Blockchain/blockchain.py at master · bipulshahi/Blockchain · GitHub

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# -*- coding: utf-8 -*-
"""
Created on Fri Jan 17 14:11:34 2020

@author: vipul
"""
#Postman
import datetime  #Each block will have own timestamp
import hashlib  #Hash the block
import json   #Encode the block before we hash them
from flask import Flask, jsonify

#Create a Blockchain
#Part 1:- Building the blockchain
class Blockchain:
    def __init__(self):
        self.chain=[]
        self.create_block(proof=1,previous_hash='0')

    def create_block(self,proof,previous_hash):
        #Define Dict. for essential keys of block
        block = {'index':len(self.chain)+1,
                 'timestamp':str(datetime.datetime.now()),
                 'proof' :proof,
                 'previous_hash':previous_hash
                }
        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_operation=hashlib.sha256(str(new_proof**2-previous_proof**2).encode()).hexdigest()
            if hash_operation[:4] == '0000':
                check_proof=True
            else:
                new_proof += 1
        return new_proof

    def hash(self,block):
        encoded_block=json.dumps(block, sort_keys=True).encode()
        return hashlib.sha256(encoded_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_operation=hashlib.sha256(str(proof**2-previous_proof**2).encode()).hexdigest()
            if hash_operation[:4] != '0000':
                return False
            previous_block = block
            block_index += 1
        return True
#Create a web app
app = Flask(__name__)

blockchain=Blockchain()

#Part 2:- Mining of Blockchain
@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)
    block = blockchain.create_block(proof, previous_hash)

    response = {'message':'Congrats, You mined a block',
                'index': block['index'],
                'timestamp': block['timestamp'],
                'proof' : block['proof'],
                'previous_hash': block['previous_hash']}
    return jsonify(response), 200

#Getting the chain of blocks
@app.route('/get_chain', methods=['GET'])
def get_chain():
    response = {'chain':blockchain.chain,
                'length':len(blockchain.chain)
                }
    return jsonify(response), 200

@app.route('/is_valid', methods=['GET'])
def is_valid():
    is_valid = blockchain.is_chain_valid(blockchain.chain)
    if is_valid:
        response = {'Message':'The Chain is valid'}
    else:
        response = {'Message':'The Chain is not valid'}
    return jsonify(response), 200

#Run the app
app.run(host='0.0.0.0', port=5001)