tlnchannel.available_to_spend: consider both receiver's and sender's ctx - electrum - Electrum Bitcoin wallet
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---
DIR commit 7fccd4fc5e0044d35b4cf717b1fc0137b6321b0e
DIR parent 817411b889fa57ea8205ed4abea1cc08aa2d666a
HTML Author: SomberNight <somber.night@protonmail.com>
Date: Wed, 10 Jun 2020 20:23:12 +0200
lnchannel.available_to_spend: consider both receiver's and sender's ctx
Diffstat:
M electrum/lnchannel.py | 85 ++++++++++++++-----------------
1 file changed, 38 insertions(+), 47 deletions(-)
---
DIR diff --git a/electrum/lnchannel.py b/electrum/lnchannel.py
t@@ -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,