[Twisted-Python] Isolating ISFTPServer in Conch's SFTP

[Andy Gayton]

I'm looking to create a filesystem backend for twisted that could be 
used by any filelike twisted application (sftp, webdav etc).

I've got a proof of concept filesystem interface working - IFileSystem 
.. not the best of names ;), which I'm about to try and sftp into.

ISFTPServer is a nice clean interface which it'd be easy to write an 
adapter for from my IFileSystem - but its implementation is bolted into 
FileTransferServer along with a bunch of protocol stuff ..

I had been vaguely planning to break ISFTPServer's implementation out of 
FileTransferServer and move it into a realm avatar when I got this far 
so different users could have different filesystems but now that I get 
to looking at it - FileTransferServer is brought into existance when a 
sftp sybsystem is requested by the sftp client, which happens after 
authentication ..

It's beginning to look like most of conch/ssh/session.py would need to 
move into an avatar - so the avatar for a given user could be asked for 
a shell, or a sftp subsystem and they would get the right shell/ sftp 
onto a filesystem for that user ..

I was hoping that Paul, or someone else may have some thoughts in this 
area to guide me ..

cheers,
Andy.