crypto/tls, net/http: HTTPS + IPv6 literal == bogus SNI

[willmo]

Following up #13111, in Go 1.6 the SNI is still incorrectly sent when using IPv6 literals with HTTPS. HTTP encloses IPv6 literals in square brackets, but when tls prepares to send the SNI it uses net.ParseIP to check for address literals, and that doesn't know about square brackets. Hence the bracket-enclosed literal ends up being sent as the SNI.

I'm not sure if tls should handle square brackets (like x509.Certificate.VerifyHostname does), or if http should strip the brackets before setting ServerName (i.e. in tlsHost()), or what.

[gopherbot]

CL https://golang.org/cl/19704 mentions this issue.