
``telnetlib`` --- Telnet client
*******************************

The ``telnetlib`` module provides a ``Telnet`` class that implements
the Telnet protocol.  See **RFC 854** for details about the protocol.
In addition, it provides symbolic constants for the protocol
characters (see below), and for the telnet options. The symbolic names
of the telnet options follow the definitions in ``arpa/telnet.h``,
with the leading ``TELOPT_`` removed. For symbolic names of options
which are traditionally not included in ``arpa/telnet.h``, see the
module source itself.

The symbolic constants for the telnet commands are: IAC, DONT, DO,
WONT, WILL, SE (Subnegotiation End), NOP (No Operation), DM (Data
Mark), BRK (Break), IP (Interrupt process), AO (Abort output), AYT
(Are You There), EC (Erase Character), EL (Erase Line), GA (Go Ahead),
SB (Subnegotiation Begin).

class class telnetlib.Telnet([host[, port[, timeout]]])

   ``Telnet`` represents a connection to a Telnet server. The instance
   is initially not connected by default; the ``open()`` method must
   be used to establish a connection.  Alternatively, the host name
   and optional port and timeout can be passed to the constructor, in
   which case the connection to the server will be established before
   the constructor returns.  The optional *timeout* parameter
   specifies a timeout in seconds for the connection attempt (if not
   specified, the global default timeout setting will be used).

   number can be passed to the constructor, to, in which case the
   connection to the server will be established before the constructor
   returns. The optional *timeout* parameter specifies a timeout in
   seconds for blocking operations like the connection attempt (if not
   specified, or passed as None, the global default timeout setting
   will be used).

   Do not 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 descriptions below.

   Changed in version 2.6: *timeout* was added.

See also:

   **RFC 854** - Telnet Protocol Specification
      Definition of the Telnet protocol.


Telnet Objects
==============

``Telnet`` instances have the following methods:

Telnet.read_until(expected[, timeout])

   Read until a given string, *expected*, is encountered or until
   *timeout* seconds have passed.

   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.

Telnet.read_all()

   Read all data until EOF; block until connection closed.

Telnet.read_some()

   Read at least one byte of cooked data unless EOF is hit. Return
   ``''`` if EOF is hit.  Block if no data is immediately available.

Telnet.read_very_eager()

   Read everything that can be without blocking in I/O (eager).

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

Telnet.read_eager()

   Read readily available data.

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

Telnet.read_lazy()

   Process and return data already in the queues (lazy).

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

Telnet.read_very_lazy()

   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.  This method
   never blocks.

Telnet.read_sb_data()

   Return the data collected between a SB/SE pair (suboption
   begin/end). The callback should access these data when it was
   invoked with a ``SE`` command. This method never blocks.

   New in version 2.3.

Telnet.open(host[, port[, timeout]])

   Connect to a host. The optional second argument is the port number,
   which defaults to the standard Telnet port (23). The optional
   *timeout* parameter specifies a timeout in seconds for blocking
   operations like the connection attempt (if not specified, the
   global default timeout setting will be used).

   Do not try to reopen an already connected instance.

   Changed in version 2.6: *timeout* was added.

Telnet.msg(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.

Telnet.set_debuglevel(debuglevel)

   Set the debug level.  The higher the value of *debuglevel*, the
   more debug output you get (on ``sys.stdout``).

Telnet.close()

   Close the connection.

Telnet.get_socket()

   Return the socket object used internally.

Telnet.fileno()

   Return the file descriptor of the socket object used internally.

Telnet.write(buffer)

   Write a string to the socket, doubling any IAC characters. This can
   block if the connection is blocked.  May raise ``socket.error`` if
   the connection is closed.

Telnet.interact()

   Interaction function, emulates a very dumb Telnet client.

Telnet.mt_interact()

   Multithreaded version of ``interact()``.

Telnet.expect(list[, timeout])

   Read until one from a list of a regular expressions matches.

   The first argument is a list of regular expressions, either
   compiled (``re.RegexObject`` instances) or uncompiled (strings).
   The optional second argument is a timeout, in seconds; the default
   is to block indefinitely.

   Return a tuple of three items: the index in the list of the first
   regular expression that matches; the match object returned; and the
   text read up till and including the match.

   If end of file is found and no text was read, raise ``EOFError``.
   Otherwise, when nothing matches, return ``(-1, None, text)`` where
   *text* is the text received so far (may be the empty string if a
   timeout happened).

   If a regular expression ends with a greedy match (such as ``.*``)
   or if more than one expression can match the same input, the
   results are indeterministic, and may depend on the I/O timing.

Telnet.set_option_negotiation_callback(callback)

   Each time a telnet option is read on the input flow, this
   *callback* (if set) is called with the following parameters :
   callback(telnet socket, command (DO/DONT/WILL/WONT), option).  No
   other action is done afterwards by telnetlib.


Telnet Example
==============

A simple example illustrating typical use:

   import getpass
   import sys
   import telnetlib

   HOST = "localhost"
   user = raw_input("Enter your remote account: ")
   password = getpass.getpass()

   tn = telnetlib.Telnet(HOST)

   tn.read_until("login: ")
   tn.write(user + "\n")
   if password:
       tn.read_until("Password: ")
       tn.write(password + "\n")

   tn.write("ls\n")
   tn.write("exit\n")

   print tn.read_all()
