blockchain.py

# coding: utf-8
'''
@Title : Blockchain From Scratch
@Author : Shengyang Li
@Email : sl137@iu.edu
@Date : 23-04-2022
@Reference: https://www.activestate.com/blog/how-to-build-a-blockchain-in-python/
'''
import json
import time
from hashlib import sha256
from flask import Flask, request
import requests
import bflec as bf #import the federated learning
import numpy as np



class Block:
    def __init__(self, index, transactions, timestamp, previous_hash):
        self.index = index
        self.transactions = transactions
        self.timestamp = timestamp
        self.previous_hash = previous_hash
        self.nonce = 0

    def compute_hash(self):
        """
        A function that return the hash of the block contents.
        """
        block_string = json.dumps(self.__dict__, sort_keys=True)
        return sha256(block_string.encode()).hexdigest()


class Blockchain:
    # difficulty of our PoW algorithm
    difficulty = 4

    def __init__(self):
        self.unconfirmed_transactions = []
        self.chain = []
        self.create_genesis_block()

    def create_genesis_block(self):
        """
        A function to generate genesis block and appends it to
        the chain. The block has index 0, previous_hash as 0, and
        a valid hash.
        """
        genesis_block = Block(0, [], time.time(), "0")
        genesis_block.hash = genesis_block.compute_hash()
        self.chain.append(genesis_block)

    @property
    def last_block(self):
        return self.chain[-1]

    def add_block(self, block, proof):
        """
        A function that adds the block to the chain after verification.
        Verification includes:
        * Checking if the proof is valid.
        * The previous_hash referred in the block and the hash of latest block
          in the chain match.
        """
        previous_hash = self.last_block.hash

        if previous_hash != block.previous_hash:
            return False

        if not self.is_valid_proof(block, proof):
            return False

        block.hash = proof
        self.chain.append(block)
        return True

    def is_valid_proof(self, block, block_hash):
        """
        Check if block_hash is valid hash of block and satisfies
        the difficulty criteria.
        """
        return (block_hash.startswith('0' * Blockchain.difficulty) and
                block_hash == block.compute_hash())

    def proof_of_work(self, block):
        """
        Function that tries different values of nonce to get a hash
        that satisfies our difficulty criteria.
        """
        block.nonce = 0

        computed_hash = block.compute_hash()
        while not computed_hash.startswith('0' * Blockchain.difficulty):
            block.nonce += 1
            computed_hash = block.compute_hash()

        return computed_hash

    def add_new_transaction(self, transaction):
        self.unconfirmed_transactions.append(transaction)

    def mine(self):
        """
        This function serves as an interface to add the pending
        transactions to the blockchain by adding them to the block
        and figuring out Proof Of Work.
        """
        if not self.unconfirmed_transactions:
            return False

        last_block = self.last_block

        new_block = Block(index=last_block.index + 1,
                          transactions=self.unconfirmed_transactions,
                          timestamp=time.time(),
                          previous_hash=last_block.hash)

        proof = self.proof_of_work(new_block)
        self.add_block(new_block, proof)

        self.unconfirmed_transactions = []
        return new_block.index

def data_list(data):
  d_list=[]
  for i in data:
    for j in i:
      d_list.append(j)
  return d_list

app = Flask(__name__)

blockchain = Blockchain()

a=[10 for i in range(10)]

weights=bf.client_train(10,50,5)

for i in range(5):
    
    transactions=blockchain.add_new_transaction(np.array(weights[i][0][0]).tolist())
#t_1=blockchain.add_new_transaction(a)
#blockchain.mine()

blockchain.mine()

@app.route('/chain', methods=['GET'])
def get_chain():
    chain_data = []
    for block in blockchain.chain:
        chain_data.append(block.__dict__)
    return json.dumps({"length": len(chain_data),
                       "chain": chain_data})
    #return len(chain_data),chain_data

app.run(debug=True, port=5000)