net: better docs for PreferGo in Resolver

[renanbastos93]

Guys, how are you?

I have a suggestion to improve doc about parameter PreferGo on struct Resolver based on a comment in another issue. #19268 (comment)

Suggestion adds more a small text:

When you use the variable PreferGo set to true you will be 
able to use your dial, If you use PreferGo set to false it will ignore 
your dial and use directly "/etc/resolv.conf "

Reference Doc:

go/src/net/lookup.go

Line 120 in a38a917

// PreferGo controls whether Go's built-in DNS resolver is preferred

[ianlancetaylor]

If I understand you correctly, you are suggesting that we clearly document that if PreferGo is set to false, then the Dial method in the Resolver will not be used. Is that correct?

[renanbastos93]

If I understand you correctly, you are suggesting that we clearly document that if PreferGo is set to false, then the Dial method in the Resolver will not be used. Is that correct?

Hello, @ianlancetaylor

I am so sorry for my English. I'm in a constant improvement in English skills.
Well, yes correctly. When set false in PreferGo it will ignore your Dial and will be using a default.

[renanbastos93]

I was thinking if you agreed to this improvement, I can open a pull request.

[ianlancetaylor]

I agree with the improvement in general, but I don't agree with the text proposed in the original message.

[renanbastos93]

I agree with the improvement in general, but I don't agree with the text proposed in the original message.

Ok, no problem.
What's your suggestion?

[ianlancetaylor]

I'm sorry, I don't have one right now. It will take some thought and this doesn't seem urgent.

[ozn17]

@ianlancetaylor , I see the documentation is updated (at https://golang.org/pkg/net/#Resolver) indicting that "PreferGo" is a switch between Go's built-in DNS resolver or CGO resolver (which uses "getaddrinfo" or "getnameinfo"). Does using CGO resolver disable us using DNS dialer? Suppose I want to use CGO resolver with custom DNS server.

[ianlancetaylor]

@ozn0417 Yes, using the cgo resolver means that it will use the DNS servers listed in /etc/resolv.conf or equivalent, and will not use whatever nameservers you want to specify. This should ideally also be part of the documentation.