goroutine leak detected in the driver package: callConverter

[crobert-1]

Context
Hello, I'm currently working on open-telemetry/opentelemetry-collector-contrib#30438 to enable goleak to check for leaked goroutines.

Bug
Here's the stack trace for the leaked goroutine:

[Goroutine 9 in state select, with database/sql.(*DB).connectionOpener on top of the stack:
database/sql.(*DB).connectionOpener(0xc002123d40, {0x10895f940, 0xc002209770})
        /usr/local/Cellar/go/1.21.0/libexec/src/database/sql/sql.go:1218 +0x87
created by database/sql.OpenDB in goroutine 1
        /usr/local/Cellar/go/1.21.0/libexec/src/database/sql/sql.go:791 +0x165

I used a debugger to find the source of the leaking goroutine which is the following line:

go-hdb/driver/callconverter.go

Line 22 in 36ea7b4

var callConverter = sql.OpenDB(new(callConnector))

This line is executed when any package simply imports "github.com/SAP/go-hdb/driver". sql.OpenDB starts a goroutine to open the connection. There's currently no way to properly close the SQL DB connection as callConverter is a private variable.

Suggested solution
The best solution here would be a lazy instantiation, to only open the SQL DB connection when required. Also, the package should handle closing the connection on Close.

[stfnmllr]

should be fixed with https://github.com/SAP/go-hdb/releases/tag/v1.7.5