py/tools/ghost.py

#!/usr/bin/python -u
# -*- coding: utf-8 -*-
#
# Copyright 2015 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import argparse
import contextlib
import fcntl
import hashlib
import json
import logging
import os
import Queue
import re
import select
import signal
import socket
import struct
import subprocess
import sys
import termios
import threading
import time
import traceback
import tty
import urllib2
import uuid

import jsonrpclib
from jsonrpclib.SimpleJSONRPCServer import SimpleJSONRPCServer


_GHOST_RPC_PORT = 4499

_OVERLORD_PORT = 4455
_OVERLORD_LAN_DISCOVERY_PORT = 4456
_OVERLORD_HTTP_PORT = 9000

_BUFSIZE = 8192
_RETRY_INTERVAL = 2
_SEPARATOR = '\r\n'
_PING_TIMEOUT = 3
_PING_INTERVAL = 5
_REQUEST_TIMEOUT_SECS = 60
_SHELL = os.getenv('SHELL', '/bin/bash')
_DEFAULT_BIND_ADDRESS = '0.0.0.0'

_CONTROL_START = 128
_CONTROL_END = 129

_BLOCK_SIZE = 4096
_CONNECT_TIMEOUT = 3

# Stream control
_STDIN_CLOSED = '##STDIN_CLOSED##'

SUCCESS = 'success'
FAILED = 'failed'
DISCONNECTED = 'disconnected'


class PingTimeoutError(Exception):
  pass


class RequestError(Exception):
  pass


class BufferedSocket(socket.socket):
  """A buffered socket that supports unrecv.

  Allow putting back data back to the socket for the next recv() call.
  """
  def __init__(self, *args, **kwargs):
    super(BufferedSocket, self).__init__(*args, **kwargs)
    self._buf = ''

  def Recv(self, bufsize, flags=0):
    if self._buf:
      if len(self._buf) >= bufsize:
        ret = self._buf[:bufsize]
        self._buf = self._buf[bufsize:]
        return ret
      else:
        ret = self._buf
        self._buf = ''
        return ret + super(BufferedSocket, self).recv(bufsize - len(ret), flags)
    else:
      return super(BufferedSocket, self).recv(bufsize, flags)

  def UnRecv(self, buf):
    self._buf = buf + self._buf

  def Send(self, *args, **kwargs):
    return super(BufferedSocket, self).send(*args, **kwargs)

  def RecvBuf(self):
    """Only recive from buffer."""
    ret = self._buf
    self._buf = ''
    return ret


class Ghost(object):
  """Ghost implements the client protocol of Overlord.

  Ghost provide terminal/shell/logcat functionality and manages the client
  side connectivity.
  """
  NONE, AGENT, TERMINAL, SHELL, LOGCAT, FILE, FORWARD = range(7)

  MODE_NAME = {
      NONE: 'NONE',
      AGENT: 'Agent',
      TERMINAL: 'Terminal',
      SHELL: 'Shell',
      LOGCAT: 'Logcat',
      FILE: 'File',
      FORWARD: 'Forward'
      }

  RANDOM_MID = '##random_mid##'

  def __init__(self, overlord_addrs, mode=AGENT, mid=None, sid=None,
               prop_file=None, terminal_sid=None, tty_device=None,
               command=None, file_op=None, port=None):
    """Constructor.

    Args:
      overlord_addrs: a list of possible address of overlord.
      mode: client mode, either AGENT, SHELL or LOGCAT
      mid: a str to set for machine ID. If mid equals Ghost.RANDOM_MID, machine
        id is randomly generated.
      sid: session ID. If the connection is requested by overlord, sid should
        be set to the corresponding session id assigned by overlord.
      prop_file: properties file filename.
      terminal_sid: the terminal session ID associate with this client. This is
        use for file download.
      tty_device: the terminal device to open, if tty_device is None, as pseudo
        terminal will be opened instead.
      command: the command to execute when we are in SHELL mode.
      file_op: a tuple (action, filepath, perm). action is either 'download' or
        'upload'. perm is the permission to set for the file.
      port: port number to forward.
    """
    assert mode in [Ghost.AGENT, Ghost.TERMINAL, Ghost.SHELL, Ghost.FILE,
                    Ghost.FORWARD]
    if mode == Ghost.SHELL:
      assert command is not None
    if mode == Ghost.FILE:
      assert file_op is not None

    self._overlord_addrs = overlord_addrs
    self._connected_addr = None
    self._mid = mid
    self._sock = None
    self._mode = mode
    self._machine_id = self.GetMachineID()
    self._session_id = sid if sid is not None else str(uuid.uuid4())
    self._terminal_session_id = terminal_sid
    self._ttyname_to_sid = {}
    self._terminal_sid_to_pid = {}
    self._prop_file = prop_file
    self._properties = {}
    self._register_status = DISCONNECTED
    self._reset = threading.Event()

    # RPC
    self._requests = {}
    self._queue = Queue.Queue()

    # Protocol specific
    self._last_ping = 0
    self._tty_device = tty_device
    self._shell_command = command
    self._file_op = file_op
    self._download_queue = Queue.Queue()
    self._port = port

  def SetIgnoreChild(self, status):
    # Only ignore child for Agent since only it could spawn child Ghost.
    if self._mode == Ghost.AGENT:
      signal.signal(signal.SIGCHLD,
                    signal.SIG_IGN if status else signal.SIG_DFL)

  def GetFileSha1(self, filename):
    with open(filename, 'r') as f:
      return hashlib.sha1(f.read()).hexdigest()

  def UseSSL(self):
    """Determine if SSL is enabled on the Overlord server."""
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    try:
      sock.settimeout(_CONNECT_TIMEOUT)
      sock.connect((self._connected_addr[0], _OVERLORD_HTTP_PORT))
      sock.send('GET\r\n')

      data = sock.recv(16)
      return 'HTTP' not in data
    except Exception:
      return False  # For whatever reason above failed, assume HTTP

  def Upgrade(self):
    logging.info('Upgrade: initiating upgrade sequence...')

    scriptpath = os.path.abspath(sys.argv[0])
    url = 'http%s://%s:%d/upgrade/ghost.py' % (
        's' if self.UseSSL() else '', self._connected_addr[0],
        _OVERLORD_HTTP_PORT)

    # Download sha1sum for ghost.py for verification
    try:
      with contextlib.closing(
          urllib2.urlopen(url + '.sha1', timeout=_CONNECT_TIMEOUT)) as f:
        if f.getcode() != 200:
          raise RuntimeError('HTTP status %d' % f.getcode())
        sha1sum = f.read().strip()
    except Exception:
      logging.error('Upgrade: failed to download sha1sum file, abort')
      return

    if self.GetFileSha1(scriptpath) == sha1sum:
      logging.info('Upgrade: ghost is already up-to-date, skipping upgrade')
      return

    # Download upgrade version of ghost.py
    try:
      with contextlib.closing(
          urllib2.urlopen(url, timeout=_CONNECT_TIMEOUT)) as f:
        if f.getcode() != 200:
          raise RuntimeError('HTTP status %d' % f.getcode())
        data = f.read()
    except Exception:
      logging.error('Upgrade: failed to download upgrade, abort')
      return

    # Compare SHA1 sum
    if hashlib.sha1(data).hexdigest() != sha1sum:
      logging.error('Upgrade: sha1sum mismatch, abort')
      return

    try:
      with open(scriptpath, 'w') as f:
        f.write(data)
    except Exception:
      logging.error('Upgrade: failed to write upgrade onto disk, abort')
      return

    logging.info('Upgrade: restarting ghost...')
    self.CloseSockets()
    self.SetIgnoreChild(False)
    os.execve(scriptpath, [scriptpath] + sys.argv[1:], os.environ)

  def LoadProperties(self):
    try:
      if self._prop_file:
        with open(self._prop_file, 'r') as f:
          self._properties = json.loads(f.read())
    except Exception as e:
      logging.exception('LoadProperties: ' + str(e))

  def CloseSockets(self):
    # Close sockets opened by parent process, since we don't use it anymore.
    for fd in os.listdir('/proc/self/fd/'):
      try:
        real_fd = os.readlink('/proc/self/fd/%s' % fd)
        if real_fd.startswith('socket'):
          os.close(int(fd))
      except Exception:
        pass

  def SpawnGhost(self, mode, sid=None, terminal_sid=None, tty_device=None,
                 command=None, file_op=None, port=None):
    """Spawn a child ghost with specific mode.

    Returns:
      The spawned child process pid.
    """
    # Restore the default signal handler, so our child won't have problems.
    self.SetIgnoreChild(False)

    pid = os.fork()
    if pid == 0:
      self.CloseSockets()
      g = Ghost([self._connected_addr], mode, Ghost.RANDOM_MID, sid,
                terminal_sid=terminal_sid, tty_device=tty_device,
                command=command, file_op=file_op, port=port)
      g.Start()
      sys.exit(0)
    else:
      self.SetIgnoreChild(True)
      return pid

  def Timestamp(self):
    return int(time.time())

  def GetGateWayIP(self):
    with open('/proc/net/route', 'r') as f:
      lines = f.readlines()

    ips = []
    for line in lines:
      parts = line.split('\t')
      if parts[2] == '00000000':
        continue

      try:
        h = parts[2].decode('hex')
        ips.append('%d.%d.%d.%d' % tuple(ord(x) for x in reversed(h)))
      except TypeError:
        pass

    return ips

  def GetShopfloorIP(self):
    try:
      import factory_common  # pylint: disable=W0612
      from cros.factory.test import shopfloor

      url = shopfloor.get_server_url()
      match = re.match(r'^https?://(.*):.*$', url)
      if match:
        return [match.group(1)]
    except Exception:
      pass
    return []

  def GetMachineID(self):
    """Generates machine-dependent ID string for a machine.
    There are many ways to generate a machine ID:
    1. factory device_id
    2. factory device-data
    3. /sys/class/dmi/id/product_uuid (only available on intel machines)
    4. MAC address
    We follow the listed order to generate machine ID, and fallback to the next
    alternative if the previous doesn't work.
    """
    if self._mid == Ghost.RANDOM_MID:
      return str(uuid.uuid4())
    elif self._mid:
      return self._mid

    # Try factory device id
    try:
      import factory_common  # pylint: disable=W0612
      from cros.factory.test import event_log
      with open(event_log.DEVICE_ID_PATH) as f:
        return f.read().strip()
    except Exception:
      pass

    # Try factory device data
    try:
      p = subprocess.Popen('factory device-data | grep mlb_serial_number | '
                           'cut -d " " -f 2', stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE, shell=True)
      stdout, unused_stderr = p.communicate()
      if stdout == '':
        raise RuntimeError('empty mlb number')
      return stdout.strip()
    except Exception:
      pass

    # Try DMI product UUID
    try:
      with open('/sys/class/dmi/id/product_uuid', 'r') as f:
        return f.read().strip()
    except Exception:
      pass

    # Use MAC address if non is available
    try:
      macs = []
      ifaces = sorted(os.listdir('/sys/class/net'))
      for iface in ifaces:
        if iface == 'lo':
          continue

        with open('/sys/class/net/%s/address' % iface, 'r') as f:
          macs.append(f.read().strip())

      return ';'.join(macs)
    except Exception:
      pass

    raise RuntimeError('can\'t generate machine ID')

  def Reset(self):
    """Reset state and clear request handlers."""
    self._reset.clear()
    self._last_ping = 0
    self._requests = {}
    self.LoadProperties()
    self._register_status = DISCONNECTED

  def SendMessage(self, msg):
    """Serialize the message and send it through the socket."""
    self._sock.Send(json.dumps(msg) + _SEPARATOR)

  def SendRequest(self, name, args, handler=None,
                  timeout=_REQUEST_TIMEOUT_SECS):
    if handler and not callable(handler):
      raise RequestError('Invalid request handler for msg "%s"' % name)

    rid = str(uuid.uuid4())
    msg = {'rid': rid, 'timeout': timeout, 'name': name, 'params': args}
    if timeout >= 0:
      self._requests[rid] = [self.Timestamp(), timeout, handler]
    self.SendMessage(msg)

  def SendResponse(self, omsg, status, params=None):
    msg = {'rid': omsg['rid'], 'response': status, 'params': params}
    self.SendMessage(msg)

  def HandleTTYControl(self, fd, control_str):
    msg = json.loads(control_str)
    command = msg['command']
    params = msg['params']
    if command == 'resize':
      # some error happened on websocket
      if len(params) != 2:
        return
      winsize = struct.pack('HHHH', params[0], params[1], 0, 0)
      fcntl.ioctl(fd, termios.TIOCSWINSZ, winsize)
    else:
      logging.warn('Invalid request command "%s"', command)

  def SpawnTTYServer(self, unused_var):
    """Spawn a TTY server and forward I/O to the TCP socket."""
    logging.info('SpawnTTYServer: started')

    try:
      if self._tty_device is None:
        pid, fd = os.forkpty()

        if pid == 0:
          ttyname = os.readlink('/proc/%d/fd/0' % os.getpid())
          try:
            server = GhostRPCServer()
            server.RegisterTTY(self._session_id, ttyname)
            server.RegisterSession(self._session_id, os.getpid())
          except Exception:
            # If ghost is launched without RPC server, the call will fail but we
            # can ignore it.
            pass

          # The directory that contains the current running ghost script
          script_dir = os.path.dirname(os.path.abspath(sys.argv[0]))

          env = os.environ.copy()
          env['USER'] = os.getenv('USER', 'root')
          env['HOME'] = os.getenv('HOME', '/root')
          env['PATH'] = os.getenv('PATH') + ':%s' % script_dir
          os.chdir(env['HOME'])
          os.execve(_SHELL, [_SHELL], env)
      else:
        fd = os.open(self._tty_device, os.O_RDWR)
        tty.setraw(fd)
        attr = termios.tcgetattr(fd)
        attr[0] &= ~(termios.IXON | termios.IXOFF)
        attr[2] |= termios.CLOCAL
        attr[2] &= ~termios.CRTSCTS
        attr[4] = termios.B115200
        attr[5] = termios.B115200
        termios.tcsetattr(fd, termios.TCSANOW, attr)

      nonlocals = {'control_state': None, 'control_str': ''}

      def _ProcessBuffer(buf):
        write_buffer = ''
        while buf:
          if nonlocals['control_state']:
            if chr(_CONTROL_END) in buf:
              index = buf.index(chr(_CONTROL_END))
              nonlocals['control_str'] += buf[:index]
              self.HandleTTYControl(fd, nonlocals['control_str'])
              nonlocals['control_state'] = None
              nonlocals['control_str'] = ''
              buf = buf[index+1:]
            else:
              nonlocals['control_str'] += buf
              buf = ''
          else:
            if chr(_CONTROL_START) in buf:
              nonlocals['control_state'] = _CONTROL_START
              index = buf.index(chr(_CONTROL_START))
              write_buffer += buf[:index]
              buf = buf[index+1:]
            else:
              write_buffer += buf
              buf = ''

        if write_buffer:
          os.write(fd, write_buffer)

      _ProcessBuffer(self._sock.RecvBuf())

      while True:
        rd, unused_wd, unused_xd = select.select([self._sock, fd], [], [])

        if fd in rd:
          self._sock.Send(os.read(fd, _BUFSIZE))

        if self._sock in rd:
          buf = self._sock.Recv(_BUFSIZE)
          if len(buf) == 0:
            raise RuntimeError('connection terminated')
          _ProcessBuffer(buf)
    except Exception as e:
      logging.error('SpawnTTYServer: %s', e)
    finally:
      self._sock.close()

    logging.info('SpawnTTYServer: terminated')
    sys.exit(0)

  def SpawnShellServer(self, unused_var):
    """Spawn a shell server and forward input/output from/to the TCP socket."""
    logging.info('SpawnShellServer: started')

    # Add ghost executable to PATH
    script_dir = os.path.dirname(os.path.abspath(sys.argv[0]))
    env = os.environ.copy()
    env['PATH'] = '%s:%s' % (script_dir, os.getenv('PATH'))

    # Execute shell command from HOME directory
    os.chdir(os.getenv('HOME', '/tmp'))

    p = subprocess.Popen(self._shell_command, stdin=subprocess.PIPE,
                         stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                         shell=True, env=env)

    def make_non_block(fd):
      fl = fcntl.fcntl(fd, fcntl.F_GETFL)
      fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)

    make_non_block(p.stdout)
    make_non_block(p.stderr)

    try:
      p.stdin.write(self._sock.RecvBuf())

      while True:
        rd, unused_wd, unused_xd = select.select(
            [p.stdout, p.stderr, self._sock], [], [self._sock])
        if p.stdout in rd:
          self._sock.Send(p.stdout.read(_BUFSIZE))

        if p.stderr in rd:
          self._sock.Send(p.stderr.read(_BUFSIZE))

        if self._sock in rd:
          ret = self._sock.Recv(_BUFSIZE)
          if len(ret) == 0:
            raise RuntimeError('connection terminated')

          try:
            idx = ret.index(_STDIN_CLOSED * 2)
            p.stdin.write(ret[:idx])
            p.stdin.close()
          except ValueError:
            p.stdin.write(ret)
        p.poll()
        if p.returncode != None:
          break
    except Exception as e:
      logging.error('SpawnShellServer: %s', e)
    finally:
      # Check if the process is terminated. If not, Send SIGTERM to process,
      # then wait for 1 second. Send another SIGKILL to make sure the process is
      # terminated.
      p.poll()
      if p.returncode is None:
        try:
          p.terminate()
          time.sleep(1)
          p.kill()
        except Exception:
          pass

      p.wait()
      self._sock.close()

    logging.info('SpawnShellServer: terminated')
    sys.exit(0)

  def InitiateFileOperation(self, unused_var):
    if self._file_op[0] == 'download':
      try:
        size = os.stat(self._file_op[1]).st_size
      except OSError as e:
        logging.error('InitiateFileOperation: download: %s', e)
        sys.exit(1)

      self.SendRequest('request_to_download',
                       {'terminal_sid': self._terminal_session_id,
                        'filename': os.path.basename(self._file_op[1]),
                        'size': size})
    elif self._file_op[0] == 'upload':
      self.SendRequest('clear_to_upload', {}, timeout=-1)
      self.StartUploadServer()
    else:
      logging.error('InitiateFileOperation: unknown file operation, ignored')

  def StartDownloadServer(self):
    logging.info('StartDownloadServer: started')

    try:
      with open(self._file_op[1], 'rb') as f:
        while True:
          data = f.read(_BLOCK_SIZE)
          if len(data) == 0:
            break
          self._sock.Send(data)
    except Exception as e:
      logging.error('StartDownloadServer: %s', e)
    finally:
      self._sock.close()

    logging.info('StartDownloadServer: terminated')
    sys.exit(0)

  def StartUploadServer(self):
    logging.info('StartUploadServer: started')
    try:
      filepath = self._file_op[1]
      dirname = os.path.dirname(filepath)
      if not os.path.exists(dirname):
        try:
          os.makedirs(dirname)
        except Exception:
          pass

      self._sock.setblocking(False)
      with open(filepath, 'wb') as f:
        if self._file_op[2]:
          os.fchmod(f.fileno(), self._file_op[2])

        f.write(self._sock.RecvBuf())

        while True:
          rd, unused_wd, unused_xd = select.select([self._sock], [], [])
          if self._sock in rd:
            buf = self._sock.Recv(_BLOCK_SIZE)
            if len(buf) == 0:
              break
            f.write(buf)
    except socket.error as e:
      logging.error('StartUploadServer: socket error: %s', e)
    except Exception as e:
      logging.error('StartUploadServer: %s', e)
    finally:
      self._sock.close()

    logging.info('StartUploadServer: terminated')
    sys.exit(0)

  def SpawnPortForwardServer(self, unused_var):
    """Spawn a port forwarding server and forward I/O to the TCP socket."""
    logging.info('SpawnPortForwardServer: started')

    src_sock = None
    try:
      src_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      src_sock.settimeout(_CONNECT_TIMEOUT)
      src_sock.connect(('localhost', self._port))
      src_sock.setblocking(False)

      src_sock.send(self._sock.RecvBuf())

      while True:
        rd, unused_wd, unused_xd = select.select([self._sock, src_sock], [], [])

        if self._sock in rd:
          data = self._sock.Recv(_BUFSIZE)
          if len(data) == 0:
            raise RuntimeError('connection terminated')
          src_sock.send(data)

        if src_sock in rd:
          data = src_sock.recv(_BUFSIZE)
          if len(data) == 0:
            break
          self._sock.Send(data)
    except Exception as e:
      logging.error('SpawnPortForwardServer: %s', e)
    finally:
      if src_sock:
        src_sock.close()
      self._sock.close()

    logging.info('SpawnPortForwardServer: terminated')
    sys.exit(0)

  def Ping(self):
    def timeout_handler(x):
      if x is None:
        raise PingTimeoutError

    self._last_ping = self.Timestamp()
    self.SendRequest('ping', {}, timeout_handler, 5)

  def HandleFileDownloadRequest(self, msg):
    params = msg['params']
    filepath = params['filename']
    if not os.path.isabs(filepath):
      filepath = os.path.join(os.getenv('HOME', '/tmp'), filepath)

    try:
      with open(filepath, 'r') as _:
        pass
    except Exception as e:
      return self.SendResponse(msg, str(e))

    self.SpawnGhost(self.FILE, params['sid'],
                    file_op=('download', filepath))
    self.SendResponse(msg, SUCCESS)

  def HandleFileUploadRequest(self, msg):
    params = msg['params']

    # Resolve upload filepath
    filename = params['filename']
    dest_path = filename

    # If dest is specified, use it first
    dest_path = params.get('dest', '')
    if dest_path:
      if not os.path.isabs(dest_path):
        dest_path = os.path.join(os.getenv('HOME', '/tmp'), dest_path)

      if os.path.isdir(dest_path):
        dest_path = os.path.join(dest_path, filename)
    else:
      target_dir = os.getenv('HOME', '/tmp')

      # Terminal session ID found, upload to it's current working directory
      if params.has_key('terminal_sid'):
        pid = self._terminal_sid_to_pid.get(params['terminal_sid'], None)
        if pid:
          target_dir = os.readlink('/proc/%d/cwd' % pid)

      dest_path = os.path.join(target_dir, filename)

    try:
      os.makedirs(os.path.dirname(dest_path))
    except Exception:
      pass

    try:
      with open(dest_path, 'w') as _:
        pass
    except Exception as e:
      return self.SendResponse(msg, str(e))

    # If not check_only, spawn FILE mode ghost agent to handle upload
    if not params.get('check_only', False):
      self.SpawnGhost(self.FILE, params['sid'],
                      file_op=('upload', dest_path, params.get('perm', None)))
    self.SendResponse(msg, SUCCESS)

  def HandleRequest(self, msg):
    command = msg['name']
    params = msg['params']

    if command == 'upgrade':
      self.Upgrade()
    elif command == 'terminal':
      self.SpawnGhost(self.TERMINAL, params['sid'],
                      tty_device=params['tty_device'])
      self.SendResponse(msg, SUCCESS)
    elif command == 'shell':
      self.SpawnGhost(self.SHELL, params['sid'], command=params['command'])
      self.SendResponse(msg, SUCCESS)
    elif command == 'file_download':
      self.HandleFileDownloadRequest(msg)
    elif command == 'clear_to_download':
      self.StartDownloadServer()
    elif command == 'file_upload':
      self.HandleFileUploadRequest(msg)
    elif command == 'forward':
      self.SpawnGhost(self.FORWARD, params['sid'], port=params['port'])
      self.SendResponse(msg, SUCCESS)

  def HandleResponse(self, response):
    rid = str(response['rid'])
    if rid in self._requests:
      handler = self._requests[rid][2]
      del self._requests[rid]
      if callable(handler):
        handler(response)
    else:
      logging.warning('Received unsolicited response, ignored')

  def ParseMessage(self, buf, single=True):
    if single:
      index = buf.index(_SEPARATOR)
      msgs_json = [buf[:index]]
      self._sock.UnRecv(buf[index + 2:])
    else:
      msgs_json = buf.split(_SEPARATOR)
      self._sock.UnRecv(msgs_json.pop())

    for msg_json in msgs_json:
      try:
        msg = json.loads(msg_json)
      except ValueError:
        # Ignore mal-formed message.
        logging.error('mal-formed JSON request, ignored')
        continue

      if 'name' in msg:
        self.HandleRequest(msg)
      elif 'response' in msg:
        self.HandleResponse(msg)
      else:  # Ingnore mal-formed message.
        logging.error('mal-formed JSON request, ignored')

  def ScanForTimeoutRequests(self):
    """Scans for pending requests which have timed out.

    If any timed-out requests are discovered, their handler is called with the
    special response value of None.
    """
    for rid in self._requests.keys()[:]:
      request_time, timeout, handler = self._requests[rid]
      if self.Timestamp() - request_time > timeout:
        if callable(handler):
          handler(None)
        else:
          logging.error('Request %s timeout', rid)
        del self._requests[rid]

  def InitiateDownload(self):
    ttyname, filename = self._download_queue.get()
    sid = self._ttyname_to_sid[ttyname]
    self.SpawnGhost(self.FILE, terminal_sid=sid,
                    file_op=('download', filename))

  def Listen(self):
    try:
      while True:
        rds, unused_wd, unused_xd = select.select([self._sock], [], [],
                                                  _PING_INTERVAL / 2)

        if self._sock in rds:
          data = self._sock.Recv(_BUFSIZE)

          # Socket is closed
          if len(data) == 0:
            self.Reset()
            break

          self.ParseMessage(data, self._register_status != SUCCESS)

        if (self._mode == self.AGENT and
            self.Timestamp() - self._last_ping > _PING_INTERVAL):
          self.Ping()
        self.ScanForTimeoutRequests()

        if not self._download_queue.empty():
          self.InitiateDownload()

        if self._reset.is_set():
          self.Reset()
          break
    except socket.error:
      raise RuntimeError('Connection dropped')
    except PingTimeoutError:
      raise RuntimeError('Connection timeout')
    finally:
      self._sock.close()

    self._queue.put('resume')

    if self._mode != Ghost.AGENT:
      sys.exit(1)

  def Register(self):
    non_local = {}
    for addr in self._overlord_addrs:
      non_local['addr'] = addr
      def registered(response):
        if response is None:
          self._reset.set()
          raise RuntimeError('Register request timeout')

        self._register_status = response['response']
        if response['response'] != SUCCESS:
          self._reset.set()
          raise RuntimeError('Reigster: ' + response['response'])
        else:
          logging.info('Registered with Overlord at %s:%d', *non_local['addr'])
          self._connected_addr = non_local['addr']
          self.Upgrade()  # Check for upgrade
          self._queue.put('pause', True)

      try:
        logging.info('Trying %s:%d ...', *addr)
        self.Reset()
        self._sock = BufferedSocket(socket.AF_INET, socket.SOCK_STREAM)
        self._sock.settimeout(_CONNECT_TIMEOUT)
        self._sock.connect(addr)

        logging.info('Connection established, registering...')
        handler = {
            Ghost.AGENT: registered,
            Ghost.TERMINAL: self.SpawnTTYServer,
            Ghost.SHELL: self.SpawnShellServer,
            Ghost.FILE: self.InitiateFileOperation,
            Ghost.FORWARD: self.SpawnPortForwardServer,
            }[self._mode]

        # Machine ID may change if MAC address is used (USB-ethernet dongle
        # plugged/unplugged)
        self._machine_id = self.GetMachineID()
        self.SendRequest('register',
                         {'mode': self._mode, 'mid': self._machine_id,
                          'sid': self._session_id,
                          'properties': self._properties}, handler)
      except socket.error:
        pass
      else:
        self._sock.settimeout(None)
        self.Listen()

    raise RuntimeError('Cannot connect to any server')

  def Reconnect(self):
    logging.info('Received reconnect request from RPC server, reconnecting...')
    self._reset.set()

  def GetStatus(self):
    return self._register_status

  def AddToDownloadQueue(self, ttyname, filename):
    self._download_queue.put((ttyname, filename))

  def RegisterTTY(self, session_id, ttyname):
    self._ttyname_to_sid[ttyname] = session_id

  def RegisterSession(self, session_id, process_id):
    self._terminal_sid_to_pid[session_id] = process_id

  def StartLanDiscovery(self):
    """Start to listen to LAN discovery packet at
    _OVERLORD_LAN_DISCOVERY_PORT."""

    def thread_func():
      s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
      s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
      s.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
      try:
        s.bind(('0.0.0.0', _OVERLORD_LAN_DISCOVERY_PORT))
      except socket.error as e:
        logging.error('LAN discovery: %s, abort', e)
        return

      logging.info('LAN Discovery: started')
      while True:
        rd, unused_wd, unused_xd = select.select([s], [], [], 1)

        if s in rd:
          data, source_addr = s.recvfrom(_BUFSIZE)
          parts = data.split()
          if parts[0] == 'OVERLORD':
            ip, port = parts[1].split(':')
            if not ip:
              ip = source_addr[0]
            self._queue.put((ip, int(port)), True)

        try:
          obj = self._queue.get(False)
        except Queue.Empty:
          pass
        else:
          if type(obj) is not str:
            self._queue.put(obj)
          elif obj == 'pause':
            logging.info('LAN Discovery: paused')
            while obj != 'resume':
              obj = self._queue.get(True)
            logging.info('LAN Discovery: resumed')

    t = threading.Thread(target=thread_func)
    t.daemon = True
    t.start()

  def StartRPCServer(self):
    logging.info('RPC Server: started')
    rpc_server = SimpleJSONRPCServer((_DEFAULT_BIND_ADDRESS, _GHOST_RPC_PORT),
                                     logRequests=False)
    rpc_server.register_function(self.Reconnect, 'Reconnect')
    rpc_server.register_function(self.GetStatus, 'GetStatus')
    rpc_server.register_function(self.RegisterTTY, 'RegisterTTY')
    rpc_server.register_function(self.RegisterSession, 'RegisterSession')
    rpc_server.register_function(self.AddToDownloadQueue, 'AddToDownloadQueue')
    t = threading.Thread(target=rpc_server.serve_forever)
    t.daemon = True
    t.start()

  def ScanServer(self):
    for meth in [self.GetGateWayIP, self.GetShopfloorIP]:
      for addr in [(x, _OVERLORD_PORT) for x in meth()]:
        if addr not in self._overlord_addrs:
          self._overlord_addrs.append(addr)

  def Start(self, lan_disc=False, rpc_server=False):
    logging.info('%s started', self.MODE_NAME[self._mode])
    logging.info('MID: %s', self._machine_id)
    logging.info('SID: %s', self._session_id)

    # We don't care about child process's return code, not wait is needed.  This
    # is used to prevent zombie process from lingering in the system.
    self.SetIgnoreChild(True)

    if lan_disc:
      self.StartLanDiscovery()

    if rpc_server:
      self.StartRPCServer()

    try:
      while True:
        try:
          addr = self._queue.get(False)
        except Queue.Empty:
          pass
        else:
          if type(addr) == tuple and addr not in self._overlord_addrs:
            logging.info('LAN Discovery: got overlord address %s:%d', *addr)
            self._overlord_addrs.append(addr)

        try:
          self.ScanServer()
          self.Register()
        # Don't show stack trace for RuntimeError, which we use in this file for
        # plausible and expected errors (such as can't connect to server).
        except RuntimeError as e:
          logging.info('%s, retrying in %ds', e.message, _RETRY_INTERVAL)
          time.sleep(_RETRY_INTERVAL)
        except Exception as e:
          unused_x, unused_y, exc_traceback = sys.exc_info()
          traceback.print_tb(exc_traceback)
          logging.info('%s: %s, retrying in %ds',
                       e.__class__.__name__, e.message, _RETRY_INTERVAL)
          time.sleep(_RETRY_INTERVAL)

        self.Reset()
    except KeyboardInterrupt:
      logging.error('Received keyboard interrupt, quit')
      sys.exit(0)


def GhostRPCServer():
  """Returns handler to Ghost's JSON RPC server."""
  return jsonrpclib.Server('http://localhost:%d' % _GHOST_RPC_PORT)


def ForkToBackground():
  """Fork process to run in background."""
  pid = os.fork()
  if pid != 0:
    logging.info('Ghost(%d) running in background.', pid)
    sys.exit(0)


def DownloadFile(filename):
  """Initiate a client-initiated file download."""
  filepath = os.path.abspath(filename)
  if not os.path.exists(filepath):
    logging.error('file `%s\' does not exist', filename)
    sys.exit(1)

  # Check if we actually have permission to read the file
  if not os.access(filepath, os.R_OK):
    logging.error('can not open %s for reading', filepath)
    sys.exit(1)

  server = GhostRPCServer()
  server.AddToDownloadQueue(os.ttyname(0), filepath)
  sys.exit(0)


def main():
  # Setup logging format
  logger = logging.getLogger()
  logger.setLevel(logging.INFO)
  handler = logging.StreamHandler()
  formatter = logging.Formatter('%(asctime)s %(message)s', '%Y/%m/%d %H:%M:%S')
  handler.setFormatter(formatter)
  logger.addHandler(handler)

  parser = argparse.ArgumentParser()
  parser.add_argument('--fork', dest='fork', action='store_true', default=False,
                      help='fork procecess to run in background')
  parser.add_argument('--mid', metavar='MID', dest='mid', action='store',
                      default=None, help='use MID as machine ID')
  parser.add_argument('--rand-mid', dest='mid', action='store_const',
                      const=Ghost.RANDOM_MID, help='use random machine ID')
  parser.add_argument('--no-lan-disc', dest='lan_disc', action='store_false',
                      default=True, help='disable LAN discovery')
  parser.add_argument('--no-rpc-server', dest='rpc_server',
                      action='store_false', default=True,
                      help='disable RPC server')
  parser.add_argument('--prop-file', metavar='PROP_FILE', dest='prop_file',
                      type=str, default=None,
                      help='file containing the JSON representation of client '
                           'properties')
  parser.add_argument('--download', metavar='FILE', dest='download', type=str,
                      default=None, help='file to download')
  parser.add_argument('--reset', dest='reset', default=False,
                      action='store_true',
                      help='reset ghost and reload all configs')
  parser.add_argument('overlord_ip', metavar='OVERLORD_IP', type=str,
                      nargs='*', help='overlord server address')
  args = parser.parse_args()

  if args.fork:
    ForkToBackground()

  if args.reset:
    GhostRPCServer().Reconnect()
    sys.exit()

  if args.download:
    DownloadFile(args.download)

  addrs = [('localhost', _OVERLORD_PORT)]
  addrs += [(x, _OVERLORD_PORT) for x in args.overlord_ip]

  g = Ghost(addrs, Ghost.AGENT, args.mid, prop_file=args.prop_file)
  g.Start(args.lan_disc, args.rpc_server)


if __name__ == '__main__':
  main()