blockchain.py

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

import requests
from flask import Flask, jsonify, request

class Blockchain:
    def __init__(self):
        self.current_transactions = []
        self.chain = []
        self.nodes = set()

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

    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 valid_chain(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['previous_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 new_block(self, proof, previous_hash):
        """
        Create a new Block in the Blockchain

        :param proof: The proof given by the Proof of Work algorithm
        :param previous_hash: Hash of previous Block
        :return: New Block
        """

        block = {
            'index': len(self.chain) + 1,
            'timestamp': time.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, cmd, amount):
        """
        Creates a new transaction to go into the next mined Block

        :param sender: Address of the Sender
        :param recipient: Address of the Recipient
        :param cmd: command
        :param amount: Bonus
        :return: The index of the Block that will hold this transaction
        """
        if amount:
            self.current_transactions.append({
                'sender': sender,
                'recipient': recipient,
                'amount': hashlib.sha256(cmd).hexdigest(),
            })
        else:
            self.current_transactions.append({
                'sender': sender,
                'recipient': recipient,
                'amount':amount,
            })

        return self.last_block['index'] + 1

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

    @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()

    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']
        last_hash = self.hash(last_block)

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

        return proof

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

        :param last_proof: <int> Previous Proof
        :param proof: <int> Current Proof
        :param last_hash: <str> The hash of the Previous Block
        :return: <bool> True if correct, False if not.

        """

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


# Instantiate the Node
app = Flask(__name__)

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

# Instantiate the Blockchain
blockchain = Blockchain()


def resolve(chain):
    chain.resolve_conflicts()


from multiprocessing import Process,Queue
import threading
commandqueue = Queue()
resultqueue = Queue()
#Define a new process to do blockchain activity
def backgroundProcess(command,result):
    while 1:
        if command.empty():
            if blockchain.current_transactions:
                # 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",
                    recipient=node_identifier,
                    amount=1,
                )

                # Forge the new Block by adding it to the chain
                previous_hash = blockchain.hash(last_block)
                blockchain.new_block(proof, previous_hash)
            else:
                t = threading.Thread(target=resolve,args=(blockchain,))
                t.start()
            time.sleep(1)
            continue


        comm = command.get()
        if comm['command'] == "/chain":
            response = {
                'chain': blockchain.chain,
                'length': len(blockchain.chain),
            }
            result.put(response)
            print("haha")
        elif comm['command'] =="/nodes/register":
            values = comm['values']
            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),
            }
            result.put(response)
            print("haha")
        elif comm['command'] == "/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",
                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'],
            }
            result.put(response)
            print("haha")
        elif comm['command'] =="/transactions/new":
            values = comm['values']
            # Check that the required fields are in the POST'ed data
            required = ['sender', 'recipient', 'cmd']
            if not all(k in values for k in required):
                response = {'message': 'Missing values'}
            else:
                # Create a new Transaction
                index = blockchain.new_transaction(values['sender'], values['recipient'], values['cmd'])
                response = {'message': f'Transaction will be added to Block {index}'}
            result.put(response)
            print("haha")



@app.route('/mine', methods=['GET'])
def mine():
    command = {'command': '/mine'}
    commandqueue.put(command)
    response = resultqueue.get()
    return jsonify(response), 200


@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    values = request.get_json()
    command = {'command': '/transactions/new',
               'values': values}
    commandqueue.put(command)
    response = resultqueue.get()
    return jsonify(response), 201


@app.route('/chain', methods=['GET'])
def full_chain():
    command = {'command':'/chain'}
    commandqueue.put(command)
    response = resultqueue.get()
    return jsonify(response), 200


@app.route('/nodes/register', methods=['POST'])
def register_nodes():
    values = request.get_json()
    command = {'command':'/nodes/register',
               'values':values}
    commandqueue.put(command)
    response = resultqueue.get()
    return jsonify(response), 201

from Crypto.PublicKey import RSA
@app.route('/generate', methods=['GET'])
def generate():
    key = RSA.generate(2048)
    pk = key.exportKey(pkcs=1)
    sk = key.exportKey(pkcs=8)
    id = hashlib.sha256(pk).hexdigest()
    response = {
        'id':id,
        'pk':pk.decode(),
        'sk':sk.decode()
    }
    return jsonify(response), 200

@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
    
    p = Process(target=backgroundProcess, args=(commandqueue,resultqueue))
    p.start()

    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)