@tmbill/push-client

FCM (Google MCS) push receiver for Node >= 18 and Electron >= 24, built for bad networks: one reconnect state machine (classified backoff with jitter, endpoint rotation :5228 -> :443, every step bounded), proxy support (env and system/PAC, HTTP CONNECT), its own happy eyeballs for IPv6, TLS-inspection detection, bounded check-in and registration. No Electron dependency: the host passes resolveProxy.

const { PushClient, createNetwork } = require('@tmbill/push-client');

const client = new PushClient({
  firebase: { apiKey, projectId, messagingSenderId, appId }, // the Firebase WEB config
  credentials, // from a previous 'credentials' event; omit to register a new identity
  persistentIds, // ids already handled (acknowledged at the next login)
  network: createNetwork({ resolveProxy }),
});
client.on('credentials', ({ newCredentials }) => persist(newCredentials));
client.on('notification', ({ message, persistentId }) => {
  // throw to keep it unacknowledged (redelivered); throw an error with `holdAck: true` if YOUR storage failed
});
client.on('credentials-rejected', (e) => {}); // Google refuses the identity: re-register (repeats while it lasts)
client.start();
client.setOnline(false); // host network hints; reconnectNow() after resume
client.status(); // state, counters, route, last errors (no secrets)

Most hosts should use @tmbill/push-service, which adds the durable outbox, dedupe, health monitoring and lossless credential rotation on top.

Contains code derived from MIT-licensed work; see lib/vendor/LICENSE and lib/vendor/NOTICE.md.