electrum/electrum/lnchannel.py

# Copyright (C) 2018 The Electrum developers
# Copyright (C) 2015-2018 The Lightning Network Developers
#
# 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.

# API (method signatures and docstrings) partially copied from lnd
# 42de4400bff5105352d0552155f73589166d162b

import os
from collections import namedtuple, defaultdict
import binascii
import json
from enum import Enum, auto
from typing import Optional, Dict, List, Tuple, NamedTuple, Set, Callable, Iterable, Sequence

from . import ecc
from .util import bfh, PrintError, bh2u
from .bitcoin import TYPE_SCRIPT, TYPE_ADDRESS
from .bitcoin import redeem_script_to_address
from .crypto import sha256, sha256d
from .simple_config import get_config
from .transaction import Transaction

from .lnutil import (Outpoint, LocalConfig, RemoteConfig, Keypair, OnlyPubkeyKeypair, ChannelConstraints,
                    get_per_commitment_secret_from_seed, secret_to_pubkey, derive_privkey, make_closing_tx,
                    sign_and_get_sig_string, RevocationStore, derive_blinded_pubkey, Direction, derive_pubkey,
                    make_htlc_tx_with_open_channel, make_commitment, make_received_htlc, make_offered_htlc,
                    HTLC_TIMEOUT_WEIGHT, HTLC_SUCCESS_WEIGHT, extract_ctn_from_tx_and_chan, UpdateAddHtlc,
                    funding_output_script, SENT, RECEIVED, LOCAL, REMOTE, HTLCOwner, make_commitment_outputs,
                    ScriptHtlc, PaymentFailure, calc_onchain_fees, RemoteMisbehaving, make_htlc_output_witness_script)
from .lnsweep import create_sweeptxs_for_their_just_revoked_ctx
from .lnsweep import create_sweeptxs_for_our_latest_ctx, create_sweeptxs_for_their_latest_ctx
from .lnhtlc import HTLCManager


class ChannelJsonEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, bytes):
            return binascii.hexlify(o).decode("ascii")
        if isinstance(o, RevocationStore):
            return o.serialize()
        if isinstance(o, set):
            return list(o)
        return super().default(o)

RevokeAndAck = namedtuple("RevokeAndAck", ["per_commitment_secret", "next_per_commitment_point"])

class FeeUpdateProgress(Enum):
    FUNDEE_SIGNED = auto()
    FUNDEE_ACKED =  auto()
    FUNDER_SIGNED = auto()

FUNDEE_SIGNED = FeeUpdateProgress.FUNDEE_SIGNED
FUNDEE_ACKED = FeeUpdateProgress.FUNDEE_ACKED
FUNDER_SIGNED = FeeUpdateProgress.FUNDER_SIGNED

class FeeUpdate(defaultdict):
    def __init__(self, chan, rate):
        super().__init__(lambda: False)
        self.rate = rate
        self.chan = chan

    def pending_feerate(self, subject):
        if self[FUNDEE_ACKED]:
            return self.rate
        if subject == REMOTE and self.chan.constraints.is_initiator:
            return self.rate
        if subject == LOCAL and not self.chan.constraints.is_initiator:
            return self.rate
        # implicit return None

def decodeAll(d, local):
    for k, v in d.items():
        if k == 'revocation_store':
            yield (k, RevocationStore.from_json_obj(v))
        elif k.endswith("_basepoint") or k.endswith("_key"):
            if local:
                yield (k, Keypair(**dict(decodeAll(v, local))))
            else:
                yield (k, OnlyPubkeyKeypair(**dict(decodeAll(v, local))))
        elif k in ["node_id", "channel_id", "short_channel_id", "pubkey", "privkey", "current_per_commitment_point", "next_per_commitment_point", "per_commitment_secret_seed", "current_commitment_signature", "current_htlc_signatures"] and v is not None:
            yield (k, binascii.unhexlify(v))
        else:
            yield (k, v)

def htlcsum(htlcs):
    return sum([x.amount_msat for x in htlcs])

# following two functions are used because json
# doesn't store int keys and byte string values
def str_bytes_dict_from_save(x):
    return {int(k): bfh(v) for k,v in x.items()}

def str_bytes_dict_to_save(x):
    return {str(k): bh2u(v) for k, v in x.items()}

class Channel(PrintError):
    def diagnostic_name(self):
        if self.name:
            return str(self.name)
        try:
            return f"lnchannel_{bh2u(self.channel_id[-4:])}"
        except:
            return super().diagnostic_name()

    def __init__(self, state, *, sweep_address=None, name=None,
                 payment_completed: Optional[Callable[['Channel', Direction, UpdateAddHtlc, bytes], None]] = None):
        self.preimages = {}
        if not payment_completed:
            payment_completed = lambda this, x, y, z: None
        self.sweep_address = sweep_address
        self.payment_completed = payment_completed
        assert 'local_state' not in state
        self.config = {}
        self.config[LOCAL] = state["local_config"]
        if type(self.config[LOCAL]) is not LocalConfig:
            conf = dict(decodeAll(self.config[LOCAL], True))
            self.config[LOCAL] = LocalConfig(**conf)
        assert type(self.config[LOCAL].htlc_basepoint.privkey) is bytes

        self.config[REMOTE] = state["remote_config"]
        if type(self.config[REMOTE]) is not RemoteConfig:
            conf = dict(decodeAll(self.config[REMOTE], False))
            self.config[REMOTE] = RemoteConfig(**conf)
        assert type(self.config[REMOTE].htlc_basepoint.pubkey) is bytes

        self.channel_id = bfh(state["channel_id"]) if type(state["channel_id"]) not in (bytes, type(None)) else state["channel_id"]
        self.constraints = ChannelConstraints(**state["constraints"]) if type(state["constraints"]) is not ChannelConstraints else state["constraints"]
        self.funding_outpoint = Outpoint(**dict(decodeAll(state["funding_outpoint"], False))) if type(state["funding_outpoint"]) is not Outpoint else state["funding_outpoint"]
        self.node_id = bfh(state["node_id"]) if type(state["node_id"]) not in (bytes, type(None)) else state["node_id"]
        self.short_channel_id = bfh(state["short_channel_id"]) if type(state["short_channel_id"]) not in (bytes, type(None)) else state["short_channel_id"]
        self.short_channel_id_predicted = self.short_channel_id
        self.onion_keys = str_bytes_dict_from_save(state.get('onion_keys', {}))

        # FIXME this is a tx serialised in the custom electrum partial tx format.
        # we should not persist txns in this format. we should persist htlcs, and be able to derive
        # any past commitment transaction and use that instead; until then...
        self.remote_commitment_to_be_revoked = Transaction(state["remote_commitment_to_be_revoked"])
        self.remote_commitment_to_be_revoked.deserialize(True)

        self.hm = HTLCManager(state.get('log'))

        self.name = name

        self.pending_fee = None

        self._is_funding_txo_spent = None  # "don't know"
        self._state = None
        if state.get('force_closed', False):
            self.set_state('FORCE_CLOSING')
        else:
            self.set_state('DISCONNECTED')

        self.lnwatcher = None

        self.local_commitment = None
        self.remote_commitment = None

    def get_payments(self):
        out = {}
        for subject in LOCAL, REMOTE:
            log = self.hm.log[subject]
            for htlc_id, htlc in log.get('adds', {}).items():
                rhash = bh2u(htlc.payment_hash)
                status = 'settled' if htlc_id in log.get('settles',{}) else 'inflight'
                direction = SENT if subject is LOCAL else RECEIVED
                out[rhash] = (self.channel_id, htlc, direction, status)
        return out

    def set_local_commitment(self, ctx):
        ctn = extract_ctn_from_tx_and_chan(ctx, self)
        assert self.signature_fits(ctx), (self.hm.log[LOCAL])
        self.local_commitment = ctx
        if self.sweep_address is not None:
            self.local_sweeptxs = create_sweeptxs_for_our_latest_ctx(self, self.local_commitment, self.sweep_address)
            initial = os.path.join(get_config().electrum_path(), 'initial_commitment_tx')
            tx = self.force_close_tx().serialize_to_network()
            if not os.path.exists(initial):
                with open(initial, 'w') as f:
                    f.write(tx)

    def set_remote_commitment(self):
        self.remote_commitment = self.current_commitment(REMOTE)
        if self.sweep_address is not None:
            self.remote_sweeptxs = create_sweeptxs_for_their_latest_ctx(self, self.remote_commitment, self.sweep_address)

    def set_state(self, state: str):
        if self._state == 'FORCE_CLOSING':
            assert state == 'FORCE_CLOSING', 'new state was not FORCE_CLOSING: ' + state
        self._state = state

    def get_state(self):
        return self._state

    def is_closed(self):
        return self.get_state() in ['CLOSED', 'FORCE_CLOSING']

    def _check_can_pay(self, amount_msat: int) -> None:
        if self.get_state() != 'OPEN':
            raise PaymentFailure('Channel not open')
        if self.available_to_spend(LOCAL) < amount_msat:
            raise PaymentFailure(f'Not enough local balance. Have: {self.available_to_spend(LOCAL)}, Need: {amount_msat}')
        if len(self.hm.htlcs(LOCAL)) + 1 > self.config[REMOTE].max_accepted_htlcs:
            raise PaymentFailure('Too many HTLCs already in channel')
        current_htlc_sum = htlcsum(self.hm.htlcs_by_direction(LOCAL, SENT)) + htlcsum(self.hm.htlcs_by_direction(LOCAL, RECEIVED))
        if current_htlc_sum + amount_msat > self.config[REMOTE].max_htlc_value_in_flight_msat:
            raise PaymentFailure(f'HTLC value sum (sum of pending htlcs: {current_htlc_sum/1000} sat plus new htlc: {amount_msat/1000} sat) would exceed max allowed: {self.config[REMOTE].max_htlc_value_in_flight_msat/1000} sat')
        if amount_msat < self.config[REMOTE].htlc_minimum_msat:
            raise PaymentFailure(f'HTLC value too small: {amount_msat} msat')

    def can_pay(self, amount_msat):
        try:
            self._check_can_pay(amount_msat)
        except PaymentFailure:
            return False
        return True

    def set_funding_txo_spentness(self, is_spent: bool):
        assert isinstance(is_spent, bool)
        self._is_funding_txo_spent = is_spent

    def should_try_to_reestablish_peer(self) -> bool:
        return self._is_funding_txo_spent is False and self._state == 'DISCONNECTED'

    def get_funding_address(self):
        script = funding_output_script(self.config[LOCAL], self.config[REMOTE])
        return redeem_script_to_address('p2wsh', script)

    def add_htlc(self, htlc: UpdateAddHtlc) -> UpdateAddHtlc:
        """
        AddHTLC adds an HTLC to the state machine's local update log. This method
        should be called when preparing to send an outgoing HTLC.

        This docstring is from LND.
        """
        if isinstance(htlc, dict):  # legacy conversion  # FIXME remove
            htlc = UpdateAddHtlc(**htlc)
        assert isinstance(htlc, UpdateAddHtlc)
        self._check_can_pay(htlc.amount_msat)
        htlc = htlc._replace(htlc_id=self.config[LOCAL].next_htlc_id)
        self.hm.send_htlc(htlc)
        self.print_error("add_htlc")
        self.config[LOCAL]=self.config[LOCAL]._replace(next_htlc_id=htlc.htlc_id + 1)
        return htlc

    def receive_htlc(self, htlc: UpdateAddHtlc) -> UpdateAddHtlc:
        """
        ReceiveHTLC adds an HTLC to the state machine's remote update log. This
        method should be called in response to receiving a new HTLC from the remote
        party.

        This docstring is from LND.
        """
        if isinstance(htlc, dict):  # legacy conversion  # FIXME remove
            htlc = UpdateAddHtlc(**htlc)
        assert isinstance(htlc, UpdateAddHtlc)
        htlc = htlc._replace(htlc_id=self.config[REMOTE].next_htlc_id)
        if 0 <= self.available_to_spend(REMOTE) < htlc.amount_msat:
            raise RemoteMisbehaving('Remote dipped below channel reserve.' +\
                    f' Available at remote: {self.available_to_spend(REMOTE)},' +\
                    f' HTLC amount: {htlc.amount_msat}')
        self.hm.recv_htlc(htlc)
        self.print_error("receive_htlc")
        self.config[REMOTE]=self.config[REMOTE]._replace(next_htlc_id=htlc.htlc_id + 1)
        return htlc

    def sign_next_commitment(self):
        """
        SignNextCommitment signs a new commitment which includes any previous
        unsettled HTLCs, any new HTLCs, and any modifications to prior HTLCs
        committed in previous commitment updates.
        The first return parameter is the signature for the commitment transaction
        itself, while the second parameter is are all HTLC signatures concatenated.
        any). The HTLC signatures are sorted according to the BIP 69 order of the
        HTLC's on the commitment transaction.

        This docstring was adapted from LND.
        """
        next_remote_ctn = self.get_current_ctn(REMOTE) + 1
        self.print_error("sign_next_commitment", next_remote_ctn)
        self.hm.send_ctx()
        pending_remote_commitment = self.pending_commitment(REMOTE)
        sig_64 = sign_and_get_sig_string(pending_remote_commitment, self.config[LOCAL], self.config[REMOTE])

        their_remote_htlc_privkey_number = derive_privkey(
            int.from_bytes(self.config[LOCAL].htlc_basepoint.privkey, 'big'),
            self.config[REMOTE].next_per_commitment_point)
        their_remote_htlc_privkey = their_remote_htlc_privkey_number.to_bytes(32, 'big')

        for_us = False

        htlcsigs = []
        # they sent => we receive
        for we_receive, htlcs in zip([True, False], [self.included_htlcs(REMOTE, SENT, ctn=next_remote_ctn),
                                                     self.included_htlcs(REMOTE, RECEIVED, ctn=next_remote_ctn)]):
            for htlc in htlcs:
                _script, htlc_tx = make_htlc_tx_with_open_channel(chan=self,
                                                                  pcp=self.config[REMOTE].next_per_commitment_point,
                                                                  for_us=for_us,
                                                                  we_receive=we_receive,
                                                                  commit=pending_remote_commitment,
                                                                  htlc=htlc)
                sig = bfh(htlc_tx.sign_txin(0, their_remote_htlc_privkey))
                htlc_sig = ecc.sig_string_from_der_sig(sig[:-1])
                htlc_output_idx = htlc_tx.inputs()[0]['prevout_n']
                htlcsigs.append((htlc_output_idx, htlc_sig))

        htlcsigs.sort()
        htlcsigs = [x[1] for x in htlcsigs]

        # TODO should add remote_commitment here and handle
        # both valid ctx'es in lnwatcher at the same time...

        return sig_64, htlcsigs

    def receive_new_commitment(self, sig, htlc_sigs):
        """
        ReceiveNewCommitment process a signature for a new commitment state sent by
        the remote party. This method should be called in response to the
        remote party initiating a new change, or when the remote party sends a
        signature fully accepting a new state we've initiated. If we are able to
        successfully validate the signature, then the generated commitment is added
        to our local commitment chain. Once we send a revocation for our prior
        state, then this newly added commitment becomes our current accepted channel
        state.

        This docstring is from LND.
        """
        self.print_error("receive_new_commitment")

        self.hm.recv_ctx()

        assert len(htlc_sigs) == 0 or type(htlc_sigs[0]) is bytes

        pending_local_commitment = self.pending_commitment(LOCAL)
        preimage_hex = pending_local_commitment.serialize_preimage(0)
        pre_hash = sha256d(bfh(preimage_hex))
        if not ecc.verify_signature(self.config[REMOTE].multisig_key.pubkey, sig, pre_hash):
            raise Exception('failed verifying signature of our updated commitment transaction: ' + bh2u(sig) + ' preimage is ' + preimage_hex)

        htlc_sigs_string = b''.join(htlc_sigs)

        htlc_sigs = htlc_sigs[:] # copy cause we will delete now
        next_local_ctn = self.get_current_ctn(LOCAL) + 1
        for htlcs, we_receive in [(self.included_htlcs(LOCAL, SENT, ctn=next_local_ctn), False),
                                  (self.included_htlcs(LOCAL, RECEIVED, ctn=next_local_ctn), True)]:
            for htlc in htlcs:
                idx = self.verify_htlc(htlc, htlc_sigs, we_receive, pending_local_commitment)
                del htlc_sigs[idx]
        if len(htlc_sigs) != 0: # all sigs should have been popped above
            raise Exception('failed verifying HTLC signatures: invalid amount of correct signatures')

        self.config[LOCAL]=self.config[LOCAL]._replace(
            current_commitment_signature=sig,
            current_htlc_signatures=htlc_sigs_string,
            got_sig_for_next=True)

        if self.pending_fee is not None:
            if not self.constraints.is_initiator:
                self.pending_fee[FUNDEE_SIGNED] = True
            if self.constraints.is_initiator and self.pending_fee[FUNDEE_ACKED]:
                self.pending_fee[FUNDER_SIGNED] = True

        self.set_local_commitment(pending_local_commitment)

    def verify_htlc(self, htlc: UpdateAddHtlc, htlc_sigs: Sequence[bytes], we_receive: bool, ctx) -> int:
        ctn = extract_ctn_from_tx_and_chan(ctx, self)
        secret = get_per_commitment_secret_from_seed(self.config[LOCAL].per_commitment_secret_seed, RevocationStore.START_INDEX - ctn)
        point = secret_to_pubkey(int.from_bytes(secret, 'big'))

        _script, htlc_tx = make_htlc_tx_with_open_channel(chan=self,
                                                          pcp=point,
                                                          for_us=True,
                                                          we_receive=we_receive,
                                                          commit=ctx,
                                                          htlc=htlc)
        pre_hash = sha256d(bfh(htlc_tx.serialize_preimage(0)))
        remote_htlc_pubkey = derive_pubkey(self.config[REMOTE].htlc_basepoint.pubkey, point)
        for idx, sig in enumerate(htlc_sigs):
            if ecc.verify_signature(remote_htlc_pubkey, sig, pre_hash):
                return idx
        else:
            raise Exception(f'failed verifying HTLC signatures: {htlc}, sigs: {len(htlc_sigs)}, we_receive: {we_receive}')

    def get_remote_htlc_sig_for_htlc(self, htlc: UpdateAddHtlc, we_receive: bool, ctx) -> bytes:
        data = self.config[LOCAL].current_htlc_signatures
        htlc_sigs = [data[i:i + 64] for i in range(0, len(data), 64)]
        idx = self.verify_htlc(htlc, htlc_sigs, we_receive=we_receive, ctx=ctx)
        remote_htlc_sig = ecc.der_sig_from_sig_string(htlc_sigs[idx]) + b'\x01'
        return remote_htlc_sig

    def revoke_current_commitment(self):
        self.print_error("revoke_current_commitment")

        last_secret, this_point, next_point, _ = self.points()

        new_feerate = self.constraints.feerate

        if self.pending_fee is not None:
            if not self.constraints.is_initiator and self.pending_fee[FUNDEE_SIGNED]:
                new_feerate = self.pending_fee.rate
                self.pending_fee = None
                print("FEERATE CHANGE COMPLETE (non-initiator)")
            if self.constraints.is_initiator and self.pending_fee[FUNDER_SIGNED]:
                new_feerate = self.pending_fee.rate
                self.pending_fee = None
                print("FEERATE CHANGE COMPLETE (initiator)")

        assert self.config[LOCAL].got_sig_for_next
        self.constraints=self.constraints._replace(
            feerate=new_feerate
        )
        self.set_local_commitment(self.pending_commitment(LOCAL))
        ctx = self.pending_commitment(LOCAL)
        self.hm.send_rev()
        self.config[LOCAL]=self.config[LOCAL]._replace(
            ctn=self.config[LOCAL].ctn + 1,
            got_sig_for_next=False,
        )
        assert self.signature_fits(ctx)

        return RevokeAndAck(last_secret, next_point), "current htlcs"

    def points(self):
        last_small_num = self.config[LOCAL].ctn
        this_small_num = last_small_num + 1
        next_small_num = last_small_num + 2
        last_secret = get_per_commitment_secret_from_seed(self.config[LOCAL].per_commitment_secret_seed, RevocationStore.START_INDEX - last_small_num)
        this_secret = get_per_commitment_secret_from_seed(self.config[LOCAL].per_commitment_secret_seed, RevocationStore.START_INDEX - this_small_num)
        this_point = secret_to_pubkey(int.from_bytes(this_secret, 'big'))
        next_secret = get_per_commitment_secret_from_seed(self.config[LOCAL].per_commitment_secret_seed, RevocationStore.START_INDEX - next_small_num)
        next_point = secret_to_pubkey(int.from_bytes(next_secret, 'big'))
        last_point = secret_to_pubkey(int.from_bytes(last_secret, 'big'))
        return last_secret, this_point, next_point, last_point

    def process_new_revocation_secret(self, per_commitment_secret: bytes):
        if not self.lnwatcher:
            return
        outpoint = self.funding_outpoint.to_str()
        ctx = self.remote_commitment_to_be_revoked  # FIXME can't we just reconstruct it?
        sweeptxs = create_sweeptxs_for_their_just_revoked_ctx(self, ctx, per_commitment_secret, self.sweep_address)
        for prev_txid, tx in sweeptxs.items():
            if tx is not None:
                self.lnwatcher.add_sweep_tx(outpoint, prev_txid, tx.as_dict())

    def receive_revocation(self, revocation) -> Tuple[int, int]:
        self.print_error("receive_revocation")

        cur_point = self.config[REMOTE].current_per_commitment_point
        derived_point = ecc.ECPrivkey(revocation.per_commitment_secret).get_public_key_bytes(compressed=True)
        if cur_point != derived_point:
            raise Exception('revoked secret not for current point')

        # FIXME not sure this is correct... but it seems to work
        # if there are update_add_htlc msgs between commitment_signed and rev_ack,
        # this might break
        prev_remote_commitment = self.pending_commitment(REMOTE)

        self.config[REMOTE].revocation_store.add_next_entry(revocation.per_commitment_secret)
        self.process_new_revocation_secret(revocation.per_commitment_secret)

        ##### start applying fee/htlc changes

        if self.pending_fee is not None:
            if not self.constraints.is_initiator:
                self.pending_fee[FUNDEE_SIGNED] = True
            if self.constraints.is_initiator and self.pending_fee[FUNDEE_ACKED]:
                self.pending_fee[FUNDER_SIGNED] = True

        received = self.hm.received_in_ctn(self.config[REMOTE].ctn + 1)
        sent = self.hm.sent_in_ctn(self.config[REMOTE].ctn + 1)
        for htlc in received:
            self.payment_completed(self, RECEIVED, htlc, None)
        for htlc in sent:
            preimage = self.preimages.pop(htlc.htlc_id)
            self.payment_completed(self, SENT, htlc, preimage)
        received_this_batch = htlcsum(received)
        sent_this_batch = htlcsum(sent)

        next_point = self.config[REMOTE].next_per_commitment_point

        self.hm.recv_rev()

        self.config[REMOTE]=self.config[REMOTE]._replace(
            ctn=self.config[REMOTE].ctn + 1,
            current_per_commitment_point=next_point,
            next_per_commitment_point=revocation.next_per_commitment_point,
        )

        if self.pending_fee is not None:
            if self.constraints.is_initiator:
                self.pending_fee[FUNDEE_ACKED] = True

        self.set_remote_commitment()
        self.remote_commitment_to_be_revoked = prev_remote_commitment

        return received_this_batch, sent_this_batch

    def balance(self, subject, ctn=None):
        """
        This balance in mSAT is not including reserve and fees.
        So a node cannot actually use it's whole balance.
        But this number is simple, since it is derived simply
        from the initial balance, and the value of settled HTLCs.
        Note that it does not decrease once an HTLC is added,
        failed or fulfilled, since the balance change is only
        commited to later when the respective commitment
        transaction as been revoked.
        """
        assert type(subject) is HTLCOwner
        initial = self.config[subject].initial_msat

        for direction, htlc in self.hm.settled_htlcs(subject, ctn):
            if direction == SENT:
                initial -= htlc.amount_msat
            else:
                initial += htlc.amount_msat

        return initial

    def balance_minus_outgoing_htlcs(self, subject):
        """
        This balance in mSAT, which includes the value of
        pending outgoing HTLCs, is used in the UI.
        """
        assert type(subject) is HTLCOwner
        ctn = self.hm.log[subject]['ctn'] + 1
        return self.balance(subject, ctn)\
                - htlcsum(self.hm.htlcs_by_direction(subject, SENT, ctn))

    def available_to_spend(self, subject):
        """
        This balance in mSAT, while technically correct, can
        not be used in the UI cause it fluctuates (commit fee)
        """
        assert type(subject) is HTLCOwner
        return self.balance_minus_outgoing_htlcs(subject)\
                - self.config[-subject].reserve_sat * 1000\
                - calc_onchain_fees(
                      # TODO should we include a potential new htlc, when we are called from receive_htlc?
                      len(self.included_htlcs(subject, SENT) + self.included_htlcs(subject, RECEIVED)),
                      self.pending_feerate(subject),
                      self.constraints.is_initiator,
                  )[subject]

    def included_htlcs(self, subject, direction, ctn=None):
        """
        return filter of non-dust htlcs for subjects commitment transaction, initiated by given party
        """
        assert type(subject) is HTLCOwner
        assert type(direction) is Direction
        if ctn is None:
            ctn = self.config[subject].ctn
        feerate = self.pending_feerate(subject)
        conf = self.config[subject]
        if (subject, direction) in [(REMOTE, RECEIVED), (LOCAL, SENT)]:
            weight = HTLC_SUCCESS_WEIGHT
        else:
            weight = HTLC_TIMEOUT_WEIGHT
        htlcs = self.hm.htlcs_by_direction(subject, direction, ctn=ctn)
        fee_for_htlc = lambda htlc: htlc.amount_msat // 1000 - (weight * feerate // 1000)
        return list(filter(lambda htlc: fee_for_htlc(htlc) >= conf.dust_limit_sat, htlcs))

    def pending_feerate(self, subject):
        assert type(subject) is HTLCOwner
        candidate = self.constraints.feerate
        if self.pending_fee is not None:
            x = self.pending_fee.pending_feerate(subject)
            if x is not None:
                candidate = x
        return candidate

    def pending_commitment(self, subject):
        assert type(subject) is HTLCOwner
        this_point = self.config[REMOTE].next_per_commitment_point if subject == REMOTE else self.points()[1]
        ctn = self.config[subject].ctn + 1
        feerate = self.pending_feerate(subject)
        return self.make_commitment(subject, this_point, ctn, feerate, True)

    def current_commitment(self, subject):
        assert type(subject) is HTLCOwner
        this_point = self.config[REMOTE].current_per_commitment_point if subject == REMOTE else self.points()[3]
        ctn = self.config[subject].ctn
        feerate = self.constraints.feerate
        return self.make_commitment(subject, this_point, ctn, feerate, False)

    def get_current_ctn(self, subject):
        return self.config[subject].ctn

    def total_msat(self, direction):
        assert type(direction) is Direction
        sub = LOCAL if direction == SENT else REMOTE
        return htlcsum(self.hm.settled_htlcs_by(sub, self.config[sub].ctn))

    def settle_htlc(self, preimage, htlc_id):
        """
        SettleHTLC attempts to settle an existing outstanding received HTLC.
        """
        self.print_error("settle_htlc")
        log = self.hm.log[REMOTE]
        htlc = log['adds'][htlc_id]
        assert htlc.payment_hash == sha256(preimage)
        assert htlc_id not in log['settles']
        self.hm.send_settle(htlc_id)
        # not saving preimage because it's already saved in LNWorker.invoices

    def receive_htlc_settle(self, preimage, htlc_id):
        self.print_error("receive_htlc_settle")
        log = self.hm.log[LOCAL]
        htlc = log['adds'][htlc_id]
        assert htlc.payment_hash == sha256(preimage)
        assert htlc_id not in log['settles']
        self.hm.recv_settle(htlc_id)
        self.preimages[htlc_id] = preimage
        # we don't save the preimage because we don't need to forward it anyway

    def fail_htlc(self, htlc_id):
        self.print_error("fail_htlc")
        self.hm.send_fail(htlc_id)

    def receive_fail_htlc(self, htlc_id):
        self.print_error("receive_fail_htlc")
        self.hm.recv_fail(htlc_id)

    @property
    def current_height(self):
        return {LOCAL: self.config[LOCAL].ctn, REMOTE: self.config[REMOTE].ctn}

    def pending_local_fee(self):
        return self.constraints.capacity - sum(x[2] for x in self.pending_commitment(LOCAL).outputs())

    def update_fee(self, feerate, initiator):
        if self.constraints.is_initiator != initiator:
            raise Exception("Cannot update_fee: wrong initiator", initiator)
        if self.pending_fee is not None:
            raise Exception("a fee update is already in progress")
        self.pending_fee = FeeUpdate(self, rate=feerate)

    def to_save(self):
        to_save = {
                "local_config": self.config[LOCAL],
                "remote_config": self.config[REMOTE],
                "channel_id": self.channel_id,
                "short_channel_id": self.short_channel_id,
                "constraints": self.constraints,
                "funding_outpoint": self.funding_outpoint,
                "node_id": self.node_id,
                "remote_commitment_to_be_revoked": str(self.remote_commitment_to_be_revoked),
                "log": self.hm.to_save(),
                "onion_keys": str_bytes_dict_to_save(self.onion_keys),
                "force_closed": self.get_state() == 'FORCE_CLOSING',
        }
        return to_save

    def serialize(self):
        namedtuples_to_dict = lambda v: {i: j._asdict() if isinstance(j, tuple) else j for i, j in v._asdict().items()}
        serialized_channel = {}
        to_save_ref = self.to_save()
        for k, v in to_save_ref.items():
            if isinstance(v, tuple):
                serialized_channel[k] = namedtuples_to_dict(v)
            else:
                serialized_channel[k] = v
        dumped = ChannelJsonEncoder().encode(serialized_channel)
        roundtripped = json.loads(dumped)
        reconstructed = Channel(roundtripped)
        to_save_new = reconstructed.to_save()
        if to_save_new != to_save_ref:
            from pprint import PrettyPrinter
            pp = PrettyPrinter(indent=168)
            try:
                from deepdiff import DeepDiff
            except ImportError:
                raise Exception("Channels did not roundtrip serialization without changes:\n" + pp.pformat(to_save_ref) + "\n" + pp.pformat(to_save_new))
            else:
                raise Exception("Channels did not roundtrip serialization without changes:\n" + pp.pformat(DeepDiff(to_save_ref, to_save_new)))
        return roundtripped

    def __str__(self):
        return str(self.serialize())

    def make_commitment(self, subject, this_point, ctn, feerate, pending) -> Transaction:
        #if subject == REMOTE and not pending:
        #    ctn -= 1
        assert type(subject) is HTLCOwner
        other = REMOTE if LOCAL == subject else LOCAL
        remote_msat, local_msat = self.balance(other, ctn), self.balance(subject, ctn)
        received_htlcs = self.hm.htlcs_by_direction(subject, SENT if subject == LOCAL else RECEIVED, ctn)
        sent_htlcs = self.hm.htlcs_by_direction(subject, RECEIVED if subject == LOCAL else SENT, ctn)
        if subject != LOCAL:
            remote_msat -= htlcsum(received_htlcs)
            local_msat -= htlcsum(sent_htlcs)
        else:
            remote_msat -= htlcsum(sent_htlcs)
            local_msat -= htlcsum(received_htlcs)
        assert remote_msat >= 0
        assert local_msat >= 0
        # same htlcs as before, but now without dust.
        received_htlcs = self.included_htlcs(subject, SENT if subject == LOCAL else RECEIVED, ctn)
        sent_htlcs = self.included_htlcs(subject, RECEIVED if subject == LOCAL else SENT, ctn)

        this_config = self.config[subject]
        other_config = self.config[-subject]
        other_htlc_pubkey = derive_pubkey(other_config.htlc_basepoint.pubkey, this_point)
        this_htlc_pubkey = derive_pubkey(this_config.htlc_basepoint.pubkey, this_point)
        other_revocation_pubkey = derive_blinded_pubkey(other_config.revocation_basepoint.pubkey, this_point)
        htlcs = []  # type: List[ScriptHtlc]
        for is_received_htlc, htlc_list in zip((subject != LOCAL, subject == LOCAL), (received_htlcs, sent_htlcs)):
            for htlc in htlc_list:
                htlcs.append(ScriptHtlc(make_htlc_output_witness_script(
                    is_received_htlc=is_received_htlc,
                    remote_revocation_pubkey=other_revocation_pubkey,
                    remote_htlc_pubkey=other_htlc_pubkey,
                    local_htlc_pubkey=this_htlc_pubkey,
                    payment_hash=htlc.payment_hash,
                    cltv_expiry=htlc.cltv_expiry), htlc))
        onchain_fees = calc_onchain_fees(
            len(htlcs),
            feerate,
            self.constraints.is_initiator == (subject == LOCAL),
        )
        payment_pubkey = derive_pubkey(other_config.payment_basepoint.pubkey, this_point)
        return make_commitment(
            ctn,
            this_config.multisig_key.pubkey,
            other_config.multisig_key.pubkey,
            payment_pubkey,
            self.config[LOCAL if     self.constraints.is_initiator else REMOTE].payment_basepoint.pubkey,
            self.config[LOCAL if not self.constraints.is_initiator else REMOTE].payment_basepoint.pubkey,
            other_revocation_pubkey,
            derive_pubkey(this_config.delayed_basepoint.pubkey, this_point),
            other_config.to_self_delay,
            *self.funding_outpoint,
            self.constraints.capacity,
            local_msat,
            remote_msat,
            this_config.dust_limit_sat,
            onchain_fees,
            htlcs=htlcs)

    def get_local_index(self):
        return int(self.config[LOCAL].multisig_key.pubkey < self.config[REMOTE].multisig_key.pubkey)

    def make_closing_tx(self, local_script: bytes, remote_script: bytes,
                        fee_sat: int) -> Tuple[bytes, int, str]:
        """ cooperative close """
        _, outputs = make_commitment_outputs({
                    LOCAL:  fee_sat * 1000 if     self.constraints.is_initiator else 0,
                    REMOTE: fee_sat * 1000 if not self.constraints.is_initiator else 0,
                },
                self.balance(LOCAL),
                self.balance(REMOTE),
                (TYPE_SCRIPT, bh2u(local_script)),
                (TYPE_SCRIPT, bh2u(remote_script)),
                [], self.config[LOCAL].dust_limit_sat)

        closing_tx = make_closing_tx(self.config[LOCAL].multisig_key.pubkey,
                                     self.config[REMOTE].multisig_key.pubkey,
                                     funding_txid=self.funding_outpoint.txid,
                                     funding_pos=self.funding_outpoint.output_index,
                                     funding_sat=self.constraints.capacity,
                                     outputs=outputs)

        der_sig = bfh(closing_tx.sign_txin(0, self.config[LOCAL].multisig_key.privkey))
        sig = ecc.sig_string_from_der_sig(der_sig[:-1])
        return sig, closing_tx

    def signature_fits(self, tx):
        remote_sig = self.config[LOCAL].current_commitment_signature
        preimage_hex = tx.serialize_preimage(0)
        pre_hash = sha256d(bfh(preimage_hex))
        assert remote_sig
        res = ecc.verify_signature(self.config[REMOTE].multisig_key.pubkey, remote_sig, pre_hash)
        return res

    def force_close_tx(self):
        tx = self.local_commitment
        assert self.signature_fits(tx)
        tx = Transaction(str(tx))
        tx.deserialize(True)
        tx.sign({bh2u(self.config[LOCAL].multisig_key.pubkey): (self.config[LOCAL].multisig_key.privkey, True)})
        remote_sig = self.config[LOCAL].current_commitment_signature
        remote_sig = ecc.der_sig_from_sig_string(remote_sig) + b"\x01"
        sigs = tx._inputs[0]["signatures"]
        none_idx = sigs.index(None)
        tx.add_signature_to_txin(0, none_idx, bh2u(remote_sig))
        assert tx.is_complete()
        return tx

    def included_htlcs_in_their_latest_ctxs(self, htlc_initiator) -> Dict[int, List[UpdateAddHtlc]]:
        """ A map from commitment number to list of HTLCs in
            their latest two commitment transactions.
            The oldest might have been revoked.  """
        assert type(htlc_initiator) is HTLCOwner
        direction = RECEIVED if htlc_initiator == LOCAL else SENT
        old_ctn = self.config[REMOTE].ctn
        old_htlcs  = self.included_htlcs(REMOTE, direction, ctn=old_ctn)

        new_ctn = self.config[REMOTE].ctn+1
        new_htlcs  = self.included_htlcs(REMOTE, direction, ctn=new_ctn)

        return {old_ctn: old_htlcs,
                new_ctn: new_htlcs, }