Tornado receive UDP packets from multicast group - asynchronous

Question

I have a server where I want to receive data from multicast group. Is there any inbuilt function that I can use to receive this multicast UDP packets?
Edit: Code implementation
I have implemented the code and that follows like this:
#!/usr/bin/env python
import socket
import struct
import os
import errno
import binascii
import tornado.ioloop
from tornado.ioloop import IOLoop
from tornado.platform.auto import set_close_exec
class UDPHandler():
"""
Connect to multicast group
"""
def __init__(self, ip, port, io_loop):
self.io_loop = io_loop
self._multiIP = ip
self.port = port
self._sock = None
self._socket = {} # fd -> socket object
def conn(self):
"""
Listner to multicast group
"""
self._sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
self._sock.settimeout(3)
self._sock.bind(('', self.port))
self._sock.setblocking(0)
group = socket.inet_aton(self._multiIP)
mreq = struct.pack('4sL', group, socket.INADDR_ANY)
self._sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
self._socket[self._sock.fileno()] = self._sock
print("self._sock:", self._sock)
def onRx(self, data, addr):
print("addr, data:", addr, len(str(data)))
print(data)
def r(self):
self.conn()
add_socket_handler(self._sock, self.onRx, self.io_loop)
def add_socket_handler(sock, callback, io_loop):
def accept_handler(fd, events):
while True:
try:
data, address = sock.recvfrom(1024)
except socket.error as e:
if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
callback(None, None)
except Exception as e:
print("except:", e)
callback(None, None)
callback(data, address)
io_loop.add_handler(sock.fileno(), accept_handler, IOLoop.READ)
def periodic():
# print("periodic")
None
def main():
MULTICAST_IP = "224.1.1.10"
RECEIVE_PORT = 10003
udpRx = UDPHandler(MULTICAST_IP, RECEIVE_PORT, tornado.ioloop.IOLoop.current())
udpRx.r()
tornado.ioloop.PeriodicCallback(periodic, 1000).start()
tornado.ioloop.IOLoop.current().start()
if __name__ == "__main__":
main()
Now the problem is is am getting same packet in a loop even if I receive one packet I am receiving the same packet over and over again. Is there something wrong with the code? Especially with add_socket_handler?
Edit 2:
I have added a break statement in the while loop that I had in add_socket_handler and now it seems to be working good.
def add_socket_handler(sock, callback, io_loop):
def accept_handler(fd, events):
while True:
try:
data, address = sock.recvfrom(1024)
callback(data, address)
except socket.error as e:
if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
raise
except Exception as e:
raise
break ## change in here
io_loop.add_handler(sock.fileno(), accept_handler, io_loop.READ)
Is this how it is suppose to be done ?

Answer 1

The break in your add_socket_handler looks backwards. You want to loop until you get EWOULDBLOCK/EAGAIN. (with the break as written, it will still work, but it will be slightly less efficient and might miss packets).
def add_socket_handler(sock, callback, io_loop):
def read_handler(fd, events):
while True:
try:
data, address = sock.recvfrom(1024)
callback(data, address):
except socket.error as e:
if e.errno in (errno.EWOULDBLOCK, errno.EAGAIN):
return
raise
io_loop.add_handler(sock, read_handler, io_loop.READ)
Other than that, this looks right, although I haven't worked with multicast UDP myself.