telnetlib —- Telnet client

Source code:Lib/telnetlib.py

The telnetlib module provides a Telnet class that implements theTelnet protocol. See RFC 854 for details about the protocol. In addition, itprovides symbolic constants for the protocol characters (see below), and for thetelnet options. The symbolic names of the telnet options follow the definitionsin arpa/telnet.h, with the leading TELOPT_ removed. For symbolic namesof options which are traditionally not included in arpa/telnet.h, see themodule 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 (EraseCharacter), EL (Erase Line), GA (Go Ahead), SB (Subnegotiation Begin).

  • class telnetlib.Telnet(host=None, port=0[, timeout])
  • Telnet represents a connection to a Telnet server. The instance isinitially not connected by default; the open() method must be used toestablish a connection. Alternatively, the host name and optional portnumber can be passed to the constructor too, in which case the connection tothe server will be established before the constructor returns. The optionaltimeout parameter specifies a timeout in seconds for blocking operationslike the connection attempt (if not specified, the global default timeoutsetting will be used).

Do not reopen an already connected instance.

This class has many read_*() methods. Note that some of them raiseEOFError when the end of the connection is read, because they can returnan empty string for other reasons. See the individual descriptions below.

A Telnet object is a context manager and can be used in awith statement. When the with block ends, theclose() method is called:

  1. >>> from telnetlib import Telnet
  2. >>> with Telnet('localhost', 23) as tn:
  3. ...     tn.interact()
  4. ...

在 3.6 版更改: Context manager support added

参见

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

Telnet Objects

Telnet instances have the following methods:

  • Telnet.readuntil(_expected, timeout=None)
  • Read until a given byte string, expected, is encountered or until _timeout_seconds have passed.

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

  • Telnet.read_all()
  • Read all data until EOF as bytes; block until connection closed.
  • Telnet.read_some()
  • Read at least one byte of cooked data unless EOF is hit. Return b'' ifEOF 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 b'' if no cooked data available otherwise. Do not block unless inthe midst of an IAC sequence.

  • Telnet.read_eager()
  • Read readily available data.

Raise EOFError if connection closed and no cooked data available.Return b'' if no cooked data available otherwise. Do not block unless inthe 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. Returnb'' if no cooked data available otherwise. Do not block unless in themidst 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. Returnb'' 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). Thecallback should access these data when it was invoked with a SE command.This method never blocks.
  • Telnet.open(host, port=0[, timeout])
  • Connect to a host. The optional second argument is the port number, whichdefaults to the standard Telnet port (23). The optional timeout parameterspecifies a timeout in seconds for blocking operations like the connectionattempt (if not specified, the global default timeout setting will be used).

Do not try to reopen an already connected instance.

  • Telnet.msg(msg, *args)
  • Print a debug message when the debug level is > 0. If extra arguments arepresent, they are substituted in the message using the standard stringformatting operator.
  • Telnet.setdebuglevel(_debuglevel)
  • Set the debug level. The higher the value of debuglevel, the more debugoutput you get (on sys.stdout).
  • Telnet.close()
  • 关闭连接对象。
  • 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 byte string to the socket, doubling any IAC characters. This canblock if the connection is blocked. May raise OSError if theconnection is closed.

在 3.3 版更改: This method used to raise socket.error, which is now an aliasof OSError.

  • Telnet.interact()
  • Interaction function, emulates a very dumb Telnet client.
  • Telnet.mt_interact()
  • Multithreaded version of interact().
  • Telnet.expect(list, timeout=None)
  • Read until one from a list of a regular expressions matches.

The first argument is a list of regular expressions, either compiled(regex objects) or uncompiled (byte strings). Theoptional second argument is a timeout, in seconds; the default is to blockindefinitely.

Return a tuple of three items: the index in the list of the first regularexpression that matches; the match object returned; and the bytes read uptill and including the match.

If end of file is found and no bytes were read, raise EOFError.Otherwise, when nothing matches, return (-1, None, data) where data isthe bytes received so far (may be empty bytes if a timeout happened).

If a regular expression ends with a greedy match (such as .*) or if morethan one expression can match the same input, the results arenon-deterministic, and may depend on the I/O timing.

  • Telnet.setoption_negotiation_callback(_callback)
  • Each time a telnet option is read on the input flow, this callback (if set) iscalled 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:

  1. import getpass
  2. import telnetlib
  3.  
  4. HOST = "localhost"
  5. user = input("Enter your remote account: ")
  6. password = getpass.getpass()
  7.  
  8. tn = telnetlib.Telnet(HOST)
  9.  
  10. tn.read_until(b"login: ")
  11. tn.write(user.encode('ascii') + b"\n")
  12. if password:
  13.     tn.read_until(b"Password: ")
  14.     tn.write(password.encode('ascii') + b"\n")
  15.  
  16. tn.write(b"ls\n")
  17. tn.write(b"exit\n")
  18.  
  19. print(tn.read_all().decode('ascii'))