blockchain.py

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

import requests
from flask import Flask, jsonify, request


class Block(object):

    def __init__(self, index, proof_number, prev_hash, data,
                 timestamp=None):
        self.index = index
        self.proof_number = proof_number
        self.prev_hash = prev_hash
        self.data = data
        self.timestamp = timestamp or time.time()

    @property
    def compute_hash(self):
        string_block = "{}{}{}{}{}".format(
            self.index, self.proof_number, self.prev_hash,
            self.data, self.timestamp)

        return hashlib.sha256(string_block.encode()).hexdigest()

    def __repr__(self):
        return "{} - {} - {} - {} - {}".format(self.index, self.proof_number,
                                               self.prev_hash, self.data,
                                               self.timestamp)


class BlockChain(object):

    def __init__(self):
        self.chain = []
        self.current_data = []
        self.nodes = set()
        self.build_genesis()

    def build_genesis(self):
        self.build_block(proof_number=0, prev_hash=0)

    def build_block(self, proof_number, prev_hash):
        block = {
            'index': len(self.chain),
            'proof_number': proof_number,
            'prev_hash': prev_hash,
            'transactions': self.current_data
        }
        self.current_data = []
        self.chain.append(block)
        return block

    def new_transaction(self, sender, receiver, amount):
        self.current_data.append({
            'sender': sender,
            'receiver': receiver,
            'amount': amount
        })
        return self.last_block['index'] + 1

    def register_node(self, address):
        """
        Add a new node to the list of nodes
        :param address: Address of node. Eg. 'http://192.168.0.5:5000'
        """

        parsed_url = urlparse(address)
        if parsed_url.netloc:
            self.nodes.add(parsed_url.netloc)
        elif parsed_url.path:
            # Accepts an URL without scheme like '192.168.0.5:5000'.
            self.nodes.add(parsed_url.path)
        else:
            raise ValueError('Invalid URL')

    def chain_validity(self, chain):
        """
        Determine if a given blockchain is valid
        :param chain: A blockchain
        :return: 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
            last_block_hash = self.hash(last_block)
            if block['prev_hash'] != last_block_hash:
                return False

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

    def block_mining(self, details_miner):
        self.new_transaction(
            #  it implies that this node has created a new block
            sender="0",
            receiver=details_miner,
            #  creating a new block (or identifying the proof number)
            #  is awarded with 1
            quantity=1,

        )
        last_block = self.last_block
        last_proof_number = last_block.proof_number
        proof_number = self.proof_of_work(last_proof_number)
        last_hash = last_block.compute_hash
        block = self.build_block(proof_number, last_hash)
        return vars(block)

    def create_node(self, address):
        self.nodes.add(address)
        return True

    def proof_of_work(self, last_block):
        """
        Simple Proof of Work Algorithm:
         - Find a number p' such that hash(pp') contains leading 4 zeroes
         - Where p is the previous proof, and p' is the new proof

        :param last_block: <dict> last Block
        :return: <int>
        """
        last_proof = last_block['proof_number']
        proof_number = 0
        while BlockChain.verifying_proof(proof_number, last_proof) is False:
            proof_number += 1
        return proof_number

    @staticmethod
    def hash(block):
        """
        Creates a SHA-256 hash of a Block
        :param block: Block
        """
        # 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()

    @staticmethod
    def confirm_validity(block, previous_block):
        if previous_block.index + 1 != block.index:
            return False

        elif previous_block.compute_hash != block.prev_hash:
            return False

        elif not BlockChain.verifying_proof(block.proof_number,
                                            previous_block.proof_number):
            return False

        elif block.timestamp <= previous_block.timestamp:
            return False

        return True

    @staticmethod
    def verifying_proof(last_proof, proof):
        """
        Validates the Proof
        :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"

    @property
    def last_block(self):
        return self.chain[-1]

    @staticmethod
    def get_block_object(block_data):
        return Block(
            block_data['index'],
            block_data['proof_number'],
            block_data['prev_hash'],
            block_data['transactions'],
            timestamp=block_data['timestamp']
        )


def test():
    """
    For testing
    """
    print("MINING ABOUT TO START")
    print(blockchain.chain)

    last_block = blockchain.last_block
    last_proof_number = last_block.proof_number
    proof_number = blockchain.proof_of_work(last_proof_number)

    blockchain.new_transaction(
        #  this means that this node has constructed another block
        sender="0",
        receiver="Test User",
        #  building a new block (or figuring out the proof number)
        #  is awarded with 1
        amount=1,
    )

    last_hash = last_block.compute_hash
    block = blockchain.build_block(proof_number, last_hash)

    print(block)
    print("MINING HAS BEEN SUCCESSFUL!")
    print(blockchain.chain)


# Initiate the Node
app = Flask(__name__)

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

# Initiate the Blockchain
print("Initializing BlockChain...")
blockchain = BlockChain()
print("BlockChain initialized!")
print("Last Block: {}".format(blockchain.last_block))


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

    # 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",
        receiver=node_identifier,
        amount=1,
    )

    # Forge the new Block by adding it to the chain
    previous_hash = blockchain.hash(last_block)
    block = blockchain.build_block(proof, previous_hash)
    response = {
        'message': "New Block Forged",
        'index': block['index'],
        'transactions': block['transactions'],
        'proof_number': block['proof_number'],
        'previous_hash': block['prev_hash'],
    }
    print("Last Block: {}".format(blockchain.last_block))
    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


@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


if __name__ == '__main__':
    from argparse import ArgumentParser

    parser = ArgumentParser()
    parser.add_argument('-p', '--port', default=5000,
                        type=int, help='port to listen on')
    args = parser.parse_args()
    port = args.port

    app.run(host='0.0.0.0', port=port)