by applying this patch we:
- would introduce the check command;
- have an alternative to avoid having the fetch command downloading all binary updates;
- folks can now use check to only fetch (and verify sanity) of a remote tag to report if there's an update available, or not;
- save FreeBSD's update servers from getting unnecessary HTTP requests - by not serving every single fetch request from freebsd-update(8);
- help improving users to just verify if updates are available, or not;
- freebsd-update(8) will just report the status of an available update be ready or not, and exit.
it's also important to note that at least the tag must be fetched (and sanitized). we are doing that - still preventing replay attacks and unsupported downgrades.
we are mainly focusing on supporting RELEASE here, as other versions (ALPHA/BETA/RC) can only be upgraded instead of patched using the install command.
the motivation to produce this changes come from: