Sub class this and implement the code to handle callbacks generated
when we send or receive data. This can be used to give the user
an indication it is still working on a large transfer, or abort the transfer. This
class is used with
Subclass this and add any code that you want called at regular intervals when receiving data from the Ftp server.
Subclass this and add any code that you want called at regular intervals when sending data to the Ftp server.