pear-docs/guide/connecting-two-peers.md

Hyperswarm's DHT: Connecting Two Peers by Key

Get setup by creating a project folder and installing dependencies:

mkdir connect-two-peers
cd connect-two-peers
pear init -y -t terminal
npm install hyperdht b4a graceful-goodbye

Hyperswarm helps to find and connect to peers who are announcing a common 'topic'. The swarm topic can be anything. The HyperDHT uses a series of holepunching techniques to establish direct connections between peers, even if they're located on home networks with tricky NATs.

In the HyperDHT, peers are identified by a public key, not by an IP address. With the public key, users can connect to each other irrespective of their location, even if they move between different networks.

Hyperswarm's holepunching will fail if both the client peer and the server peer are on randomizing NATs, in which case the connection must be relayed through a third peer. Hyperswarm does not do any relaying by default.

For example, Keet implements its relaying system wherein other call participants can serve as relays -- the more participants in the call, the stronger overall connectivity becomes.

Use the HyperDHT to create a basic CLI chat app where a client peer connects to a server peer by public key. This example consists of two files: client.js and server.js.

server.js will create a key pair and then start a server that will listen on the generated key pair. The public key is logged into the console. Copy it for instantiating the client.

//server.js
import DHT from 'hyperdht'
import goodbye from 'graceful-goodbye'
import b4a from 'b4a'

const dht = new DHT()

// This keypair is your peer identifier in the DHT
const keyPair = DHT.keyPair()

const server = dht.createServer(conn => {
  console.log('got connection!')
  process.stdin.pipe(conn).pipe(process.stdout)
})

server.listen(keyPair).then(() => {
  console.log('listening on:', b4a.toString(keyPair.publicKey, 'hex'))
})

// Unnannounce the public key before exiting the process
// (This is not a requirement, but it helps avoid DHT pollution)
goodbye(() => server.close())

client.js will spin up a client, and the public key copied earlier must be supplied as a command line argument for connecting to the server. The client process will log got connection into the console when it connects to the server.

Once it's connected, try typing in both terminals!

//client.js
import DHT from 'hyperdht'
import b4a from 'b4a'

console.log('Connecting to:', process.argv[2])
const publicKey = b4a.from(process.argv[2], 'hex')

const dht = new DHT()
const conn = dht.connect(publicKey)
conn.once('open', () => console.log('got connection!'))

process.stdin.pipe(conn).pipe(process.stdout)