cpython/Lib/telnetlib.py

"""TELNET client class.

Based on RFC 854: TELNET Protocol Specification, by J. Postel and
J. Reynolds

Example:

>>> from telnetlib import Telnet
>>> tn = Telnet('www.python.org', 79)   # connect to finger port
>>> tn.write('guido\r\n')
>>> print tn.read_all()
Login       Name               TTY         Idle    When    Where
guido    Guido van Rossum      pts/2        <Dec  2 11:10> snag.cnri.reston..
 
>>>

Note that read_all() won't read until eof -- it just reads some data
-- but it guarantees to read at least one byte unless EOF is hit.

It is possible to pass a Telnet object to select.select() in order to
wait until more data is available.  Note that in this case,
read_eager() may return '' even if there was data on the socket,
because the protocol negotiation may have eaten the data.  This is why
EOFError is needed in some cases to distinguish between "no data" and
"connection closed" (since the socket also appears ready for reading
when it is closed).

Bugs:
- may hang when connection is slow in the middle of an IAC sequence

To do:
- option negotiation

"""


# Imported modules
import socket
import select
import string
import regsub

# Tunable parameters
DEBUGLEVEL = 0

# Telnet protocol defaults
TELNET_PORT = 23

# Telnet protocol characters (don't change)
IAC  = chr(255) # "Interpret As Command"
DONT = chr(254)
DO   = chr(253)
WONT = chr(252)
WILL = chr(251)
theNULL = chr(0)


class Telnet:

    """Telnet interface class.

    An instance of this class represents a connection to a telnet
    server.  The instance is initially not connected; the open()
    method must be used to establish a connection.  Alternatively, the
    host name and optional port number can be passed to the
    constructor, too.

    Don't try to reopen an already connected instance.

    This class has many read_*() methods.  Note that some of them
    raise EOFError when the end of the connection is read, because
    they can return an empty string for other reasons.  See the
    individual doc strings.

    read_until(expected, [timeout])
        Read until the expected string has been seen, or a timeout is
	hit (default is no timeout); may block.

    read_all()
        Read all data until EOF; may block.

    read_some()
        Read at least one byte or EOF; may block.

    read_very_eager()
        Read all data available already queued or on the socket,
	without blocking.

    read_eager()
        Read either data already queued or some data available on the
	socket, without blocking.

    read_lazy()
        Read all data in the raw queue (processing it first), without
	doing any socket I/O.

    read_very_lazy()
        Reads all data in the cooked queue, without doing any socket
	I/O.

    """

    def __init__(self, host=None, port=0):
	"""Constructor.

	When called without arguments, create an unconnected instance.
	With a hostname argument, it connects the instance; a port
	number is optional.

	"""
	self.debuglevel = DEBUGLEVEL
	self.host = host
	self.port = port
	self.sock = None
	self.rawq = ''
	self.irawq = 0
	self.cookedq = ''
	self.eof = 0
	if host:
	    self.open(host, port)

    def open(self, host, port=0):
	"""Connect to a host.

	The optional second argument is the port number, which
	defaults to the standard telnet port (23).

	Don't try to reopen an already connected instance.

	"""
	self.eof = 0
	if not port:
	    port = TELNET_PORT
	self.host = host
	self.port = port
	self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
	self.sock.connect((self.host, self.port))

    def __del__(self):
	"""Destructor -- close the connection."""
	self.close()

    def msg(self, msg, *args):
	"""Print a debug message, when the debug level is > 0.

	If extra arguments are present, they are substituted in the
	message using the standard string formatting operator.

	"""
	if self.debuglevel > 0:
	    print 'Telnet(%s,%d):' % (self.host, self.port),
	    if args:
		print msg % args
	    else:
		print msg

    def set_debuglevel(self, debuglevel):
	"""Set the debug level.

	The higher it is, the more debug output you get (on sys.stdout).

	"""
	self.debuglevel = debuglevel

    def close(self):
	"""Close the connection."""
	if self.sock:
	    self.sock.close()
	self.sock = 0
	self.eof = 1

    def get_socket(self):
	"""Return the socket object used internally."""
	return self.sock

    def fileno(self):
	"""Return the fileno() of the socket object used internally."""
	return self.sock.fileno()

    def write(self, buffer):
	"""Write a string to the socket, doubling any IAC characters.

	Can block if the connection is blocked.  May raise
	socket.error if the connection is closed.

	"""
	if IAC in buffer:
	    buffer = regsub.gsub(IAC, IAC+IAC, buffer)
	self.sock.send(buffer)

    def read_until(self, match, timeout=None):
	"""Read until a given string is encountered or until timeout.

	When no match is found, return whatever is available instead,
	possibly the empty string.  Raise EOFError if the connection
	is closed and no cooked data is available.

	"""
	n = len(match)
	self.process_rawq()
	i = string.find(self.cookedq, match)
	if i >= 0:
	    i = i+n
	    buf = self.cookedq[:i]
	    self.cookedq = self.cookedq[i:]
	    return buf
	s_reply = ([self], [], [])
	s_args = s_reply
	if timeout is not None:
	    s_args = s_args + (timeout,)
	while not self.eof and apply(select.select, s_args) == s_reply:
	    i = max(0, len(self.cookedq)-n)
	    self.fill_rawq()
	    self.process_rawq()
	    i = string.find(self.cookedq, match, i)
	    if i >= 0:
		i = i+n
		buf = self.cookedq[:i]
		self.cookedq = self.cookedq[i:]
		return buf
	return self.read_very_lazy()

    def read_all(self):
	"""Read all data until EOF; block until connection closed."""
	self.process_rawq()
	while not self.eof:
	    self.fill_rawq()
	    self.process_rawq()
	buf = self.cookedq
	self.cookedq = ''
	return buf

    def read_some(self):
	"""Read at least one byte of cooked data unless EOF is hit.

	Return '' if EOF is hit.  Block if no data is immediately
	available.

	"""
	self.process_rawq()
	while not self.cookedq and not self.eof:
	    self.fill_rawq()
	    self.process_rawq()
	buf = self.cookedq
	self.cookedq = ''
	return buf

    def read_very_eager(self):
	"""Read everything that's possible without blocking in I/O (eager).
	
	Raise EOFError if connection closed and no cooked data
	available.  Return '' if no cooked data available otherwise.
	Don't block unless in the midst of an IAC sequence.

	"""
	self.process_rawq()
	while not self.eof and self.sock_avail():
	    self.fill_rawq()
	    self.process_rawq()
	return self.read_very_lazy()

    def read_eager(self):
	"""Read readily available data.

	Raise EOFError if connection closed and no cooked data
	available.  Return '' if no cooked data available otherwise.
	Don't block unless in the midst of an IAC sequence.

	"""
	self.process_rawq()
	while not self.cookedq and not self.eof and self.sock_avail():
	    self.fill_rawq()
	    self.process_rawq()
	return self.read_very_lazy()

    def read_lazy(self):
	"""Process and return data that's already in the queues (lazy).
	
	Raise EOFError if connection closed and no data available.
	Return '' if no cooked data available otherwise.  Don't block
	unless in the midst of an IAC sequence.

	"""
	self.process_rawq()
	return self.read_very_lazy()

    def read_very_lazy(self):
	"""Return any data available in the cooked queue (very lazy).

	Raise EOFError if connection closed and no data available.
	Return '' if no cooked data available otherwise.  Don't block.

	"""
	buf = self.cookedq
	self.cookedq = ''
	if not buf and self.eof and not self.rawq:
	    raise EOFError, 'telnet connection closed'
	return buf

    def process_rawq(self):
	"""Transfer from raw queue to cooked queue.

	Set self.eof when connection is closed.  Don't block unless in
	the midst of an IAC sequence.

	"""
	buf = ''
	try:
	    while self.rawq:
		c = self.rawq_getchar()
		if c == theNULL:
		    continue
		if c == "\021":
		    continue
		if c != IAC:
		    buf = buf + c
		    continue
		c = self.rawq_getchar()
		if c == IAC:
		    buf = buf + c
		elif c in (DO, DONT):
		    opt = self.rawq_getchar()
		    self.msg('IAC %s %d', c == DO and 'DO' or 'DONT', ord(c))
		    self.sock.send(IAC + WONT + opt)
		elif c in (WILL, WONT):
		    opt = self.rawq_getchar()
		    self.msg('IAC %s %d',
			     c == WILL and 'WILL' or 'WONT', ord(c))
		else:
		    self.msg('IAC %s not recognized' % `c`)
	except EOFError: # raised by self.rawq_getchar()
	    pass
	self.cookedq = self.cookedq + buf

    def rawq_getchar(self):
	"""Get next char from raw queue.

	Block if no data is immediately available.  Raise EOFError
	when connection is closed.

	"""
	if not self.rawq:
	    self.fill_rawq()
	    if self.eof:
		raise EOFError
	c = self.rawq[self.irawq]
	self.irawq = self.irawq + 1
	if self.irawq >= len(self.rawq):
	    self.rawq = ''
	    self.irawq = 0
	return c

    def fill_rawq(self):
	"""Fill raw queue from exactly one recv() system call.

	Block if no data is immediately available.  Set self.eof when
	connection is closed.

	"""
	if self.irawq >= len(self.rawq):
	    self.rawq = ''
	    self.irawq = 0
	# The buffer size should be fairly small so as to avoid quadratic
	# behavior in process_rawq() above
	buf = self.sock.recv(50)
	self.eof = (not buf)
	self.rawq = self.rawq + buf

    def sock_avail(self):
	"""Test whether data is available on the socket."""
	return select.select([self], [], [], 0) == ([self], [], [])

    def interact(self):
	"""Interaction function, emulates a very dumb telnet client."""
	import sys, select
	while 1:
	    rfd, wfd, xfd = select.select([self, sys.stdin], [], [])
	    if sys.stdin in rfd:
		line = sys.stdin.readline()
		self.write(line)
	    if self in rfd:
		try:
		    text = self.read_eager()
		except EOFError:
		    print '*** Connection closed by remote host ***'
		    break
		if text:
		    sys.stdout.write(text)
		    sys.stdout.flush()
	self.close()



def test():
    """Test program for telnetlib.

    Usage: python telnetlib.py [-d] ... [host [port]]

    Default host is localhost; default port is 23.

    """
    import sys
    debuglevel = 0
    while sys.argv[1:] and sys.argv[1] == '-d':
	debuglevel = debuglevel+1
	del sys.argv[1]
    host = 'localhost'
    if sys.argv[1:]:
	host = sys.argv[1]
    port = 0
    if sys.argv[2:]:
	portstr = sys.argv[2]
	try:
	    port = int(portstr)
	except ValueError:
	    port = socket.getservbyname(portstr, 'tcp')
    tn = Telnet()
    tn.set_debuglevel(debuglevel)
    tn.open(host, port)
    tn.interact()
    tn.close()

if __name__ == '__main__':
    test()