Decided to add the telnet library that I wrote long ago (it's still in
the Demos/cwilib directory). Converted comments to doc strings and used default arguments instead of *args. Updated the example.
This commit is contained in:
Guido van Rossum
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"""TELNET client class.
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Based on RFC 854: TELNET Protocol Specification, by J. Postel and
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J. Reynolds
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Example:
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>>> from telnetlib import Telnet
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>>> tn = Telnet('www.python.org', 79) # connect to finger port
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>>> tn.write('guido\r\n')
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>>> print tn.read_all()
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Login Name TTY Idle When Where
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guido Guido van Rossum pts/2 <Dec 2 11:10> snag.cnri.reston..
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>>>
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Note that read_all() won't read until eof -- it just reads some data
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-- but it guarantees to read at least one byte unless EOF is hit.
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It is possible to pass a Telnet object to select.select() in order to
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wait until more data is available. Note that in this case,
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read_eager() may return '' even if there was data on the socket,
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because the protocol negotiation may have eaten the data. This is why
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EOFError is needed in some cases to distinguish between "no data" and
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"connection closed" (since the socket also appears ready for reading
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when it is closed).
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Bugs:
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- may hang when connection is slow in the middle of an IAC sequence
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To do:
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- option negotiation
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"""
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# Imported modules
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import socket
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import select
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import string
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import regsub
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# Tunable parameters
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DEBUGLEVEL = 0
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# Telnet protocol defaults
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TELNET_PORT = 23
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# Telnet protocol characters (don't change)
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IAC = chr(255) # "Interpret As Command"
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DONT = chr(254)
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DO = chr(253)
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WONT = chr(252)
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WILL = chr(251)
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theNULL = chr(0)
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class Telnet:
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"""Telnet interface class.
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An instance of this class represents a connection to a telnet
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server. The instance is initially not connected; the open()
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method must be used to establish a connection. Alternatively, the
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host name and optional port number can be passed to the
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constructor, too.
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Don't try to reopen an already connected instance.
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This class has many read_*() methods. Note that some of them
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raise EOFError when the end of the connection is read, because
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they can return an empty string for other reasons. See the
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individual doc strings.
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read_until(expected, [timeout])
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Read until the expected string has been seen, or a timeout is
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hit (default is no timeout); may block.
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read_all()
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Read all data until EOF; may block.
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read_some()
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Read at least one byte or EOF; may block.
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read_very_eager()
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Read all data available already queued or on the socket,
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without blocking.
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read_eager()
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Read either data already queued or some data available on the
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socket, without blocking.
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read_lazy()
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Read all data in the raw queue (processing it first), without
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doing any socket I/O.
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read_very_lazy()
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Reads all data in the cooked queue, without doing any socket
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I/O.
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"""
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def __init__(self, host=None, port=0):
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"""Constructor.
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When called without arguments, create an unconnected instance.
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With a hostname argument, it connects the instance; a port
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number is optional.
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"""
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self.debuglevel = DEBUGLEVEL
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self.host = host
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self.port = port
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self.sock = None
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self.rawq = ''
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self.irawq = 0
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self.cookedq = ''
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self.eof = 0
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if host:
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self.open(host, port)
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def open(self, host, port=0):
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"""Connect to a host.
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The optional second argument is the port number, which
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defaults to the standard telnet port (23).
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Don't try to reopen an already connected instance.
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"""
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self.eof = 0
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if not port:
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port = TELNET_PORT
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self.host = host
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self.port = port
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self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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self.sock.connect((self.host, self.port))
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def __del__(self):
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"""Destructor -- close the connection."""
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self.close()
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def msg(self, msg, *args):
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"""Print a debug message, when the debug level is > 0.
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If extra arguments are present, they are substituted in the
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message using the standard string formatting operator.
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"""
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if self.debuglevel > 0:
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print 'Telnet(%s,%d):' % (self.host, self.port),
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if args:
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print msg % args
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else:
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print msg
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def set_debuglevel(self, debuglevel):
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"""Set the debug level.
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The higher it is, the more debug output you get (on sys.stdout).
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"""
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self.debuglevel = debuglevel
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def close(self):
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"""Close the connection."""
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if self.sock:
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self.sock.close()
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self.sock = 0
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self.eof = 1
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def get_socket(self):
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"""Return the socket object used internally."""
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return self.sock
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def fileno(self):
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"""Return the fileno() of the socket object used internally."""
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return self.sock.fileno()
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def write(self, buffer):
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"""Write a string to the socket, doubling any IAC characters.
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Can block if the connection is blocked. May raise
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socket.error if the connection is closed.
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"""
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if IAC in buffer:
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buffer = regsub.gsub(IAC, IAC+IAC, buffer)
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self.sock.send(buffer)
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def read_until(self, match, timeout=None):
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"""Read until a given string is encountered or until timeout.
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When no match is found, return whatever is available instead,
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possibly the empty string. Raise EOFError if the connection
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is closed and no cooked data is available.
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"""
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n = len(match)
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self.process_rawq()
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i = string.find(self.cookedq, match)
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if i >= 0:
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i = i+n
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buf = self.cookedq[:i]
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self.cookedq = self.cookedq[i:]
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return buf
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s_reply = ([self], [], [])
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s_args = s_reply
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if timeout is not None:
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s_args = s_args + (timeout,)
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while not self.eof and apply(select.select, s_args) == s_reply:
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i = max(0, len(self.cookedq)-n)
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self.fill_rawq()
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self.process_rawq()
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i = string.find(self.cookedq, match, i)
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if i >= 0:
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i = i+n
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buf = self.cookedq[:i]
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self.cookedq = self.cookedq[i:]
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return buf
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return self.read_very_lazy()
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def read_all(self):
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"""Read all data until EOF; block until connection closed."""
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self.process_rawq()
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while not self.eof:
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self.fill_rawq()
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self.process_rawq()
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buf = self.cookedq
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self.cookedq = ''
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return buf
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def read_some(self):
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"""Read at least one byte of cooked data unless EOF is hit.
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Return '' if EOF is hit. Block if no data is immediately
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available.
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"""
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self.process_rawq()
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while not self.cookedq and not self.eof:
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self.fill_rawq()
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self.process_rawq()
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buf = self.cookedq
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self.cookedq = ''
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return buf
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def read_very_eager(self):
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"""Read everything that's possible without blocking in I/O (eager).
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Raise EOFError if connection closed and no cooked data
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available. Return '' if no cooked data available otherwise.
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Don't block unless in the midst of an IAC sequence.
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"""
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self.process_rawq()
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while not self.eof and self.sock_avail():
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self.fill_rawq()
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self.process_rawq()
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return self.read_very_lazy()
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def read_eager(self):
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"""Read readily available data.
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Raise EOFError if connection closed and no cooked data
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available. Return '' if no cooked data available otherwise.
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Don't block unless in the midst of an IAC sequence.
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"""
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self.process_rawq()
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while not self.cookedq and not self.eof and self.sock_avail():
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self.fill_rawq()
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self.process_rawq()
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return self.read_very_lazy()
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def read_lazy(self):
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"""Process and return data that's already in the queues (lazy).
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Raise EOFError if connection closed and no data available.
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Return '' if no cooked data available otherwise. Don't block
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unless in the midst of an IAC sequence.
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"""
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self.process_rawq()
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return self.read_very_lazy()
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def read_very_lazy(self):
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"""Return any data available in the cooked queue (very lazy).
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Raise EOFError if connection closed and no data available.
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Return '' if no cooked data available otherwise. Don't block.
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"""
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buf = self.cookedq
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self.cookedq = ''
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if not buf and self.eof and not self.rawq:
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raise EOFError, 'telnet connection closed'
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return buf
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def process_rawq(self):
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"""Transfer from raw queue to cooked queue.
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Set self.eof when connection is closed. Don't block unless in
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the midst of an IAC sequence.
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"""
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buf = ''
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try:
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while self.rawq:
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c = self.rawq_getchar()
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if c == theNULL:
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continue
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if c == "\021":
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continue
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if c != IAC:
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buf = buf + c
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continue
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c = self.rawq_getchar()
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if c == IAC:
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buf = buf + c
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elif c in (DO, DONT):
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opt = self.rawq_getchar()
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self.msg('IAC %s %d', c == DO and 'DO' or 'DONT', ord(c))
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self.sock.send(IAC + WONT + opt)
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elif c in (WILL, WONT):
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opt = self.rawq_getchar()
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self.msg('IAC %s %d',
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c == WILL and 'WILL' or 'WONT', ord(c))
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else:
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self.msg('IAC %s not recognized' % `c`)
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except EOFError: # raised by self.rawq_getchar()
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pass
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self.cookedq = self.cookedq + buf
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def rawq_getchar(self):
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"""Get next char from raw queue.
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Block if no data is immediately available. Raise EOFError
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when connection is closed.
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"""
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if not self.rawq:
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self.fill_rawq()
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if self.eof:
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raise EOFError
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c = self.rawq[self.irawq]
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self.irawq = self.irawq + 1
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if self.irawq >= len(self.rawq):
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self.rawq = ''
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self.irawq = 0
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return c
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def fill_rawq(self):
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"""Fill raw queue from exactly one recv() system call.
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Block if no data is immediately available. Set self.eof when
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connection is closed.
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"""
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if self.irawq >= len(self.rawq):
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self.rawq = ''
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self.irawq = 0
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# The buffer size should be fairly small so as to avoid quadratic
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# behavior in process_rawq() above
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buf = self.sock.recv(50)
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self.eof = (not buf)
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self.rawq = self.rawq + buf
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def sock_avail(self):
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"""Test whether data is available on the socket."""
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return select.select([self], [], [], 0) == ([self], [], [])
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def interact(self):
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"""Interaction function, emulates a very dumb telnet client."""
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import sys, select
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while 1:
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rfd, wfd, xfd = select.select([self, sys.stdin], [], [])
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if sys.stdin in rfd:
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line = sys.stdin.readline()
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self.write(line)
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if self in rfd:
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try:
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text = self.read_eager()
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except EOFError:
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print '*** Connection closed by remote host ***'
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break
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if text:
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sys.stdout.write(text)
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sys.stdout.flush()
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self.close()
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def test():
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"""Test program for telnetlib.
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Usage: python telnetlib.py [-d] ... [host [port]]
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Default host is localhost; default port is 23.
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"""
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import sys
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debuglevel = 0
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while sys.argv[1:] and sys.argv[1] == '-d':
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debuglevel = debuglevel+1
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del sys.argv[1]
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host = 'localhost'
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if sys.argv[1:]:
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host = sys.argv[1]
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port = 0
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if sys.argv[2:]:
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portstr = sys.argv[2]
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try:
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port = int(portstr)
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except ValueError:
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port = socket.getservbyname(portstr, 'tcp')
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tn = Telnet()
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tn.set_debuglevel(debuglevel)
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tn.open(host, port)
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tn.interact()
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tn.close()
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if __name__ == '__main__':
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test()
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