How Chore Calendar syncs every phone in about a second

Chore Calendar runs in a small Docker container on the home Wi-Fi. Every phone in the house opens the same page, and when someone checks off a chore, every other phone shows it within about a second. Nobody signs in.

I expected that to need WebSockets. It didn't: browsers already have a built-in way to hold a connection open and receive updates, called Server-Sent Events.

One stream per phone

When a phone loads the page, it opens a request the server never finishes. The server sends the current state right away, keeps the response in a set of listeners, and writes to every listener whenever something changes.

// each phone keeps this stream open for live updates
function stream(req, res) {
  res.writeHead(200, { "Content-Type": "text/event-stream" });
  res.write(`event: state\ndata: ${JSON.stringify(publicState())}\n\n`);
  listeners.add(res);
  req.on("close", () => listeners.delete(res));
}

Why not WebSockets?

The phones only need to hear about changes; checking something off goes up as a normal request. Server-Sent Events are one-way, run over plain HTTP, and reconnect on their own when a phone wakes up.

What carried over to StarChores

The native app syncs through iCloud instead, but the idea stayed the same: one source of truth, and every device listens.