用 Python 构建 UDP 数据包

Question

There's already a code in the internet which shows how to build and send a TCP packet in Python using raw sockets, but I desperately need an example of how building a UDP one.

I read this link http://www.ietf.org/rfc/rfc768.txt and understands that udp header consists only of src ip, src port, length and checksum, and also read that if I create an IPPROTO_UDP socket instead of IPPROTO_RAW socket, the IP header should be filled automatically by the kernel.

Yet, I had no success in doing such.

Here's the code building tcp packets with raw socket:

import socket
import struct

def make_ip(proto, srcip, dstip, ident=54321):
    saddr = socket.inet_aton(srcip)
    daddr = socket.inet_aton(dstip)
    ihl_ver = (4 << 4) | 5
    return struct.pack('!BBHHHBBH4s4s' , 
                       ihl_ver, 0, 0, ident, 0, 255, proto, 0, saddr, daddr)

def make_tcp(srcport, dstport, payload, seq=123, ackseq=0,
             fin=False, syn=True, rst=False, psh=False, ack=False, urg=False,
             window=5840):
    offset_res = (5 << 4) | 0
    flags = (fin | (syn << 1) | (rst << 2) | 
             (psh <<3) | (ack << 4) | (urg << 5))
    return struct.pack('!HHLLBBHHH', 
                       srcport, dstport, seq, ackseq, offset_res, 
                       flags, window, 0, 0)

srcip = dstip = '127.0.0.1'
srcport, dstport = 11001, 11000
payload = '[TESTING]\n'

ip = make_ip(socket.IPPROTO_TCP, srcip, dstip)
tcp = make_tcp(srcport, dstport, payload)
packet = ip + tcp + payload

s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_RAW)
s.sendto(packet, (dstip, 0))
response, addr = s.recvfrom(65535)
response_id = struct.unpack('!H', response[4:6])
print response_id

How to make the same thing with UDP instead?

Best solution for me is just editing the existing code, since reading abstract information didn't help me much.

I'm using Python 2.7 on Windows XP.

Answer 1

Just this:

import socket
sock = socket.socket(socket.AF_INET, # Internet
                 socket.SOCK_DGRAM) # UDP
sock.bind((IP,PORT))

To send:

sock.sendto(message,(IP,PORT))

To receive:

sock.recvfrom(1024)

The 1024 displays the buffer size. There are not other changes necessary as far as the socket part