PrismLauncher/libraries/launcher/org/prismlauncher/utils/ReflectionUtils.java

// SPDX-License-Identifier: GPL-3.0-only
/*
 *  Prism Launcher - Minecraft Launcher
 *  Copyright (C) 2022 icelimetea <fr3shtea@outlook.com>
 *  Copyright (C) 2022 solonovamax <solonovamax@12oclockpoint.com>
 *  Copyright (C) 2022 TheKodeToad <TheKodeToad@proton.me>
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, version 3.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  Linking this library statically or dynamically with other modules is
 *  making a combined work based on this library. Thus, the terms and
 *  conditions of the GNU General Public License cover the whole
 *  combination.
 *
 *  As a special exception, the copyright holders of this library give
 *  you permission to link this library with independent modules to
 *  produce an executable, regardless of the license terms of these
 *  independent modules, and to copy and distribute the resulting
 *  executable under terms of your choice, provided that you also meet,
 *  for each linked independent module, the terms and conditions of the
 *  license of that module. An independent module is a module which is
 *  not derived from or based on this library. If you modify this
 *  library, you may extend this exception to your version of the
 *  library, but you are not obliged to do so. If you do not wish to do
 *  so, delete this exception statement from your version.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * This file incorporates work covered by the following copyright and
 * permission notice:
 *
 *      Copyright 2013-2021 MultiMC Contributors
 *
 *      Licensed under the Apache License, Version 2.0 (the "License");
 *      you may not use this file except in compliance with the License.
 *      You may obtain a copy of the License at
 *
 *          http://www.apache.org/licenses/LICENSE-2.0
 *
 *      Unless required by applicable law or agreed to in writing, software
 *      distributed under the License is distributed on an "AS IS" BASIS,
 *      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *      See the License for the specific language governing permissions and
 *      limitations under the License.
 */

package org.prismlauncher.utils;

import org.prismlauncher.utils.logging.Log;

import java.applet.Applet;
import java.io.File;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

public final class ReflectionUtils {
    private static final MethodHandles.Lookup LOOKUP = MethodHandles.lookup();
    private static final ClassLoader LOADER = ClassLoader.getSystemClassLoader();

    /**
     * Construct a Java applet by its class name.
     *
     * @param clazz The class name
     * @return The applet instance
     * @throws Throwable
     */
    public static Applet createAppletClass(String clazz) throws Throwable {
        Class<?> appletClass = LOADER.loadClass(clazz);

        MethodHandle appletConstructor = LOOKUP.findConstructor(appletClass, MethodType.methodType(void.class));
        return (Applet) appletConstructor.invoke();
    }

    /**
     * Best guess of the game directory field within net.minecraft.client.Minecraft.
     * Designed for legacy versions - newer versions do not use a static field.
     *
     * @param clazz The class
     * @return The first field matching criteria
     */
    public static Field findMinecraftGameDirField(Class<?> clazz) {
        Log.debug("Resolving minecraft game directory field");

        // search for private static File
        for (Field field : clazz.getDeclaredFields()) {
            if (field.getType() != File.class) {
                continue;
            }

            int fieldModifiers = field.getModifiers();

            if (!Modifier.isStatic(fieldModifiers)) {
                Log.debug("Rejecting field " + field.getName() + " because it is not static");
                continue;
            }

            if (!Modifier.isPrivate(fieldModifiers)) {
                Log.debug("Rejecting field " + field.getName() + " because it is not private");
                continue;
            }

            if (Modifier.isFinal(fieldModifiers)) {
                Log.debug("Rejecting field " + field.getName() + " because it is final");
                continue;
            }

            Log.debug("Identified field " + field.getName() + " to match conditions for game directory field");

            return field;
        }

        return null;
    }

    /**
     * Gets the main method within a class.
     *
     * @param clazz The class
     * @return A method matching the descriptor of a main method
     * @throws ClassNotFoundException
     * @throws NoSuchMethodException
     * @throws IllegalAccessException
     */
    public static MethodHandle findMainMethod(Class<?> clazz) throws NoSuchMethodException, IllegalAccessException {
        return LOOKUP.findStatic(clazz, "main", MethodType.methodType(void.class, String[].class));
    }

    /**
     * Gets the main method within a class by its name.
     *
     * @param clazz The class name
     * @return A method matching the descriptor of a main method
     * @throws ClassNotFoundException
     * @throws NoSuchMethodException
     * @throws IllegalAccessException
     */
    public static MethodHandle findMainMethod(String clazz) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException {
        return findMainMethod(LOADER.loadClass(clazz));
    }
}