telnetlib3 is a Telnet Client and Server library for python. This project requires python 3.7 and later, using the asyncio module.
This library also contains a copy of telnetlib.py from the standard library of Python 3.12 before it was removed in Python 3.13. asyncio is not required.
To migrate code from Python 3.11 and earlier, install this library and change instances of telnetlib to telnetlib3:
# OLD imports:
import telnetlib
# - or -
from telnetlib import Telnet, ECHO, BINARY
# NEW imports:
import telnetlib3.telnetlib as telnetlib
# - or -
from telnetlib3 import Telnet, ECHO, BINARY
from telnetlib3.telnetlib import Telnet, ECHO, BINARYWriting a Telnet Server that offers a basic "war game":
import asyncio, telnetlib3
async def shell(reader, writer):
writer.write('\r\nWould you like to play a game? ')
inp = await reader.read(1)
if inp:
writer.echo(inp)
writer.write('\r\nThey say the only way to win '
'is to not play at all.\r\n')
await writer.drain()
writer.close()
async def main():
server = await telnetlib3.create_server('127.0.0.1', 6023, shell=shell)
await server.wait_closed()
asyncio.run(main())Writing a Telnet Client that plays the "war game" against this server:
import asyncio, telnetlib3
async def shell(reader, writer):
while True:
# read stream until '?' mark is found
outp = await reader.read(1024)
if not outp:
# End of File
break
elif '?' in outp:
# reply all questions with 'y'.
writer.write('y')
# display all server output
print(outp, flush=True)
# EOF
print()
async def main():
reader, writer = await telnetlib3.open_connection('localhost', 6023, shell=shell)
await writer.protocol.waiter_closed
asyncio.run(main())Two command-line scripts are distributed with this package, telnetlib3-client and telnetlib3-server.
Both command-line scripts accept argument --shell=my_module.fn_shell
describing a python module path to an function of signature
async def shell(reader, writer), as in the above examples.
These scripts also serve as more advanced server and client examples that perform advanced telnet option negotation and may serve as a basis for creating your own custom negotiation behaviors.
Find their filepaths using command:
python -c 'import telnetlib3.server;print(telnetlib3.server.__file__, telnetlib3.client.__file__)'
This is an entry point for command python -m telnetlib3.client
Small terminal telnet client. Some example destinations and options:
telnetlib3-client --loglevel warn 1984.ws telnetlib3-client --loglevel debug --logfile logfile.txt nethack.alt.org telnetlib3-client --encoding=cp437 --force-binary blackflag.acid.org
See section Encoding about arguments, --encoding=cp437 and --force-binary.
usage: telnetlib3-client [-h] [--term TERM] [--loglevel LOGLEVEL]
[--logfmt LOGFMT] [--logfile LOGFILE] [--shell SHELL]
[--encoding ENCODING] [--speed SPEED]
[--encoding-errors {replace,ignore,strict}]
[--force-binary] [--connect-minwait CONNECT_MINWAIT]
[--connect-maxwait CONNECT_MAXWAIT]
host [port]
Telnet protocol client
positional arguments:
host hostname
port port number (default: 23)
optional arguments:
-h, --help show this help message and exit
--term TERM terminal type (default: xterm-256color)
--loglevel LOGLEVEL log level (default: warn)
--logfmt LOGFMT log format (default: %(asctime)s %(levelname)s
%(filename)s:%(lineno)d %(message)s)
--logfile LOGFILE filepath (default: None)
--shell SHELL module.function_name (default:
telnetlib3.telnet_client_shell)
--encoding ENCODING encoding name (default: utf8)
--speed SPEED connection speed (default: 38400)
--encoding-errors {replace,ignore,strict}
handler for encoding errors (default: replace)
--force-binary force encoding (default: True)
--connect-minwait CONNECT_MINWAIT
shell delay for negotiation (default: 1.0)
--connect-maxwait CONNECT_MAXWAIT
timeout for pending negotiation (default: 4.0)
This is an entry point for command python -m telnetlib3.server
Telnet server providing the default debugging shell. This provides a simple shell server that allows introspection of the session's values.
Example session:
tel:sh> help quit, writer, slc, toggle [option|all], reader, proto tel:sh> writer <TelnetWriter server mode:kludge +lineflow -xon_any +slc_sim server-will:BINARY,ECHO,SGA client-will:BINARY,NAWS,NEW_ENVIRON,TTYPE> tel:sh> reader <TelnetReaderUnicode encoding='utf8' limit=65536 buflen=0 eof=False> tel:sh> toggle all wont echo. wont suppress go-ahead. wont outbinary. dont inbinary. xon-any enabled. lineflow disabled. tel:sh> reader <TelnetReaderUnicode encoding='US-ASCII' limit=65536 buflen=1 eof=False> tel:sh> writer <TelnetWriter server mode:local -lineflow +xon_any +slc_sim client-will:NAWS,NEW_ENVIRON,TTYPE>
usage: telnetlib3-server [-h] [--loglevel LOGLEVEL] [--logfile LOGFILE]
[--logfmt LOGFMT] [--shell SHELL]
[--encoding ENCODING] [--force-binary]
[--timeout TIMEOUT]
[--connect-maxwait CONNECT_MAXWAIT]
[host] [port]
Telnet protocol server
positional arguments:
host bind address (default: localhost)
port bind port (default: 6023)
optional arguments:
-h, --help show this help message and exit
--loglevel LOGLEVEL level name (default: info)
--logfile LOGFILE filepath (default: None)
--logfmt LOGFMT log format (default: %(asctime)s %(levelname)s
%(filename)s:%(lineno)d %(message)s)
--shell SHELL module.function_name (default: telnet_server_shell)
--encoding ENCODING encoding name (default: utf8)
--force-binary force binary transmission (default: False)
--timeout TIMEOUT idle disconnect (0 disables) (default: 300)
--connect-maxwait CONNECT_MAXWAIT
timeout for pending negotiation (default: 4.0)
In this client connection example:
telnetlib3-client --encoding=cp437 --force-binary blackflag.acid.org
Note the use of --encoding=cp437 to translate input and output characters of the remote end. This example legacy telnet BBS is unable to negotiate about or present characters in any other encoding but CP437. Without these arguments, Telnet protocol would dictate our session to be US-ASCII.
Argument --force-binary is also required in many cases, with both
telnetlib3-client and telnetlib3-server. In the original Telnet protocol
specifications, the Network Virtual Terminal (NVT) is defined as 7-bit US-ASCII,
and this is the default state for both ends until negotiated otherwise by RFC-856
by negotiation of BINARY TRANSMISSION.
However, many common telnet clients and servers fail to negotiate for BINARY
correctly or at all. Using --force-binary allows non-ASCII encodings to be
used with those kinds of clients.
A Telnet Server that prefers "utf8" encoding, and, transmits it even in the case of failed BINARY negotiation, to support a "dumb" telnet client like netcat:
telnetlib3-server --encoding=utf8 --force-binary
Connecting with "dumb" client:
nc -t localhost 6023
The following RFC specifications are implemented:
- rfc-727, "Telnet Logout Option," Apr 1977.
- rfc-779, "Telnet Send-Location Option", Apr 1981.
- rfc-854, "Telnet Protocol Specification", May 1983.
- rfc-855, "Telnet Option Specifications", May 1983.
- rfc-856, "Telnet Binary Transmission", May 1983.
- rfc-857, "Telnet Echo Option", May 1983.
- rfc-858, "Telnet Suppress Go Ahead Option", May 1983.
- rfc-859, "Telnet Status Option", May 1983.
- rfc-860, "Telnet Timing mark Option", May 1983.
- rfc-885, "Telnet End of Record Option", Dec 1983.
- rfc-1073, "Telnet Window Size Option", Oct 1988.
- rfc-1079, "Telnet Terminal Speed Option", Dec 1988.
- rfc-1091, "Telnet Terminal-Type Option", Feb 1989.
- rfc-1096, "Telnet X Display Location Option", Mar 1989.
- rfc-1123, "Requirements for Internet Hosts", Oct 1989.
- rfc-1184, "Telnet Linemode Option (extended options)", Oct 1990.
- rfc-1372, "Telnet Remote Flow Control Option", Oct 1992.
- rfc-1408, "Telnet Environment Option", Jan 1993.
- rfc-1571, "Telnet Environment Option Interoperability Issues", Jan 1994.
- rfc-1572, "Telnet Environment Option", Jan 1994.
- rfc-2066, "Telnet Charset Option", Jan 1997.
Further documentation available at https://telnetlib3.readthedocs.io/