CLOSE is request the close of this transport but does not shutdown the connection itself.

MESSAGE is actual message, client and server should call their callbacks with the data.

NOOP is a noop packet.

OPEN is sent from the server when a new transport is opened (recheck).

PING is sent by the client.

PONG is sent by the server to respond to ping packets.

UPGRADE is sent before engine.io switches a transport to test if server and client can communicate over this transport.

Type is the type of packet.