How do you UDP multicast in Python

Question

How do you send and receive UDP multicast in Python  Is there a standard library to do so

User · Answer

Just another answer to explain some subtle points in the code of the other answers:

socket.INADDR_ANY - (Edited) In the context of IP_ADD_MEMBERSHIP, this doesn't really bind the socket to all interfaces but just choose the default interface where multicast is up (according to routing table)
Joining a multicast group isn't the same as binding a socket to a local interface address

see What does it mean to bind a multicast (UDP) socket? for more on how multicast works

Multicast receiver:

import socket
import struct
import argparse


def run(groups, port, iface=None, bind_group=None):
    # generally speaking you want to bind to one of the groups you joined in
    # this script,
    # but it is also possible to bind to group which is added by some other
    # programs (like another python program instance of this)

    # assert bind_group in groups + [None], \
    #     'bind group not in groups to join'
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)

    # allow reuse of socket (to allow another instance of python running this
    # script binding to the same ip/port)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

    sock.bind(('' if bind_group is None else bind_group, port))
    for group in groups:
        mreq = struct.pack(
            '4sl' if iface is None else '4s4s',
            socket.inet_aton(group),
            socket.INADDR_ANY if iface is None else socket.inet_aton(iface))

        sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)

    while True:
        print(sock.recv(10240))


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--port', type=int, default=19900)
    parser.add_argument('--join-mcast-groups', default=[], nargs='*',
                        help='multicast groups (ip addrs) to listen to join')
    parser.add_argument(
        '--iface', default=None,
        help='local interface to use for listening to multicast data; '
        'if unspecified, any interface would be chosen')
    parser.add_argument(
        '--bind-group', default=None,
        help='multicast groups (ip addrs) to bind to for the udp socket; '
        'should be one of the multicast groups joined globally '
        '(not necessarily joined in this python program) '
        'in the interface specified by --iface. '
        'If unspecified, bind to 0.0.0.0 '
        '(all addresses (all multicast addresses) of that interface)')
    args = parser.parse_args()
    run(args.join_mcast_groups, args.port, args.iface, args.bind_group)

sample usage: (run the below in two consoles and choose your own --iface (must be same as the interface that receives the multicast data))

python3 multicast_recv.py --iface='192.168.56.102' --join-mcast-groups '224.1.1.1' '224.1.1.2' '224.1.1.3' --bind-group '224.1.1.2'

python3 multicast_recv.py --iface='192.168.56.102' --join-mcast-groups '224.1.1.4'

Multicast sender:

import socket
import argparse


def run(group, port):
    MULTICAST_TTL = 20
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, MULTICAST_TTL)
    sock.sendto(b'from multicast_send.py: ' +
                f'group: {group}, port: {port}'.encode(), (group, port))


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--mcast-group', default='224.1.1.1')
    parser.add_argument('--port', default=19900)
    args = parser.parse_args()
    run(args.mcast_group, args.port)

sample usage: # assume the receiver binds to the below multicast group address and that some program requests to join that group. And to simplify the case, assume the receiver and the sender are under the same subnet

python3 multicast_send.py --mcast-group '224.1.1.2'

python3 multicast_send.py --mcast-group '224.1.1.4'

User · Answer

To make the client code  from tolomea  work on Solaris you need to pass the ttl value for the IP MULTICAST TTL socket option as an unsigned char  Otherwise you will get an error   This worked for me on Solaris 10 and 11    import socket import struct  MCAST GRP    224 1 1 1  MCAST PORT   5007 ttl   struct pack  B   2   sock   socket socket socket AF INET  socket SOCK DGRAM  socket IPPROTO UDP  sock setsockopt socket IPPROTO IP  socket IP MULTICAST TTL  ttl  sock sendto  robot    MCAST GRP  MCAST PORT

User · Answer

This works for me   Receive  import socket import struct  MCAST GRP    224 1 1 1  MCAST PORT   5007 IS ALL GROUPS   True  sock   socket socket socket AF INET  socket SOCK DGRAM  socket IPPROTO UDP  sock setsockopt socket SOL SOCKET  socket SO REUSEADDR  1  if IS ALL GROUPS        on this port  receives ALL multicast groups     sock bind      MCAST PORT   else        on this port  listen ONLY to MCAST GRP     sock bind  MCAST GRP  MCAST PORT   mreq   struct pack  4sl   socket inet aton MCAST GRP   socket INADDR ANY   sock setsockopt socket IPPROTO IP  socket IP ADD MEMBERSHIP  mreq   while True      For Python 3  change next line to  print sock recv 10240      print sock recv 10240    Send  import socket  MCAST GRP    224 1 1 1  MCAST PORT   5007   regarding socket IP MULTICAST TTL   ---------------------------------   for all packets sent  after two hops on the network the packet will not    be re-sent broadcast  see https   www tldp org HOWTO Multicast-HOWTO-6 html  MULTICAST TTL   2  sock   socket socket socket AF INET  socket SOCK DGRAM  socket IPPROTO UDP  sock setsockopt socket IPPROTO IP  socket IP MULTICAST TTL  MULTICAST TTL     For Python 3  change next line to  sock sendto b robot        to avoid the    bytes-like object is required  msg  https   stackoverflow com a 42612820  sock sendto  robot    MCAST GRP  MCAST PORT     It is based off the examples from http   wiki python org moin UdpCommunication which didn t work   My system is    Linux 2 6 31-15-generic  50-Ubuntu SMP Tue Nov 10 14 54 29 UTC 2009 i686 GNU Linux Python 2 6 4

User · Answer

This example doesn t work for me  for an obscure reason   Not obscure  it s simple routing  On OpenBSD route add -inet 224 0 0 0 4 224 0 0 1  You can set the route to a dev on Linux route add -net 224 0 0 0 netmask 240 0 0 0 dev wlp2s0  force all multicast traffic to one interface on Linux    ifconfig wlp2s0 allmulti  tcpdump is super simple tcpdump -n multicast  In your code you have  while True      For Python 3  change next line to  quot print sock recv 10240   quot   Why 10240   multicast packet size should be 1316 bytes

User · Answer

Multicast sender that broadcasts to a multicast group      usr bin env python  import socket import struct  def main      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  32    sock sendto  Hello World     MCAST GRP  MCAST PORT    if   name         main       main     Multicast receiver that reads from a multicast group and prints hex data to the console      usr bin env python  import socket import binascii  def main      MCAST GRP    224 1 1 1     MCAST PORT   5007   sock   socket socket socket AF INET  socket SOCK DGRAM  socket IPPROTO UDP    try      sock setsockopt socket SOL SOCKET  socket SO REUSEADDR  1    except AttributeError      pass   sock setsockopt socket IPPROTO IP  socket IP MULTICAST TTL  32     sock setsockopt socket IPPROTO IP  socket IP MULTICAST LOOP  1     sock bind  MCAST GRP  MCAST PORT     host   socket gethostbyname socket gethostname      sock setsockopt socket SOL IP  socket IP MULTICAST IF  socket inet aton host     sock setsockopt socket SOL IP  socket IP ADD MEMBERSHIP                      socket inet aton MCAST GRP    socket inet aton host      while 1      try        data  addr   sock recvfrom 1024      except socket error  e        print  Expection        hexdata   binascii hexlify data        print  Data    s    hexdata  if   name         main       main

User · Answer

Have a look at py-multicast  Network module can check if an interface supports multicast  on Linux at least     import multicast from multicast import network  receiver   multicast MulticastUDPReceiver   eth0    238 0 0 1   1234   data   receiver read   receiver close    config   network ifconfig   print config  eth0   addresses     10 0 0 1   print config  eth0   multicast  True - eth0 supports multicast print config  eth0   up  True - eth0 is up   Perhaps problems with not seeing IGMP  were caused by an interface not supporting multicast

User · Answer

In order to Join multicast group Python uses native OS socket interface  Due to portability and stability of Python environment many of socket options are directly forwarded to native socket setsockopt call  Multicast mode of operation such as joining and dropping group membership can be accomplished by setsockopt only  Basic program for receiving multicast IP packet can look like  from socket import    multicast port    55555 multicast group    quot 224 1 1 1 quot  interface ip       quot 10 11 1 43 quot   s   socket AF INET  SOCK DGRAM   s bind   quot  quot   multicast port    mreq   inet aton multicast group    inet aton interface ip  s setsockopt IPPROTO IP  IP ADD MEMBERSHIP  str mreq    while 1      print s recv 1500   Firstly it creates socket  binds it and triggers triggers multicast group joining by issuing setsockopt  At very end it receives packets forever  Sending multicast IP frames is straight forward  If you have single NIC in your system sending such packets does not differ from usual UDP frames sending  All you need to take care of is just set correct destination IP address in sendto   method  I noticed that lot of examples around Internet works by accident in fact  Even on official python documentation  Issue for all of them are using struct pack incorrectly  Please be advised that typical example uses 4sl as format and it is not aligned with actual OS socket interface structure  I will try to describe what happens underneath the hood when exercising setsockopt call for python socket object  Python forwards setsockopt method call to native C socket interface  Linux socket documentation  see man 7 ip  introduces two forms of ip mreqn structure for IP ADD MEMBERSHIP option  Shortest is form is 8 bytes long and longer is 12 bytes long  Above example generates 8 byte setsockopt call where first four bytes define multicast group and second four bytes define interface ip

User · Answer

tolomea s answer worked for me  I hacked it into socketserver UDPServer too   class ThreadedMulticastServer socketserver ThreadingMixIn  socketserver UDPServer       def   init   self   args           super     init    args          self socket   socket socket socket AF INET  socket SOCK DGRAM  socket IPPROTO UDP          self socket setsockopt socket SOL SOCKET  socket SO REUSEADDR  1          self socket bind  MCAST GRP  MCAST PORT           mreq   struct pack  4sl   socket inet aton MCAST GRP   socket INADDR ANY          self socket setsockopt socket IPPROTO IP  socket IP ADD MEMBERSHIP  mreq

User · Answer

Better use   sock bind  MCAST GRP  MCAST PORT     instead of   sock bind      MCAST PORT     because  if you want to listen to multiple multicast groups on the same port  you ll get all messages on all listeners

[python] How do you UDP multicast in Python?

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