There cannot be port in this case?

There isn't one, but because the shortUrl contains the port number, it needs to be formatted that way

shortUrl example sqlserver://[2001:0db8:85a3:0000:0000:8a2e:0370:7334]:1433.

I'm now thinking though, whether this is not appropriate for the host attribute i.e. [2001:0db8:85a3:0000:0000:8a2e:0370:7334]. What do you think?

By the way, the mariadb test is partially incorrect because it includes the port as part of the shortUrl

EDIT
For

"jdbc:mariadb:loadbalance://[2001:0660:7401:0200:0000:0000:0edf:bdd7]:33,mdb.host/mdbdb"

shortUrl becomes

"mariadb:loadbalance://2001:0660:7401:0200:0000:0000:0edf:bdd7:33"

You lost me :) I am not proficient with ip6 formats. I just see:

if (serverName.startsWith("[")) {
   portLoc = XXX
} else {
  serverName = "[" + serverName + "]";
}

and wonder, why if serverName does not start with [, then it means there is no port?

Apologies, I went neck-deep into IPv6 land. Yes, since : is a delimiter for the IPv6 parts, the only way to define a port in a URL/URI-like manner, is to wrap the address in [-] and then append the port with a :

Does this make sense, especially with regards to my point about the MariaDB tests?

Clarification, when I say

the only way to define a port in a URL/URI-like manner

, I should have said instead, "the only unambigious way to define a port in a URL/URI-like manner"

I see. I have left a comment in #1421, but that is a separate issue.