A minimal private‑blockchain prototype written in Node.js. It demonstrates Proof‑of‑Work consensus, peer‑to‑peer networking via WebSockets, and a small wallet / transaction layer built on ECDSA keys.
Why? This repo is a learning exercise—small enough to read in an afternoon, yet complete enough to mine blocks, broadcast them to peers, and transfer coins between wallets.
| Area | What you’ll find | Where |
|---|---|---|
| Blockchain | Blockchain class keeps an in‑memory chain starting with a genesis() block |
blockchain/index.js (github.com) |
| Proof‑of‑Work | Each call to mineBlock() crunches a SHA‑256 hash until it matches the current difficulty (default 3) |
blockchain/block.js (github.com) |
| Difficulty retargeting | adjustDifficulty() raises/lowers difficulty so blocks arrive ~ every MINE_RATE ms (3000) |
config.js (github.com) |
| P2P mesh | Nodes gossip chains over WebSockets (/p2p-server.js) and auto‑sync on new blocks |
app/p2p-server.js (github.com) |
| HTTP API | GET /blocks, POST /mine routes for quick testing |
app/index.js (github.com) |
| Wallet & Tx | ECDSA key‑pairs (elliptic), UTXO‑style outputs, basic signTransaction() helper |
wallet/{index,transaction}.js (github.com, github.com) |
| Testing | Jest test runner & watch mode (npm test) |
package.json (github.com) |
blockchain/ # Block & chain logic
wallet/ # Keys + transactions
app/ # Express + WebSocket servers
config.js # Tunable constants (difficulty, mining rate, etc.)
chain-util.js # Crypto helpers (hashing, key‑gen, UUID)
- Node.js ≥ 20
- npm (comes with Node) or yarn
git clone https://github.com/sagarkpatil3/Block-Chain-App.git
cd Block-Chain-App
npm install
npm run dev # starts API on :3001 and P2P on :5001# Terminal 1
npm run dev # HTTP 3001, P2P 5001
# Terminal 2
HTTP_PORT=3002 \
P2P_PORT=5002 \
PEERS="ws://localhost:5001" \
npm run devEach peer connects to addresses listed in PEERS (comma‑separated).
curl -X POST http://localhost:3001/mine \
-H 'Content-Type: application/json' \
-d '{"data":"Hello blockchain"}'The new block is mined locally, broadcast to peers, and you can verify with:
curl http://localhost:3002/blocks # peer’s view of the chain| Env Var | Purpose | Default |
|---|---|---|
HTTP_PORT |
REST API port | 3001 |
P2P_PORT |
WebSocket port | 5001 |
PEERS |
Comma‑separated list of peer WebSocket URLs | (empty) |
DIFFICULTY |
PoW leading‑zero difficulty (override config.js) |
3 |
MINE_RATE |
Target block time in ms | 3000 |
INITIAL_BALANCE |
Wallet starting balance | 500 |
npm test # jest --watchAll- Transaction pool & consensus on included TXs
- Networking handshake + message types (block, tx, peer discovery)
- Replace PoW with Proof‑of‑Stake (experiment)
- Docker compose file for multi‑node local cluster
- Front‑end dashboard to visualise the chain & mempool
Contributions or experiment branches are welcome—open a PR! 🙌
This project is licensed under the ISC License—see the LICENSE file for details.