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paymod: Update the route constraints as we apply routes and mods

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These are primarily the fee and cltv constraints that we need to keep up to
date in order to give modifiers a correct view of what is and what isn't
allowed.
This commit is contained in:
Christian Decker
2020-06-04 15:44:19 +02:00
parent 935578e567
commit 215a0ada8b
3 changed files with 80 additions and 30 deletions
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80
plugins/libplugin-pay.c
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@@ -32,8 +32,9 @@ struct payment *payment_new(tal_t *ctx, struct command *cmd,
p->payment_hash = parent->payment_hash;
p->partid = payment_root(p->parent)->next_partid++;
p->plugin = parent->plugin;
p->fee_budget = parent->fee_budget;
p->cltv_budget = parent->cltv_budget;
/* Re-establish the unmodified constraints for our sub-payment. */
p->constraints = *parent->start_constraints;
} else {
assert(cmd != NULL);
p->partid = 0;
@@ -166,6 +167,8 @@ void payment_start(struct payment *p)
p->getroute->cltv = DEFAULT_FINAL_CLTV_DELTA;
p->getroute->amount = p->amount;
p->start_constraints = tal_dup(p, struct payment_constraints, &p->constraints);
/* TODO If this is not the root, we can actually skip the getinfo call
* and just reuse the parent's value. */
send_outreq(p->plugin,
@@ -258,6 +261,41 @@ static void payment_exclude_longest_delay(struct payment *p)
tal_arr_expand(&root->channel_hints, hint);
}
static struct amount_msat payment_route_fee(struct payment *p)
{
struct amount_msat fee;
if (!amount_msat_sub(&fee, p->route[0].amount, p->amount)) {
plugin_log(
p->plugin,
LOG_BROKEN,
"gossipd returned a route with a negative fee: sending %s "
"to deliver %s",
type_to_string(tmpctx, struct amount_msat,
&p->route[0].amount),
type_to_string(tmpctx, struct amount_msat, &p->amount));
abort();
}
return fee;
}
/* Update the constraints by subtracting the delta_fee and delta_cltv if the
* result is positive. Returns whether or not the update has been applied. */
static WARN_UNUSED_RESULT bool
payment_constraints_update(struct payment_constraints *cons,
const struct amount_msat delta_fee,
const u32 delta_cltv)
{
if (delta_cltv > cons->cltv_budget)
return false;
/* amount_msat_sub performs a check before actually subtracting. */
if (!amount_msat_sub(&cons->fee_budget, cons->fee_budget, delta_fee))
return false;
cons->cltv_budget -= delta_cltv;
return true;
}
static struct command_result *payment_getroute_result(struct command *cmd,
const char *buffer,
const jsmntok_t *toks,
@@ -269,39 +307,36 @@ static struct command_result *payment_getroute_result(struct command *cmd,
p->route = tal_route_from_json(p, buffer, rtok);
p->step = PAYMENT_STEP_GOT_ROUTE;
fee = payment_route_fee(p);
/* Ensure that our fee and CLTV budgets are respected. */
if (!amount_msat_sub(&fee, p->route[0].amount, p->amount)) {
plugin_err(
p->plugin,
"gossipd returned a route with a negative fee: sending %s "
"to deliver %s",
type_to_string(tmpctx, struct amount_msat,
&p->route[0].amount),
type_to_string(tmpctx, struct amount_msat, &p->amount));
payment_fail(p);
return command_still_pending(cmd);
}
if (amount_msat_greater(fee, p->fee_budget)) {
if (amount_msat_greater(fee, p->constraints.fee_budget)) {
plugin_log(p->plugin, LOG_INFORM,
"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));
type_to_string(tmpctx, struct amount_msat, &p->constraints.fee_budget));
payment_exclude_most_expensive(p);
payment_fail(p);
return command_still_pending(cmd);
}
if (p->route[0].delay > p->cltv_budget) {
if (p->route[0].delay > p->constraints.cltv_budget) {
plugin_log(p->plugin, LOG_INFORM,
"CLTV delay exceeds our CLTV budget: %d > %d",
p->route[0].delay, p->cltv_budget);
p->route[0].delay, p->constraints.cltv_budget);
payment_exclude_longest_delay(p);
payment_fail(p);
return command_still_pending(cmd);
}
/* Now update the constraints in fee_budget and cltv_budget so
* modifiers know what constraints they need to adhere to. */
if (!payment_constraints_update(&p->constraints, fee, p->route[0].delay)) {
plugin_log(p->plugin, LOG_BROKEN,
"Could not update constraints.");
abort();
}
/* Allow modifiers to modify the route, before
* payment_compute_onion_payloads uses the route to generate the
* onion_payloads */
@@ -1557,13 +1592,14 @@ 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;
if (amount_msat_greater_eq(d->amount, p->constraints.fee_budget)) {
p->constraints.fee_budget = d->amount;
p->start_constraints->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));
type_to_string(tmpctx, struct amount_msat, &p->constraints.fee_budget));
}
return payment_continue(p);
}