Fixes and improvements for multiple problems of jdbc_v2 and client_v2

[oleg-zinovev]

Summary

Contains several improvements and fixes for the v2 of the client and driver

Improvements:

• PreparedStatementImpl: getMetaData returns result set metadata using describe query
• StatementImpl: maxRows handling
• Driver: unload method fixed (DriverManager search driver for unregister by reference equality)
• HttpAPIClientHelper: added sslmode option (presents in v1), support to skip ssl validation

Fixes:

• PreparedStatementImpl: ignores question mark (?) in comments, string literals and quoted identifiers
• StatementImpl: multiline block comments trim
• HttpAPIClientHelper: null pointer exception with unpooled connection (poolControl is null)

Closes #2290

Checklist

Delete items not relevant to your PR:

• Closes Question marks '?' break queries with filters #2290
• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

[chernser]

Should it return an empty result set?
I think, null is not expected.

[oleg-zinovev]

Null is expected according to PreparedStatement javadoc:

* @return the description of a {@code ResultSet} object's columns or * {@code null} if the driver cannot return a * {@code ResultSetMetaData} object

[oleg-zinovev]

@chernser Removed

[chernser]

Thank you!

I agree that specification allows to return null, but some frameworks doesn't accept it so we need to implement this another way - at least return an empty result set.

[chernser]

@oleg-zinovev thank you for the contribution!
Would you please exclude:

• PreparedStatementImpl: getMetaData returns result set metadata using describe query - I'm working on it and have a bigger change to support more cases
• HttpAPIClientHelper: added sslmode option (presents in v1), support to skip ssl validation - We need to discuss this because why to exclude ssl validation when you do not use it. In other cases we need to support self signed certificates but need another way to do so.

Thanks!

[oleg-zinovev]

@oleg-zinovev thank you for the contribution!
Would you please exclude:

PreparedStatementImpl: getMetaData returns result set metadata using describe query - I'm working on it and have a bigger change to support more cases
HttpAPIClientHelper: added sslmode option (presents in v1), support to skip ssl validation - We need to discuss this because why to exclude ssl validation when you do not use it. In other cases we need to support self signed certificates but need another way to do so.
Thanks!

Done.
Also remove DriverHolder class.

For example:

• go client (https://clickhouse.com/docs/integrations/go) allows disable tls certificate validation via InsecureSkipVerify
• python client (https://clickhouse.com/docs/integrations/python#httpstls-arguments) allows disable tls certificate validation via verify
• jdbc-v1 (as mentioned above) allows disable tls certificate validation via sslmode

sslmode is convenient for DBeaver (and similar programs). It is much easier (in the case of a self-signed certificate) to disable its verification than to explain how to specify the server certificate correctly.
Unfortunately, in our case, the use of endpoints without encryption is prohibited.

So I hope that the ability to disable tls cert validation will be added to client_v2/jdbc_v2 :)

[chernser]

@oleg-zinovev thank you for the update!
I've run CI and will approve shortly.

As for SSL strict mode I've created a separate issue #2309
I would like implement it in the way:

• It doesn't confuses users with configuration. SSL mode can be theoretically applied to SSL auth and may be need to have another configuration
• User may need more configuration over SSL (we had a request for custom SSL factory)
  So yes, we will work on it.