[MERGE] Refactor loopback/paramiko/openssh/ssh connection opening

[Andrew Bennetts]

Martin Pool wrote:
[...]
> > > +    def connect_ssh(self, username, password, host, port, command):
> > > +        """Make an SSH connection, and return a pipe-like object."""
> > > +        raise NotImplementedError(self.connect_ssh)
> > > +        
> > 
> > ^-- I realize you haven't implemented this yet. but it seems you would
> > need more than a 'pipe-like' object. Either you need 2 pipes for
> > bidirectional support, or you need a socket-like object. Or maybe even a
> > real class.
> 
> I think he meant socket-like.
> 
> (We may need to be clear about just what methods can be called -- recv
> like a socket, or read like a file?)

Probably socket-like.  I'd prefer to defer worrying about the precise interface
until it's actually implemented.

> > > +class LoopbackVendor(SSHVendor):
> > > +    """SSH "vendor" that connects over a plain TCP socket, not SSH."""
> > > +    
> > > +    def connect_sftp(self, username, password, host, port):
> > > +        sock = socket.socket()
> > > +        try:
> > > +            sock.connect((host, port))
> > > +        except socket.error, e:
> > > +            raise ConnectionError('Unable to connect to SSH host %s:%s: %s'
> > > +                                  % (host, port, e))
> > > +        return SFTPClient(LoopbackSFTP(sock))
> > > +
> > 
> > ^- loopback is fairly unique, but I think it could be:
> 
> In passing I think 'loopback' is an imperfect name, because it doesn't
> really loop back to where it came from.  Instead the distinguishing
> feature is that it runs across bare unencrypted tcp.

Agreed.  However, this is a naming bug that already exists without these
changes, so I don't think this should block this merge.  Someone can easily
enough change it later when they think of a better name (and update all the
references to 'loopback' in tests, presumably).

-Andrew.