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fix: improve error message for exhausted blinded path route hints #4398

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fix: improve error message for exhausted blinded path route hints #4398

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17 changes: 12 additions & 5 deletions lightning/src/routing/router.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3637,6 +3637,9 @@ pub(crate) fn get_route<L: Logger, S: ScoreLookUp>(

// Step (5).
if payment_paths.len() == 0 {
if matches!(payment_params.payee, Payee::Blinded { .. }) {
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@TheBlueMatt TheBlueMatt Mar 4, 2026

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Huh? #4308 has nothing to do with blinded paths but rather with when we've tried every last-hop. Also this is the wrong check - at this point in the code we simply failed to find a path, you can't say anything about why.

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@okekefrancis112 okekefrancis112 Mar 5, 2026 •
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Huh? #4308 has nothing to do with blinded paths but rather with when we've tried every last-hop. Also this is the wrong check - at this point in the code we simply failed to find a path, you can't say anything about why.

Thanks for the review! (@TheBlueMatt) I understand the two issues:

  1. This should also cover Payee::Clear with route hints, not just Payee::Blinded
  2. At this point in the code we only know pathfinding failed, not why

For (2), would the right approach be to track inside add_entry! when route hint candidates (both blinded and private hop) are specifically rejected due to exhausted liquidity via used_liquidities, and only emit the specific error when that was the reason all hints failed? Or were you thinking of something simpler/different?

return Err("Failed to find a path to the given destination: all provided blinded path route hints were exhausted");
}
return Err("Failed to find a path to the given destination");
}

Expand Down Expand Up @@ -8475,7 +8478,7 @@ mod tests {
if let Err(err) = get_route(&nodes[0], &route_params, &netgraph,
Some(&first_hops.iter().collect::<Vec<_>>()), Arc::clone(&logger), &scorer,
&Default::default(), &random_seed_bytes) {
assert_eq!(err, "Failed to find a path to the given destination");
assert_eq!(err, "Failed to find a path to the given destination: all provided blinded path route hints were exhausted");
} else { panic!("Expected error") }

// Sending an exact amount accounting for the blinded path fee works.
Expand Down Expand Up @@ -8587,7 +8590,7 @@ mod tests {
if let Err(err) = get_route(
&our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes
) {
assert_eq!(err, "Failed to find a path to the given destination");
assert_eq!(err, "Failed to find a path to the given destination: all provided blinded path route hints were exhausted");
} else { panic!() }
}

Expand Down Expand Up @@ -8635,7 +8638,7 @@ mod tests {
if let Err(err) = get_route(
&our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes
) {
assert_eq!(err, "Failed to find a path to the given destination");
assert_eq!(err, "Failed to find a path to the given destination: all provided blinded path route hints were exhausted");
} else { panic!() }
}

Expand Down Expand Up @@ -8706,7 +8709,11 @@ mod tests {
&our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes
) {
assert_eq!(err, "Failed to find a path to the given destination");
if blinded_payee {
assert_eq!(err, "Failed to find a path to the given destination: all provided blinded path route hints were exhausted");
} else {
assert_eq!(err, "Failed to find a path to the given destination");
}
} else { panic!() }
}

Expand Down Expand Up @@ -8852,7 +8859,7 @@ mod tests {
Arc::clone(&logger), &scorer, &ProbabilisticScoringFeeParameters::default(),
&random_seed_bytes
) {
assert_eq!(err, "Failed to find a path to the given destination");
assert_eq!(err, "Failed to find a path to the given destination: all provided blinded path route hints were exhausted");
} else { panic!() }
}

Expand Down
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