RST报文段的意义

客户端代码，服务端代码如下

客户端代码

import socket

SERVER_ADDR = '127.0.0.1'
PORT        = 18000
CHUNK_SIZE  = 1024 * 4

def main():
    """ echo 客户端: 基于 AF_INET domain and TCP type 的 socket """
    # socket -> s.connect -> s.sendall -> s.shutdown -> loop s.recv -> s.close
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect((SERVER_ADDR, PORT))
        s.sendall(b"hello")
        s.shutdown(socket.SHUT_WR)  # if without this line code, the server and client will be deadlocked!

        response = b""
        while data := s.recv(CHUNK_SIZE):
            response += data
        print(response.decode())

if __name__ == "__main__":
    main()

服务端代码

import socket

HOST = '0.0.0.0'
PORT = 18000
BACKLOG = 16
CHUNK_SIZE = 1024 * 4

def handle_client(conn, addr):
    with conn:
        print(f"{addr[0]}:{addr[1]}", flush=True, end=' ')

        request = b""
        while data := conn.recv(CHUNK_SIZE):
            request += data
        print(request.decode(), flush=True)

        conn.sendall(request)

def main():
    """ echo 服务器: 基于 AF_INET domain and TCP type 的 socket """
    # socket -> s.bind -> s.listen -> s.accept -> s.close
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        s.bind((HOST, PORT))
        s.listen(BACKLOG)
        print(f"Listening on {HOST}:{PORT}\n", flush=True) 

        try:
            while True:
                conn, addr = s.accept()
                handle_client(conn, addr)
        except KeyboardInterrupt:
            print("\nServer shutting down...")

if __name__ == "__main__":
    main()

运行结果如下

删除客户端一行代码就会发生死锁，如下

s.shutdown(socket.SHUT_WR)  # if without this line code, the server and client will be deadlocked!

死锁发生的时候，按下Ctrl + C 结束客户端的运行，则有以下过程

1. 客户端的内核开始清理客户端的socket资源，首先向服务端发送一个FIN报文
2. 服务端内核收到FIN报文，然后服务端从recv返回，打印数据，然后sendall发送数据
3. 客户端收到服务端发送的数据，不处理，向客户端发送RST报文，表示客户端的socket已经不存在，不要再发送数据了
4. 服务端收到RST报文，关闭conn socket，重新回到main函数的while循环中