GreenScripter's Minecraft Bot Swarm Library

A lightweight headless Java library reimplementing a Minecraft client from scratch for programmatically controlling bot players in large swarms of up to 100-1000 bots to play on cracked vanilla and paper servers on version 1.21.
See the greenscripter.minecraft.atests package for some examples of varying quality.
In order to actually support a swarm on the larger end you need a fairly powerful minecraft server. (Not for this library, but the server the bots are connecting to.) Making most of the bots not load chunks and instead rely on the shared world of a global WorldPlayHandler is recommended.

Handlers

Handlers are the primary means of extension and can listen for packet and tick events either on an entire swarm, or individual bots. The following are the standard handlers that need to be registered for a fully featured bot:

• KeepAlivePlayHandler responds to keep alive packets, the bare minimum to stay connected.
• TeleportRequestPlayHandler responds to teleport requests and updates the bot player's position, required to move the player.
• PlayerPlayHandler tracks the bot player's health, experience, food and other base information.
• DeathPlayHandler makes the bot instantly respawn on death.
• InventoryPlayHandler tracks inventory information and provides convenience methods to interact with various kinds of in game GUIs.
• WorldPlayHandler reads and maintains the world state, sharing the world between all bots using the same handler.
• EntityPlayHandler add on to the world handler that reads entity related packets and controls the entity world state.

Data Objects

While there aren't restrictions to prevent other methods of sharing data between handlers, Data objects provide a convenient way to associate the current state of a bot with it's ServerConnection and allow different handlers to access that state.

• ClientConfigData storage for the client config information like view distance
• InventoryData maintained by the inventory handler, provides access to the player's inventory and convenience methods to modify it.
• PlayerData maintained by the player handler, and contains references to a few other data objects.
• PositionData maintained by the teleport handler, and is the bare minimum needed to do basic movements.
• RegistryData maintained by the ServerConnection login system, used by the world handler to look up dimension ids to determine world heights.
• WorldData maintained by the world handler, references the current world and provides functions to break and place blocks.

Custom data objects can be registered using PlayData.playData and then used like normal.

Packet Handlers

Packet Handlers are the primary extension block of the entire swarm, and act on a subset of packets by id numbers. Packets are passed as a general unknown packet type and must be converted to the target type. The conversion itself isn't really a safe operation, and it is up to the caller to ensure that the packet really is of the target type. New or missing packet types can be created by extending Packet, and need not be registered in any way to be used. See the existing handler classes for examples, the built in handlers are in no way special and alternate custom implementations could be used instead.

Raw Game Info

Sometimes you need to find a piece of info about a generic item or block state. In this library, everything is tracked by its protocol id in almost every case. To look up information about an item or block state by id, the greenscripter.minecraft.gameinfo package provides lookup tables by id for determining various information, such as what block identifier (eg. minecraft:dirt) a block state has, or if an item's max stack size.

Authentication

This library does not support logging in as premium minecraft players directly, however it does support connecting to BungeeCord backends.
To log in to premium servers, sign in to all bot accounts with https://github.com/GreenScripter/MultiViaProxy and then set up the bots to join the proxy using the correct uuids on bungee mode. The proxy can then select the right accounts and handle authentication.
This also allows the bots to connected to other versions of the game, though note that ViaProxy is not a perfect analog to an actual server of the appropriate version, so there may be some issues.