crypto/tls: don't send IP literals as SNI values.
(This relands commit
a4dcc692011bf1ceca9b1a363fd83f3e59e399ee.)
https://tools.ietf.org/html/rfc6066#section-3 states:
“Literal IPv4 and IPv6 addresses are not permitted in "HostName".”
However, if an IP literal was set as Config.ServerName (which could
happen as easily as calling Dial with an IP address) then the code would
send the IP literal as the SNI value.
This change filters out IP literals, as recognised by net.ParseIP, from
being sent as the SNI value.
Fixes #13111.
Change-Id: I6e544a78a01388f8fe98150589d073b917087f75
Reviewed-on: https://go-review.googlesource.com/16776
Run-TryBot: Adam Langley <agl@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>