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Account for zero fee HTLC transaction within dust limit calculation
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With the zero fee HTLC transaction anchors variant, HTLCs can no longer
be trimmed due to their amount being too low to have a mempool valid
HTLC transaction. Now they can only be trimmed based on the dust limit
of each party within the channel.
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@wpaulino
wpaulino committed Sep 6, 2022
1 parent f43a7e8 commit d65e464
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Showing 2 changed files with 70 additions and 14 deletions.
78 changes: 64 additions & 14 deletions lightning/src/ln/channel.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1466,7 +1466,12 @@ impl<Signer: Sign> Channel<Signer> {
($htlc: expr, $outbound: expr, $source: expr, $state_name: expr) => {
if $outbound == local { // "offered HTLC output"
let htlc_in_tx = get_htlc_in_commitment!($htlc, true);
if $htlc.amount_msat / 1000 >= broadcaster_dust_limit_satoshis + (feerate_per_kw as u64 * htlc_timeout_tx_weight(self.opt_anchors()) / 1000) {
let htlc_tx_fee = if self.opt_anchors() {
0
} else {
feerate_per_kw as u64 * htlc_timeout_tx_weight(false) / 1000
};
if $htlc.amount_msat / 1000 >= broadcaster_dust_limit_satoshis + htlc_tx_fee {
log_trace!(logger, " ...including {} {} HTLC {} (hash {}) with value {}", if $outbound { "outbound" } else { "inbound" }, $state_name, $htlc.htlc_id, log_bytes!($htlc.payment_hash.0), $htlc.amount_msat);
included_non_dust_htlcs.push((htlc_in_tx, $source));
} else {
Expand All @@ -1475,7 +1480,12 @@ impl<Signer: Sign> Channel<Signer> {
}
} else {
let htlc_in_tx = get_htlc_in_commitment!($htlc, false);
if $htlc.amount_msat / 1000 >= broadcaster_dust_limit_satoshis + (feerate_per_kw as u64 * htlc_success_tx_weight(self.opt_anchors()) / 1000) {
let htlc_tx_fee = if self.opt_anchors() {
0
} else {
feerate_per_kw as u64 * htlc_success_tx_weight(false) / 1000
};
if $htlc.amount_msat / 1000 >= broadcaster_dust_limit_satoshis + htlc_tx_fee {
log_trace!(logger, " ...including {} {} HTLC {} (hash {}) with value {}", if $outbound { "outbound" } else { "inbound" }, $state_name, $htlc.htlc_id, log_bytes!($htlc.payment_hash.0), $htlc.amount_msat);
included_non_dust_htlcs.push((htlc_in_tx, $source));
} else {
Expand Down Expand Up @@ -2396,8 +2406,15 @@ impl<Signer: Sign> Channel<Signer> {
on_holder_tx_holding_cell_htlcs_count: 0,
};

let counterparty_dust_limit_timeout_sat = (self.get_dust_buffer_feerate(outbound_feerate_update) as u64 * htlc_timeout_tx_weight(self.opt_anchors()) / 1000) + self.counterparty_dust_limit_satoshis;
let holder_dust_limit_success_sat = (self.get_dust_buffer_feerate(outbound_feerate_update) as u64 * htlc_success_tx_weight(self.opt_anchors()) / 1000) + self.holder_dust_limit_satoshis;
let (htlc_timeout_dust_limit, htlc_success_dust_limit) = if self.opt_anchors() {
(0, 0)
} else {
let dust_buffer_feerate = self.get_dust_buffer_feerate(outbound_feerate_update) as u64;
(dust_buffer_feerate * htlc_timeout_tx_weight(false) / 1000,
dust_buffer_feerate * htlc_success_tx_weight(false) / 1000)
};
let counterparty_dust_limit_timeout_sat = htlc_timeout_dust_limit + self.counterparty_dust_limit_satoshis;
let holder_dust_limit_success_sat = htlc_success_dust_limit + self.holder_dust_limit_satoshis;
for ref htlc in self.pending_inbound_htlcs.iter() {
stats.pending_htlcs_value_msat += htlc.amount_msat;
if htlc.amount_msat / 1000 < counterparty_dust_limit_timeout_sat {
Expand All @@ -2421,8 +2438,15 @@ impl<Signer: Sign> Channel<Signer> {
on_holder_tx_holding_cell_htlcs_count: 0,
};

let counterparty_dust_limit_success_sat = (self.get_dust_buffer_feerate(outbound_feerate_update) as u64 * htlc_success_tx_weight(self.opt_anchors()) / 1000) + self.counterparty_dust_limit_satoshis;
let holder_dust_limit_timeout_sat = (self.get_dust_buffer_feerate(outbound_feerate_update) as u64 * htlc_timeout_tx_weight(self.opt_anchors()) / 1000) + self.holder_dust_limit_satoshis;
let (htlc_timeout_dust_limit, htlc_success_dust_limit) = if self.opt_anchors() {
(0, 0)
} else {
let dust_buffer_feerate = self.get_dust_buffer_feerate(outbound_feerate_update) as u64;
(dust_buffer_feerate * htlc_timeout_tx_weight(false) / 1000,
dust_buffer_feerate * htlc_success_tx_weight(false) / 1000)
};
let counterparty_dust_limit_success_sat = htlc_success_dust_limit + self.counterparty_dust_limit_satoshis;
let holder_dust_limit_timeout_sat = htlc_timeout_dust_limit + self.holder_dust_limit_satoshis;
for ref htlc in self.pending_outbound_htlcs.iter() {
stats.pending_htlcs_value_msat += htlc.amount_msat;
if htlc.amount_msat / 1000 < counterparty_dust_limit_success_sat {
Expand Down Expand Up @@ -2512,8 +2536,14 @@ impl<Signer: Sign> Channel<Signer> {
fn next_local_commit_tx_fee_msat(&self, htlc: HTLCCandidate, fee_spike_buffer_htlc: Option<()>) -> u64 {
assert!(self.is_outbound());

let real_dust_limit_success_sat = (self.feerate_per_kw as u64 * htlc_success_tx_weight(self.opt_anchors()) / 1000) + self.holder_dust_limit_satoshis;
let real_dust_limit_timeout_sat = (self.feerate_per_kw as u64 * htlc_timeout_tx_weight(self.opt_anchors()) / 1000) + self.holder_dust_limit_satoshis;
let (htlc_success_dust_limit, htlc_timeout_dust_limit) = if self.opt_anchors() {
(0, 0)
} else {
(self.feerate_per_kw as u64 * htlc_success_tx_weight(false) / 1000,
self.feerate_per_kw as u64 * htlc_timeout_tx_weight(false) / 1000)
};
let real_dust_limit_success_sat = htlc_success_dust_limit + self.holder_dust_limit_satoshis;
let real_dust_limit_timeout_sat = htlc_timeout_dust_limit + self.holder_dust_limit_satoshis;

let mut addl_htlcs = 0;
if fee_spike_buffer_htlc.is_some() { addl_htlcs += 1; }
Expand Down Expand Up @@ -2603,8 +2633,14 @@ impl<Signer: Sign> Channel<Signer> {
fn next_remote_commit_tx_fee_msat(&self, htlc: HTLCCandidate, fee_spike_buffer_htlc: Option<()>) -> u64 {
assert!(!self.is_outbound());

let real_dust_limit_success_sat = (self.feerate_per_kw as u64 * htlc_success_tx_weight(self.opt_anchors()) / 1000) + self.counterparty_dust_limit_satoshis;
let real_dust_limit_timeout_sat = (self.feerate_per_kw as u64 * htlc_timeout_tx_weight(self.opt_anchors()) / 1000) + self.counterparty_dust_limit_satoshis;
let (htlc_success_dust_limit, htlc_timeout_dust_limit) = if self.opt_anchors() {
(0, 0)
} else {
(self.feerate_per_kw as u64 * htlc_success_tx_weight(false) / 1000,
self.feerate_per_kw as u64 * htlc_timeout_tx_weight(false) / 1000)
};
let real_dust_limit_success_sat = htlc_success_dust_limit + self.counterparty_dust_limit_satoshis;
let real_dust_limit_timeout_sat = htlc_timeout_dust_limit + self.counterparty_dust_limit_satoshis;

let mut addl_htlcs = 0;
if fee_spike_buffer_htlc.is_some() { addl_htlcs += 1; }
Expand Down Expand Up @@ -2727,7 +2763,14 @@ impl<Signer: Sign> Channel<Signer> {
}
}

let exposure_dust_limit_timeout_sats = (self.get_dust_buffer_feerate(None) as u64 * htlc_timeout_tx_weight(self.opt_anchors()) / 1000) + self.counterparty_dust_limit_satoshis;
let (htlc_timeout_dust_limit, htlc_success_dust_limit) = if self.opt_anchors() {
(0, 0)
} else {
let dust_buffer_feerate = self.get_dust_buffer_feerate(None) as u64;
(dust_buffer_feerate * htlc_timeout_tx_weight(false) / 1000,
dust_buffer_feerate * htlc_success_tx_weight(false) / 1000)
};
let exposure_dust_limit_timeout_sats = htlc_timeout_dust_limit + self.counterparty_dust_limit_satoshis;
if msg.amount_msat / 1000 < exposure_dust_limit_timeout_sats {
let on_counterparty_tx_dust_htlc_exposure_msat = inbound_stats.on_counterparty_tx_dust_exposure_msat + outbound_stats.on_counterparty_tx_dust_exposure_msat + msg.amount_msat;
if on_counterparty_tx_dust_htlc_exposure_msat > self.get_max_dust_htlc_exposure_msat() {
Expand All @@ -2737,7 +2780,7 @@ impl<Signer: Sign> Channel<Signer> {
}
}

let exposure_dust_limit_success_sats = (self.get_dust_buffer_feerate(None) as u64 * htlc_success_tx_weight(self.opt_anchors()) / 1000) + self.holder_dust_limit_satoshis;
let exposure_dust_limit_success_sats = htlc_success_dust_limit + self.holder_dust_limit_satoshis;
if msg.amount_msat / 1000 < exposure_dust_limit_success_sats {
let on_holder_tx_dust_htlc_exposure_msat = inbound_stats.on_holder_tx_dust_exposure_msat + outbound_stats.on_holder_tx_dust_exposure_msat + msg.amount_msat;
if on_holder_tx_dust_htlc_exposure_msat > self.get_max_dust_htlc_exposure_msat() {
Expand Down Expand Up @@ -5441,7 +5484,14 @@ impl<Signer: Sign> Channel<Signer> {
}
}

let exposure_dust_limit_success_sats = (self.get_dust_buffer_feerate(None) as u64 * htlc_success_tx_weight(self.opt_anchors()) / 1000) + self.counterparty_dust_limit_satoshis;
let (htlc_success_dust_limit, htlc_timeout_dust_limit) = if self.opt_anchors() {
(0, 0)
} else {
let dust_buffer_feerate = self.get_dust_buffer_feerate(None) as u64;
(dust_buffer_feerate * htlc_success_tx_weight(false) / 1000,
dust_buffer_feerate * htlc_timeout_tx_weight(false) / 1000)
};
let exposure_dust_limit_success_sats = htlc_success_dust_limit + self.counterparty_dust_limit_satoshis;
if amount_msat / 1000 < exposure_dust_limit_success_sats {
let on_counterparty_dust_htlc_exposure_msat = inbound_stats.on_counterparty_tx_dust_exposure_msat + outbound_stats.on_counterparty_tx_dust_exposure_msat + amount_msat;
if on_counterparty_dust_htlc_exposure_msat > self.get_max_dust_htlc_exposure_msat() {
Expand All @@ -5450,7 +5500,7 @@ impl<Signer: Sign> Channel<Signer> {
}
}

let exposure_dust_limit_timeout_sats = (self.get_dust_buffer_feerate(None) as u64 * htlc_timeout_tx_weight(self.opt_anchors()) / 1000) + self.holder_dust_limit_satoshis;
let exposure_dust_limit_timeout_sats = htlc_timeout_dust_limit + self.holder_dust_limit_satoshis;
if amount_msat / 1000 < exposure_dust_limit_timeout_sats {
let on_holder_dust_htlc_exposure_msat = inbound_stats.on_holder_tx_dust_exposure_msat + outbound_stats.on_holder_tx_dust_exposure_msat + amount_msat;
if on_holder_dust_htlc_exposure_msat > self.get_max_dust_htlc_exposure_msat() {
Expand Down
6 changes: 6 additions & 0 deletions lightning/src/util/config.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -325,6 +325,12 @@ pub struct ChannelConfig {
/// to such payments may be sustantial if there are many dust HTLCs present when the
/// channel is force-closed.
///
/// The dust threshold for each HTLC is based on the `dust_limit_satoshis` for each party in a
/// channel negotiated throughout the channel open process, along with the fees required to have
/// a broadcastable HTLC spending transaction. When a channel supports anchor outputs
/// (specifically the zero fee HTLC transaction variant), this threshold no longer takes into
/// account the HTLC transaction fee as it is zero.
///
/// This limit is applied for sent, forwarded, and received HTLCs and limits the total
/// exposure across all three types per-channel. Setting this too low may prevent the
/// sending or receipt of low-value HTLCs on high-traffic nodes, and this limit is very
Expand Down

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