python xinetd client disconnection handling

This may or may not being a coding issue. It may also be an xinetd deamon issue, i do not know.

I have a python script which is triggered from a linux server running xinetd. Xinetd has been setup to only allow one instance as I only want one machine to be able to connect to the service, which is therefore also limited by IP.

Currently when the client connects to xinetd the service works correctly and the script begins sending its output to the client machine. However, w开发者_如何学JAVAhen the client disconnects (i.e: due to reboot), the process is still alive on the server, and this blocks the ability for the client to connect once its finished rebooting or so on.

Q: How can i detect in python that the client has disconnected. Perhaps i can test if stdout is no longer being read from by the client (and then exit the script), or is there a much eaiser way in xinetd to have the child process be killed when the client disconnects ?

(I'm using python 2.4.3 on RHEL5 linux - solutions for 2.4 are needed, but 3.1 solutions would be useful to know also.)

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Add a signal handler for SIGHUP. (x)inetd sends this upon the socket disconnecting.

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Monitor the signals sent to your proccess. Maybe your script isn't responding to the SIGHUP sent by xinet, monitor the signal and let it die.

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You don't seem to get a SIGHUP, but you do get a SIGPIPE, at least so long as you are attempting any IO on the connection. If the application spends long periods of time not doing any IO, then you could just start a thread reading stdin to ensure you get the SIGPIPE as soon as the disconnection occurs. This was good enough for my application but then I didn't use any pipes other than the ones xinetd gave me.

I've seen several places on the net where people talk about the SIGHUP getting sent on client disconnection, so I've written an inetd python script to test out a couple of servers (one inetd and another xinetd), so you could use that to check on the signals getting sent. It just logs what it finds to /var/log/test.log. Perhaps it will be useful.

#!/usr/bin/python

import os, signal, sys

skip = ["SIGKILL", "SIG_DFL", "SIGSTOP", "SIG_IGN", "SIGCLD", "SIGCHLD"]
name_map = {}
identifiers = [i for i in dir(signal) if i.startswith("SIG") and not i in skip]

for i in identifiers:
    name_map[getattr(signal, i)] = i

def handler(num, frame):
    signame = name_map[num]
    os.system("echo handled %s >> /var/log/test.log" % signame)

if __name__ == "__main__":
    for id, name in name_map.iteritems():
        signal.signal(id, handler)

    while True:
        print sys.stdin.readline()
        sys.stdout.flush()