Tweak htlc dust exposure due to excess fees #3572
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We account for the fees of the htlc transaction only in case the channel does _not_ support zero fee htlc transactions.
tankyleo
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See commit 51bf78d for further background. |
lightning/src/ln/channel.rs
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| let htlc_dust_exposure_msat = | ||
| per_outbound_htlc_counterparty_commit_tx_fee_msat(excess_feerate, &self.context.channel_type); | ||
| let counterparty_tx_dust_exposure = | ||
| htlc_stats.on_counterparty_tx_dust_exposure_msat.saturating_add(htlc_dust_exposure_msat); |
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IIUC, since can_accept_incoming_htlc is now called once it's been irrevocably committed on both sides, I think the dust exposure for this HTLC is already being accounted for in get_pending_htlc_stats. I think we just need to enforce the check below? Having a test would be helpful here to confirm the behavior.
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thanks for the review. I mistakenly assumed can_accept_incoming_htlc == "can we add this htlc to the commit tx?"
But at this point in the flow, the htlc is already on the commit tx !
Now I struggle to understand the point of checking here whether that htlc pushes us over the dust limit if it has already been added to the commit tx.
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as i understand now, this is a limitation of the spec - you cannot really complain about dust limits in direct response to an update_add_htlc msg.
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Thanks! Some test coverage here would still be nice if you're keen and it's not too much trouble. |
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In `can_accept_incoming_htlc`, `get_pending_htlc_stats` accounts for the incoming htlc. Therefore, `on_counterparty_tx_dust_exposure_msat` already includes the excess tx fees of the incoming non-dust htlc.
The widely used sats/kWU ratio is equivalent to msats/WU
The goal is to align `per_outbound_htlc_counterparty_commit_tx_fee_msat` with the slope `commit_tx_fee_sat` / `num_htlcs`. This is a minor detail - no existing LDK code multiplies the value returned by `per_outbound_htlc_counterparty_commit_tx_fee_msat` with `num_htlcs`.
Specifically, we check that the slope `commit_tx_fee_sat` / `num_htlcs` is consistent with `per_outbound_htlc_counterparty_commit_tx_fee_msat`.
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