Make a P2P connection in 10 minutes

This is a short guide on how to make a P2P chat. My aim is to give you only a taste, if you like I could write a more deeper article explaining how all this things work. That said, lets start.

Preparation

The only thing you will need is the latest NodeJS and your favorite editor, mine is Visual Studio Code. Now create a folder for our project, open a command line, initialize an npm repo with npm init and install some libraries we will need with:

npm i --save discovery-swarm dat-swarm-defaults portfinder get-port

I will explain what this libraries does later.

Our fisrt P2P connection

Lets start by doing a simple P2P connection, thanks to some great libraries from the Node.js community it is too simple:

const crypto = require('crypto')
const Swarm = require('discovery-swarm')
const defaults = require('dat-swarm-defaults')
const getPort = require('get-port')
const readline = require('readline')

/**
 * Here we will save our TCP peer connections
 * using the peer id as key: { peer_id: TCP_Connection }
 */
const peers = {}
// Counter for connections, used for identify connections
let connSeq = 0

// Peer Identity, a random hash for identify your peer
const myId = crypto.randomBytes(32)
console.log('Your identity: ' + myId.toString('hex'))

// reference to redline interface
let rl
/**
 * Function for safely call console.log with readline interface active
 */
function log () {
  if (rl) {
    rl.clearLine()    
    rl.close()
    rl = undefined
  }
  for (let i = 0, len = arguments.length; i < len; i++) {
    console.log(arguments[i])
  }
  askUser()
}

/*
* Function to get text input from user and send it to other peers
* Like a chat :)
*/
const askUser = async () => {
  rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
  })

  rl.question('Send message: ', message => {
    // Broadcast to peers
    for (let id in peers) {
      peers[id].conn.write(message)
    }
    rl.close()
    rl = undefined
    askUser()
  });
}

/** 
 * Default DNS and DHT servers
 * This servers are used for peer discovery and establishing connection
 */
const config = defaults({
  // peer-id
  id: myId,
})

/**
 * discovery-swarm library establishes a TCP p2p connection and uses
 * discovery-channel library for peer discovery
 */
const sw = Swarm(config)


;(async () => {

  // Choose a random unused port for listening TCP peer connections
  const port = await getPort()

  sw.listen(port)
  console.log('Listening to port: ' + port)

  /**
   * The channel we are connecting to.
   * Peers should discover other peers in this channel
   */
  sw.join('our-fun-channel')

  sw.on('connection', (conn, info) => {
    // Connection id
    const seq = connSeq

    const peerId = info.id.toString('hex')
    log(`Connected #${seq} to peer: ${peerId}`)

    // Keep alive TCP connection with peer
    if (info.initiator) {
      try {
        conn.setKeepAlive(true, 600)
      } catch (exception) {
        log('exception', exception)
      }
    }

    conn.on('data', data => {
      // Here we handle incomming messages
      log(
        'Received Message from peer ' + peerId,
        '----> ' + data.toString()
      )
    })

    conn.on('close', () => {
      // Here we handle peer disconnection
      log(`Connection ${seq} closed, peer id: ${peerId}`)
      // If the closing connection is the last connection with the peer, removes the peer
      if (peers[peerId].seq === seq) {
        delete peers[peerId]
      }
    })

    // Save the connection
    if (!peers[peerId]) {
      peers[peerId] = {}
    }
    peers[peerId].conn = conn
    peers[peerId].seq = seq
    connSeq++

  })

  // Read user message from command line
  askUser()  

})()

Run this code in two consoles and this is it!. Now you can run it in other device right in your LAN and should work even without internet, also you can share and run this script in any other computer with internet, it just works, so nice!

What’s is next?

We will build a P2P chat for our long term project using this code. The chat will have end-to-end encryption and can verify messages.

Make a P2P chat in 10 minutes (Soon …)

I love feedback, ask me questions, comment your experience with P2P technologies and share your ideas!

This series is possible thanks to the awesome tools delivered by the DatProject, Webtorrent and the NodeJS community.

This article is part of a medium-term project you can find here:

Create a P2P Real-Time Game App