// TCP连接终止的四次挥手过程示例

class Client implements Runnable {
    public void run() {
        // Step 1: 客户端发送FIN报文给服务器
        System.out.println("Step 1: Client sends FIN packet to Server");
        try {
            Thread.sleep(1000); // 模拟网络延迟
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Client: Sending FIN packet...");
        System.out.println("Client: Receiving ACK packet...");
    }
}

class Server implements Runnable {
    public void run() {
        // Step 2: 服务器收到客户端的FIN报文，向客户端发送ACK报文
        System.out.println("Step 2: Server receives FIN packet from Client and sends ACK packet");
        System.out.println("Server: Receiving FIN packet...");
        try {
            Thread.sleep(1000); // 模拟网络延迟
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Server: Sending ACK packet...");
        // Step 3: 服务器关闭发送通道，向客户端发送FIN报文
        System.out.println("Step 3: Server closes sending channel and sends FIN packet to Client");
        System.out.println("Server: Sending FIN packet...");
        System.out.println("Server: Receiving ACK packet...");
        // Step 4: 服务器收到客户端的ACK报文
        System.out.println("Step 4: Server receives ACK packet from Client");
    }
}

// 主程序
public class FourWayHandshakeDemo {
    public static void main(String[] args) {
        System.out.println("===== TCP Connection Termination (Four-way Handshake) =====");

        // 创建客户端和服务器线程
        Client client = new Client();
        Server server = new Server();
        Thread clientThread = new Thread(client);
        Thread serverThread = new Thread(server);

        // 启动客户端和服务器线程
        clientThread.start();
        try {
            clientThread.join(); // 等待客户端线程执行完毕
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        serverThread.start();
    }
}