offers: only use blinded path nodes from offers when creating invoice for invoice_request.

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

Author: rustyrussell

plugins/offers_invreq_hook.c

@@ -39,6 +39,9 @@ struct invreq {
 
 	/* Optional secret. */
 	const struct secret *secret;
+
+	/* Fronting nodes to use for invoice. */
+	const struct pubkey *fronting_nodes;
 };
 
 static struct command_result *WARN_UNUSED_RESULT
@@ -278,9 +281,11 @@ static struct command_result *found_best_peer(struct command *cmd,
 	 */
 	if (!best) {
 		/* Don't allow bare invoices if they explicitly told us to front */
-		if (od->fronting_nodes) {
+		if (ir->fronting_nodes) {
 			return fail_invreq(cmd, ir,
-					   "Could not find path from payment-fronting-node");
+					   "Could not find path from %zu nodes (%s)",
+					   tal_count(ir->fronting_nodes),
+					   fmt_pubkey(tmpctx, ir->fronting_nodes));
 		}
 
 		/* Note: since we don't make one, createinvoice adds a dummy. */
@@ -393,12 +398,10 @@ static struct command_result *found_best_peer(struct command *cmd,
 static struct command_result *add_blindedpaths(struct command *cmd,
 					       struct invreq *ir)
 {
-	const struct offers_data *od = get_offers_data(cmd->plugin);
-
-	if (!we_want_blinded_path(cmd->plugin, od->fronting_nodes, true))
+	if (!we_want_blinded_path(cmd->plugin, ir->fronting_nodes, true))
 		return create_invoicereq(cmd, ir);
 
-	return find_best_peer(cmd, OPT_ROUTE_BLINDING, od->fronting_nodes,
+	return find_best_peer(cmd, OPT_ROUTE_BLINDING, ir->fronting_nodes,
 			      found_best_peer, ir);
 }
 
@@ -828,6 +831,7 @@ static struct command_result *listoffers_done(struct command *cmd,
 	struct command_result *err;
 	struct amount_msat amt;
 	struct tlv_invoice_request_invreq_recurrence_cancel *cancel;
+	struct pubkey *offer_fronts;
 
 	/* BOLT #12:
 	 *
@@ -913,6 +917,29 @@ static struct command_result *listoffers_done(struct command *cmd,
 		return fail_invreq(cmd, ir, "Offer expired");
 	}
 
+	/* If offer used fronting nodes, we use them too. */
+	offer_fronts = tal_arr(NULL, struct pubkey, 0);
+	for (size_t i = 0; i < tal_count(ir->invreq->offer_paths); i++) {
+		const struct blinded_path *p = ir->invreq->offer_paths[i];
+		struct sciddir_or_pubkey first = p->first_node_id;
+
+		/* In dev mode we could set this.  Fail if we can't map */
+		if (!first.is_pubkey && !gossmap_scidd_pubkey(get_gossmap(cmd->plugin), &first))
+			return fail_invreq(cmd, ir, "Fronting failed");
+		assert(first.is_pubkey);
+		/* Self-paths are not fronting nodes */
+		if (!pubkey_eq(&od->id, &first.pubkey))
+			tal_arr_expand(&offer_fronts, first.pubkey);
+	}
+
+	if (tal_count(offer_fronts) != 0)
+		ir->fronting_nodes = tal_steal(ir, offer_fronts);
+	else {
+		/* Otherwise, use defaults */
+		tal_free(offer_fronts);
+		ir->fronting_nodes = od->fronting_nodes;
+	}
+
 	/* BOLT-recurrence #12:
 	 * - if `offer_quantity_max` is present:
 	 *   - MUST reject the invoice request if `invreq_recurrence_cancel`

tests/test_invoices.py

@@ -991,3 +991,33 @@ def test_payment_fronting(node_factory):
     l3invreq = l3.rpc.invoicerequest(amount=1000, description='l3invreq')['bolt12']
     assert only_one(l3.rpc.decode(l3invreq)['invreq_paths'])['first_node_id'] == l1.info['id']
     l4.rpc.sendinvoice(invreq=l3invreq, label='l3invreq')
+
+
+def test_offer_fronting(node_factory):
+    # l1 -> l2 -> l3
+    #         \   /
+    #          l4
+    # Nodes will front for offers if they don't have an advertized address.
+    l1, l2, l3, l4 = node_factory.get_nodes(4, opts={'dev-allow-localhost': None})
+    node_factory.join_nodes([l1, l2, l3], wait_for_announce=True)
+    node_factory.join_nodes([l2, l4], wait_for_announce=True)
+    node_factory.join_nodes([l3, l4], wait_for_announce=True)
+
+    offer_nofront = l4.rpc.offer("any", "nofront")['bolt12']
+    assert 'offer_paths' not in l1.rpc.decode(offer_nofront)
+    offer_front_l2 = l4.rpc.offer("any", "frontl2", fronting_nodes=[l2.info['id']])['bolt12']
+    assert only_one(l1.rpc.decode(offer_front_l2)['offer_paths'])['first_node_id'] == l2.info['id']
+    offer_front_l2l3 = l4.rpc.offer("any", "frontl2l3", fronting_nodes=[l2.info['id'], l3.info['id']])['bolt12']
+    assert [p['first_node_id'] for p in l1.rpc.decode(offer_front_l2)['offer_paths']] == [l2.info['id'], l3.info['id']]
+
+    inv_nofront = l1.rpc.fetchinvoice(offer_nofront, 1)['invoice']
+    assert only_one(l1.rpc.decode(inv_nofront)['invoice_paths'])['first_node_id'] == l4.info['id']
+    l1.rpc.xpay(inv_nofront)
+
+    inv_front_l2 = l1.rpc.fetchinvoice(offer_front_l2, 2)['invoice']
+    assert only_one(l1.rpc.decode(inv_front_l2)['invoice_paths'])['first_node_id'] == l2.info['id']
+    l1.rpc.xpay(inv_front_l2)
+
+    inv_front_l2l3 = l1.rpc.fetchinvoice(offer_front_l2l3, 3)['invoice']
+    assert only_one(l1.rpc.decode(inv_front_l2l3)['invoice_paths'])['first_node_id'] in (l2.info['id'], l3.info['id'])
+    l1.rpc.xpay(inv_front_l2l3)