pytest: test fetchinvoice reply path which is not a direct peer.

Our fetchinvoice always creates a reply path which terminates at their peer,
so we need a dev overrride for that.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

plugins/fetchinvoice.c

@@ -42,6 +42,9 @@ struct sent {
 	/* When creating blinded return path, use scid not pubkey for intro node. */
 	struct short_channel_id_dir *dev_path_use_scidd;
 
+	/* Force reply path, for testing. */
+	struct pubkey *dev_reply_path;
+
 	/* The invreq we sent, OR the invoice we sent */
 	struct tlv_invoice_request *invreq;
 
@@ -603,11 +606,15 @@ static struct command_result *make_reply_path(struct command *cmd,
 	sending->sent->reply_secret = tal(sending->sent, struct secret);
 	randombytes_buf(sending->sent->reply_secret, sizeof(struct secret));
 
-	/* FIXME: Could create an independent reply path, not just
-	 * reverse existing. */
-	ids = tal_arr(tmpctx, struct pubkey, nhops - 1);
-	for (int i = nhops - 2; i >= 0; i--)
-		ids[nhops - 2 - i] = sending->sent->path[i];
+	if (sending->sent->dev_reply_path) {
+		ids = sending->sent->dev_reply_path;
+	} else {
+		/* FIXME: Could create an independent reply path, not just
+		 * reverse existing. */
+		ids = tal_arr(tmpctx, struct pubkey, nhops - 1);
+		for (int i = nhops - 2; i >= 0; i--)
+			ids[nhops - 2 - i] = sending->sent->path[i];
+	}
 
 	rpath = blinded_path(cmd, cmd, ids, sending->sent->dev_path_use_scidd,
 			     sending->sent->reply_secret);
@@ -802,6 +809,29 @@ static struct command_result *param_dev_scidd(struct command *cmd, const char *n
 				     "should be a short_channel_id of form NxNxN/dir");
 }
 
+static struct command_result *param_dev_reply_path(struct command *cmd, const char *name,
+						   const char *buffer, const jsmntok_t *tok,
+						   struct pubkey **path)
+{
+	size_t i;
+	const jsmntok_t *t;
+
+	if (!plugin_developer_mode(cmd->plugin))
+		return command_fail_badparam(cmd, name, buffer, tok,
+					     "not available outside --developer mode");
+
+	if (tok->type != JSMN_ARRAY)
+		return command_fail_badparam(cmd, name, buffer, tok, "Must be array");
+
+	*path = tal_arr(cmd, struct pubkey, tok->size);
+
+	json_for_each_arr(i, t, tok) {
+		if (!json_to_pubkey(buffer, t, &(*path)[i]))
+			return command_fail_badparam(cmd, name, buffer, t, "invalid pubkey");
+	}
+	return NULL;
+}
+
 /* Fetches an invoice for this offer, and makes sure it corresponds. */
 static struct command_result *json_fetchinvoice(struct command *cmd,
 						const char *buffer,
@@ -826,6 +856,7 @@ static struct command_result *json_fetchinvoice(struct command *cmd,
 		   p_opt_def("timeout", param_number, &timeout, 60),
 		   p_opt("payer_note", param_string, &payer_note),
 		   p_opt("dev_path_use_scidd", param_dev_scidd, &sent->dev_path_use_scidd),
+		   p_opt("dev_reply_path", param_dev_reply_path, &sent->dev_reply_path),
 		   NULL))
 		return command_param_failed();
 
@@ -1274,6 +1305,7 @@ static struct command_result *json_sendinvoice(struct command *cmd,
 		return command_param_failed();
 
 	sent->dev_path_use_scidd = NULL;
+	sent->dev_reply_path = NULL;
 
 	/* BOLT-offers #12:
 	 *   - if the invoice is in response to an `invoice_request`:
@@ -1392,6 +1424,7 @@ static struct command_result *json_dev_rawrequest(struct command *cmd,
 	sent->cmd = cmd;
 	sent->offer = NULL;
 	sent->dev_path_use_scidd = NULL;
+	sent->dev_reply_path = NULL;
 
 	return establish_onion_path(cmd, get_gossmap(cmd->plugin), &local_id,
 				    node_id,

tests/test_pay.py

@@ -4731,6 +4731,28 @@ def test_fetchinvoice_autoconnect(node_factory, bitcoind):
     assert l3.rpc.listpeers(l2.info['id'])['peers'] != []
 
 
+def test_fetchinvoice_disconnected_reply(node_factory, bitcoind):
+    """We ask for invoice, but reply path doesn't lead directly from recipient"""
+    l1, l2, l3 = node_factory.get_nodes(3,
+                                        opts={'experimental-offers': None,
+                                              'may_reconnect': True,
+                                              'dev-no-reconnect': None,
+                                              'dev-allow-localhost': None})
+    l3.rpc.connect(l2.info['id'], 'localhost', l2.port)
+
+    # Make l1, l2 public (so l3 can auto connect).
+    node_factory.join_nodes([l1, l2], wait_for_announce=True)
+    wait_for(lambda: l3.rpc.listnodes(l1.info['id'])['nodes'] != [])
+
+    offer = l3.rpc.offer(amount='5msat', description='test_fetchinvoice_disconnected_reply')
+
+    # l2 sets reply_path to be l1->l2, l3 will connect to l1 to send reply.
+    # FIXME: if code were smarter, it would simply send via l2, and this test
+    # would have to get more sophisticated!
+    l2.rpc.fetchinvoice(offer=offer['bolt12'], dev_reply_path=[l1.info['id'], l2.info['id']])
+    assert only_one(l1.rpc.listpeers(l3.info['id'])['peers'])
+
+
 def test_pay_blockheight_mismatch(node_factory, bitcoind):
     """Test that we can send a payment even if not caught up with the chain.