Creating sample Blockchain using Python, Flask and Postman

# Creating a Blockchain using Python by Dr B P Sharma

# To be installed:
# pip install Flask
# Postman HTTP Client from https://www.getpostman.com

# Importing the required libraries
import datetime
import hashlib
import json
from flask import Flask, jsonify

# Building a sample Blockchain

class Blockchain:

    def __init__(self):
        self.chain = []
        self.createBlock(proof = 1, previousHash = '0')

    def createBlock(self, proof, previousHash):
        block = {'index': len(self.chain) + 1,
                 'timestamp': str(datetime.datetime.now()),
                 'proof': proof,  #nonce
                 'previousHash': previousHash}
        self.chain.append(block)
        return block

    def getPreviousBlock(self):
        return self.chain[-1]

    def proofOfWork(self, previousProof):
        new_proof = 1
        check_proof = False
        while check_proof is False:
            hash_operation = hashlib.sha256(str(new_proof**2 - previousProof**2).encode()).hexdigest()
            if hash_operation[:4] == '0000':
                check_proof = True
            else:
                new_proof += 1
        return new_proof
 
    def hash(self, block):
        encoded_block = json.dumps(block, sort_keys = True).encode()
        return hashlib.sha256(encoded_block).hexdigest()
 
    def isChainValid(self, chain):
        previousBlock = chain[0]
        blockIndex = 1
        while blockIndex < len(chain):
            block = chain[blockIndex]
            if block['previousHash'] != self.hash(previousBlock):
                return False
            previousProof = previousBlock['proof']
            proof = block['proof']
            hash_operation = hashlib.sha256(str(proof**2 - previousProof**2).encode()).hexdigest()
            if hash_operation[:4] != '0000':
                return False
            previousBlock = block
            blockIndex += 1
        return True

# Mining the Blockchain

# Creating a Web Application using Flask
app = Flask(__name__)

# Creating a Blockchain instance
blockchain = Blockchain()

# Mining a new block
@app.route('/mineBlock', methods = ['GET'])
def mineBlock():
    previousBlock = blockchain.getPreviousBlock()
    previousProof = previousBlock['proof']
    proof = blockchain.proofOfWork(previousProof)
    previousHash = blockchain.hash(previousBlock)
    block = blockchain.createBlock(proof, previousHash)
    response = {'message': 'Congratulations, you just mined a block!',
                'index': block['index'],
                'timestamp': block['timestamp'],
                'proof': block['proof'],
                'previousHash': block['previousHash']}
    return jsonify(response), 200

# Getting the full Blockchain
@app.route('/getChain', methods = ['GET'])
def getChain():
    response = {'chain': blockchain.chain,
                'length': len(blockchain.chain)}
    return jsonify(response), 200

# Checking if the Blockchain is valid
@app.route('/isValid', methods = ['GET'])
def isValid():
    isValid = blockchain.isChainValid(blockchain.chain)
    if isValid:
        response = {'message': 'All good. The Blockchain is valid.'}
    else:
        response = {'message': 'Houston, we have a problem. The Blockchain is not valid.'}
    return jsonify(response), 200

# Running the app
app.run(host = '0.0.0.0', port = 5000)

#run the application in web browser or postman using URLs

# http://localhost:5000/getChain

# http://localhost:5000/mineBlock

# http://localhsot:5000/isValid

# Keep Learning