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UDPmulticaster.py
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UDPmulticaster.py
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#!/usr/bin/env python
import subprocess
import socket
import time
import re
import os
def main():
# if the Pi was allocated a static IP, set it again
found = True
try:
file = open("/home/pi/static_ip.txt", 'r')
line = file.read()
found = line != ""
except:
found = False
if found:
ipseg, interface = line.split("#")
os.system("sudo ip address add " + ipseg + " dev " + interface)
# keep looping until Raspi has been allocated an IPv4 address
while True:
while not has_ipv4_address():
time.sleep(10)
multicast()
def multicast():
""" UDP multicasts every 5 seconds to the multicast group while there is a valid IPv4 address. """
# UDP code from https://wiki.python.org/moin/UdpCommunication
MCAST_GRP = '224.1.1.1'
MCAST_PORT = 5007
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
# mutlicast every 5 seonds while there is a valip IP.
while has_ipv4_address():
sock.sendto("Alive", (MCAST_GRP, MCAST_PORT))
time.sleep(5)
def has_ipv4_address():
""" This function checks to see if the Raspi has been allocated an IPv4 address"""
# list of network interfaces on the Raspi to check for an ipv4 address.
cmds = [
"ifconfig eth0 | grep \"inet addr\"",
"ifconfig wlan0 | grep \"inet addr\""
]
#map over the list of cmds passing each cmd to be executed in the shell, then loop over the list of results.
for result in map(lambda x: shell(x), cmds):
# the following regex checks to see a valid ipv4 address follows after addr. e.g inet addr:192.168.1.1
if re.search(r"addr\:(\d{1,3}\.){3}(\d{1,3})", str(result)):
return True
return False
def shell(cmd):
""" Executes a given shell command and returns the output """
return (subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)).communicate()[0]
if __name__ == "__main__":
main()