A brief discussion on the net module in nodejs

TCP services are very common in network applications. Most of the current applications are built based on TCP. The net module provides an asynchronous network wrapper for TCP network programming, which contains methods for creating servers and clients. This article will introduce the net module in nodeJS in detail.

Related recommendations: "nodejs Tutorial"

IP Test

[net.isIP(input)]

Test whether the input is an IP address. Returns 0 if the string is invalid. In the case of IPV4, it returns 4, in the case of IPV6 it returns 6

var net = require('net');
console.log(net.isIP('1.1.1.1'));//4
console.log(net.isIP('1.1'));//0
console.log(net.isIP('AD80::ABAA:0000:00C2:0002'));//6

[net.isIPv4(input)]

If the input address is IPV4, it returns true, otherwise it returns false

var net = require('net');
console.log(net.isIPv4('1.1.1.1'));//true
console.log(net.isIPv4('1.1'));//false

[net.isIPv6(input)]

If the input address is IPV6, return true, otherwise return false

var net = require('net');
console.log(net.isIPv6('1.1.1.1'));//true
console.log(net.isIPv6('AD80::ABAA:0000:00C2:0002'));//true

Server

【 net.createServer([options][, connectionListener])]

Create a TCP server with the following parameters

options
    allowHalfOpen: false(默认)，如果为true，当另一端socket发送FIN包时socket不会自动发送FIN包。socket变为不可读但可写(半关闭)
    pauseOnConnect: false(默认)，如果为true，当连接到来的时候相关联的socket将会暂停。它允许在初始进程不读取数据情况下，让连接在进程间传递。调用resume()从暂停的socket里读取数据
connectionListener 自动给 'connection' 事件创建监听器

var server = net.createServer(function() {

});

[server.listen(port[, host][, backlog][, callback ])】

Start accepting connections from the specified port and host. If host is omitted, the server will accept direct connections from any IPv4 address (INADDR_ANY). If the port is 0, a random port

will be allocated. The backlog is the maximum length of the connection waiting queue. The actual length is set by the operating system through sysctl, such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511

The 'listening' event will be triggered when the server is bound. The last parameter callback will be used as a listener for the 'listening' event. Some users will encounter an EADDRINUSE error, which indicates that another server is already running on the requested port. The way to deal with this situation is to wait for a period of time and try again

server.listen(6000);

[server.close([callback])]

The server stops receiving new connections and keeps existing connections. When all connections are completed the server will be closed and the 'close' event will be triggered. You can pass a callback function to listen for the 'close' event. If present, the callback function will be called with the error (if any) as the only parameter

[server.address()]

The operating system returns the bound address, protocol family name and server port. Very useful when finding which port has been bound by the system

[Note] Do not call server.address() before the 'listening' event is triggered

server.listen(function() {
    //{ address: '::', family: 'IPv6', port: 53806 }
    console.log(server.address());
});

[server.maxConnections]

After setting this option, new connections will be rejected when the number of server connections exceeds the number

Once the socket has been sent to the child process using the child_process.fork() method, this option is not recommended

【server.getConnections(callback)】

Asynchronously obtains the number of currently active connections on the server. It is only valid when the socket is sent to the child process;

The callback function has 2 parameters err and count

server.getConnections(function(err,count){
    console.log(count);//0
})

[Event listening]

When the server calls server.listen binding It will be triggered later

[Event connection]

{Socket object} 连接对象

Will be triggered when a new connection is created. The socket is an instance of net.Socket

[Event close]

Will be triggered when the server is closed

[Note] If there are connections, this event will not be triggered until all connections are connected Close

【Event error】

Triggered when an error occurs

Client

[net.connect(options[, connectionListener ])】

【net.createConnection(options[, connectionListener])】

The alias of connect() is the createConnection() method

This method returns a new ' net.Socket' and connect to the specified address and port. When the socket is established, the 'connect' event will be triggered. It has the same method as 'net.Socket'

For TCP sockets, the parameter options are as follows

port: 客户端连接到 Port 的端口（必须）
host: 客户端要连接到得主机。默认 'localhost'
localAddress: 网络连接绑定的本地接口
localPort: 网络连接绑定的本地端口
family : IP 栈版本。默认 4

For local domain sockets, the parameter options are as follows

path: 客户端连接到得路径(必须)

var client = net.connect({port: 5000}, function() {});

Socket

【new net.Socket([options])】

Construct a new socket object

The options object has the following default values:

{ fd: null
  allowHalfOpen: false,
  readable: false,
  writable: false
}

The parameter fd allows specifying an existing file descriptor. Set readable and (or) writable to true to allow reading or writing on this socket (only when the parameter fd is valid)

[socket.connect(port[, host][, connectListener])]

【socket.connect(path[, connectListener])】

Use the incoming socket to open a connection. If port and host are specified, TCP socket will open the socket. If the host parameter is omitted, it defaults to localhost. If path is specified, the socket will be opened by the unix socket of the specified path

The parameter connectListener will be added to the 'connect' event as a listener

[socket.write(data[, encoding] [, callback])]

Send data on the socket. The second parameter specifies the encoding of the string. The default is UTF8 encoding

　　如果所有数据成功刷新到内核缓冲区，返回true。如果数据全部或部分在用户内存里，返回false。当缓冲区为空的时候会触发'drain'

　　当数据最终被完整写入的的时候，可选的callback参数会被执行，但不一定会马上执行

【socket.end([data][, encoding])】

　　半关闭socket。例如，它发送一个FIN包。可能服务器仍在发送数据。

　　如果参数data不为空，等同于调用socket.write(data,encoding)后再调用socket.end()

【socket.destroy()】

　　确保没有 I/O 活动在这个套接字上。只有在错误发生情况下才需要

【socket.pause()】

　　暂停读取数据。就是说，不会再触发 data 事件。对于控制上传非常有用

【socket.resume()】

　　调用 pause() 后想恢复读取数据

【socket.setTimeout(timeout[, callback])】

　　socket 闲置时间超过 timeout 毫秒后 ，将 socket 设置为超时。触发空闲超时事件时，socket 将会收到 'timeout'事件，但是连接不会被断开。用户必须手动调用 end() 或 destroy() 这个socket。

　　如果 timeout = 0, 那么现有的闲置超时会被禁用。可选的 callback 参数将会被添加成为 'timeout' 事件的一次性监听器

【socket.setNoDelay([noDelay])】

　　禁用纳格（Nagle）算法。默认情况下 TCP 连接使用纳格算法，在发送前他们会缓冲数据。将 noDelay 设置为 true 将会在调用 socket.write() 时立即发送数据。noDelay 默认值为 true

【socket.setKeepAlive([enable][, initialDelay])】

　　禁用/启用长连接功能，在发送第一个在闲置socket上的长连接probe之前，可选地设定初始延时。默认false

　　设定initialDelay（毫秒），来设定收到的最后一个数据包和第一个长连接probe之间的延时。将 initialDelay 设为0，将会保留默认（或者之前）的值。默认值为0

【socket.address()】

　　操作系统返回绑定的地址，协议族名和服务器端口。返回的对象有 3 个属性，比如{ port: 12346, family: 'IPv4', address: '127.0.0.1' }

【socket.remoteAddress】

　　远程的 IP 地址字符串

【socket.remoteFamily】

　　远程IP协议族字符串

【socket.remotePort】

　　远程端口，数字表示

【socket.localAddress】

　　远程客户端正在连接的本地IP地址，字符串表示

【socket.localPort】

　　本地端口地址，数字表示

【socket.bytesRead】

　　接收的字节数

【socket.bytesWritten】

　　发送的字节数

【事件lookup】

　　在解析域名后，但在连接前，触发这个事件。对 UNIX sokcet 不适用

err {Error | Null} 错误对象
address {String} IP 地址。
family {String | Null} 地址类型

【事件connect】

　　当成功建立 socket 连接时触发、

【事件data】

{Buffer object}

　　当接收到数据时触发。参数 data 可以是 Buffer 或 String

　　当 Socket 触发一个 'data' 事件时，如果没有监听器，数据将会丢失

【事件end】

　　当 socket 另一端发送 FIN 包时，触发该事件

【事件timeout】

　　当 socket 空闲超时时触发，仅是表明 socket 已经空闲。用户必须手动关闭连接

【事件drain】

　　当写缓存为空得时候触发。可用来控制上传

【事件error】

　　错误发生时触发

【事件close】

had_error {Boolean} 如果 socket 传输错误，为 true

　　当 socket 完全关闭时触发。参数 had_error 是 boolean，它表示是否因为传输错误导致 socket 关闭

简易服务器

【服务器】

//server.js
var net = require('net') ;
var server = net.createServer(function(socket) { 
    socket.write("Hi!\n");
    socket.on("data", function(data) {
      console.log(data.toString());
    });
    socket.on("end", function() {
      console.log('有客户机下线了！！！');
    });
    socket.on('error', function() {
      console.log('发生意外错误！！！');
    });
}) ;
server.listen(8080) ;

【客户机】

//client.js
var net = require('net') ;
var client = net.connect({port: 8080},function(){
    client.name = '客户机1';
    client.write(client.name + ' 上线了！\n');
    client.end(client.name + ' 下线了！\n');
    client.on("data", function(data) {
        console.log(data.toString());
    });
});

简易聊天室

【服务器】

//chatServer.js
var net = require('net');
var i = 0;
//保存客户机
var clientList = [];
var server = net.createServer(function(socket) {
    socket.name = '用户' + (++i);
    socket.write('【聊天室提示】欢迎' + socket.name + '\n');
    //更新客户机数组
    clientList.push(socket); 
    function showClients(){
        console.log('【当前在线用户】：');
        for(var i=0;i<clientList.length;i++) { 
            console.log(clientList[i].name);
        }        
    }
    showClients();
    socket.on("data", function(data) {
        //把当前连接的客户机的信息转发到其他客户机  
        for(var i=0;i<clientList.length;i++) { 
            if(socket !== clientList[i]) {      
                clientList[i].write('【' + socket.name + '】：' + data);   
            }  
        }
    });
    socket.on("close", function() {
        //当前客户机下线时，将其从客户机数组中移除
        clientList.splice(clientList.indexOf(socket), 1);
        showClients();
    });
    socket.on('error', function(err) {
        console.log(socket.name + '退出');
    });
});
server.listen(8080) ;

【客户机】

//chatClient.js
var net = require('net');
process.stdin.resume();
process.stdin.setEncoding('utf8');
var client = net.connect({port: 8080},function(){
    console.log('【本机提示】登录到聊天室');
    process.stdin.on('data',function(data){
        client.write(data);
    })
    client.on("data", function(data) {
        console.log(data.toString());
    });
    client.on('end', function() {
        console.log('【本机提示】退出聊天室');
        process.exit();
    });
    client.on('error', function() {
        console.log('【本机提示】聊天室异常');
        process.exit();
    });
});

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