编写 UDP 程序，通过多路 IO 复用同时处理标准输入和套接字。当输入为 quit 时程序结束；当通过套 接字收到对方消息时回射给对方

在编写UDP程序时，我们可以利用操作系统提供的多路复用技术，如epoll、kqueue（Linux）、Select或IOCP（Windows），以便在一个事件循环中同时处理标准输入和网络套接字。以下是一个简单的Python示例，使用`selectors`模块实现多路IO复用：

import selectors
import socket
import sys

def handle_stdin(key, mask):
    if key.data == 'quit':
        sel.unregister(sys.stdin)
        print("Closing due to 'quit'")
        return False
    else:
        print(f"Received from stdin: {key.data}")
        sock.sendto(key.data.encode(), (remote_host, remote_port))
        return True

def handle_socket(key, mask):
    data, addr = key.fileobj.recvfrom(4096)
    print(f"Received message from {addr}: {data.decode()}")
    key.fileobj.sendto(data, addr)
    return True

def main():
    selector = selectors.DefaultSelector()
    std_in_key = selectors.SelectorKey(fileobj=sys.stdin, events=selectors.EVENT_READ, data='quit')
    selector.register(std_in_key, handle_stdin)

    remote_host = '127.0.0.1' # Replace with your server's IP address
    remote_port = 12345 # Replace with the desired port
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    sock.bind(('localhost', 0)) # Bind to a random available port
    sock.setblocking(False) # Make it non-blocking
    skey = selectors.SelectorKey(fileobj=sock, events=selectors.EVENT_READ | selectors.EVENT_WRITE, data=sock)
    selector.register(skey, handle_socket)

    while True:
        events = selector.select(timeout=None)
        for key, mask in events:
            callback = key.data
            callback(key, mask)

if __name__ == "__main__":
    main()

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