Handle overflowing route-hint fee aggregates#4716

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Merged
TheBlueMatt merged 1 commit into from
Jun 18, 2026
Merged

Handle overflowing route-hint fee aggregates #4716

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94 changes: 90 additions & 4 deletions lightning/src/routing/router.rs
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
/// contribution this path can make to the final value of the payment.
/// May be slightly lower than the actual max due to rounding errors when aggregating fees
/// along the path.
/// Returns an error with the index of a later hop to discard if the following hops' aggregate
/// fees overflow.
#[rustfmt::skip]
fn max_final_value_msat(
&self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
) -> (usize, u64) {
) -> Result<(usize, u64), usize> {
let mut max_path_contribution = (0, u64::MAX);
for (idx, (hop, _)) in self.hops.iter().enumerate() {
let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
// Aggregate the fees of the hops that come after this one, and use those fees to compute the
// maximum amount that this hop can contribute to the final value received by the payee.
let (next_hops_aggregated_base, next_hops_aggregated_prop) =
crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
.map_err(|_| idx + 1)?;

// floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
} else { debug_assert!(false); }
}

max_path_contribution
Ok(max_path_contribution)
}
}

fn mark_candidate_liquidity_exhausted(
used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
let exhausted = u64::max_value();
if let Some(scid) = candidate.short_channel_id() {
*used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
*used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
} else {
*used_liquidities.entry(candidate.id()).or_default() = exhausted;
}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
// underpaid htlc_minimum_msat with fees.
debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
let (lowest_value_contrib_hop, max_path_contribution_msat) =
payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
Ok(contribution) => contribution,
Err(candidate_idx_to_skip) => {
let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;

@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.

log_trace!(logger,
"Ignoring path because aggregate fees including hop {} overflow.",
LoggedCandidateHop(candidate));
mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
continue 'paths_collection;
}
};
let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
}

#[test]
fn aggregated_prop_fee_overflow_fails_route() {
// If the fee cap is disabled, we may consider invoice hints with very large
// proportional fees. Aggregating those fees can overflow, in which case we should fail
// routing cleanly rather than panic.
let secp_ctx = Secp256k1::new();
let logger = Arc::new(ln_test_utils::TestLogger::new());
let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
let scorer = ln_test_utils::TestScorer::new();
let random_seed_bytes = [42; 32];
let config = UserConfig::default();

let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
let route_hint = RouteHint(vec![
RouteHintHop {
src_node_id: nodes[0],
short_channel_id: 100,
fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
cltv_expiry_delta: 10,
htlc_minimum_msat: None,
htlc_maximum_msat: None,
},
RouteHintHop {
src_node_id: nodes[1],
short_channel_id: 101,
fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
cltv_expiry_delta: 10,
htlc_minimum_msat: None,
htlc_maximum_msat: None,
},
]);

let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
.with_route_hints(vec![route_hint])
.unwrap()
.with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
.unwrap();
let first_hops = [get_channel_details(
Some(1),
nodes[0],
channelmanager::provided_init_features(&config),
100_000_000,
)];
let route_params = RouteParameters {
payment_params,
final_value_msat: 1,
max_total_routing_fee_msat: None,
};
let route = get_route(
&our_node_id,
&route_params,
&network_graph.read_only(),
Some(&first_hops.iter().collect::<Vec<_>>()),
Arc::clone(&logger),
&scorer,
&Default::default(),
&random_seed_bytes,
);
assert!(route.is_err());
}

#[test]
fn prefers_paths_by_cost_amt_ratio() {
// Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down
, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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Handle overflowing route-hint fee aggregates#4716

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 Merged

TheBlueMatt
merged 1 commit into

from

Jun 18, 2026
 Merged


Handle overflowing route-hint fee aggregates
#4716
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94 changes: 90 additions & 4 deletions
lightning/src/routing/router.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
	/// contribution this path can make to the final value of the payment.
	/// May be slightly lower than the actual max due to rounding errors when aggregating fees
	/// along the path.
	/// Returns an error with the index of a later hop to discard if the following hops' aggregate
	/// fees overflow.
	#[rustfmt::skip]
	fn max_final_value_msat(
 &self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
	) -> (usize, u64) {
	) -> Result<(usize, u64), usize> {
 let mut max_path_contribution = (0, u64::MAX);
 for (idx, (hop, _)) in self.hops.iter().enumerate() {
 let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
 // Aggregate the fees of the hops that come after this one, and use those fees to compute the
 // maximum amount that this hop can contribute to the final value received by the payee.
 let (next_hops_aggregated_base, next_hops_aggregated_prop) =
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
 .map_err(|_| idx + 1)?;

 // floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
 let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
 } else { debug_assert!(false); }
 }

 max_path_contribution
 Ok(max_path_contribution)
	}
}

fn mark_candidate_liquidity_exhausted(
	used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
	let exhausted = u64::max_value();
	if let Some(scid) = candidate.short_channel_id() {
 *used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
 *used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
	} else {
 *used_liquidities.entry(candidate.id()).or_default() = exhausted;
	}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
 // underpaid htlc_minimum_msat with fees.
 debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
 let (lowest_value_contrib_hop, max_path_contribution_msat) =
 payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
 match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
 Ok(contribution) => contribution,
 Err(candidate_idx_to_skip) => {
 let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;
@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.
 log_trace!(logger,
 "Ignoring path because aggregate fees including hop {} overflow.",
 LoggedCandidateHop(candidate));
 mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
 continue 'paths_collection;
 }
 };
 let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
 value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
 assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
	}

	#[test]
	fn aggregated_prop_fee_overflow_fails_route() {
 // If the fee cap is disabled, we may consider invoice hints with very large
 // proportional fees. Aggregating those fees can overflow, in which case we should fail
 // routing cleanly rather than panic.
 let secp_ctx = Secp256k1::new();
 let logger = Arc::new(ln_test_utils::TestLogger::new());
 let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
 let scorer = ln_test_utils::TestScorer::new();
 let random_seed_bytes = [42; 32];
 let config = UserConfig::default();

 let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
 let route_hint = RouteHint(vec![
 RouteHintHop {
 src_node_id: nodes[0],
 short_channel_id: 100,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 RouteHintHop {
 src_node_id: nodes[1],
 short_channel_id: 101,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 ]);

 let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
 .with_route_hints(vec![route_hint])
 .unwrap()
 .with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
 .unwrap();
 let first_hops = [get_channel_details(
 Some(1),
 nodes[0],
 channelmanager::provided_init_features(&config),
 100_000_000,
 )];
 let route_params = RouteParameters {
 payment_params,
 final_value_msat: 1,
 max_total_routing_fee_msat: None,
 };
 let route = get_route(
 &our_node_id,
 &route_params,
 &network_graph.read_only(),
 Some(&first_hops.iter().collect::<Vec<_>>()),
 Arc::clone(&logger),
 &scorer,
 &Default::default(),
 &random_seed_bytes,
 );
 assert!(route.is_err());
	}

	#[test]
	fn prefers_paths_by_cost_amt_ratio() {
 // Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Handle overflowing route-hint fee aggregates#4716

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 Merged

TheBlueMatt
merged 1 commit into

from

Jun 18, 2026
 Merged


Handle overflowing route-hint fee aggregates
#4716
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94 changes: 90 additions & 4 deletions
lightning/src/routing/router.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
	/// contribution this path can make to the final value of the payment.
	/// May be slightly lower than the actual max due to rounding errors when aggregating fees
	/// along the path.
	/// Returns an error with the index of a later hop to discard if the following hops' aggregate
	/// fees overflow.
	#[rustfmt::skip]
	fn max_final_value_msat(
 &self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
	) -> (usize, u64) {
	) -> Result<(usize, u64), usize> {
 let mut max_path_contribution = (0, u64::MAX);
 for (idx, (hop, _)) in self.hops.iter().enumerate() {
 let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
 // Aggregate the fees of the hops that come after this one, and use those fees to compute the
 // maximum amount that this hop can contribute to the final value received by the payee.
 let (next_hops_aggregated_base, next_hops_aggregated_prop) =
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
 .map_err(|_| idx + 1)?;

 // floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
 let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
 } else { debug_assert!(false); }
 }

 max_path_contribution
 Ok(max_path_contribution)
	}
}

fn mark_candidate_liquidity_exhausted(
	used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
	let exhausted = u64::max_value();
	if let Some(scid) = candidate.short_channel_id() {
 *used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
 *used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
	} else {
 *used_liquidities.entry(candidate.id()).or_default() = exhausted;
	}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
 // underpaid htlc_minimum_msat with fees.
 debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
 let (lowest_value_contrib_hop, max_path_contribution_msat) =
 payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
 match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
 Ok(contribution) => contribution,
 Err(candidate_idx_to_skip) => {
 let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;
@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.
 log_trace!(logger,
 "Ignoring path because aggregate fees including hop {} overflow.",
 LoggedCandidateHop(candidate));
 mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
 continue 'paths_collection;
 }
 };
 let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
 value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
 assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
	}

	#[test]
	fn aggregated_prop_fee_overflow_fails_route() {
 // If the fee cap is disabled, we may consider invoice hints with very large
 // proportional fees. Aggregating those fees can overflow, in which case we should fail
 // routing cleanly rather than panic.
 let secp_ctx = Secp256k1::new();
 let logger = Arc::new(ln_test_utils::TestLogger::new());
 let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
 let scorer = ln_test_utils::TestScorer::new();
 let random_seed_bytes = [42; 32];
 let config = UserConfig::default();

 let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
 let route_hint = RouteHint(vec![
 RouteHintHop {
 src_node_id: nodes[0],
 short_channel_id: 100,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 RouteHintHop {
 src_node_id: nodes[1],
 short_channel_id: 101,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 ]);

 let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
 .with_route_hints(vec![route_hint])
 .unwrap()
 .with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
 .unwrap();
 let first_hops = [get_channel_details(
 Some(1),
 nodes[0],
 channelmanager::provided_init_features(&config),
 100_000_000,
 )];
 let route_params = RouteParameters {
 payment_params,
 final_value_msat: 1,
 max_total_routing_fee_msat: None,
 };
 let route = get_route(
 &our_node_id,
 &route_params,
 &network_graph.read_only(),
 Some(&first_hops.iter().collect::<Vec<_>>()),
 Arc::clone(&logger),
 &scorer,
 &Default::default(),
 &random_seed_bytes,
 );
 assert!(route.is_err());
	}

	#[test]
	fn prefers_paths_by_cost_amt_ratio() {
 // Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Handle overflowing route-hint fee aggregates
#4716
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94 changes: 90 additions & 4 deletions
lightning/src/routing/router.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
	/// contribution this path can make to the final value of the payment.
	/// May be slightly lower than the actual max due to rounding errors when aggregating fees
	/// along the path.
	/// Returns an error with the index of a later hop to discard if the following hops' aggregate
	/// fees overflow.
	#[rustfmt::skip]
	fn max_final_value_msat(
 &self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
	) -> (usize, u64) {
	) -> Result<(usize, u64), usize> {
 let mut max_path_contribution = (0, u64::MAX);
 for (idx, (hop, _)) in self.hops.iter().enumerate() {
 let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
 // Aggregate the fees of the hops that come after this one, and use those fees to compute the
 // maximum amount that this hop can contribute to the final value received by the payee.
 let (next_hops_aggregated_base, next_hops_aggregated_prop) =
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
 .map_err(|_| idx + 1)?;

 // floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
 let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
 } else { debug_assert!(false); }
 }

 max_path_contribution
 Ok(max_path_contribution)
	}
}

fn mark_candidate_liquidity_exhausted(
	used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
	let exhausted = u64::max_value();
	if let Some(scid) = candidate.short_channel_id() {
 *used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
 *used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
	} else {
 *used_liquidities.entry(candidate.id()).or_default() = exhausted;
	}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
 // underpaid htlc_minimum_msat with fees.
 debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
 let (lowest_value_contrib_hop, max_path_contribution_msat) =
 payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
 match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
 Ok(contribution) => contribution,
 Err(candidate_idx_to_skip) => {
 let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;
@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.
 log_trace!(logger,
 "Ignoring path because aggregate fees including hop {} overflow.",
 LoggedCandidateHop(candidate));
 mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
 continue 'paths_collection;
 }
 };
 let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
 value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
 assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
	}

	#[test]
	fn aggregated_prop_fee_overflow_fails_route() {
 // If the fee cap is disabled, we may consider invoice hints with very large
 // proportional fees. Aggregating those fees can overflow, in which case we should fail
 // routing cleanly rather than panic.
 let secp_ctx = Secp256k1::new();
 let logger = Arc::new(ln_test_utils::TestLogger::new());
 let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
 let scorer = ln_test_utils::TestScorer::new();
 let random_seed_bytes = [42; 32];
 let config = UserConfig::default();

 let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
 let route_hint = RouteHint(vec![
 RouteHintHop {
 src_node_id: nodes[0],
 short_channel_id: 100,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 RouteHintHop {
 src_node_id: nodes[1],
 short_channel_id: 101,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 ]);

 let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
 .with_route_hints(vec![route_hint])
 .unwrap()
 .with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
 .unwrap();
 let first_hops = [get_channel_details(
 Some(1),
 nodes[0],
 channelmanager::provided_init_features(&config),
 100_000_000,
 )];
 let route_params = RouteParameters {
 payment_params,
 final_value_msat: 1,
 max_total_routing_fee_msat: None,
 };
 let route = get_route(
 &our_node_id,
 &route_params,
 &network_graph.read_only(),
 Some(&first_hops.iter().collect::<Vec<_>>()),
 Arc::clone(&logger),
 &scorer,
 &Default::default(),
 &random_seed_bytes,
 );
 assert!(route.is_err());
	}

	#[test]
	fn prefers_paths_by_cost_amt_ratio() {
 // Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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Handle overflowing route-hint fee aggregates#4716

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 Merged

TheBlueMatt
merged 1 commit into

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Jun 18, 2026
 Merged


Handle overflowing route-hint fee aggregates
#4716
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94 changes: 90 additions & 4 deletions
lightning/src/routing/router.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
	/// contribution this path can make to the final value of the payment.
	/// May be slightly lower than the actual max due to rounding errors when aggregating fees
	/// along the path.
	/// Returns an error with the index of a later hop to discard if the following hops' aggregate
	/// fees overflow.
	#[rustfmt::skip]
	fn max_final_value_msat(
 &self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
	) -> (usize, u64) {
	) -> Result<(usize, u64), usize> {
 let mut max_path_contribution = (0, u64::MAX);
 for (idx, (hop, _)) in self.hops.iter().enumerate() {
 let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
 // Aggregate the fees of the hops that come after this one, and use those fees to compute the
 // maximum amount that this hop can contribute to the final value received by the payee.
 let (next_hops_aggregated_base, next_hops_aggregated_prop) =
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
 .map_err(|_| idx + 1)?;

 // floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
 let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
 } else { debug_assert!(false); }
 }

 max_path_contribution
 Ok(max_path_contribution)
	}
}

fn mark_candidate_liquidity_exhausted(
	used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
	let exhausted = u64::max_value();
	if let Some(scid) = candidate.short_channel_id() {
 *used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
 *used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
	} else {
 *used_liquidities.entry(candidate.id()).or_default() = exhausted;
	}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
 // underpaid htlc_minimum_msat with fees.
 debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
 let (lowest_value_contrib_hop, max_path_contribution_msat) =
 payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
 match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
 Ok(contribution) => contribution,
 Err(candidate_idx_to_skip) => {
 let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;
@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.
 log_trace!(logger,
 "Ignoring path because aggregate fees including hop {} overflow.",
 LoggedCandidateHop(candidate));
 mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
 continue 'paths_collection;
 }
 };
 let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
 value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
 assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
	}

	#[test]
	fn aggregated_prop_fee_overflow_fails_route() {
 // If the fee cap is disabled, we may consider invoice hints with very large
 // proportional fees. Aggregating those fees can overflow, in which case we should fail
 // routing cleanly rather than panic.
 let secp_ctx = Secp256k1::new();
 let logger = Arc::new(ln_test_utils::TestLogger::new());
 let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
 let scorer = ln_test_utils::TestScorer::new();
 let random_seed_bytes = [42; 32];
 let config = UserConfig::default();

 let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
 let route_hint = RouteHint(vec![
 RouteHintHop {
 src_node_id: nodes[0],
 short_channel_id: 100,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 RouteHintHop {
 src_node_id: nodes[1],
 short_channel_id: 101,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 ]);

 let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
 .with_route_hints(vec![route_hint])
 .unwrap()
 .with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
 .unwrap();
 let first_hops = [get_channel_details(
 Some(1),
 nodes[0],
 channelmanager::provided_init_features(&config),
 100_000_000,
 )];
 let route_params = RouteParameters {
 payment_params,
 final_value_msat: 1,
 max_total_routing_fee_msat: None,
 };
 let route = get_route(
 &our_node_id,
 &route_params,
 &network_graph.read_only(),
 Some(&first_hops.iter().collect::<Vec<_>>()),
 Arc::clone(&logger),
 &scorer,
 &Default::default(),
 &random_seed_bytes,
 );
 assert!(route.is_err());
	}

	#[test]
	fn prefers_paths_by_cost_amt_ratio() {
 // Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Handle overflowing route-hint fee aggregates#4716

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 Merged

TheBlueMatt
merged 1 commit into

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Jun 18, 2026
 Merged


Handle overflowing route-hint fee aggregates
#4716
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94 changes: 90 additions & 4 deletions
lightning/src/routing/router.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
	/// contribution this path can make to the final value of the payment.
	/// May be slightly lower than the actual max due to rounding errors when aggregating fees
	/// along the path.
	/// Returns an error with the index of a later hop to discard if the following hops' aggregate
	/// fees overflow.
	#[rustfmt::skip]
	fn max_final_value_msat(
 &self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
	) -> (usize, u64) {
	) -> Result<(usize, u64), usize> {
 let mut max_path_contribution = (0, u64::MAX);
 for (idx, (hop, _)) in self.hops.iter().enumerate() {
 let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
 // Aggregate the fees of the hops that come after this one, and use those fees to compute the
 // maximum amount that this hop can contribute to the final value received by the payee.
 let (next_hops_aggregated_base, next_hops_aggregated_prop) =
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
 .map_err(|_| idx + 1)?;

 // floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
 let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
 } else { debug_assert!(false); }
 }

 max_path_contribution
 Ok(max_path_contribution)
	}
}

fn mark_candidate_liquidity_exhausted(
	used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
	let exhausted = u64::max_value();
	if let Some(scid) = candidate.short_channel_id() {
 *used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
 *used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
	} else {
 *used_liquidities.entry(candidate.id()).or_default() = exhausted;
	}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
 // underpaid htlc_minimum_msat with fees.
 debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
 let (lowest_value_contrib_hop, max_path_contribution_msat) =
 payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
 match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
 Ok(contribution) => contribution,
 Err(candidate_idx_to_skip) => {
 let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;
@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.
 log_trace!(logger,
 "Ignoring path because aggregate fees including hop {} overflow.",
 LoggedCandidateHop(candidate));
 mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
 continue 'paths_collection;
 }
 };
 let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
 value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
 assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
	}

	#[test]
	fn aggregated_prop_fee_overflow_fails_route() {
 // If the fee cap is disabled, we may consider invoice hints with very large
 // proportional fees. Aggregating those fees can overflow, in which case we should fail
 // routing cleanly rather than panic.
 let secp_ctx = Secp256k1::new();
 let logger = Arc::new(ln_test_utils::TestLogger::new());
 let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
 let scorer = ln_test_utils::TestScorer::new();
 let random_seed_bytes = [42; 32];
 let config = UserConfig::default();

 let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
 let route_hint = RouteHint(vec![
 RouteHintHop {
 src_node_id: nodes[0],
 short_channel_id: 100,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 RouteHintHop {
 src_node_id: nodes[1],
 short_channel_id: 101,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 ]);

 let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
 .with_route_hints(vec![route_hint])
 .unwrap()
 .with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
 .unwrap();
 let first_hops = [get_channel_details(
 Some(1),
 nodes[0],
 channelmanager::provided_init_features(&config),
 100_000_000,
 )];
 let route_params = RouteParameters {
 payment_params,
 final_value_msat: 1,
 max_total_routing_fee_msat: None,
 };
 let route = get_route(
 &our_node_id,
 &route_params,
 &network_graph.read_only(),
 Some(&first_hops.iter().collect::<Vec<_>>()),
 Arc::clone(&logger),
 &scorer,
 &Default::default(),
 &random_seed_bytes,
 );
 assert!(route.is_err());
	}

	#[test]
	fn prefers_paths_by_cost_amt_ratio() {
 // Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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TheBlueMatt
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Jun 18, 2026
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Handle overflowing route-hint fee aggregates
#4716
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94 changes: 90 additions & 4 deletions
lightning/src/routing/router.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
	/// contribution this path can make to the final value of the payment.
	/// May be slightly lower than the actual max due to rounding errors when aggregating fees
	/// along the path.
	/// Returns an error with the index of a later hop to discard if the following hops' aggregate
	/// fees overflow.
	#[rustfmt::skip]
	fn max_final_value_msat(
 &self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
	) -> (usize, u64) {
	) -> Result<(usize, u64), usize> {
 let mut max_path_contribution = (0, u64::MAX);
 for (idx, (hop, _)) in self.hops.iter().enumerate() {
 let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
 // Aggregate the fees of the hops that come after this one, and use those fees to compute the
 // maximum amount that this hop can contribute to the final value received by the payee.
 let (next_hops_aggregated_base, next_hops_aggregated_prop) =
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
 .map_err(|_| idx + 1)?;

 // floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
 let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
 } else { debug_assert!(false); }
 }

 max_path_contribution
 Ok(max_path_contribution)
	}
}

fn mark_candidate_liquidity_exhausted(
	used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
	let exhausted = u64::max_value();
	if let Some(scid) = candidate.short_channel_id() {
 *used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
 *used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
	} else {
 *used_liquidities.entry(candidate.id()).or_default() = exhausted;
	}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
 // underpaid htlc_minimum_msat with fees.
 debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
 let (lowest_value_contrib_hop, max_path_contribution_msat) =
 payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
 match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
 Ok(contribution) => contribution,
 Err(candidate_idx_to_skip) => {
 let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;
@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.
 log_trace!(logger,
 "Ignoring path because aggregate fees including hop {} overflow.",
 LoggedCandidateHop(candidate));
 mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
 continue 'paths_collection;
 }
 };
 let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
 value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
 assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
	}

	#[test]
	fn aggregated_prop_fee_overflow_fails_route() {
 // If the fee cap is disabled, we may consider invoice hints with very large
 // proportional fees. Aggregating those fees can overflow, in which case we should fail
 // routing cleanly rather than panic.
 let secp_ctx = Secp256k1::new();
 let logger = Arc::new(ln_test_utils::TestLogger::new());
 let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
 let scorer = ln_test_utils::TestScorer::new();
 let random_seed_bytes = [42; 32];
 let config = UserConfig::default();

 let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
 let route_hint = RouteHint(vec![
 RouteHintHop {
 src_node_id: nodes[0],
 short_channel_id: 100,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 RouteHintHop {
 src_node_id: nodes[1],
 short_channel_id: 101,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 ]);

 let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
 .with_route_hints(vec![route_hint])
 .unwrap()
 .with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
 .unwrap();
 let first_hops = [get_channel_details(
 Some(1),
 nodes[0],
 channelmanager::provided_init_features(&config),
 100_000_000,
 )];
 let route_params = RouteParameters {
 payment_params,
 final_value_msat: 1,
 max_total_routing_fee_msat: None,
 };
 let route = get_route(
 &our_node_id,
 &route_params,
 &network_graph.read_only(),
 Some(&first_hops.iter().collect::<Vec<_>>()),
 Arc::clone(&logger),
 &scorer,
 &Default::default(),
 &random_seed_bytes,
 );
 assert!(route.is_err());
	}

	#[test]
	fn prefers_paths_by_cost_amt_ratio() {
 // Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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Handle overflowing route-hint fee aggregates#4716

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 Merged

TheBlueMatt
merged 1 commit into

from

Jun 18, 2026
 Merged


Handle overflowing route-hint fee aggregates
#4716
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94 changes: 90 additions & 4 deletions
lightning/src/routing/router.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2421,10 +2421,12 @@ impl<'a> PaymentPath<'a> {
	/// contribution this path can make to the final value of the payment.
	/// May be slightly lower than the actual max due to rounding errors when aggregating fees
	/// along the path.
	/// Returns an error with the index of a later hop to discard if the following hops' aggregate
	/// fees overflow.
	#[rustfmt::skip]
	fn max_final_value_msat(
 &self, used_liquidities: &HashMap<CandidateHopId, u64>, channel_saturation_pow_half: u8
	) -> (usize, u64) {
	) -> Result<(usize, u64), usize> {
 let mut max_path_contribution = (0, u64::MAX);
 for (idx, (hop, _)) in self.hops.iter().enumerate() {
 let hop_effective_capacity_msat = hop.candidate.effective_capacity();
Expand All@@ -2440,7 +2442,8 @@ impl<'a> PaymentPath<'a> {
 // Aggregate the fees of the hops that come after this one, and use those fees to compute the
 // maximum amount that this hop can contribute to the final value received by the payee.
 let (next_hops_aggregated_base, next_hops_aggregated_prop) =
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter).unwrap();
 crate::blinded_path::payment::compute_aggregated_base_prop_fee(next_hops_feerates_iter)
 .map_err(|_| idx + 1)?;

 // floor(((hop_max_msat - agg_base) * 1_000_000) / (1_000_000 + agg_prop))
 let hop_max_final_value_contribution = (hop_max_msat as u128)
Expand All@@ -2457,7 +2460,19 @@ impl<'a> PaymentPath<'a> {
 } else { debug_assert!(false); }
 }

 max_path_contribution
 Ok(max_path_contribution)
	}
}

fn mark_candidate_liquidity_exhausted(
	used_liquidities: &mut HashMap<CandidateHopId, u64>, candidate: &CandidateRouteHop,
) {
	let exhausted = u64::max_value();
	if let Some(scid) = candidate.short_channel_id() {
 *used_liquidities.entry(CandidateHopId::Clear((scid, false))).or_default() = exhausted;
 *used_liquidities.entry(CandidateHopId::Clear((scid, true))).or_default() = exhausted;
	} else {
 *used_liquidities.entry(candidate.id()).or_default() = exhausted;
	}
}

Expand DownExpand Up@@ -3637,7 +3652,17 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(
 // underpaid htlc_minimum_msat with fees.
 debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
 let (lowest_value_contrib_hop, max_path_contribution_msat) =
 payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half);
 match payment_path.max_final_value_msat(&used_liquidities, channel_saturation_pow_half) {
 Ok(contribution) => contribution,
 Err(candidate_idx_to_skip) => {
 let candidate = &payment_path.hops[candidate_idx_to_skip].0.candidate;
@TheBlueMattTheBlueMattJun 18, 2026

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The fact that this can't index OOB is incredibly subtle (compute_aggregated_base_prop_fee won't fail if next_hops_feerates_iter is empty, which will happen if we're at the end). Might be worth clarifying somewhere in a comment.
 log_trace!(logger,
 "Ignoring path because aggregate fees including hop {} overflow.",
 LoggedCandidateHop(candidate));
 mark_candidate_liquidity_exhausted(&mut used_liquidities, candidate);
 continue 'paths_collection;
 }
 };
 let desired_value_contribution = cmp::min(max_path_contribution_msat, final_value_msat);
 value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);

Expand DownExpand Up@@ -9332,6 +9357,67 @@ mod tests {
 assert_eq!(route.paths[0].hops[0].short_channel_id, 44);
	}

	#[test]
	fn aggregated_prop_fee_overflow_fails_route() {
 // If the fee cap is disabled, we may consider invoice hints with very large
 // proportional fees. Aggregating those fees can overflow, in which case we should fail
 // routing cleanly rather than panic.
 let secp_ctx = Secp256k1::new();
 let logger = Arc::new(ln_test_utils::TestLogger::new());
 let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
 let scorer = ln_test_utils::TestScorer::new();
 let random_seed_bytes = [42; 32];
 let config = UserConfig::default();

 let (_, our_node_id, _, nodes) = get_nodes(&secp_ctx);
 let route_hint = RouteHint(vec![
 RouteHintHop {
 src_node_id: nodes[0],
 short_channel_id: 100,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 RouteHintHop {
 src_node_id: nodes[1],
 short_channel_id: 101,
 fees: RoutingFees { base_msat: 0, proportional_millionths: u32::MAX },
 cltv_expiry_delta: 10,
 htlc_minimum_msat: None,
 htlc_maximum_msat: None,
 },
 ]);

 let payment_params = PaymentParameters::from_node_id(nodes[2], 42)
 .with_route_hints(vec![route_hint])
 .unwrap()
 .with_bolt11_features(channelmanager::provided_bolt11_invoice_features(&config))
 .unwrap();
 let first_hops = [get_channel_details(
 Some(1),
 nodes[0],
 channelmanager::provided_init_features(&config),
 100_000_000,
 )];
 let route_params = RouteParameters {
 payment_params,
 final_value_msat: 1,
 max_total_routing_fee_msat: None,
 };
 let route = get_route(
 &our_node_id,
 &route_params,
 &network_graph.read_only(),
 Some(&first_hops.iter().collect::<Vec<_>>()),
 Arc::clone(&logger),
 &scorer,
 &Default::default(),
 &random_seed_bytes,
 );
 assert!(route.is_err());
	}

	#[test]
	fn prefers_paths_by_cost_amt_ratio() {
 // Previously, we preferred paths during MPP selection based on their absolute cost, rather
Expand Down