Abstract nextPacket from Connection

[invisal]

I was trying to implement cache_sha2_password. Since cache_sha2_password need several communication back and fore, it is not possible to do it with current buildAuth.

I think it is better for us to have ability to pass connection and use nextPacket. But since nextPacket is private, it is not possible to use it inside the handleHandshake.

export class Connection {
  //...
  private async _connect() {
      // ....
      await handleHandshake(this, this.client.config);
      // ....
  }
}

Another way we wrap the raw connection with another helper class. Then we just pass helper class to other function.

class ConnectionHelper {
   next(): Promise<RecievePacket>
   send(data, sequence?: number): Promise<void>
   startTls() // for future SSL support implementation
}

Then in the Connection class

class Connection {
    private raw: Deno.Conn;
    private conn: ConnectionHelper;

    private async _connect() {
       // ....
      this.conn = new ConnectionHelper(raw);
      await handleHandshake(this.conn, this.client.config);
      // ....
    }
}

[manyuanrong]

I think it is ok

[wenjoy]

@invisal What's the progress on it? Have u r alreday working on a branch? I also would like to give a hand.