PyHeartBeat.py

#!/usr/bin/env python3

# Copyright (c) 2001, Nicola Larosa
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# modification, are permitted provided that the following conditions
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#      notice, this list of conditions and the following disclaimer.
#    * Redistributions in binary form must reproduce the above
#      copyright notice, this list of conditions and the following
#      disclaimer in the documentation and/or other materials provided
#      with the distribution.
#    * Neither the name of the <ORGANIZATION> nor the names of its
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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""" PyHeartBeat server: receives and tracks UDP packets from all clients.

While the BeatLog thread logs each UDP packet in a dictionary, the main
thread periodically scans the dictionary and prints the IP addresses of the
clients that sent at least one packet during the run, but have
not sent any packet since a time longer than the definition of the timeout.

Adjust the constant parameters as needed, or call as:

    PyHeartBeat.py [udpport [timeout]]

Set the environment variable "DEBUG" to "1" in order to emit more detailed
debug messages.
In addition "127.0.0.1" is marked as a previously active peer.


Manual heartbeat messages can be easily sent via "netcat":

    echo foo | nc -q 1 -u localhost 43334


https://www.oreilly.com/library/view/python-cookbook/0596001673/ch10s13.html
"""

import os
import socket
import sys
from threading import Lock, Thread, Event
from time import time, ctime, sleep


DEFAULT_HEARTBEAT_PORT = 43334
DEFAULT_WAIT_PERIOD = 10
DEBUG_ENABLED = os.getenv("DEBUG", "0") == "1"


class BeatDict:
    "Manage heartbeat dictionary"

    def __init__(self):
        self.beatDict = {}
        if DEBUG_ENABLED:
            self.beatDict["127.0.0.1"] = time()
        self.dictLock = Lock()

    def __repr__(self):
        result = ""
        self.dictLock.acquire()
        for key in self.beatDict.keys():
            result += "IP address: %s - Last time: %s\n" % (
                key,
                ctime(self.beatDict[key]),
            )
        self.dictLock.release()
        return result

    def update(self, entry):
        "Create or update a dictionary entry"
        self.dictLock.acquire()
        self.beatDict[entry] = time()
        self.dictLock.release()

    def extractSilent(self, howPast):
        "Returns a list of entries older than howPast"
        silent = []
        when = time() - howPast
        self.dictLock.acquire()
        for key in self.beatDict.keys():
            if self.beatDict[key] < when:
                silent.append(key)
        self.dictLock.release()
        return silent


class BeatRec(Thread):
    "Receive UDP packets, log them in heartbeat dictionary"

    def __init__(self, goOnEvent, updateDictFunc, port):
        Thread.__init__(self)
        self.goOnEvent = goOnEvent
        self.updateDictFunc = updateDictFunc
        self.port = port
        self.recSocket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        self.recSocket.settimeout(0.2)
        self.recSocket.bind(("", port))

    def __repr__(self):
        return f"Heartbeat Server on port: {self.port}"

    def run(self):
        while self.goOnEvent.isSet():
            if DEBUG_ENABLED:
                print("Waiting to receive...")
            try:
                data, addr = self.recSocket.recvfrom(6)
            except socket.timeout:
                # no incoming message -> no timestamp update -> check again
                pass
            else:
                if DEBUG_ENABLED:
                    print(f"Received packet from {addr}")
                self.updateDictFunc(addr[0])


def main():
    "Listen to the heartbeats and detect inactive clients"
    if len(sys.argv) > 1:
        heartbeat_port = int(sys.argv[1])
    else:
        heartbeat_port = DEFAULT_HEARTBEAT_PORT
    if len(sys.argv) > 2:
        wait_period = float(sys.argv[2])
    else:
        wait_period = DEFAULT_WAIT_PERIOD

    beatRecGoOnEvent = Event()
    beatRecGoOnEvent.set()
    beatDictObject = BeatDict()
    beatRecThread = BeatRec(beatRecGoOnEvent, beatDictObject.update, heartbeat_port)
    if DEBUG_ENABLED:
        print(beatRecThread)
    beatRecThread.start()
    print(f"PyHeartBeat server listening on port {heartbeat_port}")
    print("\n*** Press Ctrl-C to stop ***\n")
    while True:
        try:
            if DEBUG_ENABLED:
                print(f"Beat Dictionary: {beatDictObject}")
            silent = beatDictObject.extractSilent(wait_period)
            if silent:
                print(f"Silent clients: {' '.join(silent)}")
            sleep(wait_period)
        except KeyboardInterrupt:
            print("Exiting.")
            beatRecGoOnEvent.clear()
            beatRecThread.join()
            break


if __name__ == "__main__":
    main()