mc-launcher-core

This is an mc launcher core written in Rust.

You can use the functions provided by this library to create an mc launcher, offering only basic functionalities.

Installation

Use cargo add mc-launcher-core to add it to your project.

Example

Here's an example of installing Fabric and launching offline:

use std::process::Command;

use mc_launcher_core::prelude::*;

fn main() -> mc_launcher_core::Result<()> {
    let minecraft_dir = std::env::current_dir()?.join(".minecraft");
    let launcher = Launcher::new(minecraft_dir);

    let install = launcher.install(InstallRequest {
        minecraft_version: "1.20.1".to_string(),
        loader: Some(LoaderSpec::Fabric {
            version: LoaderVersion::LatestStable,
        }),
        java: JavaInstallPolicy::Auto,
    })?;
    let version_json = launcher.load_version(&install.version_id)?;

    let command = launcher.build_launch_command_from_version(
        &version_json,
        LaunchOptions {
            account: Account::offline("Steve"),
            ..Default::default()
        },
    )?;

    let mut child = Command::new(&command.executable)
        .args(&command.args)
        .current_dir(&command.working_dir)
        .spawn()?;
    child.wait()?;
    Ok(())
}

Launcher::install performs a complete client install for vanilla, Fabric, and Quilt profiles: version JSON, client jar, libraries, asset index, asset objects, and native extraction are all handled by Rust library functions.

By default, launch commands use a version-isolated game directory at <minecraft_dir>/versions/<version_id>. Pass LaunchOptions::game_directory to use a custom instance directory.

Compatibility

On macOS Apple Silicon, Minecraft versions that still use LWJGL 2 or older LWJGL 3 metadata need extra compatibility handling. By default, launch command building and download planning apply the needed macOS arm64 patches automatically.

The patches replace old LWJGL, Java Objective-C bridge, and input-related libraries with ManyMC/MinecraftMachina arm64-compatible metadata. The legacy LWJGL 2 patch also adds missing JVM arguments such as -XstartOnFirstThread, -Djava.library.path, and -cp for versions that still use minecraftArguments.

The library does not bundle a Java runtime. For these legacy versions on Apple Silicon, use an arm64 Java runtime matching the version metadata and pass it via LaunchOptions::java_executable. Set LaunchOptions::compatibility or plan_vanilla_downloads_for_platform to CompatibilityPolicy::Disabled if a launcher wants to manage these patches itself.

The library separates library/native compatibility from window-hosting compatibility. For legacy LWJGL 2 versions on macOS arm64, apply_compatibility returns CompatibilityResult::windowing with WindowingStrategy::MacOsAppBundle and requires_visible_window_verification = true. This reflects the observed behavior that a direct CLI-spawned Java process can initialize Minecraft and still create a 0x0 invisible window. A desktop launcher should run these versions from a real macOS app bundle or equivalent GUI host, then verify that a visible game window was created.

Todo list

Crate library
Install original version
Offline launch
Microsoft account login
Support for Forge, Fabric, Quilt, and NeoForge loader metadata
Install of mrpack modpacks
Comprehensive documentation

Note