Making a Pear Desktop Application

This guide demonstrates how to build a peer-to-peer chat application.

It continues where Starting a Pear Desktop Project left off.

Build with Pear - Episode 01: Developing with Pear

Step 1. HTML Structure and CSS Styles

The project folder should contain:

package.json
index.html
app.js
test/index.test.js

Start by defining the app's layout in index.html:

<!DOCTYPE html>
<html>
  <head>
    <style>
      pear-ctrl {
        margin-top: 9px;
        margin-left: 9px;
        position: absolute;
      }
      pear-ctrl[data-platform="darwin"] { float: left; margin-top: 4px; }

      pear-ctrl:after {
        content: '';
        display: block;
        height: 1.8rem;
        position: fixed;
        z-index: -1;
        left: 0;
        top: 0;
        width: 100%;
        background-color: #B0D94413;
        filter: drop-shadow(2px 10px 6px #888);
      }

      button, input {
        all: unset;
        border: 1px ridge #B0D944;
        background: #000;
        color: #B0D944;
        padding: .45rem;
        font-family: monospace;
        font-size: 1rem;
        line-height: 1rem;
      }

      body {
        background-color: #001601;
        font-family: monospace;
        margin: 0;
        padding: 0;
      }

      main {
        display: flex;
        height: 100vh;
        color: white;
        justify-content: center;
        margin: 0;
        padding: 0;
      }

      .hidden {
        display: none !important;
      }

      #or {
        margin: 1.5rem auto;
      }

      #setup {
        display: flex;
        flex-direction: column;
        align-items: center;
        justify-content: center;
      }

      #loading {
        align-self: center;
      }

      #chat {
        display: flex;
        flex-direction: column;
        width: 100vw;
        padding: .75rem;
      }

      #header {
        margin-top: 2.2rem;
        margin-bottom: 0.75rem;
      }

      #details {
        display: flex;
        justify-content: space-between;
      }

      #messages {
        flex: 1;
        font-family: 'Courier New', Courier, monospace;
        overflow-y: scroll;
      }

      #message-form {
        display: flex;
      }

      #message {
        flex: 1;
      }
    </style>
    <script type='module' src='./app.js'></script>
  </head>
  <body>
    <pear-ctrl></pear-ctrl>
    <main>
      <div id="setup">
        <div>
          <button id="create-chat-room">Create</button>
        </div>
        <div id="or">
          - or -
        </div>
        <form id="join-form">
          <button type="submit" id="join-chat-room">Join</button>
          <input required id="join-chat-room-topic" type="text" placeholder="Chat room Topic" />
        </form>
      </div>
      <div id="loading" class="hidden">Loading ...</div>
      <div id="chat" class="hidden">
        <div id="header">
          <div id="details">
            <div>
              Topic: <span id="chat-room-topic"></span>
            </div>
            <div>
              Peers: <span id="peers-count">0</span>
            </div>
          </div>
        </div>
        <div id="messages"></div>
        <form id="message-form">
          <input id="message" type="text" />
          <input type="submit" value="Send" />
        </form>
      </div>
    </main>
  </body>
</html>

Running pear dev should show

Step 2. Module dependencies

Note: Close the app before installing dependencies. If dependencies are installed while the app is running, an error is thrown.

The app uses these modules:

hyperswarm to connect peers on a "topic".
hypercore-crypto for basic cryptography.
b4a to manipulate buffers.

Install the dependencies with:

npm install hyperswarm hypercore-crypto b4a

Step 3. JavaScript

Replace app.js with

/* global Pear */
import Hyperswarm from 'hyperswarm'   // Module for P2P networking and connecting peers
import crypto from 'hypercore-crypto' // Cryptographic functions for generating the key in app
import b4a from 'b4a'                 // Module for buffer-to-string and vice-versa conversions 
const { teardown } = Pear             // Cleanup function

const swarm = new Hyperswarm()

// Unannounce the public key before exiting the process
// (This is not a requirement, but it helps avoid DHT pollution)
teardown(() => swarm.destroy())

// When there's a new connection, listen for new messages, and add them to the UI
swarm.on('connection', (peer) => {
  // name incoming peers after first 6 chars of its public key as hex
  const name = b4a.toString(peer.remotePublicKey, 'hex').substr(0, 6)
  peer.on('data', message => onMessageAdded(name, message))
  peer.on('error', e => console.log(`Connection error: ${e}`))
})

// When there's updates to the swarm, update the peers count
swarm.on('update', () => {
  document.querySelector('#peers-count').textContent = swarm.connections.size
})

document.querySelector('#create-chat-room').addEventListener('click', createChatRoom)
document.querySelector('#join-form').addEventListener('submit', joinChatRoom)
document.querySelector('#message-form').addEventListener('submit', sendMessage)

async function createChatRoom() {
  // Generate a new random topic (32 byte string)
  const topicBuffer = crypto.randomBytes(32)
  joinSwarm(topicBuffer)
}

async function joinChatRoom (e) {
  e.preventDefault()
  const topicStr = document.querySelector('#join-chat-room-topic').value
  const topicBuffer = b4a.from(topicStr, 'hex')
  joinSwarm(topicBuffer)
}

async function joinSwarm (topicBuffer) {
  document.querySelector('#setup').classList.add('hidden')
  document.querySelector('#loading').classList.remove('hidden')

  // Join the swarm with the topic. Setting both client/server to true means that this app can act as both.
  const discovery = swarm.join(topicBuffer, { client: true, server: true })
  await discovery.flushed()

  const topic = b4a.toString(topicBuffer, 'hex')
  document.querySelector('#chat-room-topic').innerText = topic
  document.querySelector('#loading').classList.add('hidden')
  document.querySelector('#chat').classList.remove('hidden')
}

function sendMessage (e) {
  const message = document.querySelector('#message').value
  document.querySelector('#message').value = ''
  e.preventDefault()

  onMessageAdded('You', message)

  // Send the message to all peers (that you are connected to)
  const peers = [...swarm.connections]
  for (const peer of peers) peer.write(message)
}

// appends element to #messages element with content set to sender and message
function onMessageAdded (from, message) {
  const $div = document.createElement('div')
  $div.textContent = `<${from}> ${message}`
  document.querySelector('#messages').appendChild($div)
}

Note that the pear dependency is used, even though it was not installed. This is the Pear API, available to any Pear project.

Step 4. Chat

Open two app instances by running pear dev in two terminals. For now, you will need to specify a different storage directory for the second pear instance to allow for two instances to run simultaneously:

pear dev -s /tmp/tmp_pear_instance

In the first app, click on Create. A random topic will appear at the top.

Note that topics consist of 64 hexadecimal characters (32 bytes).

Paste the topic into the second app, then click on Join.

Once connected, messages can be sent between each chat application.

Discussion

Chatting With Another Machine

The two application instances used Hyperswarm's distributed hash table (DHT) to connect with each other.

The DHT enables connections across different machines, so chatting with other people is also possible, as long as they run the same application.

One option is to copy the code, but it is also possible to distribute the application itself over the DHT. This is the topic of Sharing a Pear Application.

Joining Topics VS Joining Servers

In a traditional client-server setup, the server is hosted at an IP address (or hostname) and a port, e.g. http://localhost:3000. This is what clients use to connect to the server.

The code in app.js contains the line swarm.join(topicBuffer, { client: true, server: true }).

topicBuffer is the invitation: anyone who knows this topic can join the room and message the other members.

Note that all members are equal: there is no separate client or server. If the room creator goes offline, or even deletes the room from their machine, the other members can continue chatting.