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askrene: consider fees during *explain failure*

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We would try to explain a failure by simply finding a path between
source and destination and then checking the constraints.
However, we did not add fees.

Changelog-None

Signed-off-by: Lagrang3 <lagrang3@protonmail.com>
This commit is contained in:
Lagrang3
2026-01-30 06:38:47 +01:00
committed by Rusty Russell
parent bb3be7e8f8
commit 41a5c68aa8
1 changed files with 36 additions and 9 deletions
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45
plugins/askrene/explain_failure.c
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@@ -215,6 +215,11 @@ const char *explain_failure(const tal_t *ctx,
const struct dijkstra *dij;
char *path;
const char *cap_check;
const char *explanation;
struct short_channel_id_dir scidd;
struct gossmap_chan *c;
struct amount_msat rolling_amount;
struct amount_msat *path_amount;
/* Do we have enough funds? */
cap_check = check_capacity(ctx, rq, srcnode, OUT_OF_NODE,
@@ -247,11 +252,33 @@ const char *explain_failure(const tal_t *ctx,
fmt_short_channel_id(tmpctx, hops[i].scid));
}
path_amount = tal_arr(tmpctx, struct amount_msat, tal_count(hops));
rolling_amount = amount;
for (size_t i = tal_count(hops) - 1; i < tal_count(hops); i--) {
scidd.scid = hops[i].scid;
scidd.dir = hops[i].direction;
c = gossmap_find_chan(rq->gossmap, &scidd.scid);
path_amount[i] = rolling_amount;
if (!amount_msat_add_fee(&rolling_amount,
c->half[scidd.dir].base_fee,
c->half[scidd.dir].proportional_fee)) {
/* Should not happen, but since the branch exists we use
* it. */
explanation = tal_fmt(
tmpctx, "produces a fee overflow for amount %s",
fmt_amount_msat(tmpctx, rolling_amount));
return rq_log(ctx, rq, LOG_INFORM,
NO_USABLE_PATHS_STRING
" The shortest path is %s, but %s %s",
path,
fmt_short_channel_id_dir(tmpctx, &scidd),
explanation);
}
}
/* Now walk through this: is it disabled? Insuff capacity? */
for (size_t i = 0; i < tal_count(hops); i++) {
const char *explanation;
struct short_channel_id_dir scidd;
struct gossmap_chan *c;
struct amount_msat cap_msat, min, max, htlc_max, htlc_min;
scidd.scid = hops[i].scid;
@@ -266,16 +293,16 @@ const char *explain_failure(const tal_t *ctx,
explanation = "has no gossip";
else if (!c->half[scidd.dir].enabled)
explanation = describe_disabled(tmpctx, rq, c, &scidd);
else if (amount_msat_greater(amount, cap_msat))
explanation = describe_capacity(tmpctx, rq, &scidd, amount);
else if (amount_msat_greater(amount, max))
else if (amount_msat_greater(path_amount[i], cap_msat))
explanation = describe_capacity(tmpctx, rq, &scidd, path_amount[i]);
else if (amount_msat_greater(path_amount[i], max))
explanation = why_max_constrained(tmpctx, rq,
&scidd, amount);
else if (amount_msat_greater(amount, htlc_max))
&scidd, path_amount[i]);
else if (amount_msat_greater(path_amount[i], htlc_max))
explanation = tal_fmt(tmpctx,
"exceeds htlc_maximum_msat ~%s",
fmt_amount_msat(tmpctx, htlc_max));
else if (amount_msat_less(amount, htlc_min))
else if (amount_msat_less(path_amount[i], htlc_min))
explanation = tal_fmt(tmpctx,
"below htlc_minumum_msat ~%s",
fmt_amount_msat(tmpctx, htlc_min));