Mod loader

modLoader/build.gradle

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+/*
+ * This file contains an application project which integrates the Fabric mod loader.
+ */
+
+plugins {
+    // Apply the application plugin to add support for building a CLI application in Java.
+    id 'java-library'
+}
+
+repositories {
+    // Maven Central for core dependencies
+    mavenCentral()
+
+    // SpongePowered Maven repository for Mixins
+    maven {
+        url "https://repo.spongepowered.org/maven/"
+    }
+    // FabricMC Maven repository for Fabric Loader
+    maven {
+        url "https://maven.fabricmc.net/"
+    }
+}
+
+sourceCompatibility = JavaVersion.VERSION_16
+targetCompatibility = JavaVersion.VERSION_16
+
+version = '1.0.0'
+group = "com.elitemastereric"
+archivesBaseName = "modloader"
+
+dependencies {
+    api "com.google.guava:guava:21.0"
+    api "com.google.code.gson:gson:2.8.7"
+
+    // Fabric dependencies
+    api "net.fabricmc:fabric-loader:0.13.3"
+    api "net.fabricmc:tiny-mappings-parser:0.2.2.14"
+    api "net.fabricmc:access-widener:2.1.0"
+
+    // Mixin dependencies
+    api "org.ow2.asm:asm:9.2"
+    api "org.ow2.asm:asm-analysis:9.2"
+    api "org.ow2.asm:asm-commons:9.2"
+    api "org.ow2.asm:asm-tree:9.2"
+    api "org.ow2.asm:asm-util:9.2"
+    api 'org.spongepowered:mixin:0.8.5'
+
+}
+
+sourceSets {
+    main {
+        java {
+            srcDir 'src'
+        }
+    }
+}
+
+jar {
+	manifest {
+		attributes(
+			'Class-Path': configurations.runtimeClasspath.collect { it.getName() }.join(' '),
+			'Specification-Version': 8.0,
+			'Multi-Release': 'true'
+		)
+	}
+}
+
+task copyDependencies(type: Copy) {
+  group 'build'
+  from configurations.runtimeClasspath
+  into "build/libs/deps/"
+}
+
+assemble {
+    group 'build'
+    dependsOn 'jar'
+    dependsOn 'copyDependencies'
+}
+
+task buildAndCopy(type: Copy) {
+  group 'build'
+  dependsOn 'assemble'
+  from "build/libs/"
+  into "../run/"
+}

modLoader/src/main/java/com/elitemastereric/modloader/AppGameProvider.java

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+package com.elitemastereric.modloader;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.stream.Collectors;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.ArrayList;
+
+import net.fabricmc.loader.impl.FormattedException;
+import net.fabricmc.loader.impl.game.GameProvider;
+import net.fabricmc.loader.impl.game.GameProviderHelper;
+import net.fabricmc.loader.impl.game.patch.GameTransformer;
+import net.fabricmc.loader.impl.launch.FabricLauncher;
+import net.fabricmc.loader.impl.metadata.BuiltinModMetadata;
+import net.fabricmc.loader.impl.metadata.ContactInformationImpl;
+import net.fabricmc.loader.impl.util.Arguments;
+import net.fabricmc.loader.impl.util.SystemProperties;
+import net.fabricmc.loader.impl.util.log.Log;
+import net.fabricmc.loader.impl.util.log.LogCategory;
+
+/*
+ * A custom GameProvider which grants Fabric Loader the necessary information to launch the app.
+ */
+public class AppGameProvider implements GameProvider {
+    public static final String CLIENT_ENTRYPOINT = "com.elitemastereric.helloworld.Launch";
+    public static final String[] ENTRYPOINTS = { CLIENT_ENTRYPOINT };
+
+    public static final String PROPERTY_APP_DIRECTORY = "appDirectory";
+
+    private static final GameTransformer TRANSFORMER = new AppGameTransformer();
+
+    private Arguments arguments;
+    private Path appJar;
+
+    /*
+     * Display an identifier for the app.
+     */ @Override
+    public String getGameId() {
+        return "helloworld";
+    }
+
+    /*
+     * Display a readable name for the app.
+     */ @Override
+    public String getGameName() {
+        return "Hello World";
+    }
+
+    /*
+     * Display a raw version string that may include build numbers or git hashes.
+     */ @Override
+    public String getRawGameVersion() {
+        return "1.0.0-abcdef";
+    }
+
+    /*
+     * Display a clean version string for display.
+     */ @Override
+    public String getNormalizedGameVersion() {
+        return "1.0.0";
+    }
+
+    /*
+     * Provides built-in mods, for example a mod that represents the app itself so
+     * that mods can depend on specific versions.
+     */
+    @Override
+    public Collection<BuiltinMod> getBuiltinMods() {
+        HashMap<String, String> contactMap = new HashMap<>();
+        contactMap.put("homepage", "https://elitemastereric.com/");
+
+        BuiltinModMetadata.Builder modMetadata = new BuiltinModMetadata.Builder(getGameId(), getNormalizedGameVersion())
+            .setName(getGameName())
+            .addAuthor("EliteMasterEric", contactMap)
+            .setContact(new ContactInformationImpl(contactMap))
+            .setDescription("A simple Hello World app for Fabric Loader.");
+
+        BuiltinMod mod = new BuiltinMod(Collections.singletonList(appJar), modMetadata.build());
+
+        return Collections.singletonList(mod);
+    }
+
+    /*
+     * Provides the full class name of the app's entrypoint.
+     */
+    @Override
+    public String getEntrypoint() {
+        return CLIENT_ENTRYPOINT;
+    }
+
+    /*
+     * Provides the directory path where the app's resources (such as config) should
+     * be located
+     * This is where the `mods` folder will be located.
+     */
+    @Override
+    public Path getLaunchDirectory() {
+        if (arguments == null) {
+            return Paths.get(".");
+        }
+
+        return getLaunchDirectory(arguments);
+    }
+
+    private static Path getLaunchDirectory(Arguments arguments) {
+        return Paths.get(arguments.getOrDefault(PROPERTY_APP_DIRECTORY, "."));
+    }
+
+    /*
+     * Return true if the app needs to be deobfuscated.
+     */
+    @Override
+    public boolean isObfuscated() {
+        return false;
+    }
+
+    @Override
+    public boolean requiresUrlClassLoader() {
+        return false;
+    }
+
+    @Override
+    public boolean isEnabled() {
+        return true;
+    }
+
+    /*
+     * Parse the arguments, locate the game directory, and return true if the game
+     * directory is valid.
+     */
+    @Override
+    public boolean locateGame(FabricLauncher launcher, String[] args) {
+        this.arguments = new Arguments();
+        this.arguments.parse(args);
+
+        // Build a list of possible locations for the app JAR.
+        List<String> appLocations = new ArrayList<>();
+        // Respect "fabric.gameJarPath" if it is set.
+        if (System.getProperty(SystemProperties.GAME_JAR_PATH) != null) {
+            appLocations.add(System.getProperty(SystemProperties.GAME_JAR_PATH));
+        }
+        // List out default locations.
+        appLocations.add("./helloworld-" + getNormalizedGameVersion() + ".jar");
+
+        // Filter the list of possible locations based on whether the file exists.
+        List<Path> existingAppLocations = appLocations.stream().map(p -> Paths.get(p).toAbsolutePath().normalize())
+                .filter(Files::exists).toList();
+
+        // Filter the list of possible locations based on whether they contain the required entrypoints
+        GameProviderHelper.FindResult result = GameProviderHelper.findFirst(existingAppLocations, new HashMap<>(), true, ENTRYPOINTS);
+
+        if (result == null || result.path == null) {
+            // Tell the user we couldn't find the app JAR.
+            String appLocationsString = appLocations.stream().map(p -> (String.format("* %s", Paths.get(p).toAbsolutePath().normalize())))
+                .collect(Collectors.joining("\n"));
+            
+            Log.error(LogCategory.GAME_PROVIDER, "Could not locate the application JAR! We looked in: \n" + appLocationsString);
+
+            return false;
+        }
+
+        this.appJar = result.path;
+
+        return true;
+    }
+
+    /*
+     * Add additional configuration to the FabricLauncher, but do not launch your
+     * app.
+     */
+    @Override
+    public void initialize(FabricLauncher launcher) {
+        TRANSFORMER.locateEntrypoints(launcher, appJar);
+    }
+
+    /*
+     * Return a GameTransformer that does extra modification on the app's JAR.
+     */
+    @Override
+    public GameTransformer getEntrypointTransformer() {
+        return TRANSFORMER;
+    }
+
+    /*
+     * Called after transformers were initialized and mods were detected and loaded
+     * (but not initialized).
+     */
+    @Override
+    public void unlockClassPath(FabricLauncher launcher) {
+        launcher.addToClassPath(appJar);
+    }
+
+    /*
+     * Launch the app in this function. This MUST be done via reflection.
+     */
+    @Override
+    public void launch(ClassLoader loader) {
+        try {
+            Class<?> main = loader.loadClass(this.getEntrypoint());
+            Method method = main.getMethod("main", String[].class);
+
+            method.invoke(null, (Object) this.arguments.toArray());
+        } catch (InvocationTargetException e) {
+            throw new FormattedException("App has crashed!", e.getCause());
+        } catch (ReflectiveOperationException e) {
+            throw new FormattedException("Failed to launch App", e);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+    @Override
+    public Arguments getArguments() {
+        return this.arguments;
+    }
+
+    @Override
+    public String[] getLaunchArguments(boolean sanitize) {
+        if (arguments == null) return new String[0];
+
+        String[] ret = arguments.toArray();
+        return ret;
+    }
+}

modLoader/src/main/java/com/elitemastereric/modloader/AppGameTransformer.java

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+package com.elitemastereric.modloader;
+
+import net.fabricmc.loader.impl.game.patch.GameTransformer;
+
+public class AppGameTransformer extends GameTransformer {
+    /*
+	 * @param className The class name,
+	 * @return The transformed class data.
+	 */
+    @Override
+    public byte[] transform(String name) {
+        return null;
+    }
+}

modLoader/src/main/java/com/elitemastereric/modloader/README.md

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+This is the app which performs the mod loading and allows for transformation of the target application.

modLoader/src/main/resources/META-INF/services/net.fabricmc.loader.impl.game.GameProvider

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+com.elitemastereric.modloader.AppGameProvider