VaultPrint

Zero-storage, peer-to-peer confidential printing for public shops.

A customer sends a PDF or image from their phone; the print shop opens a link on their PC, enters a short session code, previews the document in the browser, and prints. Your file never touches our servers.

Note: Working Demo at the End✌️.

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Use case

Who	Device	Route
Customer (sender)	Phone	/
Print shop (receiver)	Desktop	/receive

Typical flow: Xerox / photocopy shop, library printer, campus print kiosk — anywhere you need to print a sensitive document without emailing it, using a USB stick, or uploading to a third-party cloud.

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How it works (in one picture)

 Phone (sender)                    Signaling server              Shop PC (receiver)
      │                           (no file bytes)                      │
      │  ① create room → PIN        │                                  │
      │ ─────────────────────────►  │                                  │
      │                             │  ② join with PIN                 │
      │                             │ ◄──────────────────────────────  │
      │  ③ WebRTC offer/answer/ICE relayed only                        │
      │ ◄──────────────────────────────────────────────────────────►  │
      │  ④ encrypted P2P data channel — PDF/image chunks               │
      │ ═══════════════════════════════════════════════════════════►  │
      │                             │                          preview & print

Signaling helps two browsers find each other and negotiate encryption. Transfer happens directly between devices over WebRTC. The server only sees socket IDs, session codes, and SDP/ICE metadata — never document content.

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Core principles

1. Zero storage — No database, no S3, no disk writes for documents. Rooms live in memory and die when a peer disconnects.
2. Peer-to-peer transfer — File bytes travel over an encrypted RTCDataChannel, not through the signaling server.
3. Ephemeral sessions — A numeric code binds one sender to one receiver for a short window (~60s, extendable). Closing the shop tab destroys the room; the code cannot be reused.
4. Client-side only preview — PDF/DOCX/image rendering happens in the browser from an in-memory ArrayBuffer. Nothing is saved to disk by the app.
5. Defense in depth — Rate limits on signaling, strict production CORS, configurable STUN/TURN for real-world NAT.

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Why you can trust it

Claim	Why it's true
Server never sees your PDF	Data channels are browser-to-browser. Signaling relays only JSON SDP/ICE messages.
No persistent storage	rooms.ts is a Map in RAM. No upload API exists.
Session ends cleanly	Receiver disconnect deletes the room. After print, the receiver wipes preview buffers and closes the peer connection.
You can verify	Open DevTools → Network: no document POST. Inspect server/src/index.ts: no body parser for files.

Caveats (honest limits): The shop PC holds the document in RAM while the tab is open. A compromised browser or malicious shop operator could still capture the screen. VaultPrint removes the cloud middleman, not the need to trust the person at the counter. Use TURN in production so connections work behind strict NAT; TURN relays encrypted WebRTC traffic but still does not decrypt document bytes for VaultPrint's app layer.

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Folder structure

XeroxConfidentiality/
├── README.md                 # This file
├── study.readme              # Deep technical walkthrough (concepts, functions, flows)
├── .github/workflows/ci.yml  # Lint, build, typecheck on push
│
├── server/                   # Signaling service (Node + Express + Socket.io)
│   ├── src/
│   │   ├── index.ts          # Socket events, WebRTC signal relay, health check
│   │   ├── rooms.ts          # In-memory PIN rooms (sender + receiver socket IDs)
│   │   ├── sessionCode.ts    # 6/8-digit code generation & validation
│   │   └── rateLimit.ts      # Per-IP limits on join / create-room
│   ├── .env.example
│   └── package.json
│
└── web/                      # Next.js 14 app (sender + receiver UI)
    ├── app/
    │   ├── page.tsx          # Sender (mobile)
    │   ├── receive/page.tsx  # Receiver (desktop)
    │   ├── layout.tsx
    │   └── globals.css       # Print CSS (only document region on paper)
    ├── components/
    │   ├── SenderClient.tsx      # WebRTC sender, file queue, timer
    │   ├── ReceiverClient.tsx    # WebRTC receiver, batch ingest, print
    │   ├── DocumentPreview.tsx   # Per-file preview (all PDF pages)
    │   ├── FileDropzone.tsx      # Multi-file picker / drop
    │   ├── ImageCropToA4Modal.tsx
    │   └── OtpInput.tsx          # Session code entry
    ├── lib/
    │   ├── protocol.ts       # Data-channel message types & chunk size
    │   ├── ice.ts            # STUN/TURN RTCConfiguration
    │   ├── iceStatus.ts      # Detect direct vs TURN path
    │   ├── renderDocument.ts # PDF / image / DOCX preview rendering
    │   ├── mime.ts           # Magic-byte & extension MIME sniffing
    │   ├── config.ts         # Signaling URL, app origin
    │   └── sessionCode.ts    # Client code length (must match server)
    ├── public/pdf.worker.min.mjs
    └── .env.local.example

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Quick start (local)

Terminal 1 — signaling

cd server
cp .env.example .env
npm install
npm run dev
# → http://localhost:4000

Terminal 2 — web

cd web
cp .env.local.example .env.local
npm install
npm run dev
# → http://localhost:3000

1. Open http://localhost:3000 on your phone (or a second browser tab).
2. Open http://localhost:3000/receive on your desktop.
3. Drop a PDF (or multiple files), share the code, connect, preview, print.

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Environment variables

Service	Variable	Purpose
Server	PORT	HTTP + Socket.io port (default 4000)
Server	SESSION_CODE_LENGTH	6 or 8
Server	CORS_ORIGINS	Allowed web origins (required in production)
Web	NEXT_PUBLIC_SIGNALING_URL	Signaling server URL
Web	NEXT_PUBLIC_SESSION_CODE_LENGTH	Must match server
Web	NEXT_PUBLIC_TURN_*	TURN credentials for production NAT traversal

See server/.env.example and web/.env.local.example for full lists.

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Deployment (two services)

Service	Suggested host	Root directory
Signaling	Render, Fly.io, Railway	server
Web	Vercel	web

Set CORS_ORIGINS on the server to your Vercel URL. Set NEXT_PUBLIC_SIGNALING_URL on Vercel to your signaling HTTPS URL.

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Supported formats

• PDF — multi-page preview and print
• Images (PNG, JPEG, WebP, GIF) — crop/rotate to A4 PDF on sender, then send
• DOCX — in-browser preview via docx-preview
• Batch — multiple files per session, sent sequentially over one data channel

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vault-print.mp4