[Python] Blockchain 區塊鏈實作

程式語言:Python3.6+
Package:
requests
flask
json
time
uuid
urllib
程式碼皆是來自於 Learn Blockchains by Building One,感謝作者的無私貢獻

功能:簡單實現區塊鏈

簡單來說
  • 區塊鏈就是由無數的區塊(帳本)所組成的,而區塊(帳本)中有著一定數目的交易
  • 區塊(帳本)之間則是由 hash 所串連起來
    每一個區塊(帳本)都會記錄著前一個區塊(帳本)的 hash 值,並依此產生該區塊(帳本)的 hash 值
  • hash 值有指定格式,俗稱挖礦
    例如:再加上某個值後,hash 的前四位需為零,也就是 0000...,隨著 0 的數量上升,所需的計算量會大增
  • 最正確的區塊鏈則是最長的那個,因為耗費的計算力最大 
因以上特性,當偷改了一個區塊(帳本)等同要把之後所有的區塊(帳本)包含未來的都需更改
這幾乎是不可能的,除非計算力超過整體網路的 50%,但與其這麼辛苦倒不如乖乖的挖礦獲利

使用方法
建立節點
# 可看到相關參數
python web.py -h

# 建立指令
python web.py
python web.py -P 5000
python web.py -H 127.0.0.1 -P 5000

目前的區塊鏈
http://127.0.0.1:5000/chain

新增交易(POST),在此用 curl 實現 POST
curl http://127.0.0.1:5000/transactions/new -X POST -H "Content-Type: application/json" -d '{"sender": "d4ee26eee15148ee92c6cd394edd974e", "recipient": "someone-other-address", "amount": 5}'

# windows 需改為
curl http://127.0.0.1:5000/transactions/new -X POST -H "Content-Type: application/json" -d "{\"sender\": \"d4ee26eee15148ee92c6cd394edd974e\", \"recipient\": \"someone-other-address\", \"amount\": 5}"

新增區塊
http://127.0.0.1:5000/mine

註冊節點(POST),在此用 curl 實現 POST
curl http://127.0.0.1:5000/nodes/register -X POST -H "Content-Type: application/json" -d '{"nodes": ["http://127.0.0.1:5001"]}'

# windows 需改為
curl http://127.0.0.1:5000/nodes/register -X POST -H "Content-Type: application/json" -d "{\"nodes\": [\"http://127.0.0.1:5001\"]}"

同步區塊鏈
# 先建立新的節點
python web.py -H 127.0.0.1 -P 5001
# 觀看目前的狀況
http://127.0.0.1:5001/chain
# 註冊已存在節點
curl http://127.0.0.1:5001/nodes/register -X POST -H "Content-Type: application/json" -d "{\"nodes\": [\"http://127.0.0.1:5000\"]}"
# 同步
http://127.0.0.1:5001/nodes/resolve
程式碼

web.py

from flask import Flask, jsonify, request
from uuid import uuid4

from blockchain import Blockchain

# Instantiate our Node
app = Flask(__name__)

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

# Instantiate the Blockchain
blockchain = Blockchain()


@app.route('/chain', methods=['GET'])
def full_chain():
    """
    目前的區塊鏈
    """
    response = {
        'chain': blockchain.chain,
        'length': len(blockchain.chain),
    }
    return jsonify(response), 200


@app.route('/transactions/new', methods=['POST'])
def new_transaction():
    """
    新增交易
    """
    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('/mine', methods=['GET'])
def mine():
    """
    產生新的 block
    """
    # We run the proof of work algorithm to get the next proof...
    last_block = blockchain.last_block
    last_proof = last_block['proof']
    proof = blockchain.proof_of_work(last_proof)

    # 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'],
    }
    return jsonify(response), 200


@app.route('/nodes/register', methods=['POST'])
def register_nodes():
    """
    註冊節點,別註冊到自己的
    """
    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():
    """
    更新成最長的區塊鏈
    """
    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')
    parser.add_argument('-H', '--host', default='127.0.0.1', type=str, help='host to listen on')
    args = parser.parse_args()
    port = args.port
    host = args.host
    
    app.run(host=host, port=port)

blockchain.py

import hashlib
import json
from time import time

import requests
from urllib.parse import urlparse


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

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

    def new_block(self, proof, previous_hash=None):
        """
        Create a new Block in the Blockchain
        :param proof: <int> The proof given by the Proof of Work algorithm
        :param previous_hash: (Optional) <str> Hash of previous Block
        :return: <dict> New Block
        """

        block = {
            'index': len(self.chain) + 1,
            'timestamp': 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, amount):
        """
        Creates a new transaction to go into the next mined Block
        :param sender: <str> Address of the Sender
        :param recipient: <str> Address of the Recipient
        :param amount: <int> Amount
        :return: <int> The index of the Block that will hold this transaction
        """
        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: <dict> Block
        :return: <str>
        """

        # 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_proof):
        """
        Simple Proof of Work Algorithm:
         - Find a number p' such that hash(pp') contains leading 4 zeroes
         - p is the previous proof, and p' is the new proof
        :param last_proof: <int>
        :return: <int>
        """

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

        return proof

    @staticmethod
    def valid_proof(last_proof, proof):
        """
        Validates the Proof: Does hash(last_proof, proof) contain 4 leading zeroes?
        :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"

    def register_node(self, address):
        """
        Add a new node to the list of nodes
        :param address: <str> Address of node. Eg. 'http://192.168.0.5:5000'
        :return: None
        """

        parsed_url = urlparse(address)
        self.nodes.add(parsed_url.netloc)

    def valid_chain(self, chain):
        """
        Determine if a given blockchain is valid
        :param chain: <list> A blockchain
        :return: <bool> 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
            if block['previous_hash'] != self.hash(last_block):
                return False

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

參考

gochain

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