hadcoin_node_5002.py

# Module 1 - Create a Blockchain

# To be installed:
# Flask: pip install flask
# pip install requests
# Postman HTTP Client: https://www.getpostman.com
# Useful Links: https://tools.superdatascience.com/blockchain/hash
# Video: Blockchain & Cryptocurrency A-Z Complete Masterclass | Learn How To Build Your First Blockchain

# Importing the libraries

import datetime
import hashlib
import json
from urllib import response
from flask import Flask, jsonify, request
import requests

from uuid import uuid4
from urllib.parse import urlparse


# Part 1 - Building a Blockchain

class Blockchain:
    def __init__(self):
        self.chain = []
        self.transactions = []
        self.create_block(proof=1, previous_hash='0')
        self.nodes = set()

    def create_block(self, proof, previous_hash):
        block = {'index': len(self.chain)+1,
                 'timestamp': str(datetime.datetime.now()),
                 'proof': proof,
                 'previous_hash': previous_hash,
                 'transactions': self.transactions }
        self.transactions = []
        self.chain.append(block)
        return block
    
    def get_previous_block(self):
        return self.chain[-1]

    def proof_of_work(self,previous_proof):
        new_proof = 1
        check_proof = False
        while check_proof is False:
            hash_operation = hashlib.sha256(str(new_proof**2 - previous_proof**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 is_chain_valid(self, chain):
        previous_block = chain[0]
        block_index = 1
        while block_index < len(chain):
            block = chain[block_index]        
            if block['previous_hash'] !=  self.hash(previous_block):
                return False
            previous_proof = previous_block['proof']
            proof = block['proof']
            hash_operation = hashlib.sha256(str(proof**2 - previous_proof**2).encode()).hexdigest()
            if hash_operation[:4] != '0000':
                return False
            previous_block = block
            block_index += 1
        return True

    def add_transaction(self, sender, receiver, amount):
        self.transactions.append({'sender':sender,
                                   'receiver':receiver,
                                   'amount':amount})

        previous_block = self.get_previous_block()
        return previous_block['index'] +1

    def add_node(self,address):
        parsed_url = urlparse(address)
        self.nodes.add(parsed_url.netloc)

    def replace_chain(self):
        network = self.nodes
        longest_chain = None
        max_length = len(self.chain)
        for node in network:
            response = requests.get(f'http://{node}/get_chain')
            if response.status_code == 200:
                length = response.json()['length']
                chain = response.json()['chain']
                if length > max_length and self.is_chain_valid(chain):
                    max_length = length
                    longest_chain = chain
        
        if longest_chain:
            self.chain = longest_chain
            return True
        return False

    
            

# Part 2- Mining our Blockchain

# Creating a web app
app = Flask(__name__)

# Creating an address for the node on port 5000
node_address = str(uuid4()).replace('-','')

# Creating a Blockchain
blockchain = Blockchain()

# Mining a new block
@app.route('/mine_block', methods = ['GET'])
def mine_block():
    previous_block = blockchain.get_previous_block()
    previous_proof = previous_block['proof']
    proof = blockchain.proof_of_work(previous_proof)
    blockchain.add_transaction(sender = node_address, receiver= 'kirlill', amount =1)
    previous_hash = blockchain.hash(previous_block)
    block = blockchain.create_block(proof, previous_hash)
    response = {'message': 'Congrulations, you just mined a block!',
                'index':block['index'],
                'timestamp':block['timestamp'],
                'proof':block['proof'],
                'previous_hash':block['previous_hash'],
                'transactions':block['transactions']}
    return jsonify(response), 200


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


@app.route('/is_valid', methods=['GET'] )
def is_valid():
    is_valid =blockchain.is_chain_valid(blockchain.chain)
    if is_valid:
        response = {'message': 'All good. The Blockchain is valid'}
    else:
        response = {'message': 'Hey!, We have a problem. The Blockchain is not valid'}

    return jsonify(response), 200

@app.route('/add_transaction', methods = ['POST'])
def add_transaction():
    json = request.get_json()
    transaction_keys = {'sender', 'receiver', 'amount'}
    if not all (key in json for key in transaction_keys):
        return 'Some elements of the transaction are missing', 400
    index = blockchain.add_transaction(json['sender'], json['receiver'], json['amount'])
    response = {'message': f'This transaction will be added to Block {index}'}
    return jsonify(response), 201


# Part 3 - Decentralizing our Blockchain

# Connecting new nodes
@app.route('/connect_node', methods = ['POST'])
def connect_node():
    json = request.get_json()
    nodes = json.get('nodes')
    if nodes is None:
        return "No node", 400
    for node in nodes:
        blockchain.add_node(node)
    response = {'message':'All the new nodes are now connected. The Hardcoin Blockchain now contains the following nodes',
                'total_nodes':list(blockchain.nodes)}
    return jsonify(response), 201


# Replacing the chain by the longest chain if needed
@app.route('/replace_chain', methods =['GET'])
def replace_chain():
    is_chain_replaced = blockchain.replace_chain()
    if is_chain_replaced:
        response = {'message': 'The nodes had different chains so the chain was replaced by the longer chain',
                    'new_chain':blockchain.chain}
    else:
        response = {'message': 'All good. The chain is the largest one.',
                    'new_chain':blockchain.chain}
    return jsonify(response), 200


# Running the app
app.run(host = '0.0.0.0', port =5002)