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paymod: Fix the adaptive splitter partitioning

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We were using the current constraints, including any shadow route and other
modifications, when computing the remainder that the second child should
use. Instead we should use the `start_constraints` on the parent payment,
which is a copy of `constraints` created in `payment_start` exactly for this
purpose.

Also added an assert for the invariant on the multiplier.
This commit is contained in:
Christian Decker
2020-07-19 21:44:03 +02:00
committed by Rusty Russell
parent cb20dfc59e
commit f950153f98
1 changed files with 8 additions and 2 deletions
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10
plugins/libplugin-pay.c
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@@ -2335,6 +2335,8 @@ static void adaptive_splitter_cb(struct presplit_mod_data *d, struct payment *p)
double rand = pseudorand_double() * 0.2 + 0.9;
u64 mid = p->amount.millisatoshis / 2 * rand; /* Raw: multiplication */
bool ok;
/* Use the start constraints, not the ones updated by routes and shadow-routes. */
struct payment_constraints *pconstraints = p->start_constraints;
a = payment_new(p, NULL, p, p->modifiers);
b = payment_new(p, NULL, p, p->modifiers);
@@ -2342,11 +2344,15 @@ static void adaptive_splitter_cb(struct presplit_mod_data *d, struct payment *p)
a->amount.millisatoshis = mid; /* Raw: split. */
b->amount.millisatoshis -= mid; /* Raw: split. */
double multiplier = (double)a->amount.millisatoshis / (double)p->amount.millisatoshis; /* Raw: msat division */
assert(multiplier >= 0.4 && multiplier < 0.6);
/* Adjust constraints since we don't want to double our
* fee allowance when we split. */
a->constraints.fee_budget.millisatoshis *= (double)a->amount.millisatoshis / (double)p->amount.millisatoshis; /* Raw: msat division. */
a->constraints.fee_budget.millisatoshis = pconstraints->fee_budget.millisatoshis * multiplier; /* Raw: msat multiplication. */
ok = amount_msat_sub(&b->constraints.fee_budget,
p->constraints.fee_budget,
pconstraints->fee_budget,
a->constraints.fee_budget);
/* Should not fail, mid is less than 55% of original