text: # Copyright (C) 2003-2007  Robey Pointer <robeypointer@gmail.com>
  #
  # This file is part of paramiko.
  #
  # 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 distributed 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.,
  # 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
  
  """
  Core protocol implementation
  """
  
  import os
  import socket
  import sys
  import threading
  import time
  import weakref
  from hashlib import md5, sha1
  
  import paramiko
  from paramiko import util
  from paramiko.auth_handler import AuthHandler
  from paramiko.channel import Channel
  from paramiko.common import xffffffff, cMSG_CHANNEL_OPEN, cMSG_IGNORE, \
      cMSG_GLOBAL_REQUEST, DEBUG, MSG_KEXINIT, MSG_IGNORE, MSG_DISCONNECT, \
      MSG_DEBUG, ERROR, WARNING, cMSG_UNIMPLEMENTED, INFO, cMSG_KEXINIT, \
      cMSG_NEWKEYS, MSG_NEWKEYS, cMSG_REQUEST_SUCCESS, cMSG_REQUEST_FAILURE, \
      CONNECTION_FAILED_CODE, OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED, \
      OPEN_SUCCEEDED, cMSG_CHANNEL_OPEN_FAILURE, cMSG_CHANNEL_OPEN_SUCCESS, \
      MSG_GLOBAL_REQUEST, MSG_REQUEST_SUCCESS, MSG_REQUEST_FAILURE, \
      MSG_CHANNEL_OPEN_SUCCESS, MSG_CHANNEL_OPEN_FAILURE, MSG_CHANNEL_OPEN, \
      MSG_CHANNEL_SUCCESS, MSG_CHANNEL_FAILURE, MSG_CHANNEL_DATA, \
      MSG_CHANNEL_EXTENDED_DATA, MSG_CHANNEL_WINDOW_ADJUST, MSG_CHANNEL_REQUEST, \
      MSG_CHANNEL_EOF, MSG_CHANNEL_CLOSE
  from paramiko.compress import ZlibCompressor, ZlibDecompressor
  from paramiko.dsskey import DSSKey
  from paramiko.kex_gex import KexGex
  from paramiko.kex_group1 import KexGroup1
  from paramiko.message import Message
  from paramiko.packet import Packetizer, NeedRekeyException
  from paramiko.primes import ModulusPack
  from paramiko.py3compat import string_types, long, byte_ord, b
  from paramiko.rsakey import RSAKey
  from paramiko.ecdsakey import ECDSAKey
  from paramiko.server import ServerInterface
  from paramiko.sftp_client import SFTPClient
  from paramiko.ssh_exception import (SSHException, BadAuthenticationType,
                                      ChannelException, ProxyCommandFailure)
  from paramiko.util import retry_on_signal
  
  from Crypto.Cipher import Blowfish, AES, DES3, ARC4
  try:
      from Crypto.Util import Counter
  except ImportError:
      from paramiko.util import Counter
  
  
  # for thread cleanup
  _active_threads = []
  
  def _join_lingering_threads():
      for thr in _active_threads:
          thr.stop_thread()
  
  import atexit
  atexit.register(_join_lingering_threads)
  
  
  class Transport (threading.Thread):
      """
      An SSH Transport attaches to a stream (usually a socket), negotiates an
      encrypted session, authenticates, and then creates stream tunnels, called
      `channels <.Channel>`, across the session.  Multiple channels can be
      multiplexed across a single session (and often are, in the case of port
      forwardings).
      """
      _PROTO_ID = '2.0'
      _CLIENT_ID = 'paramiko_%s' % paramiko.__version__
  
      _preferred_ciphers = ('aes128-ctr', 'aes256-ctr', 'aes128-cbc', 'blowfish-cbc',
                            'aes256-cbc', '3des-cbc', 'arcfour128', 'arcfour256')
      _preferred_macs = ('hmac-sha1', 'hmac-md5', 'hmac-sha1-96', 'hmac-md5-96')
      _preferred_keys = ('ssh-rsa', 'ssh-dss', 'ecdsa-sha2-nistp256')
      _preferred_kex = ('diffie-hellman-group1-sha1', 'diffie-hellman-group-exchange-sha1')
      _preferred_compression = ('none',)
  
      _cipher_info = {
          'aes128-ctr': {'class': AES, 'mode': AES.MODE_CTR, 'block-size': 16, 'key-size': 16},
          'aes256-ctr': {'class': AES, 'mode': AES.MODE_CTR, 'block-size': 16, 'key-size': 32},
          'blowfish-cbc': {'class': Blowfish, 'mode': Blowfish.MODE_CBC, 'block-size': 8, 'key-size': 16},
          'aes128-cbc': {'class': AES, 'mode': AES.MODE_CBC, 'block-size': 16, 'key-size': 16},
          'aes256-cbc': {'class': AES, 'mode': AES.MODE_CBC, 'block-size': 16, 'key-size': 32},
          '3des-cbc': {'class': DES3, 'mode': DES3.MODE_CBC, 'block-size': 8, 'key-size': 24},
          'arcfour128': {'class': ARC4, 'mode': None, 'block-size': 8, 'key-size': 16},
          'arcfour256': {'class': ARC4, 'mode': None, 'block-size': 8, 'key-size': 32},
      }
  
      _mac_info = {
          'hmac-sha1': {'class': sha1, 'size': 20},
          'hmac-sha1-96': {'class': sha1, 'size': 12},
          'hmac-md5': {'class': md5, 'size': 16},
          'hmac-md5-96': {'class': md5, 'size': 12},
      }
  
      _key_info = {
          'ssh-rsa': RSAKey,
          'ssh-dss': DSSKey,
          'ecdsa-sha2-nistp256': ECDSAKey,
      }
  
      _kex_info = {
          'diffie-hellman-group1-sha1': KexGroup1,
          'diffie-hellman-group-exchange-sha1': KexGex,
      }
  
      _compression_info = {
          # zlib@openssh.com is just zlib, but only turned on after a successful
          # authentication.  openssh servers may only offer this type because
          # they've had troubles with security holes in zlib in the past.
          'zlib@openssh.com': (ZlibCompressor, ZlibDecompressor),
          'zlib': (ZlibCompressor, ZlibDecompressor),
          'none': (None, None),
      }
  
      _modulus_pack = None
  
      def __init__(self, sock):
          """
          Create a new SSH session over an existing socket, or socket-like
          object.  This only creates the `.Transport` object; it doesn't begin the
          SSH session yet.  Use `connect` or `start_client` to begin a client
          session, or `start_server` to begin a server session.
  
          If the object is not actually a socket, it must have the following
          methods:
  
          - ``send(str)``: Writes from 1 to ``len(str)`` bytes, and returns an
            int representing the number of bytes written.  Returns
            0 or raises ``EOFError`` if the stream has been closed.
          - ``recv(int)``: Reads from 1 to ``int`` bytes and returns them as a
            string.  Returns 0 or raises ``EOFError`` if the stream has been
            closed.
          - ``close()``: Closes the socket.
          - ``settimeout(n)``: Sets a (float) timeout on I/O operations.
  
          For ease of use, you may also pass in an address (as a tuple) or a host
          string as the ``sock`` argument.  (A host string is a hostname with an
          optional port (separated by ``":"``) which will be converted into a
          tuple of ``(hostname, port)``.)  A socket will be connected to this
          address and used for communication.  Exceptions from the ``socket``
          call may be thrown in this case.
  
          :param socket sock:
              a socket or socket-like object to create the session over.
          """
          if isinstance(sock, string_types):
              # convert "host:port" into (host, port)
              hl = sock.split(':', 1)
              if len(hl) == 1:
                  sock = (hl[0], 22)
              else:
                  sock = (hl[0], int(hl[1]))
          if type(sock) is tuple:
              # connect to the given (host, port)
              hostname, port = sock
              reason = 'No suitable address family'
              for (family, socktype, proto, canonname, sockaddr) in socket.getaddrinfo(hostname, port, socket.AF_UNSPEC, socket.SOCK_STREAM):
                  if socktype == socket.SOCK_STREAM:
                      af = family
                      addr = sockaddr
                      sock = socket.socket(af, socket.SOCK_STREAM)
                      try:
                          retry_on_signal(lambda: sock.connect((hostname, port)))
                      except socket.error as e:
                          reason = str(e)
                      else:
                          break
              else:
                  raise SSHException(
                      'Unable to connect to %s: %s' % (hostname, reason))
          # okay, normal socket-ish flow here...
          threading.Thread.__init__(self)
          self.setDaemon(True)
          self.sock = sock
          # Python < 2.3 doesn't have the settimeout method - RogerB
          try:
              # we set the timeout so we can check self.active periodically to
              # see if we should bail.  socket.timeout exception is never
              # propagated.
              self.sock.settimeout(0.1)
          except AttributeError:
              pass
  
          # negotiated crypto parameters
          self.packetizer = Packetizer(sock)
          self.local_version = 'SSH-' + self._PROTO_ID + '-' + self._CLIENT_ID
          self.remote_version = ''
          self.local_cipher = self.remote_cipher = ''
          self.local_kex_init = self.remote_kex_init = None
          self.local_mac = self.remote_mac = None
          self.local_compression = self.remote_compression = None
          self.session_id = None
          self.host_key_type = None
          self.host_key = None
  
          # state used during negotiation
          self.kex_engine = None
          self.H = None
          self.K = None
  
          self.active = False
          self.initial_kex_done = False
          self.in_kex = False
          self.authenticated = False
          self._expected_packet = tuple()
          self.lock = threading.Lock()    # synchronization (always higher level than write_lock)
  
          # tracking open channels
          self._channels = ChannelMap()
          self.channel_events = {}       # (id -> Event)
          self.channels_seen = {}        # (id -> True)
          self._channel_counter = 1
          self.window_size = 65536
          self.max_packet_size = 34816
          self._forward_agent_handler = None
          self._x11_handler = None
          self._tcp_handler = None
  
          self.saved_exception = None
          self.clear_to_send = threading.Event()
          self.clear_to_send_lock = threading.Lock()
          self.clear_to_send_timeout = 30.0
          self.log_name = 'paramiko.transport'
          self.logger = util.get_logger(self.log_name)
          self.packetizer.set_log(self.logger)
          self.auth_handler = None
          self.global_response = None     # response Message from an arbitrary global request
          self.completion_event = None    # user-defined event callbacks
          self.banner_timeout = 15        # how long (seconds) to wait for the SSH banner
  
          # server mode:
          self.server_mode = False
          self.server_object = None
          self.server_key_dict = {}
          self.server_accepts = []
          self.server_accept_cv = threading.Condition(self.lock)
          self.subsystem_table = {}
  
      def __repr__(self):
          """
          Returns a string representation of this object, for debugging.
          """
          out = '<paramiko.Transport at %s' % hex(long(id(self)) & xffffffff)
          if not self.active:
              out += ' (unconnected)'
          else:
              if self.local_cipher != '':
                  out += ' (cipher %s, %d bits)' % (self.local_cipher,
                                                    self._cipher_info[self.local_cipher]['key-size'] * 8)
              if self.is_authenticated():
                  out += ' (active; %d open channel(s))' % len(self._channels)
              elif self.initial_kex_done:
                  out += ' (connected; awaiting auth)'
              else:
                  out += ' (connecting)'
          out += '>'
          return out
  
      def atfork(self):
          """
          Terminate this Transport without closing the session.  On posix
          systems, if a Transport is open during process forking, both parent
          and child will share the underlying socket, but only one process can
          use the connection (without corrupting the session).  Use this method
          to clean up a Transport object without disrupting the other process.
  
          .. versionadded:: 1.5.3
          """
          self.close()
  
      def get_security_options(self):
          """
          Return a `.SecurityOptions` object which can be used to tweak the
          encryption algorithms this transport will permit (for encryption,
          digest/hash operations, public keys, and key exchanges) and the order
          of preference for them.
          """
          return SecurityOptions(self)
  
      def start_client(self, event=None):
          """
          Negotiate a new SSH2 session as a client.  This is the first step after
          creating a new `.Transport`.  A separate thread is created for protocol
          negotiation.
  
          If an event is passed in, this method returns immediately.  When
          negotiation is done (successful or not), the given ``Event`` will
          be triggered.  On failure, `is_active` will return ``False``.
  
          (Since 1.4) If ``event`` is ``None``, this method will not return until
          negotation is done.  On success, the method returns normally.
          Otherwise an SSHException is raised.
  
          After a successful negotiation, you will usually want to authenticate,
          calling `auth_password <Transport.auth_password>` or
          `auth_publickey <Transport.auth_publickey>`.
  
          .. note:: `connect` is a simpler method for connecting as a client.
  
          .. note:: After calling this method (or `start_server` or `connect`),
              you should no longer directly read from or write to the original
              socket object.
  
          :param .threading.Event event:
              an event to trigger when negotiation is complete (optional)
  
          :raises SSHException: if negotiation fails (and no ``event`` was passed
              in)
          """
          self.active = True
          if event is not None:
              # async, return immediately and let the app poll for completion
              self.completion_event = event
              self.start()
              return
  
          # synchronous, wait for a result
          self.completion_event = event = threading.Event()
          self.start()
          while True:
              event.wait(0.1)
              if not self.active:
                  e = self.get_exception()
                  if e is not None:
                      raise e
                  raise SSHException('Negotiation failed.')
              if event.isSet():
                  break
  
      def start_server(self, event=None, server=None):
          """
          Negotiate a new SSH2 session as a server.  This is the first step after
          creating a new `.Transport` and setting up your server host key(s).  A
          separate thread is created for protocol negotiation.
  
          If an event is passed in, this method returns immediately.  When
          negotiation is done (successful or not), the given ``Event`` will
          be triggered.  On failure, `is_active` will return ``False``.
  
          (Since 1.4) If ``event`` is ``None``, this method will not return until
          negotation is done.  On success, the method returns normally.
          Otherwise an SSHException is raised.
  
          After a successful negotiation, the client will need to authenticate.
          Override the methods `get_allowed_auths
          <.ServerInterface.get_allowed_auths>`, `check_auth_none
          <.ServerInterface.check_auth_none>`, `check_auth_password
          <.ServerInterface.check_auth_password>`, and `check_auth_publickey
          <.ServerInterface.check_auth_publickey>` in the given ``server`` object
          to control the authentication process.
  
          After a successful authentication, the client should request to open a
          channel.  Override `check_channel_request
          <.ServerInterface.check_channel_request>` in the given ``server``
          object to allow channels to be opened.
  
          .. note::
              After calling this method (or `start_client` or `connect`), you
              should no longer directly read from or write to the original socket
              object.
  
          :param .threading.Event event:
              an event to trigger when negotiation is complete.
          :param .ServerInterface server:
              an object used to perform authentication and create `channels
              <.Channel>`
  
          :raises SSHException: if negotiation fails (and no ``event`` was passed
              in)
          """
          if server is None:
              server = ServerInterface()
          self.server_mode = True
          self.server_object = server
          self.active = True
          if event is not None:
              # async, return immediately and let the app poll for completion
              self.completion_event = event
              self.start()
              return
  
          # synchronous, wait for a result
          self.completion_event = event = threading.Event()
          self.start()
          while True:
              event.wait(0.1)
              if not self.active:
                  e = self.get_exception()
                  if e is not None:
                      raise e
                  raise SSHException('Negotiation failed.')
              if event.isSet():
                  break
  
      def add_server_key(self, key):
          """
          Add a host key to the list of keys used for server mode.  When behaving
          as a server, the host key is used to sign certain packets during the
          SSH2 negotiation, so that the client can trust that we are who we say
          we are.  Because this is used for signing, the key must contain private
          key info, not just the public half.  Only one key of each type (RSA or
          DSS) is kept.
  
          :param .PKey key:
              the host key to add, usually an `.RSAKey` or `.DSSKey`.
          """
          self.server_key_dict[key.get_name()] = key
  
      def get_server_key(self):
          """
          Return the active host key, in server mode.  After negotiating with the
          client, this method will return the negotiated host key.  If only one
          type of host key was set with `add_server_key`, that's the only key
          that will ever be returned.  But in cases where you have set more than
          one type of host key (for example, an RSA key and a DSS key), the key
          type will be negotiated by the client, and this method will return the
          key of the type agreed on.  If the host key has not been negotiated
          yet, ``None`` is returned.  In client mode, the behavior is undefined.
  
          :return:
              host key (`.PKey`) of the type negotiated by the client, or
              ``None``.
          """
          try:
              return self.server_key_dict[self.host_key_type]
          except KeyError:
              pass
          return None
  
      def load_server_moduli(filename=None):
          """
          (optional)
          Load a file of prime moduli for use in doing group-exchange key
          negotiation in server mode.  It's a rather obscure option and can be
          safely ignored.
  
          In server mode, the remote client may request "group-exchange" key
          negotiation, which asks the server to send a random prime number that
          fits certain criteria.  These primes are pretty difficult to compute,
          so they can't be generated on demand.  But many systems contain a file
          of suitable primes (usually named something like ``/etc/ssh/moduli``).
          If you call `load_server_moduli` and it returns ``True``, then this
          file of primes has been loaded and we will support "group-exchange" in
          server mode.  Otherwise server mode will just claim that it doesn't
          support that method of key negotiation.
  
          :param str filename:
              optional path to the moduli file, if you happen to know that it's
              not in a standard location.
          :return:
              True if a moduli file was successfully loaded; False otherwise.
  
          .. note:: This has no effect when used in client mode.
          """
          Transport._modulus_pack = ModulusPack()
          # places to look for the openssh "moduli" file
          file_list = ['/etc/ssh/moduli', '/usr/local/etc/moduli']
          if filename is not None:
              file_list.insert(0, filename)
          for fn in file_list:
              try:
                  Transport._modulus_pack.read_file(fn)
                  return True
              except IOError:
                  pass
          # none succeeded
          Transport._modulus_pack = None
          return False
      load_server_moduli = staticmethod(load_server_moduli)
  
      def close(self):
          """
          Close this session, and any open channels that are tied to it.
          """
          if not self.active:
              return
          self.stop_thread()
          for chan in list(self._channels.values()):
              chan._unlink()
          self.sock.close()
  
      def get_remote_server_key(self):
          """
          Return the host key of the server (in client mode).
  
          .. note::
              Previously this call returned a tuple of ``(key type, key
              string)``. You can get the same effect by calling `.PKey.get_name`
              for the key type, and ``str(key)`` for the key string.
  
          :raises SSHException: if no session is currently active.
  
          :return: public key (`.PKey`) of the remote server
          """
          if (not self.active) or (not self.initial_kex_done):
              raise SSHException('No existing session')
          return self.host_key
  
      def is_active(self):
          """
          Return true if this session is active (open).
  
          :return:
              True if the session is still active (open); False if the session is
              closed
          """
          return self.active
  
      def open_session(self):
          """
          Request a new channel to the server, of type ``"session"``.  This is
          just an alias for calling `open_channel` with an argument of
          ``"session"``.
  
          :return: a new `.Channel`
  
          :raises SSHException: if the request is rejected or the session ends
              prematurely
          """
          return self.open_channel('session')
  
      def open_x11_channel(self, src_addr=None):
          """
          Request a new channel to the client, of type ``"x11"``.  This
          is just an alias for ``open_channel('x11', src_addr=src_addr)``.
  
          :param tuple src_addr:
              the source address (``(str, int)``) of the x11 server (port is the
              x11 port, ie. 6010)
          :return: a new `.Channel`
  
          :raises SSHException: if the request is rejected or the session ends
              prematurely
          """
          return self.open_channel('x11', src_addr=src_addr)
  
      def open_forward_agent_channel(self):
          """
          Request a new channel to the client, of type
          ``"auth-agent@openssh.com"``.
  
          This is just an alias for ``open_channel('auth-agent@openssh.com')``.
  
          :return: a new `.Channel`
  
          :raises SSHException:
              if the request is rejected or the session ends prematurely
          """
          return self.open_channel('auth-agent@openssh.com')
  
      def open_forwarded_tcpip_channel(self, src_addr, dest_addr):
          """
          Request a new channel back to the client, of type ``"forwarded-tcpip"``.
          This is used after a client has requested port forwarding, for sending
          incoming connections back to the client.
  
          :param src_addr: originator's address
          :param dest_addr: local (server) connected address
          """
          return self.open_channel('forwarded-tcpip', dest_addr, src_addr)
  
      def open_channel(self, kind, dest_addr=None, src_addr=None):
          """
          Request a new channel to the server. `Channels <.Channel>` are
          socket-like objects used for the actual transfer of data across the
          session. You may only request a channel after negotiating encryption
          (using `connect` or `start_client`) and authenticating.
  
          :param str kind:
              the kind of channel requested (usually ``"session"``,
              ``"forwarded-tcpip"``, ``"direct-tcpip"``, or ``"x11"``)
          :param tuple dest_addr:
              the destination address (address + port tuple) of this port
              forwarding, if ``kind`` is ``"forwarded-tcpip"`` or
              ``"direct-tcpip"`` (ignored for other channel types)
          :param src_addr: the source address of this port forwarding, if
              ``kind`` is ``"forwarded-tcpip"``, ``"direct-tcpip"``, or ``"x11"``
          :return: a new `.Channel` on success
  
          :raises SSHException: if the request is rejected or the session ends
              prematurely
          """
          if not self.active:
              raise SSHException('SSH session not active')
          self.lock.acquire()
          try:
              chanid = self._next_channel()
              m = Message()
              m.add_byte(cMSG_CHANNEL_OPEN)
              m.add_string(kind)
              m.add_int(chanid)
              m.add_int(self.window_size)
              m.add_int(self.max_packet_size)
              if (kind == 'forwarded-tcpip') or (kind == 'direct-tcpip'):
                  m.add_string(dest_addr[0])
                  m.add_int(dest_addr[1])
                  m.add_string(src_addr[0])
                  m.add_int(src_addr[1])
              elif kind == 'x11':
                  m.add_string(src_addr[0])
                  m.add_int(src_addr[1])
              chan = Channel(chanid)
              self._channels.put(chanid, chan)
              self.channel_events[chanid] = event = threading.Event()
              self.channels_seen[chanid] = True
              chan._set_transport(self)
              chan._set_window(self.window_size, self.max_packet_size)
          finally:
              self.lock.release()
          self._send_user_message(m)
          while True:
              event.wait(0.1)
              if not self.active:
                  e = self.get_exception()
                  if e is None:
                      e = SSHException('Unable to open channel.')
                  raise e
              if event.isSet():
                  break
          chan = self._channels.get(chanid)
          if chan is not None:
              return chan
          e = self.get_exception()
          if e is None:
              e = SSHException('Unable to open channel.')
          raise e
  
      def request_port_forward(self, address, port, handler=None):
          """
          Ask the server to forward TCP connections from a listening port on
          the server, across this SSH session.
  
          If a handler is given, that handler is called from a different thread
          whenever a forwarded connection arrives.  The handler parameters are::
  
              handler(channel, (origin_addr, origin_port), (server_addr, server_port))
  
          where ``server_addr`` and ``server_port`` are the address and port that
          the server was listening on.
  
          If no handler is set, the default behavior is to send new incoming
          forwarded connections into the accept queue, to be picked up via
          `accept`.
  
          :param str address: the address to bind when forwarding
          :param int port:
              the port to forward, or 0 to ask the server to allocate any port
          :param callable handler:
              optional handler for incoming forwarded connections, of the form
              ``func(Channel, (str, int), (str, int))``.
          :return: the port number (`int`) allocated by the server
  
          :raises SSHException: if the server refused the TCP forward request
          """
          if not self.active:
              raise SSHException('SSH session not active')
          port = int(port)
          response = self.global_request('tcpip-forward', (address, port), wait=True)
          if response is None:
              raise SSHException('TCP forwarding request denied')
          if port == 0:
              port = response.get_int()
          if handler is None:
              def default_handler(channel, src_addr, dest_addr_port):
                  #src_addr, src_port = src_addr_port
                  #dest_addr, dest_port = dest_addr_port
                  self._queue_incoming_channel(channel)
              handler = default_handler
          self._tcp_handler = handler
          return port
  
      def cancel_port_forward(self, address, port):
          """
          Ask the server to cancel a previous port-forwarding request.  No more
          connections to the given address & port will be forwarded across this
          ssh connection.
  
          :param str address: the address to stop forwarding
          :param int port: the port to stop forwarding
          """
          if not self.active:
              return
          self._tcp_handler = None
          self.global_request('cancel-tcpip-forward', (address, port), wait=True)
  
      def open_sftp_client(self):
          """
          Create an SFTP client channel from an open transport.  On success, an
          SFTP session will be opened with the remote host, and a new
          `.SFTPClient` object will be returned.
  
          :return:
              a new `.SFTPClient` referring to an sftp session (channel) across
              this transport
          """
          return SFTPClient.from_transport(self)
  
      def send_ignore(self, byte_count=None):
          """
          Send a junk packet across the encrypted link.  This is sometimes used
          to add "noise" to a connection to confuse would-be attackers.  It can
          also be used as a keep-alive for long lived connections traversing
          firewalls.
  
          :param int byte_count:
              the number of random bytes to send in the payload of the ignored
              packet -- defaults to a random number from 10 to 41.
          """
          m = Message()
          m.add_byte(cMSG_IGNORE)
          if byte_count is None:
              byte_count = (byte_ord(os.urandom(1)) % 32) + 10
          m.add_bytes(os.urandom(byte_count))
          self._send_user_message(m)
  
      def renegotiate_keys(self):
          """
          Force this session to switch to new keys.  Normally this is done
          automatically after the session hits a certain number of packets or
          bytes sent or received, but this method gives you the option of forcing
          new keys whenever you want.  Negotiating new keys causes a pause in
          traffic both ways as the two sides swap keys and do computations.  This
          method returns when the session has switched to new keys.
  
          :raises SSHException: if the key renegotiation failed (which causes the
              session to end)
          """
          self.completion_event = threading.Event()
          self._send_kex_init()
          while True:
              self.completion_event.wait(0.1)
              if not self.active:
                  e = self.get_exception()
                  if e is not None:
                      raise e
                  raise SSHException('Negotiation failed.')
              if self.completion_event.isSet():
                  break
          return
  
      def set_keepalive(self, interval):
          """
          Turn on/off keepalive packets (default is off).  If this is set, after
          ``interval`` seconds without sending any data over the connection, a
          "keepalive" packet will be sent (and ignored by the remote host).  This
          can be useful to keep connections alive over a NAT, for example.
  
          :param int interval:
              seconds to wait before sending a keepalive packet (or
              0 to disable keepalives).
          """
          self.packetizer.set_keepalive(interval,
                                        lambda x=weakref.proxy(self): x.global_request('keepalive@lag.net', wait=False))
  
      def global_request(self, kind, data=None, wait=True):
          """
          Make a global request to the remote host.  These are normally
          extensions to the SSH2 protocol.
  
          :param str kind: name of the request.
          :param tuple data:
              an optional tuple containing additional data to attach to the
              request.
          :param bool wait:
              ``True`` if this method should not return until a response is
              received; ``False`` otherwise.
          :return:
              a `.Message` containing possible additional data if the request was
              successful (or an empty `.Message` if ``wait`` was ``False``);
              ``None`` if the request was denied.
          """
          if wait:
              self.completion_event = threading.Event()
          m = Message()
          m.add_byte(cMSG_GLOBAL_REQUEST)
          m.add_string(kind)
          m.add_boolean(wait)
          if data is not None:
              m.add(*data)
          self._log(DEBUG, 'Sending global request "%s"' % kind)
          self._send_user_message(m)
          if not wait:
              return None
          while True:
              self.completion_event.wait(0.1)
              if not self.active:
                  return None
              if self.completion_event.isSet():
                  break
          return self.global_response
  
      def accept(self, timeout=None):
          """
          Return the next channel opened by the client over this transport, in
          server mode.  If no channel is opened before the given timeout, ``None``
          is returned.
  
          :param int timeout:
              seconds to wait for a channel, or ``None`` to wait forever
          :return: a new `.Channel` opened by the client
          """
          self.lock.acquire()
          try:
              if len(self.server_accepts) > 0:
                  chan = self.server_accepts.pop(0)
              else:
                  self.server_accept_cv.wait(timeout)
                  if len(self.server_accepts) > 0:
                      chan = self.server_accepts.pop(0)
                  else:
                      # timeout
                      chan = None
          finally:
              self.lock.release()
          return chan
  
      def connect(self, hostkey=None, username='', password=None, pkey=None):
          """
          Negotiate an SSH2 session, and optionally verify the server's host key
          and authenticate using a password or private key.  This is a shortcut
          for `start_client`, `get_remote_server_key`, and
          `Transport.auth_password` or `Transport.auth_publickey`.  Use those
          methods if you want more control.
  
          You can use this method immediately after creating a Transport to
          negotiate encryption with a server.  If it fails, an exception will be
          thrown.  On success, the method will return cleanly, and an encrypted
          session exists.  You may immediately call `open_channel` or
          `open_session` to get a `.Channel` object, which is used for data
          transfer.
  
          .. note::
              If you fail to supply a password or private key, this method may
              succeed, but a subsequent `open_channel` or `open_session` call may
              fail because you haven't authenticated yet.
  
          :param .PKey hostkey:
              the host key expected from the server, or ``None`` if you don't
              want to do host key verification.
          :param str username: the username to authenticate as.
          :param str password:
              a password to use for authentication, if you want to use password
              authentication; otherwise ``None``.
          :param .PKey pkey:
              a private key to use for authentication, if you want to use private
              key authentication; otherwise ``None``.
  
          :raises SSHException: if the SSH2 negotiation fails, the host key
              supplied by the server is incorrect, or authentication fails.
          """
          if hostkey is not None:
              self._preferred_keys = [hostkey.get_name()]
  
          self.start_client()
  
          # check host key if we were given one
          if hostkey is not None:
              key = self.get_remote_server_key()
              if (key.get_name() != hostkey.get_name()) or (key.asbytes() != hostkey.asbytes()):
                  self._log(DEBUG, 'Bad host key from server')
                  self._log(DEBUG, 'Expected: %s: %s' % (hostkey.get_name(), repr(hostkey.asbytes())))
                  self._log(DEBUG, 'Got     : %s: %s' % (key.get_name(), repr(key.asbytes())))
                  raise SSHException('Bad host key from server')
              self._log(DEBUG, 'Host key verified (%s)' % hostkey.get_name())
  
          if (pkey is not None) or (password is not None):
              if password is not None:
                  self._log(DEBUG, 'Attempting password auth...')
                  self.auth_password(username, password)
              else:
                  self._log(DEBUG, 'Attempting public-key auth...')
                  self.auth_publickey(username, pkey)
  
          return
  
      def get_exception(self):
          """
          Return any exception that happened during the last server request.
          This can be used to fetch more specific error information after using
          calls like `start_client`.  The exception (if any) is cleared after
          this call.
  
          :return:
              an exception, or ``None`` if there is no stored exception.
  
          .. versionadded:: 1.1
          """
          self.lock.acquire()
          try:
              e = self.saved_exception
              self.saved_exception = None
              return e
          finally:
              self.lock.release()
  
      def set_subsystem_handler(self, name, handler, *larg, **kwarg):
          """
          Set the handler class for a subsystem in server mode.  If a request
          for this subsystem is made on an open ssh channel later, this handler
          will be constructed and called -- see `.SubsystemHandler` for more
          detailed documentation.
  
          Any extra parameters (including keyword arguments) are saved and
          passed to the `.SubsystemHandler` constructor later.
  
          :param str name: name of the subsystem.
          :param class handler:
              subclass of `.SubsystemHandler` that handles this subsystem.
          """
          try:
              self.lock.acquire()
              self.subsystem_table[name] = (handler, larg, kwarg)
          finally:
              self.lock.release()
  
      def is_authenticated(self):
          """
          Return true if this session is active and authenticated.
  
          :return:
              True if the session is still open and has been authenticated
              successfully; False if authentication failed and/or the session is
              closed.
          """
          return self.active and (self.auth_handler is not None) and self.auth_handler.is_authenticated()
  
      def get_username(self):
          """
          Return the username this connection is authenticated for.  If the
          session is not authenticated (or authentication failed), this method
          returns ``None``.
  
          :return: username that was authenticated (a `str`), or ``None``.
          """
          if not self.active or (self.auth_handler is None):
              return None
          return self.auth_handler.get_username()
  
      def get_banner(self):
          """
          Return the banner supplied by the server upon connect. If no banner is
          supplied, this method returns C{None}.
  
          @return: server supplied banner, or C{None}.
          @rtype: string
          """
          if not self.active or (self.auth_handler is None):
              return None
          return self.auth_handler.banner
  
      def auth_none(self, username):
          """
          Try to authenticate to the server using no authentication at all.
          This will almost always fail.  It may be useful for determining the
          list of authentication types supported by the server, by catching the
          `.BadAuthenticationType` exception raised.
  
          :param str username: the username to authenticate as
          :return:
              `list` of auth types permissible for the next stage of
              authentication (normally empty)
  
          :raises BadAuthenticationType: if "none" authentication isn't allowed
              by the server for this user
          :raises SSHException: if the authentication failed due to a network
              error
  
          .. versionadded:: 1.5
          """
          if (not self.active) or (not self.initial_kex_done):
              raise SSHException('No existing session')
          my_event = threading.Event()
          self.auth_handler = AuthHandler(self)
          self.auth_handler.auth_none(username, my_event)
          return self.auth_handler.wait_for_response(my_event)
  
      def auth_password(self, username, password, event=None, fallback=True):
          """
          Authenticate to the server using a password.  The username and password
          are sent over an encrypted link.
  
          If an ``event`` is passed in, this method will return immediately, and
          the event will be triggered once authentication succeeds or fails.  On
          success, `is_authenticated` will return ``True``.  On failure, you may
          use `get_exception` to get more detailed error information.
  
          Since 1.1, if no event is passed, this method will block until the
          authentication succeeds or fails.  On failure, an exception is raised.
          Otherwise, the method simply returns.
  
          Since 1.5, if no event is passed and ``fallback`` is ``True`` (the
          default), if the server doesn't support plain password authentication
          but does support so-called "keyboard-interactive" mode, an attempt
          will be made to authenticate using this interactive mode.  If it fails,
          the normal exception will be thrown as if the attempt had never been
          made.  This is useful for some recent Gentoo and Debian distributions,
          which turn off plain password authentication in a misguided belief
          that interactive authentication is "more secure".  (It's not.)
  
          If the server requires multi-step authentication (which is very rare),
          this method will return a list of auth types permissible for the next
          step.  Otherwise, in the normal case, an empty list is returned.
  
          :param str username: the username to authenticate as
          :param basestring password: the password to authenticate with
          :param .threading.Event event:
              an event to trigger when the authentication attempt is complete
              (whether it was successful or not)
          :param bool fallback:
              ``True`` if an attempt at an automated "interactive" password auth
              should be made if the server doesn't support normal password auth
          :return:
              `list` of auth types permissible for the next stage of
              authentication (normally empty)
  
          :raises BadAuthenticationType: if password authentication isn't
              allowed by the server for this user (and no event was passed in)
          :raises AuthenticationException: if the authentication failed (and no
              event was passed in)
          :raises SSHException: if there was a network error
          """
          if (not self.active) or (not self.initial_kex_done):
              # we should never try to send the password unless we're on a secure link
              raise SSHException('No existing session')
          if event is None:
              my_event = threading.Event()
          else:
              my_event = event
          self.auth_handler = AuthHandler(self)
          self.auth_handler.auth_password(username, password, my_event)
          if event is not None:
              # caller wants to wait for event themselves
              return []
          try:
              return self.auth_handler.wait_for_response(my_event)
          except BadAuthenticationType as e:
              # if password auth isn't allowed, but keyboard-interactive *is*, try to fudge it
              if not fallback or ('keyboard-interactive' not in e.allowed_types):
                  raise
              try:
                  def handler(title, instructions, fields):
                      if len(fields) > 1:
                          raise SSHException('Fallback authentication failed.')
                      if len(fields) == 0:
                          # for some reason, at least on os x, a 2nd request will
                          # be made with zero fields requested.  maybe it's just
                          # to try to fake out automated scripting of the exact
                          # type we're doing here.  *shrug* :)
                          return []
                      return [password]
                  return self.auth_interactive(username, handler)
              except SSHException:
                  # attempt failed; just raise the original exception
                  raise e
  
      def auth_publickey(self, username, key, event=None):
          """
          Authenticate to the server using a private key.  The key is used to
          sign data from the server, so it must include the private part.
  
          If an ``event`` is passed in, this method will return immediately, and
          the event will be triggered once authentication succeeds or fails.  On
          success, `is_authenticated` will return ``True``.  On failure, you may
          use `get_exception` to get more detailed error information.
  
          Since 1.1, if no event is passed, this method will block until the
          authentication succeeds or fails.  On failure, an exception is raised.
          Otherwise, the method simply returns.
  
          If the server requires multi-step authentication (which is very rare),
          this method will return a list of auth types permissible for the next
          step.  Otherwise, in the normal case, an empty list is returned.
  
          :param str username: the username to authenticate as
          :param .PKey key: the private key to authenticate with
          :param .threading.Event event:
              an event to trigger when the authentication attempt is complete
              (whether it was successful or not)
          :return:
              `list` of auth types permissible for the next stage of
              authentication (normally empty)
  
          :raises BadAuthenticationType: if public-key authentication isn't
              allowed by the server for this user (and no event was passed in)
          :raises AuthenticationException: if the authentication failed (and no
              event was passed in)
          :raises SSHException: if there was a network error
          """
          if (not self.active) or (not self.initial_kex_done):
              # we should never try to authenticate unless we're on a secure link
              raise SSHException('No existing session')
          if event is None:
              my_event = threading.Event()
          else:
              my_event = event
          self.auth_handler = AuthHandler(self)
          self.auth_handler.auth_publickey(username, key, my_event)
          if event is not None:
              # caller wants to wait for event themselves
              return []
          return self.auth_handler.wait_for_response(my_event)
  
      def auth_interactive(self, username, handler, submethods=''):
          """
          Authenticate to the server interactively.  A handler is used to answer
          arbitrary questions from the server.  On many servers, this is just a
          dumb wrapper around PAM.
  
          This method will block until the authentication succeeds or fails,
          peroidically calling the handler asynchronously to get answers to
          authentication questions.  The handler may be called more than once
          if the server continues to ask questions.
  
          The handler is expected to be a callable that will handle calls of the
          form: ``handler(title, instructions, prompt_list)``.  The ``title`` is
          meant to be a dialog-window title, and the ``instructions`` are user
          instructions (both are strings).  ``prompt_list`` will be a list of
          prompts, each prompt being a tuple of ``(str, bool)``.  The string is
          the prompt and the boolean indicates whether the user text should be
          echoed.
  
          A sample call would thus be:
          ``handler('title', 'instructions', [('Password:', False)])``.
  
          The handler should return a list or tuple of answers to the server's
          questions.
  
          If the server requires multi-step authentication (which is very rare),
          this method will return a list of auth types permissible for the next
          step.  Otherwise, in the normal case, an empty list is returned.
  
          :param str username: the username to authenticate as
          :param callable handler: a handler for responding to server questions
          :param str submethods: a string list of desired submethods (optional)
          :return:
              `list` of auth types permissible for the next stage of
              authentication (normally empty).
  
          :raises BadAuthenticationType: if public-key authentication isn't
              allowed by the server for this user
          :raises AuthenticationException: if the authentication failed
          :raises SSHException: if there was a network error
  
          .. versionadded:: 1.5
          """
          if (not self.active) or (not self.initial_kex_done):
              # we should never try to authenticate unless we're on a secure link
              raise SSHException('No existing session')
          my_event = threading.Event()
          self.auth_handler = AuthHandler(self)
          self.auth_handler.auth_interactive(username, handler, my_event, submethods)
          return self.auth_handler.wait_for_response(my_event)
  
      def set_log_channel(self, name):
          """
          Set the channel for this transport's logging.  The default is
          ``"paramiko.transport"`` but it can be set to anything you want. (See
          the `.logging` module for more info.)  SSH Channels will log to a
          sub-channel of the one specified.
  
          :param str name: new channel name for logging
  
          .. versionadded:: 1.1
          """
          self.log_name = name
          self.logger = util.get_logger(name)
          self.packetizer.set_log(self.logger)
  
      def get_log_channel(self):
          """
          Return the channel name used for this transport's logging.
  
          :return: channel name as a `str`
  
          .. versionadded:: 1.2
          """
          return self.log_name
  
      def set_hexdump(self, hexdump):
          """
          Turn on/off logging a hex dump of protocol traffic at DEBUG level in
          the logs.  Normally you would want this off (which is the default),
          but if you are debugging something, it may be useful.
  
          :param bool hexdump:
              ``True`` to log protocol traffix (in hex) to the log; ``False``
              otherwise.
          """
          self.packetizer.set_hexdump(hexdump)
  
      def get_hexdump(self):
          """
          Return ``True`` if the transport is currently logging hex dumps of
          protocol traffic.
  
          :return: ``True`` if hex dumps are being logged, else ``False``.
  
          .. versionadded:: 1.4
          """
          return self.packetizer.get_hexdump()
  
      def use_compression(self, compress=True):
          """
          Turn on/off compression.  This will only have an affect before starting
          the transport (ie before calling `connect`, etc).  By default,
          compression is off since it negatively affects interactive sessions.
  
          :param bool compress:
              ``True`` to ask the remote client/server to compress traffic;
              ``False`` to refuse compression
  
          .. versionadded:: 1.5.2
          """
          if compress:
              self._preferred_compression = ('zlib@openssh.com', 'zlib', 'none')
          else:
              self._preferred_compression = ('none',)
  
      def getpeername(self):
          """
          Return the address of the remote side of this Transport, if possible.
          This is effectively a wrapper around ``'getpeername'`` on the underlying
          socket.  If the socket-like object has no ``'getpeername'`` method,
          then ``("unknown", 0)`` is returned.
  
          :return:
              the address of the remote host, if known, as a ``(str, int)``
              tuple.
          """
          gp = getattr(self.sock, 'getpeername', None)
          if gp is None:
              return 'unknown', 0
          return gp()
  
      def stop_thread(self):
          self.active = False
          self.packetizer.close()
          while self.isAlive():
              self.join(10)
  
      ###  internals...
  
      def _log(self, level, msg, *args):
          if issubclass(type(msg), list):
              for m in msg:
                  self.logger.log(level, m)
          else:
              self.logger.log(level, msg, *args)
  
      def _get_modulus_pack(self):
          """used by KexGex to find primes for group exchange"""
          return self._modulus_pack
  
      def _next_channel(self):
          """you are holding the lock"""
          chanid = self._channel_counter
          while self._channels.get(chanid) is not None:
              self._channel_counter = (self._channel_counter + 1) & 0xffffff
              chanid = self._channel_counter
          self._channel_counter = (self._channel_counter + 1) & 0xffffff
          return chanid
  
      def _unlink_channel(self, chanid):
          """used by a Channel to remove itself from the active channel list"""
          self._channels.delete(chanid)
  
      def _send_message(self, data):
          self.packetizer.send_message(data)
  
      def _send_user_message(self, data):
          """
          send a message, but block if we're in key negotiation.  this is used
          for user-initiated requests.
          """
          start = time.time()
          while True:
              self.clear_to_send.wait(0.1)
              if not self.active:
                  self._log(DEBUG, 'Dropping user packet because connection is dead.')
                  return
              self.clear_to_send_lock.acquire()
              if self.clear_to_send.isSet():
                  break
              self.clear_to_send_lock.release()
              if time.time() > start + self.clear_to_send_timeout:
                  raise SSHException('Key-exchange timed out waiting for key negotiation')
          try:
              self._send_message(data)
          finally:
              self.clear_to_send_lock.release()
  
      def _set_K_H(self, k, h):
          """used by a kex object to set the K (root key) and H (exchange hash)"""
          self.K = k
          self.H = h
          if self.session_id is None:
              self.session_id = h
  
      def _expect_packet(self, *ptypes):
          """used by a kex object to register the next packet type it expects to see"""
          self._expected_packet = tuple(ptypes)
  
      def _verify_key(self, host_key, sig):
          key = self._key_info[self.host_key_type](Message(host_key))
          if key is None:
              raise SSHException('Unknown host key type')
          if not key.verify_ssh_sig(self.H, Message(sig)):
              raise SSHException('Signature verification (%s) failed.' % self.host_key_type)
          self.host_key = key
  
      def _compute_key(self, id, nbytes):
          """id is 'A' - 'F' for the various keys used by ssh"""
          m = Message()
          m.add_mpint(self.K)
          m.add_bytes(self.H)
          m.add_byte(b(id))
          m.add_bytes(self.session_id)
          out = sofar = sha1(m.asbytes()).digest()
          while len(out) < nbytes:
              m = Message()
              m.add_mpint(self.K)
              m.add_bytes(self.H)
              m.add_bytes(sofar)
              digest = sha1(m.asbytes()).digest()
              out += digest
              sofar += digest
          return out[:nbytes]
  
      def _get_cipher(self, name, key, iv):
          if name not in self._cipher_info:
              raise SSHException('Unknown client cipher ' + name)
          if name in ('arcfour128', 'arcfour256'):
              # arcfour cipher
              cipher = self._cipher_info[name]['class'].new(key)
              # as per RFC 4345, the first 1536 bytes of keystream
              # generated by the cipher MUST be discarded
              cipher.encrypt(" " * 1536)
              return cipher
          elif name.endswith("-ctr"):
              # CTR modes, we need a counter
              counter = Counter.new(nbits=self._cipher_info[name]['block-size'] * 8, initial_value=util.inflate_long(iv, True))
              return self._cipher_info[name]['class'].new(key, self._cipher_info[name]['mode'], iv, counter)
          else:
              return self._cipher_info[name]['class'].new(key, self._cipher_info[name]['mode'], iv)
  
      def _set_forward_agent_handler(self, handler):
          if handler is None:
              def default_handler(channel):
                  self._queue_incoming_channel(channel)
              self._forward_agent_handler = default_handler
          else:
              self._forward_agent_handler = handler
  
      def _set_x11_handler(self, handler):
          # only called if a channel has turned on x11 forwarding
          if handler is None:
              # by default, use the same mechanism as accept()
              def default_handler(channel, src_addr_port):
                  self._queue_incoming_channel(channel)
              self._x11_handler = default_handler
          else:
              self._x11_handler = handler
  
      def _queue_incoming_channel(self, channel):
          self.lock.acquire()
          try:
              self.server_accepts.append(channel)
              self.server_accept_cv.notify()
          finally:
              self.lock.release()
  
      def run(self):
          # (use the exposed "run" method, because if we specify a thread target
          # of a private method, threading.Thread will keep a reference to it
          # indefinitely, creating a GC cycle and not letting Transport ever be
          # GC'd. it's a bug in Thread.)
  
          # Hold reference to 'sys' so we can test sys.modules to detect
          # interpreter shutdown.
          self.sys = sys
  
          # active=True occurs before the thread is launched, to avoid a race
          _active_threads.append(self)
          if self.server_mode:
              self._log(DEBUG, 'starting thread (server mode): %s' % hex(long(id(self)) & xffffffff))
          else:
              self._log(DEBUG, 'starting thread (client mode): %s' % hex(long(id(self)) & xffffffff))
          try:
              try:
                  self.packetizer.write_all(b(self.local_version + '\r\n'))
                  self._check_banner()
                  self._send_kex_init()
                  self._expect_packet(MSG_KEXINIT)
  
                  while self.active:
                      if self.packetizer.need_rekey() and not self.in_kex:
                          self._send_kex_init()
                      try:
                          ptype, m = self.packetizer.read_message()
                      except NeedRekeyException:
                          continue
                      if ptype == MSG_IGNORE:
                          continue
                      elif ptype == MSG_DISCONNECT:
                          self._parse_disconnect(m)
                          self.active = False
                          self.packetizer.close()
                          break
                      elif ptype == MSG_DEBUG:
                          self._parse_debug(m)
                          continue
                      if len(self._expected_packet) > 0:
                          if ptype not in self._expected_packet:
                              raise SSHException('Expecting packet from %r, got %d' % (self._expected_packet, ptype))
                          self._expected_packet = tuple()
                          if (ptype >= 30) and (ptype <= 39):
                              self.kex_engine.parse_next(ptype, m)
                              continue
  
                      if ptype in self._handler_table:
                          self._handler_table[ptype](self, m)
                      elif ptype in self._channel_handler_table:
                          chanid = m.get_int()
                          chan = self._channels.get(chanid)
                          if chan is not None:
                              self._channel_handler_table[ptype](chan, m)
                          elif chanid in self.channels_seen:
                              self._log(DEBUG, 'Ignoring message for dead channel %d' % chanid)
                          else:
                              self._log(ERROR, 'Channel request for unknown channel %d' % chanid)
                              self.active = False
                              self.packetizer.close()
                      elif (self.auth_handler is not None) and (ptype in self.auth_handler._handler_table):
                          self.auth_handler._handler_table[ptype](self.auth_handler, m)
                      else:
                          self._log(WARNING, 'Oops, unhandled type %d' % ptype)
                          msg = Message()
                          msg.add_byte(cMSG_UNIMPLEMENTED)
                          msg.add_int(m.seqno)
                          self._send_message(msg)
              except SSHException as e:
                  self._log(ERROR, 'Exception: ' + str(e))
                  self._log(ERROR, util.tb_strings())
                  self.saved_exception = e
              except EOFError as e:
                  self._log(DEBUG, 'EOF in transport thread')
                  #self._log(DEBUG, util.tb_strings())
                  self.saved_exception = e
              except socket.error as e:
                  if type(e.args) is tuple:
                      if e.args:
                          emsg = '%s (%d)' % (e.args[1], e.args[0])
                      else:  # empty tuple, e.g. socket.timeout
                          emsg = str(e) or repr(e)
                  else:
                      emsg = e.args
                  self._log(ERROR, 'Socket exception: ' + emsg)
                  self.saved_exception = e
              except Exception as e:
                  self._log(ERROR, 'Unknown exception: ' + str(e))
                  self._log(ERROR, util.tb_strings())
                  self.saved_exception = e
              _active_threads.remove(self)
              for chan in list(self._channels.values()):
                  chan._unlink()
              if self.active:
                  self.active = False
                  self.packetizer.close()
                  if self.completion_event is not None:
                      self.completion_event.set()
                  if self.auth_handler is not None:
                      self.auth_handler.abort()
                  for event in self.channel_events.values():
                      event.set()
                  try:
                      self.lock.acquire()
                      self.server_accept_cv.notify()
                  finally:
                      self.lock.release()
              self.sock.close()
          except:
              # Don't raise spurious 'NoneType has no attribute X' errors when we
              # wake up during interpreter shutdown. Or rather -- raise
              # everything *if* sys.modules (used as a convenient sentinel)
              # appears to still exist.
              if self.sys.modules is not None:
                  raise
  
      ###  protocol stages
  
      def _negotiate_keys(self, m):
          # throws SSHException on anything unusual
          self.clear_to_send_lock.acquire()
          try:
              self.clear_to_send.clear()
          finally:
              self.clear_to_send_lock.release()
          if self.local_kex_init is None:
              # remote side wants to renegotiate
              self._send_kex_init()
          self._parse_kex_init(m)
          self.kex_engine.start_kex()
  
      def _check_banner(self):
          # this is slow, but we only have to do it once
          for i in range(100):
              # give them 15 seconds for the first line, then just 2 seconds
              # each additional line.  (some sites have very high latency.)
              if i == 0:
                  timeout = self.banner_timeout
              else:
                  timeout = 2
              try:
                  buf = self.packetizer.readline(timeout)
              except ProxyCommandFailure:
                  raise
              except Exception as e:
                  raise SSHException('Error reading SSH protocol banner' + str(e))
              if buf[:4] == 'SSH-':
                  break
              self._log(DEBUG, 'Banner: ' + buf)
          if buf[:4] != 'SSH-':
              raise SSHException('Indecipherable protocol version "' + buf + '"')
          # save this server version string for later
          self.remote_version = buf
          # pull off any attached comment
          comment = ''
          i = buf.find(' ')
          if i >= 0:
              comment = buf[i+1:]
              buf = buf[:i]
          # parse out version string and make sure it matches
          segs = buf.split('-', 2)
          if len(segs) < 3:
              raise SSHException('Invalid SSH banner')
          version = segs[1]
          client = segs[2]
          if version != '1.99' and version != '2.0':
              raise SSHException('Incompatible version (%s instead of 2.0)' % (version,))
          self._log(INFO, 'Connected (version %s, client %s)' % (version, client))
  
      def _send_kex_init(self):
          """
          announce to the other side that we'd like to negotiate keys, and what
          kind of key negotiation we support.
          """
          self.clear_to_send_lock.acquire()
          try:
              self.clear_to_send.clear()
          finally:
              self.clear_to_send_lock.release()
          self.in_kex = True
          if self.server_mode:
              if (self._modulus_pack is None) and ('diffie-hellman-group-exchange-sha1' in self._preferred_kex):
                  # can't do group-exchange if we don't have a pack of potential primes
                  pkex = list(self.get_security_options().kex)
                  pkex.remove('diffie-hellman-group-exchange-sha1')
                  self.get_security_options().kex = pkex
              available_server_keys = list(filter(list(self.server_key_dict.keys()).__contains__,
                                                  self._preferred_keys))
          else:
              available_server_keys = self._preferred_keys
  
          m = Message()
          m.add_byte(cMSG_KEXINIT)
          m.add_bytes(os.urandom(16))
          m.add_list(self._preferred_kex)
          m.add_list(available_server_keys)
          m.add_list(self._preferred_ciphers)
          m.add_list(self._preferred_ciphers)
          m.add_list(self._preferred_macs)
          m.add_list(self._preferred_macs)
          m.add_list(self._preferred_compression)
          m.add_list(self._preferred_compression)
          m.add_string(bytes())
          m.add_string(bytes())
          m.add_boolean(False)
          m.add_int(0)
          # save a copy for later (needed to compute a hash)
          self.local_kex_init = m.asbytes()
          self._send_message(m)
  
      def _parse_kex_init(self, m):
          cookie = m.get_bytes(16)
          kex_algo_list = m.get_list()
          server_key_algo_list = m.get_list()
          client_encrypt_algo_list = m.get_list()
          server_encrypt_algo_list = m.get_list()
          client_mac_algo_list = m.get_list()
          server_mac_algo_list = m.get_list()
          client_compress_algo_list = m.get_list()
          server_compress_algo_list = m.get_list()
          client_lang_list = m.get_list()
          server_lang_list = m.get_list()
          kex_follows = m.get_boolean()
          unused = m.get_int()
  
          self._log(DEBUG, 'kex algos:' + str(kex_algo_list) + ' server key:' + str(server_key_algo_list) +
                    ' client encrypt:' + str(client_encrypt_algo_list) +
                    ' server encrypt:' + str(server_encrypt_algo_list) +
                    ' client mac:' + str(client_mac_algo_list) +
                    ' server mac:' + str(server_mac_algo_list) +
                    ' client compress:' + str(client_compress_algo_list) +
                    ' server compress:' + str(server_compress_algo_list) +
                    ' client lang:' + str(client_lang_list) +
                    ' server lang:' + str(server_lang_list) +
                    ' kex follows?' + str(kex_follows))
  
          # as a server, we pick the first item in the client's list that we support.
          # as a client, we pick the first item in our list that the server supports.
          if self.server_mode:
              agreed_kex = list(filter(self._preferred_kex.__contains__, kex_algo_list))
          else:
              agreed_kex = list(filter(kex_algo_list.__contains__, self._preferred_kex))
          if len(agreed_kex) == 0:
              raise SSHException('Incompatible ssh peer (no acceptable kex algorithm)')
          self.kex_engine = self._kex_info[agreed_kex[0]](self)
  
          if self.server_mode:
              available_server_keys = list(filter(list(self.server_key_dict.keys()).__contains__,
                                                  self._preferred_keys))
              agreed_keys = list(filter(available_server_keys.__contains__, server_key_algo_list))
          else:
              agreed_keys = list(filter(server_key_algo_list.__contains__, self._preferred_keys))
          if len(agreed_keys) == 0:
              raise SSHException('Incompatible ssh peer (no acceptable host key)')
          self.host_key_type = agreed_keys[0]
          if self.server_mode and (self.get_server_key() is None):
              raise SSHException('Incompatible ssh peer (can\'t match requested host key type)')
  
          if self.server_mode:
              agreed_local_ciphers = list(filter(self._preferred_ciphers.__contains__,
                                             server_encrypt_algo_list))
              agreed_remote_ciphers = list(filter(self._preferred_ciphers.__contains__,
                                            client_encrypt_algo_list))
          else:
              agreed_local_ciphers = list(filter(client_encrypt_algo_list.__contains__,
                                            self._preferred_ciphers))
              agreed_remote_ciphers = list(filter(server_encrypt_algo_list.__contains__,
                                             self._preferred_ciphers))
          if (len(agreed_local_ciphers) == 0) or (len(agreed_remote_ciphers) == 0):
              raise SSHException('Incompatible ssh server (no acceptable ciphers)')
          self.local_cipher = agreed_local_ciphers[0]
          self.remote_cipher = agreed_remote_ciphers[0]
          self._log(DEBUG, 'Ciphers agreed: local=%s, remote=%s' % (self.local_cipher, self.remote_cipher))
  
          if self.server_mode:
              agreed_remote_macs = list(filter(self._preferred_macs.__contains__, client_mac_algo_list))
              agreed_local_macs = list(filter(self._preferred_macs.__contains__, server_mac_algo_list))
          else:
              agreed_local_macs = list(filter(client_mac_algo_list.__contains__, self._preferred_macs))
              agreed_remote_macs = list(filter(server_mac_algo_list.__contains__, self._preferred_macs))
          if (len(agreed_local_macs) == 0) or (len(agreed_remote_macs) == 0):
              raise SSHException('Incompatible ssh server (no acceptable macs)')
          self.local_mac = agreed_local_macs[0]
          self.remote_mac = agreed_remote_macs[0]
  
          if self.server_mode:
              agreed_remote_compression = list(filter(self._preferred_compression.__contains__, client_compress_algo_list))
              agreed_local_compression = list(filter(self._preferred_compression.__contains__, server_compress_algo_list))
          else:
              agreed_local_compression = list(filter(client_compress_algo_list.__contains__, self._preferred_compression))
              agreed_remote_compression = list(filter(server_compress_algo_list.__contains__, self._preferred_compression))
          if (len(agreed_local_compression) == 0) or (len(agreed_remote_compression) == 0):
              raise SSHException('Incompatible ssh server (no acceptable compression) %r %r %r' % (agreed_local_compression, agreed_remote_compression, self._preferred_compression))
          self.local_compression = agreed_local_compression[0]
          self.remote_compression = agreed_remote_compression[0]
  
          self._log(DEBUG, 'using kex %s; server key type %s; cipher: local %s, remote %s; mac: local %s, remote %s; compression: local %s, remote %s' %
                    (agreed_kex[0], self.host_key_type, self.local_cipher, self.remote_cipher, self.local_mac,
                     self.remote_mac, self.local_compression, self.remote_compression))
  
          # save for computing hash later...
          # now wait!  openssh has a bug (and others might too) where there are
          # actually some extra bytes (one NUL byte in openssh's case) added to
          # the end of the packet but not parsed.  turns out we need to throw
          # away those bytes because they aren't part of the hash.
          self.remote_kex_init = cMSG_KEXINIT + m.get_so_far()
  
      def _activate_inbound(self):
          """switch on newly negotiated encryption parameters for inbound traffic"""
          block_size = self._cipher_info[self.remote_cipher]['block-size']
          if self.server_mode:
              IV_in = self._compute_key('A', block_size)
              key_in = self._compute_key('C', self._cipher_info[self.remote_cipher]['key-size'])
          else:
              IV_in = self._compute_key('B', block_size)
              key_in = self._compute_key('D', self._cipher_info[self.remote_cipher]['key-size'])
          engine = self._get_cipher(self.remote_cipher, key_in, IV_in)
          mac_size = self._mac_info[self.remote_mac]['size']
          mac_engine = self._mac_info[self.remote_mac]['class']
          # initial mac keys are done in the hash's natural size (not the potentially truncated
          # transmission size)
          if self.server_mode:
              mac_key = self._compute_key('E', mac_engine().digest_size)
          else:
              mac_key = self._compute_key('F', mac_engine().digest_size)
          self.packetizer.set_inbound_cipher(engine, block_size, mac_engine, mac_size, mac_key)
          compress_in = self._compression_info[self.remote_compression][1]
          if (compress_in is not None) and ((self.remote_compression != 'zlib@openssh.com') or self.authenticated):
              self._log(DEBUG, 'Switching on inbound compression ...')
              self.packetizer.set_inbound_compressor(compress_in())
  
      def _activate_outbound(self):
          """switch on newly negotiated encryption parameters for outbound traffic"""
          m = Message()
          m.add_byte(cMSG_NEWKEYS)
          self._send_message(m)
          block_size = self._cipher_info[self.local_cipher]['block-size']
          if self.server_mode:
              IV_out = self._compute_key('B', block_size)
              key_out = self._compute_key('D', self._cipher_info[self.local_cipher]['key-size'])
          else:
              IV_out = self._compute_key('A', block_size)
              key_out = self._compute_key('C', self._cipher_info[self.local_cipher]['key-size'])
          engine = self._get_cipher(self.local_cipher, key_out, IV_out)
          mac_size = self._mac_info[self.local_mac]['size']
          mac_engine = self._mac_info[self.local_mac]['class']
          # initial mac keys are done in the hash's natural size (not the potentially truncated
          # transmission size)
          if self.server_mode:
              mac_key = self._compute_key('F', mac_engine().digest_size)
          else:
              mac_key = self._compute_key('E', mac_engine().digest_size)
          sdctr = self.local_cipher.endswith('-ctr')
          self.packetizer.set_outbound_cipher(engine, block_size, mac_engine, mac_size, mac_key, sdctr)
          compress_out = self._compression_info[self.local_compression][0]
          if (compress_out is not None) and ((self.local_compression != 'zlib@openssh.com') or self.authenticated):
              self._log(DEBUG, 'Switching on outbound compression ...')
              self.packetizer.set_outbound_compressor(compress_out())
          if not self.packetizer.need_rekey():
              self.in_kex = False
          # we always expect to receive NEWKEYS now
          self._expect_packet(MSG_NEWKEYS)
  
      def _auth_trigger(self):
          self.authenticated = True
          # delayed initiation of compression
          if self.local_compression == 'zlib@openssh.com':
              compress_out = self._compression_info[self.local_compression][0]
              self._log(DEBUG, 'Switching on outbound compression ...')
              self.packetizer.set_outbound_compressor(compress_out())
          if self.remote_compression == 'zlib@openssh.com':
              compress_in = self._compression_info[self.remote_compression][1]
              self._log(DEBUG, 'Switching on inbound compression ...')
              self.packetizer.set_inbound_compressor(compress_in())
  
      def _parse_newkeys(self, m):
          self._log(DEBUG, 'Switch to new keys ...')
          self._activate_inbound()
          # can also free a bunch of stuff here
          self.local_kex_init = self.remote_kex_init = None
          self.K = None
          self.kex_engine = None
          if self.server_mode and (self.auth_handler is None):
              # create auth handler for server mode
              self.auth_handler = AuthHandler(self)
          if not self.initial_kex_done:
              # this was the first key exchange
              self.initial_kex_done = True
          # send an event?
          if self.completion_event is not None:
              self.completion_event.set()
          # it's now okay to send data again (if this was a re-key)
          if not self.packetizer.need_rekey():
              self.in_kex = False
          self.clear_to_send_lock.acquire()
          try:
              self.clear_to_send.set()
          finally:
              self.clear_to_send_lock.release()
          return
  
      def _parse_disconnect(self, m):
          code = m.get_int()
          desc = m.get_text()
          self._log(INFO, 'Disconnect (code %d): %s' % (code, desc))
  
      def _parse_global_request(self, m):
          kind = m.get_text()
          self._log(DEBUG, 'Received global request "%s"' % kind)
          want_reply = m.get_boolean()
          if not self.server_mode:
              self._log(DEBUG, 'Rejecting "%s" global request from server.' % kind)
              ok = False
          elif kind == 'tcpip-forward':
              address = m.get_text()
              port = m.get_int()
              ok = self.server_object.check_port_forward_request(address, port)
              if ok:
                  ok = (ok,)
          elif kind == 'cancel-tcpip-forward':
              address = m.get_text()
              port = m.get_int()
              self.server_object.cancel_port_forward_request(address, port)
              ok = True
          else:
              ok = self.server_object.check_global_request(kind, m)
          extra = ()
          if type(ok) is tuple:
              extra = ok
              ok = True
          if want_reply:
              msg = Message()
              if ok:
                  msg.add_byte(cMSG_REQUEST_SUCCESS)
                  msg.add(*extra)
              else:
                  msg.add_byte(cMSG_REQUEST_FAILURE)
              self._send_message(msg)
  
      def _parse_request_success(self, m):
          self._log(DEBUG, 'Global request successful.')
          self.global_response = m
          if self.completion_event is not None:
              self.completion_event.set()
  
      def _parse_request_failure(self, m):
          self._log(DEBUG, 'Global request denied.')
          self.global_response = None
          if self.completion_event is not None:
              self.completion_event.set()
  
      def _parse_channel_open_success(self, m):
          chanid = m.get_int()
          server_chanid = m.get_int()
          server_window_size = m.get_int()
          server_max_packet_size = m.get_int()
          chan = self._channels.get(chanid)
          if chan is None:
              self._log(WARNING, 'Success for unrequested channel! [??]')
              return
          self.lock.acquire()
          try:
              chan._set_remote_channel(server_chanid, server_window_size, server_max_packet_size)
              self._log(INFO, 'Secsh channel %d opened.' % chanid)
              if chanid in self.channel_events:
                  self.channel_events[chanid].set()
                  del self.channel_events[chanid]
          finally:
              self.lock.release()
          return
  
      def _parse_channel_open_failure(self, m):
          chanid = m.get_int()
          reason = m.get_int()
          reason_str = m.get_text()
          lang = m.get_text()
          reason_text = CONNECTION_FAILED_CODE.get(reason, '(unknown code)')
          self._log(INFO, 'Secsh channel %d open FAILED: %s: %s' % (chanid, reason_str, reason_text))
          self.lock.acquire()
          try:
              self.saved_exception = ChannelException(reason, reason_text)
              if chanid in self.channel_events:
                  self._channels.delete(chanid)
                  if chanid in self.channel_events:
                      self.channel_events[chanid].set()
                      del self.channel_events[chanid]
          finally:
              self.lock.release()
          return
  
      def _parse_channel_open(self, m):
          kind = m.get_text()
          chanid = m.get_int()
          initial_window_size = m.get_int()
          max_packet_size = m.get_int()
          reject = False
          if (kind == 'auth-agent@openssh.com') and (self._forward_agent_handler is not None):
              self._log(DEBUG, 'Incoming forward agent connection')
              self.lock.acquire()
              try:
                  my_chanid = self._next_channel()
              finally:
                  self.lock.release()
          elif (kind == 'x11') and (self._x11_handler is not None):
              origin_addr = m.get_text()
              origin_port = m.get_int()
              self._log(DEBUG, 'Incoming x11 connection from %s:%d' % (origin_addr, origin_port))
              self.lock.acquire()
              try:
                  my_chanid = self._next_channel()
              finally:
                  self.lock.release()
          elif (kind == 'forwarded-tcpip') and (self._tcp_handler is not None):
              server_addr = m.get_text()
              server_port = m.get_int()
              origin_addr = m.get_text()
              origin_port = m.get_int()
              self._log(DEBUG, 'Incoming tcp forwarded connection from %s:%d' % (origin_addr, origin_port))
              self.lock.acquire()
              try:
                  my_chanid = self._next_channel()
              finally:
                  self.lock.release()
          elif not self.server_mode:
              self._log(DEBUG, 'Rejecting "%s" channel request from server.' % kind)
              reject = True
              reason = OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED
          else:
              self.lock.acquire()
              try:
                  my_chanid = self._next_channel()
              finally:
                  self.lock.release()
              if kind == 'direct-tcpip':
                  # handle direct-tcpip requests comming from the client
                  dest_addr = m.get_text()
                  dest_port = m.get_int()
                  origin_addr = m.get_text()
                  origin_port = m.get_int()
                  reason = self.server_object.check_channel_direct_tcpip_request(
                      my_chanid, (origin_addr, origin_port), (dest_addr, dest_port))
              else:
                  reason = self.server_object.check_channel_request(kind, my_chanid)
              if reason != OPEN_SUCCEEDED:
                  self._log(DEBUG, 'Rejecting "%s" channel request from client.' % kind)
                  reject = True
          if reject:
              msg = Message()
              msg.add_byte(cMSG_CHANNEL_OPEN_FAILURE)
              msg.add_int(chanid)
              msg.add_int(reason)
              msg.add_string('')
              msg.add_string('en')
              self._send_message(msg)
              return
  
          chan = Channel(my_chanid)
          self.lock.acquire()
          try:
              self._channels.put(my_chanid, chan)
              self.channels_seen[my_chanid] = True
              chan._set_transport(self)
              chan._set_window(self.window_size, self.max_packet_size)
              chan._set_remote_channel(chanid, initial_window_size, max_packet_size)
          finally:
              self.lock.release()
          m = Message()
          m.add_byte(cMSG_CHANNEL_OPEN_SUCCESS)
          m.add_int(chanid)
          m.add_int(my_chanid)
          m.add_int(self.window_size)
          m.add_int(self.max_packet_size)
          self._send_message(m)
          self._log(INFO, 'Secsh channel %d (%s) opened.', my_chanid, kind)
          if kind == 'auth-agent@openssh.com':
              self._forward_agent_handler(chan)
          elif kind == 'x11':
              self._x11_handler(chan, (origin_addr, origin_port))
          elif kind == 'forwarded-tcpip':
              chan.origin_addr = (origin_addr, origin_port)
              self._tcp_handler(chan, (origin_addr, origin_port), (server_addr, server_port))
          else:
              self._queue_incoming_channel(chan)
  
      def _parse_debug(self, m):
          always_display = m.get_boolean()
          msg = m.get_string()
          lang = m.get_string()
          self._log(DEBUG, 'Debug msg: ' + util.safe_string(msg))
  
      def _get_subsystem_handler(self, name):
          try:
              self.lock.acquire()
              if name not in self.subsystem_table:
                  return None, [], {}
              return self.subsystem_table[name]
          finally:
              self.lock.release()
  
      _handler_table = {
          MSG_NEWKEYS: _parse_newkeys,
          MSG_GLOBAL_REQUEST: _parse_global_request,
          MSG_REQUEST_SUCCESS: _parse_request_success,
          MSG_REQUEST_FAILURE: _parse_request_failure,
          MSG_CHANNEL_OPEN_SUCCESS: _parse_channel_open_success,
          MSG_CHANNEL_OPEN_FAILURE: _parse_channel_open_failure,
          MSG_CHANNEL_OPEN: _parse_channel_open,
          MSG_KEXINIT: _negotiate_keys,
      }
  
      _channel_handler_table = {
          MSG_CHANNEL_SUCCESS: Channel._request_success,
          MSG_CHANNEL_FAILURE: Channel._request_failed,
          MSG_CHANNEL_DATA: Channel._feed,
          MSG_CHANNEL_EXTENDED_DATA: Channel._feed_extended,
          MSG_CHANNEL_WINDOW_ADJUST: Channel._window_adjust,
          MSG_CHANNEL_REQUEST: Channel._handle_request,
          MSG_CHANNEL_EOF: Channel._handle_eof,
          MSG_CHANNEL_CLOSE: Channel._handle_close,
      }
  
  
  class SecurityOptions (object):
      """
      Simple object containing the security preferences of an ssh transport.
      These are tuples of acceptable ciphers, digests, key types, and key
      exchange algorithms, listed in order of preference.
  
      Changing the contents and/or order of these fields affects the underlying
      `.Transport` (but only if you change them before starting the session).
      If you try to add an algorithm that paramiko doesn't recognize,
      ``ValueError`` will be raised.  If you try to assign something besides a
      tuple to one of the fields, ``TypeError`` will be raised.
      """
      #__slots__ = [ 'ciphers', 'digests', 'key_types', 'kex', 'compression', '_transport' ]
      __slots__ = '_transport'
  
      def __init__(self, transport):
          self._transport = transport
  
      def __repr__(self):
          """
          Returns a string representation of this object, for debugging.
          """
          return '<paramiko.SecurityOptions for %s>' % repr(self._transport)
  
      def _get_ciphers(self):
          return self._transport._preferred_ciphers
  
      def _get_digests(self):
          return self._transport._preferred_macs
  
      def _get_key_types(self):
          return self._transport._preferred_keys
  
      def _get_kex(self):
          return self._transport._preferred_kex
  
      def _get_compression(self):
          return self._transport._preferred_compression
  
      def _set(self, name, orig, x):
          if type(x) is list:
              x = tuple(x)
          if type(x) is not tuple:
              raise TypeError('expected tuple or list')
          possible = list(getattr(self._transport, orig).keys())
          forbidden = [n for n in x if n not in possible]
          if len(forbidden) > 0:
              raise ValueError('unknown cipher')
          setattr(self._transport, name, x)
  
      def _set_ciphers(self, x):
          self._set('_preferred_ciphers', '_cipher_info', x)
  
      def _set_digests(self, x):
          self._set('_preferred_macs', '_mac_info', x)
  
      def _set_key_types(self, x):
          self._set('_preferred_keys', '_key_info', x)
  
      def _set_kex(self, x):
          self._set('_preferred_kex', '_kex_info', x)
  
      def _set_compression(self, x):
          self._set('_preferred_compression', '_compression_info', x)
  
      ciphers = property(_get_ciphers, _set_ciphers, None,
                         "Symmetric encryption ciphers")
      digests = property(_get_digests, _set_digests, None,
                         "Digest (one-way hash) algorithms")
      key_types = property(_get_key_types, _set_key_types, None,
                           "Public-key algorithms")
      kex = property(_get_kex, _set_kex, None, "Key exchange algorithms")
      compression = property(_get_compression, _set_compression, None,
                             "Compression algorithms")
  
  
  class ChannelMap (object):
      def __init__(self):
          # (id -> Channel)
          self._map = weakref.WeakValueDictionary()
          self._lock = threading.Lock()
  
      def put(self, chanid, chan):
          self._lock.acquire()
          try:
              self._map[chanid] = chan
          finally:
              self._lock.release()
  
      def get(self, chanid):
          self._lock.acquire()
          try:
              return self._map.get(chanid, None)
          finally:
              self._lock.release()
  
      def delete(self, chanid):
          self._lock.acquire()
          try:
              try:
                  del self._map[chanid]
              except KeyError:
                  pass
          finally:
              self._lock.release()
  
      def values(self):
          self._lock.acquire()
          try:
              return list(self._map.values())
          finally:
              self._lock.release()
  
      def __len__(self):
          self._lock.acquire()
          try:
              return len(self._map)
          finally:
              self._lock.release()
  