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  • UDP learn by Python3

    Find max packet size

    # coding: utf-8
    
    import socket
    
    
    def find_max_udp_packet_size():
        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        max_sz = 0
        l, r = 0, 65535 - 8 - 20
        while l <= r:
            mid = int((l + r) / 2)
            ok = True
    
            try:
                sock.sendto(b'A' * mid, ('localhost', 9))
            except socket.error:
                ok = False
    
            if ok:
                max_sz = mid
                l = mid + 1
            else:
                r = mid - 1
    
        return max_sz
    
    
    def main():
        max_sz = find_max_udp_packet_size()
        print('max_sz = %s' % max_sz)
    
    
    if __name__ == '__main__':
        main()
    
    

    I used the code above to find the max size of a UDP packet size by default configuration.
    The result on my computer is:

    $ uname -v
    Darwin Kernel Version 19.2.0: Sat Nov  9 03:47:04 PST 2019; root:xnu-6153.61.1~20/RELEASE_X86_64
    $ python3 --version
    Python 3.6.4
    $ python3 udp_packet_size.py
    max_sz = 9216
    

    More test

    Use the code below to test.

    # coding: utf-8
    
    import socket
    
    from IPython import embed
    
    
    def main():
        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        embed()
        sock.close()
    
    
    if __name__ == '__main__':
        main()
    
    
    In [1]: sock.bind(('localhost', 10001))
    
    In [2]: receiver = ('localhost', 10002)
    
    In [3]: sock.sendto(b'01234567', receiver)
    Out[3]: 8
    
    In [4]: sock.sendto(b'01234567', receiver)
    Out[4]: 8
    
    In [5]: sock.sendto(b'01234567', receiver)
    Out[5]: 8
    
    In [6]: sock.sendto(b'01234567', receiver)
    Out[6]: 8
    
    
    In [1]: sock.bind(('localhost', 10002))
    
    In [2]: receiver = ('localhost', 10001)
    
    In [3]: print(sock.recvfrom(1024))
    (b'01234567', ('127.0.0.1', 10001))
    
    In [4]: print(sock.recvfrom(4))
    (b'0123', ('127.0.0.1', 10001))
    
    In [5]: print(sock.recvfrom(4))
    (b'0123', ('127.0.0.1', 10001))
    
    In [6]: print(sock.recvfrom(4))
    (b'0123', ('127.0.0.1', 10001))
    
    In [7]: print(sock.recvfrom(4))
    

    We can see that if the bufsize is smaller the length of the packet received, will only read bufsize bytes of the received data, and the rest of that packet will not be returned in subsequent reads.

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  • 原文地址:https://www.cnblogs.com/ToRapture/p/12788732.html
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