blockchain/blockchain.py at main · krvaibhaw/blockchain · GitHub

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# Importing modules

import datetime      # To keep track of time, as each block has its own timestamp (exact date and time at which the block is created)
import json         # For encoding the blocks before hashing them
import hashlib      # For finding hashes for the blocks
from flask import Flask, jsonify      # For creating a web application interface

# Building the blockchain architecture

class Blockchain:

    def __init__(self):

        # List of chains (to cryptographically link the blocks)
        self.chain = []

        # Creating the Genesis Block
        self.createblock(proof = 1, prevhash = "0")

    def createblock(self, proof, prevhash):

        # Defining the structure of our block
        block = {'index': len(self.chain) + 1,
                 'timestamp': str(datetime.datetime.now()),
                 'proof': proof,
                 'prevhash': prevhash}

        # Establishing a cryptographic link
        self.chain.append(block)
        return block

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

    def proofofwork(self, prevproof):
        newproof = 1
        checkproof = False

        # Defining crypto puzzle for the miners and iterating until able to mine it
        while checkproof is False:
            op = hashlib.sha256(str(newproof**2 - prevproof**5).encode()).hexdigest()

            if op[:5] == "00000":
                checkproof = True
            else:
                newproof += 1

        return newproof

    def hash(self, block):
        encodedblock = json.dumps(block, sort_keys = True).encode()
        return hashlib.sha256(encodedblock).hexdigest()

    def ischainvalid(self, chain):
        prevblock = chain[0]   # Initilized to Genesis block
        blockindex = 1         # Initilized to Next block

        while blockindex < len(chain):

            # First Check : For each block check if the previous hash field is equal to the hash of the previous block
            #               i.e. to verify the cryptographic link

            currentblock = chain[blockindex]
            if currentblock['prevhash'] != self.hash(prevblock):
                return False

            # Second Check : To check if the proof of work for each block is valid according to problem defined in proofofwork() function
            #                i.e. to check if the correct block is mined or not

            prevproof = prevblock['proof']
            currentproof = currentblock['proof']
            op = hashlib.sha256(str(currentproof**2 - prevproof**5).encode()).hexdigest()

            if op[:5] != "00000":
                return True

            prevblock = currentblock
            blockindex += 1

        return True


# Building a Flask based Web App for interacting with the blockchain
app = Flask(__name__)


# Creating a blockchain based on architecture defined
blockchain = Blockchain()


# Welcome page
@app.route('/', methods=['GET'])

def welcome():
    wl = '''
        <html>
        <head><title>Spyder</title></head>
        <body>
        <h1>Spyder Blockchain</h1>
        Welcome to our Blockchain Page
        <br>Lets Go !!!
        <br>
            <ul>
            <li>For Mining Blocks Visit : <a href="http://127.0.0.1:5000/mineblock">http://127.0.0.1:5000/mineblock</a></li>
            <li>For Viewing the Blockchain Visit : <a href="http://127.0.0.1:5000/getchain">http://127.0.0.1:5000/getchain</a></li>
            <li>For Validating Blockchain Visit : <a href="http://127.0.0.1:5000/validate">http://127.0.0.1:5000/validate</a></li>
            </ul>
        </body>
        </html>
        '''
    return wl


# Mining the blockchain
@app.route('/mineblock', methods=['GET'])

def mineblock():

    # Mining a new block
    prevblock = blockchain.getprevblock()
    prevproof = prevblock['proof']
    proof = blockchain.proofofwork(prevproof)
    prevhash = blockchain.hash(prevblock)
    block = blockchain.createblock(proof, prevhash)

    # Sending the response to Postman API to display it
    response = {'message': "Congratulations, You just mined a block !",
                'index': block['index'],
                'timestamp': block['timestamp'],
                'proof': block['proof'],
                'prevhash': block['prevhash']}

    return jsonify(response), 200


# Gwtting the full blockchain displayed in Postman
@app.route('/getchain', methods=['GET'])

def getchain():
    response = {'chain': blockchain.chain,
                'len': len(blockchain.chain)}
    return jsonify(response), 200


# Validating the Blockchain
@app.route('/validate', methods=['GET'])

def validate():
    if blockchain.ischainvalid(blockchain.chain):
        response = {'message': "The Blockchain is Valid"}
    else:
        response = {'message': "The Blockchain is Invalid"}

    return jsonify(response), 200


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