Features

The hard part of realtime, already running

A realtime feature is a little product code on a lot of delivery machinery: who is subscribed, who is allowed, who is still there. PushCaster is that second part.

Channels

Four kinds, and the prefix is the contract

A channel's name decides how it behaves. The prefix tells the library whether to ask your server for authorisation, whether to expect a member list, and whether to encrypt.

Channel types, who may subscribe, what they are for, and how a subscription is authorised
Prefix	Who can subscribe	What it is for	Auth
public	Anyone with the app key.	Build status, live scores, public feeds.	None
private-	Your server decides, per subscriber.	Anything scoped to an account or resource.	Signed
presence-	Authorised, and carries the member list.	Rooms and sessions, where membership is the feature.	Signed
private-encrypted-	Authorised; payloads encrypted by your clients.	Payloads that should stay opaque to us too.	Signed

cache- channels deliver live events but do not replay stored state — see known differences.

Authorisation

Your server stays the authority

We do not grant private and presence subscriptions. Your application does, and signs its answer with your app secret. We verify the signature and nothing else.

One endpointPOST /pusher/auth keeps its request and response shape.
Your rulesWhether this socket may join this channel is a question only you can answer.
Presence identityThe same call returns the member id and whatever other members should see.

routes/pusher-auth.js

import Pusher from 'pusher'const pusher = new Pusher({  appId: process.env.PUSHCASTER_APP_ID,  key: process.env.PUSHCASTER_KEY,  secret: process.env.PUSHCASTER_SECRET,  host: 'api-eu1.pushcaster.io',  useTLS: true,})// Called by the client library whenever it subscribes to a// private-, presence- or private-encrypted- channel.app.post('/pusher/auth', (req, res) => {  const { socket_id, channel_name } = req.body  const user = req.session.user  if (!user || !mayJoin(user, channel_name)) {    return res.sendStatus(403)  }  res.send(    pusher.authorizeChannel(socket_id, channel_name, {      user_id: String(user.id),      user_info: { name: user.name },    }),  )})

Webhooks

What the socket layer sees, your backend hears

Occupancy and membership are only visible at the connection. Webhooks post them back, signed — so you can start work when the first viewer arrives and stop when the last leaves.

Webhook event types and when each fires
Event	Fires when
channel_occupied	First subscriber joined an empty channel.
channel_vacated	The last subscriber left.
member_added	Someone joined a presence channel.
member_removed	Someone left a presence channel.
client_event	A client sent an event directly to a channel.
cache_miss	A cache channel was asked for state it did not hold.

routes/webhooks.js

app.post('/pushcaster/webhooks', (req, res) => {  const hook = pusher.webhook({ headers: req.headers, rawBody: req.rawBody })  // The signature is computed with your app secret, so an  // unsigned or mismatched delivery never reaches your logic.  if (!hook.isValid()) return res.sendStatus(401)  for (const event of hook.getEvents()) {    if (event.name === 'channel_occupied') startFeed(event.channel)    if (event.name === 'channel_vacated') stopFeed(event.channel)  }  res.sendStatus(200)})

Libraries

There is no PushCaster SDK, on purpose

PushCaster speaks the Pusher Channels protocol on the wire, so the official libraries work against it unmodified. No package of ours to add, and nothing that breaks when we ship.

pusher-js
Laravel Echo
pusher/pusher-php-server
pusher-http-node
Python
Go
Ruby
Java
Android
iOS
Flutter
Unity

Install line, in full: npm i pusher-js.

Infrastructure

Two planes, and a cluster you choose

Delivery runs on a plane separate from billing and configuration, so a control-plane outage degrades the dashboard without interrupting delivery.

Running now

eu1Europe West
eu2Europe Central

Clusters are highly available for messaging and not for presence: if a presence store is lost, presence and occupancy degrade while public and private channels keep delivering. Better read here than discovered later.

See how a publish travels

Create an application and connect a client.

Start building Read the docs