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Filename : forward.py
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#
# This file is adapted from a paramiko demo, and thus licensed under LGPL 2.1.
# Original Copyright (C) 2003-2007  Robey Pointer <robeypointer@gmail.com>
# Edits Copyright (C) 2010 The IPython Team
#
# Paramiko is free software; you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation; either version 2.1 of the License, or (at your option)
# any later version.
#
# Paramiko is distrubuted in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with Paramiko; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA  02111-1301  USA.

"""
Sample script showing how to do local port forwarding over paramiko.

This script connects to the requested SSH server and sets up local port
forwarding (the openssh -L option) from a local port through a tunneled
connection to a destination reachable from the SSH server machine.
"""

from __future__ import print_function

import logging
import select
try:  # Python 3
    import socketserver
except ImportError:  # Python 2
    import SocketServer as socketserver

logger = logging.getLogger('ssh')

class ForwardServer (socketserver.ThreadingTCPServer):
    daemon_threads = True
    allow_reuse_address = True
    

class Handler (socketserver.BaseRequestHandler):

    def handle(self):
        try:
            chan = self.ssh_transport.open_channel('direct-tcpip',
                                                   (self.chain_host, self.chain_port),
                                                   self.request.getpeername())
        except Exception as e:
            logger.debug('Incoming request to %s:%d failed: %s' % (self.chain_host,
                                                              self.chain_port,
                                                              repr(e)))
            return
        if chan is None:
            logger.debug('Incoming request to %s:%d was rejected by the SSH server.' %
                    (self.chain_host, self.chain_port))
            return

        logger.debug('Connected!  Tunnel open %r -> %r -> %r' % (self.request.getpeername(),
                                                            chan.getpeername(), (self.chain_host, self.chain_port)))
        while True:
            r, w, x = select.select([self.request, chan], [], [])
            if self.request in r:
                data = self.request.recv(1024)
                if len(data) == 0:
                    break
                chan.send(data)
            if chan in r:
                data = chan.recv(1024)
                if len(data) == 0:
                    break
                self.request.send(data)
        chan.close()
        self.request.close()
        logger.debug('Tunnel closed ')


def forward_tunnel(local_port, remote_host, remote_port, transport):
    # this is a little convoluted, but lets me configure things for the Handler
    # object.  (SocketServer doesn't give Handlers any way to access the outer
    # server normally.)
    class SubHander (Handler):
        chain_host = remote_host
        chain_port = remote_port
        ssh_transport = transport
    ForwardServer(('127.0.0.1', local_port), SubHander).serve_forever()


__all__ = ['forward_tunnel']