sendonion: add total_amount_msat parameter

Changelog-Added: sendonion: a new paramter total_amount_msat to make MPP payments with sendpay and sendonion compatible.

[ Reordered to put new parameter at the end --RR ]
Signed-off-by: Lagrang3 <lagrang3@protonmail.com>

Author: Lagrang3

.msggen.json

@@ -3400,7 +3400,8 @@
             "SendOnion.onion": 1,
             "SendOnion.partid": 6,
             "SendOnion.payment_hash": 3,
-            "SendOnion.shared_secrets[]": 5
+            "SendOnion.shared_secrets[]": 5,
+            "SendOnion.total_amount_msat": 15
         },
         "SendonionResponse": {
             "SendOnion.amount_msat": 4,
@@ -12077,6 +12078,10 @@
             "added": "pre-v0.10.1",
             "deprecated": null
         },
+        "SendOnion.total_amount_msat": {
+            "added": "v25.05",
+            "deprecated": null
+        },
         "SendOnion.updated_index": {
             "added": "v23.11",
             "deprecated": null

cln-grpc/proto/node.proto

@@ -30975,6 +30975,15 @@
             "description": [
               "If provided, it will be returned in *waitsendpay* and *listsendpays* results."
             ]
+          },
+          "total_amount_msat": {
+            "type": "msat",
+            "description": [
+              "This is the full amount requested by the destination in the invoice. It is needed internally for multi-part payments.",
+              "Its default value is 0 msat for backwards compatibility."
+            ],
+            "default": "0",
+            "added": "v25.05"
           }
         }
       },

cln-grpc/src/convert.rs

@@ -125,6 +125,15 @@
         "description": [
           "If provided, it will be returned in *waitsendpay* and *listsendpays* results."
         ]
+      },
+      "total_amount_msat": {
+        "type": "msat",
+        "description": [
+          "This is the full amount requested by the destination in the invoice. It is needed internally for multi-part payments.",
+          "Its default value is 0 msat for backwards compatibility."
+        ],
+        "default": "0",
+        "added": "v25.05"
       }
     }
   },

cln-rpc/src/model.rs

@@ -1329,7 +1329,7 @@ static struct command_result *json_sendonion(struct command *cmd,
 	const char *label, *invstring, *description;
 	struct node_id *destination;
 	struct secret *path_secrets;
-	struct amount_msat *msat;
+	struct amount_msat *msat, *total_msat;
 	u64 *partid, *group;
 	struct sha256 *local_invreq_id = NULL;
 
@@ -1347,6 +1347,7 @@ static struct command_result *json_sendonion(struct command *cmd,
 			 p_opt("localinvreqid", param_sha256, &local_invreq_id),
 			 p_opt("groupid", param_u64, &group),
 			 p_opt("description", param_string, &description),
+			 p_opt_def("total_amount_msat", param_msat, &total_msat, AMOUNT_MSAT(0)),
 			 NULL))
 		return command_param_failed();
 
@@ -1370,7 +1371,7 @@ static struct command_result *json_sendonion(struct command *cmd,
 		return command_check_done(cmd);
 
 	return send_payment_core(ld, cmd, payment_hash, *partid, *group,
-				 first_hop, *msat, AMOUNT_MSAT(0),
+				 first_hop, *msat, *total_msat,
 				 label, invstring, description,
 				 packet, destination, NULL, NULL,
 				 path_secrets, local_invreq_id);

contrib/msggen/msggen/schema.json

@@ -6862,3 +6862,79 @@ def test_decode_expired_bolt12(node_factory):
         'type': 'bolt12 invoice',
         'valid': True,
     }
+
+
+def test_sendonion_sendpay(node_factory, bitcoind):
+    """
+    Check that a payment initiated with sendpay can be completed by sendonion.
+    """
+    opts = [
+        {"disable-mpp": None, "fee-base": 1000, "fee-per-satoshi": 1000},
+    ]
+    l1, l2, l3 = node_factory.line_graph(3, wait_for_announce=True, opts=opts * 3)
+
+    total_amount = "10000sat"
+    # First case, do not overpay a pending MPP payment
+    invstr = l3.rpc.invoice("10000sat", "inv", "description")["bolt11"]
+    inv = l1.rpc.decode(invstr)
+    route2 = l1.rpc.getroute(inv["payee"], "2000sat", 10)["route"]
+    route8 = l1.rpc.getroute(inv["payee"], "8000sat", 10)["route"]
+
+    def pay_with_sendpay(invoice, route, groupid, partid):
+        l1.rpc.sendpay(
+            route=route,
+            payment_hash=invoice["payment_hash"],
+            payment_secret=invoice["payment_secret"],
+            amount_msat=invoice["amount_msat"],
+            groupid=groupid,
+            partid=partid,
+        )
+
+    def pay_with_sendonion(invoice, route, groupid, partid):
+        blockheight = l1.rpc.getinfo()["blockheight"]
+        # Need to shift the parameters by one hop
+        hops = []
+        for h, n in zip(route[:-1], route[1:]):
+            # We tell the node h about the parameters to use for n (a.k.a. h + 1)
+            hops.append(
+                {
+                    "pubkey": h["id"],
+                    "payload": serialize_payload_tlv(
+                        n["amount_msat"], n["delay"], n["channel"], blockheight
+                    ).hex(),
+                }
+            )
+        # The last hop has a special payload:
+        hops.append(
+            {
+                "pubkey": route[-1]["id"],
+                "payload": serialize_payload_final_tlv(
+                    route[-1]["amount_msat"],
+                    route[-1]["delay"],
+                    invoice["amount_msat"],
+                    blockheight,
+                    invoice["payment_secret"],
+                ).hex(),
+            }
+        )
+        onion = l1.rpc.createonion(hops=hops, assocdata=invoice["payment_hash"])
+        l1.rpc.call(
+            "sendonion",
+            {
+                "onion": onion["onion"],
+                "shared_secrets": onion["shared_secrets"],
+                "first_hop": route[0],
+                "payment_hash": invoice["payment_hash"],
+                "total_amount_msat": invoice["amount_msat"],
+                "groupid": groupid,
+                "partid": partid,
+            },
+        )
+
+    pay_with_sendpay(inv, route2, 1, 1)
+    pay_with_sendonion(inv, route8, 1, 2)
+
+    l1.wait_for_htlcs()
+    invoice = only_one(l3.rpc.listinvoices("inv")["invoices"])
+    # the receive amount should be exact
+    assert invoice["amount_received_msat"] == Millisatoshi(total_amount)