text: #!/usr/bin/env python
  #
  # Electrum - lightweight Bitcoin client
  # Copyright (C) 2014 Thomas Voegtlin
  #
  # Permission is hereby granted, free of charge, to any person
  # obtaining a copy of this software and associated documentation files
  # (the "Software"), to deal in the Software without restriction,
  # including without limitation the rights to use, copy, modify, merge,
  # publish, distribute, sublicense, and/or sell copies of the Software,
  # and to permit persons to whom the Software is furnished to do so,
  # subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be
  # included in all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  # EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  # MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  # NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  # BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  # ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  # SOFTWARE.
  
  import time
  from xmlrpc.client import ServerProxy
  from typing import TYPE_CHECKING, Union, List, Tuple
  
  from PyQt5.QtCore import QObject, pyqtSignal
  from PyQt5.QtWidgets import QPushButton
  
  from electrum_ltc import util, keystore, ecc, crypto
  from electrum_ltc import transaction
  from electrum_ltc.transaction import Transaction, PartialTransaction, tx_from_any
  from electrum_ltc.bip32 import BIP32Node
  from electrum_ltc.plugin import BasePlugin, hook
  from electrum_ltc.i18n import _
  from electrum_ltc.wallet import Multisig_Wallet
  from electrum_ltc.util import bh2u, bfh
  
  from electrum_ltc.gui.qt.transaction_dialog import show_transaction, TxDialog
  from electrum_ltc.gui.qt.util import WaitingDialog
  
  if TYPE_CHECKING:
      from electrum_ltc.gui.qt.main_window import ElectrumWindow
  
  
  server = ServerProxy('https://cosigner.electrum.org/', allow_none=True)
  
  
  class Listener(util.DaemonThread):
  
      def __init__(self, parent):
          util.DaemonThread.__init__(self)
          self.daemon = True
          self.parent = parent
          self.received = set()
          self.keyhashes = []
  
      def set_keyhashes(self, keyhashes):
          self.keyhashes = keyhashes
  
      def clear(self, keyhash):
          server.delete(keyhash)
          self.received.remove(keyhash)
  
      def run(self):
          while self.running:
              if not self.keyhashes:
                  time.sleep(2)
                  continue
              for keyhash in self.keyhashes:
                  if keyhash in self.received:
                      continue
                  try:
                      message = server.get(keyhash)
                  except Exception as e:
                      self.logger.info("cannot contact cosigner pool")
                      time.sleep(30)
                      continue
                  if message:
                      self.received.add(keyhash)
                      self.logger.info(f"received message for {keyhash}")
                      self.parent.obj.cosigner_receive_signal.emit(
                          keyhash, message)
              # poll every 30 seconds
              time.sleep(30)
  
  
  class QReceiveSignalObject(QObject):
      cosigner_receive_signal = pyqtSignal(object, object)
  
  
  class Plugin(BasePlugin):
  
      def __init__(self, parent, config, name):
          BasePlugin.__init__(self, parent, config, name)
          self.listener = None
          self.obj = QReceiveSignalObject()
          self.obj.cosigner_receive_signal.connect(self.on_receive)
          self.keys = []  # type: List[Tuple[str, str, ElectrumWindow]]
          self.cosigner_list = []  # type: List[Tuple[ElectrumWindow, str, bytes, str]]
  
      @hook
      def init_qt(self, gui):
          for window in gui.windows:
              self.on_new_window(window)
  
      @hook
      def on_new_window(self, window):
          self.update(window)
  
      @hook
      def on_close_window(self, window):
          self.update(window)
  
      def is_available(self):
          return True
  
      def update(self, window: 'ElectrumWindow'):
          wallet = window.wallet
          if type(wallet) != Multisig_Wallet:
              return
          assert isinstance(wallet, Multisig_Wallet)  # only here for type-hints in IDE
          if self.listener is None:
              self.logger.info("starting listener")
              self.listener = Listener(self)
              self.listener.start()
          elif self.listener:
              self.logger.info("shutting down listener")
              self.listener.stop()
              self.listener = None
          self.keys = []
          self.cosigner_list = []
          for key, keystore in wallet.keystores.items():
              xpub = keystore.get_master_public_key()  # type: str
              pubkey = BIP32Node.from_xkey(xpub).eckey.get_public_key_bytes(compressed=True)
              _hash = bh2u(crypto.sha256d(pubkey))
              if not keystore.is_watching_only():
                  self.keys.append((key, _hash, window))
              else:
                  self.cosigner_list.append((window, xpub, pubkey, _hash))
          if self.listener:
              self.listener.set_keyhashes([t[1] for t in self.keys])
  
      @hook
      def transaction_dialog(self, d: 'TxDialog'):
          d.cosigner_send_button = b = QPushButton(_("Send to cosigner"))
          b.clicked.connect(lambda: self.do_send(d.tx))
          d.buttons.insert(0, b)
          b.setVisible(False)
  
      @hook
      def transaction_dialog_update(self, d: 'TxDialog'):
          if not d.finalized or d.tx.is_complete() or d.wallet.can_sign(d.tx):
              d.cosigner_send_button.setVisible(False)
              return
          for window, xpub, K, _hash in self.cosigner_list:
              if window.wallet == d.wallet and self.cosigner_can_sign(d.tx, xpub):
                  d.cosigner_send_button.setVisible(True)
                  break
          else:
              d.cosigner_send_button.setVisible(False)
  
      def cosigner_can_sign(self, tx: Transaction, cosigner_xpub: str) -> bool:
          # TODO implement this properly:
          #      should return True iff cosigner (with given xpub) can sign and has not yet signed.
          #      note that tx could also be unrelated from wallet?... (not ismine inputs)
          return True
  
      def do_send(self, tx: Union[Transaction, PartialTransaction]):
          def on_success(result):
              window.show_message(_("Your transaction was sent to the cosigning pool.") + '\n' +
                                  _("Open your cosigner wallet to retrieve it."))
          def on_failure(exc_info):
              e = exc_info[1]
              try: self.logger.error("on_failure", exc_info=exc_info)
              except OSError: pass
              window.show_error(_("Failed to send transaction to cosigning pool") + ':\n' + repr(e))
  
          for window, xpub, K, _hash in self.cosigner_list:
              if not self.cosigner_can_sign(tx, xpub):
                  continue
              # construct message
              raw_tx_bytes = tx.serialize_as_bytes()
              public_key = ecc.ECPubkey(K)
              message = public_key.encrypt_message(raw_tx_bytes).decode('ascii')
              # send message
              task = lambda: server.put(_hash, message)
              msg = _('Sending transaction to cosigning pool...')
              WaitingDialog(window, msg, task, on_success, on_failure)
  
      def on_receive(self, keyhash, message):
          self.logger.info(f"signal arrived for {keyhash}")
          for key, _hash, window in self.keys:
              if _hash == keyhash:
                  break
          else:
              self.logger.info("keyhash not found")
              return
  
          wallet = window.wallet
          if isinstance(wallet.keystore, keystore.Hardware_KeyStore):
              window.show_warning(_('An encrypted transaction was retrieved from cosigning pool.') + '\n' +
                                  _('However, hardware wallets do not support message decryption, '
                                    'which makes them not compatible with the current design of cosigner pool.'))
              return
          elif wallet.has_keystore_encryption():
              password = window.password_dialog(_('An encrypted transaction was retrieved from cosigning pool.') + '\n' +
                                                _('Please enter your password to decrypt it.'))
              if not password:
                  return
          else:
              password = None
              if not window.question(_("An encrypted transaction was retrieved from cosigning pool.") + '\n' +
                                     _("Do you want to open it now?")):
                  return
  
          xprv = wallet.keystore.get_master_private_key(password)
          if not xprv:
              return
          try:
              privkey = BIP32Node.from_xkey(xprv).eckey
              message = privkey.decrypt_message(message)
          except Exception as e:
              self.logger.exception('')
              window.show_error(_('Error decrypting message') + ':\n' + repr(e))
              return
  
          self.listener.clear(keyhash)
          tx = tx_from_any(message)
          show_transaction(tx, parent=window, prompt_if_unsaved=True)
  