使用 Python 接收外部 UDP 广播

Question

我在 192.168.123.204 的网络中有一个设备，它将 UDP 数据报 (Artnet) 作为 2.168.123.204 广播到 2.255.255.255:6454。（网络地址是 192.168.123.204 但数据报以 2.168.123.204 作为源发送。）地址 2.255.255.255 无法更改（没有设置）。

我的 Python 脚本在设备 192.168.123.148 上运行。我可以使用 wireshark 在那里接收数据报：但是绑定到 0.0.0.0:6454 的 Python 套接字无法接收它们。将它绑定到 2.168.123.204 或 2.255.255.255 不起作用。该脚本正在运行，因为我可以从 127.0.0.1.

接收数据包

如果用Python解决不了，我可以用iptables(linux)重定向UDP广播吗？

网络：
路由器192.168.123.1
/ \
主播：192.168.123.204 脚本：192.168.123.148

基本脚本：

import socket
import asyncio


HOST, PORT = 'localhost', 6454


class SyslogProtocol(asyncio.DatagramProtocol):
    def __init__(self):
        super().__init__()

    def connection_made(self, transport) -> "Used by asyncio":
        self.transport = transport

    def datagram_received(self, data, addr) -> "Main entrypoint for processing message":
        # Here is where you would push message to whatever methods/classes you want.
      
        print(data)


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    t = loop.create_datagram_endpoint(SyslogProtocol, local_addr=('0.0.0.0', PORT))
    loop.run_until_complete(t) # Server starts listening
    loop.run_forever()

完整脚本：

#import pygame
from ctypes import *
import socket
import asyncio
import os, random

class ArtNetPackage(LittleEndianStructure):
    PORT = 0x1936
    _fields_ = [("id", c_char * 8),
                ("opcode", c_ushort),
                ("protverh", c_ubyte),
                ("protver", c_ubyte),
                ("sequence", c_ubyte),
                ("physical", c_ubyte),         
                ("universe", c_ushort),
                ("lengthhi", c_ubyte),
                ("length", c_ubyte),
                ("payload", c_ubyte * 512)]
    
    def get_length(self):
        return self.lengthhi*256+self.length
        
    def __init__(self,data=b''):
        if len(data) == 0:
            self.id = b"Art-Net"
            self.opcode = 0x5000
            self.protver = 14
            self.universe = 0
            self.lengthhi = 2
        else:
            self.id = data[:8]
            self.opcode = data[8]+data[9]*256
            if self.opcode == 0x5000:
                self.protverh = data[10]
                self.protver = data[11]
                self.sequence = data[12]
                self.physical = data[13]
                self.universe = data[14]+data[15]*256
                self.lengthhi = data[16]
                self.length = data[17]
                self.payload = (c_ubyte * 512).from_buffer_copy(
                        data[18:530])#.ljust(512,b'\x00'))

#pygame.init()

HOST, PORT = 'localhost', 6454


class SyslogProtocol(asyncio.DatagramProtocol):
    def __init__(self):
        super().__init__()
        
    def connection_made(self, transport) -> "Used by asyncio":
        self.transport = transport

    def datagram_received(self, data, addr) -> "Main entrypoint for processing message":
        # Here is where you would push message to whatever methods/classes you want.
        try:
            dmx = ArtNetPackage(data)
            if not dmx.opcode == 0x5000:
                return
            print(dmx.payload[0])
        except:
            print("error")


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    t = loop.create_datagram_endpoint(SyslogProtocol, local_addr=('0.0.0.0', PORT))
    loop.run_until_complete(t) # Server starts listening
    loop.run_forever()

接口：

$ ip a
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
    inet 192.168.123.148/24 brd 192.168.123.255 scope global dynamic wlan0
       valid_lft 86393sec preferred_lft 86393sec
    inet6 XXXXXXXX/64 scope link 
       valid_lft forever preferred_lft forever

Answer 1

使用原始套接字。

import struct

SRC_IPv4 = slice(26, 30)
DST_IPv4 = slice(30, 34)

SRC_PORTv4 = slice(34, 36)
DST_PORTv4 = slice(36, 38)

sock = socket.socket(socket.PF_PACKET, socket.SOCK_RAW, socket.htons(3))
while 1:
    raw, (nic, ptype, *x) = sock.recvfrom(2048)
    if ptype == 2048 and raw[23] == 17:
        src_host = socket.inet_ntoa(raw[SRC_IPv4])
        src_port, = struct.Struct("!H").unpack(raw[SRC_PORTv4])
        dst_host = socket.inet_ntoa(raw[DST_IPv4])
        dst_port, = struct.Struct("!H").unpack(raw[DST_PORTv4])
        print(f'{src_host}:{src_port} => {dst_host}:{dst_port}')```

Answer 2

我误读了你的问题，你处理的是广播地址而不是多播地址。你的问题是你没有发送 SO_BROADCAST 标志

IPv4 addresses are divided into unicast, broadcast and multicast addresses. Unicast addresses specify a single interface of a host, broadcast addresses specify all hosts on a network and multicast addresses address all hosts in a multicast group. Datagrams to broadcast addresses can be only sent or received when the SO_BROADCAST socket flag is set. In the current implementation, connection-oriented sockets are only allowed to use unicast addresses.

有一个明确的例子here。最重要的部分是：

    def connection_made(self, transport):
        print('started')
        self.transport = transport
        sock = transport.get_extra_info("socket")
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
        self.broadcast()

您还需要将该子网上的地址添加到接口。这很简单，只需输入：

ip addr add 2.255.255.254/8 dev eth1

假设广播在 2.0.0.0/8 上，接口名称是 eth1 并且 2.255.255.254 没有被其他主机占用。

使用 Python 接收外部 UDP 广播

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