Add documentation

2 files changed, 122 insertions, 0 deletions

diff --git a/agent/src/main/java/moe/nea/modernjava/agent/Pack200Retransformer.java b/agent/src/main/java/moe/nea/modernjava/agent/Pack200Retransformer.java
new file mode 100644
index 0000000..67480bf
--- /dev/null
+++ b/agent/src/main/java/moe/nea/modernjava/agent/Pack200Retransformer.java
@@ -0,0 +1,52 @@
+package moe.nea.modernjava.agent;
+
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.commons.ClassRemapper;
+import org.objectweb.asm.commons.Remapper;
+
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Transforms all classes such that they use dev.architectury.pack200.java instead of java.util.jar for Pack200 packing
+ * and unpacking. We cannot simply transform the jar on the classpath, since defining a package in the java directory
+ * is impossible in most versions of java, even from the boot class path. In theory this could be a custom class loader,
+ * but the java agent is far more reliable.
+ */
+public class Pack200Retransformer implements ClassFileTransformer {
+    // relocate("dev.architectury.pack200.java", "java.util.jar")
+    List<String> classes = Arrays.asList("AdaptiveCoding", "Attribute", "BandStructure", "ClassReader", "ClassWriter", "Code", "Coding", "CodingChooser", "CodingMethod", "ConstantPool", "Constants", "Driver", "DriverResource", "DriverResource_ja", "DriverResource_zh_CN", "FixedList", "Fixups", "Histogram", "Instruction", "NativeUnpack", "Pack200", "Pack200Adapter", "Pack200Plugin", "Package", "PackageReader", "PackageWriter", "PackerImpl", "PopulationCoding", "PropMap", "TLGlobals", "UnpackerImpl", "Utils");
+    String architecturyPackage = "dev/architectury/pack200/java/";
+    String javaPackage = "java/util/jar/";
+
+    public static void premain(String agentArgs, Instrumentation inst) {
+        inst.addTransformer(new Pack200Retransformer());
+    }
+
+    @Override
+    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
+        ClassReader reader = new ClassReader(classfileBuffer);
+        ClassWriter writer = new ClassWriter(reader, 0);
+        Remapper remapper = new Remapper() {
+            @Override
+            public String map(String internalName) {
+                if (internalName.startsWith(javaPackage)) {
+                    for (String aClass : classes) {
+                        if (internalName.equals(javaPackage + aClass) || (internalName.startsWith(javaPackage + aClass + "$")))
+                            return internalName.replace(javaPackage, architecturyPackage);
+                    }
+                }
+                return internalName;
+            }
+        };
+        ClassVisitor visitor = new ClassRemapper(writer, remapper);
+        reader.accept(visitor, 0);
+        return writer.toByteArray();
+    }
+}
diff --git a/agent/src/main/java/moe/nea/modernjava/agent/RelaunchEntryPoint.java b/agent/src/main/java/moe/nea/modernjava/agent/RelaunchEntryPoint.java
new file mode 100644
index 0000000..e39a677
--- /dev/null
+++ b/agent/src/main/java/moe/nea/modernjava/agent/RelaunchEntryPoint.java
@@ -0,0 +1,70 @@
+package moe.nea.modernjava.agent;
+
+import java.io.File;
+import java.lang.reflect.Method;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.Arrays;
+
+/**
+ * The main class for the new java runtime.
+ */
+public class RelaunchEntryPoint {
+    /**
+     * Logs things with a prefix to indicate it's coming from the new java runtime.
+     */
+    public static void log(String text) {
+        System.out.println("[MODERNJAVA] " + text);
+
+    }
+
+    /**
+     * Wrap {@link #setupLaunch(String[])} in a crash handler for logging.
+     */
+    public static void main(String[] args) {
+        log("This is modern java relaunch talking!");
+        try {
+            setupLaunch(args);
+        } catch (Throwable t) {
+            log("Encountered exception during relaunching");
+            t.printStackTrace();
+        }
+    }
+
+    private static void setupLaunch(String[] args) throws Exception {
+
+        // Check if old class loader can load java modules.
+        log("Original SQLException: " + Thread.currentThread().getContextClassLoader().loadClass("java.sql.SQLException"));
+
+        log("Setting up fake launch class loader");
+        ClassLoader urlClassLoader = new URLClassLoader(retrieveClassPath(), Thread.currentThread().getContextClassLoader());
+
+        log("Created fake url class loader");
+        Thread.currentThread().setContextClassLoader(urlClassLoader);
+        log("Handing off to Launch");
+
+        // Check if new class loader can load java modules.
+        log("LaunchClass ClassLoader SQLException: " + urlClassLoader.loadClass("java.sql.SQLException"));
+
+        // Load launch wrapper and check launch class loader
+        Class<?> launchClass = urlClassLoader.loadClass("net.minecraft.launchwrapper.Launch");
+        log("LaunchClass: " + launchClass);
+        log("LaunchClass ClassLoader: " + launchClass.getClassLoader());
+
+        // Hand off to launch wrapper
+        Method main = launchClass.getMethod("main", String[].class);
+        main.invoke(null, new Object[]{args});
+    }
+
+    private static URL[] retrieveClassPath() throws MalformedURLException {
+        String property = System.getProperty("modernjava.relaunchclasspath");
+        String[] split = property.split(File.pathSeparator);
+        URL[] urls = new URL[split.length];
+        for (int i = 0; i < split.length; i++) {
+            urls[i] = new File(split[i]).toURI().toURL();
+        }
+        log("Retrieved classpath: " + Arrays.toString(urls));
+        return urls;
+    }
+}