text: # Copyright (C) 2003-2007  John Rochester <john@jrochester.org>
  #
  # 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 distrubuted in the hope that it will be useful, but WITHOUT ANY
  # WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  # A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
  # details.
  #
  # You should have received a copy of the GNU Lesser General Public License
  # along with Paramiko; if not, write to the Free Software Foundation, Inc.,
  # 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
  
  """
  SSH Agent interface for Unix clients.
  """
  
  import os
  import socket
  import struct
  import sys
  
  from paramiko.ssh_exception import SSHException
  from paramiko.message import Message
  from paramiko.pkey import PKey
  
  
  SSH2_AGENTC_REQUEST_IDENTITIES, SSH2_AGENT_IDENTITIES_ANSWER, \
      SSH2_AGENTC_SIGN_REQUEST, SSH2_AGENT_SIGN_RESPONSE = range(11, 15)
  
  
  class Agent:
      """
      Client interface for using private keys from an SSH agent running on the
      local machine.  If an SSH agent is running, this class can be used to
      connect to it and retreive L{PKey} objects which can be used when
      attempting to authenticate to remote SSH servers.
      
      Because the SSH agent protocol uses environment variables and unix-domain
      sockets, this probably doesn't work on Windows.  It does work on most
      posix platforms though (Linux and MacOS X, for example).
      """
      
      def __init__(self):
          """
          Open a session with the local machine's SSH agent, if one is running.
          If no agent is running, initialization will succeed, but L{get_keys}
          will return an empty tuple.
          
          @raise SSHException: if an SSH agent is found, but speaks an
              incompatible protocol
          """
          self.conn = None
          self.keys = ()
          if ('SSH_AUTH_SOCK' in os.environ) and (sys.platform != 'win32'):
              conn = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
              try:
                  conn.connect(os.environ['SSH_AUTH_SOCK'])
              except:
                  # probably a dangling env var: the ssh agent is gone
                  return
              self.conn = conn
          elif sys.platform == 'win32':
              import win_pageant
              if win_pageant.can_talk_to_agent():
                  self.conn = win_pageant.PageantConnection()
              else:
                  return
          else:
              # no agent support
              return
              
          ptype, result = self._send_message(chr(SSH2_AGENTC_REQUEST_IDENTITIES))
          if ptype != SSH2_AGENT_IDENTITIES_ANSWER:
              raise SSHException('could not get keys from ssh-agent')
          keys = []
          for i in range(result.get_int()):
              keys.append(AgentKey(self, result.get_string()))
              result.get_string()
          self.keys = tuple(keys)
  
      def close(self):
          """
          Close the SSH agent connection.
          """
          if self.conn is not None:
              self.conn.close()
          self.conn = None
          self.keys = ()
  
      def get_keys(self):
          """
          Return the list of keys available through the SSH agent, if any.  If
          no SSH agent was running (or it couldn't be contacted), an empty list
          will be returned.
          
          @return: a list of keys available on the SSH agent
          @rtype: tuple of L{AgentKey}
          """
          return self.keys
  
      def _send_message(self, msg):
          msg = str(msg)
          self.conn.send(struct.pack('>I', len(msg)) + msg)
          l = self._read_all(4)
          msg = Message(self._read_all(struct.unpack('>I', l)[0]))
          return ord(msg.get_byte()), msg
  
      def _read_all(self, wanted):
          result = self.conn.recv(wanted)
          while len(result) < wanted:
              if len(result) == 0:
                  raise SSHException('lost ssh-agent')
              extra = self.conn.recv(wanted - len(result))
              if len(extra) == 0:
                  raise SSHException('lost ssh-agent')
              result += extra
          return result
  
  
  class AgentKey(PKey):
      """
      Private key held in a local SSH agent.  This type of key can be used for
      authenticating to a remote server (signing).  Most other key operations
      work as expected.
      """
      
      def __init__(self, agent, blob):
          self.agent = agent
          self.blob = blob
          self.name = Message(blob).get_string()
  
      def __str__(self):
          return self.blob
  
      def get_name(self):
          return self.name
  
      def sign_ssh_data(self, rng, data):
          msg = Message()
          msg.add_byte(chr(SSH2_AGENTC_SIGN_REQUEST))
          msg.add_string(self.blob)
          msg.add_string(data)
          msg.add_int(0)
          ptype, result = self.agent._send_message(msg)
          if ptype != SSH2_AGENT_SIGN_RESPONSE:
              raise SSHException('key cannot be used for signing')
          return result.get_string()
  