udp穿透的方法

服务端缓存客户端ip+端口信息，如果有新的客户端连接上来返回给对方。

server

import socket

def main():
    udp_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    udp_socket.bind(("0.0.0.0", 2023))
    cache = {}
    while True:
        packet = udp_socket.recvfrom(2048)
        current = packet[1]
        key = packet[0].decode("utf-8")
        print("recvfrom key:", key)
        if key not in cache:
            cache[key] = packet[1]
            print("pending:", current)
        else:
            last = cache[key]
            udp_socket.sendto((current[0] + ":" + str(current[1])).encode("utf-8"), last)
            udp_socket.sendto((last[0] + ":" + str(last[1])).encode("utf-8"), current)
            del cache[key]
            print("done:", last, current)

    udp_socket.close()


if __name__ == "__main__":
    main()

客户端先请求服务端，请求后获取p2p的地址，然后开始周期echo。

client

import socket
import sys
import time

def main():
    udp_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    udp_socket.settimeout(10)
    server = (u"192.168.3.20",2023)
    key = u"----uni-key-yeshen----"
    this_client = sys.platform + str(time.time())

    udp_socket.sendto(key.encode("utf-8"), server)
    print("waiting..")
    packet = udp_socket.recvfrom(2048)
    print("packet",packet)
    peer = packet[0].split(":")
    target_peer = (peer[0],int(peer[1]))

    while True:
        udp_socket.sendto(this_client.encode("utf-8"), target_peer)
        print("peer send",this_client,target_peer)
        msg = udp_socket.recvfrom(2048)
        print("peer recv",msg)
        time.sleep(1)

    udp_socket.close()


if __name__ == "__main__":
    main()

自测效果：

1. 在服务端上开启，两个客户端都在同一个局域网里面，有70%左右的概率连通（10个端口，有7个能成功）。数据和wifi都是这样。
2. 一个设备在wifi、一个在数据上，连通的概率大约是0%，我还没成功过...