def message(self, pubnub, message_object):
print('Message channel: %s | Message object: %s' %
(message_object.channel, message_object.message))
#check if a block was received through the BLOCK channel and then add it to the chaina and then perform replace chain
if message_object.channel == 'BLOCK':
block = Block.from_json(message_object.message)
potential_chain = self.blockchain.chain[:]
#add received block to the chain
potential_chain.append(block)
#perform replace_chain operation
try:
self.blockchain.replace_chain(potential_chain)
#After everytime a block is mined, we need to clear the transaction pool.
self.transaction_pool.clear_transaction(self.blockchain)
print("Chain replacement was successful")
except Exception as e:
print("Chain replacement was not successful: %s" % (e))
elif message_object.channel == 'TRANSACTIONS':
transaction = Transactions.from_json(message_object.message)
self.transaction_pool.set_transaction(transaction)
def is_chain_transaction_valid(chain):
"""
Method to verify if each of the transactions in the chain is valid.
Transaction is valid if:
1. Each transation appears only once in the blockchain.
2. There is only one reward transaction.
3. The transaction is valid.
"""
transaction_ids = set()
for index, block in enumerate(chain):
if index == 0:
continue
has_reward_transaction = False
for transaction_json in block.data:
transaction = Transactions.from_json(transaction_json)
if transaction.input == MINING_REWARD_INPUT:
if has_reward_transaction is True:
raise Exception(
"Transaction with id %s has multiple rewards" %
(transaction.id))
has_reward_transaction = True
else:
#calculate historical balance using a historical balance
historical_chain = chain[:index]
historical_blockchain = Blockchain()
historical_blockchain.chain = historical_chain
#get the balance amount of the address
balance = Wallet.calculate_balance(
historical_blockchain, transaction.input['address'])
if balance != transaction.input['amount']:
raise Exception(
"Transaction id %s did not have the correct balance"
% (transaction.id))
if transaction.id in transaction_ids:
raise Exception("Transaction with id %s is not unique" %
(transaction.id))
transaction_ids.add(transaction.id)
Transactions.verify_transaction(transaction)
