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paymod: Exclude most expensive/slowest chan if limits are exceeded

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This commit is contained in:
Christian Decker
2020-06-03 17:58:20 +02:00
parent 4648d2867f
commit 935578e567
4 changed files with 126 additions and 3 deletions
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78
plugins/libplugin-pay.c
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@@ -216,6 +216,48 @@ tal_route_from_json(const tal_t *ctx, const char *buffer, const jsmntok_t *toks)
return hops;
}
static void payment_exclude_most_expensive(struct payment *p)
{
struct payment *root = payment_root(p);
struct route_hop *e = &p->route[0];
struct amount_msat fee, worst = AMOUNT_MSAT(0);
struct channel_hint hint;
for (size_t i = 0; i < tal_count(p->route)-1; i++) {
if (!amount_msat_sub(&fee, p->route[i].amount, p->route[i+1].amount))
plugin_err(p->plugin, "Negative fee in a route.");
if (amount_msat_greater_eq(fee, worst)) {
e = &p->route[i];
worst = fee;
}
}
hint.scid.scid = e->channel_id;
hint.scid.dir = e->direction;
hint.enabled = false;
tal_arr_expand(&root->channel_hints, hint);
}
static void payment_exclude_longest_delay(struct payment *p)
{
struct payment *root = payment_root(p);
struct route_hop *e = &p->route[0];
u32 delay, worst = 0;
struct channel_hint hint;
for (size_t i = 0; i < tal_count(p->route)-1; i++) {
delay = p->route[i].delay - p->route[i+1].delay;
if (delay >= worst) {
e = &p->route[i];
worst = delay;
}
}
hint.scid.scid = e->channel_id;
hint.scid.dir = e->direction;
hint.enabled = false;
tal_arr_expand(&root->channel_hints, hint);
}
static struct command_result *payment_getroute_result(struct command *cmd,
const char *buffer,
const jsmntok_t *toks,
@@ -246,6 +288,7 @@ static struct command_result *payment_getroute_result(struct command *cmd,
"Fee exceeds our fee budget: %s > %s, discarding route",
type_to_string(tmpctx, struct amount_msat, &fee),
type_to_string(tmpctx, struct amount_msat, &p->fee_budget));
payment_exclude_most_expensive(p);
payment_fail(p);
return command_still_pending(cmd);
}
@@ -254,6 +297,7 @@ static struct command_result *payment_getroute_result(struct command *cmd,
plugin_log(p->plugin, LOG_INFORM,
"CLTV delay exceeds our CLTV budget: %d > %d",
p->route[0].delay, p->cltv_budget);
payment_exclude_longest_delay(p);
payment_fail(p);
return command_still_pending(cmd);
}
@@ -1493,3 +1537,37 @@ static struct routehints_data *routehint_data_init(struct payment *p)
REGISTER_PAYMENT_MODIFIER(routehints, struct routehints_data *,
routehint_data_init, routehint_step_cb);
/* For tiny payments the fees incurred due to the fixed base_fee may dominate
* the overall cost of the payment. Since these payments are often used as a
* way to signal, rather than actually transfer the amount, we add an
* exemption that allows tiny payments to exceed the fee allowance. This is
* implemented by setting a larger allowance than we would normally do if the
* payment is below the threshold. */
static struct exemptfee_data *exemptfee_data_init(struct payment *p)
{
struct exemptfee_data *d = tal(p, struct exemptfee_data);
d->amount = AMOUNT_MSAT(5000);
return d;
}
static void exemptfee_cb(struct exemptfee_data *d, struct payment *p)
{
if (p->step != PAYMENT_STEP_INITIALIZED)
return payment_continue(p);
if (amount_msat_greater_eq(d->amount, p->amount)) {
p->fee_budget = d->amount;
plugin_log(
p->plugin, LOG_INFORM,
"Payment amount is below exemption threshold, "
"allowing a maximum fee of %s",
type_to_string(tmpctx, struct amount_msat, &p->fee_budget));
}
return payment_continue(p);
}
REGISTER_PAYMENT_MODIFIER(exemptfee, struct exemptfee_data *,
exemptfee_data_init, exemptfee_cb);