Blockchain Example

Simple implementation of a blockchain with a small Flask REST API.

This project contains two runnable nodes:

• blockchain.py (default node, runs on port 5000)
• blockchain_node2.py (second node, runs on port 5001)

Features

• Simple proof-of-work blockchain
• Endpoints to mine blocks, create transactions, view the chain
• Node registration and a simple consensus algorithm (replace chain with longest valid chain)

Requirements

• Python 3.8+ (or a recent Python 3.x)
• pip
• The Python packages: Flask, requests

Quick setup (Windows PowerShell)

1. Create and activate a virtual environment (recommended):

python -m venv .venv
.\.venv\Scripts\Activate.ps1

2. Install dependencies:

python -m pip install --upgrade pip
python -m pip install flask requests

3. (Optional) Save dependencies:

python -m pip freeze > requirements.txt

Run the nodes

Open two PowerShell windows (or use separate terminals):

Terminal 1 (node 1):

# from project root
python blockchain.py

Terminal 2 (node 2):

# from project root
python blockchain_node2.py

Node 1 will listen on port 5000, node 2 on port 5001.

Example usage (API)

Mine a block (GET):

Invoke-RestMethod -Uri http://localhost:5000/mine -Method GET
# or using curl
curl http://localhost:5000/mine

Create a transaction (POST):

Invoke-RestMethod -Uri http://localhost:5000/transactions/new -Method POST -Body (@{sender='A'; recipient='B'; amount=5} | ConvertTo-Json) -ContentType 'application/json'

Get the full chain:

curl http://localhost:5000/get_chain

Register nodes (to add peers):

Invoke-RestMethod -Uri http://localhost:5000/nodes/register -Method POST -Body (@{nodes=@('http://127.0.0.1:5001')} | ConvertTo-Json) -ContentType 'application/json'

Resolve consensus (ask nodes to reconcile to the longest valid chain):

curl http://localhost:5000/nodes/resolve