#!/usr/bin/env python
"""Back door shell server

This exposes a shell terminal emulator on a socket.

    --hostname : sets the remote host name to open an ssh connection to.
    --username : sets the user name to login with
    --password : (optional) sets the password to login with
    --port     : set the local port for the server to listen on
"""
# Having the password on the command line is not a good idea, but
# then this entire project is probably not the most security concious thing
# I've ever built. This should be considered an experimental tool.
import pxssh, pexpect, ANSI
import socket
import time, sys, os, getopt, getpass
import threading

def exit_with_usage(exit_code=1):
    print globals()['__doc__']
    os._exit(exit_code)

class roller (threading.Thread):
    """This runs a function in a loop in a thread."""
    def __init__(self, interval, function, args=[], kwargs={}):
        """The interval parameter defines time between each call to the function.
        """
        threading.Thread.__init__(self)
        self.interval = interval
        self.function = function
        self.args = args
        self.kwargs = kwargs
        self.finished = threading.Event()
    def cancel(self):
        """Stop the roller."""
        self.finished.set()
    def run(self):
        while not self.finished.isSet():
            # self.finished.wait(self.interval)
            self.function(*self.args, **self.kwargs)

def daemonize (stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
    '''This forks the current process into a daemon.
    Almost none of this is necessary (or advisable) if your daemon 
    is being started by inetd. In that case, stdin, stdout and stderr are 
    all set up for you to refer to the network connection, and the fork()s 
    and session manipulation should not be done (to avoid confusing inetd). 
    Only the chdir() and umask() steps remain as useful. 

    References:
        UNIX Programming FAQ
        1.7 How do I get my program to act like a daemon?
        http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16

        Advanced Programming in the Unix Environment
        W. Richard Stevens, 1992, Addison-Wesley, ISBN 0-201-56317-7.

    The stdin, stdout, and stderr arguments are file names that
    will be opened and be used to replace the standard file descriptors
    in sys.stdin, sys.stdout, and sys.stderr.
    These arguments are optional and default to /dev/null.
    Note that stderr is opened unbuffered, so
    if it shares a file with stdout then interleaved output
    may not appear in the order that you expect.
    '''

    # Do first fork.
    try: 
        pid = os.fork() 
        if pid > 0:
            sys.exit(0)   # Exit first parent.
    except OSError, e: 
        sys.stderr.write ("fork #1 failed: (%d) %s\n" % (e.errno, e.strerror) )
        sys.exit(1)

    # Decouple from parent environment.
    os.chdir("/") 
    os.umask(0) 
    os.setsid() 

    # Do second fork.
    try: 
        pid = os.fork() 
        if pid > 0:
            sys.exit(0)   # Exit second parent.
    except OSError, e: 
        sys.stderr.write ("fork #2 failed: (%d) %s\n" % (e.errno, e.strerror) )
        sys.exit(1)

    # Now I am a daemon!
    
    # Redirect standard file descriptors.
    si = open(stdin, 'r')
    so = open(stdout, 'a+')
    se = open(stderr, 'a+', 0)
    os.dup2(si.fileno(), sys.stdin.fileno())
    os.dup2(so.fileno(), sys.stdout.fileno())
    os.dup2(se.fileno(), sys.stderr.fileno())

    # I now return as the daemon
    return 0

def add_cursor_blink (response, row, col):
    i = (row-1) * 80 + col
    return response[:i]+'<img src="http://www.noah.org/cursor.gif">'+response[i:]

def endless_poll (child, prompt, screen, refresh_timeout=1):
    """This keeps the screen updated with the output of the child.
        This runs in a separate thread.
    """
    child.logfile = screen
    while True:
        child.prompt (timeout=refresh_timeout)
        #i = child.expect ([prompt, pexpect.TIMEOUT], timeout=refresh_timeout)

def main ():
    try:
        optlist, args = getopt.getopt(sys.argv[1:], 'h?d', ['help','h','?', 'hostname', 'username', 'password', 'port'])
    except Exception, e:
        print str(e)
        exit_with_usage()

    command_line_options = dict(optlist)
    options = dict(optlist)
    # There are a million ways to cry for help. These are but a few of them.
    if [elem for elem in command_line_options if elem in ['-h','--h','-?','--?','--help']]:
        exit_with_usage(0)
  
    hostname = "127.0.0.1"
    port = 1664
    username = os.getenv('USER')
    password = ""

    if '-d' in options:
        daemon_mode = True
    else:
        daemon_mode = False

    if '--hostname' in options:
        hostname = options['--hostname']
    if '--port' in options:
        port = int(options['--port'])
    if '--username' in options:
        username = options['--username']
    print "Login for %s@%s:%s" % (username, hostname, port)
    if '--password' in options:
        password = options['--password']
    else:
        password = getpass.getpass('password: ')
   
    #if daemon_mode: 
    #    print "daemonizing server"
    #    daemonize ()
    #daemonize('/dev/null','/tmp/daemon.log','/tmp/daemon.log')
    
    sys.stdout.write ('server started with pid %d\n' % os.getpid() )

    virtual_screen = ANSI.ANSI (24,80) 
    child = pxssh.pxssh()
    child.login (hostname, username, password)
    print 'created shell. command line prompt is', child.PROMPT
    #child.sendline ('stty -echo')
    virtual_screen.write (child.before)
    virtual_screen.write (child.after)

    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    localhost = '127.0.0.1'
    s.bind((localhost, port))
    print 'Listen'
    s.listen(1)
    print 'Accept'

    r = roller (0.01, endless_poll, (child, child.PROMPT, virtual_screen))
    r.start()
    print "screen poll updater started in background thread"
    sys.stdout.flush()

    try:
        while True:
            conn, addr = s.accept()
            print 'Connected by', addr
            data = conn.recv(1024)
            request = data.split(' ', 1)
            if len(request) < 2:
                conn.send(error_response('request did not have enough arguments.'))
                conn.close()
                continue   
            cmd = request[0].strip()
            arg = request[1].strip()

            if cmd == 'command' or cmd == 'pretty':
                child.sendline (arg)
                child.prompt(timeout=1)
            elif cmd == 'refresh':
                pass
                shell_window = pretty_box(virtual_screen.rows,virtual_screen.cols,str(virtual_screen))
            elif cmd == 'skip':
            # Wait until the TIMEOUT then throw away all data from the child.
            # Use to catch up the screen with the shell if state gets out of sync.
                child.expect (pexpect.TIMEOUT)
                sh_response = child.before.replace ('\r', '')
                virtual_screen.write (sh_response)
            if cmd == 'command':
                shell_window = virtual_screen.dump()
            elif cmd == 'pretty':
                shell_window = pretty_box(virtual_screen.rows,virtual_screen.cols,str(virtual_screen))
            response = []
            response.append ('%03d' % virtual_screen.rows)
            response.append ('%03d' % virtual_screen.cols)
            response.append (shell_window)
            #response = add_cursor_blink (response, row, col)
            sent = conn.send('\n'.join(response))
            if sent < len (response):
                print "Sent is too short. Some data was cut off."
            conn.close()
            if arg == 'exit':
                s.close()
                break
    finally:
        print "cleaning up socket"
        s.close()

def pretty_box (rows, cols, s):
    """This puts an ASCII text box around the given string, s.
    """
    top_bot = '+' + '-'*cols + '+\n'
    return top_bot + '\n'.join(['|'+line+'|' for line in s.split('\n')]) + '\n' + top_bot
    
def error_response (msg):
    response = []
    response.append ('000')
    response.append ('000')
    response.append ("""{REQUEST} {ARGUMENT}
{REQUEST} may be one of the following:
    command : Run the ARGUMENT as a shell command. Returns raw screen array.
    pretty  : Like 'command', but formats the screen array for printing.
    skip    : Use to catch up the screen with the shell if state gets out of sync.
Example:
    pretty ls -l
""")
    response.append (msg)
    return '\n'.join(response)
     
if __name__ == "__main__":
#    daemonize('/dev/null','/tmp/daemon.log','/tmp/daemon.log')
    main()