We always allocate a new `struct command` when we get a full JSON
object from stdin:
b2df01dc73/plugins/libplugin.c (L1229-L1233)
If it happens to be a notification, we pass the `struct command` to
the handler, and not free it ourselves:
b2df01dc73/plugins/libplugin.c (L1270-L1275)
There are only nine points in `plugins/libplugin.c` where we `tal_free`
anything, and only one of them frees a `struct command`:
b2df01dc73/plugins/libplugin.c (L224-L234)
The above function `command_complete` is not appropriate for
notification handlers; the above function sends out a response
to our stdout, which a notification handler should not do.
However, as-is, it does mean that notification handling leaks
`struct command` objects, which can be problematic if we ever
have future built-in plugins which are significantly more
dependent on notifications.
This commit changes notification handlers to return
`struct command_result *`, because possibly in the future
notification handlers may want to perform `send_outreq`, so we
might as well use our standard convention for callbacks, and
to encourage future developers to check how to properly
terminate notification handlers (and free up the
`struct command`).
We also now provide a `notification_handled` function which a
notification handler must eventually call, as well as a
`notification_handler_pending` which is just a snowclone of
`command_still_pending`.
d4690358d9