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lnchannel.available_to_spend: consider both receiver's and sender's ctx

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SomberNight 2020-06-10 20:23:12 +02:00
parent 817411b889
commit 7fccd4fc5e
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1 changed files with 38 additions and 47 deletions
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85
electrum/lnchannel.py
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@ -1054,53 +1054,44 @@ class Channel(AbstractChannel):
assert type(subject) is HTLCOwner
sender = subject
receiver = subject.inverted()
ctx_owner = receiver
# TODO but what about the other ctx? BOLT-02 only talks about checking the receiver's ctx,
# however the channel reserve is only meaningful if we also check the sender's ctx!
# in particular, note that dust limits can be different between the parties!
# but due to the racy nature of this, we cannot be sure exactly what the sender's
# next ctx will look like (e.g. what feerate it will use). hmmm :/
ctn = self.get_next_ctn(ctx_owner)
sender_balance_msat = self.balance_minus_outgoing_htlcs(whose=sender, ctx_owner=ctx_owner, ctn=ctn)
receiver_balance_msat = self.balance_minus_outgoing_htlcs(whose=receiver, ctx_owner=ctx_owner, ctn=ctn)
sender_reserve_msat = self.config[receiver].reserve_sat * 1000
receiver_reserve_msat = self.config[sender].reserve_sat * 1000
initiator = LOCAL if self.constraints.is_initiator else REMOTE
# the initiator/funder pays on-chain fees
num_htlcs_in_ctx = len(self.included_htlcs(ctx_owner, SENT, ctn=ctn) + self.included_htlcs(ctx_owner, RECEIVED, ctn=ctn))
feerate = self.get_feerate(ctx_owner, ctn=ctn)
ctx_fees_msat = calc_fees_for_commitment_tx(
num_htlcs=num_htlcs_in_ctx,
feerate=feerate,
is_local_initiator=self.constraints.is_initiator,
round_to_sat=False,
)
# note: if this supposed new HTLC is large enough to create an output, the initiator needs to pay for that too
# note: if sender != initiator, both the sender and the receiver need to "afford" the payment
htlc_fee_msat = fee_for_htlc_output(feerate=feerate)
# TODO stuck channels. extra funder reserve? "fee spike buffer" (maybe only if "strict")
# see https://github.com/lightningnetwork/lightning-rfc/issues/728
# note: in terms of on-chain outputs, as we are considering the htlc_receiver's ctx, this is a "received" HTLC
htlc_trim_threshold_msat = received_htlc_trim_threshold_sat(dust_limit_sat=self.config[receiver].dust_limit_sat, feerate=feerate) * 1000
if strict:
# also consider the other ctx, where the trim threshold is different
# note: the 'feerate' we use is not technically correct but we have no way
# of knowing the actual future feerate ahead of time (this is a protocol bug)
htlc_trim_threshold_msat = min(htlc_trim_threshold_msat,
offered_htlc_trim_threshold_sat(dust_limit_sat=self.config[sender].dust_limit_sat, feerate=feerate) * 1000)
max_send_msat = sender_balance_msat - sender_reserve_msat - ctx_fees_msat[sender]
if max_send_msat < htlc_trim_threshold_msat:
# there will be no corresponding HTLC output
return max_send_msat
if sender == initiator:
max_send_after_htlc_fee_msat = max_send_msat - htlc_fee_msat
max_send_msat = max(htlc_trim_threshold_msat - 1, max_send_after_htlc_fee_msat)
return max_send_msat
else:
# the receiver is the initiator, so they need to be able to pay tx fees
if receiver_balance_msat - receiver_reserve_msat - ctx_fees_msat[receiver] - htlc_fee_msat < 0:
max_send_msat = htlc_trim_threshold_msat - 1
return max_send_msat
initiator = LOCAL if self.constraints.is_initiator else REMOTE # the initiator/funder pays on-chain fees
def consider_ctx(*, ctx_owner: HTLCOwner) -> int:
ctn = self.get_next_ctn(ctx_owner)
sender_balance_msat = self.balance_minus_outgoing_htlcs(whose=sender, ctx_owner=ctx_owner, ctn=ctn)
receiver_balance_msat = self.balance_minus_outgoing_htlcs(whose=receiver, ctx_owner=ctx_owner, ctn=ctn)
sender_reserve_msat = self.config[receiver].reserve_sat * 1000
receiver_reserve_msat = self.config[sender].reserve_sat * 1000
num_htlcs_in_ctx = len(self.included_htlcs(ctx_owner, SENT, ctn=ctn) + self.included_htlcs(ctx_owner, RECEIVED, ctn=ctn))
feerate = self.get_feerate(ctx_owner, ctn=ctn)
ctx_fees_msat = calc_fees_for_commitment_tx(
num_htlcs=num_htlcs_in_ctx,
feerate=feerate,
is_local_initiator=self.constraints.is_initiator,
round_to_sat=False,
)
htlc_fee_msat = fee_for_htlc_output(feerate=feerate)
htlc_trim_func = received_htlc_trim_threshold_sat if ctx_owner == receiver else offered_htlc_trim_threshold_sat
htlc_trim_threshold_msat = htlc_trim_func(dust_limit_sat=self.config[ctx_owner].dust_limit_sat, feerate=feerate) * 1000
max_send_msat = sender_balance_msat - sender_reserve_msat - ctx_fees_msat[sender]
if max_send_msat < htlc_trim_threshold_msat:
# there will be no corresponding HTLC output
return max_send_msat
if sender == initiator:
max_send_after_htlc_fee_msat = max_send_msat - htlc_fee_msat
max_send_msat = max(htlc_trim_threshold_msat - 1, max_send_after_htlc_fee_msat)
return max_send_msat
else:
# the receiver is the initiator, so they need to be able to pay tx fees
if receiver_balance_msat - receiver_reserve_msat - ctx_fees_msat[receiver] - htlc_fee_msat < 0:
max_send_msat = htlc_trim_threshold_msat - 1
return max_send_msat
max_send_msat = min(consider_ctx(ctx_owner=receiver),
consider_ctx(ctx_owner=sender))
max_send_msat = max(max_send_msat, 0)
return max_send_msat
def included_htlcs(self, subject: HTLCOwner, direction: Direction, ctn: int = None) -> Sequence[UpdateAddHtlc]:
"""Returns list of non-dust HTLCs for subject's commitment tx at ctn,