This document describes how Firefox implements the Web Push standard internally, and is intended for developers working directly on Push. If you are looking for how to consume push, please refer to the following MDN document

High level push architecture

The following sequence diagram describes the high level push architecture as observed by web application. The diagram describes the interactions between a Web application’s client code running in the browser, Firefox, Autopush (Firefox’s push server that delivers push notifications) and a third party server that sends the push notifications to Autopush

The dotted lines are done by the consumer of push.

sequenceDiagram participant TP as Web Application JS participant F as Firefox participant A as Autopush participant TPS as Third party Server TP->>F: subscribe(scope) activate TP activate F F->>A: subscribe(scope) using web socket activate A A->>F: URL deactivate A F->>F: Create pub/privKey Encryption pair F->>F: Persist URL, pubKey, privKey indexed using an id derived from scope F->>TP: URL + pubKey deactivate F TP-->>TPS: URL + pubKey deactivate TP TPS-->>TPS: Encrypt payload using pubKey TPS-->>A: Send encrypted payload using URL activate A A->>F: Send encrypted payload using web socket deactivate A activate F F->>F: Decrypt payload using privKey F->>F: Display Notification deactivate F

Flow diagram for source code

The source code for push is available under dom/push in mozilla-central.

The following flow diagram describes how different modules interact with each other to provide the push API to consumers.

flowchart TD subgraph Public API W[Third party Web app]-->|imports| P[PushManager.webidl] end subgraph Browser Code P-->|Implemented by| MM MM{Main Thread?}-->|Yes| B[Push.sys.mjs] MM -->|NO| A[PushManager.cpp] B-->|subscribe,getSubscription| D[PushComponents.sys.mjs] A-->|subscribe,getSubscription| D D-->|subscribe,getSubscription| M[PushService.sys.mjs] M-->|Storage| S[PushDB.sys.mjs] M-->|Network| N[PushWebSocket.sys.mjs] F[FxAccountsPush.sys.mjs] -->|uses| D end subgraph Server N-. Send, Receive.-> O[Autopush] end subgraph Local Storage S-->|Read,Write| PP[(IndexedDB)] end

The Push Web Socket

Push in Firefox Desktop communicates with Autopush using a web socket connection.

The web socket connection is created as the browser initializes and is managed by the following state diagram.

stateDiagram-v2 state "Shut Down" as SD state "Waiting for WebSocket to start" as W1 state "Waiting for server hello" as W2 state "Ready" as R [*] --> SD SD --> W1: beginWSSetup W1 --> W2: wsOnStart Success W2 --> R: handleHelloReply R --> R: send (subscribe) R --> R: Receive + notify observers R --> SD: wsOnStop R --> SD: sendPing Fails W1 --> SD: wsOnStart fails W2 --> SD: invalid server hello R --> [*]

Once the Push web socket is on the Ready state, it is ready to send new subscriptions to Autopush, and receive push notifications from those subscriptions.

Push uses an observer pattern to notify observers of any incoming push notifications. See the high level architecture section.

Push Storage

Push uses IndexedDB to store subscriptions for the following reasons:

  1. In case the consumer attempts to re-subscribe, storage is used as a cache to serve the URL and the public key

  2. In order to persist the private key, so that it can be used to decrypt any incoming push notifications

The following is what gets persisted:

erDiagram Subscription { string channelID "Key, Derived from scope" string pushEndpoint "Unique endpoint for this subscription" string scope "Usually the origin, unique value for internal consumers" Object p256dhPublicKey "Object representing the public key" Object p256dhPrivateKey "Object representing the private key" }