Count TLS/non-TLS connections separately, by TLS version

[deepthi]

Signed-off-by: deepthi deepthi@planetscale.com

[dveeden]

Please also count TLSv1.3 connections. I don't think I have ever seen a MySQL client that supported SSLv3 (Initially MySQL only supported TLSv1.0). And vtgate should never allow SSLv3, but I'm not sure if that's currently the case. So counts for SSLv3 are pretty much useless.

[deepthi]

TLS1.3 in go is still WIP.
golang/go#9671
The protocol versions covered here are the ones supported in go-1.10 (crypto/tls/common.go)
const (
VersionSSL30 = 0x0300
VersionTLS10 = 0x0301
VersionTLS11 = 0x0302
VersionTLS12 = 0x0303
)

I'll add a comment to the code to say that we should update our handling when we move to a newer version of go.

[sougou]

Since these are tags, it's risky to use spaces (or dots). Some value parsers may treat them as separators. Underscores are safe. Even - could cause trouble. Personally, I'd just go with SSL30, TLS10, etc.