channeld: Send messages if instructed to by lightningd

channeld/channeld.c

@@ -2852,6 +2852,14 @@ static void handle_dev_memleak(struct peer *peer, const u8 *msg)
 			 take(towire_channel_dev_memleak_reply(NULL,
 							       found_leak)));
 }
+
+/* We were told to send a custommsg to the peer by `lightningd`. All the
+ * verification is done on the side of `lightningd` so we should be good to
+ * just forward it here. */
+static void channeld_send_custommsg(struct peer *peer, const u8 *msg)
+{
+	sync_crypto_write(peer->pps, take(msg));
+}
 #endif /* DEVELOPER */
 
 static void req_in(struct peer *peer, const u8 *msg)
@@ -2917,7 +2925,7 @@ static void req_in(struct peer *peer, const u8 *msg)
 	switch ((enum common_wire_type)t) {
 #if DEVELOPER
 	case WIRE_CUSTOMMSG_OUT:
-		/* TODO(cdecker) Add handling of custom messages. */
+		channeld_send_custommsg(peer, msg);
 		return;
 #else
 	case WIRE_CUSTOMMSG_OUT:

tests/test_misc.py

@@ -2096,11 +2096,23 @@ def test_sendcustommsg(node_factory):
     with pytest.raises(RpcError, match=r'Cannot send messages of type 18 .WIRE_PING.'):
         l2.rpc.dev_sendcustommsg(l2.info['id'], r'0012')
 
+    # This should work since the peer is currently owned by `channeld`
     l2.rpc.dev_sendcustommsg(l1.info['id'], msg)
+    l2.daemon.wait_for_log(
+        r'{peer_id}-{owner}-chan#[0-9]: \[OUT\] {serialized}'.format(
+            owner='channeld', serialized=serialized, peer_id=l1.info['id']
+        )
+    )
+    l1.daemon.wait_for_log(r'\[IN\] {}'.format(serialized))
+    l1.daemon.wait_for_log(
+        r'Got a custom message {serialized} from peer {peer_id}'.format(
+            serialized=serialized, peer_id=l2.info['id']))
+
+    # This should work since the peer is currently owned by `openingd`
     l2.rpc.dev_sendcustommsg(l4.info['id'], msg)
     l2.daemon.wait_for_log(
-        r'{peer_id}-openingd-chan#[0-9]: \[OUT\] {serialized}'.format(
+        r'{peer_id}-{owner}-chan#[0-9]: \[OUT\] {serialized}'.format(
-            serialized=serialized, peer_id=l4.info['id']
+            owner='openingd', serialized=serialized, peer_id=l4.info['id']
         )
     )
     l4.daemon.wait_for_log(r'\[IN\] {}'.format(serialized))