receipts.cafe

Anonymous messages, physically printed as thermal receipts.

Live site · Security policy · Contributing

receipts.cafe is a small public art project. A visitor submits a short anonymous message online; an always-on local print worker renders it as a receipt and prints it on an Epson TM-T88V thermal printer.

At A Glance

Public interface	Text-only anonymous message submission
Delivery path	Vercel → Upstash Redis → local print worker → CUPS
Runtime printer	Epson TM-T88V thermal printer
Website	receipts.cafe
Archive	Private while the visual archive is being prepared

The public Vercel deployment never connects directly to the home network or printer. The always-on Mac runs the isolated print worker. A development Mac is used for source changes and deployments, but is not required for normal printing.

How It Works

visitor
  → Vercel web app and API
  → Upstash Redis queue
  → always-on Mac poller
  → CUPS
  → Epson TM-T88V thermal printer

1. A visitor submits a short message through the website.
2. The Vercel API validates it and places it in the Redis queue.
3. The private poller claims the message and renders the shared receipt template locally.
4. CUPS prints the receipt. The job is acknowledged only after printing succeeds.
5. If the printer is unavailable, the message stays queued. Stale in-flight claims recover automatically.

Public Safeguards

• 300 characters per message
• 3 messages per IP per hour
• 10 messages per IP per day
• 100 messages globally per day
• Duplicate suppression, link rejection, a honeypot field, and same-origin JSON submission handling
• A private bearer token protects poller routes

These limits are operational safeguards, not a promise that every message prints immediately. Do not submit passwords, private information, or anything that must remain confidential.

Repository Boundaries

This repository contains the public site, Vercel API routes, and a portable copy of the poller source. It intentionally does not include:

• production secrets, Redis credentials, or poller tokens
• visitor messages, receipt scans, or archive images
• local printer output or machine-specific configuration
• home-network details, hostnames, IP addresses, or launch-agent files

The live poller is installed separately on the always-on Mac. Changes to scripts/receipt-drop-poller.py require a deliberate, separately verified worker deployment. GitHub and Vercel deployments do not update the printer worker automatically.

Local Development

The normal local preview uses a credential-free stub. It never writes to Redis or prints.

npm install
npm run check
npm run dev

For real deployment testing, use a private .env.local file that is ignored by Git. Never commit environment files, Vercel metadata, private messages, archives, or local machine configuration.

Deployment

The main branch deploys to Vercel and serves receipts.cafe. Review changes locally, run npm run check, then push them to GitHub.

The Vercel project owns production environment variables. vercel.json provides baseline browser protections including a restrictive content security policy, anti-framing protection, no-sniff, referrer, permissions, and HTTPS transport headers.

Contributing

Small fixes and documentation improvements are welcome. Please read CONTRIBUTING.md and SECURITY.md before opening a pull request or reporting a problem.

License

Copyright (c) 2026 David Sutrin. All rights reserved. See LICENSE.