blockchain.py

import requests
from dataclasses import dataclass
from time import time
from urllib.parse import urlparse
from flask import Flask, jsonify, request
from uuid import uuid4

class Blockchain:
    
    @dataclass
    class Block:
        index: str
        timestamp: float
        transactions: list
        proof: int
        previousHash: int

    class GenesisBlock(Block):
        def __post_init__(self) -> None:
            self.index = 0

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

    def __len__(self) -> int:
        return len(self.chain)
    
    def register_node(self, add:str) -> None:
        parsed_url = urlparse(add)

        self.nodes.add(parsed_url.netloc)

    def valid_chain(self, chain:list) -> bool:
        
        last_block = chain[0]
        current_index = 1

        while current_index < len(chain):
            block = self.Block
            print(f'{last_block}')
            print(f'{block}')
            print("\n-----------\n")

            if block["previousHash"] != hash(last_block):
                return False
            
            if not self.valid_proof(last_block["proof"], block["proof"]):
                return False
            
            last_block = block
            current_index += 1

        return True
    
    def resolve_conflicts(self) -> bool:
        """
        This is the Consensus Algorithm, it resolves conflicts
        by replacing our chain with the longest one in the network.
        """

        neighbours = self.nodes
        self.chain = None

        max_length = len(self)

        for node in neighbours:
            response = requests.get(f"https://{node}/chain")

            if response.status_code == 200:
                length = response.json()["length"]
                chain = response.json()["chain"]

                if length > max_length and self.valid_chain(chain):
                    max_length = length
                    new_chain = chain

        if new_chain:
            self.chain = new_chain
            return True
        
        return False
    
    def add_block(self, proof:int, previousHash:str=None):

        if len(self) == 0:
            cls = self.GenesisBlock

            def gph():
                return None
        else:
            cls = self.Block

            def gph():
                return hash(self.chain[-1])
            
        self.chain.append(cls(index=len(self), timestamp=time(), transactions=self.transactions, proof=proof, previousHash=previousHash or gph()))
        self.transactions = []
        return cls
    
    def new_transaction(self, sender:str, recipient:str, amount:int):
        self.transactions.append({"sender":sender, "recipient":recipient, "amount": amount})

        return self.last_block["index"] + 1


    @property
    def last_block(self):
        return self.chain[-1] if len(self) > 0 else 0
    
    def proof_of_work(self, last_proof:int) -> int:
        
        """
        Simple Proof of Work Algorithm:
         - Find a number p' such that hash(pp') contains 4 leading zeroes, where p is the previous p'
         - p is the previous proof, and p' is the new proof
         """

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

    @staticmethod
    def valid_proof(last_proof:int, proof:int) -> bool:
        
        """
        Validates the Proof: Does hash(last_proof, proof) contain 4 leading zeroes?
        """
        
        guess = f'{last_proof}{proof}'.encode()
        guess_hash = hash(guess)
        return guess_hash[:4] == "0000"
    
app = Flask(__name__)

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

# Instantiate the Blockchain
blockchain = Blockchain()

# /mine to tell the server to mine a new block
# GET request endpoint
@app.route('/mine', methods=['GET']) #
def mine():
    last_block = blockchain.last_block
    last_proof = last_block['proof']
    proof = blockchain.proof_of_work(last_proof)

    # 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 = hash(last_block)

    block = blockchain.add_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

# /transactions/new to create a new transaction to a block  
# POST request endpoint, since we’ll be posting data to it
@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    values = request.get_json() # extracts the JSON data from the POST request

    # Check that the required fields are in the POST 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 

# /chain to return the full Blockchain
@app.route('/chain', methods=['GET'])
def full_chain():
    response = {
        'chain': blockchain.chain,
        'length': len(blockchain),
    }
    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__':
    app.run(host='0.0.0.0', port=5000)