Add option to allow even custom messages to be sent

Changelog-Experimental: config: new option --experimental-all-onion-messages, which behaves like --experimental-onion-messages but also allow even-numbered messages to be sent

connectd/multiplex.c

@@ -622,6 +622,7 @@ static bool handle_custommsg(struct daemon *daemon,
 			     const u8 *msg)
 {
 	enum peer_wire type = fromwire_peektype(msg);
+	// fixme use allow_even_custom_message config here
 	if (type % 2 == 1 && !peer_wire_is_defined(type)) {
 		/* The message is not part of the messages we know how to
 		 * handle. Assuming this is a custommsg, we just forward it to the

doc/lightning-listconfigs.7.md

@@ -54,6 +54,7 @@ On success, an object is returned, containing:
 - **large-channels** (boolean, optional): `large-channels` field from config or cmdline, or default
 - **experimental-dual-fund** (boolean, optional): `experimental-dual-fund` field from config or cmdline, or default
 - **experimental-onion-messages** (boolean, optional): `experimental-onion-messages` field from config or cmdline, or default
+- **experimental-all-onion-messages** (boolean, optional): `experimental-all-onion-messages` field from config or cmdline, or default
 - **experimental-offers** (boolean, optional): `experimental-offers` field from config or cmdline, or default
 - **experimental-shutdown-wrong-funding** (boolean, optional): `experimental-shutdown-wrong-funding` field from config or cmdline, or default
 - **experimental-websocket-port** (u16, optional): `experimental-websocket-port` field from config or cmdline, or default

doc/lightning-sendcustommsg.7.md

@@ -16,8 +16,9 @@ top, not for direct use by end-users.
 
 The message must be a hex encoded well-formed message, including the 2-byte
 type prefix, but excluding the length prefix which will be added by the RPC
-method. The messages must not use even-numbered types, since these may require
-synchronous handling on the receiving side, and can cause the connection to be
+method. The messages must not use even-numbered types, unless using
+`--experimental-all-onion-messages`, since these may require synchronous
+handling on the receiving side, and can cause the connection to be
 dropped. The message types may also not use one of the internally handled
 types, since that may cause issues with the internal state tracking of
 Core Lightning.

doc/lightningd-config.5.md

@@ -535,6 +535,11 @@ be listed with `lightningd --list-features-only`.
 Specifying this enables sending, forwarding and receiving onion messages,
 which are in draft status in the BOLT specifications.
 
+ **experimental-all-onion-messages**
+
+Specifying this enables the same as **experimental-onion-messages**,
+but also allows even numbered messages to be sent.
+
  **experimental-offers**
 
 Specifying this enables the `offers` and `fetchinvoice` plugins and

doc/schemas/listconfigs.schema.json

@@ -117,6 +117,10 @@
       "type": "boolean",
       "description": "`experimental-onion-messages` field from config or cmdline, or default"
     },
+    "experimental-all-onion-messages": {
+      "type": "boolean",
+      "description": "`experimental-all-onion-messages` field from config or cmdline, or default"
+    },
     "experimental-offers": {
       "type": "boolean",
       "description": "`experimental-offers` field from config or cmdline, or default"

lightningd/connect_control.c

@@ -656,13 +656,15 @@ static struct command_result *json_sendcustommsg(struct command *cmd,
 		    type, peer_wire_name(type));
 	}
 
-	if (type % 2 == 0) {
+	if (type % 2 == 0 && !cmd->ld->config.allow_even_custom_message) {
 		return command_fail(
 		    cmd, JSONRPC2_INVALID_REQUEST,
 		    "Cannot send even-typed %d custom message. Currently "
 		    "custom messages are limited to odd-numbered message "
 		    "types, as even-numbered types might result in "
-		    "disconnections.",
+		    "disconnections. If you really want to send even custom "
+                    "messages, add the --experimental-all-onion-messages "
+                    "to the lightningd configuration",
 		    type);
 	}
 

lightningd/lightningd.h

@@ -70,6 +70,9 @@ struct config {
 
 	/* EXPERIMENTAL: offers support */
 	bool exp_offers;
+
+	/* Do we allow even custom messages to be sent */
+	bool allow_even_custom_messages;
 };
 
 typedef STRMAP(const char *) alt_subdaemon_map;

lightningd/options.c

@@ -797,6 +797,8 @@ static const struct config testnet_config = {
 	.connection_timeout_secs = 60,
 
 	.exp_offers = IFEXPERIMENTAL(true, false),
+
+	.allow_even_custom_messages = false,
 };
 
 /* aka. "Dude, where's my coins?" */
@@ -861,6 +863,8 @@ static const struct config mainnet_config = {
 	.connection_timeout_secs = 60,
 
 	.exp_offers = IFEXPERIMENTAL(true, false),
+
+	.allow_even_custom_messages = false,
 };
 
 static void check_config(struct lightningd *ld)
@@ -997,6 +1001,12 @@ static char *opt_set_onion_messages(struct lightningd *ld)
 	return NULL;
 }
 
+static char *opt_set_all_onion_messages(struct lightningd *ld)
+{
+	ld->config.allow_even_custom_messages = true;
+	return opt_set_onion_messages(ld);
+}
+
 static char *opt_set_shutdown_wrong_funding(struct lightningd *ld)
 {
 	feature_set_or(ld->our_features,
@@ -1063,6 +1073,10 @@ static void register_opts(struct lightningd *ld)
 				 opt_set_onion_messages, ld,
 				 "EXPERIMENTAL: enable send, receive and relay"
 				 " of onion messages");
+	opt_register_early_noarg("--experimental-all-onion-messages",
+				 opt_set_all_onion_messages, ld,
+				 "EXPERIMENTAL: enable send, receive and relay"
+				 " of all onion messages");
 	opt_register_early_noarg("--experimental-offers",
 				 opt_set_offers, ld,
 				 "EXPERIMENTAL: enable send and receive of offers"
@@ -1519,6 +1533,8 @@ static void add_config(struct lightningd *ld,
 				      feature_offered(ld->our_features
 						      ->bits[INIT_FEATURE],
 						      OPT_ONION_MESSAGES));
+		} else if (opt->cb == (void *)opt_set_all_onion_messages) {
+			json_add_bool(response, name0, ld->config.allow_even_custom_messages);
 		} else if (opt->cb == (void *)opt_set_offers) {
 			json_add_bool(response, name0, ld->config.exp_offers);
 		} else if (opt->cb == (void *)opt_set_shutdown_wrong_funding) {

tests/test_misc.py

@@ -2209,6 +2209,59 @@ def test_sendcustommsg(node_factory):
     ])
 
 
+def test_even_sendcustommsg(node_factory):
+    """Check that we can send even custommsgs to peers in various states.
+
+    `l2` is the node under test. `l1` has a channel with `l2` and should
+    therefore be attached to `channeld`. `l4` is just connected, so it should
+    be attached to `openingd`. `l3` has a channel open, but is disconnected
+    and we can't send to it.
+
+    """
+    opts = {'log-level': 'io', 'experimental-all-onion-messages': None,
+            'experimental-accept-extra-tlv-types': '43690', 'plugin': [
+        os.path.join(os.path.dirname(__file__), "plugins", "custommsg_b.py"),
+        os.path.join(os.path.dirname(__file__), "plugins", "custommsg_a.py")
+    ]}
+    l1, l2, l3, l4 = node_factory.get_nodes(4, opts=opts)
+    node_factory.join_nodes([l1, l2, l3])
+    l2.connect(l4)
+    l3.stop()
+
+    # Even-numbered message
+    msg = hex(43690)[2:] + ('ff' * 30) + 'bb'
+
+    # This should work since the peer is currently owned by `channeld`
+    l2.rpc.sendcustommsg(l1.info['id'], msg)
+    l2.daemon.wait_for_log(
+        r'{peer_id}-{owner}-chan#[0-9]: \[OUT\] {msg}'.format(
+            owner='channeld', msg=msg, peer_id=l1.info['id']
+        )
+    )
+    l1.daemon.wait_for_log(r'\[IN\] {}'.format(msg))
+    l1.daemon.wait_for_logs([
+        r'Got custommessage_a {msg} from peer {peer_id}'.format(
+            msg=msg, peer_id=l2.info['id']),
+        r'Got custommessage_b {msg} from peer {peer_id}'.format(
+            msg=msg, peer_id=l2.info['id'])
+    ])
+
+    # This should work since the peer is currently owned by `openingd`
+    l2.rpc.sendcustommsg(l4.info['id'], msg)
+    l2.daemon.wait_for_log(
+        r'{peer_id}-{owner}-chan#[0-9]: \[OUT\] {msg}'.format(
+            owner='openingd', msg=msg, peer_id=l4.info['id']
+        )
+    )
+    l4.daemon.wait_for_log(r'\[IN\] {}'.format(msg))
+    l4.daemon.wait_for_logs([
+        r'Got custommessage_a {msg} from peer {peer_id}'.format(
+            msg=msg, peer_id=l2.info['id']),
+        r'Got custommessage_b {msg} from peer {peer_id}'.format(
+            msg=msg, peer_id=l2.info['id']),
+    ])
+
+
 @pytest.mark.developer("needs --dev-force-privkey")
 def test_getsharedsecret(node_factory):
     """