There are many ways to create a plugin, and many pitfalls for an unwary developer. Here we describe the plugin development practices that will make the most of the Sponge API, setting sensible boundaries for the benefit of compatibility. This information may change and expand as the Sponge project matures.
Plugin Development Guidelines
The following guidelines have been prepared to aid Sponge plugin developers. It is not a definitive or comprehensive list, merely an attempt to detail some issues that are likely to arise during plugin development, and propose our best solutions.
We reserve the use of Sponge for official SpongePowered works. Please don’t use Sponge as part of your plugin name, unless (1) your plugin primarily concerns the Minecraft block «Sponge», or (2) your plugin also has versions for other APIs (in which case you may append «for Sponge» to the title).
The Economy API is used to link economy plugins with other plugins that use the economy (i.e. shops). You can read about the Economy API here, which details everything you need to know about the API.
Anything to do with intercepting packets, or introducing custom items/blocks/entities/etc, is not planned to be part of the Sponge API. Note that using packets may be looking at the problem the wrong way, as there may be a solution achievable with the existing Sponge API. In some cases it may be possible to add whatever is needed to the Sponge API; otherwise, the alternative is to use the Forge API and create a Mod instead.
Using Forge or NMS Classes
We do not recommend working with Forge or Minecraft base classes at all, unless it is to provide compatibility with a mod for Sponge API. Most uses of NMS (net.minecraft.server) code in plugins do not fail gracefully, making troubleshooting very difficult. Maintaining NMS modifications is also more difficult than using the Sponge API. Mods that add to the Sponge API using code internals will have to specifically write an API, which does not rely on underlying Minecraft code, to be usable by Sponge plugins. However, plugins can be created that load separate “compatibility” modules to interact with the underlying implementation (SpongeForge or SpongeVanilla).
Plugins using implementation-specific code are very likely to break between versions, and should be clearly labelled as such wherever they are hosted. These may more appropriately labelled as «Mods».
Mixins are specifically for transforming classes before other mods/plugins start. ForgeModLoader calls these mods “Coremods”. SpongeForge is a Coremod, and deploys mixins on startup. Mixins can be used by plugins, but be aware of the additional complexities involved.
Sponge plugins which leverage mixins may also be a considered core mods, based on content.
To use mixins in FML, it must be a coremod. The jar may also contain a Sponge plugin, so most properly the container is a «hybrid mod».
To use mixins in SpongeVanilla, intentions must be declared in the manifest. SpongeVanilla then injects the mixins.
Having both types in a single jar is entirely possible. (Indeed, a single jar could easily contain a tweaker, FML mod, coremod, bukkit plugin, sponge plugin, and/or litemod.)
Some definitions may be helpful here.
- Tweak Mod (aka Tweaker)
a subsystem-level mod which hooks directly into the game using LaunchWrapper, usually used for ModSystems (eg. LiteLoader, FML) and stand-alone mods (eg. Optifine). Can interact with any aspect of the game environment directly. Generally breaks every version.
- Core Mod
has almost equivalent power of a Tweak Mod but must be bootstrapped by a ModSystem. Can interact with any aspect of the game environment directly. Generally breaks on every new Game version.
interacts with the game only via a ModSystem, the mod is exposed to game objects directly but will generally only hook into the game via hooks provided by the ModSystem. Generally breaks every major version of the Game (depending on features used). The term mod is also used as an umbrella term for anything which modifies the game, though for the sake of clarity we’ll use this definition.
interacts with the game only via an API, does not interact with game objects directly in any way, only leverages objects exposed by the API. Generally breaks only when the API is revised (and sometimes not even then).
It’s also important to distinguish the container from the contents. Issues with terminology tends to arise because a jar containing a mod tends to get referred to as a «mod». Any plugin which is not fully decoupled via the API puts itself into the category of Mod. This type of «plugin» may be prevalent where there are shortcomings in an API.
Advantages of Hybrid Mods
A hybrid mod leverages both a plugin component which interacts via the API, and a mod (or even coremod) in the same package. This has the disadvantages of a mod (breaks every version) but also the power of a mod (can interact with the game directly) coupled with some of the benefits of a Plugin (high-level abstract access to the game, and can also interact with other plugins as a peer).
The primary benefit of this system is that the maintenance burden is reduced when updating the mod, because any features accessed via the API are likely to be much more stable.
This type of mod can be used to implement plugins whose needs overflow the capability of the API (in the case of a plugin which needs to leverage mixins for a particular feature); but can also be used for mods which want to leverage services afforded by the API (eg. a mod which wants to provide direct support for permissions or chat channels).
Unlike NMS-exploiting «plugins», a hybrid mod makes its nature clear.
An explanation of how to communicate with other plugins, TBA.