看看代码的实现：
import hashlib
import json
from time import time
from urllib.parse import urlparse
from uuid import uuid4
import requests
from flask import Flask, jsonify, request
class Blockchain:
def __init__(self):
self.current_transactions = []
self.chain = []
self.nodes = set()
# Create the genesis block
self.new_block(previous_hash='1', proof=100)
def register_node(self, address):
"""
Add a new node to the list of nodes
:param address: Address of node. Eg. 'http://192.168.0.5:5000'
"""
parsed_url = urlparse(address)
if parsed_url.netloc:
self.nodes.add(parsed_url.netloc)
elif parsed_url.path:
# Accepts an URL without scheme like '192.168.0.5:5000'.
self.nodes.add(parsed_url.path)
else:
raise ValueError('Invalid URL')
def valid_chain(self, chain):
"""
Determine if a given blockchain is valid
:param chain: A blockchain
:return: 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'], last_block['previous_hash']):
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: 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
def new_block(self, proof, previous_hash):
"""
Create a new Block in the Blockchain
:param proof: The proof given by the Proof of Work algorithm
:param previous_hash: Hash of previous Block
:return: 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: Address of the Sender
:param recipient: Address of the Recipient
:param amount: Amount
:return: 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: Block
"""
# 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_block):
"""
Simple Proof of Work Algorithm:
- Find a number p' such that hash(pp') contains leading 4 zeroes
- Where p is the previous proof, and p' is the new proof
:param last_block: <dict> last Block
:return: <int>
"""
last_proof = last_block['proof']
last_hash = self.hash(last_block)
proof = 0
while self.valid_proof(last_proof, proof, last_hash) is False:
proof += 1
return proof
@staticmethod
def valid_proof(last_proof, proof, last_hash):
"""
Validates the Proof
:param last_proof: <int> Previous Proof
:param proof: <int> Current Proof
:param last_hash: <str> The hash of the Previous Block
:return: <bool> True if correct, False if not.
"""
guess = f'{last_proof}{proof}{last_hash}'.encode()
guess_hash = hashlib.sha256(guess).hexdigest()
return guess_hash[:4] == "0000"
# Instantiate the Node
app = Flask(__name__)
# Generate a globally unique address for this node
node_identifier = str(uuid4()).replace('-', '')
# Instantiate the Blockchain
blockchain = Blockchain()
@app.route('/mine', methods=['GET'])
def mine():
# We run the proof of work algorithm to get the next proof...
last_block = blockchain.last_block
proof = blockchain.proof_of_work(last_block)
# 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('/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('/chain', methods=['GET'])
def full_chain():
response = {
'chain': blockchain.chain,
'length': len(blockchain.chain),
}
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__':
from argparse import ArgumentParser
parser = ArgumentParser()
parser.add_argument('-p', '--port', default=5000, type=int, help='port to listen on')
args = parser.parse_args()
port = args.port
app.run(host='0.0.0.0', port=port)
提供了几个url:
mine GET
transactions/new POST
chain GET
nodes/register POST
nodes/resolve GET
/transactions/new to create a new transaction to a block
/mine to tell our server to mine a new block.
/chain to return the full Blockchain.
/nodes/register to accept a list of new nodes in the form of URLs.
/nodes/resolve to implement our Consensus Algorithm, which resolves any
conflicts—to ensure a node has the correct chain.
单个区块：
block = {
'index': 1,
'timestamp': 1506057125.900785,
'transactions': [
{
'sender': "8527147fe1f5426f9dd545de4b27ee00",
'recipient': "a77f5cdfa2934df3954a5c7c7da5df1f",
'amount': 5,
}
],
'proof': 324984774000,
'previous_hash': "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
}