Node.js Net Socket连接未正常关闭，后续连接无响应问题求助

编写Node.js TCP服务器时遇到问题：客户端或服务器未真正关闭Socket连接，导致服务器对后续连接无响应。客户端发送第二次请求后挂起，服务器未进入socket.on('data' ...)监听器。

服务端代码(server.js) #

const net = require('net');
const serverAddress = '127.0.0.1'; // Replace with the actual server address
const serverPort = 3000; // Replace with the actual server port

const server = net.createServer(socket => {
    socket.on('data', data => {
        console.log('Received request: ', data.toString())
        socket.write('Hi, this is server response');
    });
    socket.on('close', () => {
        socket.end();
        socket.destroy();
        console.log('Connection closed');
    });
    socket.on('end', () => {
        console.log('Connection end');
        socket.end();
    });
    socket.on('error', error => {
        console.error('Socket error:', error);
    });
});

server.listen(serverPort, serverAddress, () => {
    console.log(`Server listening on ${serverAddress}:${serverPort}`);
});

客户端代码(client.js) #

const net = require('net');
const serverAddress = '127.0.0.1'; // Replace with the actual server address
const serverPort = 3000; // Replace with the actual server port

const client = net.createConnection(serverPort, serverAddress, () => {
    console.log('Connected to the server');
    let msg = 'First request';
    client.write(msg);
    console.log("Sent2 to server:", msg)

    client.on('data',  data => {
        console.log('Server response:', data.toString());
        client.end();
    });
    client.on('close', () => {
        console.log('Connection closed');
    });
    client.on('end', async () => {
        console.log('Connection end');
        setTimeout(runSecondConnection, 3000);
    });
});

function runSecondConnection() {
    let client2 = net.createConnection(serverPort, serverAddress, () => {
        console.log('Connected2 to the server');
        let msg = 'Second request';
        client.write(msg);
        console.log("Sent2 to server:", msg)
    })

    client2.on('data', data => {
        console.log('Server2 response:', data.toString());
        client.end();
    });
    client2.on('close', () => {
        console.log('Connection2 closed');
    });
    client2.on('end', () => {
        console.log('Connection2 end');
    });

}

实际运行结果 #

服务器输出 #

Received request:  First request
Connection end
Connection closed

客户端输出 #

Connected to the server
Sent2 to server: First request
Server response: Hi, this is server response
Connection end
Connection closed
Connected2 to the server
Sent2 to server: Second request

预期运行结果 #

服务器输出 #

Received request:  First request
Connection end
Connection closed
Received request:  Second request
Connection end
Connection closed

客户端输出 #

Connected to the server
Sent2 to server: First request
Server response: Hi, this is server response
Connection end
Connection closed
Connected2 to the server
Sent2 to server: Second request
Server response: Hi, this is server response
Connection end
Connection closed

额外现象 #

当客户端挂起时终止脚本，服务器会打印错误并再次输出"Connection closed"：

Server listening on 127.0.0.1:3000
Received request:  First request
Connection end
Connection closed
Socket error: Error: read ECONNRESET
    at TCP.onStreamRead (node:internal/stream_base_commons:220:20) {
  errno: -4077,
  code: 'ECONNRESET',
  syscall: 'read'
}
Connection closed

问题 #

为何错误后会出现"Connection closed"消息？是存在两个连接吗？还是第一次的Connection closed并未真正关闭连接？

问题根源与修复方案 #

1. 客户端核心错误
   在runSecondConnection函数中，发送第二次请求时错误使用了第一个客户端的client对象，而非新创建的client2：

// 错误代码
client.write(msg);
// 正确代码
client2.write(msg);

这导致第二次请求根本没有通过新连接发送到服务器，客户端2一直等待响应，因此出现挂起现象。

2. 服务器端冗余操作清理

• socket.on('close')中调用socket.end()和socket.destroy()完全多余，close事件触发时连接已经处于关闭状态，这些操作不会产生任何效果。
• socket.on('end')中调用socket.end()属于重复操作，end事件本身就是对方调用end()后触发的，此时socket已经进入关闭流程。

简化后的服务器端代码：

const net = require('net');
const serverAddress = '127.0.0.1';
const serverPort = 3000;

const server = net.createServer(socket => {
    socket.on('data', data => {
        console.log('Received request: ', data.toString())
        socket.write('Hi, this is server response');
    });
    socket.on('close', () => {
        console.log('Connection closed');
    });
    socket.on('end', () => {
        console.log('Connection end');
    });
    socket.on('error', error => {
        console.error('Socket error:', error);
    });
});

server.listen(serverPort, serverAddress, () => {
    console.log(`Server listening on ${serverAddress}:${serverPort}`);
});

3. 错误后二次打印Connection closed的原因
   当终止挂起的客户端脚本时，第一个客户端连接因强制退出触发服务器端socket的ECONNRESET错误（表示连接被对方强制重置），而socket在触发error事件后会自动触发close事件，因此会再次打印"Connection closed"。这并非存在两个未关闭的连接，而是第一个连接的错误处理流程触发了第二次close事件。

内容的提问来源于stack exchange，提问作者Andrey Fedotov