net: case conversion for hostname in local database

[mikioh]

The commit d96a3a2 makes hostname entries in local database lowercase forcibly during go1.6 development. I don't think it's a good idea because /etc/hosts-like local database is a last resort for name resolution and https://tools.ietf.org/html/rfc4343 never says that "don't preserve case on input and output" for some reasons; perhaps it was for internetworking with old-plain systems and it is just for future use.

I don't see any rationale for the change in d96a3a2, so can you please restore the behavior that preserves case on input and output?

Note that we know a few name resolver libraries don't preserve case of hostnames and DNS labels, for example libc for OS X/iOS that supports both unicast and multicast DNS, but I still don't think we need to do case conversion for now especially with inconsistency that providing case-converted hostnames and case-preserved DNS labels.

[bradfitz]

Why?

That commit fixed a bug. Are you proposing un-fixing that bug? Or fixing it a different way? How?

[mikioh]

Why?

I think I've already described that that commit fixed a bug in a wrong way. Like handling DNS labels, we need case insensitivity comparison with preserving case on input and output, not case conversion on input and output.

[rakyll]

Lowercased host is only preserved in the internal cache for comparison. It is not mutating anything. Could you explain the case with a snippet where it breaks things? I guess I am missing something.

[mikioh]

See golang.org/cl/17210.

[gopherbot]

CL https://golang.org/cl/17217 mentions this issue.