Validation

Incoming values are checked in two steps. First the codec rejects anything outside its bounds, before your code runs. Then any check attached to the codec with :validate runs.

A check on one field, rejecting a sender who fires faster than ten times a second.

Damage = Lync.int(0, 500):validate(function(amount, context)
    if context.last ~= nil and context.now - context.last < 0.1 then
        return "faster than 10 Hz"
    end
    return nil
end),

A check on a whole record, for a rule between fields.

Trade = Lync.struct({
    give = Lync.int(0, 1000),
    take = Lync.int(0, 1000),
}):validate(function(offer)
    if offer.give == 0 and offer.take == 0 then
        return "empty trade"
    end
    return nil
end),

Return nil to pass or a string to drop. The string becomes the reason in the log.

context field
player	The player who sent the value. Nil for a value the server sent to itself.
now	When it arrived.
last	When the previous value from this sender for this definition arrived, whether it was accepted or not.

last is updated on every arrival, including rejected ones, so a sender cannot reset it by sending invalid values. The context table is reused between calls, so copy anything you keep from it.

What a drop does

The listener	Never runs.
The log	Gets one warning with the reason, the definition, the file and line it was declared at, and the player.
A request	Gets no reply, so the requester ends with the timeout code.