messages using the connection of the this.
If they cannot be sent immediately, they will be queued for transmission in this. The contents of
messages will then be serialized and transmitted when the connection of the this becomes writable. In
messages are queued, the ID returned in
id will be non-zero and used as the ID argument in the message_sent
callback once the last message is sent. The callback will only be called once for the last message.
the messages to send
location for a message ID or
the number of messages to send
OK on success.