fix: skip SNI for IP addresses in TLS connection

[mex]

When connecting using TLS there is an optional field, servername, for setting the Server Name Indication (SNI) but this field only makes sense to set if we are using a hostname to connect and not an IP. Since v12 of Node.js, it's been deprecated to provide an IP address as the SNI so it will be ignored at some point anyway.

This PR prevents setting servername in the TLS config if the MySQL config host field is an IP which in turn quiets this deprecation warning:

(node:1) [DEP0123] DeprecationWarning: Setting the TLS ServerName to an IP address is not permitted by RFC 6066. This will be ignored in a future version.

The logic for setting SNI to the host was originally added in #1554.

Fixes #2588

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.78%. Comparing base (e38aeea) to head (a5831ae).
⚠️ Report is 17 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3835      +/-   ##
==========================================
- Coverage   89.83%   89.78%   -0.06%     
==========================================
  Files          86       86              
  Lines       13596    13607      +11     
  Branches     1606     1607       +1     
==========================================
+ Hits        12214    12217       +3     
- Misses       1382     1390       +8     

Flag	Coverage Δ
compression-0	88.89% <100.00%> (-0.05%)	⬇️
compression-1	89.76% <100.00%> (-0.06%)	⬇️
static-parser-0	87.35% <100.00%> (-0.05%)	⬇️
static-parser-1	88.12% <100.00%> (-0.05%)	⬇️
tls-0	89.18% <0.00%> (-0.07%)	⬇️
tls-1	89.55% <100.00%> (-0.06%)	⬇️

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[bertho-zero]

It should be possible to choose the servername. I connect with an IP address, but the certificate is generated with a domain (the FQDN) in the alt_names that isn't on any public DNS.

By connecting with an IP address as host and a servername for the SSL configuration, this warning disappears.

[mex]

It should be possible to choose the servername. I connect with an IP address, but the certificate is generated with a domain (the FQDN) in the alt_names that isn't on any public DNS.

By connecting with an IP address as host and a servername for the SSL configuration, this warning disappears.

I think it makes a lot of sense to allow specifically setting the servername as you do in #3845. I considered adding it as part of this as well but I would classify it as a separate feature. If the SSL certificate does not have a FQDN/SAN, I will still need the change as proposed here.

[wellwelwel]

Thanks, @mex! It's already available in mysql2@canary and soon in the latest version too 🤝

[mex]

Perfect, thanks!