Allow user to configure default MotherDuck database in postgresql.conf

[naoyak]

Fixes #459

Allow the user to configure a different default MotherDuck database from my_db in postgresql.conf. This affords flexibility because there is currently no user-facing API to change the internal "default" DB in MotherDuck.

[JelteF]

Thanks a lot for the PR!

[JelteF]

Instead of overriding the default database that motherduck sets, let's instead make motherduck set the correct default database by providing the database in the connection string:

connection_string = psprintf("md:%s?motherduck_token=%s", duckdb_motherduck_default_database, duckdb_motherduck_token);

For that you need to escape the database name though using URI escaping. I think the following function should work for that:

char *
uri_escape(const char *input)
{
    StringInfoData buf;
    initStringInfo(&buf);

    while (*str)
    {
        char c = *str++;
        if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '-' || c == '_' || c == '.' || c == '~')
        {
            appendStringInfoChar(&buf, c);
        }
        else
        {
            appendStringInfo(&buf, "%%%02X", (unsigned char)c);
        }
    }

    return buf.data;
}

[naoyak]

Thanks for the tip! I didn't realize you could just stick the db name in the connection string, clean solution.

Is it ok that I just stuck the uri_escape function in the same file?

[JelteF]

Thanks a lot for your work on this. I played a bit with your changes and realized that duckdb tables were not being cleaned up when changing the default database. So I implemented a fix for that. I also updated did some small other tweaks, and updated the docs in some more places.

[Y--]

LGTM!