创建一个区块链，是由三个节点组成的去中心化网络。-Toy模板网

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一、准备工作：

1、创建三个python文件：

2、创建nodes.json文件

3、transaction.json文件

4、打开三个控制台

二、在三个节点上进行交互。

二、添加交易发布请求（a向b发送10000coin）

一、准备工作：

1、创建三个python文件：

lancoin_node_5001.py、lancoin_node_5002.py、lancoin_node_5003.py。

它们每个都将连接到不同的端口，一个端口用于a，一个端口用于b，一个端口用于c。

a在端口5001上，b在端口5002上，c在端口5003上

代码示例（lancoin_node_5001.py）：

 # Module 1 -Create a Cryptocurrency
#To be installed:
#Flask==0.12.2:pip install Flask==0.12.2
#Postman HTrp Client:https://www.getpostman.com
#requests==2.18.4:pip install requests=-2.18.4
#时间戳
import datetime
import hashlib
import json
#Flask可以定义Web应用的路由（URL到Python函数的映射），并处理HTTP请求和响应。jsonify是一个函数，用于将Python对象转换为JSON格式的响应。当你在Flask路由函数中返回一个jsonify对象时，Flask会自动将该对象对应的数据转换为JSON格式，并设置合适的HTTP响应头，以便客户端可以正确解析响应内容。
from flask import Flask, jsonify,request
import requests
from uuid import uuid4
from urllib.parse import urlparse

#  1******Building a Blockchain
class Blockchain:
    def __init__(self):
        self.transactions=[]
        self.chain=[]
        self.create_block(proof=1,previous_hash='0')
        self.nodes=set()
    
    def create_block(self,proof,previous_hash):
        block={'index':len(self.chain)+1,
               'timestamp':str(datetime.datetime.now()),
               'proof':proof,
               'previous_hash':previous_hash,
               'transactions':self.transactions}
        self.transactions=[]
        self.chain.append(block) 
        return block
    def get_previous_block(self):
        return self.chain[-1] 
    
    def proof_of_work(self,previous_proof):
        new_proof=1
        check_proof=False
        while check_proof is False:
            hash_oparation=hashlib.sha256(str(new_proof**2-previous_proof**2).encode()).hexdigest()
            if hash_oparation[:4]=='0000':
                check_proof=True
            else:
                new_proof+=1
        return new_proof
    
    def hash(self, block):
        encode_block = json.dumps(block, sort_keys=True).encode()
        return hashlib.sha256(encode_block).hexdigest()

    def is_chain_valid(self,chain):
        previous_block=chain[0]
        block_index=1
        while block_index<len(chain):
          block=chain[block_index]
          if block['previous_hash'] !=self.hash(previous_block):
              return False
          previous_proof=previous_block['proof']
          proof=block['proof']
          hash_oparation=hashlib.sha256(str(proof**2-previous_proof**2).encode()).hexdigest()
          if hash_oparation[:4] !='0000':
              return False
          previous_block=block
          block_index+=1
        return True
    
    def add_transaction(self,sender,receiver,amount):
        self.transactions.append({'sender':sender,
                                  'receiver':receiver,
                                  'amount':amount})
        previous_block=self.get_previous_block()
        return previous_block['index']+1
            
    def add_node(self,address):
        parsed_url=urlparse(address)
        self.nodes.add(parsed_url.netloc)
        
    def replace_chain(self):
        network = self.nodes
        longest_chain = None
        max_length = len(self.chain)
    
        for node in network:
            try:
                response = requests.get(f'http://{node}/get_chain')
                response.raise_for_status()  # 这将抛出异常，如果请求失败
            except requests.exceptions.RequestException as e:
                print(f"Failed to get the chain from {node}. Exception: {e}")
                continue
    
            if response.status_code == 200:
                length = response.json()['length']
                chain = response.json()['chain']
                if length > max_length and self.is_chain_valid(chain):
                    max_length = length
                    longest_chain = chain
    
        if longest_chain:
            self.chain = longest_chain
            return True
        return False
#Part 2 -Mining our Blockchain

#Creating a Web App
app = Flask(__name__)

#Creating an address for the node on Port 5000
node_address=str(uuid4()).replace('-', '')

#Creating a Blockchain
blockchain=Blockchain()
#Mining a new block
@app.route('/mine_block',methods=['GET'])
def mine_block():
    previous_block=blockchain.get_previous_block()
    previous_proof=previous_block['proof']
    proof=blockchain.proof_of_work(previous_proof)
    previous_hash=blockchain.hash(previous_block)
    blockchain.add_transaction(sender=node_address,receiver='a',amount=1)
    block=blockchain.create_block(proof, previous_hash)
    response={'message':'Congratulation,you just mined a block',
              'index':block['index'],
              'timestamp':block['timestamp'],
              'proof':block['proof'],
              'previous_hash':block['previous_hash'],
              'transactions':block['transactions']}
    return jsonify(response),200
            
#Getting the full Blockchain
@app.route('/get_chain',methods=['GET'])
def get_chain():
    response={'chain':blockchain.chain,
             'length':len(blockchain.chain)}
    return jsonify(response),200      
            
#Checking if the Blockchain is valid
@app.route('/is_valid',methods=['GET']) 
def get_valid():
    is_valid=blockchain.is_chain_valid(blockchain.chain)
    if is_valid:
        response={'message':'All good. The Blockchain is valid.'}
    else:
        response={'message':'Houston,we have a problem.The Blockchain is not valid.'}
    return jsonify(response),200

#Addling a new transaction to the Blockchain
@app.route('/add_transaction',methods=['POST']) 
def add_transaction():
    json =request.get_json()
    transaction_keys=['sender','receiver','amount']
    if not all(key in json for key in transaction_keys):
        return 'Some elements of the transaction are missing',400
    index=blockchain.add_transaction(json['sender'], json['receiver'],json['amount'])
    response={'message':f'This transaction will be added to Block {index}'}
    return jsonify(response),201

#Connecting new nodes
@app.route('/connect_node', methods=['POST'])
def connect_node():
    json = request.get_json()
    nodes = json.get('nodes')
    if nodes is None:
        return "No nodes provided", 400
    for node in nodes:
        blockchain.add_node(node)
    # 将响应构建移到循环外，并在所有节点添加后才返回
    response = {
        'message': 'All the nodes are now connected. The Lancoin Blockchain now contains the following nodes:',
        'total_nodes': list(blockchain.nodes)
    }
    return jsonify(response), 201
#Replacing the chain by the longest chain if needed
@app.route('/replace_chain', methods=['GET'])
def replace_chain():
    is_chain_replaced = blockchain.replace_chain()
    if is_chain_replaced:
        response = {
            'message': 'The nodes had different chains so the chain was replaced by the longest one.',
            'new_chain': blockchain.chain
        }
    else:
        response = {
            'message': 'All good. the chain is the largest one.',
            'actual_chain': blockchain.chain
        }
    return jsonify(response), 200   
        
app.run(host='0.0.0.0',port=5001)

lancoin_node_5002.py、lancoin_node_5003.py则是lancoin_node_5001.py中的mine_block函数的blockchain.add_transaction(sender=node_address,receiver='a',amount=1)，a改为b、c，然后app.run(host='0.0.0.0',port=5001)中的5001改为5002、5003

2、创建nodes.json文件

{
    "nodes":["http://127.0.0.1:5001",
             "http://127.0.0.1:5002",
             "http://127.0.0.1:5003"]
}