cardoCoin.py

# Module 2 - Create cryptocurrency

import datetime
import hashlib
import json
from flask import Flask, jsonify, request
import requests
from uuid import uuid4
from urllib.parse import urlparse


# 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):
        """creates a block for the blockchain"""

        block = {'index': len(self.chain) + 1,
                 'timestamp': str(datetime.datetime.now()),  # needs to be string for json
                 'proof': proof,
                 'previous_hash': previous_hash,
                 'transactions': self.transactions}

        # since transactions have been added to block they should be cleared to not be added again
        self.transactions = []

        # add block to blockchain
        self.chain.append(block)

        return block

    def get_previous_block(self):
        """returns the previous block in the chain"""
        return self.chain[-1]

    def proof_of_work(self, previous_proof):
        """performs proof of work function to mine block"""

        # increments new_proof for each time a proof is tested
        new_proof = 1

        # True if proof is found
        check_proof = False

        while check_proof is False:
            hash_operation = hashlib.sha256(
                str(new_proof ** 2 - previous_proof ** 2).encode()).hexdigest()  # creates the problem to solve
            if hash_operation[:5] == '00000':  # the more leading 0's the harder to find
                check_proof = True
            else:
                new_proof += 1

        return new_proof

    def hash(self, block):
        """hashes 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[:5] != '00000':
                return False

            previous_block = block
            block_index += 1

        return True

    def add_transaction(self, sender, receiver, amount):
        """formats and adds a transaction to transactions list"""
        self.transactions.append({'sender': sender,
                                  'receiver': receiver,
                                  'amount': amount})

        # used to get the previous block's index to appropriately assign the index to the current block
        previous_block = self.get_previous_block()

        return previous_block['index'] + 1

    def add_node(self, address):
        """adds node to set of all nodes"""
        parsed_url = urlparse(address)
        self.nodes.add(parsed_url.netloc)

    def replace_chain(self):
        """replaces chains on nodes with longest chain"""
        # all nodes on the network across the world
        network = self.nodes
        longest_chain = None
        max_length = len(self.chain)

        # gets length of each chain in the network
        for node in network:
            response = requests.get(f'http://{node}/get_chain')

            if response.status_code == 200:  # check to make sure status code is successful
                length = response.json()['length']
                chain = response.json()['chain']

                # if current node's chain is the longest and is valid, update max length and longest chain
                if length > max_length and self.is_chain_valid(chain):
                    max_length = length
                    longest_chain = chain

        # if True, chain was replaced while comparing the network
        if longest_chain:
            self.chain = longest_chain
            return True

        return False


# 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 blockchain
@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)
    previous_hash = blockchain.hash(previous_block)
    blockchain.add_transaction(sender=node_address, receiver='cardo', amount=1)
    block = blockchain.create_block(proof, previous_hash)

    response = {'message': 'Congrats, 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  # 200 = status code for success


# 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  # 200 = status code for success


# checking if the Blockchain is valid
@app.route('/is_valid', methods=['GET'])
def is_valid():
    is_valid = blockchain.is_chain_valid(blockchain.chain)

    if is_valid:
        response = {'message': 'All good, VALID.'}
    else:
        response = {'message': 'Not good, INVALID.'}

    return jsonify(response), 200


# adding a new transaction to the Blockchain
@app.route('/add_transaction', methods=['POST'])
def add_transaction():
    json = request.get_json()
    transaction_keys = ['sender', 'receiver', 'amount']

    # makes sure all the keys in the json file are what they should be
    if not all (key in json for key in transaction_keys):
        return 'Some elements of the transactions are missing', 400

    # add transaction and grab transaction index
    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


# 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 nodes are now connected. The Cardocoin 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 node had different chains so the chain was replaced by the longest one.',
                    'new_chain': blockchain.chain}
    else:
        response = {'message': 'All good, the chain is the longest chain.',
                    'actual_chain': blockchain.chain}

    return jsonify(response), 200


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