# Copyright (C) 2011  John Rochester <john@jrochester.org>
#
# This file is part of ssh.
#
# 'ssh' 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.
#
# 'ssh' 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 'ssh'; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Suite 500, Boston, MA  02110-1335  USA.

"""
SSH Agent interface for Unix clients.
"""

import os
import socket
import struct
import sys
import threading
import time
import tempfile
import stat
from select import select

from ssh.ssh_exception import SSHException
from ssh.message import Message
from ssh.pkey import PKey
from ssh.channel import Channel
from ssh.common import io_sleep

SSH2_AGENTC_REQUEST_IDENTITIES, SSH2_AGENT_IDENTITIES_ANSWER, \
    SSH2_AGENTC_SIGN_REQUEST, SSH2_AGENT_SIGN_RESPONSE = range(11, 15)

class AgentSSH(object):
    """
    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):
        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 _connect(self, conn):
        self._conn = conn
        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):
        #self._conn.close()
        self._conn = None
        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 AgentProxyThread(threading.Thread):
    """ Class in charge of communication between two chan """
    def __init__(self, agent):
        threading.Thread.__init__(self, target=self.run)
        self._agent = agent
        self._exit = False

    def run(self):
        try:
            (r,addr) = self.get_connection()
            self.__inr = r
            self.__addr = addr
            self._agent.connect()
            self._communicate()
        except:
            #XXX Not sure what to do here ... raise or pass ?
            raise

    def _communicate(self):
        import fcntl
        oldflags = fcntl.fcntl(self.__inr, fcntl.F_GETFL)
        fcntl.fcntl(self.__inr, fcntl.F_SETFL, oldflags | os.O_NONBLOCK)
        while not self._exit:
            events = select([self._agent._conn, self.__inr], [], [], 0.5)
            for fd in events[0]:
                if self._agent._conn == fd:
                    data = self._agent._conn.recv(512)
                    if len(data) != 0:
                        self.__inr.send(data)
                    else:
                        break
                elif self.__inr == fd:
                    data = self.__inr.recv(512)
                    if len(data) != 0:
                        self._agent._conn.send(data)
                    else:
                        break
            time.sleep(io_sleep)

class AgentLocalProxy(AgentProxyThread):
    """
    Class to be used when wanting to ask a local SSH Agent being
    asked from a remote fake agent (so use a unix socket for ex.)
    """
    def __init__(self, agent):
        AgentProxyThread.__init__(self, agent)

    def get_connection(self):
        """ Return a pair of socket object and string address
        May Block !
        """
        conn = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        try:
            conn.bind(self._agent._get_filename())
            conn.listen(1)
            (r,addr) = conn.accept()
            return (r, addr)
        except:
            raise
        return None

class AgentRemoteProxy(AgentProxyThread):
    """
    Class to be used when wanting to ask a remote SSH Agent
    """
    def __init__(self, agent, chan):
        AgentProxyThread.__init__(self, agent)
        self.__chan = chan

    def get_connection(self):
        """
        Class to be used when wanting to ask a local SSH Agent being
        asked from a remote fake agent (so use a unix socket for ex.)
        """
        return (self.__chan, None)

class AgentClientProxy(object):
    """
    Class proxying request as a client:
       -> client ask for a request_forward_agent()
       -> server creates a proxy and a fake SSH Agent
       -> server ask for establishing a connection when needed,
       calling the forward_agent_handler at client side.
       -> the forward_agent_handler launch a thread for connecting
       the remote fake agent and the local agent
       -> Communication occurs ...
    """
    def __init__(self, chanClient):
        self._conn = None
        self.__chanC = chanClient
        chanClient.request_forward_agent(self._forward_agent_handler)

    def __del__(self):
        self.close()

    def connect(self):
        """
        Method automatically called by the run() method of the AgentProxyThread
        """
        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
        elif sys.platform == 'win32':
            import win_pageant
            if win_pageant.can_talk_to_agent():
                conn = win_pageant.PageantConnection()
            else:
                return
        else:
            # no agent support
            return
        self._conn = conn

    def close(self):
        """
        Close the current connection and terminate the agent
        Should be called manually
        """
        if hasattr(self, "thread"):
            self.thread._exit = True
            self.thread.join(1000)
        if self._conn is not None:
            self._conn.close()

    def _forward_agent_handler(self, chanRemote):
        self.thread = AgentRemoteProxy(self, chanRemote)
        self.thread.start()

class AgentServerProxy(AgentSSH):
    """
    @param t : transport used for the Forward for SSH Agent communication

    @raise SSHException: mostly if we lost the agent
    """
    def __init__(self, t):
        AgentSSH.__init__(self)
        self.__t = t
        self._dir = tempfile.mkdtemp('sshproxy')
        os.chmod(self._dir, stat.S_IRWXU)
        self._file = self._dir + '/sshproxy.ssh'
        self.thread = AgentLocalProxy(self)
        self.thread.start()

    def __del__(self):
        self.close()

    def connect(self):
         conn_sock = self.__t.open_forward_agent_channel()
         if conn_sock is None:
             raise SSHException('lost ssh-agent')
         conn_sock.set_name('auth-agent')
         self._connect(conn_sock)

    def close(self):
        """
        Terminate the agent, clean the files, close connections
        Should be called manually
        """
        os.remove(self._file)
        os.rmdir(self._dir)
        self.thread._exit = True
        self.thread.join(1000)
        self._close()

    def get_env(self):
        """
        Helper for the environnement under unix

        @return: the SSH_AUTH_SOCK Environnement variables
        @rtype: dict
        """
        env = {}
        env['SSH_AUTH_SOCK'] = self._get_filename()
        return env

    def _get_filename(self):
        return self._file

class Agent(AgentSSH):
    """
    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
        """
        AgentSSH.__init__(self)

        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
        elif sys.platform == 'win32':
            import win_pageant
            if win_pageant.can_talk_to_agent():
                conn = win_pageant.PageantConnection()
            else:
                return
        else:
            # no agent support
            return
        self._connect(conn)

    def close(self):
        """
        Close the SSH agent connection.
        """
        self._close()

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()