LocalHtmlDataTest/nostr

FolderSyncDB — Nostr + Folder Variant

Local-first browser key-value and document store with dual-sync: shared folder for local/offline use, plus Nostr relays for cross-device reach over the internet.

Why this variant?

The other variants sync browsers via a shared folder on disk. This only works when both browsers can access the same folder (same machine or network drive).

This variant adds Nostr relay sync as a second transport. Nostr relays are public WebSocket servers that relay messages between clients. Your browser connects directly to them — no server of your own, no accounts, no setup.

Laptop (file://)                       Phone (browser)
  ┌──────────┐                           ┌──────────┐
  │ IndexedDB │                           │ IndexedDB │
  └─────┬─────┘                           └─────┬─────┘
        │                                       │
   ┌────┴────┐                             ┌────┴────┐
   │  Sync   │                             │  Sync   │
   │ Engine  │                             │ Engine  │
   └──┬───┬──┘                             └──┬───┬──┘
      │   │                                   │   │
   Folder Nostr ──── wss://relay ──────── Nostr Folder

Use either or both:

• Folder only — local multi-browser sync, works offline
• Nostr only — cross-device sync, no folder needed
• Both — folder for local speed, Nostr for internet reach

How it works

NIP-78 application data (kind 30078)

Events are stored on relays as NIP-78 application-specific data (kind 30078). This is the Nostr standard for apps that use relays as a personal database. Unlike regular kind 1 notes, relays are designed to store and index kind 30078 events long-term.

Each sync event becomes one NIP-78 event:

• d tag = foldersync:{roomKey}:{filename} — makes each event addressable
• t tag = foldersync-{roomKey} — indexed by relays for room-wide queries
• content = AES-256-GCM encrypted JSON (see Encryption below)

Encryption

All data is end-to-end encrypted using AES-256-GCM via the browser's native Web Crypto API.

Room key string
      ↓
   PBKDF2 (100k iterations, SHA-256)
      ↓
   AES-256-GCM key
      ↓
   encrypt(JSON payload) → base64(iv + ciphertext)
      ↓
   stored on Nostr relay (relay sees only opaque bytes)

• The room key IS the shared secret — only peers who know it can decrypt
• Each message gets a random 96-bit IV (no IV reuse)
• PBKDF2 key derivation makes brute-force expensive
• Relay operators cannot read your data
• Zero extra dependencies — uses only crypto.subtle

Write flow

1. Update IndexedDB (fast, immediate)
2. Emit change event (UI updates instantly)
3. Write event file to folder (background, fire-and-forget)
4. Encrypt + publish to Nostr relay (background, fire-and-forget)

Sync / join flow

1. Query relay: { kinds: [30078], '#t': ['foldersync-{room}'] } → full history
2. Decrypt each event with the room key
3. Subscribe for real-time updates
4. Scan folder for new local events
5. Merge both, deduplicate by filename
6. Apply unseen events to IndexedDB
7. Bridge: folder events get published to Nostr, Nostr events get written to folder

Large data (images)

Events larger than 48KB are automatically chunked into multiple NIP-78 events:

• Each chunk gets its own d tag: foldersync:{room}:{filename}:chunk:{n}
• Chunks are individually encrypted
• Reassembled on the receiving side before decryption

Real-time push

When a Nostr subscription receives a new event, sync() is triggered immediately — no waiting for the polling interval.

Quick start

import { FolderSyncDB } from './nostr/src/index.ts';

const db = await FolderSyncDB.open({
  autoSyncIntervalMs: 5000,
});

// Local folder sync (optional)
await db.selectFolder();

// Cross-device sync via Nostr (encrypted)
await db.joinRoom('my-secret-room-key');

// Use normally
await db.kv.set('theme', 'dark');
const theme = await db.kv.get('theme');

// Listen for events
db.on('nostr:connected', ({ roomKey }) => console.log('joined:', roomKey));
db.on('change', (e) => console.log('changed:', e));

API additions

On top of the standard FolderSyncDB API, this variant adds:

Method	Description
joinRoom(roomKey)	Join an encrypted Nostr sync room. All clients with the same key sync together.
leaveRoom()	Disconnect from the current room.
isConnected()	Whether a room is currently joined and relay is connected.
currentRoom	The current room key, or null.

OpenOptions additions

Option	Type	Default	Description
relays	string[]	3 popular public relays	Nostr relay WebSocket URLs
roomKey	string	none	Auto-join this room on open

Events additions

Event	Payload	When
nostr:connected	{ roomKey }	Joined a Nostr room
nostr:disconnected	--	Left a Nostr room

Security model

• Room key = encryption key — treat it like a password
• AES-256-GCM — authenticated encryption, tamper-proof
• PBKDF2 key derivation — 100k iterations slows brute-force
• Per-message random IV — no ciphertext patterns
• Relay sees nothing — tags contain the room name (which you can obscure), content is encrypted
• Each client generates its own Nostr keypair (stored in IndexedDB) for signing

Works from file://

Nostr relays use WebSocket (wss://), which works from file:// origins in Chrome. Unlike WebRTC or fetch(), browsers don't block outgoing WebSocket connections from file:// pages.

Dependencies

• nostr-tools — lightweight Nostr protocol library (keypair generation, event signing, relay pool management). Pure JS, no WASM.

Local cache

Uses IndexedDB (same as the indexeddb/ variant). Zero-overhead, browser-managed persistence.