How to check if Telnet connection is still established? using telnetlib

Question

I'd like to check if a connection using the telnetlib is still up.

The way I do it is to send a ls command and check the answer, but I'm sure there must be a smoother solution.

Answer 1

I've got the idea from here, so kudos to them, the code could be something like this

def check_alive(telnet_object):
    try:
        if telnet_object.sock:
            telnet_object.sock.send(telnetlib.IAC + telnetlib.NOP)
            telnet_object.sock.send(telnetlib.IAC + telnetlib.NOP)
            telnet_object.sock.send(telnetlib.IAC + telnetlib.NOP)
            return True
    except:
        pass 

the idea is pretty simple:

• if the close() was called .sock will be 0, so we do nothing
• otherwise, we try to send something harmless, that should not interact with what ever the underlying service is, the IAC + NOP was a good candidate. LaterEdit: seems that doing the send only once is not enough, so I just did it 3 times, it's not very professional I know, but ... "if it looks stupid, but it works ... than it's not stupid"
• if everything goes well we get to the "return True" thous we get our answer, otherwise, the exception will get ignored, and, as there's no return, we will get a None as a response

I've used this method for both direct and proxied(SocksiPy) connections against a couple of Cisco routers