Detailed explanation of TCP/IP data communication in Node.js

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1. Use the net module to implement TCP-based data communication

Provides a net module dedicated to realizing communication between the TCP server and the TCP client

1.1 Create a TCP server

Use the net module to create a TCP server in Node.js

var server = net.createServer([options],[connectionListener])
//options：false当TCP服务器接收到客户端发送的一个FIN包时将会回发一个FIN包
   true当TCP服务器接收到客户端发送的一个FIN包时将不会回发FIN包，这使得TCP服务器可以继续向客户端发送数据，但不会继续接收客户端发送的数据。来发者必须调用end方法来关闭socket连接。默认为false
connectionListener：指定当客户端与服务器端简历连接时所要调用的回调函数
function(socket){
 //回调函数代码
}

The parameter value is the socket port object that the TCP server listens to. The createServer method returns the created TCP server

When the client establishes a connection with the server, the connection event is triggered. You can use the following method to execute the callback function

server.on('connection',function(socket){
//回调函数代码
})

After creating the TCP server, use the listen method to notify the server to start monitoring the client connection

server.listen(port,[host],[backlog],[callback])
//port指定需要监听的端口号，
host：指定需要监听的IP地址或主机名，如果省略，服务器将监听来自于任何IPv4地址的客户端连接
backlog：指定位于等待队列中的客户端连接的最大数量
callback：无参回调函数

server.listen(path,[callback])
//server:代表一个使用unix端口的服务器
path：指定需要监听的路径，会触发listening事件，然后执行回调函数callback

server.listenting（handle，[callback]）
//server 代表一个TCP服务器
handle：指定需要监听的socket句柄（该句柄可以为一个TCP服务器对象，socket端口对象，文件描述符）

Here is an example to create a TCP server:

var net = require('net')
var server = net.createServer(function(socket){
 console.log('客户端与服务器连接已建立')
})
server.listen(8431,'localhost',function(){
 console.log('服务器端开始监听')
})

After running, you can get the following results:

Use telnet to access the corresponding server:

telnet localhost 8431

The results that will appear are as follows:

socket port object example:

var net = require('net')
var file = require('fs').createWriteStream('./message.txt');
var server = net.createServer(function(socket){
console.log('客户端与服务器连接已建立')
server.getConnections(function(err,count){
 console.log('当前存在%d个客户端连接。',count);
 server.maxConnections = 4;
 console.log('TCP服务器的最大连接数为%d',server.maxConnections);
 
})

// server.close(function(){
 // console.log('TCP服务器被关闭。');
// })
})
server.listen(8431,'localhost',function(){
console.log('服务器端开始监听')

})
server.on('connection',function(socket){
address = socket.address();
console.log('被监视的地址信息为%j',address);
socket.pipe(file);
socket.setEncoding('utf8');
socket.on('data',function(data){
 console.log(data.toString());
 console.log('已接受到%d字节数据。',socket.bytesRead);
});
socket.on('end',function(){
 file.end('再见')
 console.log('客户端连接被关闭。')
})

socket.pause();
setTimeout(function(){
 console.log('*************')
 socket.resume();
 socket.pipe(file,{end:false});
},30*1000);
// socket.pipe(file,{end:false});
// setTimeout(function(){
 // file.end('再见。');
 // socket.unpipe(file);
// },5000);
socket.setTimeout(10*1000);
socket.on('timeout',function(){
 console.log('客户端连接超时');
 socket.setTimeout(0);
})

})

1.2 Create TCP client

Establish TCP client example:

var net = require("net");
var client = new net.Socket();
client.setEncoding('utf8');
client.connect(8431,'localhost',function(){
console.log('已连接到服务器');
client.write('你好');
console.log('当前已发送%d字节',client.bytesWritten);
client.end('再见')
console.log('当前已发送%d字节',client.bytesWritten);
// setTimeout(function(){
 // client.end('再见');  
// },10*1000)

});
client.on('data',function(data){
//console.log('已接收服务器端发送的数据： '+data);
console.log('已接收服务器端发送的数据');
})
client.on('error',function(err){
console.log('与服务器连接或通信的过程中发生了一个错误，错误编码为%s',err.code);
client.destroy();
})

At the same time, the corresponding server needs to be established:

var net = require('net');
var fs = require('fs');
var server = net.createServer();
server.on('connection',function(socket){
console.log('客户端与服务器端连接已建立');
socket.setEncoding('utf8');
var readStream = fs.createReadStream('./server.js');
readStream.on('data',function(data){
 var flag = socket.write(data);
 console.log('write方法的返回值为：'+flag);
 console.log('缓存队列中当前缓存了%d字符。',socket.bufferSize);
})
socket.on('data',function(data){
 console.log('已连接客户端发送的数据:'+data);
 socket.write('确认数据：'+data);
})
socket.on('error',function(err){
 console.log('客户端通信的过程中发生了一个错误，错误编码为%s',err.code);
 socket.destroy();
})
socket.on('end',function(){
 console.log('客户端连接被关闭。');
 server.unref();
})
socket.on('close',function(had_error){
 if(had_error){
  console.log('由于一个错误导致socket端口被关闭。');
  server.unref();
 }else{
  console.log('socket端口被正常关闭。');
 }
})
server.getConnections(function(err,count){
 if(count==2)
  server.close();
});
});

server.listen(8431,'localhost');
server.on('close',function(){
console.log('TCP服务器被关闭。');
})

In Node.js, the following method can be used to continuously send detection packets to the client or server to determine the connection status;

socket.setKeepAlive([enable],[initialDelay])
//enable:true:启用Keep-alive机制，不断向对方发送一个探测包，如果没有回应表示连接关闭
initialDelay：间隔时间（毫秒）

Related recommendations:

Node.js creates Web and TCP servers

A brief analysis of the three-way handshake four of TCP transmission Wave strategy

What is the difference between TCP/IP and UDP

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