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TLATER / nix-minecraft-servers

Nix flake that provides utilities for hosting minecraft servers
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nix-minecraft-servers

Manage Minecraft servers with nix!

This is still WIP, almost none of the actual functionality is implemented. Treat this as a kind of information dump with an initial design spec hidden in it.

This very explicitly will not implement anything for client-side use. There are better user-facing interfaces, and a lot of these projects rely on users downloading them via ad-displaying services.

This intends to make server management easier, which hopefully will help increase the number of users downloading mods via means approved by their upstreams.

Modloaders

Regarding forge

Forge is distributed as an installer, which downloads all kinds of libraries when run. This is the definition of impure.

Luckily, this distribution also includes a list of the libraries it will download in a convenient JSON file. We can use this to determine what the installer will want to download, and provide the dependencies for it before it attempts to do so (to my knowledge, this will skip the download step; if not we can hopefully work with upstream to change that, or patch the binary downstream).

Forge does kindly ask that the installation process is not automated, however this is specifically so that they can get users to visit their download page and display ads to them.

We will therefore not download the forge installer itself, and use nix' store-add feature, requiring users to download the installer at least once themselves.

The intention is to keep a database of libraries required for each version of forge, and match the version requested by a user against this, then to download the required libraries and produce a derivation of running the forge installer in a directory with these dependencies. This will allow it to extract its own jar and patch Minecraft, resulting in download-less forge installation.

Unfortunately, the Minecraft patching process appears to still be impure, but at least all inputs will be accounted for (and perhaps the MPC team will in the future solve their reproducibility issues).

Regarding fabric

I have not yet hosted a server using this mod loader, so I have no experience with it.

Regarding mods

Mods are generally hosted on https://www.curseforge.com/minecraft. While they are an integral component of gameplay for most people still playing this game, them being tied to this platform is a bit problematic. curseforge is presumably unable to comfortably handle all the requests to their platform, and therefore make it quite awkward to try and automatically pull anything from there (their attempt at monetizing the platform through the "twitch launcher" probably doesn't help).

Yet this is exactly what we want to do. Mods come in two shapes, either as mod packs or as individual mod files. Here's how these are handled:

Modpacks

Modpacks are pre-configured, pre-collected sets of mods. Think of them as analogous to Linux distributions. In theory, a manifest file format exists to define these modpacks that can be used to define the mods that need to be installed, and it is distributed with a zip file containing "overrides" which add additional things like configuration files, server icons and scripts.

Conveniently, this is a json format! Inconveniently, it is entirely proprietary, with no public documentation, and the only real implementation that can create or read these is an electron-based web app (the aforementioned "twitch launcher"). This means that, unless you are curseforge you practically must have a personal twitch account and be using their "twitch launcher" to install modpacks (attempts of using anything else may be thwarted by cloudflare).

This obviously doesn't work well on servers.

It seems that some people upstream noticed this as well, and a pattern emerges: Most (but not all) modpacks provide a second set of pre-configured "server" directories, which simply contain a full, working Minecraft server directory.

Conveniently, this puts the whole ordeal under a single download, which makes it easier to evade bans from cloudflare.

Inconveniently, these are entirely created to the modpack author's whims. Some include software which explicitly cannot be redistributed this way according to their licenses (e.g. the forge installer, which is present in almost all of these, but explicitly forbids redistribution because it has a special license from a group of Minecraft modders who write special tools to patch the Minecraft binary so that Forge can hook into it; but themselves are proprietary). Some include BAT scripts to install and run the server. Some include installers.

All of that is a long way to say that we are stuck with two incredibly problematic formats for modpacks:

manifest.json

Currently unsupported; Modpacks I am interested in don't use this, and I'm not keen on wading through this. However, some thoughts for a potential future implementation:

Rough algorithm might be:

  1. Add a new download script that:
    • Extracts manifest.json from a modpack.
    • Creates a json file with an array of (project, id, filename) tuples as expected by fetchModFromCurseForge.
      • This example of their "API" may help extract the filename, which is not recorded in the manifest but required for downloads.
    • Also stores a reference to the original modpack so that we can access the "overrides".
  2. Add a new library function that:
    • Downloads all files in one of the above json files with fetchModFromCurseForge.
    • Allows user overrides with additional mods and arbitrary configuration.
    • Stitches all the above together into a proper Minecraft directory, giving priority to user overrides.

"Server files"

Since these are entirely arbitrary, there is not too much we can do. We'll assume the following:

A proper installation therefore requires that we know the forge version to be installed before the derivation is built, and inject the correct set of libraries before the download.