Prototypes HavnekaffeP17 · Ordering for a café

The tables’ codes

Each code opens the menu for its table on a guest’s phone. The kitchen sees the table’s number on every order from it.

How Havnekaffe is built
  1. A code on each table opens the menu with the table’s number in the address. The menu comes from the server, with each item’s options and whether it is sold out.
  2. The phone sends the items, the options and a key it made for this order. The server looks the prices up in its own menu, so the total is the server’s. The same key sent again, after a double tap or a lost answer, returns the order that is already stored.
  3. The kitchen’s screen and the guest’s phone keep a WebSocket to the café’s server, a Durable Object that sleeps while nothing happens. The server sends them a new order when it is stored, and it sends a change of status or an item marked sold out the same way.
  4. A screen that loses its connection tries again after a pause that doubles up to 8 seconds. When it is back, it reads every open order, so it shows the orders placed while it was away.
  5. Payment opens Stripe Checkout with the server’s prices. Only Stripe’s webhook marks the order paid. The server checks its HMAC-SHA256 signature with the endpoint’s secret and refuses a signature older than 5 minutes. The amount must match the order, and an event sent twice changes nothing.
  6. Anyone behind the portfolio’s login can open the kitchen’s screen. A café would sign the screen in with a passkey, as the club in P15 does.