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#! /usr/bin/env python3
# Minimal interface to the Internet telnet protocol.
#
# It refuses all telnet options and does not recognize any of the other
# telnet commands, but can still be used to connect in line-by-line mode.
# It's also useful to play with a number of other services,
# like time, finger, smtp and even ftp.
#
# Usage: telnet host [port]
#
# The port may be a service name or a decimal port number;
# it defaults to 'telnet'.
import sys, posix, time
from socket import *
BUFSIZE = 1024
# Telnet protocol characters
IAC = chr(255) # Interpret as command
DONT = chr(254)
DO = chr(253)
WONT = chr(252)
WILL = chr(251)
def main():
host = sys.argv[1]
try:
hostaddr = gethostbyname(host)
except error:
sys.stderr.write(sys.argv[1] + ': bad host name\n')
sys.exit(2)
#
if len(sys.argv) > 2:
servname = sys.argv[2]
else:
servname = 'telnet'
#
if '0' <= servname[:1] <= '9':
port = eval(servname)
else:
try:
port = getservbyname(servname, 'tcp')
except error:
sys.stderr.write(servname + ': bad tcp service name\n')
sys.exit(2)
#
s = socket(AF_INET, SOCK_STREAM)
#
try:
s.connect((host, port))
except error as msg:
sys.stderr.write('connect failed: ' + repr(msg) + '\n')
sys.exit(1)
#
pid = posix.fork()
#
if pid == 0:
# child -- read stdin, write socket
while 1:
line = sys.stdin.readline()
s.send(line)
else:
# parent -- read socket, write stdout
iac = 0 # Interpret next char as command
opt = '' # Interpret next char as option
while 1:
data = s.recv(BUFSIZE)
if not data:
# EOF; kill child and exit
sys.stderr.write( '(Closed by remote host)\n')
posix.kill(pid, 9)
sys.exit(1)
cleandata = ''
for c in data:
if opt:
print(ord(c))
s.send(opt + c)
opt = ''
elif iac:
iac = 0
if c == IAC:
cleandata = cleandata + c
elif c in (DO, DONT):
if c == DO: print('(DO)', end=' ')
else: print('(DONT)', end=' ')
opt = IAC + WONT
elif c in (WILL, WONT):
if c == WILL: print('(WILL)', end=' ')
else: print('(WONT)', end=' ')
opt = IAC + DONT
else:
print('(command)', ord(c))
elif c == IAC:
iac = 1
print('(IAC)', end=' ')
else:
cleandata = cleandata + c
sys.stdout.write(cleandata)
sys.stdout.flush()
try:
main()
except KeyboardInterrupt:
pass
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