* 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.
It is no longer possible for get_node_force to return nil if the target
location does, in fact, exist, because a VM will always be able to load
it (whereas a forceload might not, due to exhaustion of forceload
resources). So it is no longer necessary to handle get_node_force
returning nil by deferring processing.
VoxelManipulator-based transactions are used to hopefully speed up
scanning and replacing of networks of conductors when receptors start or
stop driving signals into them.
Rather than calling out through the Lua-to-C API for each node that
needs to be read or written, a group of map reads (and optionally
writes) can be grouped into a transaction. Access to map data within the
transaction is provided at high speed by means of VoxelManipulators.
Once the reads and writes are finished, the transaction can be committed
or aborted.
A VoxelManipulator, when asked to read a mapblock, in addition to making
that mapblock available to the caller, also pulls it into the server’s
map cache, thus making get_node calls in the immediate future succeed.
This has the dual advantages that not every mapblock containing a
Mesecons circuit need remain loaded at all times (rather mapblocks can
be loaded on demand as signals are sent), and that the server need not
bother running ABMs and ticking entities within those mapblocks that are
loaded due to Mesecons signalling.
Christopher Head