def message(self, pubnub, message_obj):
print(
f"\n -- Channel: {message_obj.channel} | Message: {message_obj.message}"
)
if (message_obj.channel == CHANNELS["BLOCK"]):
prospective_block = Block.deserialize_from_json(
message_obj.message)
prospective_chain = self.blockchain.chain[:]
prospective_chain.append(prospective_block)
try:
self.blockchain.surrogate_chain(prospective_chain)
# purge recorded Tx from Pool
self.transaction_pool.purge(self.blockchain)
print(f"\n -- Chain surrogation successful.")
except Exception as err:
print(f"\n -- Chain surrogation failed. See: {err}")
elif (message_obj.channel == CHANNELS["TRANSACTION"]):
transaction = Transaction.deserialize_from_json(
message_obj.message)
self.transaction_pool.set_transaction(transaction)
print(
"\n -- New transaction successfully broadcast, added to the transaction pool."
)
def is_tx_chain_valid(blockchain):
"""
Validate incoming blockchain comprised of blocks with Tx therein qua the following ruleset:
- each Tx occurs once in the blockchain (i.e. 'double spend')
- there is only one valid reward Tx per block
- transaction obj must be intrinsically valid
"""
# Tx tracked by id, raise if duplicate
tx_tracking_pool = set()
# unwrap blockchain, unwrap blocks therein, deserialize ea block's Tx and parse them
for i in range(len(blockchain)):
block = blockchain[i]
mining_reward_extant = False
for serialized_tx in block.data:
deserialized_tx = Transaction.deserialize_from_json(
serialized_tx)
# if Tx already exists
if (deserialized_tx.id in tx_tracking_pool):
raise Exception(
f"Transaction {deserialized_tx.id} is not unique; this transaction is therefore invalid."
)
# add Tx to tracking pool
tx_tracking_pool.add(deserialized_tx.id)
# if Tx is a block reward, only validate against reward fields
if (deserialized_tx.input == MINING_REWARD_INPUT):
if (mining_reward_extant):
raise Exception(f"""
There can only be one mining reward per block.
Evaluation of block with hash: {block.hash} recommended."""
)
mining_reward_extant = True
else:
# recalc balance after every Tx to prevent input tamper
blockchain_provenance = Blockchain()
blockchain_provenance.chain = blockchain[0:i]
balance_provenance = Wallet.calculate_balance(
blockchain_provenance,
deserialized_tx.input["address"])
if (balance_provenance != deserialized_tx.input["amount"]):
raise Exception(
f"Transaction {deserialized_tx.id} contains an invalid input amount."
)
# last, run validator to check format
Transaction.is_tx_valid(deserialized_tx)
