blockchain.py

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

class Blockchain(object):
	"""docstring for Blockchain"""
	def __init__(self):
		self.chain = []
		self.current_transactions = []

		# Create the genesis block
		self.new_block(previous_hash=1, proof=100)

		self.nodes = set()
		
	def new_block(self, proof, previous_hash=None):
		"""
        Create a new Block in the Blockchain
        :param proof: <int> The proof given by the Proof of Work algorithm
        :param previous_hash: (Optional) <str> Hash of previous Block
        :return: <dict> New Block
        """

		# Creates a new Block and adds it to the chain

		block = {
            'index': len(self.chain) + 1,
            'timestamp': time(),
            'transactions': self.current_transactions,
            'proof': proof,
            'previous_hash': previous_hash or self.hash(self.chain[-1]),
		}

		# Reset the current list of transactions
		self.current_transactions = []
		self.chain.append(block)
		return block

	def new_transaction(self, sender, recipient, amount):
		# Adds a new transaction to the list of transactions
		# Creates a new transaction to go into the next mined Block
		"""
        Creates a new transaction to go into the next mined Block
        :param sender: <str> Address of the Sender
        :param recipient: <str> Address of the Recipient
        :param amount: <int> Amount
        :return: <int> The index of the Block that will hold this transaction
        """

		self.current_transactions.append({
		    'sender': sender,
		    'recipient': recipient,
		    'amount': amount,
		})
		return self.last_block['index'] + 1

	@staticmethod
	def hash(block):
		# Hashes a block
		"""
        Creates a SHA-256 hash of a Block
        :param block: <dict> Block
        :return: <str>
        """

        # We must make sure that the Dictionary is Ordered, or we'll have inconsistent hashes
		block_string = json.dumps(block, sort_keys=True).encode()
		return hashlib.sha256(block_string).hexdigest()
		
	@property
	def last_block(self):
		# Returns the last Block in the chain
		return self.chain[-1]

	def proof_of_work(self, last_proof):
		"""
		Simple Proof of Work Algorithm:
		 - Find a number p' such that hash(pp') contains leading 4 zeroes, where p is the previous p'
		 - p is the previous proof, and p' is the new proof
		:param last_proof: <int>
		:return: <int>
		"""

		proof = 0
		while self.valid_proof(last_proof, proof) is False:
		    proof += 1

		return proof

	@staticmethod
	def valid_proof(last_proof, proof):
	    """
	    Validates the Proof: Does hash(last_proof, proof) contain 4 leading zeroes?
	    :param last_proof: <int> Previous Proof
	    :param proof: <int> Current Proof
	    :return: <bool> True if correct, False if not.
	    """

	    guess = f'{last_proof}{proof}'.encode()
	    guess_hash = hashlib.sha256(guess).hexdigest()
	    return guess_hash[:4] == "0000"

	def register_node(self, address):
		"""
		Add a new node to the list of nodes
		:param address: <str> Address of node. Eg. 'http://192.168.0.5:5000'
		:return: None
		"""

		parsed_url = urlparse(address)
		self.nodes.add(parsed_url.netloc)

	def valid_chain(self, chain):
		"""
		Determine if a given blockchain is valid
		:param chain: <list> A blockchain
		:return: <bool> True if valid, False if not
		"""

		last_block = chain[0]
		current_index = 1

		while current_index < len(chain):
		    block = chain[current_index]
		    print(f'{last_block}')
		    print(f'{block}')
		    print("\n-----------\n")
		    # Check that the hash of the block is correct
		    if block['previous_hash'] != self.hash(last_block):
		        return False

		    # Check that the Proof of Work is correct
		    if not self.valid_proof(last_block['proof'], block['proof']):
		        return False

		    last_block = block
		    current_index += 1

		return True

	def resolve_conflicts(self):
		"""
		This is our Consensus Algorithm, it resolves conflicts
		by replacing our chain with the longest one in the network.
		:return: <bool> True if our chain was replaced, False if not
		"""

		neighbours = self.nodes
		new_chain = None

		# We're only looking for chains longer than ours
		max_length = len(self.chain)

		# Grab and verify the chains from all the nodes in our network
		for node in neighbours:
		    response = requests.get(f'http://{node}/chain')

		    if response.status_code == 200:
		        length = response.json()['length']
		        chain = response.json()['chain']

		        # Check if the length is longer and the chain is valid
		        if length > max_length and self.valid_chain(chain):
		            max_length = length
		            new_chain = chain

		# Replace our chain if we discovered a new, valid chain longer than ours
		if new_chain:
		    self.chain = new_chain
		    return True

		return False


# Instantiate our Node
app = Flask(__name__)

# Generate a globally unique address for this node
node_identifier = str(uuid4()).replace('-', '')

# Instantiate the Blockchain
blockchain = Blockchain()

@app.route('/nodes/register', methods=['POST'])
def register_nodes():
	values = request.get_json()

	nodes = values.get('nodes')
	if nodes is None:
	    return "Error: Please supply a valid list of nodes", 400

	for node in nodes:
	    blockchain.register_node(node)

	response = {
	    'message': 'New nodes have been added',
	    'total_nodes': list(blockchain.nodes),
	}
	return jsonify(response), 201


@app.route('/nodes/resolve', methods=['GET'])
def consensus():
	replaced = blockchain.resolve_conflicts()

	if replaced:
	    response = {
	        'message': 'Our chain was replaced',
	        'new_chain': blockchain.chain
	    }
	else:
	    response = {
	        'message': 'Our chain is authoritative',
	        'chain': blockchain.chain
	    }

	return jsonify(response), 200

@app.route('/mine', methods=['GET'])
def mine():
    # We run the proof of work algorithm to get the next proof...
    last_block = blockchain.last_block
    last_proof = last_block['proof']
    proof = blockchain.proof_of_work(last_proof)

    # We must receive a reward for finding the proof.
    # The sender is "0" to signify that this node has mined a new coin.
    blockchain.new_transaction(
        sender="0",
        recipient=node_identifier,
        amount=1,
    )

    # Forge the new Block by adding it to the chain
    previous_hash = blockchain.hash(last_block)
    block = blockchain.new_block(proof, previous_hash)

    response = {
        'message': "New Block Forged",
        'index': block['index'],
        'transactions': block['transactions'],
        'proof': block['proof'],
        'previous_hash': block['previous_hash'],
    }
    return jsonify(response), 200
  
@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    values = request.get_json()

    # Check that the required fields are in the POST'ed data
    required = ['sender', 'recipient', 'amount']
    if not all(k in values for k in required):
        return 'Missing values', 400

    # Create a new Transaction
    index = blockchain.new_transaction(values['sender'], values['recipient'], values['amount'])

    response = {'message': f'Transaction will be added to Block {index}'}

    return jsonify(response), 201


@app.route('/chain', methods=['GET'])
def full_chain():
    response = {
        'chain': blockchain.chain,
        'length': len(blockchain.chain),
    }
    return jsonify(response), 200

if __name__ == '__main__':
	app.run(host='0.0.0.0', port=5000)