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Add the ability to also relay Sonos Discovery packets that are sent
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as broadcast UDP packets on port 6969.
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@alsmith
alsmith committed Aug 6, 2018
1 parent 8a093d5 commit 44992c4
Showing 1 changed file with 64 additions and 37 deletions.
101 changes: 64 additions & 37 deletions multicast-relay.py
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@
def log():
return logging.getLogger(__file__)

class MulticastRelay():
class PacketRelay():
def __init__(self, interfaces, verbose, waitForIP, ttl=None):
self.interfaces = interfaces
self.verbose = verbose
Expand All @@ -31,14 +31,8 @@ def __init__(self, interfaces, verbose, waitForIP, ttl=None):
self.etherAddrs = {}
self.etherType = struct.pack('!h', 0x0800)

def addListener(self, addr, port, service):
# Compute the MAC address that we will use to send
# packets out to. Multicast MACs are derived from
# the multicast IP address.
multicastMac = 0x01005e000000
multicastMac |= self.ip2long(addr) & 0x7fffff
multicastMac = struct.pack('!Q', multicastMac)[2:]
self.etherAddrs[addr] = multicastMac
def addListener(self, addr, port, service, ipToMac):
self.etherAddrs[addr] = ipToMac(addr)

# Set up the receiving socket and corresponding IP and interface information.
# One receiving socket is required per multicast address.
Expand All @@ -48,16 +42,19 @@ def addListener(self, addr, port, service):
for interface in self.interfaces:
(mac, ip, netmask) = self.getInterface(interface)

# Add this interface to the receiving socket's list.
packedAddress = struct.pack('4s4s', socket.inet_aton(addr), socket.inet_aton(ip))
rx.setsockopt(socket.SOL_IP, socket.IP_ADD_MEMBERSHIP, packedAddress)
if ipToMac == PacketRelay.multicastIpToMac:
# Add this interface to the receiving socket's list.
packedAddress = struct.pack('4s4s', socket.inet_aton(addr), socket.inet_aton(ip))
rx.setsockopt(socket.SOL_IP, socket.IP_ADD_MEMBERSHIP, packedAddress)
elif ipToMac == PacketRelay.broadcastIpToMac:
rx.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)

# Also generate a transmitter socket. Each interface
# Generate a transmitter socket. Each interface
# requires its own transmitting socket.
tx = socket.socket(socket.AF_PACKET, socket.SOCK_RAW)
tx.bind((interface, 0))

self.transmitters.append({'multicast': {'addr': addr, 'port': port}, 'interface': interface, 'addr': ip, 'mac': mac, 'netmask': netmask, 'socket': tx, 'service': service})
self.transmitters.append({'relay': {'addr': addr, 'port': port}, 'interface': interface, 'addr': ip, 'mac': mac, 'netmask': netmask, 'socket': tx, 'service': service})

rx.bind((addr, port))
self.receivers.append(rx)
Expand Down Expand Up @@ -91,32 +88,31 @@ def loop(self):
if len(recentChecksums) > 256:
recentChecksums = recentChecksums[1:]

multicastAddress = socket.inet_ntoa(data[16:20])
destinationAddress = socket.inet_ntoa(data[16:20])

# Compute the length of the IP header so that we can then move
# past it and delve into the UDP packet to find out what multicastPort
# Compute the length of the IP header so that we can then move past
# it and delve into the UDP packet to find out what destination port
# this packet was sent to. The length is encoded in the first least
# significant nybble of the IP packet and is specified in nybbles.
firstDataByte = data[0]
if sys.version_info > (3, 0):
firstDataByte = bytes([data[0]])
ipHeaderLength = (struct.unpack('B', firstDataByte)[0] & 0x0f) * 4
multicastPort = struct.unpack('!h', data[ipHeaderLength+2:ipHeaderLength+4])[0]
destinationPort = struct.unpack('!h', data[ipHeaderLength+2:ipHeaderLength+4])[0]

# Work out the name of the interface we received the packet
# on.
# Work out the name of the interface we received the packet on.
receivingInterface = 'unknown'
for tx in self.transmitters:
if multicastAddress == tx['multicast']['addr'] and multicastPort == tx['multicast']['port'] and self.onNetwork(addr[0], tx['addr'], tx['netmask']):
if destinationAddress == tx['relay']['addr'] and destinationPort == tx['relay']['port'] and self.onNetwork(addr[0], tx['addr'], tx['netmask']):
receivingInterface = tx['interface']

for tx in self.transmitters:
# Re-transmit on all other interfaces than on the interface that we received this multicast packet from...
if multicastAddress == tx['multicast']['addr'] and multicastPort == tx['multicast']['port'] and not self.onNetwork(addr[0], tx['addr'], tx['netmask']):
packet = self.etherAddrs[multicastAddress] + tx['mac'] + self.etherType + data
# Re-transmit on all other interfaces than on the interface that we received this packet from...
if destinationAddress == tx['relay']['addr'] and destinationPort == tx['relay']['port'] and not self.onNetwork(addr[0], tx['addr'], tx['netmask']):
packet = self.etherAddrs[destinationAddress] + tx['mac'] + self.etherType + data
tx['socket'].send(packet)
if self.verbose:
log().info('%sRelayed %s byte%s from %s on %s [ttl %s] to %s:%s via %s/%s' % (tx['service'] and '[%s] ' % tx['service'] or '', len(data), len(data) != 1 and 's' or '', addr[0], receivingInterface, ttl, multicastAddress, multicastPort, tx['interface'], tx['addr']))
log().info('%sRelayed %s byte%s from %s on %s [ttl %s] to %s:%s via %s/%s' % (tx['service'] and '[%s] ' % tx['service'] or '', len(data), len(data) != 1 and 's' or '', addr[0], receivingInterface, ttl, destinationAddress, destinationPort, tx['interface'], tx['addr']))

def getInterface(self, ifname):
if ifname not in netifaces.interfaces():
Expand Down Expand Up @@ -146,7 +142,7 @@ def getInterface(self, ifname):
# find a MAC address there.
if netifaces.AF_LINK not in i and ifname.find(':') != -1:
i = netifaces.ifaddresses(ifname[:ifname.find(':')])

if netifaces.AF_LINK not in i:
print('Unable to detect MAC address for interface %s.' % ifname)
sys.exit(1)
Expand Down Expand Up @@ -179,11 +175,25 @@ def onNetwork(ip, network, netmask):
Given an IP address and a network/netmask tuple, work out
if that IP address is on that network.
"""
ipL = MulticastRelay.ip2long(ip)
networkL = MulticastRelay.ip2long(network)
netmaskL = MulticastRelay.ip2long(netmask)
ipL = PacketRelay.ip2long(ip)
networkL = PacketRelay.ip2long(network)
netmaskL = PacketRelay.ip2long(netmask)
return (ipL & netmaskL) == (networkL & netmaskL)

@staticmethod
def multicastIpToMac(addr):
# Compute the MAC address that we will use to send
# packets out to. Multicast MACs are derived from
# the multicast IP address.
multicastMac = 0x01005e000000
multicastMac |= PacketRelay.ip2long(addr) & 0x7fffff
return struct.pack('!Q', multicastMac)[2:]

@staticmethod
def broadcastIpToMac(addr):
broadcastMac = 0xffffffffffff
return struct.pack('!Q', broadcastMac)[2:]

def main():
parser = argparse.ArgumentParser()
parser.add_argument('--interfaces', nargs='+', required=True,
Expand All @@ -194,6 +204,8 @@ def main():
help='Do not relay mDNS packets.')
parser.add_argument('--noSSDP', action='store_true',
help='Do not relay SSDP packets.')
parser.add_argument('--noSonosDiscovery', action='store_true',
help='Do not relay broadcast Sonos discovery packets.')
parser.add_argument('--wait', action='store_true',
help='Wait for IPv4 address assignment.')
parser.add_argument('--ttl', type=int,
Expand Down Expand Up @@ -244,26 +256,41 @@ def main():
for relay in args.relay:
relays.add((relay, None))

multicastRelay = MulticastRelay(args.interfaces, args.verbose, args.wait, args.ttl)
packetRelay = PacketRelay(args.interfaces, args.verbose, args.wait, args.ttl)
for relay in relays:
try:
(addr, port) = relay[0].split(':')
ip = MulticastRelay.ip2long(addr)
ip = PacketRelay.ip2long(addr)
port = int(port)
except:
print('%s: Expecting --relay A.B.C.D:P, where A.B.C.D is a multicast IP address and P is a valid port number' % relay)
if args.foreground:
print('%s: Expecting --relay A.B.C.D:P, where A.B.C.D is a multicast IP address and P is a valid port number' % relay)
else:
log().warning('%s: Expecting --relay A.B.C.D:P, where A.B.C.D is a multicast IP address and P is a valid port number' % relay)
return 1

if ip < MulticastRelay.ip2long('224.0.0.0') or ip > MulticastRelay.ip2long('239.255.255.255'):
print('IP address %s not a multicast address' % addr)
if ip < PacketRelay.ip2long('224.0.0.0') or ip > PacketRelay.ip2long('239.255.255.255'):
if args.foreground:
print('IP address %s not a multicast address' % addr)
else:
log().warning('IP address %s not a multicast address' % addr)
return 1
if port < 0 or port > 65535:
print('UDP port %s out of range' % port)
if args.foreground:
print('UDP port %s out of range' % port)
else:
log().warning('UDP port %s out of range' % port)
return 1

log().info('Adding multicast relay for %s:%s%s' % (addr, port, relay[1] and ' (%s)' % relay[1] or ''))
multicastRelay.addListener(addr, port, relay[1])
multicastRelay.loop()
packetRelay.addListener(addr, port, relay[1], packetRelay.multicastIpToMac)

if not args.noSonosDiscovery:
port = 6969
log().info('Adding broadcast relay for %s' % port)
packetRelay.addListener('255.255.255.255', port, 'Sonos Discovery', packetRelay.broadcastIpToMac)

packetRelay.loop()

if __name__ == '__main__':
sys.exit(main())
Expand Down

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