def is_valid_transaction_chain(chain):
"""
Enforce the rules of a chain composed of blocks of transactions.
- Each transaction must only appear once in the chain.
- There can be one mining reward per block.
- Each transaction must be valid.
"""
transaction_ids = set()
for i in range(len(chain)):
block = chain[i]
has_mining_reward = False
for transaction_json in block.data:
transaction = Transaction.from_json(transaction_json)
if transaction.id in transaction_ids:
raise Exception(
f'Transaction: {transaction.id} is not unique')
transaction_ids.add(transaction.id)
if transaction.input == MINING_REWARD_INPUT:
if has_mining_reward:
raise Exception(
'There can only be one mining reward per block.'\
f'Check block with hash: {block.hash}'
)
has_mining_reward = True
else:
historic_blockchain = Blockchain()
historic_blockchain.chain = chain[0:i]
historic_balance = Wallet.calculate_balance(
historic_blockchain, transaction.input['address'])
if historic_balance != transaction.input['amount']:
raise Exception(
f'Transaction {transaction.id} has an invalid '\
'input amount')
Transaction.is_valid_transaction(transaction)
def message(self, pubnub, message_object):
print(
f'\n-- Channel: {message_object.channel} | Message: {message_object.message}'
)
if message_object.channel == CHANNELS['BLOCK']:
block = Block.from_json(message_object.message)
# [:] -> all the elements in the array, in that case all blocks in chain
potential_chain = self.blockchain.chain[:]
potential_chain.append(block)
try:
self.blockchain.replace_chain(potential_chain)
self.transaction_pool.clear_blockchain_transactions(
self.blockchain)
print('\n -- Successfully replaced the local chain')
except Exception as e:
print(f'\n -- Did not replace chain: {e}')
elif message_object.channel == CHANNELS['TRANSACTION']:
transaction = Transaction.from_json(message_object.message)
self.transaction_pool.set_transaction(transaction)
print('\n -- Set the new transaction in the transaction pool')
