from uuid import uuid4 from queue import Queue from threading import Thread from common.cryptographer import Cryptographer from common.appointment import Appointment from common.tools import compute_locator from common.logger import Logger from pisa import LOG_PREFIX from pisa.cleaner import Cleaner from pisa.block_processor import BlockProcessor logger = Logger(actor="Watcher", log_name_prefix=LOG_PREFIX) class Watcher: """ The :class:`Watcher` is the class in charge to watch for channel breaches for the appointments accepted by the tower. The :class:`Watcher` keeps track of the accepted appointments in ``appointments`` and, for new received block, checks if any breach has happened by comparing the txids with the appointment locators. If a breach is seen, the :obj:`EncryptedBlob ` of the corresponding appointment is decrypted and the data is passed to the :obj:`Responder `. If an appointment reaches its end with no breach, the data is simply deleted. The :class:`Watcher` receives information about new received blocks via the ``block_queue`` that is populated by the :obj:`ChainMonitor `. Args: db_manager (:obj:`DBManager `): a ``DBManager`` instance to interact with the database. sk_der (:obj:`bytes`): a DER encoded private key used to sign appointment receipts (signaling acceptance). config (:obj:`dict`): a dictionary containing all the configuration parameters. Used locally to retrieve ``MAX_APPOINTMENTS`` and ``EXPIRY_DELTA``. responder (:obj:`Responder `): a ``Responder`` instance. Attributes: appointments (:obj:`dict`): a dictionary containing a simplification of the appointments (:obj:`Appointment ` instances) accepted by the tower (``locator`` and ``end_time``). It's populated trough ``add_appointment``. locator_uuid_map (:obj:`dict`): a ``locator:uuid`` map used to allow the :obj:`Watcher` to deal with several appointments with the same ``locator``. block_queue (:obj:`Queue`): A queue used by the :obj:`Watcher` to receive block hashes from ``bitcoind``. It is populated by the :obj:`ChainMonitor `. config (:obj:`dict`): a dictionary containing all the configuration parameters. Used locally to retrieve ``MAX_APPOINTMENTS`` and ``EXPIRY_DELTA``. db_manager (:obj:`DBManager `): A db manager instance to interact with the database. signing_key (:mod:`EllipticCurvePrivateKey`): a private key used to sign accepted appointments. Raises: ValueError: if `pisa_sk_file` is not found. """ def __init__(self, db_manager, responder, sk_der, config): self.appointments = dict() self.locator_uuid_map = dict() self.block_queue = Queue() self.config = config self.db_manager = db_manager self.responder = responder self.signing_key = Cryptographer.load_private_key_der(sk_der) def awake(self): watcher_thread = Thread(target=self.do_watch, daemon=True) watcher_thread.start() return watcher_thread def add_appointment(self, appointment): """ Adds a new appointment to the ``appointments`` dictionary if ``max_appointments`` has not been reached. ``add_appointment`` is the entry point of the Watcher. Upon receiving a new appointment it will start monitoring the blockchain (``do_watch``) until ``appointments`` is empty. Once a breach is seen on the blockchain, the :obj:`Watcher` will decrypt the corresponding :obj:`EncryptedBlob ` and pass the information to the :obj:`Responder `. The tower may store multiple appointments with the same ``locator`` to avoid DoS attacks based on data rewriting. `locators`` should be derived from the ``dispute_txid``, but that task is performed by the user, and the tower has no way of verifying whether or not they have been properly derived. Therefore, appointments are identified by ``uuid`` and stored in ``appointments`` and ``locator_uuid_map``. Args: appointment (:obj:`Appointment `): the appointment to be added to the :obj:`Watcher`. Returns: :obj:`tuple`: A tuple signaling if the appointment has been added or not (based on ``max_appointments``). The structure looks as follows: - ``(True, signature)`` if the appointment has been accepted. - ``(False, None)`` otherwise. """ if len(self.appointments) < self.config.get("MAX_APPOINTMENTS"): uuid = uuid4().hex self.appointments[uuid] = {"locator": appointment.locator, "end_time": appointment.end_time} if appointment.locator in self.locator_uuid_map: self.locator_uuid_map[appointment.locator].append(uuid) else: self.locator_uuid_map[appointment.locator] = [uuid] self.db_manager.store_watcher_appointment(uuid, appointment.to_json()) self.db_manager.create_append_locator_map(appointment.locator, uuid) appointment_added = True signature = Cryptographer.sign(appointment.serialize(), self.signing_key) logger.info("New appointment accepted", locator=appointment.locator) else: appointment_added = False signature = None logger.info("Maximum appointments reached, appointment rejected", locator=appointment.locator) return appointment_added, signature def do_watch(self): """ Monitors the blockchain whilst there are pending appointments. This is the main method of the :obj:`Watcher` and the one in charge to pass appointments to the :obj:`Responder ` upon detecting a breach. """ while True: block_hash = self.block_queue.get() block = BlockProcessor.get_block(block_hash) logger.info("New block received", block_hash=block_hash, prev_block_hash=block.get("previousblockhash")) if len(self.appointments) > 0 and block is not None: txids = block.get("tx") logger.info("List of transactions", txids=txids) expired_appointments = [ uuid for uuid, appointment_data in self.appointments.items() if block["height"] > appointment_data.get("end_time") + self.config.get("EXPIRY_DELTA") ] Cleaner.delete_expired_appointments( expired_appointments, self.appointments, self.locator_uuid_map, self.db_manager ) valid_breaches, invalid_breaches = self.filter_valid_breaches(self.get_breaches(txids)) triggered_flags = [] appointments_to_delete = [] for uuid, breach in valid_breaches.items(): logger.info( "Notifying responder and deleting appointment", penalty_txid=breach["penalty_txid"], locator=breach["locator"], uuid=uuid, ) receipt = self.responder.handle_breach( uuid, breach["locator"], breach["dispute_txid"], breach["penalty_txid"], breach["penalty_rawtx"], self.appointments[uuid].get("end_time"), block_hash, ) # FIXME: Only necessary because of the triggered appointment approach. Fix if it changes. if receipt.delivered: Cleaner.delete_appointment_from_memory(uuid, self.appointments, self.locator_uuid_map) triggered_flags.append(uuid) else: appointments_to_delete.append(uuid) # Appointments are only flagged as triggered if they are delivered, otherwise they are just deleted. appointments_to_delete.extend(invalid_breaches) self.db_manager.batch_create_triggered_appointment_flag(triggered_flags) Cleaner.delete_completed_appointments( appointments_to_delete, self.appointments, self.locator_uuid_map, self.db_manager ) if len(self.appointments) is 0: logger.info("No more pending appointments") # Register the last processed block for the watcher self.db_manager.store_last_block_hash_watcher(block_hash) self.block_queue.task_done() def get_breaches(self, txids): """ Gets a list of channel breaches given the list of transaction ids. Args: txids (:obj:`list`): the list of transaction ids included in the last received block. Returns: :obj:`dict`: A dictionary (``locator:txid``) with all the breaches found. An empty dictionary if none are found. """ potential_locators = {compute_locator(txid): txid for txid in txids} # Check is any of the tx_ids in the received block is an actual match intersection = set(self.locator_uuid_map.keys()).intersection(potential_locators.keys()) breaches = {locator: potential_locators[locator] for locator in intersection} if len(breaches) > 0: logger.info("List of breaches", breaches=breaches) else: logger.info("No breaches found") return breaches def filter_valid_breaches(self, breaches): """ Filters what of the found breaches contain valid transaction data. The :obj:`Watcher` cannot if a given :obj:`EncryptedBlob ` contains a valid transaction until a breach if seen. Blobs that contain arbitrary data are dropped and not sent to the :obj:`Responder `. Args: breaches (:obj:`dict`): a dictionary containing channel breaches (``locator:txid``). Returns: :obj:`dict`: A dictionary containing all the breaches flagged either as valid or invalid. The structure is as follows: ``{locator, dispute_txid, penalty_txid, penalty_rawtx, valid_breach}`` """ valid_breaches = {} invalid_breaches = [] # A cache of the already decrypted blobs so replicate decryption can be avoided decrypted_blobs = {} for locator, dispute_txid in breaches.items(): for uuid in self.locator_uuid_map[locator]: appointment = Appointment.from_dict(self.db_manager.load_watcher_appointment(uuid)) if appointment.encrypted_blob.data in decrypted_blobs: penalty_tx, penalty_rawtx = decrypted_blobs[appointment.encrypted_blob.data] else: try: penalty_rawtx = Cryptographer.decrypt(appointment.encrypted_blob, dispute_txid) except ValueError: penalty_rawtx = None penalty_tx = BlockProcessor.decode_raw_transaction(penalty_rawtx) decrypted_blobs[appointment.encrypted_blob.data] = (penalty_tx, penalty_rawtx) if penalty_tx is not None: valid_breaches[uuid] = { "locator": locator, "dispute_txid": dispute_txid, "penalty_txid": penalty_tx.get("txid"), "penalty_rawtx": penalty_rawtx, } logger.info( "Breach found for locator", locator=locator, uuid=uuid, penalty_txid=penalty_tx.get("txid") ) else: invalid_breaches.append(uuid) return valid_breaches, invalid_breaches