Add initial AccessWidener

2026-06-11 12:22:44 +02:00
parent e176b3bca8
commit 786257ad0e
15 changed files with 979 additions and 6 deletions
@@ -0,0 +1,149 @@
+/*
+ *   This file is a part of the SteamWar software.
+ *
+ *   Copyright (C) 2026 SteamWar.de-Serverteam
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU Affero 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 Affero General Public License for more details.
+ *
+ *   You should have received a copy of the GNU Affero General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package de.steamwar;
+
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassWriter;
+
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.Instrumentation;
+import java.lang.instrument.UnmodifiableClassException;
+import java.security.ProtectionDomain;
+import java.util.*;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.logging.Logger;
+import java.util.stream.Collectors;
+
+/**
+ * Transforms class bytecode to apply access widening rules.
+ * <p>
+ * Also monitors for new plugin ClassLoaders appearing (when plugins load after
+ * the agent attaches) and automatically picks up their .accesswidener files.
+ */
+public class WideningTransformer implements ClassFileTransformer {
+
+    private static final Logger LOG = Logger.getLogger("WidenerTransformer");
+
+    private final Instrumentation instrumentation;
+
+    /**
+     * All entries collected across all plugins. Thread-safe for concurrent plugin loads.
+     */
+    private final List<AccessWidenerEntry> entries = new CopyOnWriteArrayList<>();
+
+    /**
+     * ClassLoaders we have already scanned, to avoid re-scanning.
+     */
+    private final Set<ClassLoader> scannedLoaders = Collections.synchronizedSet(Collections.newSetFromMap(new IdentityHashMap<>()));
+
+    public WideningTransformer(Instrumentation instrumentation) {
+        this.instrumentation = instrumentation;
+    }
+
+    /**
+     * Add entries — used during initial scan before the transformer is registered.
+     */
+    public void addEntries(List<AccessWidenerEntry> newEntries) {
+        entries.addAll(newEntries);
+    }
+
+    // -------------------------------------------------------------------------
+    // ClassFileTransformer
+    // -------------------------------------------------------------------------
+
+    @Override
+    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
+
+        // Check for new plugin classloaders we haven't seen yet
+        if (loader != null && AccessWidenerScanner.isPluginClassLoader(loader) && scannedLoaders.add(loader)) {
+            onNewPluginClassLoader(loader);
+        }
+
+        // No entries for this class — skip transformation entirely
+        if (className == null) return classfileBuffer;
+        boolean relevant = entries.stream().anyMatch(e -> e.targets(className));
+        if (!relevant) return classfileBuffer;
+
+        // Apply widening via ASM
+        try {
+            ClassReader cr = new ClassReader(classfileBuffer);
+            ClassWriter cw = new ClassWriter(cr, 0);
+            cr.accept(new ClassTransformer(cw, className, entries), 0);
+            return cw.toByteArray();
+        } catch (Exception e) {
+            LOG.warning("[AccessWidener] Failed to transform " + className + ": " + e.getMessage());
+            return classfileBuffer;
+        }
+    }
+
+    // -------------------------------------------------------------------------
+    // New ClassLoader detection
+    // -------------------------------------------------------------------------
+
+    private void onNewPluginClassLoader(ClassLoader loader) {
+        List<AccessWidenerEntry> newEntries = AccessWidenerScanner.scanClassLoader(loader);
+        if (newEntries.isEmpty()) return;
+
+        entries.addAll(newEntries);
+        LOG.info("[AccessWidener] Picked up " + newEntries.size() + " new entr" + (newEntries.size() == 1 ? "y" : "ies") + " from " + loader);
+
+        // Retransform already-loaded classes that are now targeted
+        scheduleRetransform(newEntries);
+    }
+
+    /**
+     * Retransformation cannot be called from within a transform() call,
+     * so we dispatch it to a short-lived daemon thread.
+     */
+    private void scheduleRetransform(List<AccessWidenerEntry> newEntries) {
+        Set<String> targets = newEntries.stream().map(e -> e.target().replace('/', '.')).collect(Collectors.toSet());
+
+        Thread t = new Thread(() -> retransform(targets), "access-widener-retransform");
+        t.setDaemon(true);
+        t.start();
+    }
+
+    private void retransform(Set<String> dotNames) {
+        List<Class> toRetransform = Arrays.stream(instrumentation.getAllLoadedClasses())
+                .filter(c -> dotNames.contains(c.getName()))
+                .filter(instrumentation::isModifiableClass)
+                .collect(Collectors.toList());
+
+        if (toRetransform.isEmpty()) return;
+
+        LOG.info("[AccessWidener] Retransforming " + toRetransform.size() + " class(es).");
+        List<String> failed = new ArrayList<>();
+
+        for (Class<?> clazz : toRetransform) {
+            try {
+                instrumentation.retransformClasses(clazz);
+            } catch (UnmodifiableClassException | UnsupportedOperationException e) {
+                failed.add(clazz.getName());
+            }
+        }
+
+        if (!failed.isEmpty()) {
+            LOG.warning("[AccessWidener] The following classes were already loaded before the agent"
+                    + " and cannot be retransformed. Add -javaagent: to your start script"
+                    + " to fix this:");
+            failed.forEach(name -> LOG.warning("  - " + name));
+        }
+    }
+}