentions this issue: proxy: add Dial (with context)