plugins/pay: implement maxfeepercent, maxdelay and exemptfee.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

plugins/pay.c

@@ -19,6 +19,11 @@ struct pay_command {
 	u64 msatoshi;
 	double riskfactor;
 
+	/* Limits on what routes we'll accept. */
+	double maxfeepercent;
+	unsigned int maxdelay;
+	u64 exemptfee;
+
 	/* Payment hash, as text. */
 	const char *payment_hash;
 
@@ -121,10 +126,40 @@ static struct command_result *getroute_done(struct command *cmd,
 	struct pay_attempt attempt;
 	const jsmntok_t *t = json_get_member(buf, result, "route");
 	char *json_desc;
+	u64 fee;
+	u32 delay;
+	double feepercent;
+
 	if (!t)
 		plugin_err("getroute gave no 'route'? '%.*s'",
 			   result->end - result->start, buf);
 
+	if (!json_to_u64(buf, json_delve(buf, t, "[0].msatoshi"), &fee))
+		plugin_err("getroute with invalid msatoshi? '%.*s'",
+			   result->end - result->start, buf);
+	fee -= pc->msatoshi;
+
+	if (!json_to_number(buf, json_delve(buf, t, "[0].delay"), &delay))
+		plugin_err("getroute with invalid delay? '%.*s'",
+			   result->end - result->start, buf);
+
+	/* Casting u64 to double will lose some precision. The loss of precision
+	 * in feepercent will be like 3.0000..(some dots)..1 % - 3.0 %.
+	 * That loss will not be representable in double. So, it's Okay to
+	 * cast u64 to double for feepercent calculation. */
+	feepercent = ((double)fee) * 100.0 / ((double) pc->msatoshi);
+
+	if (fee > pc->exemptfee && feepercent > pc->maxfeepercent) {
+		return command_fail(cmd, PAY_ROUTE_TOO_EXPENSIVE,
+				    "Route wanted fee of %"PRIu64" msatoshis",
+				    fee);
+	}
+
+	if (delay > pc->maxdelay) {
+		return command_fail(cmd, PAY_ROUTE_TOO_EXPENSIVE,
+				    "Route wanted delay of %u blocks", delay);
+	}
+
 	attempt.route = json_strdup(pc->attempts, buf, result);
 	tal_arr_expand(&pc->attempts, attempt);
 
@@ -230,11 +265,9 @@ static struct command_result *handle_pay(struct command *cmd,
 	double *riskfactor;
 	unsigned int *retryfor;
 	struct pay_command *pc = tal(cmd, struct pay_command);
-
-	/* FIXME! */
 	double *maxfeepercent;
 	unsigned int *maxdelay;
-	unsigned int *exemptfee;
+	u64 *exemptfee;
 
 	setup_locale();
 
@@ -248,7 +281,7 @@ static struct command_result *handle_pay(struct command *cmd,
 		   p_opt_def("maxdelay", param_number, &maxdelay,
 			     /* FIXME! */
 			     14 * 24 * 6),
-		   p_opt_def("exemptfee", param_number, &exemptfee, 5000),
+		   p_opt_def("exemptfee", param_u64, &exemptfee, 5000),
 		   NULL))
 		return NULL;
 
@@ -276,6 +309,9 @@ static struct command_result *handle_pay(struct command *cmd,
 		pc->msatoshi = *msatoshi;
 	}
 
+	pc->maxfeepercent = *maxfeepercent;
+	pc->maxdelay = *maxdelay;
+	pc->exemptfee = *exemptfee;
 	pc->riskfactor = *riskfactor;
 	pc->dest = type_to_string(cmd, struct pubkey, &b11->receiver_id);
 	pc->payment_hash = type_to_string(pc, struct sha256,

tests/test_pay.py

@@ -59,6 +59,31 @@ def test_pay(node_factory):
     assert len(payments) == 1 and payments[0]['payment_preimage'] == preimage
 
 
+def test_pay_limits(node_factory):
+    """Test that we enforce fee max percentage and max delay"""
+    l1, l2, l3 = node_factory.line_graph(3, wait_for_announce=True)
+
+    # FIXME: pylightning should define these!
+    PAY_ROUTE_TOO_EXPENSIVE = 206
+
+    inv = l3.rpc.invoice("any", "any", 'description')
+
+    # Fee too high.
+    with pytest.raises(RpcError, match=r'Route wanted fee of .* msatoshis') as err:
+        l1.rpc.call('pay2', {'bolt11': inv['bolt11'], 'msatoshi': 100000, 'maxfeepercent': 0.0001, 'exemptfee': 0})
+
+    assert err.value.error['code'] == PAY_ROUTE_TOO_EXPENSIVE
+
+    # Delay too high.
+    with pytest.raises(RpcError, match=r'Route wanted delay of .* blocks') as err:
+        l1.rpc.call('pay2', {'bolt11': inv['bolt11'], 'msatoshi': 100000, 'maxdelay': 0})
+
+    assert err.value.error['code'] == PAY_ROUTE_TOO_EXPENSIVE
+
+    # This works, because fee is less than exemptfee.
+    l1.rpc.call('pay2', {'bolt11': inv['bolt11'], 'msatoshi': 100000, 'maxfeepercent': 0.0001, 'exemptfee': 2000})
+
+
 def test_pay0(node_factory):
     """Test paying 0 amount
     """