* Close vulnerability and optimize digiline_send
`digiline_send` as it previously existed was vulnerable to a
time-of-check-to-time-of-use vulnerability in which a table could be
sent, size-checked, and then modified after the send but before
delivery. This would allow larger tables to be sent. It was also slow
because it called `minetest.serialize`. Fix both of these by
implementing custom message cleanup logic which simultaneously computes
the message’s cost.
* Clean up interaction with Digilines
Use `minetest.global_exists` to avoid an undefined global variable
warning when operating a Luacontroller with Digilines not available. Use
the new `digilines` table in preference to the old `digiline` table.
* Copy received messages
When a Digiline message is received at a Luacontroller, copy it so that
local modifications made by the Luacontroller code will not modify
copies of the table that are being passed to other nodes on the Digiline
network.
This uses a fairly simple trick: the textures are animated, while the
model is static and has a number of rotated copies of the parts that are
seen to move (four copies of the blades, eight copies of the top/bottom
and their edges). The opaque parts of the textures then decide which of
those faces' copies are visible in each frame.
Buttons and levers can now also be pointed upwards / downwards which will make them connect to corresponding up / down receivers. You will need to use the screwdriver for this.
Receivers cannot be rotated using the screwdriver anymore.
Thanks to @ShadowNinja for reporting this
Make sure functions that are keys in tables and functions inside nested tables also get removed when using digiline_send.
Restrict maximum length of messages to 50.000 characters and disable sending functions or table references over the wire. Restrict types of channel variable to string, number or boolean.
The missing length restriction made DoS-like attacks possible by overflowing memory using string concatenation. Thanks to gamemanj for disclosing this issue.
