electrum/electrum/lnchan.py

# ported from lnd 42de4400bff5105352d0552155f73589166d162b
from collections import namedtuple, defaultdict
import binascii
import json
from enum import Enum, auto
from typing import Optional

from .util import bfh, PrintError, bh2u
from .bitcoin import Hash, TYPE_SCRIPT, TYPE_ADDRESS
from .bitcoin import redeem_script_to_address
from .crypto import sha256
from . import ecc
from .lnutil import Outpoint, LocalConfig, RemoteConfig, Keypair, OnlyPubkeyKeypair, ChannelConstraints, RevocationStore, EncumberedTransaction
from .lnutil import get_per_commitment_secret_from_seed
from .lnutil import make_commitment_output_to_remote_address, make_commitment_output_to_local_witness_script
from .lnutil import secret_to_pubkey, derive_privkey, derive_pubkey, derive_blinded_pubkey, derive_blinded_privkey
from .lnutil import sign_and_get_sig_string
from .lnutil import make_htlc_tx_with_open_channel, make_commitment, make_received_htlc, make_offered_htlc
from .lnutil import HTLC_TIMEOUT_WEIGHT, HTLC_SUCCESS_WEIGHT
from .lnutil import funding_output_script, LOCAL, REMOTE, HTLCOwner, make_closing_tx, make_outputs
from .lnutil import ScriptHtlc, SENT, RECEIVED
from .transaction import Transaction, TxOutput, construct_witness
from .simple_config import SimpleConfig, FEERATE_FALLBACK_STATIC_FEE


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

class UpdateAddHtlc(namedtuple('UpdateAddHtlc', ['amount_msat', 'payment_hash', 'cltv_expiry', 'locked_in', 'htlc_id'])):
    __slots__ = ()
    def __new__(cls, *args, **kwargs):
        if len(args) > 0:
            args = list(args)
            if type(args[1]) is str:
                args[1] = bfh(args[1])
            args[3] = {HTLCOwner(int(x)): y for x,y in args[3].items()}
            return super().__new__(cls, *args)
        if type(kwargs['payment_hash']) is str:
            kwargs['payment_hash'] = bfh(kwargs['payment_hash'])
        if 'locked_in' not in kwargs:
            kwargs['locked_in'] = {LOCAL: None, REMOTE: None}
        else:
            kwargs['locked_in'] = {HTLCOwner(int(x)): y for x,y in kwargs['locked_in'].items()}
        return super().__new__(cls, **kwargs)

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])

class Channel(PrintError):
    def diagnostic_name(self):
        return str(self.name)

    def __init__(self, state, name = None):
        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 = {int(k): bfh(v) for k,v in state['onion_keys'].items()} if 'onion_keys' in state else {}

        # 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"])

        template = lambda: {'adds': {}, 'settles': []}
        self.log = {LOCAL: template(), REMOTE: template()}
        for strname, subject in [('remote_log', REMOTE), ('local_log', LOCAL)]:
            if strname not in state: continue
            for y in state[strname]:
                htlc = UpdateAddHtlc(**y)
                self.log[subject]['adds'][htlc.htlc_id] = htlc

        self.name = name

        self.fee_mgr = []

        self.local_commitment = self.pending_local_commitment
        self.remote_commitment = self.pending_remote_commitment

        self._is_funding_txo_spent = None  # "don't know"
        self.set_state('DISCONNECTED')

        self.lnwatcher = None

        self.settled = {LOCAL: state.get('settled_local', []), REMOTE: state.get('settled_remote', [])}

    def set_state(self, state: str):
        self._state = state

    def get_state(self):
        return self._state

    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):
        """
        AddHTLC adds an HTLC to the state machine's local update log. This method
        should be called when preparing to send an outgoing HTLC.
        """
        assert type(htlc) is dict
        htlc = UpdateAddHtlc(**htlc, htlc_id=self.config[LOCAL].next_htlc_id)
        self.log[LOCAL]['adds'][htlc.htlc_id] = htlc
        self.print_error("add_htlc")
        self.config[LOCAL]=self.config[LOCAL]._replace(next_htlc_id=htlc.htlc_id + 1)
        return htlc.htlc_id

    def receive_htlc(self, htlc):
        """
        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.
        """
        assert type(htlc) is dict
        htlc = UpdateAddHtlc(**htlc, htlc_id = self.config[REMOTE].next_htlc_id)
        self.log[REMOTE]['adds'][htlc.htlc_id] = htlc
        self.print_error("receive_htlc")
        self.config[REMOTE]=self.config[REMOTE]._replace(next_htlc_id=htlc.htlc_id + 1)
        return htlc.htlc_id

    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. Signing a new commitment
        decrements the available revocation window by 1. After a successful method
        call, the remote party's commitment chain is extended by a new commitment
        which includes all updates to the HTLC log prior to this method invocation.
        The first return parameter is the signature for the commitment transaction
        itself, while the second parameter is a slice of all HTLC signatures (if
        any). The HTLC signatures are sorted according to the BIP 69 order of the
        HTLC's on the commitment transaction.
        """
        for htlc in self.log[LOCAL]['adds'].values():
            if htlc.locked_in[LOCAL] is None:
                htlc.locked_in[LOCAL] = self.config[LOCAL].ctn
        self.print_error("sign_next_commitment")

        pending_remote_commitment = self.pending_remote_commitment
        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 = []
        for we_receive, htlcs in zip([True, False], [self.included_htlcs(REMOTE, REMOTE), self.included_htlcs(REMOTE, LOCAL)]):
            for htlc in htlcs:
                args = [self.config[REMOTE].next_per_commitment_point, for_us, we_receive, pending_remote_commitment, htlc]
                htlc_tx = make_htlc_tx_with_open_channel(self, *args)
                sig = bfh(htlc_tx.sign_txin(0, their_remote_htlc_privkey))
                htlc_sig = ecc.sig_string_from_der_sig(sig[:-1])
                htlcsigs.append((pending_remote_commitment.htlc_output_indices[htlc.payment_hash], htlc_sig))

        for pending_fee in self.fee_mgr:
            if not self.constraints.is_initiator:
                pending_fee[FUNDEE_SIGNED] = True
            if self.constraints.is_initiator and pending_fee[FUNDEE_ACKED]:
                pending_fee[FUNDER_SIGNED] = True

        self.process_new_offchain_ctx(pending_remote_commitment, ours=False)

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

        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.
        """

        self.print_error("receive_new_commitment")
        for htlc in self.log[REMOTE]['adds'].values():
            if htlc.locked_in[REMOTE] is None:
                htlc.locked_in[REMOTE] = self.config[REMOTE].ctn
        assert len(htlc_sigs) == 0 or type(htlc_sigs[0]) is bytes

        pending_local_commitment = self.pending_local_commitment
        preimage_hex = pending_local_commitment.serialize_preimage(0)
        pre_hash = Hash(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)

        _, this_point, _ = self.points

        for htlcs, we_receive in [(self.included_htlcs(LOCAL, REMOTE), True), (self.included_htlcs(LOCAL, LOCAL), False)]:
            for htlc in htlcs:
                htlc_tx = make_htlc_tx_with_open_channel(self, this_point, True, we_receive, pending_local_commitment, htlc)
                pre_hash = Hash(bfh(htlc_tx.serialize_preimage(0)))
                remote_htlc_pubkey = derive_pubkey(self.config[REMOTE].htlc_basepoint.pubkey, this_point)
                for idx, sig in enumerate(htlc_sigs):
                    if ecc.verify_signature(remote_htlc_pubkey, sig, pre_hash):
                        del htlc_sigs[idx]
                        break
                else:
                    raise Exception(f'failed verifying HTLC signatures: {htlc}')
        if len(htlc_sigs) != 0: # all sigs should have been popped above
            raise Exception('failed verifying HTLC signatures: invalid amount of correct signatures')

        for pending_fee in self.fee_mgr:
            if not self.constraints.is_initiator:
                pending_fee[FUNDEE_SIGNED] = True
            if self.constraints.is_initiator and pending_fee[FUNDEE_ACKED]:
                pending_fee[FUNDER_SIGNED] = True

        self.process_new_offchain_ctx(pending_local_commitment, ours=True)


    def revoke_current_commitment(self):
        """
        RevokeCurrentCommitment revokes the next lowest unrevoked commitment
        transaction in the local commitment chain. As a result the edge of our
        revocation window is extended by one, and the tail of our local commitment
        chain is advanced by a single commitment. This now lowest unrevoked
        commitment becomes our currently accepted state within the channel. This
        method also returns the set of HTLC's currently active within the commitment
        transaction. This return value allows callers to act once an HTLC has been
        locked into our commitment transaction.
        """
        self.print_error("revoke_current_commitment")

        last_secret, this_point, next_point = self.points

        new_feerate = self.constraints.feerate

        for pending_fee in self.fee_mgr[:]:
            if not self.constraints.is_initiator and pending_fee[FUNDEE_SIGNED]:
                new_feerate = pending_fee.rate
                self.fee_mgr.remove(pending_fee)
                print("FEERATE CHANGE COMPLETE (non-initiator)")
            if self.constraints.is_initiator and pending_fee[FUNDER_SIGNED]:
                new_feerate = pending_fee.rate
                self.fee_mgr.remove(pending_fee)
                print("FEERATE CHANGE COMPLETE (initiator)")

        self.config[LOCAL]=self.config[LOCAL]._replace(
            ctn=self.config[LOCAL].ctn + 1,
        )
        self.constraints=self.constraints._replace(
            feerate=new_feerate
        )

        self.local_commitment = self.pending_local_commitment

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

    @property
    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'))
        return last_secret, this_point, next_point

    # TODO batch sweeps
    # TODO sweep HTLC outputs
    def process_new_offchain_ctx(self, ctx, ours: bool):
        if not self.lnwatcher:
            return
        outpoint = self.funding_outpoint.to_str()
        if ours:
            ctn = self.config[LOCAL].ctn + 1
            our_per_commitment_secret = get_per_commitment_secret_from_seed(
                self.config[LOCAL].per_commitment_secret_seed, RevocationStore.START_INDEX - ctn)
            our_cur_pcp = ecc.ECPrivkey(our_per_commitment_secret).get_public_key_bytes(compressed=True)
            encumbered_sweeptx = maybe_create_sweeptx_for_our_ctx_to_local(self, ctx, our_cur_pcp, self.sweep_address)
        else:
            their_cur_pcp = self.config[REMOTE].next_per_commitment_point
            encumbered_sweeptx = maybe_create_sweeptx_for_their_ctx_to_remote(self, ctx, their_cur_pcp, self.sweep_address)
        if encumbered_sweeptx:
            self.lnwatcher.add_sweep_tx(outpoint, ctx.txid(), encumbered_sweeptx.to_json())

    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
        encumbered_sweeptx = maybe_create_sweeptx_for_their_ctx_to_local(self, ctx, per_commitment_secret, self.sweep_address)
        if encumbered_sweeptx:
            self.lnwatcher.add_sweep_tx(outpoint, ctx.txid(), encumbered_sweeptx.to_json())

    def receive_revocation(self, revocation):
        """
        ReceiveRevocation processes a revocation sent by the remote party for the
        lowest unrevoked commitment within their commitment chain. We receive a
        revocation either during the initial session negotiation wherein revocation
        windows are extended, or in response to a state update that we initiate. If
        successful, then the remote commitment chain is advanced by a single
        commitment, and a log compaction is attempted.

        Returns the forwarding package corresponding to the remote commitment height
        that was revoked.
        """
        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_remote_commitment

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

        def mark_settled(subject):
            """
            find pending settlements for subject (LOCAL or REMOTE) and mark them settled, return value of settled htlcs
            """
            old_amount = htlcsum(self.htlcs(subject, False))

            for htlc_id in self.log[-subject]['settles']:
                adds = self.log[subject]['adds']
                htlc = adds.pop(htlc_id)
                self.settled[subject].append(htlc.amount_msat)
            self.log[-subject]['settles'].clear()

            return old_amount - htlcsum(self.htlcs(subject, False))

        sent_this_batch = mark_settled(LOCAL)
        received_this_batch = mark_settled(REMOTE)

        next_point = self.config[REMOTE].next_per_commitment_point

        print("RECEIVED", received_this_batch)
        print("SENT", sent_this_batch)
        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,
            amount_msat=self.config[REMOTE].amount_msat + (sent_this_batch - received_this_batch)
        )
        self.config[LOCAL]=self.config[LOCAL]._replace(
            amount_msat = self.config[LOCAL].amount_msat + (received_this_batch - sent_this_batch)
        )

        for pending_fee in self.fee_mgr:
            if self.constraints.is_initiator:
                pending_fee[FUNDEE_ACKED] = True

        self.local_commitment = self.pending_local_commitment
        self.remote_commitment = self.pending_remote_commitment
        self.remote_commitment_to_be_revoked = prev_remote_commitment
        return received_this_batch, sent_this_batch

    def balance(self, subject):
        initial = self.config[subject].initial_msat

        initial -= sum(self.settled[subject])
        initial += sum(self.settled[-subject])

        assert initial == self.config[subject].amount_msat
        return initial

    def amounts(self):
        remote_settled= htlcsum(self.htlcs(REMOTE, False))
        local_settled= htlcsum(self.htlcs(LOCAL, False))
        unsettled_local = htlcsum(self.htlcs(LOCAL, True))
        unsettled_remote = htlcsum(self.htlcs(REMOTE, True))
        remote_msat = self.config[REMOTE].amount_msat -\
          unsettled_remote + local_settled - remote_settled
        local_msat = self.config[LOCAL].amount_msat -\
          unsettled_local + remote_settled - local_settled
        return remote_msat, local_msat

    def included_htlcs(self, subject, htlc_initiator):
        """
        return filter of non-dust htlcs for subjects commitment transaction, initiated by given party
        """
        feerate = self.pending_feerate(subject)
        conf = self.config[subject]
        weight = HTLC_SUCCESS_WEIGHT if subject != htlc_initiator else HTLC_TIMEOUT_WEIGHT
        htlcs = self.htlcs(htlc_initiator, only_pending=True)
        fee_for_htlc = lambda htlc: htlc.amount_msat // 1000 - (weight * feerate // 1000)
        return filter(lambda htlc: fee_for_htlc(htlc) >= conf.dust_limit_sat, htlcs)

    @property
    def pending_remote_commitment(self):
        this_point = self.config[REMOTE].next_per_commitment_point
        return self.make_commitment(REMOTE, this_point)

    def pending_feerate(self, subject):
        candidate = self.constraints.feerate
        for pending_fee in self.fee_mgr:
            x = pending_fee.pending_feerate(subject)
            if x is not None:
                candidate = x

        return candidate

    @property
    def pending_local_commitment(self):
        _, this_point, _ = self.points
        return self.make_commitment(LOCAL, this_point)

    def total_msat(self, sub):
        return sum(self.settled[sub])

    def htlcs(self, subject, only_pending):
        """
        only_pending: require the htlc's settlement to be pending (needs additional signatures/acks)
        """
        update_log = self.log[subject]
        other_log = self.log[-subject]
        res = []
        for htlc in update_log['adds'].values():
            locked_in = htlc.locked_in[subject]

            if locked_in is None or only_pending == (htlc.htlc_id in other_log['settles']):
                continue
            res.append(htlc)
        return res

    def settle_htlc(self, preimage, htlc_id):
        """
        SettleHTLC attempts to settle an existing outstanding received HTLC.
        """
        self.print_error("settle_htlc")
        htlc = self.log[REMOTE]['adds'][htlc_id]
        assert htlc.payment_hash == sha256(preimage)
        self.log[LOCAL]['settles'].append(htlc_id)

    def receive_htlc_settle(self, preimage, htlc_index):
        self.print_error("receive_htlc_settle")
        htlc = self.log[LOCAL]['adds'][htlc_index]
        assert htlc.payment_hash == sha256(preimage)
        self.log[REMOTE]['settles'].append(htlc_index)

    def receive_fail_htlc(self, htlc_id):
        self.print_error("receive_fail_htlc")
        self.log[LOCAL]['adds'].pop(htlc_id)

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

    @property
    def pending_local_fee(self):
        return self.constraints.capacity - sum(x[2] for x in self.pending_local_commitment.outputs())

    def update_fee(self, feerate):
        if not self.constraints.is_initiator:
            raise Exception("only initiator can update_fee, this counterparty is not initiator")
        pending_fee = FeeUpdate(self, rate=feerate)
        self.fee_mgr.append(pending_fee)

    def receive_update_fee(self, feerate):
        if self.constraints.is_initiator:
            raise Exception("only the non-initiator can receive_update_fee, this counterparty is initiator")
        pending_fee = FeeUpdate(self, rate=feerate)
        self.fee_mgr.append(pending_fee)

    def remove_uncommitted_htlcs_from_log(self, subject):
        """
        returns
        - the htlcs with uncommited (not locked in) htlcs removed
        - a list of htlc_ids that were removed
        """
        removed = []
        htlcs = []
        for i in self.log[subject]['adds'].values():
            locked_in = i.locked_in[LOCAL] is not None or i.locked_in[REMOTE] is not None
            if locked_in:
                htlcs.append(i._asdict())
            else:
                removed.append(i.htlc_id)
        return htlcs, removed

    def to_save(self):
        # need to forget about uncommited htlcs
        # since we must assume they don't know about it,
        # if it was not acked
        remote_filtered, remote_removed = self.remove_uncommitted_htlcs_from_log(REMOTE)
        local_filtered, local_removed = self.remove_uncommitted_htlcs_from_log(LOCAL)
        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),
                "remote_log": remote_filtered,
                "local_log": local_filtered,
                "onion_keys": {str(k): bh2u(v) for k, v in self.onion_keys.items()},
                "settled_local": self.settled[LOCAL],
                "settled_remote": self.settled[REMOTE],
        }

        # htlcs number must be monotonically increasing,
        # so we have to decrease the counter
        if len(remote_removed) != 0:
            assert min(remote_removed) < to_save['remote_config'].next_htlc_id
            to_save['remote_config'] = to_save['remote_config']._replace(next_htlc_id = min(remote_removed))

        if len(local_removed) != 0:
            assert min(local_removed) < to_save['local_config'].next_htlc_id
            to_save['local_config'] = to_save['local_config']._replace(next_htlc_id = min(local_removed))

        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 = {k: namedtuples_to_dict(v) if isinstance(v, tuple) else v for k, v in self.to_save().items()}
        class MyJsonEncoder(json.JSONEncoder):
            def default(self, o):
                if isinstance(o, bytes):
                    return binascii.hexlify(o).decode("ascii")
                if isinstance(o, RevocationStore):
                    return o.serialize()
                return super(MyJsonEncoder, self)
        dumped = MyJsonEncoder().encode(serialized_channel)
        roundtripped = json.loads(dumped)
        reconstructed = Channel(roundtripped)
        if reconstructed.to_save() != self.to_save():
            from pprint import pformat
            try:
                from deepdiff import DeepDiff
            except ImportError:
                raise Exception("Channels did not roundtrip serialization without changes:\n" + pformat(reconstructed.to_save()) + "\n" + pformat(self.to_save()))
            else:
                raise Exception("Channels did not roundtrip serialization without changes:\n" + pformat(DeepDiff(reconstructed.to_save(), self.to_save())))
        return roundtripped

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

    def make_commitment(self, subject, this_point) -> Transaction:
        remote_msat, local_msat = self.amounts()
        assert local_msat >= 0
        assert remote_msat >= 0
        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 = []
        for htlc in self.included_htlcs(subject, -subject):
            htlcs.append( ScriptHtlc( make_received_htlc(
                other_revocation_pubkey,
                other_htlc_pubkey,
                this_htlc_pubkey,
                htlc.payment_hash,
                htlc.cltv_expiry), htlc))
        for htlc in self.included_htlcs(subject, subject):
            htlcs.append(
                ScriptHtlc( make_offered_htlc(
                    other_revocation_pubkey,
                    other_htlc_pubkey,
                    this_htlc_pubkey,
                    htlc.payment_hash), htlc))
        if subject != LOCAL:
            remote_msat, local_msat = local_msat, remote_msat
        payment_pubkey = derive_pubkey(other_config.payment_basepoint.pubkey, this_point)
        return make_commitment(
            self.config[subject].ctn + 1,
            this_config.multisig_key.pubkey,
            other_config.multisig_key.pubkey,
            payment_pubkey,
            self.config[LOCAL].payment_basepoint.pubkey,
            self.config[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,
            self.pending_feerate(subject),
            subject == LOCAL,
            self.constraints.is_initiator,
            htlcs=htlcs)

    def make_closing_tx(self, local_script: bytes, remote_script: bytes, fee_sat: Optional[int] = None) -> (bytes, int):
        if fee_sat is None:
            fee_sat = self.pending_local_fee

        _, outputs = make_outputs(fee_sat * 1000, True,
                self.config[LOCAL].amount_msat,
                self.config[REMOTE].amount_msat,
                (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,
                self.config[LOCAL].payment_basepoint.pubkey,
                self.config[REMOTE].payment_basepoint.pubkey,
                # TODO hardcoded we_are_initiator:
                True, *self.funding_outpoint, self.constraints.capacity,
                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, fee_sat

def maybe_create_sweeptx_for_their_ctx_to_remote(chan, ctx, their_pcp: bytes,
                                                 sweep_address) -> Optional[EncumberedTransaction]:
    assert isinstance(their_pcp, bytes)
    payment_bp_privkey = ecc.ECPrivkey(chan.config[LOCAL].payment_basepoint.privkey)
    our_payment_privkey = derive_privkey(payment_bp_privkey.secret_scalar, their_pcp)
    our_payment_privkey = ecc.ECPrivkey.from_secret_scalar(our_payment_privkey)
    our_payment_pubkey = our_payment_privkey.get_public_key_bytes(compressed=True)
    to_remote_address = make_commitment_output_to_remote_address(our_payment_pubkey)
    for output_idx, (type_, addr, val) in enumerate(ctx.outputs()):
        if type_ == TYPE_ADDRESS and addr == to_remote_address:
            break
    else:
        return None
    sweep_tx = create_sweeptx_their_ctx_to_remote(address=sweep_address,
                                                  ctx=ctx,
                                                  output_idx=output_idx,
                                                  our_payment_privkey=our_payment_privkey)
    return EncumberedTransaction(sweep_tx, csv_delay=0)


def maybe_create_sweeptx_for_their_ctx_to_local(chan, ctx, per_commitment_secret: bytes,
                                                sweep_address) -> Optional[EncumberedTransaction]:
    assert isinstance(per_commitment_secret, bytes)
    per_commitment_point = ecc.ECPrivkey(per_commitment_secret).get_public_key_bytes(compressed=True)
    revocation_privkey = derive_blinded_privkey(chan.config[LOCAL].revocation_basepoint.privkey,
                                                per_commitment_secret)
    revocation_pubkey = ecc.ECPrivkey(revocation_privkey).get_public_key_bytes(compressed=True)
    to_self_delay = chan.config[LOCAL].to_self_delay
    delayed_pubkey = derive_pubkey(chan.config[REMOTE].delayed_basepoint.pubkey,
                                   per_commitment_point)
    witness_script = bh2u(make_commitment_output_to_local_witness_script(
        revocation_pubkey, to_self_delay, delayed_pubkey))
    to_local_address = redeem_script_to_address('p2wsh', witness_script)
    for output_idx, o in enumerate(ctx.outputs()):
        if o.type == TYPE_ADDRESS and o.address == to_local_address:
            break
    else:
        return None
    sweep_tx = create_sweeptx_ctx_to_local(address=sweep_address,
                                           ctx=ctx,
                                           output_idx=output_idx,
                                           witness_script=witness_script,
                                           privkey=revocation_privkey,
                                           is_revocation=True)
    return EncumberedTransaction(sweep_tx, csv_delay=0)


def maybe_create_sweeptx_for_our_ctx_to_local(chan, ctx, our_pcp: bytes,
                                              sweep_address) -> Optional[EncumberedTransaction]:
    assert isinstance(our_pcp, bytes)
    delayed_bp_privkey = ecc.ECPrivkey(chan.config[LOCAL].delayed_basepoint.privkey)
    our_localdelayed_privkey = derive_privkey(delayed_bp_privkey.secret_scalar, our_pcp)
    our_localdelayed_privkey = ecc.ECPrivkey.from_secret_scalar(our_localdelayed_privkey)
    our_localdelayed_pubkey = our_localdelayed_privkey.get_public_key_bytes(compressed=True)
    revocation_pubkey = derive_blinded_pubkey(chan.config[REMOTE].revocation_basepoint.pubkey,
                                              our_pcp)
    to_self_delay = chan.config[REMOTE].to_self_delay
    witness_script = bh2u(make_commitment_output_to_local_witness_script(
        revocation_pubkey, to_self_delay, our_localdelayed_pubkey))
    to_local_address = redeem_script_to_address('p2wsh', witness_script)
    for output_idx, o in enumerate(ctx.outputs()):
        if o.type == TYPE_ADDRESS and o.address == to_local_address:
            break
    else:
        return None
    sweep_tx = create_sweeptx_ctx_to_local(address=sweep_address,
                                           ctx=ctx,
                                           output_idx=output_idx,
                                           witness_script=witness_script,
                                           privkey=our_localdelayed_privkey.get_secret_bytes(),
                                           is_revocation=False,
                                           to_self_delay=to_self_delay)

    return EncumberedTransaction(sweep_tx, csv_delay=to_self_delay)


def create_sweeptx_their_ctx_to_remote(address, ctx, output_idx: int, our_payment_privkey: ecc.ECPrivkey,
                                       fee_per_kb: int=None) -> Transaction:
    our_payment_pubkey = our_payment_privkey.get_public_key_hex(compressed=True)
    val = ctx.outputs()[output_idx].value
    sweep_inputs = [{
        'type': 'p2wpkh',
        'x_pubkeys': [our_payment_pubkey],
        'num_sig': 1,
        'prevout_n': output_idx,
        'prevout_hash': ctx.txid(),
        'value': val,
        'coinbase': False,
        'signatures': [None],
    }]
    tx_size_bytes = 110  # approx size of p2wpkh->p2wpkh
    if fee_per_kb is None: fee_per_kb = FEERATE_FALLBACK_STATIC_FEE
    fee = SimpleConfig.estimate_fee_for_feerate(fee_per_kb, tx_size_bytes)
    sweep_outputs = [TxOutput(TYPE_ADDRESS, address, val-fee)]
    sweep_tx = Transaction.from_io(sweep_inputs, sweep_outputs)
    sweep_tx.set_rbf(True)
    sweep_tx.sign({our_payment_pubkey: (our_payment_privkey.get_secret_bytes(), True)})
    if not sweep_tx.is_complete():
        raise Exception('channel close sweep tx is not complete')
    return sweep_tx


def create_sweeptx_ctx_to_local(address, ctx, output_idx: int, witness_script: str,
                                privkey: bytes, is_revocation: bool,
                                to_self_delay: int=None,
                                fee_per_kb: int=None) -> Transaction:
    """Create a txn that sweeps the 'to_local' output of a commitment
    transaction into our wallet.

    privkey: either revocation_privkey or localdelayed_privkey
    is_revocation: tells us which ^
    """
    val = ctx.outputs()[output_idx].value
    sweep_inputs = [{
        'scriptSig': '',
        'type': 'p2wsh',
        'signatures': [],
        'num_sig': 0,
        'prevout_n': output_idx,
        'prevout_hash': ctx.txid(),
        'value': val,
        'coinbase': False,
        'preimage_script': witness_script,
    }]
    if to_self_delay is not None:
        sweep_inputs[0]['sequence'] = to_self_delay
    tx_size_bytes = 121  # approx size of to_local -> p2wpkh
    if fee_per_kb is None: fee_per_kb = FEERATE_FALLBACK_STATIC_FEE
    fee = SimpleConfig.estimate_fee_for_feerate(fee_per_kb, tx_size_bytes)
    sweep_outputs = [TxOutput(TYPE_ADDRESS, address, val - fee)]
    sweep_tx = Transaction.from_io(sweep_inputs, sweep_outputs, version=2)
    sig = sweep_tx.sign_txin(0, privkey)
    witness = construct_witness([sig, int(is_revocation), witness_script])
    sweep_tx.inputs()[0]['witness'] = witness
    return sweep_tx