blockchain.py

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

class Blockchain(object):
    def __init__(self):
        self.current_transactions = []
        self.chain = []
        self.new_block(previous_hash=1, proof=100)

    def proof_of_work(self, last_proof):
        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] == "1111"

    @staticmethod
    def hash(block):
        # Check dictionary is ordered
        block_str = json.dumps(block, sort_keys=True).encode()
        return hashlib.sha256(block_str).hexdigest()

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

    def new_block(self, proof, previous_hash=None):
        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):

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

        return self.last_block['index'] + 1

# Instantiate node
app = Flask(__name__)

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

# Instantiate the Blockchain
blockchain = Blockchain()

# API methods:
# POST: Create new transaction
@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    values = request.get_json()
    # Check required fields
    required = ['sender', 'recipient', 'amount']
    if not all(k in values for k in required):
        return 'Missing values', 400
    # Create 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

# GET: display full chain
@app.route('/chain', methods=['GET'])
def full_chain():
    response = {
        'chain': blockchain.chain,
        'length': len(blockchain.chain),
    }
    return jsonify(response), 200

# GET: mine new block
@app.route('/mine', methods=['GET'])
def mine():
    # POW algorithm
    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,
    )

    # Add the new block to the chain
    previous_hash = blockchain.hash(last_block)
    block = blockchain.new_block(proof, previous_hash)

    response = {
        'message': "New Block",
        'index': block['index'],
        'transactions': block['transactions'],
        'proof': block['proof'],
        'previous_hash': block['previous_hash'],
    }
    return jsonify(response), 200
# Run app
if __name__ == '__main__':
    app.run(host='127.0.0.1', port=4444)