Some test UDP server code for implementing multiplayer functionality into Undertale (or other basic GameMaker games). It is not particularly great, but it works well enough for its purpose.
This code is purely Java with no external dependencies, so building it should be fairly simple.
After building, place the binaries (such as a JAR file) in a directory that is able to be filled with a config file and log files.
By default it will spin up a server on port 1337, listening for UDP packets from proper clients. This behavior and more can be configured with the (generated) config.properties file.
Log files are generated for the main thread and each server. Servers will generate new log files if they have activity after one hour of using a particular log file.