Push

Notifications on people's devices: browsers by Web Push, iPhones and Macs by Apple's APNs, Android phones by Firebase Cloud Messaging (FCM). Chime keeps each person's devices, sends to each one that is on, and forgets those a service says are gone.

The keys

Each service needs keys of your app's. Keep them as secrets, read in config/runtime.exs.

# config/runtime.exs
config :my_app, :chime_push,
  web: [
    public_key: System.fetch_env!("VAPID_PUBLIC_KEY"),
    private_key: System.fetch_env!("VAPID_PRIVATE_KEY"),
    subject: "mailto:ops@myapp.com"
  ],
  apns: [
    key: System.fetch_env!("APNS_KEY"),
    key_id: System.fetch_env!("APNS_KEY_ID"),
    team_id: System.fetch_env!("APNS_TEAM_ID"),
    topic: "com.myapp.ios",
    env: :production
  ],
  fcm: [service_account: System.fetch_env!("FIREBASE_SERVICE_ACCOUNT")]

{Chime, ..., push: Application.fetch_env!(:my_app, :chime_push)}

Give only the services you use. With :push, the :push channel is there, and in the preferences. Chime sends with Req: add {:req, "~> 0.5"} to your deps.

A notifier

deliver :push, unless: :seen

def push(data, _recipient, notification) do
  %{
    title: "#{Chime.actors(notification)} commented",
    body: data["text"],
    url: "/stories/#{data["story_id"]}",
    icon: "/images/icon-192.png",
    badge: "/images/badge-72.png",
    image: data["cover_url"]
  }
end

Without push/3, a push says what the feed says. Chime adds the link that reads the notification in the feed when the push is opened (Chime.link/2), and the notification's group as its tag: a newer push of the group replaces the one on the device (the tag of Web Push and Android, with renotify, and APNs' collapse id and thread). The delivery rules work as for email: throttle:, quiet hours, limits.

Browsers

Serve Chime's service worker from your root, and register it:

# endpoint.ex: /chime-sw.js from deps/chime/priv/static
plug Plug.Static, at: "/", from: {:chime, "priv/static"}, only: ~w(chime-sw.js)

Then, in your page, ask for permission and send the subscription to the JSON API (chime_api):

const api = "/api/v1/notifications";

export async function enablePush() {
  const { vapidPublicKey } = await (await fetch(`${api}/push`)).json();
  const registration = await navigator.serviceWorker.register("/chime-sw.js");
  if ((await Notification.requestPermission()) !== "granted") return;

  const subscription = await registration.pushManager.subscribe({
    userVisibleOnly: true,
    applicationServerKey: vapidPublicKey,
  });

  const { endpoint, keys } = subscription.toJSON();
  await fetch(`${api}/devices`, {
    method: "POST",
    headers: { "content-type": "application/json", "x-csrf-token": csrfToken },
    body: JSON.stringify({ kind: "web", token: endpoint, keys, name: navigator.userAgent }),
  });
}

chime-sw.js shows each push and opens its link on a click. An app with a service worker of its own copies its two listeners.

Phones

Your iOS or Android app gets a token from Apple or Firebase, and sends it to the API, signed in as the person:

POST /api/v1/notifications/devices
Content-Type: application/json

{"kind": "apns", "token": "<the device token, hex>", "name": "Ana's iPhone"}

"fcm" for Firebase's tokens (Android, or iOS through Firebase). A token registered again, by another person, is that person's device now.

Devices

GET /devices, PATCH /devices/:id with {"enabled": false} (the device kept, its pushes off) or {"name": ...}, DELETE /devices/:id; and Chime.devices/1, Chime.register_device/2, Chime.update_device/3, Chime.remove_device/2 on the server.

A push goes to every device of the person that is on. A device the service says is gone (an unsubscribed browser, 404 or 410; an app removed from a phone, APNs' 410 or BadDeviceToken; FCM's UNREGISTERED) is forgotten. The log says how many devices it reached and which were gone:

2026-10-25 14:02:11Z  push       sent        1 of 2 devices; 1 gone, forgotten: the app is no longer on the device (410)

A push that reaches no device because each failed is tried again, as any delivery.