Fix injectpaymentonion fees

contrib/msggen/msggen/schema.json

@@ -16068,7 +16068,7 @@
           "amount_msat": {
             "type": "msat",
             "description": [
-              "The amount for the first HTLC in millisatoshis.  This is also the amount which will be forwarded to the first peer (if any) as we do not charge fees on our own payments.  Note: this is shown in listsendpays as `amount_sent_msat`."
+              "The amount in millisatoshis this node would receive from a peer before forwarding the payment to the next."
             ]
           },
           "cltv_expiry": {

doc/schemas/injectpaymentonion.json

@@ -34,7 +34,7 @@
       "amount_msat": {
         "type": "msat",
         "description": [
-          "The amount for the first HTLC in millisatoshis.  This is also the amount which will be forwarded to the first peer (if any) as we do not charge fees on our own payments.  Note: this is shown in listsendpays as `amount_sent_msat`."
+          "The amount in millisatoshis this node would receive from a peer before forwarding the payment to the next."
         ]
       },
       "cltv_expiry": {

lightningd/pay.c

@@ -1970,15 +1970,15 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 		register_payment_and_waiter(cmd,
 					    payment_hash,
 					    *partid, *groupid,
-					    *destination_msat, *msat, AMOUNT_MSAT(0),
+					    *destination_msat, payload->amt_to_forward, AMOUNT_MSAT(0),
 					    label, invstring, local_invreq_id,
 					    &shared_secret,
 					    destination);
 
 		/* Mark it pending now, though htlc_set_add might
 		 * not resolve immediately */
 		fixme_ignore(command_still_pending(cmd));
-		htlc_set_add(cmd->ld, cmd->ld->log, *msat, *payload->total_msat,
+		htlc_set_add(cmd->ld, cmd->ld->log, payload->amt_to_forward, *payload->total_msat,
 			     NULL, payment_hash, payload->payment_secret,
 			     selfpay_mpp_fail, selfpay_mpp_succeeded,
 			     selfpay);
@@ -2014,22 +2014,22 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 					    "Unknown peer %s",
 					    fmt_node_id(tmpctx, &nid));
 
-		next = best_channel(cmd->ld, next_peer, *msat, NULL);
+		next = best_channel(cmd->ld, next_peer, payload->amt_to_forward, NULL);
 		if (!next)
 			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 					    "No available channel with peer %s",
 					    fmt_node_id(tmpctx, &nid));
 	}
 
-	if (amount_msat_greater(*msat, next->htlc_maximum_msat)
-	    || amount_msat_less(*msat, next->htlc_minimum_msat)) {
+	if (amount_msat_greater(payload->amt_to_forward, next->htlc_maximum_msat)
+	    || amount_msat_less(payload->amt_to_forward, next->htlc_minimum_msat)) {
 		/* Are we in old-range grace-period? */
 		if (!timemono_before(time_mono(), next->old_feerate_timeout)
-		    || amount_msat_less(*msat, next->old_htlc_minimum_msat)
-		    || amount_msat_greater(*msat, next->old_htlc_maximum_msat)) {
+		    || amount_msat_less(payload->amt_to_forward, next->old_htlc_minimum_msat)
+		    || amount_msat_greater(payload->amt_to_forward, next->old_htlc_maximum_msat)) {
 			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 					    "Amount %s not in htlc min/max range %s-%s",
-					    fmt_amount_msat(tmpctx, *msat),
+					    fmt_amount_msat(tmpctx, payload->amt_to_forward),
 					    fmt_amount_msat(tmpctx, next->htlc_minimum_msat),
 					    fmt_amount_msat(tmpctx, next->htlc_maximum_msat));
 		}
@@ -2082,11 +2082,11 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 	if (command_check_only(cmd))
 		return command_check_done(cmd);
 
-	failmsg = send_htlc_out(tmpctx, next, *msat,
+	failmsg = send_htlc_out(tmpctx, next, payload->amt_to_forward,
 				*cltv,
 				/* If unknown, we set this equal (so accounting logs 0 fees) */
 				amount_msat_eq(*destination_msat, AMOUNT_MSAT(0))
-				? *msat : *destination_msat,
+				? payload->amt_to_forward : *destination_msat,
 				payment_hash,
 				next_path_key, NULL, *partid, *groupid,
 				serialize_onionpacket(tmpctx, rs->next),
@@ -2101,7 +2101,7 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 	register_payment_and_waiter(cmd,
 				    payment_hash,
 				    *partid, *groupid,
-				    *destination_msat, *msat, AMOUNT_MSAT(0),
+				    *destination_msat, payload->amt_to_forward, AMOUNT_MSAT(0),
 				    label, invstring, local_invreq_id,
 				    &shared_secret,
 				    destination);

plugins/xpay/xpay.c

@@ -343,6 +343,13 @@ send_payment_req(struct command *aux_cmd,
 
 /* For self-pay, we don't have hops. */
 static struct amount_msat initial_sent(const struct attempt *attempt)
+{
+	if (tal_count(attempt->hops) == 0)
+		return attempt->delivers;
+	return attempt->hops[0].amount_out;
+}
+
+static struct amount_msat inject_amount(const struct attempt *attempt)
 {
 	if (tal_count(attempt->hops) == 0)
 		return attempt->delivers;
@@ -1143,7 +1150,7 @@ static struct command_result *do_inject(struct command *aux_cmd,
 	json_add_hex_talarr(req->js, "onion", onion);
 	json_add_sha256(req->js, "payment_hash", &attempt->payment->payment_hash);
 	/* If no route, its the same as delivery (self-pay) */
-	json_add_amount_msat(req->js, "amount_msat", initial_sent(attempt));
+	json_add_amount_msat(req->js, "amount_msat", inject_amount(attempt));
 	json_add_u32(req->js, "cltv_expiry", initial_cltv_delta(attempt) + effective_bheight);
 	json_add_u64(req->js, "partid", attempt->partid);
 	json_add_u64(req->js, "groupid", attempt->payment->group_id);
@@ -1458,7 +1465,8 @@ static struct command_result *getroutes_for(struct command *aux_cmd,
 	json_array_start(req->js, "layers");
 	/* Add local channels */
 	json_add_string(req->js, NULL, "auto.localchans");
-	/* We don't pay fees for ourselves */
+	/* For the MCF computation we must discard the cost of routing through
+	 * our own channels because we don't pay fees for that. */
 	json_add_string(req->js, NULL, "auto.sourcefree");
 	/* Add xpay global channel */
 	json_add_string(req->js, NULL, "xpay");

tests/test_pay.py

@@ -6366,7 +6366,7 @@ def test_injectpaymentonion_selfpay(node_factory, executor):
              'payload': serialize_payload_final_tlv(333, 18, 1000, blockheight, inv5['payment_secret']).hex()}]
     onion1 = l1.rpc.createonion(hops=hops1, assocdata=inv5['payment_hash'])
     hops2 = [{'pubkey': l1.info['id'],
-             'payload': serialize_payload_final_tlv(666, 18, 1000, blockheight, inv5['payment_secret']).hex()}]
+             'payload': serialize_payload_final_tlv(667, 18, 1000, blockheight, inv5['payment_secret']).hex()}]
     onion2 = l1.rpc.createonion(hops=hops2, assocdata=inv5['payment_hash'])
 
     fut1 = executor.submit(l1.rpc.injectpaymentonion,

tests/test_xpay.py

@@ -1072,3 +1072,34 @@ def mock_getblockhash(req):
     # Now let it catch up, and it will retry, and succeed.
     l1.daemon.rpcproxy.mock_rpc('getblockhash')
     fut.result(TIMEOUT)
+
+
+def test_bolt12_fees(node_factory):
+    AMT_MSAT = 10000
+    FEES_MSAT = 5000
+    l1, l2 = node_factory.get_nodes(
+        2, opts={"may_reconnect": True, "fee-base": FEES_MSAT, "fee-per-satoshi": 0}
+    )
+    node_factory.join_nodes([l1, l2], wait_for_announce=True)
+
+    # BOLT 12, direct peer
+    offer = l2.rpc.offer("any")["bolt12"]
+    b12 = l1.rpc.fetchinvoice(offer, AMT_MSAT)["invoice"]
+
+    b12_decode = l1.rpc.decode(b12)
+    assert b12_decode["invoice_amount_msat"] == AMT_MSAT
+    assert len(b12_decode["invoice_paths"]) == 1
+    assert b12_decode["invoice_paths"][0]["first_node_id"] == l1.info["id"]
+    assert b12_decode["invoice_paths"][0]["payinfo"]["fee_base_msat"] == FEES_MSAT
+    assert b12_decode["invoice_paths"][0]["payinfo"]["fee_proportional_millionths"] == 0
+
+    ret = l1.rpc.xpay(invstring=b12)
+    assert ret["failed_parts"] == 0
+    assert ret["successful_parts"] == 1
+    assert ret["amount_msat"] == AMT_MSAT
+    assert ret["amount_sent_msat"] == AMT_MSAT
+
+    htlcs = l1.rpc.listhtlcs()["htlcs"]
+    assert len(htlcs) == 1
+    assert htlcs[0]["payment_hash"] == b12_decode["invoice_payment_hash"]
+    assert htlcs[0]["amount_msat"] == AMT_MSAT