lightningd: deprecate "message": null in channel_state_changed notifications.

Somehow I missed this when deprecating `short_channel_id` being null.

Changelog-Deprecated: Plugins: `channel_state_changed` notification `message` field being `null`: it will be omitted instead.
Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

common/json_stream.c

@@ -323,11 +323,6 @@ void json_add_bool(struct json_stream *result, const char *fieldname, bool value
 	json_add_primitive(result, fieldname, value ? "true" : "false");
 }
 
-void json_add_null(struct json_stream *stream, const char *fieldname)
-{
-	json_add_primitive(stream, fieldname, "null");
-}
-
 void json_add_hex(struct json_stream *js, const char *fieldname,
 		  const void *data, size_t len)
 {

common/json_stream.h

@@ -242,8 +242,7 @@ void json_add_s32(struct json_stream *result, const char *fieldname,
 void json_add_bool(struct json_stream *result, const char *fieldname,
 		   bool value);
 
-/* '"fieldname" : null' or 'null' if fieldname is NULL */
-void json_add_null(struct json_stream *stream, const char *fieldname);
+/* Looking for json_add_null?  Don't do that: we omit fields, don't 'null' them! */
 
 /* '"fieldname" : "0189abcdef..."' or "0189abcdef..." if fieldname is NULL */
 void json_add_hex(struct json_stream *result, const char *fieldname,

doc/developers-guide/deprecated-features.md

@@ -24,6 +24,7 @@ hidden: false
 | channel_state_changed.null_scid         | Notification Field | v25.09        | v26.09         | In channel_state_changed notification, `short_channel_id` will be missing instead of `null`                                            |
 | notification.payload                    | Notification Field | v25.09        | v26.09         | Notifications from plugins used to have fields in `payload` sub-object, now they are not (just like normal notifications)              |
 | pay_notifications.raw_fields            | Field              | v25.09           | v26.09         | `channel_hint_update`, `pay_failure` and `pay_success` notifications now wrap members in an object of the same name                    |
+| channel_state_changed.null_message     | Notification Field | v25.12        | v26.12         | In channel_state_changed notification, `message` will be missing instead of `null`                                                      |
 
 Inevitably there are features which need to change: either to be generalized, or removed when they can no longer be supported.
 

lightningd/notification.c

@@ -275,6 +275,12 @@ void notify_channel_opened(struct lightningd *ld,
 	notify_send(ld, n);
 }
 
+/* Don't use this: omit fields instead! */
+static void json_add_null(struct json_stream *stream, const char *fieldname)
+{
+	json_add_primitive(stream, fieldname, "null");
+}
+
 static void channel_state_changed_notification_serialize(struct json_stream *stream,
 							 struct lightningd *ld,
 							 const struct node_id *peer_id,
@@ -304,8 +310,12 @@ static void channel_state_changed_notification_serialize(struct json_stream *str
 	json_add_string(stream, "cause", channel_change_state_reason_str(cause));
 	if (message != NULL)
 		json_add_string(stream, "message", message);
-	else
+	else if (lightningd_deprecated_out_ok(ld, ld->deprecated_ok,
+					      "channel_state_changed",
+					      "null_message",
+					      "v25.12", "v26.12")) {
 		json_add_null(stream, "message");
+	}
 }
 
 REGISTER_NOTIFICATION(channel_state_changed)

plugins/bcli.c

@@ -396,6 +396,12 @@ static struct command_result *command_err_bcli_badjson(struct bitcoin_cli *bcli,
 	return command_done_err(bcli->cmd, BCLI_ERROR, err, NULL);
 }
 
+/* Don't use this in general: it's better to omit fields. */
+static void json_add_null(struct json_stream *stream, const char *fieldname)
+{
+	json_add_primitive(stream, fieldname, "null");
+}
+
 static struct command_result *process_getutxout(struct bitcoin_cli *bcli)
 {
 	const jsmntok_t *tokens;

tests/test_plugin.py

@@ -967,12 +967,12 @@ def wait_for_event(node):
     assert(event1['old_state'] == "ONCHAIN")
     assert(event1['new_state'] == "CLOSED")
     assert(event1['cause'] == "onchain")
-    assert(event1['message'] == None)
+    assert('message' not in event1)
     event2 = wait_for_event(l2)
     assert(event2['old_state'] == "ONCHAIN")
     assert(event2['new_state'] == "CLOSED")
     assert(event2['cause'] == "onchain")
-    assert(event2['message'] == None)
+    assert('message' not in event2)
 
 
 @pytest.mark.openchannel('v1')
@@ -1102,13 +1102,13 @@ def wait_for_event(node):
     assert(event1['old_state'] == "ONCHAIN")
     assert(event1['new_state'] == "CLOSED")
     assert(event1['cause'] == "onchain")
-    assert(event1['message'] == None)
+    assert('message' not in event1)
 
     event2 = wait_for_event(l2)
     assert(event2['old_state'] == "ONCHAIN")
     assert(event2['new_state'] == "CLOSED")
     assert(event2['cause'] == "onchain")
-    assert(event2['message'] == None)
+    assert('message' not in event2)
 
 
 @pytest.mark.openchannel('v1')