Fix #1241: Use javaagent patch log4j

minecraft/libraries/log4j-patch/build.gradle

@@ -1,15 +1,21 @@
 version '1.0'
 
+sourceSets.create("agent") {
+    java {
+        srcDir 'src/main/agent'
+    }
+}
+
 dependencies {
     compileOnly group: 'org.apache.logging.log4j', name: 'log4j-core', version: '2.0-beta9'
 }
 
-tasks.compileJava {
+tasks.withType(JavaCompile) {
     sourceCompatibility = 8
     targetCompatibility = 8
 
     doLast {
-        FileTree tree = fileTree('build/classes/java/main')
+        FileTree tree = fileTree('build/classes/java')
         tree.include '**/*.class'
         tree.each {
             RandomAccessFile rf = new RandomAccessFile(it, "rw")
@@ -20,27 +26,27 @@ tasks.compileJava {
     }
 }
 
-task patchJar(type: Jar) {
+task agentJar(type: Jar) {
     dependsOn(tasks.compileJava)
 
-    baseName = 'log4j-patch'
+    baseName = 'log4j-patch-agent'
 
-    from(sourceSets.main.output) {
-        include('**/JndiLookup.class')
+    manifest {
+        attributes 'Premain-Class': 'org.glavo.log4j.patch.agent.Log4jAgent'
     }
-}
-
-task patchBeta9Jar(type: Jar) {
-    dependsOn(tasks.compileJava)
-
-    baseName = 'log4j-patch-beta9'
 
+    from(sourceSets.agent.output)
     from(sourceSets.main.output) {
-        include '**/Interpolator.class'
+        includeEmptyDirs = false
+
+        eachFile {
+            it.path = "org/glavo/log4j/patch/agent/${it.name}.bin"
+        }
     }
 }
 
 tasks.jar {
     enabled = false
-    dependsOn patchJar, patchBeta9Jar
+    dependsOn agentJar
 }
+

minecraft/libraries/log4j-patch/src/main/agent/org/glavo/log4j/patch/agent/Log4jAgent.java

@@ -0,0 +1,71 @@
+package org.glavo.log4j.patch.agent;
+
+import java.io.InputStream;
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.lang.instrument.Instrumentation;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.ProtectionDomain;
+import java.util.Arrays;
+
+public final class Log4jAgent {
+    static final String JNDI_LOOKUP_CLASS_NAME = "org/apache/logging/log4j/core/lookup/JndiLookup";
+    static final String INTERPOLATOR_CLASS_NAME = "org/apache/logging/log4j/core/lookup/Interpolator";
+
+    static final byte[] INTERPOLATOR_CLASS_SHA = {53, 103, 16, 123, 51, 29, 65, -70, -32, 71, -11, 7, 114, -15, 72, 127, 40, -38, 35, 18};
+
+    static boolean isBeta = false;
+
+    private static byte[] loadResource(String name) {
+        try {
+            try (InputStream input = Log4jAgent.class.getResourceAsStream(name)) {
+                if (input == null) {
+                    throw new AssertionError(name + " not found");
+                }
+                int available = input.available();
+                if (available <= 0) {
+                    throw new AssertionError();
+                }
+                byte[] res = new byte[available];
+                if (input.read(res) != available) {
+                    throw new AssertionError();
+                }
+
+                return res;
+            }
+        } catch (Exception ex) {
+            throw new InternalError(ex);
+        }
+    }
+
+    public static void premain(String agentArgs, Instrumentation inst) throws Exception {
+        if ("true".equals(agentArgs)) {
+            isBeta = true;
+        }
+        inst.addTransformer(new Transformer());
+    }
+
+    private static final class Transformer implements ClassFileTransformer {
+
+        @Override
+        public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
+            if (!isBeta && JNDI_LOOKUP_CLASS_NAME.equals(className)) {
+                return loadResource("JndiLookup.class.bin");
+            }
+            if (isBeta && INTERPOLATOR_CLASS_NAME.equals(className)) {
+                try {
+                    MessageDigest sha1 = MessageDigest.getInstance("SHA-1");
+                    sha1.update(classfileBuffer);
+                    if (Arrays.equals(INTERPOLATOR_CLASS_SHA, sha1.digest())) {
+                        return loadResource("Interpolator.class.bin");
+                    }
+                } catch (NoSuchAlgorithmException e) {
+                    throw new InternalError(e);
+                }
+            }
+            return null;
+        }
+    }
+
+}