Modrinth/packages/app-lib/library/MinecraftLaunch.java

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Arrays;

public final class MinecraftLaunch {
  public static void main(String[] args) throws IOException, ReflectiveOperationException {
    final String mainClass = args[0];
    final String[] gameArgs = Arrays.copyOfRange(args, 1, args.length);

    System.setProperty("modrinth.process.args", String.join("\u001f", gameArgs));
    parseInput();

    relaunch(mainClass, gameArgs);
  }

  private static void parseInput() throws IOException {
    final ByteArrayOutputStream line = new ByteArrayOutputStream();
    while (true) {
      final int b = System.in.read();
      if (b < 0) {
        throw new IllegalStateException("Stdin terminated while parsing");
      }
      if (b != '\n') {
        line.write(b);
        continue;
      }
      if (handleLine(line.toString("UTF-8"))) {
        break;
      }
      line.reset();
    }
  }

  private static boolean handleLine(String line) {
    final String[] parts = line.split("\t", 2);
    switch (parts[0]) {
      case "property": {
        final String[] keyValue = parts[1].split("\t", 2);
        System.setProperty(keyValue[0], keyValue[1]);
        return false;
      }
      case "launch":
        return true;
    }

    System.err.println("Unknown input line " + line);
    return false;
  }

  private static void relaunch(String mainClassName, String[] args) throws ReflectiveOperationException {
    final int javaVersion = getJavaVersion();
    final Class<?> mainClass = Class.forName(mainClassName);

    if (javaVersion >= 25) {
      Method mainMethod;
      try {
        mainMethod = findMainMethodJep512(mainClass);
      } catch (ReflectiveOperationException e) {
        System.err
            .println("[MODRINTH] Unable to call JDK findMainMethod. Falling back to pre-Java 25 main method finding.");
        // If the above fails due to JDK implementation details changing
        try {
          mainMethod = findSimpleMainMethod(mainClass);
        } catch (ReflectiveOperationException innerE) {
          e.addSuppressed(innerE);
          throw e;
        }
      }
      if (mainMethod == null) {
        throw new IllegalArgumentException("Could not find main() method");
      }

      Object thisObject = null;
      if (!Modifier.isStatic(mainMethod.getModifiers())) {
        thisObject = mainClass.getDeclaredConstructor().newInstance();
      }

      final Object[] parameters = mainMethod.getParameterCount() > 0
          ? new Object[] { args }
          : new Object[] {};

      mainMethod.invoke(thisObject, parameters);
    } else {
      findSimpleMainMethod(mainClass).invoke(null, new Object[] { args });
    }
  }

  private static int getJavaVersion() {
    String javaVersion = System.getProperty("java.version");

    final int dotIndex = javaVersion.indexOf('.');
    if (dotIndex != -1) {
      javaVersion = javaVersion.substring(0, dotIndex);
    }

    final int dashIndex = javaVersion.indexOf('-');
    if (dashIndex != -1) {
      javaVersion = javaVersion.substring(0, dashIndex);
    }

    return Integer.parseInt(javaVersion);
  }

  private static Method findMainMethodJep512(Class<?> mainClass) throws ReflectiveOperationException {
    // BEWARE BELOW: This code may break if JDK internals to find the main method
    // change.
    final Class<?> methodFinderClass = Class.forName("jdk.internal.misc.MethodFinder");
    final Method methodFinderMethod = methodFinderClass.getDeclaredMethod("findMainMethod", Class.class);
    final Object result = methodFinderMethod.invoke(null, mainClass);
    return (Method) result;
  }

  private static Method findSimpleMainMethod(Class<?> mainClass) throws NoSuchMethodException {
    return mainClass.getMethod("main", String[].class);
  }
}