I believe this is caused by a bug in the linux kernel, since it only impacts certain machines I tested (one, to be specific). Whatever the case, setting a max backlog size is prudent anyway, and fixes the problem.
Packets with a too-short payload would either cause the RCON thread to hang until the client disconnected, or crash the RCON thread entirely.
commit 90bb1894d7f87645b806f5fc67d1b877bb963180
Author: Dylan K. Taylor <odigiman@gmail.com>
Date: Tue Jan 22 18:15:46 2019 +0000
fix some bugs in RCON
This prevents plugins sending wrong packets at the compiler level (or would, if we had a compiler). It's more robust than a getter for client/server and throwing an exception since a static analysis tool can detect faults created by sending wrong packets from the server. This is also used to deny service to dodgy clients which send wrong packets to the server to attack it.
this is in preparation for clientbound/serverbound packet separation. I did this already on another branch, but the changeset was dependent on a massive refactor to split apart packets and binarystream which i'm still not fully happy with.
Encoded tags larger than 32KB overflow the length field, so we can't send these over network. However, it's unreasonable to randomly throw this burden off onto users by crashing their servers, so the next best solution is to just not send the NBT. This is also not an ideal solution (books and the like with too-large tags won't work on the client side) but it's better than crashing the server or client due to a protocol bug. Mojang have confirmed this will be resolved by a future MCPE release, so we'll just work around this problem until then.
The only cyclic references here are both destroyed during normal collection directly (net interface removes from sessions array, player destroys its session reference), so there's no need to destroy them again here. This just causes a giant swathe of potential crashes for no real benefit.
close#2669
future enhancements:
- make gamemode an object containing information about abilities that players have in this gamemode (gamemodes are just predefined ability sets)
- get the magic numbers out of the API
