This should prevent bouncing higher and higher (cheat).
Missing:
* The bounce effect should be set considering the last yDistance, in
order to allow negative vertical velocity to work.
* Add workaorunds for gravity with exiting cobweb.
* Allow multiple times zero y-distance (cobweb several times, slime 2).
Cobweb may need adjusting the bounding box to check with, instead.
* The server might reset the fall distance with preceding micro-moves,
so use NoFall data already on checking pre-conditions for bounce.
* Cap the bounce effect slightly smaller.
* Renew the bounce effect under certain conditions.
* Gravity, odds.
Remaining:
* Two consecutive times yDist = 0 at the maximum of a jump.
MISSING:
* Micro move onto ground, fall distance resets before sf check is run.
Done:
* Split PlayerMoveEvent processing to from -> loc + from -> to. Just if
from isn't the same coordinates as player.getLocation. This
reduces the complexity of workarounds.
* You do take fall damage falling onto slime blocks while sneaking.
* Queue bounce effect, only if the move is valid. Skip NoFall then.
* Apply bounce effect once moving up, to allow overriding.
* Cover more odd cases.
Unrelated:
* Use data.debug instead of cc.debug.
Adjust workarounds, confine velocity activation to next tick.
Cases missing:
* Lost ground cases (yOnGround has been reduced, strikes here).
* Two consecutive yDist = 0.
This will preserve the order of debug messages sent from multiple
threads. As a side effect, this might be better for performance, given
that on constant input the logging task will stay registered, so there
is little overhead and the file-io is taken off the asynchronous packet
and chat handler threads.Hopefully the thread switching is less
expensive than the gain by not delaying chat/packet threads, in case of
servers with few cores. We might adapt the used policy later, based on
cores and/or config.
* Queue outgoing positions in order to detect ACK on incoming.
* Since we can't detect relative teleports, positions are only queued,
if they match an absolute location from a teleport event (Bukkit).
* The queue is kept simple: only store the latest position.
* Cancel incoming flying/pos/look until ACK is received.
Missing:
* Are yaw/pitch are ever sent back changed.
* Configuration to turn it off.
* Might use this to just skip all violation handling until ACK.
This is a quick go with little testing, roughly up to level 60. Above
that there may be more false positives, also "no jumping" is not
enforced there.
A suggestion for the future could be to just use/part-calculate an array
for all the typical effects.
Used to be 0.0625 for a while, but intentions are to cover ground-loss
as lostground workarounds. Later switch to calculate the distance to
ground (with a given max-distance).
For efficiency (several?) other cases will be removable, once we model
the per-move ground/medium properties more accurately also for the past
move(s). At least lostground_pyramid should be removed then.
Splits CoordMap into interface, abstract hash map, implementations.
Sketch Linked version, hinting at access order, e.g. with
tracking piston effects with timeouts.
Missing:
* Implementation of a linked version.
Cancelling redundant packets has to big problems:
* The normal case is to not run in the primary thread.
* For legit players a missed micro move could mean that survivalfly can
not detect ground properly.
Better approaches could be:
* Cancel asynchronous packets if they match the last sent one (only
simple hacks).
* Check for moves passing block borders, request block shapes and such
from the main thread.
* Detect actual cheating or unusual patterns instead.
* Queue packets for processing in the main thread.
Missing:
* Actually detect ACK packets for previous outgoing teleports.
* Do something upon detecting illegal coordinates (asynchronous
disconnect? queue kicking, config).
* In addition to the "distance from set-back" check, we have a check of
the per-move distance for in-air checks, taking account of friction.
* In-air and liquid checks should consume vertical velocity once needed.
* Model vertical velocity "exact", i.e. positive and negative, use an
entry once a sub-check fails, quite strict invalidation of not matching
values, matching against the y-distance directly.
* Vertical accounting has been sharpened for the moment. The new
per-move checking might make it superfluous.
* Remove MediumLiftOff in favor of a LiftOffEnvelope carrying basic
lift-off max-gain/max-height/max-phase, enabling to distinguish between
normal lift-off and liquid near ground.
* Rename others (e.g. sfLastYDist -> lastYDist). Thus breaking internal
naming, adding velocity via MovingData still works, but should behave
slightly differently.
* Fixes (waterwalk with head obstructed, resetting of sfDirty, possibly
others).
Issues.
* Edge cases with velocity, water.
* Lava needs friction, at least with velocity.
* Lostground_edge(ydist < 0.0) ->
bunny with yDistance > 0.0. Need more flags or better model for keeping
past moves information.
* Plain ground misses (layered snow).
* lostground with yDist == 0.0, then seemingly in-air yDist== 0.0, then
bunny/lifft-off (similar to above). Needs better modeling of past moves,
because several lostgorund cases mean "the move has been on ground".
Also includes geting the distance to ground for hack-proof set-back-y.
* Vertical velocity is now matched with a margin, because the client
seems to add randomly.
* Possibly new loopholes/exploits (extreme large moves?).
* Cleanup pending.
* Group selected classes into sub-packages of moving.
* Rename classes.
* Must use LinkedList for velocity entries.
* Prepare SimpleAxisVelocity + entry for use-once accounting.
(Might not be the final naming.)
