blockchain.py

import hashlib
import json
import requests
from textwrap import dedent
from time import time
from uuid import uuid4
from flask import Flask, jsonify, request
from urllib.parse import urlparse

class Blockchain(object):
    def __init__(self):
        self.current_transactions = []
        self.chain = []
        self.nodes = set()
        self.new_block(previous_hash=1, proof=100)
    def new_block(self, proof, previous_hash=None):
        """
        生成新块
        :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):
        """
        生成新交易信息，信息将加入到下一个待挖的区块中
        :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):
        """
        生成块的 SHA-256 hash值
        :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):
        """
        简单的工作量证明:
         - 查找一个 p' 使得 hash(pp') 以4个0开头
         - p 是上一个块的证明,  p' 是当前的证明
        :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):
        """
        验证证明: 是否hash(last_proof, proof)以4个0开头?
        :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):
        """
        共识算法解决冲突
        使用网络中最长的链.
        :return: <bool> True 如果链被取代, 否则为False
        """
        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

if __name__ == '__main__':
    # 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():
        response = {
            'chain': blockchain.chain,
            'length': len(blockchain.chain),
        }
        return jsonify(response), 200

    @app.route('/transactions/new', methods=['POST'])
    def new_transaction():
        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():
        # 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)
        # 给工作量证明的节点提供奖励.
        # 发送者为 "0" 表明是新挖出的币
        blockchain.new_transaction(
            sender="0",
            recipient=node_identifier,
            amount=1,
        )
        # Forge the new Block by adding it to the chain
        block = blockchain.new_block(proof)
        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():
        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
    app.run(host='0.0.0.0', port=5000)