trystero

📯 Trystero

Easy WebRTC matchmaking for painless P2P

Trystero manages a clandestine courier network that lets your application's users talk directly with one another, encrypted and without a server middleman.

---

• Setup
• Install
• Initialize
• Join a room
• Listen for events
• Broadcast events
• Advanced
• API

---

Setup

To establish a direct peer-to-peer connection with WebRTC, a signalling channel is needed to exchange peer information (SDP). Trystero uses Firebase to do so as it's trivial to set up, requires no server maintenance, and can be used (for this purpose) for free or very cheaply. Trystero may adopt more signalling strategies in the future, but for now Firebase is the sole medium.

If you don't have an existing Firebase project:

1. Create a Firebase project
2. Create a new Realtime Database
3. Copy the Firebase config's databaseURL by registering a new web app in settings
4. [Optional] Configure the database with security rules

Install

npm i trystero

Initialize

Begin by initializing Trystero:

import * as trystero from 'trystero'

trystero.init({dbUrl: 'https://your-firebase-instance-here.firebaseio.com'})

This should be called just once globally for your app.

Join a room

Join the user to a room with a namespace:

const room = trystero.joinRoom('yoyodyne')

Listen for events

Listen for peers joining the room:

room.onPeerJoin(id => console.log(`${id} joined`))

Listen for peers leaving the room:

room.onPeerLeave(id => console.log(`${id} left`))

Listen for peers sending their audio/video streams:

room.onPeerStream((id, stream) => (peerElements[id].video.srcObject = stream))

To unsubscribe from events, leave the room:

room.leave()

Broadcast events

Send peers your video stream:

room.addStream(
  await navigator.mediaDevices.getUserMedia({audio: true, video: true})
)

Send and subscribe to custom P2P actions:

;[sendDrink, getDrink] = room.makeAction('drink')

// buy drink for a friend
sendDrink({drink: 'negroni', withIce: true}, friendId)

// buy round for the house (second argument omitted)
sendDrink({drink: 'mezcal', withIce: false})

// listen for drinks sent to you
getDrink((id, data) => console.log(`got a ${data.drink} from ${id}`))

You can also create actions that send and receive binary data, like images:

// pass true as the second argument to makeAction to make it binary capable
;[sendPic, getPic] = room.makeAction('pic', true)

// blobs are automatically handled, as are any form of TypedArray
canvas.toBlob(blob => sendPic(blob))

// binary data is received as raw ArrayBuffers so your handling code should
// interpret it in a way that makes sense
getPic((id, data) => (imgs[id].src = URL.createObjectURL(new Blob([data]))))

Advanced

Capped rooms

You can create rooms that are capped at a fixed number of members by passing a second argument to joinRoom. Since the process of checking the number of participants is async, in this case joinRoom will return a promise that throws if the room is full.

let exclusiveRoom

try {
  exclusiveRoom = await trystero.join('vips_only', 49)
} catch (e) {
  console.log('room is full')
}

Security rules

You can limit activity in your Firebase instance by setting these security rules:

{
  "rules": {
    ".read": false,
    ".write": false,
    "__trystero__": {
      ".read": false,
      ".write": false,
      "$room_id": {
        ".read": true,
        ".write": true
      }
    }
  }
}

These ensure room peer presence is only readable if the room namespace is known ahead of time.

API

selfId

A unique ID string other peers will know the local user as globally across rooms.

init(config)

Required to be called once in an application's lifespan to bootstrap peer connection process.

• config - Configuration object containing the following keys:

  • dbUrl - A URL string pointing at your Firebase database (databaseURL in the Firebase config object).

  • rootPath - (optional) Where Trystero writes its matchmaking data in your database ('__trystero__' by default). Changing this is useful if you want to run multiple apps using the same database and don't want to worry about namespace collisions.

getOccupants(namespace)

Returns a promise that resolves to a list of user ids present in the given namespace. This is useful for checking how many users are in a room without joining it.

• namespace - A namespace string that you'd pass to joinRoom().

Example:

console.log((await trystero.getOccupants('the_scope')).length)
// => 3

joinRoom(namespace, [limit])

Adds local user to room whereby other peers in the same namespace will open communication channels and send events.

• namespace - A string to namespace peers and events.

• limit - (optional) A positive integer defining a limit to the number of users allowed in the room. If defined, a promise is returned that resolves with the methods below. If the room is full, the local user does not join and the promise rejects.

Returns an object with the following methods:

• leave()

  Remove local user from room and unsubscribe from room events.

• getPeers()

  Returns a list of peer IDs present in room (not including the local user).

• addStream(stream, [peerId], [currentPeersOnly])

  Broadcasts media stream to other peers.

  • stream - A MediaStream with audio/video to send to peers in the room.

  • peerId - (optional) If specified, the stream is sent only to the target peer and not all users.

  • currentPeersOnly - (optional) If true the stream will be sent only to peers currently in the room. By default, the stream is automatically sent to peers who arrive after the stream is initially broadcast unless a peerId argument is given or currentPeersOnly is true.

• onPeerJoin(callback)

  Registers a callback function that will be called when a peer joins the room. If called more than once, only the latest callback registered is ever called.

  Example:

  onPeerJoin(id => console.log(`${id} joined`))
  

• onPeerLeave(callback)

  Registers a callback function that will be called when a peer leaves the room. If called more than once, only the latest callback registered is ever called.

  Example:

  onPeerLeave(id => console.log(`${id} left`))
  

• onPeerStream(callback)

  Registers a callback function that will be called when a peer sends a media stream. If called more than once, only the latest callback registered is ever called.

  Example:

  onPeerStream((id, stream) => console.log(`got stream from ${id}`, stream))
  

• makeAction(type, [isBinary])

  Listen for and send custom data actions.

  • type - A string to register this action consistently among all peers.

  • isBinary - (optional) If true, data sent will be interpreted as raw bytes and not JSON or a primitive. This should be used if an action is for sending files, images, etc.

  Returns a pair containing a function to send the action to peers and a function to register a listener. The sender function takes any JSON-serializable value as its first argument (primitive or object) and takes an optional second argument of a peer ID to send to. By default it will broadcast the value to all peers in the room. If makeAction() was called with a second argument of true, the sender function will accept binary data types (Blob, TypedArray) and the receiver function will be called with an ArrayBuffer of agnostic bytes.

  Example:

  const numberStations = {}
  
  ;[sendNumber, getNumber] = room.makeAction('number')
  
  sendNumber(33)
  
  getNumber((id, n) => {
    if (!numberStations[id]) {
      numberStations[id] = []
    }
    numberStations[id].push(n)
  })