net: rename Resolver.Dial to Resolver.DialContext before Go1.9rc1?

[rsc]

CL 37260 proposes add a new field to net.Resolver:

	// Dial is used by Go's built-in DNS resolver to make TCP and
	// UDP connections to DNS services. The Resolver will never call this
	// with names, only valid IP addresses. The Conn returned must be
	// a *TCPConn or *UDPConn as requested by the network parameter.
	// If nil the default dialer is used.
	Dial func(ctx context.Context, network, hostport string) (Conn, error)

Elevating that CL to a proposal, hopefully a quick one.

This would allow control over the source address for DNS lookups in multi-homed systems (#17404).

Discussion on #19268 suggests that the new Dial field would be an acceptable solution for "do DNS lookups using a custom server", by installing a Dial func that lies about what server it has connected to. Of course that only works if /etc/resolv.conf lists some name server. If there are no resolvers then Dial will never be called. This particular use seems a bit kludgy, but fine if it resolves that need.

/cc @bradfitz

[bradfitz]

I'm fine with this. But should it be named DialContext to be consistent with:

• https://golang.org/pkg/net/http/#Transport.DialContext
• https://golang.org/pkg/net/#Dialer.DialContext

?

/cc @nerdatmath

[rsc]

SGTM.

[benburkert]

CL 37260 added this method as Dial, should it be renamed to DialContext?

[gopherbot]

CL https://golang.org/cl/45153 mentions this issue.

[odeke-em]

@bradfitz and @rsc, @benburkert raises a great point that it seems like @nerdatmath's CL https://go-review.googlesource.com/c/37260/8/src/net/lookup.go#106 already added the proposed field and perhaps we just need to rename it to DialContext?

we just forgot to tag this issue in that CL.

Also by superficially skimming through the issue, I think after that rename, we'd have addressed @bradfitz's request in #19910 (comment) and then the issue can be marked as resolved. What do y'all think?

[bradfitz]

I think Dial is fine. Our other DialContext methods are named so because there was already a Dial in the way hogging the good name.

[bradfitz]

But I could see the consistency argument too. We're days away from an rc1, though, so it's a bit late (but still possible) to change.

@rsc, @ianlancetaylor?

[ianlancetaylor]

I think Dial is OK.