[Node.js] TCP Socket - net module

net module

• Node.js 기본 모듈인 net을 사용하여 소켓 프로그래밍 구현
• stream-based TCP servers/clients를 생성하기 위한 비동기 네트워크 API 제공
• const net = require('net');

methods

method	description
net.createServer([options][, connectionListener])	creates a new TCP server. returns net.Server
net.connect(port[, host][, connectListener])	creates a new net.Socket. after connection, returns net.Socket

• net.Server

method	description
server.listen()	Start a server listening for connections.
server.close([callback])	Stops the server from accepting new connections and keeps existing connections

event	description
close	Emitted when the server closes.
connection	Emitted when a new connection is made.
error	Emitted when an error occurs.
listening	Emitted when the server has been bound after calling server.listen().

• net.Socket

method	description
socket.connect()	Start a server listening for connections.
socket.write(data[, encoding][, callback])	Sends data on the socket.

event	description
close	Emitted once the socket is fully closed.
connect	Emitted when a socket connection is successfully established.
data	Emitted when data is received.
error	Emitted when an error occurs.

example source code (Echo)

• Server

const net = require('net');
const server = net.createServer((connection) => { // createServer는 net.Socket 클래스 반환
  console.log('client connected');
   
  connection.on('end', () => {    // client 커넥션이 끊기면 호출되는 이벤트
    console.log('client disconnected');
  });

  connection.pipe(connection);    // 소켓의 데이터를 그대로 전달 (echo 역할)
});

server.listen(8090, () => {   // 다른 소켓의 접속 listening
  console.log('server is listening');
});

• Client

const net = require('net');
const client = net.connect({port: 8090}, () => {  // connect는 net.Socket 클래스 반환
    console.log("client connected");    
});

client.write("client send data");   // tx 버퍼에 data 쓰기

client.on('data', (data) => {   // rx 버퍼에 데이터 읽어오기
    console.log("msg from server : " + data.toString());
    client.end();
});

client.on('end', () => {    // 연결 끊김 확인
    console.log("disconnected from server");
});

---

ref
[Node.js Doc] Net
TCP 서버 및 클라이언트