A basic block chain implementation | Learnt during FDP (Factulty development program) 2019 Blockchain

blockchain_basic.py

from time import time
import hashlib
import json
from flask import Flask, jsonify, request
from uuid import uuid4

class Blockchain:
    def __init__(self):
        self.current_transactions = []
        self.chain = []
        #genesis block
        self.add_block(previous_hash = '1', proof = 12)

    @staticmethod
    def hash(block):
        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 new_transaction(self, sender, recipient, amount):
        ts = {
            'sender': sender,
            'recipient': recipient,
            'amount': amount
        }
        self.current_transactions.append(ts)
        return self.last_block['index'] + 1

    def add_block(self, proof, previous_hash):
        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

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

    def proof_of_work(self, last_block):
        last_proof = last_block['proof']
        last_hash = self.hash(last_block)

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

        return proof

app = Flask(__name__)

node_identifier = str(uuid4()).replace('-','')

blockchain = Blockchain()

@app.route('/mine')
def mine():
    last_block = blockchain.last_block
    proof = blockchain.proof_of_work(last_block)

    blockchain.new_transaction(
        sender='0',
        recipient=node_identifier,
        amount=20
    )
    previous_hash = blockchain.hash(last_block)
    block = blockchain.add_block(proof, previous_hash)

    response = {
        'message': 'Block is created',
        '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():
    values = request.get_json()

    required = ['sender', 'recipient', 'amount']

    if not all(k in values for k in required):
        return 'Missing Values', 400
    
    sender = values['sender']
    recipient = values['recipient']
    amount = values['amount']
    index = blockchain.new_transaction(sender, recipient, amount)

    response = {
        'message': f'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 = json.loads(request.data)
    nodes = values.get('nodes')

    if nodes is None:
        return 'Error', 400

    for node in nodes:
        blockchain.register_node(
            'http://127.0.0.1:' + str(node)
        )

    response = {
        'message': "Added new nodes",
        'total_nodes': list(blockchain.nodes)
    }

    return jsonify(response), 201

if __name__ == "__main__":
    from argparse import ArgumentParser
    parser = ArgumentParser()
    parser.add_argument('-p', '--port', default=5000, type=int, help='port num')
    
    args = parser.parse_args()
    port = args.port

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