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pay: respect maxfeepercent when choosing a shadow route #3693

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May 5, 2020
Merged

pay: respect maxfeepercent when choosing a shadow route #3693

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32c2b30
Reproduce issue #3684
darosior May 2, 2020
7993285
pay: respect maxfeepercent when choosing a shadow route
darosior May 2, 2020
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17 changes: 15 additions & 2 deletions plugins/pay.c
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,8 @@ struct pay_command {

/* How much we're paying, and what riskfactor for routing. */
struct amount_msat msat;
/* Blank amount to pay, without fees and shadow route(s). */
struct amount_msat initial_msat;
/* riskfactor 12.345% -> riskfactor_millionths = 12345000 */
u64 riskfactor_millionths;
unsigned int final_cltv;
Expand Down Expand Up @@ -1046,6 +1048,12 @@ static struct command_result *add_shadow_route(struct command *cmd,
size_t i;
u64 sample = 0;
struct route_info *route = tal_arr(NULL, struct route_info, 1);
struct amount_msat fees, maxfees;
/* Don't go above this. Note how we use the initial amount to get the percentage
* of the fees, or it would increase with the addition of new shadow routes. */
if (!amount_msat_fee(&maxfees, pc->initial_msat, 0, pc->maxfee_pct_millionths))
plugin_err(cmd->plugin, "Overflow when computing maxfees for "
"shadow routes.");

json_for_each_arr(i, chan, channels) {
u64 v = pseudorand(UINT64_MAX);
Expand All @@ -1068,6 +1076,11 @@ static struct command_result *add_shadow_route(struct command *cmd,
json_to_number(buf, json_get_member(buf, chan, "fee_per_millionth"),
&route[0].fee_proportional_millionths);

if (!amount_msat_fee(&fees, pc->initial_msat, route[0].fee_base_msat,
route[0].fee_proportional_millionths)
|| amount_msat_greater_eq(fees, maxfees))
continue;

best = chan;
sample = v;
}
Expand Down Expand Up @@ -1313,13 +1326,13 @@ static struct command_result *json_pay(struct command *cmd,
return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
"msatoshi parameter unnecessary");
}
pc->msat = *b11->msat;
pc->msat = pc->initial_msat = *b11->msat;
} else {
if (!msat) {
return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
"msatoshi parameter required");
}
pc->msat = *msat;
pc->msat = pc->initial_msat = *msat;
}

/* Sanity check */
Expand Down
28 changes: 28 additions & 0 deletions tests/test_pay.py
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Original file line number Diff line number Diff line change
Expand Up @@ -452,6 +452,34 @@ def test_payment_duplicate_uncommitted(node_factory, executor):
fut2.result(10)


@unittest.skipIf(not DEVELOPER, "Too slow without --dev-fast-gossip")
def test_pay_maxfee_shadow(node_factory):
"""Test that we respect maxfeepercent for shadow routing."""
l1, l2, l3 = node_factory.line_graph(3, fundchannel=True,
wait_for_announce=True)
# We use this to search for shadow routes
wait_for(
lambda: len(l1.rpc.listchannels(source=l2.info["id"])["channels"]) > 1
)

# shadow routes are random, so run multiple times.
for i in range(5):
# A tiny amount, we must not add the base_fee between l2 and l3
amount = 2
bolt11 = l2.rpc.invoice(amount, "tiny.{}".format(i), "tiny")["bolt11"]
pay_status = l1.rpc.pay(bolt11)
assert pay_status["amount_msat"] == Millisatoshi(amount)

# shadow routes are random, so run multiple times.
for i in range(5):
# A bigger amount, shadow routing could have been used but we set a low
# maxfeepercent.
amount = 20000
bolt11 = l2.rpc.invoice(amount, "big.{}".format(i), "bigger")["bolt11"]
pay_status = l1.rpc.pay(bolt11, maxfeepercent="0.000001")
assert pay_status["amount_msat"] == Millisatoshi(amount)


def test_sendpay(node_factory):
l1, l2 = node_factory.line_graph(2, fundamount=10**6)

Expand Down