from binascii import hexlify, unhexlify from queue import Queue from threading import Thread from pisa import logging, bitcoin_cli from pisa.responder import Responder from pisa.utils.zmq_subscriber import ZMQHandler from pisa.utils.auth_proxy import JSONRPCException from hashlib import sha256 from uuid import uuid4 from pisa.conf import MAX_APPOINTMENTS, EXPIRY_DELTA class Watcher: def __init__(self, max_appointments=MAX_APPOINTMENTS): self.appointments = dict() self.locator_uuid_map = dict() self.block_queue = None self.asleep = True self.max_appointments = max_appointments self.zmq_subscriber = None self.responder = Responder() def add_appointment(self, appointment): # Rationale: # The Watcher will analyze every received block looking for appointment matches. If there is no work # to do the watcher can go sleep (if appointments = {} then asleep = True) otherwise for every received block # the watcher will get the list of transactions and compare it with the list of appointments. # If the watcher is awake, every new appointment will just be added to the appointment list until # max_appointments is reached. if len(self.appointments) < self.max_appointments: # Appointments are identified by the locator: the sha256 of commitment txid (H(tx_id)). # Two different nodes may ask for appointments using the same commitment txid, what will result in a # collision in our appointments structure (and may be an attack surface). In order to avoid such collisions # we will identify every appointment with a uuid uuid = uuid4().hex self.appointments[uuid] = appointment if appointment.locator in self.locator_uuid_map: self.locator_uuid_map[appointment.locator].append(uuid) else: self.locator_uuid_map[appointment.locator] = [uuid] if self.asleep: self.asleep = False self.block_queue = Queue() zmq_thread = Thread(target=self.do_subscribe, args=[self.block_queue]) watcher = Thread(target=self.do_watch) zmq_thread.start() watcher.start() logging.info("[Watcher] waking up!") appointment_added = True logging.info('[Watcher] new appointment accepted (locator = {})'.format(appointment.locator)) else: appointment_added = False logging.info('[Watcher] maximum appointments reached, appointment rejected (locator = {})'.format( appointment.locator)) return appointment_added def do_subscribe(self, block_queue): self.zmq_subscriber = ZMQHandler(parent='Watcher') self.zmq_subscriber.handle(block_queue) def do_watch(self): while len(self.appointments) > 0: block_hash = self.block_queue.get() try: block = bitcoin_cli.getblock(block_hash) txids = block.get('tx') logging.info("[Watcher] new block received {}".format(block_hash)) logging.info("[Watcher] list of transactions: {}".format(txids)) self.delete_expired_appointment(block) potential_locators = {sha256(unhexlify(txid)).hexdigest(): txid for txid in txids} # Check is any of the tx_ids in the received block is an actual match # Get the locators that are both in the map and in the potential locators dict. intersection = set(self.locator_uuid_map.keys()).intersection(potential_locators.keys()) potential_matches = {locator: potential_locators[locator] for locator in intersection} if len(potential_matches) > 0: logging.info("[Watcher] list of potential matches: {}".format(potential_matches)) else: logging.info("[Watcher] no potential matches found") matches = self.check_potential_matches(potential_matches) for locator, uuid, dispute_txid, justice_txid, justice_rawtx in matches: logging.info("[Watcher] notifying responder about {} and deleting appointment {} (uuid: {})" .format(justice_txid, locator, uuid)) self.responder.add_response(uuid, dispute_txid, justice_txid, justice_rawtx, self.appointments[uuid].end_time) # Delete the appointment self.appointments.pop(uuid) # If there was only one appointment that matches the locator we can delete the whole list if len(self.locator_uuid_map[locator]) == 1: # ToDo: #9-add-data-persistency self.locator_uuid_map.pop(locator) else: # Otherwise we just delete the appointment that matches locator:appointment_pos # ToDo: #9-add-data-persistency self.locator_uuid_map[locator].remove(uuid) except JSONRPCException as e: logging.error("[Watcher] couldn't get block from bitcoind. Error code {}".format(e)) # Go back to sleep if there are no more appointments self.asleep = True self.zmq_subscriber.terminate = True logging.error("[Watcher] no more pending appointments, going back to sleep") def delete_expired_appointment(self, block): to_delete = [uuid for uuid, appointment in self.appointments.items() if block["height"] > appointment.end_time + EXPIRY_DELTA] for uuid in to_delete: # ToDo: #9-add-data-persistency locator = self.appointments[uuid].locator self.appointments.pop(uuid) if len(self.locator_uuid_map[locator]) == 1: self.locator_uuid_map.pop(locator) else: self.locator_uuid_map[locator].remove(uuid) logging.info("[Watcher] end time reached with no match! Deleting appointment {} (uuid: {})".format(locator, uuid)) def check_potential_matches(self, potential_matches): matches = [] for locator, dispute_txid in potential_matches.items(): for uuid in self.locator_uuid_map[locator]: try: # ToDo: #20-test-tx-decrypting-edge-cases justice_rawtx = self.appointments[uuid].encrypted_blob.decrypt(unhexlify(dispute_txid)) justice_rawtx = hexlify(justice_rawtx).decode() justice_txid = bitcoin_cli.decoderawtransaction(justice_rawtx).get('txid') matches.append((locator, uuid, dispute_txid, justice_txid, justice_rawtx)) logging.info("[Watcher] match found for locator {} (uuid: {}): {}".format(locator, uuid, justice_txid)) except JSONRPCException as e: # Tx decode failed returns error code -22, maybe we should be more strict here. Leaving it simple # for the POC logging.error("[Watcher] can't build transaction from decoded data. Error code {}".format(e)) return matches