Add cursed code to allow replacing Via* at runtime

src/main/java/net/raphimc/viaproxy/ViaProxy.java

@@ -49,6 +49,7 @@ import net.raphimc.viaproxy.tasks.AccountRefreshTask;
 import net.raphimc.viaproxy.tasks.LoaderTask;
 import net.raphimc.viaproxy.tasks.UpdateCheckTask;
 import net.raphimc.viaproxy.ui.ViaProxyUI;
+import net.raphimc.viaproxy.util.ClassLoaderPriorityUtil;
 import net.raphimc.viaproxy.util.logging.Logger;
 
 import javax.swing.*;
@@ -116,6 +117,7 @@ public class ViaProxy {
             }
         }
 
+        ClassLoaderPriorityUtil.loadOverridingJars();
         loadNetty();
         saveManager = new SaveManager();
         PluginManager.loadPlugins();

src/main/java/net/raphimc/viaproxy/util/ClassLoaderPriorityUtil.java

@@ -0,0 +1,74 @@
+/*
+ * This file is part of ViaProxy - https://github.com/RaphiMC/ViaProxy
+ * Copyright (C) 2023 RK_01/RaphiMC and contributors
+ *
+ * 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package net.raphimc.viaproxy.util;
+
+import net.lenni0451.reflect.Classes;
+import net.lenni0451.reflect.stream.RStream;
+import net.raphimc.viaproxy.util.logging.Logger;
+
+import java.io.File;
+import java.net.URL;
+import java.util.List;
+
+public class ClassLoaderPriorityUtil {
+
+    public static void loadOverridingJars() {
+        final File jarsFolder = new File("jars");
+        if (jarsFolder.isDirectory()) {
+            for (File file : jarsFolder.listFiles()) {
+                try {
+                    if (file.getName().endsWith(".jar")) {
+                        loadWithHighestPriority(file.toURI().toURL());
+                        Logger.LOGGER.info("Loaded overriding jar " + file.getName());
+                    }
+                } catch (Throwable e) {
+                    Logger.LOGGER.error("Failed to load overriding jar " + file.getName(), e);
+                }
+            }
+        }
+    }
+
+    private static void loadWithHighestPriority(final URL url) {
+        // First add the URl into the classpath
+        final Object ucp = RStream.of(Thread.currentThread().getContextClassLoader()).withSuper().fields().by("ucp").get();
+        RStream.of(ucp).methods().by("addURL", URL.class).invokeArgs(url);
+
+        // Then move the URL to the front of the classpath, so it gets loaded first
+        final List<Object> ucpPath = RStream.of(ucp).fields().by("path").get();
+        ucpPath.add(0, ucpPath.remove(ucpPath.size() - 1));
+
+        // Force the ClassLoader to populate the whole list of Loaders (Its lazy loaded by default)
+        if (ClassLoaderPriorityUtil.class.getClassLoader().getResourceAsStream("I_HOPE_THIS_FILE_NEVER_EXISTS_" + System.nanoTime()) != null) {
+            throw new IllegalStateException("The file that should never exist exists! Please report this to the ViaProxy developers!");
+        }
+
+        // Move the loader for that URL to the front of the list
+        final Class<?> jarLoaderClazz = Classes.forName(ucp.getClass().getName() + "$JarLoader");
+        final List<Object> loaders = RStream.of(ucp).fields().by("loaders").get();
+        for (Object loader : loaders) {
+            if (jarLoaderClazz.equals(loader.getClass())) {
+                final URL loaderUrl = RStream.of(loader).fields().filter(URL.class).by(0).get();
+                if (url.equals(loaderUrl)) {
+                    loaders.add(0, loaders.remove(loaders.size() - 1));
+                    break;
+                }
+            }
+        }
+    }
+
+}