xpay blinded path fix

devtools/bolt12-cli.c

@@ -266,8 +266,6 @@ static bool print_blindedpaths(const char *fieldname,
 			       struct blinded_path **paths,
 			       struct blinded_payinfo **blindedpay)
 {
-	size_t bp_idx = 0;
-
 	for (size_t i = 0; i < tal_count(paths); i++) {
 		struct blinded_path_hop **p = paths[i]->path;
 		printf("%s %zu/%zu: first_path_key %s ",
@@ -282,22 +280,24 @@ static bool print_blindedpaths(const char *fieldname,
 			       fmt_pubkey(tmpctx,
 					      &p[j]->blinded_node_id),
 			       tal_hex(tmpctx, p[j]->encrypted_recipient_data));
-			if (blindedpay) {
-				if (bp_idx < tal_count(blindedpay))
-					printf("fee=%u/%u,cltv=%u,features=%s",
-					       blindedpay[bp_idx]->fee_base_msat,
-					       blindedpay[bp_idx]->fee_proportional_millionths,
-					       blindedpay[bp_idx]->cltv_expiry_delta,
-					       tal_hex(tmpctx,
-						       blindedpay[bp_idx]->features));
-				bp_idx++;
-			}
+		}
+		if (i < tal_count(blindedpay)) {
+			printf(" blindedpay: fee=%u/%u,cltv=%u,features=%s",
+			       blindedpay[i]->fee_base_msat,
+			       blindedpay[i]->fee_proportional_millionths,
+			       blindedpay[i]->cltv_expiry_delta,
+			       tal_hex(tmpctx, blindedpay[i]->features));
 		}
 		printf("\n");
 	}
-	if (blindedpay && tal_count(blindedpay) != bp_idx) {
+	/* BOLT #12:
+	 *   - MUST reject the invoice if `invoice_blindedpay` does not
+	 *     contain exactly one `blinded_payinfo` per
+	 *     `invoice_paths`.`blinded_path`.
+	 */
+	if (blindedpay && tal_count(blindedpay) != tal_count(paths)) {
 		fprintf(stderr, "Expected %zu blindedpay fields, got %zu\n",
-			bp_idx, tal_count(blindedpay));
+			tal_count(paths), tal_count(blindedpay));
 		return false;
 	}
 	return true;
@@ -893,7 +893,11 @@ int main(int argc, char *argv[])
 			well_formed &= print_offer_amount(invreq->offer_chains,
 							  invreq->offer_currency,
 							  *invreq->offer_amount);
-		if (must_have(invreq, offer_description))
+		if (invreq->offer_amount && !invreq->offer_description) {
+			fprintf(stderr, "Missing offer_description (with offer_amount)\n");
+			well_formed = false;
+		}
+		if (invreq->offer_description)
 			well_formed &= print_utf8("offer_description", invreq->offer_description);
 		if (invreq->offer_features)
 			print_features("offer_features", invreq->offer_features);
@@ -971,7 +975,11 @@ int main(int argc, char *argv[])
 			well_formed &= print_offer_amount(invoice->offer_chains,
 							  invoice->offer_currency,
 							  *invoice->offer_amount);
-		if (must_have(invoice, offer_description))
+		if (invoice->offer_amount && !invoice->offer_description) {
+			fprintf(stderr, "Missing offer_description (with offer_amount)\n");
+			well_formed = false;
+		}
+		if (invoice->offer_description)
 			well_formed &= print_utf8("offer_description", invoice->offer_description);
 		if (invoice->offer_features)
 			print_features("offer_features", invoice->offer_features);

plugins/xpay/xpay.c

@@ -899,7 +899,7 @@ static void append_blinded_payloads(struct sphinx_path *sp,
 				    size_t path_num)
 {
 	const struct blinded_path *path = attempt->payment->paths[path_num];
-	u32 final_cltv = attempt->payment->final_cltv + effective_bheight;
+	u32 final_cltv = effective_bheight;
 
 	for (size_t i = 0; i < tal_count(path->path); i++) {
 		bool first = (i == 0);
@@ -1635,12 +1635,10 @@ static struct command_result *json_xpay_core(struct command *cmd,
 					    "Could not resolve any paths: unknown short_channel_id");
 		}
 
-		/* Use worst-case CLTV. */
+		/* We don't actually know the final_cltv for blinded
+		 * paths, we just know the cltv we use to enter the
+		 * final hop. */
 		payment->final_cltv = 0;
-		for (size_t i = 0; i < tal_count(payment->payinfos); i++) {
-			if (payment->payinfos[i]->cltv_expiry_delta > payment->final_cltv)
-				payment->final_cltv = payment->payinfos[i]->cltv_expiry_delta;
-		}
 		/* We will start honoring this flag in future */
 		payment->disable_mpp = !feature_offered(b12inv->invoice_features, OPT_BASIC_MPP);
 		if (payment->disable_mpp && command_deprecated_in_ok(cmd, "ignore_bolt12_mpp", "v25.05", "v25.11"))

tests/test_misc.py

@@ -4680,3 +4680,13 @@ def test_listaddresses(node_factory):
     # start and limit from future
     addresses = l1.rpc.listaddresses(start=21, limit=5)["addresses"]
     assert len(addresses) == 0
+
+
+def test_bolt12_invoice_decode(node_factory):
+    """Test decode of a real invoice."""
+    l1 = node_factory.get_node()
+
+    inv = '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'
+
+    assert l1.rpc.decode(inv)['valid'] is True
+    subprocess.run(["devtools/bolt12-cli", "decode", inv], check=True)

tests/test_xpay.py

@@ -766,3 +766,50 @@ def test_fail_after_success(node_factory, bitcoind, executor, slow_mode):
                        'amount_sent_msat': res['amount_sent_msat'],
                        'failed_parts': 1,
                        'successful_parts': 1}
+
+
+def test_xpay_twohop_bug(node_factory):
+    """From https://github.com/ElementsProject/lightning/issues/8119:
+    Oh, interesting! I tried again and got a two-hop blinded path. xpay returned the same error you saw while pay was successful.
+
+lightning-cli xpay 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
+{
+   "code": 209,
+   "message": "Failed after 1 attempts. We got an error from inside the blinded path 0x0x0/1: we assume it means insufficient capacity. Then routing failed: We could not find a usable set of paths.  The shortest path is 858132x1647x1->861005x2291x1->0x0x0, but 0x0x0/1 layer xpay-0 says max is 14999msat"
+}
+lightning-cli pay 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
+{
+   "destination": "031979fe6ce0e69ece6d99a4bc4a7b30ed22a8cb8703dd7dd2dfaf619e07127e0b",
+   "payment_hash": "6a209060711d2d8c593a8217bb3b8d81dc1a731e93c5893da5fc11faf99f2d08",
+   "created_at": 1740526413.632475833,
+   "parts": 1,
+   "amount_msat": 16007,
+   "amount_sent_msat": 16010,
+   "payment_preimage": "c6c75b93dbbdbc5082350a4396afec0232ff4400ea0c9f053b977f4389f501bf",
+   "status": "complete"
+}
+    """
+    l1, l2, l3, l4 = node_factory.line_graph(4, wait_for_announce=True,
+                                             opts=[{'cltv-delta': 50},
+                                                   {'cltv-delta': 100},
+                                                   {'cltv-delta': 200},
+                                                   {'cltv-final': 400}])
+
+    offer = l4.rpc.offer('any')
+    inv = l1.rpc.fetchinvoice(offer['bolt12'], '15000msat')['invoice']
+
+    # Inserts a blinded path
+    path = only_one(l1.rpc.decode(inv)['invoice_paths'])
+    assert path['first_node_id'] == l3.info['id']
+    assert len(path['path']) == 2
+    assert path['payinfo']['cltv_expiry_delta'] == 200 + 400
+
+    # This works.
+    l1.rpc.pay(inv)
+    # CLTV is blockheight (108) + 1 + 100 + 200 + 400
+    l1.daemon.wait_for_log(f'Adding HTLC 0 amount=15002msat cltv={108 + 1 + 100 + 200 + 400}')
+
+    inv = l1.rpc.fetchinvoice(offer['bolt12'], '15000msat')['invoice']
+    # This doesn't!
+    l1.rpc.xpay(inv)
+    l1.daemon.wait_for_log(f'Adding HTLC 1 amount=15002msat cltv={108 + 1 + 100 + 200 + 400}')