Nodejs determines whether the port is occupied

Node.js is a popular server-side JavaScript runtime environment that is widely used for web development and building efficient network applications. In Node.js development, we often encounter scenarios where we need to determine whether a certain port is occupied. This article will introduce how to use Node.js to determine whether a port is occupied, as well as common solutions and best practices.

1. The net module of Node.js

Node.js provides a core module called net, which is used to handle network connections and transmit data. The net module contains some common network programming components, including socket implementations of TCP and UDP. We can use the net module to determine whether a port is occupied.

The following is a sample code that uses the net module to determine port occupancy:

const net = require('net');

const port = 3000;
const server = net.createServer();
server.once('error', function (err) {
  if (err.code === 'EADDRINUSE') {
    console.log('Port %d is in use', port);
  }
});

server.listen(port, function () {
  console.log('Server listening on port %d', port);
  server.close();
});

In this example, we create a TCP server and bind it to port 3000. If the port is occupied, we will capture the error event and output a message to the console. Otherwise, we start the server and listen on the port, then immediately shut down the server.

The disadvantage of this method is that it requires starting a server. If we just wanted to check if a process is occupying a certain port, this would be a very resource-intensive approach as it would create a complete server process.

2. The dgram module of Node.js

In Node.js, the dgram module is used to process UDP datagrams and can also be used to detect whether the port is occupied. The following is a sample code using the dgram module:

const dgram = require('dgram');
const socket = dgram.createSocket('udp4');

const port = 3000;

socket.on('error', function (err) {
  if (err.code === 'EADDRINUSE') {
    console.log('Port %d is in use', port);
  }
});

socket.bind(port, function () {
  console.log('Port %d is free', port);
  socket.close();
});

In this example, we use the dgram module to create a UDP socket and bind it to port 3000. If the port is occupied, we will capture the error event and output a message to the console. Otherwise, we print a success message and close the socket.

3. Third-party module: is-port-available

In addition to the core module of Node.js, there are many third-party modules that can be used to detect whether the port is occupied. is-port-available is a lightweight Node.js module that runs on Windows, Mac, and Linux. Using this module we can easily detect if a port is occupied without writing complex code. The following is a sample code using the is-port-available module:

const isPortAvailable = require('is-port-available');
const port = 3000;

isPortAvailable(port).then(function(available) {
  if (available) {
    console.log(`Port ${port} is free`);
  } else {
    console.log(`Port ${port} is in use`);
  }
});

In this example, we use the is-port-available module to detect whether port 3000 is occupied and output the corresponding information on the console information.

4. Summary

In Node.js development, detecting whether the port is occupied is a very important task. We introduced how to use the core modules net and dgram of Node.js to detect ports, as well as the use of the third-party module is-port-available. When choosing a detection port, we should choose the method that best suits our application. The net module is perfect when we need to start a server to handle network requests. If you just want to detect whether a certain port is occupied, dgram or is-port-available may be more suitable.

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