FTAM — ftam/ftp issue: Setting up file transfers and transfer protocols

ftam/ftp issue: Setting up file transfers and transfer protocols
----------------------------------------------------------------

In addition to the previous issues 4177, 4183 I've raised about file
transfer and protocols I would like to recommend that a somewhat more
complete approach be taken to managing the transfer operations
(transfer, append, and insert).

The current approach doesn't allow the virtual file systems to perform
any kind of real protocol negotiation, resource/socket init, set-up
acknowledge, or resource release.

For instance, when speaking "TCP" as illustrated in Chapter 4, the
port numbers are fixed by the supported_protocols attributes. A file
system cannot change the port it would like to use on a per transfer
request basis. This can be restrictive to allowing multiple transfers
to happen in parallel or determining what file's data just came in on
a socket.

I am suggesting that an approach similar to the one used in the
Audio/Video Stream specification be used. In this case an endpoint
object would be established to represent each end of the file
transfer. There is the opportunity for simple negotiation, such as
picking protocols and port numbers.

The IDL in the A/V Stream spec is far too heavy-weight for ftam/ftp
but the concepts used for connection set-up and management are
relevant. Just using a few of the A/V flow/end-point operations like
set_peer, go_to_listen, and connect_to_peer would be sufficient.

At OOC, we have begun experimenting with IDL that supports the notion
of transfer `endpoints.' A different type of endpoint is created for
each type of protocol, so matched protocol (such as TCP) endpoints
talk to each other. And a CORBA endpoint is defined so two file
systems can always transfer if they share no other common protocols.

see above