blockchain.py-e

import hashlib
import json
from textwrap import dedent
from time import time
from uuid import uuid4
from urllib.parse import urlparse

from flask import Flask, jsonify, request

import requests



class Blockchain(object):
	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: <init> The proof given by the Proof of Work algorithm
		:param previous_hash: (Optional) <str> Hash of previous Block
		:return: <dict> New Block
		"""

		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): 
		"""
		Creates a new transaction to go into the next mened 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):
		"""
		Create a SHA-256 has of a Block

		:param block: <dict> Block
		:return: <str>
		"""

		# We must make sure that the Dictionary is Ordered, or we'll have incpnsistant hash
		block_string = json.dumps(block, sort_keys=True).encode()
		return hashlib.sha256(block_string).hexdigest()
				

	@property
	def last_block(self):
		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 zeros, were p is the previous p'
		 - p is the previous proof, and p' is the new proof

		 :param last_proof <init>
		 :return: <init>
		 """

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

	@staticmethod
	def valid_proof(last_proof, proof):
		"""
		Validates the Proof: Does hash(last_proof, proof) contain 4 leading zeroes?

		:param last_proof: <init> Previous Proof
		:param proof: <init> Current Proof
		:return: <bool> True if cirrect, 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://192.168.0.1:5000'
		:return: Node
		"""

		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 hte 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 resolve 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 = request.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 discover a new, new valid chain longer than ours
		if new_chain:
			self.chain = new_chain
			return True

		return False



# Inistantiate our Node
app = Flask(__name__)

# Generate a globally unique addess 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)

	# We must recieve 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('/transaction/new', methods=['POST'])
def new_transaction():
	value = request.get_json()

	#Check that the required fields are in the  POST'd data
	require = ['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['send'], 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

@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 valida 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

if __name__== '__main__':
	app.run(host='0.0.0.0', port=5001)