telnetli.py

minimal python variant for small footprint apps like embedded apps

"""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
- timeout should be intrinsic to the connection object instead of an
  option on one of the read calls only

"""


# Imported modules
import sys
import socket
import select
import string

# 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 = string.replace(buffer, IAC, IAC+IAC)
        self.msg("send %s", `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).