injectpaymentionion: allow specification of actual amount which reach…

…es destination.

This appears in listsendpays / listpays, and is useful information (if we know!).

This doesn't fix old payments, but means that xpay can use this for new payments.

Signed-off-by: Rusty Russell <[email protected]>

.msggen.json

@@ -1809,6 +1809,7 @@
         "InjectpaymentonionRequest": {
             "InjectPaymentOnion.amount_msat": 3,
             "InjectPaymentOnion.cltv_expiry": 4,
+            "InjectPaymentOnion.destination_msat": 10,
             "InjectPaymentOnion.groupid": 6,
             "InjectPaymentOnion.invstring": 8,
             "InjectPaymentOnion.label": 7,
@@ -7548,6 +7549,10 @@
             "added": "v24.11",
             "deprecated": null
         },
+        "InjectPaymentOnion.destination_msat": {
+            "added": "v24.11.1",
+            "deprecated": null
+        },
         "InjectPaymentOnion.groupid": {
             "added": "v24.11",
             "deprecated": null

contrib/msggen/msggen/schema.json

@@ -16175,7 +16175,7 @@
           "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."
+              "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`."
             ]
           },
           "cltv_expiry": {
@@ -16213,6 +16213,13 @@
             "description": [
               "`localinvreqid` is used by offers to link a payment attempt to a local `invoice_request` offer created by lightningd-invoicerequest(7)."
             ]
+          },
+          "destination_msat": {
+            "type": "msat",
+            "added": "v24.11.1",
+            "description": [
+              "Amount that is actually delivered to the destination (i.e. `amount_msat` minus fees), for showing in listsendpays (confusingly, as `amount_msat`)."
+            ]
           }
         }
       },

doc/schemas/lightning-injectpaymentonion.json

@@ -33,7 +33,7 @@
       "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."
+          "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`."
         ]
       },
       "cltv_expiry": {
@@ -71,6 +71,13 @@
         "description": [
           "`localinvreqid` is used by offers to link a payment attempt to a local `invoice_request` offer created by lightningd-invoicerequest(7)."
         ]
+      },
+      "destination_msat": {
+        "type": "msat",
+        "added": "v24.11.1",
+        "description": [
+          "Amount that is actually delivered to the destination (i.e. `amount_msat` minus fees), for showing in listsendpays (confusingly, as `amount_msat`)."
+        ]
       }
     }
   },

lightningd/pay.c

@@ -1782,7 +1782,7 @@ static struct command_result *param_u64_nonzero(struct command *cmd,
 static void register_payment_and_waiter(struct command *cmd,
 					const struct sha256 *payment_hash,
 					u64 partid, u64 groupid,
-					struct amount_msat msat,
+					struct amount_msat destination_msat,
 					struct amount_msat msat_sent,
 					struct amount_msat total_msat,
 					const char *label,
@@ -1799,7 +1799,7 @@ static void register_payment_and_waiter(struct command *cmd,
 			   groupid,
 			   PAYMENT_PENDING,
 			   NULL,
-			   msat,
+			   destination_msat,
 			   msat_sent,
 			   total_msat,
 			   NULL,
@@ -1829,7 +1829,7 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 	struct lightningd *ld = cmd->ld;
 	const char *label, *invstring;
 	struct pubkey *blinding, *next_path_key;
-	struct amount_msat *msat;
+	struct amount_msat *destination_msat, *msat;
 	u32 *cltv;
 	u64 *partid, *groupid;
 	struct sha256 *local_invreq_id;
@@ -1857,12 +1857,13 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 			 p_opt("label", param_escaped_string, &label),
 			 p_opt("invstring", param_invstring, &invstring),
 			 p_opt("localinvreqid", param_sha256, &local_invreq_id),
+			 p_opt_def("destination_msat", param_msat, &destination_msat, AMOUNT_MSAT(0)),
 			 NULL))
 		return command_param_failed();
 
 	/* Safety check: reconcile this with previous attempts, check
-	 * partid/groupid uniqueness: we don't know amount or total. */
-	ret = check_progress(cmd->ld, cmd, payment_hash, AMOUNT_MSAT(0),
+	 * partid/groupid uniqueness: we don't know total. */
+	ret = check_progress(cmd->ld, cmd, payment_hash, *destination_msat,
 			     AMOUNT_MSAT(0),
 			     *partid, *groupid, NULL, &prev_payment);
 	if (ret)
@@ -1938,13 +1939,10 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 		selfpay->groupid = *groupid;
 		selfpay->payment_hash = *payment_hash;
 
-		/* We actually *do* know msat delivered and total msat, but
-		 * then check_progress will complain on the next part, because
-		 * we don't know it then, so leave them 0 */
 		register_payment_and_waiter(cmd,
 					    payment_hash,
 					    *partid, *groupid,
-					    AMOUNT_MSAT(0), *msat, AMOUNT_MSAT(0),
+					    *destination_msat, *msat, AMOUNT_MSAT(0),
 					    label, invstring, local_invreq_id,
 					    &shared_secret);
 
@@ -2058,14 +2056,15 @@ static struct command_result *json_injectpaymentonion(struct command *cmd,
 	register_payment_and_waiter(cmd,
 				    payment_hash,
 				    *partid, *groupid,
-				    AMOUNT_MSAT(0), *msat, AMOUNT_MSAT(0),
+				    *destination_msat, *msat, AMOUNT_MSAT(0),
 				    label, invstring, local_invreq_id,
 				    &shared_secret);
 
+	/* If unknown, we set this equal (so accounting logs 0 fees) */
+	if (amount_msat_eq(*destination_msat, AMOUNT_MSAT(0)))
+		*destination_msat = *msat;
 	failmsg = send_htlc_out(tmpctx, next, *msat,
-				/* We set final_msat to the same, so fees == 0
-				 * (in fact, we don't know!) */
-				*cltv, *msat,
+				*cltv, *destination_msat,
 				payment_hash,
 				next_path_key, *partid, *groupid,
 				serialize_onionpacket(tmpctx, rs->next),

tests/test_pay.py

@@ -6114,6 +6114,7 @@ def test_injectpaymentonion_simple(node_factory, executor):
     assert lsp['partid'] == 1
     assert lsp['payment_hash'] == inv1['payment_hash']
     assert lsp['status'] == 'complete'
+    assert 'amount_msat' not in lsp
 
     # We FAIL on reattempt
     with pytest.raises(RpcError, match="Already paid this invoice") as err:
@@ -6175,6 +6176,7 @@ def test_injectpaymentonion_mpp(node_factory, executor):
         assert lsp['partid'] == 1 or lsp['partid'] == 2
         assert lsp['payment_hash'] == inv2['payment_hash']
         assert lsp['status'] == 'complete'
+        assert 'amount_msat' not in lsp
     assert len(lsps) == 2
 
 
@@ -6198,14 +6200,16 @@ def test_injectpaymentonion_3hop(node_factory, executor):
                                     amount_msat=1001,
                                     cltv_expiry=blockheight + 18 + 6 + 6,
                                     partid=1,
-                                    groupid=0)
+                                    groupid=0,
+                                    destination_msat=1000)
     assert sha256(bytes.fromhex(ret['payment_preimage'])).hexdigest() == inv3['payment_hash']
     assert only_one(l3.rpc.listinvoices("test_injectpaymentonion3")['invoices'])['status'] == 'paid'
     lsp = only_one(l1.rpc.listsendpays(inv3['bolt11'])['payments'])
     assert lsp['groupid'] == 0
     assert lsp['partid'] == 1
     assert lsp['payment_hash'] == inv3['payment_hash']
     assert lsp['status'] == 'complete'
+    assert lsp['amount_msat'] == 1000
 
 
 def test_injectpaymentonion_selfpay(node_factory, executor):