electrum/electrum/lnpeer.py

#!/usr/bin/env python3
#
# Copyright (C) 2018 The Electrum developers
# Distributed under the MIT software license, see the accompanying
# file LICENCE or http://www.opensource.org/licenses/mit-license.php

import zlib
from collections import OrderedDict, defaultdict
import json
import asyncio
import os
import time
from functools import partial
from typing import List, Tuple, Dict, TYPE_CHECKING, Optional, Callable, Union
import traceback
import sys
from datetime import datetime

import aiorpcx

from .crypto import sha256, sha256d
from . import bitcoin, util
from . import ecc
from .ecc import sig_string_from_r_and_s, get_r_and_s_from_sig_string, der_sig_from_sig_string
from . import constants
from .util import bh2u, bfh, log_exceptions, ignore_exceptions, chunks, SilentTaskGroup
from . import transaction
from .transaction import Transaction, TxOutput, PartialTxOutput, match_script_against_template
from .logging import Logger
from .lnonion import (new_onion_packet, decode_onion_error, OnionFailureCode, calc_hops_data_for_payment,
                      process_onion_packet, OnionPacket, construct_onion_error, OnionRoutingFailureMessage,
                      ProcessedOnionPacket, UnsupportedOnionPacketVersion, InvalidOnionMac, InvalidOnionPubkey,
                      OnionFailureCodeMetaFlag)
from .lnchannel import Channel, RevokeAndAck, htlcsum, RemoteCtnTooFarInFuture, ChannelState, PeerState
from . import lnutil
from .lnutil import (Outpoint, LocalConfig, RECEIVED, UpdateAddHtlc,
                     RemoteConfig, OnlyPubkeyKeypair, ChannelConstraints, RevocationStore,
                     funding_output_script, get_per_commitment_secret_from_seed,
                     secret_to_pubkey, PaymentFailure, LnFeatures,
                     LOCAL, REMOTE, HTLCOwner, generate_keypair, LnKeyFamily,
                     ln_compare_features, privkey_to_pubkey, MIN_FINAL_CLTV_EXPIRY_ACCEPTED,
                     LightningPeerConnectionClosed, HandshakeFailed, NotFoundChanAnnouncementForUpdate,
                     MINIMUM_MAX_HTLC_VALUE_IN_FLIGHT_ACCEPTED, MAXIMUM_HTLC_MINIMUM_MSAT_ACCEPTED,
                     MAXIMUM_REMOTE_TO_SELF_DELAY_ACCEPTED, RemoteMisbehaving, DEFAULT_TO_SELF_DELAY,
                     NBLOCK_OUR_CLTV_EXPIRY_DELTA, format_short_channel_id, ShortChannelID,
                     IncompatibleLightningFeatures, derive_payment_secret_from_payment_preimage)
from .lnutil import FeeUpdate, channel_id_from_funding_tx
from .lntransport import LNTransport, LNTransportBase
from .lnmsg import encode_msg, decode_msg
from .interface import GracefulDisconnect, NetworkException
from .lnrouter import fee_for_edge_msat
from .lnutil import ln_dummy_address
from .json_db import StoredDict

if TYPE_CHECKING:
    from .lnworker import LNWorker, LNGossip, LNWallet
    from .lnrouter import RouteEdge, LNPaymentRoute
    from .transaction import PartialTransaction


LN_P2P_NETWORK_TIMEOUT = 20


class Peer(Logger):
    LOGGING_SHORTCUT = 'P'

    def __init__(self, lnworker: Union['LNGossip', 'LNWallet'], pubkey:bytes, transport: LNTransportBase):
        self._sent_init = False  # type: bool
        self._received_init = False  # type: bool
        self.initialized = asyncio.Future()
        self.querying = asyncio.Event()
        self.transport = transport
        self.pubkey = pubkey  # remote pubkey
        self.lnworker = lnworker
        self.privkey = self.transport.privkey  # local privkey
        self.features = self.lnworker.features
        self.their_features = 0
        self.node_ids = [self.pubkey, privkey_to_pubkey(self.privkey)]
        self.network = lnworker.network
        self.channel_db = lnworker.network.channel_db
        self.ping_time = 0
        self.reply_channel_range = asyncio.Queue()
        # gossip uses a single queue to preserve message order
        self.gossip_queue = asyncio.Queue()
        self.ordered_messages = ['accept_channel', 'funding_signed', 'funding_created', 'accept_channel', 'channel_reestablish', 'closing_signed']
        self.ordered_message_queues = defaultdict(asyncio.Queue) # for messsage that are ordered
        self.temp_id_to_id = {}   # to forward error messages
        self.funding_created_sent = set() # for channels in PREOPENING
        self.funding_signed_sent = set()  # for channels in PREOPENING
        self.shutdown_received = {}
        self.announcement_signatures = defaultdict(asyncio.Queue)
        self.orphan_channel_updates = OrderedDict()
        Logger.__init__(self)
        self.taskgroup = SilentTaskGroup()

    def send_message(self, message_name: str, **kwargs):
        assert type(message_name) is str
        self.logger.debug(f"Sending {message_name.upper()}")
        if message_name.upper() != "INIT" and not self.is_initialized():
            raise Exception("tried to send message before we are initialized")
        raw_msg = encode_msg(message_name, **kwargs)
        self._store_raw_msg_if_local_update(raw_msg, message_name=message_name, channel_id=kwargs.get("channel_id"))
        self.transport.send_bytes(raw_msg)

    def _store_raw_msg_if_local_update(self, raw_msg: bytes, *, message_name: str, channel_id: Optional[bytes]):
        is_commitment_signed = message_name == "commitment_signed"
        if not (message_name.startswith("update_") or is_commitment_signed):
            return
        assert channel_id
        chan = self.get_channel_by_id(channel_id)
        if not chan:
            raise Exception(f"channel {channel_id.hex()} not found for peer {self.pubkey.hex()}")
        chan.hm.store_local_update_raw_msg(raw_msg, is_commitment_signed=is_commitment_signed)
        if is_commitment_signed:
            # saving now, to ensure replaying updates works (in case of channel reestablishment)
            self.lnworker.save_channel(chan)

    def maybe_set_initialized(self):
        if self.initialized.done():
            return
        if self._sent_init and self._received_init:
            self.initialized.set_result(True)

    def is_initialized(self) -> bool:
        return (self.initialized.done()
                and not self.initialized.cancelled()
                and self.initialized.exception() is None
                and self.initialized.result() is True)

    async def initialize(self):
        if isinstance(self.transport, LNTransport):
            await self.transport.handshake()
        # FIXME: "flen" hardcoded but actually it depends on "features"...:
        self.send_message("init", gflen=0, flen=2, features=self.features.for_init_message(),
                          init_tlvs={
                              'networks':
                                  {'chains': constants.net.rev_genesis_bytes()}
                          })
        self._sent_init = True
        self.maybe_set_initialized()

    @property
    def channels(self) -> Dict[bytes, Channel]:
        return self.lnworker.channels_for_peer(self.pubkey)

    def get_channel_by_id(self, channel_id: bytes) -> Optional[Channel]:
        # note: this is faster than self.channels.get(channel_id)
        chan = self.lnworker.get_channel_by_id(channel_id)
        if not chan:
            return None
        if chan.node_id != self.pubkey:
            return None
        return chan

    def diagnostic_name(self):
        return self.lnworker.__class__.__name__ + ', ' + self.transport.name()

    def ping_if_required(self):
        if time.time() - self.ping_time > 120:
            self.send_message('ping', num_pong_bytes=4, byteslen=4)
            self.ping_time = time.time()

    def process_message(self, message):
        message_type, payload = decode_msg(message)
        if message_type in self.ordered_messages:
            chan_id = payload.get('channel_id') or payload["temporary_channel_id"]
            self.ordered_message_queues[chan_id].put_nowait((message_type, payload))
        else:
            if message_type != 'error' and 'channel_id' in payload:
                chan = self.get_channel_by_id(payload['channel_id'])
                if chan is None:
                    raise Exception('Got unknown '+ message_type)
                args = (chan, payload)
            else:
                args = (payload,)
            try:
                f = getattr(self, 'on_' + message_type)
            except AttributeError:
                #self.logger.info("Received '%s'" % message_type.upper(), payload)
                return
            # raw message is needed to check signature
            if message_type in ['node_announcement', 'channel_announcement', 'channel_update']:
                payload['raw'] = message
            execution_result = f(*args)
            if asyncio.iscoroutinefunction(f):
                asyncio.ensure_future(execution_result)

    def on_error(self, payload):
        self.logger.info(f"remote peer sent error [DO NOT TRUST THIS MESSAGE]: {payload['data'].decode('ascii')}")
        chan_id = payload.get("channel_id")
        if chan_id in self.temp_id_to_id:
            chan_id = self.temp_id_to_id[chan_id]
        self.ordered_message_queues[chan_id].put_nowait((None, {'error':payload['data']}))

    def on_ping(self, payload):
        l = payload['num_pong_bytes']
        self.send_message('pong', byteslen=l)

    def on_pong(self, payload):
        pass

    async def wait_for_message(self, expected_name, channel_id):
        q = self.ordered_message_queues[channel_id]
        name, payload = await asyncio.wait_for(q.get(), LN_P2P_NETWORK_TIMEOUT)
        if payload.get('error'):
            raise Exception('Remote peer reported error [DO NOT TRUST THIS MESSAGE]: ' + repr(payload.get('error')))
        if name != expected_name:
            raise Exception(f"Received unexpected '{name}'")
        return payload

    def on_init(self, payload):
        if self._received_init:
            self.logger.info("ALREADY INITIALIZED BUT RECEIVED INIT")
            return
        self.their_features = LnFeatures(int.from_bytes(payload['features'], byteorder="big"))
        their_globalfeatures = int.from_bytes(payload['globalfeatures'], byteorder="big")
        self.their_features |= their_globalfeatures
        # check transitive dependencies for received features
        if not self.their_features.validate_transitive_dependecies():
            raise GracefulDisconnect("remote did not set all dependencies for the features they sent")
        # check if features are compatible, and set self.features to what we negotiated
        try:
            self.features = ln_compare_features(self.features, self.their_features)
        except IncompatibleLightningFeatures as e:
            self.initialized.set_exception(e)
            raise GracefulDisconnect(f"{str(e)}")
        # check that they are on the same chain as us, if provided
        their_networks = payload["init_tlvs"].get("networks")
        if their_networks:
            their_chains = list(chunks(their_networks["chains"], 32))
            if constants.net.rev_genesis_bytes() not in their_chains:
                raise GracefulDisconnect(f"no common chain found with remote. (they sent: {their_chains})")
        # all checks passed
        self.lnworker.on_peer_successfully_established(self)
        self._received_init = True
        self.maybe_set_initialized()

    def on_node_announcement(self, payload):
        self.gossip_queue.put_nowait(('node_announcement', payload))

    def on_channel_announcement(self, payload):
        self.gossip_queue.put_nowait(('channel_announcement', payload))

    def on_channel_update(self, payload):
        self.maybe_save_remote_update(payload)
        self.gossip_queue.put_nowait(('channel_update', payload))

    def maybe_save_remote_update(self, payload):
        for chan in self.channels.values():
            if chan.short_channel_id == payload['short_channel_id']:
                chan.set_remote_update(payload['raw'])
                self.logger.info("saved remote_update")

    def on_announcement_signatures(self, chan: Channel, payload):
        if chan.config[LOCAL].was_announced:
            h, local_node_sig, local_bitcoin_sig = self.send_announcement_signatures(chan)
        else:
            self.announcement_signatures[chan.channel_id].put_nowait(payload)

    def handle_disconnect(func):
        async def wrapper_func(self, *args, **kwargs):
            try:
                return await func(self, *args, **kwargs)
            except GracefulDisconnect as e:
                self.logger.log(e.log_level, f"Disconnecting: {repr(e)}")
            except (LightningPeerConnectionClosed, IncompatibleLightningFeatures,
                    aiorpcx.socks.SOCKSError) as e:
                self.logger.info(f"Disconnecting: {repr(e)}")
            finally:
                self.close_and_cleanup()
        return wrapper_func

    @ignore_exceptions  # do not kill outer taskgroup
    @log_exceptions
    @handle_disconnect
    async def main_loop(self):
        async with self.taskgroup as group:
            await group.spawn(self._message_loop())
            await group.spawn(self.htlc_switch())
            await group.spawn(self.query_gossip())
            await group.spawn(self.process_gossip())

    async def process_gossip(self):
        await self.channel_db.data_loaded.wait()
        # verify in peer's TaskGroup so that we fail the connection
        while True:
            await asyncio.sleep(5)
            chan_anns = []
            chan_upds = []
            node_anns = []
            while True:
                name, payload = await self.gossip_queue.get()
                if name == 'channel_announcement':
                    chan_anns.append(payload)
                elif name == 'channel_update':
                    chan_upds.append(payload)
                elif name == 'node_announcement':
                    node_anns.append(payload)
                else:
                    raise Exception('unknown message')
                if self.gossip_queue.empty():
                    break
            self.logger.debug(f'process_gossip {len(chan_anns)} {len(node_anns)} {len(chan_upds)}')
            # note: data processed in chunks to avoid taking sql lock for too long
            # channel announcements
            for chan_anns_chunk in chunks(chan_anns, 300):
                self.verify_channel_announcements(chan_anns_chunk)
                self.channel_db.add_channel_announcement(chan_anns_chunk)
            # node announcements
            for node_anns_chunk in chunks(node_anns, 100):
                self.verify_node_announcements(node_anns_chunk)
                self.channel_db.add_node_announcement(node_anns_chunk)
            # channel updates
            for chan_upds_chunk in chunks(chan_upds, 1000):
                categorized_chan_upds = self.channel_db.add_channel_updates(
                    chan_upds_chunk, max_age=self.network.lngossip.max_age)
                orphaned = categorized_chan_upds.orphaned
                if orphaned:
                    self.logger.info(f'adding {len(orphaned)} unknown channel ids')
                    orphaned_ids = [c['short_channel_id'] for c in orphaned]
                    await self.network.lngossip.add_new_ids(orphaned_ids)
                    # Save (some bounded number of) orphan channel updates for later
                    # as it might be for our own direct channel with this peer
                    # (and we might not yet know the short channel id for that)
                    for chan_upd_payload in orphaned:
                        short_channel_id = ShortChannelID(chan_upd_payload['short_channel_id'])
                        self.orphan_channel_updates[short_channel_id] = chan_upd_payload
                        while len(self.orphan_channel_updates) > 25:
                            self.orphan_channel_updates.popitem(last=False)
                if categorized_chan_upds.good:
                    self.logger.debug(f'on_channel_update: {len(categorized_chan_upds.good)}/{len(chan_upds_chunk)}')

    def verify_channel_announcements(self, chan_anns):
        for payload in chan_anns:
            h = sha256d(payload['raw'][2+256:])
            pubkeys = [payload['node_id_1'], payload['node_id_2'], payload['bitcoin_key_1'], payload['bitcoin_key_2']]
            sigs = [payload['node_signature_1'], payload['node_signature_2'], payload['bitcoin_signature_1'], payload['bitcoin_signature_2']]
            for pubkey, sig in zip(pubkeys, sigs):
                if not ecc.verify_signature(pubkey, sig, h):
                    raise Exception('signature failed')

    def verify_node_announcements(self, node_anns):
        for payload in node_anns:
            pubkey = payload['node_id']
            signature = payload['signature']
            h = sha256d(payload['raw'][66:])
            if not ecc.verify_signature(pubkey, signature, h):
                raise Exception('signature failed')

    async def query_gossip(self):
        try:
            await asyncio.wait_for(self.initialized, LN_P2P_NETWORK_TIMEOUT)
        except Exception as e:
            raise GracefulDisconnect(f"Failed to initialize: {e!r}") from e
        if self.lnworker == self.lnworker.network.lngossip:
            try:
                ids, complete = await asyncio.wait_for(self.get_channel_range(), LN_P2P_NETWORK_TIMEOUT)
            except asyncio.TimeoutError as e:
                raise GracefulDisconnect("query_channel_range timed out") from e
            self.logger.info('Received {} channel ids. (complete: {})'.format(len(ids), complete))
            await self.lnworker.add_new_ids(ids)
            while True:
                todo = self.lnworker.get_ids_to_query()
                if not todo:
                    await asyncio.sleep(1)
                    continue
                await self.get_short_channel_ids(todo)

    async def get_channel_range(self):
        first_block = constants.net.BLOCK_HEIGHT_FIRST_LIGHTNING_CHANNELS
        num_blocks = self.lnworker.network.get_local_height() - first_block
        self.query_channel_range(first_block, num_blocks)
        intervals = []
        ids = set()
        # note: implementations behave differently...
        # "sane implementation that follows BOLT-07" example:
        #   query_channel_range. <<< first_block 497000, num_blocks 79038
        #   on_reply_channel_range. >>> first_block 497000, num_blocks 39516, num_ids 4648, complete True
        #   on_reply_channel_range. >>> first_block 536516, num_blocks 19758, num_ids 5734, complete True
        #   on_reply_channel_range. >>> first_block 556274, num_blocks 9879, num_ids 13712, complete True
        #   on_reply_channel_range. >>> first_block 566153, num_blocks 9885, num_ids 18114, complete True
        # lnd example:
        #   query_channel_range. <<< first_block 497000, num_blocks 79038
        #   on_reply_channel_range. >>> first_block 497000, num_blocks 79038, num_ids 8000, complete False
        #   on_reply_channel_range. >>> first_block 497000, num_blocks 79038, num_ids 8000, complete False
        #   on_reply_channel_range. >>> first_block 497000, num_blocks 79038, num_ids 8000, complete False
        #   on_reply_channel_range. >>> first_block 497000, num_blocks 79038, num_ids 8000, complete False
        #   on_reply_channel_range. >>> first_block 497000, num_blocks 79038, num_ids 5344, complete True
        while True:
            index, num, complete, _ids = await self.reply_channel_range.get()
            ids.update(_ids)
            intervals.append((index, index+num))
            intervals.sort()
            while len(intervals) > 1:
                a,b = intervals[0]
                c,d = intervals[1]
                if not (a <= c and a <= b and c <= d):
                    raise Exception(f"insane reply_channel_range intervals {(a,b,c,d)}")
                if b >= c:
                    intervals = [(a,d)] + intervals[2:]
                else:
                    break
            if len(intervals) == 1 and complete:
                a, b = intervals[0]
                if a <= first_block and b >= first_block + num_blocks:
                    break
        return ids, complete

    def request_gossip(self, timestamp=0):
        if timestamp == 0:
            self.logger.info('requesting whole channel graph')
        else:
            self.logger.info(f'requesting channel graph since {datetime.fromtimestamp(timestamp).ctime()}')
        self.send_message(
            'gossip_timestamp_filter',
            chain_hash=constants.net.rev_genesis_bytes(),
            first_timestamp=timestamp,
            timestamp_range=b'\xff'*4)

    def query_channel_range(self, first_block, num_blocks):
        self.logger.info(f'query channel range {first_block} {num_blocks}')
        self.send_message(
            'query_channel_range',
            chain_hash=constants.net.rev_genesis_bytes(),
            first_blocknum=first_block,
            number_of_blocks=num_blocks)

    def encode_short_ids(self, ids):
        return chr(1) + zlib.compress(bfh(''.join(ids)))

    def decode_short_ids(self, encoded):
        if encoded[0] == 0:
            decoded = encoded[1:]
        elif encoded[0] == 1:
            decoded = zlib.decompress(encoded[1:])
        else:
            raise Exception(f'decode_short_ids: unexpected first byte: {encoded[0]}')
        ids = [decoded[i:i+8] for i in range(0, len(decoded), 8)]
        return ids

    def on_reply_channel_range(self, payload):
        first = payload['first_blocknum']
        num = payload['number_of_blocks']
        complete = bool(int.from_bytes(payload['complete'], 'big'))
        encoded = payload['encoded_short_ids']
        ids = self.decode_short_ids(encoded)
        #self.logger.info(f"on_reply_channel_range. >>> first_block {first}, num_blocks {num}, num_ids {len(ids)}, complete {repr(payload['complete'])}")
        self.reply_channel_range.put_nowait((first, num, complete, ids))

    async def get_short_channel_ids(self, ids):
        self.logger.info(f'Querying {len(ids)} short_channel_ids')
        assert not self.querying.is_set()
        self.query_short_channel_ids(ids)
        await self.querying.wait()
        self.querying.clear()

    def query_short_channel_ids(self, ids, compressed=True):
        ids = sorted(ids)
        s = b''.join(ids)
        encoded = zlib.compress(s) if compressed else s
        prefix = b'\x01' if compressed else b'\x00'
        self.send_message(
            'query_short_channel_ids',
            chain_hash=constants.net.rev_genesis_bytes(),
            len=1+len(encoded),
            encoded_short_ids=prefix+encoded)

    async def _message_loop(self):
        try:
            await asyncio.wait_for(self.initialize(), LN_P2P_NETWORK_TIMEOUT)
        except (OSError, asyncio.TimeoutError, HandshakeFailed) as e:
            raise GracefulDisconnect(f'initialize failed: {repr(e)}') from e
        async for msg in self.transport.read_messages():
            self.process_message(msg)
            await asyncio.sleep(.01)

    def on_reply_short_channel_ids_end(self, payload):
        self.querying.set()

    def close_and_cleanup(self):
        try:
            if self.transport:
                self.transport.close()
        except:
            pass
        self.lnworker.peer_closed(self)

    def is_static_remotekey(self):
        return bool(self.features & LnFeatures.OPTION_STATIC_REMOTEKEY_OPT)

    def make_local_config(self, funding_sat: int, push_msat: int, initiator: HTLCOwner) -> LocalConfig:
        channel_seed = os.urandom(32)
        initial_msat = funding_sat * 1000 - push_msat if initiator == LOCAL else push_msat
        if self.is_static_remotekey():
            # Note: in the future, if a CSV delay is added,
            # we will want to derive that key
            wallet = self.lnworker.wallet
            assert wallet.txin_type == 'p2wpkh'
            addr = wallet.get_new_sweep_address_for_channel()
            static_remotekey = bfh(wallet.get_public_key(addr))
        else:
            static_remotekey = None
        local_config = LocalConfig.from_seed(
            channel_seed=channel_seed,
            static_remotekey=static_remotekey,
            to_self_delay=DEFAULT_TO_SELF_DELAY,
            dust_limit_sat=546,
            max_htlc_value_in_flight_msat=funding_sat * 1000,
            max_accepted_htlcs=5,
            initial_msat=initial_msat,
            reserve_sat=546,
            funding_locked_received=False,
            was_announced=False,
            current_commitment_signature=None,
            current_htlc_signatures=b'',
            htlc_minimum_msat=1,
        )
        return local_config

    def temporarily_reserve_funding_tx_change_address(func):
        # During the channel open flow, if we initiated, we might have used a change address
        # of ours in the funding tx. The funding tx is not part of the wallet history
        # at that point yet, but we should already consider this change address as 'used'.
        async def wrapper(self: 'Peer', *args, **kwargs):
            funding_tx = kwargs['funding_tx']  # type: PartialTransaction
            wallet = self.lnworker.wallet
            change_addresses = [txout.address for txout in funding_tx.outputs()
                                if wallet.is_change(txout.address)]
            for addr in change_addresses:
                wallet.set_reserved_state_of_address(addr, reserved=True)
            try:
                return await func(self, *args, **kwargs)
            finally:
                for addr in change_addresses:
                    self.lnworker.wallet.set_reserved_state_of_address(addr, reserved=False)
        return wrapper

    @log_exceptions
    @temporarily_reserve_funding_tx_change_address
    async def channel_establishment_flow(
            self, *,
            password: Optional[str],
            funding_tx: 'PartialTransaction',
            funding_sat: int,
            push_msat: int,
            temp_channel_id: bytes
    ) -> Tuple[Channel, 'PartialTransaction']:
        await asyncio.wait_for(self.initialized, LN_P2P_NETWORK_TIMEOUT)
        feerate = self.lnworker.current_feerate_per_kw()
        local_config = self.make_local_config(funding_sat, push_msat, LOCAL)
        # for the first commitment transaction
        per_commitment_secret_first = get_per_commitment_secret_from_seed(local_config.per_commitment_secret_seed,
                                                                          RevocationStore.START_INDEX)
        per_commitment_point_first = secret_to_pubkey(int.from_bytes(per_commitment_secret_first, 'big'))
        self.send_message(
            "open_channel",
            temporary_channel_id=temp_channel_id,
            chain_hash=constants.net.rev_genesis_bytes(),
            funding_satoshis=funding_sat,
            push_msat=push_msat,
            dust_limit_satoshis=local_config.dust_limit_sat,
            feerate_per_kw=feerate,
            max_accepted_htlcs=local_config.max_accepted_htlcs,
            funding_pubkey=local_config.multisig_key.pubkey,
            revocation_basepoint=local_config.revocation_basepoint.pubkey,
            htlc_basepoint=local_config.htlc_basepoint.pubkey,
            payment_basepoint=local_config.payment_basepoint.pubkey,
            delayed_payment_basepoint=local_config.delayed_basepoint.pubkey,
            first_per_commitment_point=per_commitment_point_first,
            to_self_delay=local_config.to_self_delay,
            max_htlc_value_in_flight_msat=local_config.max_htlc_value_in_flight_msat,
            channel_flags=0x00,  # not willing to announce channel
            channel_reserve_satoshis=local_config.reserve_sat,
            htlc_minimum_msat=local_config.htlc_minimum_msat,
        )
        payload = await self.wait_for_message('accept_channel', temp_channel_id)
        remote_per_commitment_point = payload['first_per_commitment_point']
        funding_txn_minimum_depth = payload['minimum_depth']
        if funding_txn_minimum_depth <= 0:
            raise Exception(f"minimum depth too low, {funding_txn_minimum_depth}")
        if funding_txn_minimum_depth > 30:
            raise Exception(f"minimum depth too high, {funding_txn_minimum_depth}")
        remote_dust_limit_sat = payload['dust_limit_satoshis']
        remote_reserve_sat = self.validate_remote_reserve(payload["channel_reserve_satoshis"], remote_dust_limit_sat, funding_sat)
        if remote_dust_limit_sat > remote_reserve_sat:
            raise Exception(f"Remote Lightning peer reports dust_limit_sat > reserve_sat which is a BOLT-02 protocol violation.")
        htlc_min = payload['htlc_minimum_msat']
        if htlc_min > MAXIMUM_HTLC_MINIMUM_MSAT_ACCEPTED:
            raise Exception(f"Remote Lightning peer reports htlc_minimum_msat={htlc_min} mSAT," +
                    f" which is above Electrums required maximum limit of that parameter ({MAXIMUM_HTLC_MINIMUM_MSAT_ACCEPTED} mSAT).")
        remote_max = payload['max_htlc_value_in_flight_msat']
        if remote_max < MINIMUM_MAX_HTLC_VALUE_IN_FLIGHT_ACCEPTED:
            raise Exception(f"Remote Lightning peer reports max_htlc_value_in_flight_msat at only {remote_max} mSAT" +
                    f" which is below Electrums required minimum ({MINIMUM_MAX_HTLC_VALUE_IN_FLIGHT_ACCEPTED} mSAT).")
        max_accepted_htlcs = payload["max_accepted_htlcs"]
        if max_accepted_htlcs > 483:
            raise Exception("Remote Lightning peer reports max_accepted_htlcs > 483, which is a BOLT-02 protocol violation.")
        remote_to_self_delay = payload['to_self_delay']
        if remote_to_self_delay > MAXIMUM_REMOTE_TO_SELF_DELAY_ACCEPTED:
            raise Exception(f"Remote Lightning peer reports to_self_delay={remote_to_self_delay}," +
                    f" which is above Electrums required maximum ({MAXIMUM_REMOTE_TO_SELF_DELAY_ACCEPTED})")
        remote_config = RemoteConfig(
            payment_basepoint=OnlyPubkeyKeypair(payload['payment_basepoint']),
            multisig_key=OnlyPubkeyKeypair(payload["funding_pubkey"]),
            htlc_basepoint=OnlyPubkeyKeypair(payload['htlc_basepoint']),
            delayed_basepoint=OnlyPubkeyKeypair(payload['delayed_payment_basepoint']),
            revocation_basepoint=OnlyPubkeyKeypair(payload['revocation_basepoint']),
            to_self_delay=remote_to_self_delay,
            dust_limit_sat=remote_dust_limit_sat,
            max_htlc_value_in_flight_msat=remote_max,
            max_accepted_htlcs=max_accepted_htlcs,
            initial_msat=push_msat,
            reserve_sat = remote_reserve_sat,
            htlc_minimum_msat = htlc_min,
            next_per_commitment_point=remote_per_commitment_point,
            current_per_commitment_point=None,
        )
        # replace dummy output in funding tx
        redeem_script = funding_output_script(local_config, remote_config)
        funding_address = bitcoin.redeem_script_to_address('p2wsh', redeem_script)
        funding_output = PartialTxOutput.from_address_and_value(funding_address, funding_sat)
        dummy_output = PartialTxOutput.from_address_and_value(ln_dummy_address(), funding_sat)
        funding_tx.outputs().remove(dummy_output)
        funding_tx.add_outputs([funding_output])
        funding_tx.set_rbf(False)
        self.lnworker.wallet.sign_transaction(funding_tx, password)
        if not funding_tx.is_complete() and not funding_tx.is_segwit():
            raise Exception('Funding transaction is not complete')
        funding_txid = funding_tx.txid()
        assert funding_txid
        funding_index = funding_tx.outputs().index(funding_output)
        # remote commitment transaction
        channel_id, funding_txid_bytes = channel_id_from_funding_tx(funding_txid, funding_index)
        outpoint = Outpoint(funding_txid, funding_index)
        constraints = ChannelConstraints(capacity=funding_sat, is_initiator=True, funding_txn_minimum_depth=funding_txn_minimum_depth)
        chan_dict = self.create_channel_storage(channel_id, outpoint, local_config, remote_config, constraints)
        chan = Channel(chan_dict,
                       sweep_address=self.lnworker.sweep_address,
                       lnworker=self.lnworker,
                       initial_feerate=feerate)
        chan.storage['funding_inputs'] = [txin.prevout.to_json() for txin in funding_tx.inputs()]
        if isinstance(self.transport, LNTransport):
            chan.add_or_update_peer_addr(self.transport.peer_addr)
        sig_64, _ = chan.sign_next_commitment()
        self.temp_id_to_id[temp_channel_id] = channel_id
        self.send_message("funding_created",
            temporary_channel_id=temp_channel_id,
            funding_txid=funding_txid_bytes,
            funding_output_index=funding_index,
            signature=sig_64)
        self.funding_created_sent.add(channel_id)
        payload = await self.wait_for_message('funding_signed', channel_id)
        self.logger.info('received funding_signed')
        remote_sig = payload['signature']
        chan.receive_new_commitment(remote_sig, [])
        chan.open_with_first_pcp(remote_per_commitment_point, remote_sig)
        chan.set_state(ChannelState.OPENING)
        self.lnworker.add_new_channel(chan)
        return chan, funding_tx

    def create_channel_storage(self, channel_id, outpoint, local_config, remote_config, constraints):
        chan_dict = {
            "node_id": self.pubkey.hex(),
            "channel_id": channel_id.hex(),
            "short_channel_id": None,
            "funding_outpoint": outpoint,
            "remote_config": remote_config,
            "local_config": local_config,
            "constraints": constraints,
            "remote_update": None,
            "state": ChannelState.PREOPENING.name,
            'onion_keys': {},
            'data_loss_protect_remote_pcp': {},
            "log": {},
            "revocation_store": {},
            "static_remotekey_enabled": self.is_static_remotekey(), # stored because it cannot be "downgraded", per BOLT2
        }
        return StoredDict(chan_dict, None, [])

    async def on_open_channel(self, payload):
        # payload['channel_flags']
        if payload['chain_hash'] != constants.net.rev_genesis_bytes():
            raise Exception('wrong chain_hash')
        funding_sat = payload['funding_satoshis']
        push_msat = payload['push_msat']
        feerate = payload['feerate_per_kw']
        temp_chan_id = payload['temporary_channel_id']
        local_config = self.make_local_config(funding_sat, push_msat, REMOTE)
        # for the first commitment transaction
        per_commitment_secret_first = get_per_commitment_secret_from_seed(local_config.per_commitment_secret_seed,
                                                                          RevocationStore.START_INDEX)
        per_commitment_point_first = secret_to_pubkey(int.from_bytes(per_commitment_secret_first, 'big'))
        min_depth = 3
        self.send_message('accept_channel',
            temporary_channel_id=temp_chan_id,
            dust_limit_satoshis=local_config.dust_limit_sat,
            max_htlc_value_in_flight_msat=local_config.max_htlc_value_in_flight_msat,
            channel_reserve_satoshis=local_config.reserve_sat,
            htlc_minimum_msat=1000,
            minimum_depth=min_depth,
            to_self_delay=local_config.to_self_delay,
            max_accepted_htlcs=local_config.max_accepted_htlcs,
            funding_pubkey=local_config.multisig_key.pubkey,
            revocation_basepoint=local_config.revocation_basepoint.pubkey,
            payment_basepoint=local_config.payment_basepoint.pubkey,
            delayed_payment_basepoint=local_config.delayed_basepoint.pubkey,
            htlc_basepoint=local_config.htlc_basepoint.pubkey,
            first_per_commitment_point=per_commitment_point_first,
        )
        funding_created = await self.wait_for_message('funding_created', temp_chan_id)
        funding_idx = funding_created['funding_output_index']
        funding_txid = bh2u(funding_created['funding_txid'][::-1])
        channel_id, funding_txid_bytes = channel_id_from_funding_tx(funding_txid, funding_idx)
        remote_balance_sat = funding_sat * 1000 - push_msat
        remote_dust_limit_sat = payload['dust_limit_satoshis']  # TODO validate
        remote_reserve_sat = self.validate_remote_reserve(payload['channel_reserve_satoshis'], remote_dust_limit_sat, funding_sat)
        remote_config = RemoteConfig(
            payment_basepoint=OnlyPubkeyKeypair(payload['payment_basepoint']),
            multisig_key=OnlyPubkeyKeypair(payload['funding_pubkey']),
            htlc_basepoint=OnlyPubkeyKeypair(payload['htlc_basepoint']),
            delayed_basepoint=OnlyPubkeyKeypair(payload['delayed_payment_basepoint']),
            revocation_basepoint=OnlyPubkeyKeypair(payload['revocation_basepoint']),
            to_self_delay=payload['to_self_delay'],
            dust_limit_sat=remote_dust_limit_sat,
            max_htlc_value_in_flight_msat=payload['max_htlc_value_in_flight_msat'],  # TODO validate
            max_accepted_htlcs=payload['max_accepted_htlcs'],  # TODO validate
            initial_msat=remote_balance_sat,
            reserve_sat = remote_reserve_sat,
            htlc_minimum_msat=payload['htlc_minimum_msat'], # TODO validate
            next_per_commitment_point=payload['first_per_commitment_point'],
            current_per_commitment_point=None,
        )
        constraints = ChannelConstraints(capacity=funding_sat, is_initiator=False, funding_txn_minimum_depth=min_depth)
        outpoint = Outpoint(funding_txid, funding_idx)
        chan_dict = self.create_channel_storage(channel_id, outpoint, local_config, remote_config, constraints)
        chan = Channel(chan_dict,
                       sweep_address=self.lnworker.sweep_address,
                       lnworker=self.lnworker,
                       initial_feerate=feerate)
        chan.storage['init_timestamp'] = int(time.time())
        if isinstance(self.transport, LNTransport):
            chan.add_or_update_peer_addr(self.transport.peer_addr)
        remote_sig = funding_created['signature']
        chan.receive_new_commitment(remote_sig, [])
        sig_64, _ = chan.sign_next_commitment()
        self.send_message('funding_signed',
            channel_id=channel_id,
            signature=sig_64,
        )
        self.funding_signed_sent.add(chan.channel_id)
        chan.open_with_first_pcp(payload['first_per_commitment_point'], remote_sig)
        chan.set_state(ChannelState.OPENING)
        self.lnworker.add_new_channel(chan)

    def validate_remote_reserve(self, remote_reserve_sat: int, dust_limit: int, funding_sat: int) -> int:
        if remote_reserve_sat < dust_limit:
            raise Exception('protocol violation: reserve < dust_limit')
        if remote_reserve_sat > funding_sat/100:
            raise Exception(f'reserve too high: {remote_reserve_sat}, funding_sat: {funding_sat}')
        return remote_reserve_sat

    async def trigger_force_close(self, channel_id):
        await self.initialized
        latest_point = 0
        self.send_message(
            "channel_reestablish",
            channel_id=channel_id,
            next_local_commitment_number=0,
            next_remote_revocation_number=0,
            your_last_per_commitment_secret=0,
            my_current_per_commitment_point=latest_point)

    async def reestablish_channel(self, chan: Channel):
        await self.initialized
        chan_id = chan.channel_id
        assert ChannelState.PREOPENING < chan.get_state() < ChannelState.FORCE_CLOSING
        if chan.peer_state != PeerState.DISCONNECTED:
            self.logger.info(f'reestablish_channel was called but channel {chan.get_id_for_log()} '
                             f'already in peer_state {chan.peer_state!r}')
            return
        chan.peer_state = PeerState.REESTABLISHING
        util.trigger_callback('channel', chan)
        # BOLT-02: "A node [...] upon disconnection [...] MUST reverse any uncommitted updates sent by the other side"
        chan.hm.discard_unsigned_remote_updates()
        # ctns
        oldest_unrevoked_local_ctn = chan.get_oldest_unrevoked_ctn(LOCAL)
        latest_local_ctn = chan.get_latest_ctn(LOCAL)
        next_local_ctn = chan.get_next_ctn(LOCAL)
        oldest_unrevoked_remote_ctn = chan.get_oldest_unrevoked_ctn(REMOTE)
        latest_remote_ctn = chan.get_latest_ctn(REMOTE)
        next_remote_ctn = chan.get_next_ctn(REMOTE)
        assert self.features & LnFeatures.OPTION_DATA_LOSS_PROTECT_OPT
        # send message
        if chan.is_static_remotekey_enabled():
            latest_secret, latest_point = chan.get_secret_and_point(LOCAL, 0)
        else:
            latest_secret, latest_point = chan.get_secret_and_point(LOCAL, latest_local_ctn)
        if oldest_unrevoked_remote_ctn == 0:
            last_rev_secret = 0
        else:
            last_rev_index = oldest_unrevoked_remote_ctn - 1
            last_rev_secret = chan.revocation_store.retrieve_secret(RevocationStore.START_INDEX - last_rev_index)
        self.send_message(
            "channel_reestablish",
            channel_id=chan_id,
            next_commitment_number=next_local_ctn,
            next_revocation_number=oldest_unrevoked_remote_ctn,
            your_last_per_commitment_secret=last_rev_secret,
            my_current_per_commitment_point=latest_point)
        self.logger.info(f'channel_reestablish ({chan.get_id_for_log()}): sent channel_reestablish with '
                         f'(next_local_ctn={next_local_ctn}, '
                         f'oldest_unrevoked_remote_ctn={oldest_unrevoked_remote_ctn})')
        msg = await self.wait_for_message('channel_reestablish', chan_id)
        their_next_local_ctn = msg["next_commitment_number"]
        their_oldest_unrevoked_remote_ctn = msg["next_revocation_number"]
        their_local_pcp = msg.get("my_current_per_commitment_point")
        their_claim_of_our_last_per_commitment_secret = msg.get("your_last_per_commitment_secret")
        self.logger.info(f'channel_reestablish ({chan.get_id_for_log()}): received channel_reestablish with '
                         f'(their_next_local_ctn={their_next_local_ctn}, '
                         f'their_oldest_unrevoked_remote_ctn={their_oldest_unrevoked_remote_ctn})')
        # sanity checks of received values
        if their_next_local_ctn < 0:
            raise RemoteMisbehaving(f"channel reestablish: their_next_local_ctn < 0")
        if their_oldest_unrevoked_remote_ctn < 0:
            raise RemoteMisbehaving(f"channel reestablish: their_oldest_unrevoked_remote_ctn < 0")
        # Replay un-acked local updates (including commitment_signed) byte-for-byte.
        # If we have sent them a commitment signature that they "lost" (due to disconnect),
        # we need to make sure we replay the same local updates, as otherwise they could
        # end up with two (or more) signed valid commitment transactions at the same ctn.
        # Multiple valid ctxs at the same ctn is a major headache for pre-signing spending txns,
        # e.g. for watchtowers, hence we must ensure these ctxs coincide.
        # We replay the local updates even if they were not yet committed.
        unacked = chan.hm.get_unacked_local_updates()
        n_replayed_msgs = 0
        for ctn, messages in unacked.items():
            if ctn < their_next_local_ctn:
                # They claim to have received these messages and the corresponding
                # commitment_signed, hence we must not replay them.
                continue
            for raw_upd_msg in messages:
                self.transport.send_bytes(raw_upd_msg)
                n_replayed_msgs += 1
        self.logger.info(f'channel_reestablish ({chan.get_id_for_log()}): replayed {n_replayed_msgs} unacked messages')

        we_are_ahead = False
        they_are_ahead = False
        # compare remote ctns
        if next_remote_ctn != their_next_local_ctn:
            if their_next_local_ctn == latest_remote_ctn and chan.hm.is_revack_pending(REMOTE):
                # We replayed the local updates (see above), which should have contained a commitment_signed
                # (due to is_revack_pending being true), and this should have remedied this situation.
                pass
            else:
                self.logger.warning(f"channel_reestablish ({chan.get_id_for_log()}): "
                                    f"expected remote ctn {next_remote_ctn}, got {their_next_local_ctn}")
                if their_next_local_ctn < next_remote_ctn:
                    we_are_ahead = True
                else:
                    they_are_ahead = True
        # compare local ctns
        if oldest_unrevoked_local_ctn != their_oldest_unrevoked_remote_ctn:
            if oldest_unrevoked_local_ctn - 1 == their_oldest_unrevoked_remote_ctn:
                # A node:
                #    if next_revocation_number is equal to the commitment number of the last revoke_and_ack
                #    the receiving node sent, AND the receiving node hasn't already received a closing_signed:
                #        MUST re-send the revoke_and_ack.
                last_secret, last_point = chan.get_secret_and_point(LOCAL, oldest_unrevoked_local_ctn - 1)
                next_secret, next_point = chan.get_secret_and_point(LOCAL, oldest_unrevoked_local_ctn + 1)
                self.send_message(
                    "revoke_and_ack",
                    channel_id=chan.channel_id,
                    per_commitment_secret=last_secret,
                    next_per_commitment_point=next_point)
            else:
                self.logger.warning(f"channel_reestablish ({chan.get_id_for_log()}): "
                                    f"expected local ctn {oldest_unrevoked_local_ctn}, got {their_oldest_unrevoked_remote_ctn}")
                if their_oldest_unrevoked_remote_ctn < oldest_unrevoked_local_ctn:
                    we_are_ahead = True
                else:
                    they_are_ahead = True
        # option_data_loss_protect
        def are_datalossprotect_fields_valid() -> bool:
            if their_local_pcp is None or their_claim_of_our_last_per_commitment_secret is None:
                return False
            if their_oldest_unrevoked_remote_ctn > 0:
                our_pcs, __ = chan.get_secret_and_point(LOCAL, their_oldest_unrevoked_remote_ctn - 1)
            else:
                assert their_oldest_unrevoked_remote_ctn == 0
                our_pcs = bytes(32)
            if our_pcs != their_claim_of_our_last_per_commitment_secret:
                self.logger.error(f"channel_reestablish ({chan.get_id_for_log()}): "
                                  f"(DLP) local PCS mismatch: {bh2u(our_pcs)} != {bh2u(their_claim_of_our_last_per_commitment_secret)}")
                return False
            if chan.is_static_remotekey_enabled():
                return True
            try:
                __, our_remote_pcp = chan.get_secret_and_point(REMOTE, their_next_local_ctn - 1)
            except RemoteCtnTooFarInFuture:
                pass
            else:
                if our_remote_pcp != their_local_pcp:
                    self.logger.error(f"channel_reestablish ({chan.get_id_for_log()}): "
                                      f"(DLP) remote PCP mismatch: {bh2u(our_remote_pcp)} != {bh2u(their_local_pcp)}")
                    return False
            return True

        if not are_datalossprotect_fields_valid():
            raise RemoteMisbehaving("channel_reestablish: data loss protect fields invalid")

        if they_are_ahead:
            self.logger.warning(f"channel_reestablish ({chan.get_id_for_log()}): "
                                f"remote is ahead of us! They should force-close. Remote PCP: {bh2u(their_local_pcp)}")
            # data_loss_protect_remote_pcp is used in lnsweep
            chan.set_data_loss_protect_remote_pcp(their_next_local_ctn - 1, their_local_pcp)
            self.lnworker.save_channel(chan)
            chan.peer_state = PeerState.BAD
            return
        elif we_are_ahead:
            self.logger.warning(f"channel_reestablish ({chan.get_id_for_log()}): we are ahead of remote! trying to force-close.")
            await self.lnworker.try_force_closing(chan_id)
            return

        chan.peer_state = PeerState.GOOD
        if chan.is_funded() and their_next_local_ctn == next_local_ctn == 1:
            self.send_funding_locked(chan)
        # checks done
        if chan.is_funded() and chan.config[LOCAL].funding_locked_received:
            self.mark_open(chan)
        util.trigger_callback('channel', chan)
        if chan.get_state() == ChannelState.CLOSING:
            await self.send_shutdown(chan)

    def send_funding_locked(self, chan: Channel):
        channel_id = chan.channel_id
        per_commitment_secret_index = RevocationStore.START_INDEX - 1
        per_commitment_point_second = secret_to_pubkey(int.from_bytes(
            get_per_commitment_secret_from_seed(chan.config[LOCAL].per_commitment_secret_seed, per_commitment_secret_index), 'big'))
        # note: if funding_locked was not yet received, we might send it multiple times
        self.send_message("funding_locked", channel_id=channel_id, next_per_commitment_point=per_commitment_point_second)
        if chan.is_funded() and chan.config[LOCAL].funding_locked_received:
            self.mark_open(chan)

    def on_funding_locked(self, chan: Channel, payload):
        self.logger.info(f"on_funding_locked. channel: {bh2u(chan.channel_id)}")
        if not chan.config[LOCAL].funding_locked_received:
            their_next_point = payload["next_per_commitment_point"]
            chan.config[REMOTE].next_per_commitment_point = their_next_point
            chan.config[LOCAL].funding_locked_received = True
            self.lnworker.save_channel(chan)
        if chan.is_funded():
            self.mark_open(chan)

    def on_network_update(self, chan: Channel, funding_tx_depth: int):
        """
        Only called when the channel is OPEN.

        Runs on the Network thread.
        """
        if not chan.config[LOCAL].was_announced and funding_tx_depth >= 6:
            # don't announce our channels
            # FIXME should this be a field in chan.local_state maybe?
            return
            chan.config[LOCAL].was_announced = True
            self.lnworker.save_channel(chan)
            coro = self.handle_announcements(chan)
            asyncio.run_coroutine_threadsafe(coro, self.network.asyncio_loop)

    @log_exceptions
    async def handle_announcements(self, chan: Channel):
        h, local_node_sig, local_bitcoin_sig = self.send_announcement_signatures(chan)
        announcement_signatures_msg = await self.announcement_signatures[chan.channel_id].get()
        remote_node_sig = announcement_signatures_msg["node_signature"]
        remote_bitcoin_sig = announcement_signatures_msg["bitcoin_signature"]
        if not ecc.verify_signature(chan.config[REMOTE].multisig_key.pubkey, remote_bitcoin_sig, h):
            raise Exception("bitcoin_sig invalid in announcement_signatures")
        if not ecc.verify_signature(self.pubkey, remote_node_sig, h):
            raise Exception("node_sig invalid in announcement_signatures")

        node_sigs = [remote_node_sig, local_node_sig]
        bitcoin_sigs = [remote_bitcoin_sig, local_bitcoin_sig]
        bitcoin_keys = [chan.config[REMOTE].multisig_key.pubkey, chan.config[LOCAL].multisig_key.pubkey]

        if self.node_ids[0] > self.node_ids[1]:
            node_sigs.reverse()
            bitcoin_sigs.reverse()
            node_ids = list(reversed(self.node_ids))
            bitcoin_keys.reverse()
        else:
            node_ids = self.node_ids

        self.send_message("channel_announcement",
            node_signatures_1=node_sigs[0],
            node_signatures_2=node_sigs[1],
            bitcoin_signature_1=bitcoin_sigs[0],
            bitcoin_signature_2=bitcoin_sigs[1],
            len=0,
            #features not set (defaults to zeros)
            chain_hash=constants.net.rev_genesis_bytes(),
            short_channel_id=chan.short_channel_id,
            node_id_1=node_ids[0],
            node_id_2=node_ids[1],
            bitcoin_key_1=bitcoin_keys[0],
            bitcoin_key_2=bitcoin_keys[1]
        )

    def mark_open(self, chan: Channel):
        assert chan.is_funded()
        # only allow state transition from "FUNDED" to "OPEN"
        old_state = chan.get_state()
        if old_state == ChannelState.OPEN:
            return
        if old_state != ChannelState.FUNDED:
            self.logger.info(f"cannot mark open ({chan.get_id_for_log()}), current state: {repr(old_state)}")
            return
        assert chan.config[LOCAL].funding_locked_received
        chan.set_state(ChannelState.OPEN)
        util.trigger_callback('channel', chan)
        # peer may have sent us a channel update for the incoming direction previously
        pending_channel_update = self.orphan_channel_updates.get(chan.short_channel_id)
        if pending_channel_update:
            chan.set_remote_update(pending_channel_update['raw'])
        self.logger.info(f"CHANNEL OPENING COMPLETED ({chan.get_id_for_log()})")
        forwarding_enabled = self.network.config.get('lightning_forward_payments', False)
        if forwarding_enabled:
            # send channel_update of outgoing edge to peer,
            # so that channel can be used to to receive payments
            self.logger.info(f"sending channel update for outgoing edge ({chan.get_id_for_log()})")
            chan_upd = chan.get_outgoing_gossip_channel_update()
            self.transport.send_bytes(chan_upd)

    def send_announcement_signatures(self, chan: Channel):
        chan_ann = chan.construct_channel_announcement_without_sigs()
        preimage = chan_ann[256+2:]
        msg_hash = sha256d(preimage)
        bitcoin_signature = ecc.ECPrivkey(chan.config[LOCAL].multisig_key.privkey).sign(msg_hash, sig_string_from_r_and_s)
        node_signature = ecc.ECPrivkey(self.privkey).sign(msg_hash, sig_string_from_r_and_s)
        self.send_message("announcement_signatures",
            channel_id=chan.channel_id,
            short_channel_id=chan.short_channel_id,
            node_signature=node_signature,
            bitcoin_signature=bitcoin_signature
        )
        return msg_hash, node_signature, bitcoin_signature

    def on_update_fail_htlc(self, chan: Channel, payload):
        htlc_id = payload["id"]
        reason = payload["reason"]
        self.logger.info(f"on_update_fail_htlc. chan {chan.short_channel_id}. htlc_id {htlc_id}")
        chan.receive_fail_htlc(htlc_id, error_bytes=reason)  # TODO handle exc and maybe fail channel (e.g. bad htlc_id)
        self.maybe_send_commitment(chan)

    def maybe_send_commitment(self, chan: Channel):
        # REMOTE should revoke first before we can sign a new ctx
        if chan.hm.is_revack_pending(REMOTE):
            return
        # if there are no changes, we will not (and must not) send a new commitment
        if not chan.has_pending_changes(REMOTE):
            return
        self.logger.info(f'send_commitment. chan {chan.short_channel_id}. ctn: {chan.get_next_ctn(REMOTE)}.')
        sig_64, htlc_sigs = chan.sign_next_commitment()
        self.send_message("commitment_signed", channel_id=chan.channel_id, signature=sig_64, num_htlcs=len(htlc_sigs), htlc_signature=b"".join(htlc_sigs))

    def pay(self, *, route: 'LNPaymentRoute', chan: Channel, amount_msat: int,
            payment_hash: bytes, min_final_cltv_expiry: int, payment_secret: bytes = None) -> UpdateAddHtlc:
        assert amount_msat > 0, "amount_msat is not greater zero"
        assert len(route) > 0
        if not chan.can_send_update_add_htlc():
            raise PaymentFailure("Channel cannot send update_add_htlc")
        # add features learned during "init" for direct neighbour:
        route[0].node_features |= self.features
        local_height = self.network.get_local_height()
        # create onion packet
        final_cltv = local_height + min_final_cltv_expiry
        hops_data, amount_msat, cltv = calc_hops_data_for_payment(route, amount_msat, final_cltv,
                                                                  payment_secret=payment_secret)
        assert final_cltv <= cltv, (final_cltv, cltv)
        secret_key = os.urandom(32)
        onion = new_onion_packet([x.node_id for x in route], secret_key, hops_data, associated_data=payment_hash)
        # create htlc
        if cltv > local_height + lnutil.NBLOCK_CLTV_EXPIRY_TOO_FAR_INTO_FUTURE:
            raise PaymentFailure(f"htlc expiry too far into future. (in {cltv-local_height} blocks)")
        htlc = UpdateAddHtlc(amount_msat=amount_msat, payment_hash=payment_hash, cltv_expiry=cltv, timestamp=int(time.time()))
        htlc = chan.add_htlc(htlc)
        chan.set_onion_key(htlc.htlc_id, secret_key)
        self.logger.info(f"starting payment. len(route)={len(route)}. route: {route}. "
                         f"htlc: {htlc}. hops_data={hops_data!r}")
        self.send_message(
            "update_add_htlc",
            channel_id=chan.channel_id,
            id=htlc.htlc_id,
            cltv_expiry=htlc.cltv_expiry,
            amount_msat=htlc.amount_msat,
            payment_hash=htlc.payment_hash,
            onion_routing_packet=onion.to_bytes())
        self.maybe_send_commitment(chan)
        return htlc

    def send_revoke_and_ack(self, chan: Channel):
        self.logger.info(f'send_revoke_and_ack. chan {chan.short_channel_id}. ctn: {chan.get_oldest_unrevoked_ctn(LOCAL)}')
        rev = chan.revoke_current_commitment()
        self.lnworker.save_channel(chan)
        self.send_message("revoke_and_ack",
            channel_id=chan.channel_id,
            per_commitment_secret=rev.per_commitment_secret,
            next_per_commitment_point=rev.next_per_commitment_point)
        self.maybe_send_commitment(chan)

    def on_commitment_signed(self, chan: Channel, payload):
        if chan.peer_state == PeerState.BAD:
            return
        self.logger.info(f'on_commitment_signed. chan {chan.short_channel_id}. ctn: {chan.get_next_ctn(LOCAL)}.')
        # make sure there were changes to the ctx, otherwise the remote peer is misbehaving
        if not chan.has_pending_changes(LOCAL):
            # TODO if feerate changed A->B->A; so there were updates but the value is identical,
            #      then it might be legal to send a commitment_signature
            #      see https://github.com/lightningnetwork/lightning-rfc/pull/618
            raise RemoteMisbehaving('received commitment_signed without pending changes')
        # REMOTE should wait until we have revoked
        if chan.hm.is_revack_pending(LOCAL):
            raise RemoteMisbehaving('received commitment_signed before we revoked previous ctx')
        data = payload["htlc_signature"]
        htlc_sigs = list(chunks(data, 64))
        chan.receive_new_commitment(payload["signature"], htlc_sigs)
        self.send_revoke_and_ack(chan)

    def on_update_fulfill_htlc(self, chan: Channel, payload):
        preimage = payload["payment_preimage"]
        payment_hash = sha256(preimage)
        htlc_id = payload["id"]
        self.logger.info(f"on_update_fulfill_htlc. chan {chan.short_channel_id}. htlc_id {htlc_id}")
        chan.receive_htlc_settle(preimage, htlc_id)  # TODO handle exc and maybe fail channel (e.g. bad htlc_id)
        self.lnworker.save_preimage(payment_hash, preimage)
        self.maybe_send_commitment(chan)

    def on_update_fail_malformed_htlc(self, chan: Channel, payload):
        htlc_id = payload["id"]
        failure_code = payload["failure_code"]
        self.logger.info(f"on_update_fail_malformed_htlc. chan {chan.get_id_for_log()}. "
                         f"htlc_id {htlc_id}. failure_code={failure_code}")
        if failure_code & OnionFailureCodeMetaFlag.BADONION == 0:
            asyncio.ensure_future(self.lnworker.try_force_closing(chan.channel_id))
            raise RemoteMisbehaving(f"received update_fail_malformed_htlc with unexpected failure code: {failure_code}")
        reason = OnionRoutingFailureMessage(code=failure_code, data=payload["sha256_of_onion"])
        chan.receive_fail_htlc(htlc_id, error_bytes=None, reason=reason)
        self.maybe_send_commitment(chan)

    def on_update_add_htlc(self, chan: Channel, payload):
        payment_hash = payload["payment_hash"]
        htlc_id = payload["id"]
        self.logger.info(f"on_update_add_htlc. chan {chan.short_channel_id}. htlc_id {htlc_id}")
        cltv_expiry = payload["cltv_expiry"]
        amount_msat_htlc = payload["amount_msat"]
        onion_packet = payload["onion_routing_packet"]
        if chan.get_state() != ChannelState.OPEN:
            raise RemoteMisbehaving(f"received update_add_htlc while chan.get_state() != OPEN. state was {chan.get_state()!r}")
        if cltv_expiry > bitcoin.NLOCKTIME_BLOCKHEIGHT_MAX:
            asyncio.ensure_future(self.lnworker.try_force_closing(chan.channel_id))
            raise RemoteMisbehaving(f"received update_add_htlc with cltv_expiry > BLOCKHEIGHT_MAX. value was {cltv_expiry}")
        # add htlc
        htlc = UpdateAddHtlc(
            amount_msat=amount_msat_htlc,
            payment_hash=payment_hash,
            cltv_expiry=cltv_expiry,
            timestamp=int(time.time()),
            htlc_id=htlc_id)
        chan.receive_htlc(htlc, onion_packet)

    def maybe_forward_htlc(self, chan: Channel, htlc: UpdateAddHtlc, *,
                           onion_packet: OnionPacket, processed_onion: ProcessedOnionPacket
                           ) -> Tuple[Optional[bytes], Optional[int], Optional[OnionRoutingFailureMessage]]:
        # Forward HTLC
        # FIXME: there are critical safety checks MISSING here
        forwarding_enabled = self.network.config.get('lightning_forward_payments', False)
        if not forwarding_enabled:
            self.logger.info(f"forwarding is disabled. failing htlc.")
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.PERMANENT_CHANNEL_FAILURE, data=b'')
        chain = self.network.blockchain()
        if chain.is_tip_stale():
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
        try:
            next_chan_scid = processed_onion.hop_data.payload["short_channel_id"]["short_channel_id"]
        except:
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_PAYLOAD, data=b'\x00\x00\x00')
        next_chan = self.lnworker.get_channel_by_short_id(next_chan_scid)
        local_height = chain.height()
        if next_chan is None:
            self.logger.info(f"cannot forward htlc. cannot find next_chan {next_chan_scid}")
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.UNKNOWN_NEXT_PEER, data=b'')
        outgoing_chan_upd = next_chan.get_outgoing_gossip_channel_update()[2:]
        outgoing_chan_upd_len = len(outgoing_chan_upd).to_bytes(2, byteorder="big")
        if not next_chan.can_send_update_add_htlc():
            self.logger.info(f"cannot forward htlc. next_chan {next_chan_scid} cannot send ctx updates. "
                             f"chan state {next_chan.get_state()!r}, peer state: {next_chan.peer_state!r}")
            data = outgoing_chan_upd_len + outgoing_chan_upd
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_CHANNEL_FAILURE, data=data)
        try:
            next_cltv_expiry = processed_onion.hop_data.payload["outgoing_cltv_value"]["outgoing_cltv_value"]
        except:
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_PAYLOAD, data=b'\x00\x00\x00')
        if htlc.cltv_expiry - next_cltv_expiry < NBLOCK_OUR_CLTV_EXPIRY_DELTA:
            data = htlc.cltv_expiry.to_bytes(4, byteorder="big") + outgoing_chan_upd_len + outgoing_chan_upd
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.INCORRECT_CLTV_EXPIRY, data=data)
        if htlc.cltv_expiry - lnutil.MIN_FINAL_CLTV_EXPIRY_ACCEPTED <= local_height \
                or next_cltv_expiry <= local_height:
            data = outgoing_chan_upd_len + outgoing_chan_upd
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.EXPIRY_TOO_SOON, data=data)
        if max(htlc.cltv_expiry, next_cltv_expiry) > local_height + lnutil.NBLOCK_CLTV_EXPIRY_TOO_FAR_INTO_FUTURE:
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.EXPIRY_TOO_FAR, data=b'')
        try:
            next_amount_msat_htlc = processed_onion.hop_data.payload["amt_to_forward"]["amt_to_forward"]
        except:
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_PAYLOAD, data=b'\x00\x00\x00')
        forwarding_fees = fee_for_edge_msat(
            forwarded_amount_msat=next_amount_msat_htlc,
            fee_base_msat=lnutil.OUR_FEE_BASE_MSAT,
            fee_proportional_millionths=lnutil.OUR_FEE_PROPORTIONAL_MILLIONTHS)
        if htlc.amount_msat - next_amount_msat_htlc < forwarding_fees:
            data = next_amount_msat_htlc.to_bytes(8, byteorder="big") + outgoing_chan_upd_len + outgoing_chan_upd
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.FEE_INSUFFICIENT, data=data)
        self.logger.info(f'forwarding htlc to {next_chan.node_id}')
        next_htlc = UpdateAddHtlc(
            amount_msat=next_amount_msat_htlc,
            payment_hash=htlc.payment_hash,
            cltv_expiry=next_cltv_expiry,
            timestamp=int(time.time()))
        next_htlc = next_chan.add_htlc(next_htlc)
        next_peer = self.lnworker.peers[next_chan.node_id]
        try:
            next_peer.send_message(
                "update_add_htlc",
                channel_id=next_chan.channel_id,
                id=next_htlc.htlc_id,
                cltv_expiry=next_cltv_expiry,
                amount_msat=next_amount_msat_htlc,
                payment_hash=next_htlc.payment_hash,
                onion_routing_packet=processed_onion.next_packet.to_bytes()
            )
        except BaseException as e:
            self.logger.info(f"failed to forward htlc: error sending message. {e}")
            data = outgoing_chan_upd_len + outgoing_chan_upd
            return None, None, OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_CHANNEL_FAILURE, data=data)
        return next_chan_scid, next_htlc.htlc_id, None

    def maybe_fulfill_htlc(self, *, chan: Channel, htlc: UpdateAddHtlc,
                           onion_packet: OnionPacket, processed_onion: ProcessedOnionPacket,
                           ) -> Tuple[Optional[bytes], Optional[OnionRoutingFailureMessage]]:
        info = self.lnworker.get_payment_info(htlc.payment_hash)
        if info is None:
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS, data=b'')
            return None, reason
        preimage = self.lnworker.get_preimage(htlc.payment_hash)
        try:
            payment_secret_from_onion = processed_onion.hop_data.payload["payment_data"]["payment_secret"]
        except:
            pass  # skip
        else:
            if payment_secret_from_onion != derive_payment_secret_from_payment_preimage(preimage):
                reason = OnionRoutingFailureMessage(code=OnionFailureCode.INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS, data=b'')
                return None, reason
        expected_received_msat = int(info.amount * 1000) if info.amount is not None else None
        if expected_received_msat is not None and \
                not (expected_received_msat <= htlc.amount_msat <= 2 * expected_received_msat):
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS, data=b'')
            return None, reason
        # Check that our blockchain tip is sufficiently recent so that we have an approx idea of the height.
        # We should not release the preimage for an HTLC that its sender could already time out as
        # then they might try to force-close and it becomes a race.
        chain = self.network.blockchain()
        if chain.is_tip_stale():
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
            return None, reason
        local_height = chain.height()
        if local_height + MIN_FINAL_CLTV_EXPIRY_ACCEPTED > htlc.cltv_expiry:
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.FINAL_EXPIRY_TOO_SOON, data=b'')
            return None, reason
        try:
            cltv_from_onion = processed_onion.hop_data.payload["outgoing_cltv_value"]["outgoing_cltv_value"]
        except:
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_PAYLOAD, data=b'\x00\x00\x00')
            return None, reason
        if cltv_from_onion != htlc.cltv_expiry:
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.FINAL_INCORRECT_CLTV_EXPIRY,
                                                data=htlc.cltv_expiry.to_bytes(4, byteorder="big"))
            return None, reason
        try:
            amount_from_onion = processed_onion.hop_data.payload["amt_to_forward"]["amt_to_forward"]
        except:
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_PAYLOAD, data=b'\x00\x00\x00')
            return None, reason
        try:
            amount_from_onion = processed_onion.hop_data.payload["payment_data"]["total_msat"]
        except:
            pass  # fall back to "amt_to_forward"
        if amount_from_onion > htlc.amount_msat:
            reason = OnionRoutingFailureMessage(code=OnionFailureCode.FINAL_INCORRECT_HTLC_AMOUNT,
                                                data=htlc.amount_msat.to_bytes(8, byteorder="big"))
            return None, reason
        # all good
        return preimage, None

    def fulfill_htlc(self, chan: Channel, htlc_id: int, preimage: bytes):
        self.logger.info(f"_fulfill_htlc. chan {chan.short_channel_id}. htlc_id {htlc_id}")
        assert chan.can_send_ctx_updates(), f"cannot send updates: {chan.short_channel_id}"
        chan.settle_htlc(preimage, htlc_id)
        self.send_message("update_fulfill_htlc",
                          channel_id=chan.channel_id,
                          id=htlc_id,
                          payment_preimage=preimage)

    def fail_htlc(self, *, chan: Channel, htlc_id: int, onion_packet: Optional[OnionPacket],
                  reason: Optional[OnionRoutingFailureMessage], error_bytes: Optional[bytes]):
        self.logger.info(f"fail_htlc. chan {chan.short_channel_id}. htlc_id {htlc_id}. reason: {reason}")
        assert chan.can_send_ctx_updates(), f"cannot send updates: {chan.short_channel_id}"
        chan.fail_htlc(htlc_id)
        if onion_packet and reason:
            error_bytes = construct_onion_error(reason, onion_packet, our_onion_private_key=self.privkey)
        if error_bytes:
            self.send_message("update_fail_htlc",
                              channel_id=chan.channel_id,
                              id=htlc_id,
                              len=len(error_bytes),
                              reason=error_bytes)
        else:
            assert reason is not None
            if not (reason.code & OnionFailureCodeMetaFlag.BADONION and len(reason.data) == 32):
                raise Exception(f"unexpected reason when sending 'update_fail_malformed_htlc': {reason!r}")
            self.send_message("update_fail_malformed_htlc",
                              channel_id=chan.channel_id,
                              id=htlc_id,
                              sha256_of_onion=reason.data,
                              failure_code=reason.code)

    def on_revoke_and_ack(self, chan: Channel, payload):
        if chan.peer_state == PeerState.BAD:
            return
        self.logger.info(f'on_revoke_and_ack. chan {chan.short_channel_id}. ctn: {chan.get_oldest_unrevoked_ctn(REMOTE)}')
        rev = RevokeAndAck(payload["per_commitment_secret"], payload["next_per_commitment_point"])
        chan.receive_revocation(rev)
        self.lnworker.save_channel(chan)
        self.maybe_send_commitment(chan)

    def on_update_fee(self, chan: Channel, payload):
        feerate = payload["feerate_per_kw"]
        chan.update_fee(feerate, False)

    async def maybe_update_fee(self, chan: Channel):
        """
        called when our fee estimates change
        """
        if not chan.can_send_ctx_updates():
            return
        feerate_per_kw = self.lnworker.current_feerate_per_kw()
        if not chan.constraints.is_initiator:
            if constants.net is not constants.BitcoinRegtest:
                chan_feerate = chan.get_latest_feerate(LOCAL)
                ratio = chan_feerate / feerate_per_kw
                if ratio < 0.5:
                    # Note that we trust the Electrum server about fee rates
                    # Thus, automated force-closing might not be a good idea
                    # Maybe we should display something in the GUI instead
                    self.logger.warning(
                        f"({chan.get_id_for_log()}) feerate is {chan_feerate} sat/kw, "
                        f"current recommended feerate is {feerate_per_kw} sat/kw, consider force closing!")
            return
        chan_fee = chan.get_next_feerate(REMOTE)
        if feerate_per_kw < chan_fee / 2:
            self.logger.info("FEES HAVE FALLEN")
        elif feerate_per_kw > chan_fee * 2:
            self.logger.info("FEES HAVE RISEN")
        else:
            return
        self.logger.info(f"(chan: {chan.get_id_for_log()}) current pending feerate {chan_fee}. "
                         f"new feerate {feerate_per_kw}")
        chan.update_fee(feerate_per_kw, True)
        self.send_message(
            "update_fee",
            channel_id=chan.channel_id,
            feerate_per_kw=feerate_per_kw)
        self.maybe_send_commitment(chan)

    @log_exceptions
    async def close_channel(self, chan_id: bytes):
        chan = self.channels[chan_id]
        self.shutdown_received[chan_id] = asyncio.Future()
        await self.send_shutdown(chan)
        payload = await self.shutdown_received[chan_id]
        txid = await self._shutdown(chan, payload, True)
        self.logger.info(f'({chan.get_id_for_log()}) Channel closed {txid}')
        return txid

    @log_exceptions
    async def on_shutdown(self, chan: Channel, payload):
        their_scriptpubkey = payload['scriptpubkey']
        # BOLT-02 restrict the scriptpubkey to some templates:
        if not (match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_WITNESS_V0)
                or match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_P2SH)
                or match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_P2PKH)):
            raise Exception(f'scriptpubkey in received shutdown message does not conform to any template: {their_scriptpubkey.hex()}')
        chan_id = chan.channel_id
        if chan_id in self.shutdown_received:
            self.shutdown_received[chan_id].set_result(payload)
        else:
            chan = self.channels[chan_id]
            await self.send_shutdown(chan)
            txid = await self._shutdown(chan, payload, False)
            self.logger.info(f'({chan.get_id_for_log()}) Channel closed by remote peer {txid}')

    def can_send_shutdown(self, chan):
        if chan.get_state() >= ChannelState.OPENING:
            return True
        if chan.constraints.is_initiator and chan.channel_id in self.funding_created_sent:
            return True
        if not chan.constraints.is_initiator and chan.channel_id in self.funding_signed_sent:
            return True
        return False

    async def send_shutdown(self, chan: Channel):
        if not self.can_send_shutdown(chan):
            raise Exception('cannot send shutdown')
        scriptpubkey = bfh(bitcoin.address_to_script(chan.sweep_address))
        # wait until no more pending updates (bolt2)
        chan.set_can_send_ctx_updates(False)
        while chan.has_pending_changes(REMOTE):
            await asyncio.sleep(0.1)
        self.send_message('shutdown', channel_id=chan.channel_id, len=len(scriptpubkey), scriptpubkey=scriptpubkey)
        chan.set_state(ChannelState.CLOSING)
        # can fullfill or fail htlcs. cannot add htlcs, because of CLOSING state
        chan.set_can_send_ctx_updates(True)

    @log_exceptions
    async def _shutdown(self, chan: Channel, payload, is_local):
        # wait until no HTLCs remain in either commitment transaction
        while len(chan.hm.htlcs(LOCAL)) + len(chan.hm.htlcs(REMOTE)) > 0:
            self.logger.info(f'(chan: {chan.short_channel_id}) waiting for htlcs to settle...')
            await asyncio.sleep(1)
        # if no HTLCs remain, we must not send updates
        chan.set_can_send_ctx_updates(False)
        their_scriptpubkey = payload['scriptpubkey']
        our_scriptpubkey = bfh(bitcoin.address_to_script(chan.sweep_address))
        # estimate fee of closing tx
        our_sig, closing_tx = chan.make_closing_tx(our_scriptpubkey, their_scriptpubkey, fee_sat=0)
        fee_rate = self.network.config.fee_per_kb()
        our_fee = fee_rate * closing_tx.estimated_size() // 1000
        # BOLT2: The sending node MUST set fee less than or equal to the base fee of the final ctx
        max_fee = chan.get_latest_fee(LOCAL if is_local else REMOTE)
        our_fee = min(our_fee, max_fee)
        drop_remote = False
        def send_closing_signed():
            our_sig, closing_tx = chan.make_closing_tx(our_scriptpubkey, their_scriptpubkey, fee_sat=our_fee, drop_remote=drop_remote)
            self.send_message('closing_signed', channel_id=chan.channel_id, fee_satoshis=our_fee, signature=our_sig)
        def verify_signature(tx, sig):
            their_pubkey = chan.config[REMOTE].multisig_key.pubkey
            preimage_hex = tx.serialize_preimage(0)
            pre_hash = sha256d(bfh(preimage_hex))
            return ecc.verify_signature(their_pubkey, sig, pre_hash)
        # the funder sends the first 'closing_signed' message
        if chan.constraints.is_initiator:
            send_closing_signed()
        # negotiate fee
        while True:
            # FIXME: the remote SHOULD send closing_signed, but some don't.
            cs_payload = await self.wait_for_message('closing_signed', chan.channel_id)
            their_fee = cs_payload['fee_satoshis']
            if their_fee > max_fee:
                raise Exception(f'the proposed fee exceeds the base fee of the latest commitment transaction {is_local, their_fee, max_fee}')
            their_sig = cs_payload['signature']
            # verify their sig: they might have dropped their output
            our_sig, closing_tx = chan.make_closing_tx(our_scriptpubkey, their_scriptpubkey, fee_sat=their_fee, drop_remote=False)
            if verify_signature(closing_tx, their_sig):
                drop_remote = False
            else:
                our_sig, closing_tx = chan.make_closing_tx(our_scriptpubkey, their_scriptpubkey, fee_sat=their_fee, drop_remote=True)
                if verify_signature(closing_tx, their_sig):
                    drop_remote = True
                else:
                    raise Exception('failed to verify their signature')
            # Agree if difference is lower or equal to one (see below)
            if abs(our_fee - their_fee) < 2:
                our_fee = their_fee
                break
            # this will be "strictly between" (as in BOLT2) previous values because of the above
            our_fee = (our_fee + their_fee) // 2
            # another round
            send_closing_signed()
        # the non-funder replies
        if not chan.constraints.is_initiator:
            send_closing_signed()
        # add signatures
        closing_tx.add_signature_to_txin(txin_idx=0,
                                         signing_pubkey=chan.config[LOCAL].multisig_key.pubkey.hex(),
                                         sig=bh2u(der_sig_from_sig_string(our_sig) + b'\x01'))
        closing_tx.add_signature_to_txin(txin_idx=0,
                                         signing_pubkey=chan.config[REMOTE].multisig_key.pubkey.hex(),
                                         sig=bh2u(der_sig_from_sig_string(their_sig) + b'\x01'))
        # broadcast
        await self.network.try_broadcasting(closing_tx, 'closing')
        return closing_tx.txid()

    async def htlc_switch(self):
        await self.initialized
        while True:
            await asyncio.sleep(0.1)
            self.ping_if_required()
            for chan_id, chan in self.channels.items():
                if not chan.can_send_ctx_updates():
                    continue
                self.maybe_send_commitment(chan)
                done = set()
                unfulfilled = chan.hm.log.get('unfulfilled_htlcs', {})
                for htlc_id, (local_ctn, remote_ctn, onion_packet_hex, forwarding_info) in unfulfilled.items():
                    if chan.get_oldest_unrevoked_ctn(LOCAL) <= local_ctn:
                        continue
                    if chan.get_oldest_unrevoked_ctn(REMOTE) <= remote_ctn:
                        continue
                    chan.logger.info(f'found unfulfilled htlc: {htlc_id}')
                    htlc = chan.hm.log[REMOTE]['adds'][htlc_id]
                    payment_hash = htlc.payment_hash
                    error_reason = None  # type: Optional[OnionRoutingFailureMessage]
                    error_bytes = None  # type: Optional[bytes]
                    preimage = None
                    onion_packet_bytes = bytes.fromhex(onion_packet_hex)
                    onion_packet = None
                    try:
                        if self.network.config.get('test_fail_malformed_htlc'): raise InvalidOnionPubkey()
                        onion_packet = OnionPacket.from_bytes(onion_packet_bytes)
                        processed_onion = process_onion_packet(onion_packet, associated_data=payment_hash, our_onion_private_key=self.privkey)
                    except UnsupportedOnionPacketVersion:
                        error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_VERSION, data=sha256(onion_packet_bytes))
                    except InvalidOnionPubkey:
                        error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_KEY, data=sha256(onion_packet_bytes))
                    except InvalidOnionMac:
                        error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_HMAC, data=sha256(onion_packet_bytes))
                    except Exception as e:
                        self.logger.info(f"error processing onion packet: {e!r}")
                        error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
                    else:
                        if self.network.config.get('test_fail_htlcs_with_temp_node_failure'):
                            error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
                        elif processed_onion.are_we_final:
                            preimage, error_reason = self.maybe_fulfill_htlc(
                                chan=chan,
                                htlc=htlc,
                                onion_packet=onion_packet,
                                processed_onion=processed_onion)
                        elif not forwarding_info:
                            next_chan_id, next_htlc_id, error_reason = self.maybe_forward_htlc(
                                chan=chan,
                                htlc=htlc,
                                onion_packet=onion_packet,
                                processed_onion=processed_onion)
                            if next_chan_id:
                                fw_info = (next_chan_id.hex(), next_htlc_id)
                                unfulfilled[htlc_id] = local_ctn, remote_ctn, onion_packet_hex, fw_info
                        else:
                            preimage = self.lnworker.get_preimage(payment_hash)
                            next_chan_id_hex, htlc_id = forwarding_info
                            next_chan = self.lnworker.get_channel_by_short_id(bytes.fromhex(next_chan_id_hex))
                            if next_chan:
                                error_bytes, error_reason = next_chan.pop_fail_htlc_reason(htlc_id)
                        if preimage:
                            await self.lnworker.enable_htlc_settle.wait()
                            self.fulfill_htlc(chan, htlc.htlc_id, preimage)
                            done.add(htlc_id)
                    if error_reason or error_bytes:
                        self.fail_htlc(chan=chan,
                                       htlc_id=htlc.htlc_id,
                                       onion_packet=onion_packet,
                                       reason=error_reason,
                                       error_bytes=error_bytes)
                        done.add(htlc_id)
                # cleanup
                for htlc_id in done:
                    unfulfilled.pop(htlc_id)