Blockchain Implementation

A blockchain built from scratch to show how one works under the hood: blocks, hashing, proof-of-work, a peer-to-peer network of nodes, and a longest-chain consensus algorithm.

The same ideas are implemented three times, in JavaScript and Python:

Folder	Language	What it covers
BLOCKCHAIN-A-Z	JavaScript	Minimal chain: mining, fetching and validating the chain
BLOCKCHAIN-USING-JAVASCRIPT	JavaScript	Multi-node network: transactions, broadcasting, node registration, consensus
BLOCKCHAIN-USING-PYTHON	Python	Python version of BLOCKCHAIN-A-Z (create_blockchain), plus a simple cryptocurrency (create_cryptocurrency)

How to run

BLOCKCHAIN-A-Z (JavaScript)

cd BLOCKCHAIN-A-Z
npm install
npm run node_1   # node_1 … node_5 start the five nodes

Base URL: http://localhost:3000/ (the port changes per node)

Endpoint	Purpose
/mine_block	Mine a new block
/get_chain	Return the full chain
/chain_is_valid	Validate the chain

BLOCKCHAIN-USING-JAVASCRIPT

cd BLOCKCHAIN-USING-JAVASCRIPT
npm install
npm run node_1   # node_1 … node_5 start the five nodes

Base URL: http://localhost:3000/

Endpoint	Purpose
/blockchain	Return the full chain
/transaction/broadcast	Create a transaction and broadcast it to the network
/mine	Mine a new block
/receive-new-block	Accept a block mined by another peer
/register-add-brodcast-node	Register a node and broadcast it to the network
/register-node	Register a single node
/register-nodes-bulk	Register several nodes at once
/consensus	Run the consensus algorithm (longest valid chain wins)

BLOCKCHAIN-USING-PYTHON

cd BLOCKCHAIN-USING-PYTHON
pip install -r requirements.txt
python create_blockchain/blockchain.py

Base URL: http://localhost:5000/. It uses the same routes as BLOCKCHAIN-A-Z.

Try create_cryptocurrency to build a simple cryptocurrency on top of the chain.