text: # Electrum - Lightweight Bitcoin Client
  # Copyright (c) 2011-2016 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
  import queue
  import os
  import random
  import re
  from collections import defaultdict
  import threading
  import socket
  import json
  import sys
  import ipaddress
  import asyncio
  from typing import NamedTuple, Optional, Sequence, List, Dict, Tuple
  import traceback
  
  import dns
  import dns.resolver
  import aiorpcx
  from aiorpcx import TaskGroup
  from aiohttp import ClientResponse
  
  from . import util
  from .util import (log_exceptions, ignore_exceptions,
                     bfh, SilentTaskGroup, make_aiohttp_session, send_exception_to_crash_reporter,
                     is_hash256_str, is_non_negative_integer)
  
  from .bitcoin import COIN
  from . import constants
  from . import blockchain
  from . import bitcoin
  from .blockchain import Blockchain, HEADER_SIZE
  from .interface import (Interface, serialize_server, deserialize_server,
                          RequestTimedOut, NetworkTimeout, BUCKET_NAME_OF_ONION_SERVERS)
  from .version import PROTOCOL_VERSION
  from .simple_config import SimpleConfig
  from .i18n import _
  from .logging import get_logger, Logger
  
  
  _logger = get_logger(__name__)
  
  
  NODES_RETRY_INTERVAL = 60
  SERVER_RETRY_INTERVAL = 10
  NUM_TARGET_CONNECTED_SERVERS = 10
  NUM_RECENT_SERVERS = 20
  
  
  def parse_servers(result: Sequence[Tuple[str, str, List[str]]]) -> Dict[str, dict]:
      """ parse servers list into dict format"""
      servers = {}
      for item in result:
          host = item[1]
          out = {}
          version = None
          pruning_level = '-'
          if len(item) > 2:
              for v in item[2]:
                  if re.match(r"[st]\d*", v):
                      protocol, port = v[0], v[1:]
                      if port == '': port = constants.net.DEFAULT_PORTS[protocol]
                      out[protocol] = port
                  elif re.match("v(.?)+", v):
                      version = v[1:]
                  elif re.match(r"p\d*", v):
                      pruning_level = v[1:]
                  if pruning_level == '': pruning_level = '0'
          if out:
              out['pruning'] = pruning_level
              out['version'] = version
              servers[host] = out
      return servers
  
  
  def filter_version(servers):
      def is_recent(version):
          try:
              return util.versiontuple(version) >= util.versiontuple(PROTOCOL_VERSION)
          except Exception as e:
              return False
      return {k: v for k, v in servers.items() if is_recent(v.get('version'))}
  
  
  def filter_noonion(servers):
      return {k: v for k, v in servers.items() if not k.endswith('.onion')}
  
  
  def filter_protocol(hostmap, protocol='t'):
      '''Filters the hostmap for those implementing protocol.
      The result is a list in serialized form.'''
      eligible = []
      for host, portmap in hostmap.items():
          port = portmap.get(protocol)
          if port:
              eligible.append(serialize_server(host, port, protocol))
      return eligible
  
  
  def pick_random_server(hostmap=None, protocol='t', exclude_set=None):
      if hostmap is None:
          hostmap = constants.net.DEFAULT_SERVERS
      if exclude_set is None:
          exclude_set = set()
      eligible = list(set(filter_protocol(hostmap, protocol)) - exclude_set)
      return random.choice(eligible) if eligible else None
  
  
  class NetworkParameters(NamedTuple):
      host: str
      port: str
      protocol: str
      proxy: Optional[dict]
      auto_connect: bool
      oneserver: bool = False
  
  
  proxy_modes = ['socks4', 'socks5']
  
  
  def serialize_proxy(p):
      if not isinstance(p, dict):
          return None
      return ':'.join([p.get('mode'), p.get('host'), p.get('port'),
                       p.get('user', ''), p.get('password', '')])
  
  
  def deserialize_proxy(s: str) -> Optional[dict]:
      if not isinstance(s, str):
          return None
      if s.lower() == 'none':
          return None
      proxy = { "mode":"socks5", "host":"localhost" }
      # FIXME raw IPv6 address fails here
      args = s.split(':')
      n = 0
      if proxy_modes.count(args[n]) == 1:
          proxy["mode"] = args[n]
          n += 1
      if len(args) > n:
          proxy["host"] = args[n]
          n += 1
      if len(args) > n:
          proxy["port"] = args[n]
          n += 1
      else:
          proxy["port"] = "8080" if proxy["mode"] == "http" else "1080"
      if len(args) > n:
          proxy["user"] = args[n]
          n += 1
      if len(args) > n:
          proxy["password"] = args[n]
      return proxy
  
  
  class BestEffortRequestFailed(Exception): pass
  
  
  class TxBroadcastError(Exception):
      def get_message_for_gui(self):
          raise NotImplementedError()
  
  
  class TxBroadcastHashMismatch(TxBroadcastError):
      def get_message_for_gui(self):
          return "{}\n{}\n\n{}" \
              .format(_("The server returned an unexpected transaction ID when broadcasting the transaction."),
                      _("Consider trying to connect to a different server, or updating Electrum."),
                      str(self))
  
  
  class TxBroadcastServerReturnedError(TxBroadcastError):
      def get_message_for_gui(self):
          return "{}\n{}\n\n{}" \
              .format(_("The server returned an error when broadcasting the transaction."),
                      _("Consider trying to connect to a different server, or updating Electrum."),
                      str(self))
  
  
  class TxBroadcastUnknownError(TxBroadcastError):
      def get_message_for_gui(self):
          return "{}\n{}" \
              .format(_("Unknown error when broadcasting the transaction."),
                      _("Consider trying to connect to a different server, or updating Electrum."))
  
  
  class UntrustedServerReturnedError(Exception):
      def __init__(self, *, original_exception):
          self.original_exception = original_exception
  
      def __str__(self):
          return _("The server returned an error.")
  
      def __repr__(self):
          return f"<UntrustedServerReturnedError original_exception: {repr(self.original_exception)}>"
  
  
  INSTANCE = None
  
  
  class Network(Logger):
      """The Network class manages a set of connections to remote electrum
      servers, each connected socket is handled by an Interface() object.
      """
  
      LOGGING_SHORTCUT = 'n'
  
      def __init__(self, config: SimpleConfig=None):
          global INSTANCE
          INSTANCE = self
  
          Logger.__init__(self)
  
          self.asyncio_loop = asyncio.get_event_loop()
          assert self.asyncio_loop.is_running(), "event loop not running"
          self._loop_thread = None  # type: threading.Thread  # set by caller; only used for sanity checks
  
          if config is None:
              config = {}  # Do not use mutables as default values!
          self.config = SimpleConfig(config) if isinstance(config, dict) else config  # type: SimpleConfig
          blockchain.read_blockchains(self.config)
          self.logger.info(f"blockchains {list(map(lambda b: b.forkpoint, blockchain.blockchains.values()))}")
          self._blockchain_preferred_block = self.config.get('blockchain_preferred_block', None)  # type: Optional[Dict]
          self._blockchain = blockchain.get_best_chain()
          # Server for addresses and transactions
          self.default_server = self.config.get('server', None)
          # Sanitize default server
          if self.default_server:
              try:
                  deserialize_server(self.default_server)
              except:
                  self.logger.warning('failed to parse server-string; falling back to random.')
                  self.default_server = None
          if not self.default_server:
              self.default_server = pick_random_server()
  
          self.main_taskgroup = None  # type: TaskGroup
  
          # locks
          self.restart_lock = asyncio.Lock()
          self.bhi_lock = asyncio.Lock()
          self.callback_lock = threading.Lock()
          self.recent_servers_lock = threading.RLock()       # <- re-entrant
          self.interfaces_lock = threading.Lock()            # for mutating/iterating self.interfaces
  
          self.server_peers = {}  # returned by interface (servers that the main interface knows about)
          self.recent_servers = self._read_recent_servers()  # note: needs self.recent_servers_lock
  
          self.banner = ''
          self.donation_address = ''
          self.relay_fee = None  # type: Optional[int]
          # callbacks set by the GUI
          self.callbacks = defaultdict(list)      # note: needs self.callback_lock
  
          dir_path = os.path.join(self.config.path, 'certs')
          util.make_dir(dir_path)
  
          # retry times
          self.server_retry_time = time.time()
          self.nodes_retry_time = time.time()
          # the main server we are currently communicating with
          self.interface = None  # type: Interface
          # set of servers we have an ongoing connection with
          self.interfaces = {}  # type: Dict[str, Interface]
          self.auto_connect = self.config.get('auto_connect', True)
          self.connecting = set()
          self.server_queue = None
          self.proxy = None
  
          # Dump network messages (all interfaces).  Set at runtime from the console.
          self.debug = False
  
          self._set_status('disconnected')
  
      def run_from_another_thread(self, coro):
          assert self._loop_thread != threading.current_thread(), 'must not be called from network thread'
          fut = asyncio.run_coroutine_threadsafe(coro, self.asyncio_loop)
          return fut.result()
  
      @staticmethod
      def get_instance() -> Optional["Network"]:
          return INSTANCE
  
      def with_recent_servers_lock(func):
          def func_wrapper(self, *args, **kwargs):
              with self.recent_servers_lock:
                  return func(self, *args, **kwargs)
          return func_wrapper
  
      def register_callback(self, callback, events):
          with self.callback_lock:
              for event in events:
                  self.callbacks[event].append(callback)
  
      def unregister_callback(self, callback):
          with self.callback_lock:
              for callbacks in self.callbacks.values():
                  if callback in callbacks:
                      callbacks.remove(callback)
  
      def trigger_callback(self, event, *args):
          with self.callback_lock:
              callbacks = self.callbacks[event][:]
          for callback in callbacks:
              # FIXME: if callback throws, we will lose the traceback
              if asyncio.iscoroutinefunction(callback):
                  asyncio.run_coroutine_threadsafe(callback(event, *args), self.asyncio_loop)
              else:
                  self.asyncio_loop.call_soon_threadsafe(callback, event, *args)
  
      def _read_recent_servers(self):
          if not self.config.path:
              return []
          path = os.path.join(self.config.path, "recent_servers")
          try:
              with open(path, "r", encoding='utf-8') as f:
                  data = f.read()
                  return json.loads(data)
          except:
              return []
  
      @with_recent_servers_lock
      def _save_recent_servers(self):
          if not self.config.path:
              return
          path = os.path.join(self.config.path, "recent_servers")
          s = json.dumps(self.recent_servers, indent=4, sort_keys=True)
          try:
              with open(path, "w", encoding='utf-8') as f:
                  f.write(s)
          except:
              pass
  
      def get_server_height(self):
          interface = self.interface
          return interface.tip if interface else 0
  
      async def _server_is_lagging(self):
          sh = self.get_server_height()
          if not sh:
              self.logger.info('no height for main interface')
              return True
          lh = self.get_local_height()
          result = (lh - sh) > 1
          if result:
              self.logger.info(f'{self.default_server} is lagging ({sh} vs {lh})')
          return result
  
      def _set_status(self, status):
          self.connection_status = status
          self.notify('status')
  
      def is_connected(self):
          interface = self.interface
          return interface is not None and interface.ready.done()
  
      def is_connecting(self):
          return self.connection_status == 'connecting'
  
      async def _request_server_info(self, interface):
          await interface.ready
          session = interface.session
  
          async def get_banner():
              self.banner = await session.send_request('server.banner')
              self.notify('banner')
          async def get_donation_address():
              addr = await session.send_request('server.donation_address')
              if not bitcoin.is_address(addr):
                  if addr:  # ignore empty string
                      self.logger.info(f"invalid donation address from server: {repr(addr)}")
                  addr = ''
              self.donation_address = addr
          async def get_server_peers():
              server_peers = await session.send_request('server.peers.subscribe')
              random.shuffle(server_peers)
              max_accepted_peers = len(constants.net.DEFAULT_SERVERS) + NUM_RECENT_SERVERS
              server_peers = server_peers[:max_accepted_peers]
              self.server_peers = parse_servers(server_peers)
              self.notify('servers')
          async def get_relay_fee():
              relayfee = await session.send_request('blockchain.relayfee')
              if relayfee is None:
                  self.relay_fee = None
              else:
                  relayfee = int(relayfee * COIN)
                  self.relay_fee = max(0, relayfee)
  
          async with TaskGroup() as group:
              await group.spawn(get_banner)
              await group.spawn(get_donation_address)
              await group.spawn(get_server_peers)
              await group.spawn(get_relay_fee)
              await group.spawn(self._request_fee_estimates(interface))
  
      async def _request_fee_estimates(self, interface):
          session = interface.session
          from .simple_config import FEE_ETA_TARGETS
          self.config.requested_fee_estimates()
          async with TaskGroup() as group:
              histogram_task = await group.spawn(session.send_request('mempool.get_fee_histogram'))
              fee_tasks = []
              for i in FEE_ETA_TARGETS:
                  fee_tasks.append((i, await group.spawn(session.send_request('blockchain.estimatefee', [i]))))
          self.config.mempool_fees = histogram = histogram_task.result()
          self.logger.info(f'fee_histogram {histogram}')
          self.notify('fee_histogram')
          fee_estimates_eta = {}
          for nblock_target, task in fee_tasks:
              fee = int(task.result() * COIN)
              fee_estimates_eta[nblock_target] = fee
              if fee < 0: continue
              self.config.update_fee_estimates(nblock_target, fee)
          self.logger.info(f'fee_estimates {fee_estimates_eta}')
          self.notify('fee')
  
      def get_status_value(self, key):
          if key == 'status':
              value = self.connection_status
          elif key == 'banner':
              value = self.banner
          elif key == 'fee':
              value = self.config.fee_estimates
          elif key == 'fee_histogram':
              value = self.config.mempool_fees
          elif key == 'servers':
              value = self.get_servers()
          else:
              raise Exception('unexpected trigger key {}'.format(key))
          return value
  
      def notify(self, key):
          if key in ['status', 'updated']:
              self.trigger_callback(key)
          else:
              self.trigger_callback(key, self.get_status_value(key))
  
      def get_parameters(self) -> NetworkParameters:
          host, port, protocol = deserialize_server(self.default_server)
          return NetworkParameters(host=host,
                                   port=port,
                                   protocol=protocol,
                                   proxy=self.proxy,
                                   auto_connect=self.auto_connect,
                                   oneserver=self.oneserver)
  
      def get_donation_address(self):
          if self.is_connected():
              return self.donation_address
  
      def get_interfaces(self) -> List[str]:
          """The list of servers for the connected interfaces."""
          with self.interfaces_lock:
              return list(self.interfaces)
  
      @with_recent_servers_lock
      def get_servers(self):
          # note: order of sources when adding servers here is crucial!
          # don't let "server_peers" overwrite anything,
          # otherwise main server can eclipse the client
          out = dict()
          # add servers received from main interface
          server_peers = self.server_peers
          if server_peers:
              out.update(filter_version(server_peers.copy()))
          # hardcoded servers
          out.update(constants.net.DEFAULT_SERVERS)
          # add recent servers
          for s in self.recent_servers:
              try:
                  host, port, protocol = deserialize_server(s)
              except:
                  continue
              if host in out:
                  out[host].update({protocol: port})
              else:
                  out[host] = {protocol: port}
          # potentially filter out some
          if self.config.get('noonion'):
              out = filter_noonion(out)
          return out
  
      def _start_interface(self, server: str):
          if server not in self.interfaces and server not in self.connecting:
              if server == self.default_server:
                  self.logger.info(f"connecting to {server} as new interface")
                  self._set_status('connecting')
              self.connecting.add(server)
              self.server_queue.put(server)
  
      def _start_random_interface(self):
          with self.interfaces_lock:
              exclude_set = self.disconnected_servers | set(self.interfaces) | self.connecting
          server = pick_random_server(self.get_servers(), self.protocol, exclude_set)
          if server:
              self._start_interface(server)
          return server
  
      def _set_proxy(self, proxy: Optional[dict]):
          self.proxy = proxy
          # Store these somewhere so we can un-monkey-patch
          if not hasattr(socket, "_getaddrinfo"):
              socket._getaddrinfo = socket.getaddrinfo
          if proxy:
              self.logger.info(f'setting proxy {proxy}')
              # prevent dns leaks, see http://stackoverflow.com/questions/13184205/dns-over-proxy
              socket.getaddrinfo = lambda *args: [(socket.AF_INET, socket.SOCK_STREAM, 6, '', (args[0], args[1]))]
          else:
              if sys.platform == 'win32':
                  # On Windows, socket.getaddrinfo takes a mutex, and might hold it for up to 10 seconds
                  # when dns-resolving. To speed it up drastically, we resolve dns ourselves, outside that lock.
                  # see #4421
                  socket.getaddrinfo = self._fast_getaddrinfo
              else:
                  socket.getaddrinfo = socket._getaddrinfo
          self.trigger_callback('proxy_set', self.proxy)
  
      @staticmethod
      def _fast_getaddrinfo(host, *args, **kwargs):
          def needs_dns_resolving(host):
              try:
                  ipaddress.ip_address(host)
                  return False  # already valid IP
              except ValueError:
                  pass  # not an IP
              if str(host) in ('localhost', 'localhost.',):
                  return False
              return True
          def resolve_with_dnspython(host):
              addrs = []
              # try IPv6
              try:
                  answers = dns.resolver.query(host, dns.rdatatype.AAAA)
                  addrs += [str(answer) for answer in answers]
              except dns.exception.DNSException as e:
                  pass
              except BaseException as e:
                  _logger.info(f'dnspython failed to resolve dns (AAAA) with error: {e}')
              # try IPv4
              try:
                  answers = dns.resolver.query(host, dns.rdatatype.A)
                  addrs += [str(answer) for answer in answers]
              except dns.exception.DNSException as e:
                  # dns failed for some reason, e.g. dns.resolver.NXDOMAIN this is normal.
                  # Simply report back failure; except if we already have some results.
                  if not addrs:
                      raise socket.gaierror(11001, 'getaddrinfo failed') from e
              except BaseException as e:
                  # Possibly internal error in dnspython :( see #4483
                  _logger.info(f'dnspython failed to resolve dns (A) with error: {e}')
              if addrs:
                  return addrs
              # Fall back to original socket.getaddrinfo to resolve dns.
              return [host]
          addrs = [host]
          if needs_dns_resolving(host):
              addrs = resolve_with_dnspython(host)
          list_of_list_of_socketinfos = [socket._getaddrinfo(addr, *args, **kwargs) for addr in addrs]
          list_of_socketinfos = [item for lst in list_of_list_of_socketinfos for item in lst]
          return list_of_socketinfos
  
      @log_exceptions
      async def set_parameters(self, net_params: NetworkParameters):
          proxy = net_params.proxy
          proxy_str = serialize_proxy(proxy)
          host, port, protocol = net_params.host, net_params.port, net_params.protocol
          server_str = serialize_server(host, port, protocol)
          # sanitize parameters
          try:
              deserialize_server(serialize_server(host, port, protocol))
              if proxy:
                  proxy_modes.index(proxy['mode']) + 1
                  int(proxy['port'])
          except:
              return
          self.config.set_key('auto_connect', net_params.auto_connect, False)
          self.config.set_key('oneserver', net_params.oneserver, False)
          self.config.set_key('proxy', proxy_str, False)
          self.config.set_key('server', server_str, True)
          # abort if changes were not allowed by config
          if self.config.get('server') != server_str \
                  or self.config.get('proxy') != proxy_str \
                  or self.config.get('oneserver') != net_params.oneserver:
              return
  
          async with self.restart_lock:
              self.auto_connect = net_params.auto_connect
              if self.proxy != proxy or self.protocol != protocol or self.oneserver != net_params.oneserver:
                  # Restart the network defaulting to the given server
                  await self._stop()
                  self.default_server = server_str
                  await self._start()
              elif self.default_server != server_str:
                  await self.switch_to_interface(server_str)
              else:
                  await self.switch_lagging_interface()
  
      def _set_oneserver(self, oneserver: bool):
          self.num_server = NUM_TARGET_CONNECTED_SERVERS if not oneserver else 0
          self.oneserver = bool(oneserver)
  
      async def _switch_to_random_interface(self):
          '''Switch to a random connected server other than the current one'''
          servers = self.get_interfaces()    # Those in connected state
          if self.default_server in servers:
              servers.remove(self.default_server)
          if servers:
              await self.switch_to_interface(random.choice(servers))
  
      async def switch_lagging_interface(self):
          '''If auto_connect and lagging, switch interface'''
          if self.auto_connect and await self._server_is_lagging():
              # switch to one that has the correct header (not height)
              best_header = self.blockchain().read_header(self.get_local_height())
              with self.interfaces_lock: interfaces = list(self.interfaces.values())
              filtered = list(filter(lambda iface: iface.tip_header == best_header, interfaces))
              if filtered:
                  chosen_iface = random.choice(filtered)
                  await self.switch_to_interface(chosen_iface.server)
  
      async def switch_unwanted_fork_interface(self):
          """If auto_connect and main interface is not on preferred fork,
          try to switch to preferred fork.
          """
          if not self.auto_connect or not self.interface:
              return
          with self.interfaces_lock: interfaces = list(self.interfaces.values())
          # try to switch to preferred fork
          if self._blockchain_preferred_block:
              pref_height = self._blockchain_preferred_block['height']
              pref_hash   = self._blockchain_preferred_block['hash']
              if self.interface.blockchain.check_hash(pref_height, pref_hash):
                  return  # already on preferred fork
              filtered = list(filter(lambda iface: iface.blockchain.check_hash(pref_height, pref_hash),
                                     interfaces))
              if filtered:
                  self.logger.info("switching to preferred fork")
                  chosen_iface = random.choice(filtered)
                  await self.switch_to_interface(chosen_iface.server)
                  return
              else:
                  self.logger.info("tried to switch to preferred fork but no interfaces are on it")
          # try to switch to best chain
          if self.blockchain().parent is None:
              return  # already on best chain
          filtered = list(filter(lambda iface: iface.blockchain.parent is None,
                                 interfaces))
          if filtered:
              self.logger.info("switching to best chain")
              chosen_iface = random.choice(filtered)
              await self.switch_to_interface(chosen_iface.server)
          else:
              # FIXME switch to best available?
              self.logger.info("tried to switch to best chain but no interfaces are on it")
  
      async def switch_to_interface(self, server: str):
          """Switch to server as our main interface. If no connection exists,
          queue interface to be started. The actual switch will
          happen when the interface becomes ready.
          """
          self.default_server = server
          old_interface = self.interface
          old_server = old_interface.server if old_interface else None
  
          # Stop any current interface in order to terminate subscriptions,
          # and to cancel tasks in interface.group.
          # However, for headers sub, give preference to this interface
          # over unknown ones, i.e. start it again right away.
          if old_server and old_server != server:
              await self._close_interface(old_interface)
              if len(self.interfaces) <= self.num_server:
                  self._start_interface(old_server)
  
          if server not in self.interfaces:
              self.interface = None
              self._start_interface(server)
              return
  
          i = self.interfaces[server]
          if old_interface != i:
              self.logger.info(f"switching to {server}")
              blockchain_updated = i.blockchain != self.blockchain()
              self.interface = i
              await i.group.spawn(self._request_server_info(i))
              self.trigger_callback('default_server_changed')
              self._set_status('connected')
              self.trigger_callback('network_updated')
              if blockchain_updated: self.trigger_callback('blockchain_updated')
  
      async def _close_interface(self, interface):
          if interface:
              with self.interfaces_lock:
                  if self.interfaces.get(interface.server) == interface:
                      self.interfaces.pop(interface.server)
              if interface.server == self.default_server:
                  self.interface = None
              await interface.close()
  
      @with_recent_servers_lock
      def _add_recent_server(self, server):
          # list is ordered
          if server in self.recent_servers:
              self.recent_servers.remove(server)
          self.recent_servers.insert(0, server)
          self.recent_servers = self.recent_servers[:NUM_RECENT_SERVERS]
          self._save_recent_servers()
  
      async def connection_down(self, interface: Interface):
          '''A connection to server either went down, or was never made.
          We distinguish by whether it is in self.interfaces.'''
          if not interface: return
          server = interface.server
          self.disconnected_servers.add(server)
          if server == self.default_server:
              self._set_status('disconnected')
          await self._close_interface(interface)
          self.trigger_callback('network_updated')
  
      def get_network_timeout_seconds(self, request_type=NetworkTimeout.Generic) -> int:
          if self.oneserver and not self.auto_connect:
              return request_type.MOST_RELAXED
          if self.proxy:
              return request_type.RELAXED
          return request_type.NORMAL
  
      @ignore_exceptions  # do not kill main_taskgroup
      @log_exceptions
      async def _run_new_interface(self, server):
          interface = Interface(self, server, self.proxy)
          # note: using longer timeouts here as DNS can sometimes be slow!
          timeout = self.get_network_timeout_seconds(NetworkTimeout.Generic)
          try:
              await asyncio.wait_for(interface.ready, timeout)
          except BaseException as e:
              self.logger.info(f"couldn't launch iface {server} -- {repr(e)}")
              await interface.close()
              return
          else:
              with self.interfaces_lock:
                  assert server not in self.interfaces
                  self.interfaces[server] = interface
          finally:
              try: self.connecting.remove(server)
              except KeyError: pass
  
          if server == self.default_server:
              await self.switch_to_interface(server)
  
          self._add_recent_server(server)
          self.trigger_callback('network_updated')
  
      def check_interface_against_healthy_spread_of_connected_servers(self, iface_to_check) -> bool:
          # main interface is exempt. this makes switching servers easier
          if iface_to_check.is_main_server():
              return True
          if not iface_to_check.bucket_based_on_ipaddress():
              return True
          # bucket connected interfaces
          with self.interfaces_lock:
              interfaces = list(self.interfaces.values())
          if iface_to_check in interfaces:
              interfaces.remove(iface_to_check)
          buckets = defaultdict(list)
          for iface in interfaces:
              buckets[iface.bucket_based_on_ipaddress()].append(iface)
          # check proposed server against buckets
          onion_servers = buckets[BUCKET_NAME_OF_ONION_SERVERS]
          if iface_to_check.is_tor():
              # keep number of onion servers below half of all connected servers
              if len(onion_servers) > NUM_TARGET_CONNECTED_SERVERS // 2:
                  return False
          else:
              bucket = iface_to_check.bucket_based_on_ipaddress()
              if len(buckets[bucket]) > 0:
                  return False
          return True
  
      async def _init_headers_file(self):
          b = blockchain.get_best_chain()
          filename = b.path()
          length = HEADER_SIZE * len(constants.net.CHECKPOINTS) * 2016
          if not os.path.exists(filename) or os.path.getsize(filename) < length:
              with open(filename, 'wb') as f:
                  if length > 0:
                      f.seek(length-1)
                      f.write(b'\x00')
              util.ensure_sparse_file(filename)
          with b.lock:
              b.update_size()
  
      def best_effort_reliable(func):
          async def make_reliable_wrapper(self, *args, **kwargs):
              for i in range(10):
                  iface = self.interface
                  # retry until there is a main interface
                  if not iface:
                      await asyncio.sleep(0.1)
                      continue  # try again
                  # wait for it to be usable
                  iface_ready = iface.ready
                  iface_disconnected = iface.got_disconnected
                  await asyncio.wait([iface_ready, iface_disconnected], return_when=asyncio.FIRST_COMPLETED)
                  if not iface_ready.done() or iface_ready.cancelled():
                      await asyncio.sleep(0.1)
                      continue  # try again
                  # try actual request
                  success_fut = asyncio.ensure_future(func(self, *args, **kwargs))
                  await asyncio.wait([success_fut, iface_disconnected], return_when=asyncio.FIRST_COMPLETED)
                  if success_fut.done() and not success_fut.cancelled():
                      if success_fut.exception():
                          try:
                              raise success_fut.exception()
                          except RequestTimedOut:
                              await iface.close()
                              await iface_disconnected
                              continue  # try again
                      return success_fut.result()
                  # otherwise; try again
              raise BestEffortRequestFailed('no interface to do request on... gave up.')
          return make_reliable_wrapper
  
      def catch_server_exceptions(func):
          async def wrapper(self, *args, **kwargs):
              try:
                  return await func(self, *args, **kwargs)
              except aiorpcx.jsonrpc.CodeMessageError as e:
                  raise UntrustedServerReturnedError(original_exception=e) from e
          return wrapper
  
      @best_effort_reliable
      @catch_server_exceptions
      async def get_merkle_for_transaction(self, tx_hash: str, tx_height: int) -> dict:
          if not is_hash256_str(tx_hash):
              raise Exception(f"{repr(tx_hash)} is not a txid")
          if not is_non_negative_integer(tx_height):
              raise Exception(f"{repr(tx_height)} is not a block height")
          return await self.interface.session.send_request('blockchain.transaction.get_merkle', [tx_hash, tx_height])
  
      @best_effort_reliable
      async def broadcast_transaction(self, tx, *, timeout=None) -> None:
          if timeout is None:
              timeout = self.get_network_timeout_seconds(NetworkTimeout.Urgent)
          try:
              out = await self.interface.session.send_request('blockchain.transaction.broadcast', [str(tx)], timeout=timeout)
              # note: both 'out' and exception messages are untrusted input from the server
          except (RequestTimedOut, asyncio.CancelledError, asyncio.TimeoutError):
              raise  # pass-through
          except aiorpcx.jsonrpc.CodeMessageError as e:
              self.logger.info(f"broadcast_transaction error [DO NOT TRUST THIS MESSAGE]: {repr(e)}")
              raise TxBroadcastServerReturnedError(self.sanitize_tx_broadcast_response(e.message)) from e
          except BaseException as e:  # intentional BaseException for sanity!
              self.logger.info(f"broadcast_transaction error2 [DO NOT TRUST THIS MESSAGE]: {repr(e)}")
              send_exception_to_crash_reporter(e)
              raise TxBroadcastUnknownError() from e
          if out != tx.txid():
              self.logger.info(f"unexpected txid for broadcast_transaction [DO NOT TRUST THIS MESSAGE]: {out} != {tx.txid()}")
              raise TxBroadcastHashMismatch(_("Server returned unexpected transaction ID."))
  
      @staticmethod
      def sanitize_tx_broadcast_response(server_msg) -> str:
          # Unfortunately, bitcoind and hence the Electrum protocol doesn't return a useful error code.
          # So, we use substring matching to grok the error message.
          # server_msg is untrusted input so it should not be shown to the user. see #4968
          server_msg = str(server_msg)
          server_msg = server_msg.replace("\n", r"\n")
          # https://github.com/bitcoin/bitcoin/blob/cd42553b1178a48a16017eff0b70669c84c3895c/src/policy/policy.cpp
          # grep "reason ="
          policy_error_messages = {
              r"version": _("Transaction uses non-standard version."),
              r"tx-size": _("The transaction was rejected because it is too large (in bytes)."),
              r"scriptsig-size": None,
              r"scriptsig-not-pushonly": None,
              r"scriptpubkey": None,
              r"bare-multisig": None,
              r"dust": _("Transaction could not be broadcast due to dust outputs."),
              r"multi-op-return": _("The transaction was rejected because it contains multiple OP_RETURN outputs."),
          }
          for substring in policy_error_messages:
              if substring in server_msg:
                  msg = policy_error_messages[substring]
                  return msg if msg else substring
          # https://github.com/bitcoin/bitcoin/blob/cd42553b1178a48a16017eff0b70669c84c3895c/src/script/script_error.cpp
          script_error_messages = {
              r"Script evaluated without error but finished with a false/empty top stack element",
              r"Script failed an OP_VERIFY operation",
              r"Script failed an OP_EQUALVERIFY operation",
              r"Script failed an OP_CHECKMULTISIGVERIFY operation",
              r"Script failed an OP_CHECKSIGVERIFY operation",
              r"Script failed an OP_NUMEQUALVERIFY operation",
              r"Script is too big",
              r"Push value size limit exceeded",
              r"Operation limit exceeded",
              r"Stack size limit exceeded",
              r"Signature count negative or greater than pubkey count",
              r"Pubkey count negative or limit exceeded",
              r"Opcode missing or not understood",
              r"Attempted to use a disabled opcode",
              r"Operation not valid with the current stack size",
              r"Operation not valid with the current altstack size",
              r"OP_RETURN was encountered",
              r"Invalid OP_IF construction",
              r"Negative locktime",
              r"Locktime requirement not satisfied",
              r"Signature hash type missing or not understood",
              r"Non-canonical DER signature",
              r"Data push larger than necessary",
              r"Only non-push operators allowed in signatures",
              r"Non-canonical signature: S value is unnecessarily high",
              r"Dummy CHECKMULTISIG argument must be zero",
              r"OP_IF/NOTIF argument must be minimal",
              r"Signature must be zero for failed CHECK(MULTI)SIG operation",
              r"NOPx reserved for soft-fork upgrades",
              r"Witness version reserved for soft-fork upgrades",
              r"Public key is neither compressed or uncompressed",
              r"Extra items left on stack after execution",
              r"Witness program has incorrect length",
              r"Witness program was passed an empty witness",
              r"Witness program hash mismatch",
              r"Witness requires empty scriptSig",
              r"Witness requires only-redeemscript scriptSig",
              r"Witness provided for non-witness script",
              r"Using non-compressed keys in segwit",
              r"Using OP_CODESEPARATOR in non-witness script",
              r"Signature is found in scriptCode",
          }
          for substring in script_error_messages:
              if substring in server_msg:
                  return substring
          # https://github.com/bitcoin/bitcoin/blob/cd42553b1178a48a16017eff0b70669c84c3895c/src/validation.cpp
          # grep "REJECT_"
          # should come after script_error.cpp (due to e.g. non-mandatory-script-verify-flag)
          validation_error_messages = {
              r"coinbase",
              r"tx-size-small",
              r"non-final",
              r"txn-already-in-mempool",
              r"txn-mempool-conflict",
              r"txn-already-known",
              r"non-BIP68-final",
              r"bad-txns-nonstandard-inputs",
              r"bad-witness-nonstandard",
              r"bad-txns-too-many-sigops",
              r"mempool min fee not met",
              r"min relay fee not met",
              r"absurdly-high-fee",
              r"too-long-mempool-chain",
              r"bad-txns-spends-conflicting-tx",
              r"insufficient fee",
              r"too many potential replacements",
              r"replacement-adds-unconfirmed",
              r"mempool full",
              r"non-mandatory-script-verify-flag",
              r"mandatory-script-verify-flag-failed",
          }
          for substring in validation_error_messages:
              if substring in server_msg:
                  return substring
          # https://github.com/bitcoin/bitcoin/blob/cd42553b1178a48a16017eff0b70669c84c3895c/src/rpc/rawtransaction.cpp
          # grep "RPC_TRANSACTION"
          # grep "RPC_DESERIALIZATION_ERROR"
          # https://github.com/bitcoin/bitcoin/blob/d7d7d315060620446bd363ca50f95f79d3260db7/src/util/error.cpp
          rawtransaction_error_messages = {
              r"Missing inputs",
              r"transaction already in block chain",
              r"Transaction already in block chain",
              r"TX decode failed",
              r"Peer-to-peer functionality missing or disabled",
              r"Transaction rejected by AcceptToMemoryPool",
              r"AcceptToMemoryPool failed",
          }
          for substring in rawtransaction_error_messages:
              if substring in server_msg:
                  return substring
          # https://github.com/bitcoin/bitcoin/blob/cd42553b1178a48a16017eff0b70669c84c3895c/src/consensus/tx_verify.cpp
          # grep "REJECT_"
          tx_verify_error_messages = {
              r"bad-txns-vin-empty",
              r"bad-txns-vout-empty",
              r"bad-txns-oversize",
              r"bad-txns-vout-negative",
              r"bad-txns-vout-toolarge",
              r"bad-txns-txouttotal-toolarge",
              r"bad-txns-inputs-duplicate",
              r"bad-cb-length",
              r"bad-txns-prevout-null",
              r"bad-txns-inputs-missingorspent",
              r"bad-txns-premature-spend-of-coinbase",
              r"bad-txns-inputvalues-outofrange",
              r"bad-txns-in-belowout",
              r"bad-txns-fee-outofrange",
          }
          for substring in tx_verify_error_messages:
              if substring in server_msg:
                  return substring
          # otherwise:
          return _("Unknown error")
  
      @best_effort_reliable
      @catch_server_exceptions
      async def request_chunk(self, height: int, tip=None, *, can_return_early=False):
          if not is_non_negative_integer(height):
              raise Exception(f"{repr(height)} is not a block height")
          return await self.interface.request_chunk(height, tip=tip, can_return_early=can_return_early)
  
      @best_effort_reliable
      @catch_server_exceptions
      async def get_transaction(self, tx_hash: str, *, timeout=None) -> str:
          if not is_hash256_str(tx_hash):
              raise Exception(f"{repr(tx_hash)} is not a txid")
          return await self.interface.session.send_request('blockchain.transaction.get', [tx_hash],
                                                           timeout=timeout)
  
      @best_effort_reliable
      @catch_server_exceptions
      async def get_history_for_scripthash(self, sh: str) -> List[dict]:
          if not is_hash256_str(sh):
              raise Exception(f"{repr(sh)} is not a scripthash")
          return await self.interface.session.send_request('blockchain.scripthash.get_history', [sh])
  
      @best_effort_reliable
      @catch_server_exceptions
      async def listunspent_for_scripthash(self, sh: str) -> List[dict]:
          if not is_hash256_str(sh):
              raise Exception(f"{repr(sh)} is not a scripthash")
          return await self.interface.session.send_request('blockchain.scripthash.listunspent', [sh])
  
      @best_effort_reliable
      @catch_server_exceptions
      async def get_balance_for_scripthash(self, sh: str) -> dict:
          if not is_hash256_str(sh):
              raise Exception(f"{repr(sh)} is not a scripthash")
          return await self.interface.session.send_request('blockchain.scripthash.get_balance', [sh])
  
      def blockchain(self) -> Blockchain:
          interface = self.interface
          if interface and interface.blockchain is not None:
              self._blockchain = interface.blockchain
          return self._blockchain
  
      def get_blockchains(self):
          out = {}  # blockchain_id -> list(interfaces)
          with blockchain.blockchains_lock: blockchain_items = list(blockchain.blockchains.items())
          with self.interfaces_lock: interfaces_values = list(self.interfaces.values())
          for chain_id, bc in blockchain_items:
              r = list(filter(lambda i: i.blockchain==bc, interfaces_values))
              if r:
                  out[chain_id] = r
          return out
  
      def _set_preferred_chain(self, chain: Blockchain):
          height = chain.get_max_forkpoint()
          header_hash = chain.get_hash(height)
          self._blockchain_preferred_block = {
              'height': height,
              'hash': header_hash,
          }
          self.config.set_key('blockchain_preferred_block', self._blockchain_preferred_block)
  
      async def follow_chain_given_id(self, chain_id: str) -> None:
          bc = blockchain.blockchains.get(chain_id)
          if not bc:
              raise Exception('blockchain {} not found'.format(chain_id))
          self._set_preferred_chain(bc)
          # select server on this chain
          with self.interfaces_lock: interfaces = list(self.interfaces.values())
          interfaces_on_selected_chain = list(filter(lambda iface: iface.blockchain == bc, interfaces))
          if len(interfaces_on_selected_chain) == 0: return
          chosen_iface = random.choice(interfaces_on_selected_chain)
          # switch to server (and save to config)
          net_params = self.get_parameters()
          host, port, protocol = deserialize_server(chosen_iface.server)
          net_params = net_params._replace(host=host, port=port, protocol=protocol)
          await self.set_parameters(net_params)
  
      async def follow_chain_given_server(self, server_str: str) -> None:
          # note that server_str should correspond to a connected interface
          iface = self.interfaces.get(server_str)
          if iface is None:
              return
          self._set_preferred_chain(iface.blockchain)
          # switch to server (and save to config)
          net_params = self.get_parameters()
          host, port, protocol = deserialize_server(server_str)
          net_params = net_params._replace(host=host, port=port, protocol=protocol)
          await self.set_parameters(net_params)
  
      def get_local_height(self):
          return self.blockchain().height()
  
      def export_checkpoints(self, path):
          """Run manually to generate blockchain checkpoints.
          Kept for console use only.
          """
          cp = self.blockchain().get_checkpoints()
          with open(path, 'w', encoding='utf-8') as f:
              f.write(json.dumps(cp, indent=4))
  
      async def _start(self):
          assert not self.main_taskgroup
          self.main_taskgroup = main_taskgroup = SilentTaskGroup()
          assert not self.interface and not self.interfaces
          assert not self.connecting and not self.server_queue
          self.logger.info('starting network')
          self.disconnected_servers = set([])
          self.protocol = deserialize_server(self.default_server)[2]
          self.server_queue = queue.Queue()
          self._set_proxy(deserialize_proxy(self.config.get('proxy')))
          self._set_oneserver(self.config.get('oneserver', False))
          self._start_interface(self.default_server)
  
          async def main():
              try:
                  await self._init_headers_file()
                  # note: if a task finishes with CancelledError, that
                  # will NOT raise, and the group will keep the other tasks running
                  async with main_taskgroup as group:
                      await group.spawn(self._maintain_sessions())
                      [await group.spawn(job) for job in self._jobs]
              except Exception as e:
                  self.logger.exception('')
                  raise e
          asyncio.run_coroutine_threadsafe(main(), self.asyncio_loop)
  
          self.trigger_callback('network_updated')
  
      def start(self, jobs: List=None):
          self._jobs = jobs or []
          asyncio.run_coroutine_threadsafe(self._start(), self.asyncio_loop)
  
      @log_exceptions
      async def _stop(self, full_shutdown=False):
          self.logger.info("stopping network")
          try:
              await asyncio.wait_for(self.main_taskgroup.cancel_remaining(), timeout=2)
          except (asyncio.TimeoutError, asyncio.CancelledError) as e:
              self.logger.info(f"exc during main_taskgroup cancellation: {repr(e)}")
          self.main_taskgroup = None  # type: TaskGroup
          self.interface = None  # type: Interface
          self.interfaces = {}  # type: Dict[str, Interface]
          self.connecting.clear()
          self.server_queue = None
          if not full_shutdown:
              self.trigger_callback('network_updated')
  
      def stop(self):
          assert self._loop_thread != threading.current_thread(), 'must not be called from network thread'
          fut = asyncio.run_coroutine_threadsafe(self._stop(full_shutdown=True), self.asyncio_loop)
          try:
              fut.result(timeout=2)
          except (asyncio.TimeoutError, asyncio.CancelledError): pass
  
      async def _ensure_there_is_a_main_interface(self):
          if self.is_connected():
              return
          now = time.time()
          # if auto_connect is set, try a different server
          if self.auto_connect and not self.is_connecting():
              await self._switch_to_random_interface()
          # if auto_connect is not set, or still no main interface, retry current
          if not self.is_connected() and not self.is_connecting():
              if self.default_server in self.disconnected_servers:
                  if now - self.server_retry_time > SERVER_RETRY_INTERVAL:
                      self.disconnected_servers.remove(self.default_server)
                      self.server_retry_time = now
              else:
                  await self.switch_to_interface(self.default_server)
  
      async def _maintain_sessions(self):
          async def launch_already_queued_up_new_interfaces():
              while self.server_queue.qsize() > 0:
                  server = self.server_queue.get()
                  await self.main_taskgroup.spawn(self._run_new_interface(server))
          async def maybe_queue_new_interfaces_to_be_launched_later():
              now = time.time()
              for i in range(self.num_server - len(self.interfaces) - len(self.connecting)):
                  # FIXME this should try to honour "healthy spread of connected servers"
                  self._start_random_interface()
              if now - self.nodes_retry_time > NODES_RETRY_INTERVAL:
                  self.logger.info('network: retrying connections')
                  self.disconnected_servers = set([])
                  self.nodes_retry_time = now
          async def maintain_healthy_spread_of_connected_servers():
              with self.interfaces_lock: interfaces = list(self.interfaces.values())
              random.shuffle(interfaces)
              for iface in interfaces:
                  if not self.check_interface_against_healthy_spread_of_connected_servers(iface):
                      self.logger.info(f"disconnecting from {iface.server}. too many connected "
                                       f"servers already in bucket {iface.bucket_based_on_ipaddress()}")
                      await self._close_interface(iface)
          async def maintain_main_interface():
              await self._ensure_there_is_a_main_interface()
              if self.is_connected():
                  if self.config.is_fee_estimates_update_required():
                      await self.interface.group.spawn(self._request_fee_estimates, self.interface)
  
          while True:
              try:
                  await launch_already_queued_up_new_interfaces()
                  await maybe_queue_new_interfaces_to_be_launched_later()
                  await maintain_healthy_spread_of_connected_servers()
                  await maintain_main_interface()
              except asyncio.CancelledError:
                  # suppress spurious cancellations
                  group = self.main_taskgroup
                  if not group or group._closed:
                      raise
              await asyncio.sleep(0.1)
  
      @classmethod
      async def _send_http_on_proxy(cls, method: str, url: str, params: str = None,
                                    body: bytes = None, json: dict = None, headers=None,
                                    on_finish=None, timeout=None):
          async def default_on_finish(resp: ClientResponse):
              resp.raise_for_status()
              return await resp.text()
          if headers is None:
              headers = {}
          if on_finish is None:
              on_finish = default_on_finish
          network = cls.get_instance()
          proxy = network.proxy if network else None
          async with make_aiohttp_session(proxy, timeout=timeout) as session:
              if method == 'get':
                  async with session.get(url, params=params, headers=headers) as resp:
                      return await on_finish(resp)
              elif method == 'post':
                  assert body is not None or json is not None, 'body or json must be supplied if method is post'
                  if body is not None:
                      async with session.post(url, data=body, headers=headers) as resp:
                          return await on_finish(resp)
                  elif json is not None:
                      async with session.post(url, json=json, headers=headers) as resp:
                          return await on_finish(resp)
              else:
                  assert False
  
      @classmethod
      def send_http_on_proxy(cls, method, url, **kwargs):
          network = cls.get_instance()
          if network:
              assert network._loop_thread is not threading.currentThread()
              loop = network.asyncio_loop
          else:
              loop = asyncio.get_event_loop()
          coro = asyncio.run_coroutine_threadsafe(cls._send_http_on_proxy(method, url, **kwargs), loop)
          # note: _send_http_on_proxy has its own timeout, so no timeout here:
          return coro.result()
  
      # methods used in scripts
      async def get_peers(self):
          while not self.is_connected():
              await asyncio.sleep(1)
          session = self.interface.session
          return parse_servers(await session.send_request('server.peers.subscribe'))
  
      async def send_multiple_requests(self, servers: List[str], method: str, params: Sequence):
          responses = dict()
          async def get_response(server):
              interface = Interface(self, server, self.proxy)
              timeout = self.get_network_timeout_seconds(NetworkTimeout.Urgent)
              try:
                  await asyncio.wait_for(interface.ready, timeout)
              except BaseException as e:
                  await interface.close()
                  return
              try:
                  res = await interface.session.send_request(method, params, timeout=10)
              except Exception as e:
                  res = e
              responses[interface.server] = res
          async with TaskGroup() as group:
              for server in servers:
                  await group.spawn(get_response(server))
          return responses
  