blockchain.py

import hashlib
import json

from time import time

from uuid import uuid4
from textwrap import dedent
from flask import Flask, jsonify, request

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

		self.new_block(proof=100, previous_hash=1)

	def new_block(self, proof, previous_hash=None):
		# 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])
		}

		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
		self.current_transactions.append({
			'sender': sender,
			'recipient': recipient,
			'amount': amount
		})

		return self.last_block['index'] + 1

	def proof_of_work(self, last_proof):
		#Simple Proof of Work Algorithm		
		proof = 0
		while self.valid_proof(last_proof, proof) is False:
			proof += 1

		return proof

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


	@staticmethod
	def hash(block):
		# Hashes a Block
		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]
	
# 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('/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)

	blockchain.new_transaction(
		sender="0",
		recipient=node_identifier,
		amount=1
	)

	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()

	required = ['sender', 'recipient', 'amount']
	if not all(key in values for key in required):
		return 'Missing values', 400

	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)