# HG changeset patch
# User Jaroslav Tulach <jaroslav.tulach@apidesign.org>
# Date 1383747354 -3600
# Node ID 86aabecda7a373dadbed93e6e4793c65e8fe9e9f
# Parent  4a93f2679691d4ae119a4860f96a4c7226bb0a40
Introducing Agent-Class to allow java.lang.instrument-like transforms of the @JavaScriptBody annotation

diff -r 4a93f2679691 -r 86aabecda7a3 boot/pom.xml
--- a/boot/pom.xml	Tue Nov 05 23:06:32 2013 +0100
+++ b/boot/pom.xml	Wed Nov 06 15:15:54 2013 +0100
@@ -21,6 +21,11 @@
           <plugin>
               <groupId>org.apache.felix</groupId>
               <artifactId>maven-bundle-plugin</artifactId>
+              <configuration>
+                  <instructions>
+                      <Agent-Class>org.apidesign.html.boot.impl.JsAgent</Agent-Class>
+                  </instructions>
+              </configuration>
           </plugin>
          <plugin>
             <groupId>org.apache.maven.plugins</groupId>
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/main/java/org/apidesign/html/boot/impl/FnContext.java
--- a/boot/src/main/java/org/apidesign/html/boot/impl/FnContext.java	Tue Nov 05 23:06:32 2013 +0100
+++ b/boot/src/main/java/org/apidesign/html/boot/impl/FnContext.java	Wed Nov 06 15:15:54 2013 +0100
@@ -32,16 +32,16 @@
 public final class FnContext implements Closeable {
     private static final Logger LOG = Logger.getLogger(FnContext.class.getName());
 
-    private Fn.Presenter prev;
+    private Object prev;
     private FnContext(Fn.Presenter p) {
         this.prev = p;
     }
 
     @Override
     public void close() throws IOException {
-        if (prev != null) {
-            currentPresenter(prev);
-            prev = null;
+        if (prev != this) {
+            currentPresenter((Fn.Presenter)prev);
+            prev = this;
         }
     }
 /*
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/main/java/org/apidesign/html/boot/impl/FnUtils.java
--- a/boot/src/main/java/org/apidesign/html/boot/impl/FnUtils.java	Tue Nov 05 23:06:32 2013 +0100
+++ b/boot/src/main/java/org/apidesign/html/boot/impl/FnUtils.java	Wed Nov 06 15:15:54 2013 +0100
@@ -20,6 +20,7 @@
  */
 package org.apidesign.html.boot.impl;
 
+import java.io.Closeable;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.Reader;
@@ -28,23 +29,41 @@
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.List;
+import java.util.concurrent.Callable;
 import org.apidesign.html.boot.spi.Fn;
+import org.objectweb.asm.AnnotationVisitor;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.Label;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+import org.objectweb.asm.Type;
+import org.objectweb.asm.signature.SignatureReader;
+import org.objectweb.asm.signature.SignatureVisitor;
+import org.objectweb.asm.signature.SignatureWriter;
 
 /**
  *
  * @author Jaroslav Tulach <jtulach@netbeans.org>
  */
-public final class FnUtils {
+public final class FnUtils implements Fn.Presenter {
     
     private FnUtils() {
     }
     
-    public static Fn define(Class<?> caller, String code, String... names) {
-        return FnContext.currentPresenter().defineFn(code, names);
-    }
-    
     public static boolean isJavaScriptCapable(ClassLoader l) {
-        return l instanceof JsClassLoader;
+        if (l instanceof JsClassLoader) {
+            return true;
+        }
+        Class<?> clazz;
+        try (Closeable c = Fn.activate(new FnUtils())) {
+            clazz = Class.forName(Test.class.getName(), true, l);
+            final Object is = ((Callable<?>)clazz.newInstance()).call();
+            return Boolean.TRUE.equals(is);
+        } catch (Exception ex) {
+            return false;
+        }
     }
     
     public static boolean isValid(Fn fn) {
@@ -100,7 +119,7 @@
         }.parse(body);
     }
 
-    static void loadScript(JsClassLoader jcl, String resource) {
+    static void loadScript(ClassLoader jcl, String resource) {
         final InputStream script = jcl.getResourceAsStream(resource);
         if (script == null) {
             throw new NullPointerException("Can't find " + resource);
@@ -109,7 +128,7 @@
             Reader isr = null;
             try {
                 isr = new InputStreamReader(script, "UTF-8");
-                jcl.loadScript(isr);
+                FnContext.currentPresenter().loadScript(isr);
             } finally {
                 if (isr != null) {
                     isr.close();
@@ -119,4 +138,429 @@
             throw new IllegalStateException("Can't execute " + resource, ex);
         } 
     }
+
+    @Override
+    public Fn defineFn(String code, String... names) {
+        return new TrueFn();
+    }
+
+    @Override
+    public void displayPage(URL page, Runnable onPageLoad) {
+    }
+
+    @Override
+    public void loadScript(Reader code) throws Exception {
+    }
+    
+    private static final class FindInClass extends ClassVisitor {
+        private String name;
+        private int found;
+        private ClassLoader loader;
+
+        public FindInClass(ClassLoader l, ClassVisitor cv) {
+            super(Opcodes.ASM4, cv);
+            this.loader = l;
+        }
+
+        @Override
+        public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {
+            this.name = name;
+            super.visit(version, access, name, signature, superName, interfaces);
+        }
+
+        @Override
+        public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
+            if ("Lnet/java/html/js/JavaScriptResource;".equals(desc)) {
+                return new LoadResource();
+            }
+            return super.visitAnnotation(desc, visible);
+        }
+
+        @Override
+        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
+            return new FindInMethod(access, name, desc,
+                    super.visitMethod(access & (~Opcodes.ACC_NATIVE), name, desc, signature, exceptions)
+            );
+        }
+
+        private final class FindInMethod extends MethodVisitor {
+
+            private final String name;
+            private final String desc;
+            private final int access;
+            private List<String> args;
+            private String body;
+            private boolean bodyGenerated;
+
+            public FindInMethod(int access, String name, String desc, MethodVisitor mv) {
+                super(Opcodes.ASM4, mv);
+                this.access = access;
+                this.name = name;
+                this.desc = desc;
+            }
+
+            @Override
+            public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
+                if ("Lnet/java/html/js/JavaScriptBody;".equals(desc) // NOI18N
+                        || "Lorg/apidesign/bck2brwsr/core/JavaScriptBody;".equals(desc) // NOI18N
+                        ) {
+                    found++;
+                    return new FindInAnno();
+                }
+                return super.visitAnnotation(desc, visible);
+            }
+
+            private void generateJSBody(List<String> args, String body) {
+                this.args = args;
+                this.body = body;
+            }
+
+            @Override
+            public void visitCode() {
+                if (body == null) {
+                    return;
+                }
+                generateBody();
+            }
+
+            private boolean generateBody() {
+                if (bodyGenerated) {
+                    return false;
+                }
+                bodyGenerated = true;
+
+                super.visitFieldInsn(
+                        Opcodes.GETSTATIC, FindInClass.this.name,
+                        "$$fn$$" + name + "_" + found,
+                        "Lorg/apidesign/html/boot/spi/Fn;"
+                );
+                super.visitInsn(Opcodes.DUP);
+                super.visitMethodInsn(
+                        Opcodes.INVOKESTATIC,
+                        "org/apidesign/html/boot/spi/Fn", "isValid",
+                        "(Lorg/apidesign/html/boot/spi/Fn;)Z"
+                );
+                Label ifNotNull = new Label();
+                super.visitJumpInsn(Opcodes.IFNE, ifNotNull);
+
+                // init Fn
+                super.visitInsn(Opcodes.POP);
+                super.visitLdcInsn(Type.getObjectType(FindInClass.this.name));
+                super.visitLdcInsn(body);
+                super.visitIntInsn(Opcodes.SIPUSH, args.size());
+                super.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/String");
+                boolean needsVM = false;
+                for (int i = 0; i < args.size(); i++) {
+                    assert !needsVM;
+                    String argName = args.get(i);
+                    needsVM = "vm".equals(argName);
+                    super.visitInsn(Opcodes.DUP);
+                    super.visitIntInsn(Opcodes.BIPUSH, i);
+                    super.visitLdcInsn(argName);
+                    super.visitInsn(Opcodes.AASTORE);
+                }
+                super.visitMethodInsn(Opcodes.INVOKESTATIC,
+                        "org/apidesign/html/boot/spi/Fn", "define",
+                        "(Ljava/lang/Class;Ljava/lang/String;[Ljava/lang/String;)Lorg/apidesign/html/boot/spi/Fn;"
+                );
+                super.visitInsn(Opcodes.DUP);
+                super.visitFieldInsn(
+                        Opcodes.PUTSTATIC, FindInClass.this.name,
+                        "$$fn$$" + name + "_" + found,
+                        "Lorg/apidesign/html/boot/spi/Fn;"
+                );
+                // end of Fn init
+
+                super.visitLabel(ifNotNull);
+
+                final int offset;
+                if ((access & Opcodes.ACC_STATIC) == 0) {
+                    offset = 1;
+                    super.visitIntInsn(Opcodes.ALOAD, 0);
+                } else {
+                    offset = 0;
+                    super.visitInsn(Opcodes.ACONST_NULL);
+                }
+
+                super.visitIntInsn(Opcodes.SIPUSH, args.size());
+                super.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Object");
+
+                class SV extends SignatureVisitor {
+
+                    private boolean nowReturn;
+                    private Type returnType;
+                    private int index;
+                    private int loadIndex = offset;
+
+                    public SV() {
+                        super(Opcodes.ASM4);
+                    }
+
+                    @Override
+                    public void visitBaseType(char descriptor) {
+                        final Type t = Type.getType("" + descriptor);
+                        if (nowReturn) {
+                            returnType = t;
+                            return;
+                        }
+                        FindInMethod.super.visitInsn(Opcodes.DUP);
+                        FindInMethod.super.visitIntInsn(Opcodes.SIPUSH, index++);
+                        FindInMethod.super.visitVarInsn(t.getOpcode(Opcodes.ILOAD), loadIndex++);
+                        String factory;
+                        switch (descriptor) {
+                            case 'I':
+                                factory = "java/lang/Integer";
+                                break;
+                            case 'J':
+                                factory = "java/lang/Long";
+                                loadIndex++;
+                                break;
+                            case 'S':
+                                factory = "java/lang/Short";
+                                break;
+                            case 'F':
+                                factory = "java/lang/Float";
+                                break;
+                            case 'D':
+                                factory = "java/lang/Double";
+                                loadIndex++;
+                                break;
+                            case 'Z':
+                                factory = "java/lang/Boolean";
+                                break;
+                            case 'C':
+                                factory = "java/lang/Character";
+                                break;
+                            case 'B':
+                                factory = "java/lang/Byte";
+                                break;
+                            default:
+                                throw new IllegalStateException(t.toString());
+                        }
+                        FindInMethod.super.visitMethodInsn(Opcodes.INVOKESTATIC,
+                                factory, "valueOf", "(" + descriptor + ")L" + factory + ";"
+                        );
+                        FindInMethod.super.visitInsn(Opcodes.AASTORE);
+                    }
+
+                    @Override
+                    public SignatureVisitor visitArrayType() {
+                        if (nowReturn) {
+                            throw new IllegalStateException("Not supported yet");
+                        }
+                        loadObject();
+                        return new SignatureWriter();
+                    }
+
+                    @Override
+                    public void visitClassType(String name) {
+                        if (nowReturn) {
+                            returnType = Type.getObjectType(name);
+                            return;
+                        }
+                        loadObject();
+                    }
+
+                    @Override
+                    public SignatureVisitor visitReturnType() {
+                        nowReturn = true;
+                        return this;
+                    }
+
+                    private void loadObject() {
+                        FindInMethod.super.visitInsn(Opcodes.DUP);
+                        FindInMethod.super.visitIntInsn(Opcodes.SIPUSH, index++);
+                        FindInMethod.super.visitVarInsn(Opcodes.ALOAD, loadIndex++);
+                        FindInMethod.super.visitInsn(Opcodes.AASTORE);
+                    }
+
+                }
+                SV sv = new SV();
+                SignatureReader sr = new SignatureReader(desc);
+                sr.accept(sv);
+
+                if (needsVM) {
+                    FindInMethod.super.visitInsn(Opcodes.DUP);
+                    FindInMethod.super.visitIntInsn(Opcodes.SIPUSH, sv.index);
+                    int lastSlash = FindInClass.this.name.lastIndexOf('/');
+                    String jsCallbacks = FindInClass.this.name.substring(0, lastSlash + 1) + "$JsCallbacks$";
+                    FindInMethod.super.visitFieldInsn(Opcodes.GETSTATIC, jsCallbacks, "VM", "L" + jsCallbacks + ";");
+                    FindInMethod.super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, jsCallbacks, "current", "()L" + jsCallbacks + ";");
+                    FindInMethod.super.visitInsn(Opcodes.AASTORE);
+                }
+
+                super.visitMethodInsn(Opcodes.INVOKEVIRTUAL,
+                        "org/apidesign/html/boot/spi/Fn", "invoke", "(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;"
+                );
+                switch (sv.returnType.getSort()) {
+                    case Type.VOID:
+                        super.visitInsn(Opcodes.RETURN);
+                        break;
+                    case Type.ARRAY:
+                    case Type.OBJECT:
+                        super.visitTypeInsn(Opcodes.CHECKCAST, sv.returnType.getInternalName());
+                        super.visitInsn(Opcodes.ARETURN);
+                        break;
+                    case Type.BOOLEAN:
+                        super.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Boolean");
+                        super.visitMethodInsn(Opcodes.INVOKEVIRTUAL,
+                                "java/lang/Boolean", "booleanValue", "()Z"
+                        );
+                        super.visitInsn(Opcodes.IRETURN);
+                        break;
+                    default:
+                        super.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
+                        super.visitMethodInsn(Opcodes.INVOKEVIRTUAL,
+                                "java/lang/Number", sv.returnType.getClassName() + "Value", "()" + sv.returnType.getDescriptor()
+                        );
+                        super.visitInsn(sv.returnType.getOpcode(Opcodes.IRETURN));
+                }
+                return true;
+            }
+
+            @Override
+            public void visitEnd() {
+                super.visitEnd();
+                if (body != null) {
+                    if (generateBody()) {
+                        // native method
+                        super.visitMaxs(1, 0);
+                    }
+                    FindInClass.this.visitField(
+                            Opcodes.ACC_PRIVATE | Opcodes.ACC_STATIC,
+                            "$$fn$$" + name + "_" + found,
+                            "Lorg/apidesign/html/boot/spi/Fn;",
+                            null, null
+                    );
+                }
+            }
+
+            private final class FindInAnno extends AnnotationVisitor {
+
+                private List<String> args = new ArrayList<String>();
+                private String body;
+                private boolean javacall = false;
+
+                public FindInAnno() {
+                    super(Opcodes.ASM4);
+                }
+
+                @Override
+                public void visit(String name, Object value) {
+                    if (name == null) {
+                        args.add((String) value);
+                        return;
+                    }
+                    if (name.equals("javacall")) { // NOI18N
+                        javacall = (Boolean) value;
+                        return;
+                    }
+                    assert name.equals("body");
+                    body = (String) value;
+                }
+
+                @Override
+                public AnnotationVisitor visitArray(String name) {
+                    return this;
+                }
+
+                @Override
+                public void visitEnd() {
+                    if (body != null) {
+                        if (javacall) {
+                            body = callback(body);
+                            args.add("vm");
+                        }
+                        generateJSBody(args, body);
+                    }
+                }
+            }
+        }
+
+        private final class LoadResource extends AnnotationVisitor {
+
+            public LoadResource() {
+                super(Opcodes.ASM4);
+            }
+
+            @Override
+            public void visit(String attrName, Object value) {
+                String relPath = (String) value;
+                if (relPath.startsWith("/")) {
+                    loadScript(loader, relPath);
+                } else {
+                    int last = name.lastIndexOf('/');
+                    String fullPath = name.substring(0, last + 1) + relPath;
+                    loadScript(loader, fullPath);
+                }
+            }
+        }
+    }
+
+    private static class ClassWriterEx extends ClassWriter {
+
+        private ClassLoader loader;
+
+        public ClassWriterEx(ClassLoader l, ClassReader classReader, int flags) {
+            super(classReader, flags);
+            this.loader = l;
+        }
+
+        @Override
+        protected String getCommonSuperClass(final String type1, final String type2) {
+            Class<?> c, d;
+            try {
+                c = Class.forName(type1.replace('/', '.'), false, loader);
+                d = Class.forName(type2.replace('/', '.'), false, loader);
+            } catch (Exception e) {
+                throw new RuntimeException(e.toString());
+            }
+            if (c.isAssignableFrom(d)) {
+                return type1;
+            }
+            if (d.isAssignableFrom(c)) {
+                return type2;
+            }
+            if (c.isInterface() || d.isInterface()) {
+                return "java/lang/Object";
+            } else {
+                do {
+                    c = c.getSuperclass();
+                } while (!c.isAssignableFrom(d));
+                return c.getName().replace('.', '/');
+            }
+        }
+    }
+
+    static byte[] transform(ClassLoader loader, byte[] arr) {
+        ClassReader cr = new ClassReader(arr) {
+            // to allow us to compile with -profile compact1 on 
+            // JDK8 while processing the class as JDK7, the highest
+            // class format asm 4.1 understands to
+            @Override
+            public short readShort(int index) {
+                short s = super.readShort(index);
+                if (index == 6 && s > Opcodes.V1_7) {
+                    return Opcodes.V1_7;
+                }
+                return s;
+            }
+        };
+        FindInClass tst = new FindInClass(loader, null);
+        cr.accept(tst, 0);
+        if (tst.found > 0) {
+            ClassWriter w = new ClassWriterEx(loader, cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);
+            FindInClass fic = new FindInClass(loader, w);
+            cr.accept(fic, 0);
+            arr = w.toByteArray();
+        }
+        return arr;
+    }
+
+    private static final class TrueFn extends Fn {
+        @Override
+        public Object invoke(Object thiz, Object... args) throws Exception {
+            return Boolean.TRUE;
+        }
+    } // end of TrueFn
 }
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/main/java/org/apidesign/html/boot/impl/JsAgent.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/boot/src/main/java/org/apidesign/html/boot/impl/JsAgent.java	Wed Nov 06 15:15:54 2013 +0100
@@ -0,0 +1,45 @@
+/**
+ * HTML via Java(tm) Language Bindings
+ * Copyright (C) 2013 Jaroslav Tulach <jaroslav.tulach@apidesign.org>
+ *
+ * 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, version 2 of the License.
+ *
+ * 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. apidesign.org
+ * designates this particular file as subject to the
+ * "Classpath" exception as provided by apidesign.org
+ * in the License file that accompanied this code.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. Look for COPYING file in the top folder.
+ * If not, see http://wiki.apidesign.org/wiki/GPLwithClassPathException
+ */
+package org.apidesign.html.boot.impl;
+
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+
+/**
+ *
+ * @author Jaroslav Tulach <jtulach@netbeans.org>
+ */
+public final class JsAgent implements ClassFileTransformer {
+    public static void agentmain(String args, Instrumentation instr) {
+        instr.addTransformer(new JsAgent());
+    }
+
+    @Override
+    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
+        try {
+            return FnUtils.transform(loader, classfileBuffer);
+        } catch (Exception ex) {
+            return classfileBuffer;
+        }
+    }
+}
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/main/java/org/apidesign/html/boot/impl/JsClassLoader.java
--- a/boot/src/main/java/org/apidesign/html/boot/impl/JsClassLoader.java	Tue Nov 05 23:06:32 2013 +0100
+++ b/boot/src/main/java/org/apidesign/html/boot/impl/JsClassLoader.java	Wed Nov 06 15:15:54 2013 +0100
@@ -25,20 +25,7 @@
 import java.io.InputStream;
 import java.io.Reader;
 import java.net.URL;
-import java.util.ArrayList;
 import java.util.Enumeration;
-import java.util.List;
-import org.objectweb.asm.AnnotationVisitor;
-import org.objectweb.asm.ClassReader;
-import org.objectweb.asm.ClassVisitor;
-import org.objectweb.asm.ClassWriter;
-import org.objectweb.asm.Label;
-import org.objectweb.asm.MethodVisitor;
-import org.objectweb.asm.Opcodes;
-import org.objectweb.asm.Type;
-import org.objectweb.asm.signature.SignatureReader;
-import org.objectweb.asm.signature.SignatureVisitor;
-import org.objectweb.asm.signature.SignatureWriter;
 
 /** 
  *
@@ -102,27 +89,7 @@
                 }
                 is.close();
                 is = null;
-                ClassReader cr = new ClassReader(arr) {
-                    // to allow us to compile with -profile compact1 on 
-                    // JDK8 while processing the class as JDK7, the highest
-                    // class format asm 4.1 understands to
-                    @Override
-                    public short readShort(int index) {
-                        short s = super.readShort(index);
-                        if (index == 6 && s > Opcodes.V1_7) {
-                            return Opcodes.V1_7;
-                        }
-                        return s;
-                    }
-                };
-                FindInClass tst = new FindInClass(null);
-                cr.accept(tst, 0);
-                if (tst.found > 0) {
-                    ClassWriter w = new ClassWriterEx(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);
-                    FindInClass fic = new FindInClass(w);
-                    cr.accept(fic, 0);
-                    arr = w.toByteArray();
-                }
+                arr = FnUtils.transform(JsClassLoader.this, arr);
                 if (arr != null) {
                     return defineClass(name, arr, 0, arr.length);
                 }
@@ -141,363 +108,4 @@
     
     protected abstract Fn defineFn(String code, String... names);
     protected abstract void loadScript(Reader code) throws Exception;
-    
-    private final class FindInClass extends ClassVisitor {
-        private String name;
-        private int found;
-        
-        public FindInClass(ClassVisitor cv) {
-            super(Opcodes.ASM4, cv);
-        }
-
-        @Override
-        public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {
-            this.name = name;
-            super.visit(version, access, name, signature, superName, interfaces);
-        }
-
-        @Override
-        public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
-            if ("Lnet/java/html/js/JavaScriptResource;".equals(desc)) {
-                return new LoadResource();
-            }
-            return super.visitAnnotation(desc, visible);
-        }
-        
-
-        @Override
-        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
-            return new FindInMethod(access, name, desc,
-                super.visitMethod(access & (~Opcodes.ACC_NATIVE), name, desc, signature, exceptions)
-            );
-        }
-        
-        private final class FindInMethod extends MethodVisitor {
-            private final String name;
-            private final String desc;
-            private final int access;
-            private List<String> args;
-            private String body;
-            private boolean bodyGenerated;
-            
-            public FindInMethod(int access, String name, String desc, MethodVisitor mv) {
-                super(Opcodes.ASM4, mv);
-                this.access = access;
-                this.name = name;
-                this.desc = desc;
-            }
-
-            @Override
-            public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
-                if (
-                    "Lnet/java/html/js/JavaScriptBody;".equals(desc) // NOI18N
-                    || "Lorg/apidesign/bck2brwsr/core/JavaScriptBody;".equals(desc) // NOI18N
-                ) {
-                    found++;
-                    return new FindInAnno();
-                }
-                return super.visitAnnotation(desc, visible);
-            }
-
-            private void generateJSBody(List<String> args, String body) {
-                this.args = args;
-                this.body = body;
-            }
-            
-            @Override
-            public void visitCode() {
-                if (body == null) {
-                    return;
-                } 
-                generateBody();
-            }
-            
-            private boolean generateBody() {
-                if (bodyGenerated) {
-                    return false;
-                }
-                bodyGenerated = true;
-                
-                super.visitFieldInsn(
-                    Opcodes.GETSTATIC, FindInClass.this.name, 
-                    "$$fn$$" + name + "_" + found, 
-                    "Lorg/apidesign/html/boot/spi/Fn;"
-                );
-                super.visitInsn(Opcodes.DUP);
-                super.visitMethodInsn(
-                    Opcodes.INVOKESTATIC, 
-                    "org/apidesign/html/boot/impl/FnUtils", "isValid", 
-                    "(Lorg/apidesign/html/boot/spi/Fn;)Z"
-                );
-                Label ifNotNull = new Label();
-                super.visitJumpInsn(Opcodes.IFNE, ifNotNull);
-                
-                // init Fn
-                super.visitInsn(Opcodes.POP);
-                super.visitLdcInsn(Type.getObjectType(FindInClass.this.name));
-                super.visitLdcInsn(body);
-                super.visitIntInsn(Opcodes.SIPUSH, args.size());
-                super.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/String");
-                boolean needsVM = false;
-                for (int i = 0; i < args.size(); i++) {
-                    assert !needsVM;
-                    String argName = args.get(i);
-                    needsVM = "vm".equals(argName);
-                    super.visitInsn(Opcodes.DUP);
-                    super.visitIntInsn(Opcodes.BIPUSH, i);
-                    super.visitLdcInsn(argName);
-                    super.visitInsn(Opcodes.AASTORE);
-                }
-                super.visitMethodInsn(Opcodes.INVOKESTATIC, 
-                    "org/apidesign/html/boot/impl/FnUtils", "define", 
-                    "(Ljava/lang/Class;Ljava/lang/String;[Ljava/lang/String;)Lorg/apidesign/html/boot/spi/Fn;"
-                );
-                super.visitInsn(Opcodes.DUP);
-                super.visitFieldInsn(
-                    Opcodes.PUTSTATIC, FindInClass.this.name, 
-                    "$$fn$$" + name + "_" + found, 
-                    "Lorg/apidesign/html/boot/spi/Fn;"
-                );
-                // end of Fn init
-                
-                super.visitLabel(ifNotNull);
-                
-                final int offset;
-                if ((access & Opcodes.ACC_STATIC) == 0) {
-                    offset = 1;
-                    super.visitIntInsn(Opcodes.ALOAD, 0);
-                } else {
-                    offset = 0;
-                    super.visitInsn(Opcodes.ACONST_NULL);
-                }
-                
-                super.visitIntInsn(Opcodes.SIPUSH, args.size());
-                super.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Object");
-                
-                class SV extends SignatureVisitor {
-                    private boolean nowReturn;
-                    private Type returnType;
-                    private int index;
-                    private int loadIndex = offset;
-                    
-                    public SV() {
-                        super(Opcodes.ASM4);
-                    }
-                    
-                    @Override
-                    public void visitBaseType(char descriptor) {
-                        final Type t = Type.getType("" + descriptor);
-                        if (nowReturn) {
-                            returnType = t;
-                            return;
-                        }
-                        FindInMethod.super.visitInsn(Opcodes.DUP);
-                        FindInMethod.super.visitIntInsn(Opcodes.SIPUSH, index++);
-                        FindInMethod.super.visitVarInsn(t.getOpcode(Opcodes.ILOAD), loadIndex++);
-                        String factory;
-                        switch (descriptor) {
-                        case 'I': factory = "java/lang/Integer"; break;
-                        case 'J': factory = "java/lang/Long"; loadIndex++; break;
-                        case 'S': factory = "java/lang/Short"; break;
-                        case 'F': factory = "java/lang/Float"; break;
-                        case 'D': factory = "java/lang/Double"; loadIndex++; break;
-                        case 'Z': factory = "java/lang/Boolean"; break;
-                        case 'C': factory = "java/lang/Character"; break;
-                        case 'B': factory = "java/lang/Byte"; break;
-                        default: throw new IllegalStateException(t.toString());
-                        }
-                        FindInMethod.super.visitMethodInsn(Opcodes.INVOKESTATIC,
-                            factory, "valueOf", "(" + descriptor + ")L" + factory + ";"
-                        );
-                        FindInMethod.super.visitInsn(Opcodes.AASTORE);
-                    }
-
-                    @Override
-                    public SignatureVisitor visitArrayType() {
-                        if (nowReturn) {
-                            throw new IllegalStateException("Not supported yet");
-                        }
-                        loadObject();
-                        return new SignatureWriter();
-                    }
-
-                    @Override
-                    public void visitClassType(String name) {
-                        if (nowReturn) {
-                            returnType = Type.getObjectType(name);
-                            return;
-                        }
-                        loadObject();
-                    }
-
-                    @Override
-                    public SignatureVisitor visitReturnType() {
-                        nowReturn = true;
-                        return this;
-                    }
-
-                    private void loadObject() {
-                        FindInMethod.super.visitInsn(Opcodes.DUP);
-                        FindInMethod.super.visitIntInsn(Opcodes.SIPUSH, index++);
-                        FindInMethod.super.visitVarInsn(Opcodes.ALOAD, loadIndex++);
-                        FindInMethod.super.visitInsn(Opcodes.AASTORE);
-                    }
-                    
-                }
-                SV sv = new SV();
-                SignatureReader sr = new SignatureReader(desc);
-                sr.accept(sv);
-                
-                if (needsVM) {
-                    FindInMethod.super.visitInsn(Opcodes.DUP);
-                    FindInMethod.super.visitIntInsn(Opcodes.SIPUSH, sv.index);
-                    int lastSlash = FindInClass.this.name.lastIndexOf('/');
-                    String jsCallbacks = FindInClass.this.name.substring(0, lastSlash + 1) + "$JsCallbacks$";
-                    FindInMethod.super.visitFieldInsn(Opcodes.GETSTATIC, jsCallbacks, "VM", "L" + jsCallbacks + ";");
-                    FindInMethod.super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, jsCallbacks, "current", "()L" + jsCallbacks + ";");
-                    FindInMethod.super.visitInsn(Opcodes.AASTORE);
-                }
-                
-                super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, 
-                    "org/apidesign/html/boot/spi/Fn", "invoke", "(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;"
-                );
-                switch (sv.returnType.getSort()) {
-                case Type.VOID: 
-                    super.visitInsn(Opcodes.RETURN);
-                    break;
-                case Type.ARRAY:
-                case Type.OBJECT:
-                    super.visitTypeInsn(Opcodes.CHECKCAST, sv.returnType.getInternalName());
-                    super.visitInsn(Opcodes.ARETURN);
-                    break;
-                case Type.BOOLEAN:
-                    super.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Boolean");
-                    super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, 
-                        "java/lang/Boolean", "booleanValue", "()Z"
-                    );
-                    super.visitInsn(Opcodes.IRETURN);
-                    break;
-                default:
-                    super.visitTypeInsn(Opcodes.CHECKCAST, "java/lang/Number");
-                    super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, 
-                        "java/lang/Number", sv.returnType.getClassName() + "Value", "()" + sv.returnType.getDescriptor()
-                    );
-                    super.visitInsn(sv.returnType.getOpcode(Opcodes.IRETURN));
-                }
-                return true;
-            }
-
-            @Override
-            public void visitEnd() {
-                super.visitEnd();
-                if (body != null) {
-                    if (generateBody()) {
-                        // native method
-                        super.visitMaxs(1, 0);
-                    }
-                    FindInClass.this.visitField(
-                        Opcodes.ACC_PRIVATE | Opcodes.ACC_STATIC, 
-                        "$$fn$$" + name + "_" + found, 
-                        "Lorg/apidesign/html/boot/spi/Fn;", 
-                        null, null
-                    );
-                }
-            }
-            
-            
-            
-            
-        
-            private final class FindInAnno extends AnnotationVisitor {
-                private List<String> args = new ArrayList<String>();
-                private String body;
-                private boolean javacall = false;
-
-                public FindInAnno() {
-                    super(Opcodes.ASM4);
-                }
-
-                @Override
-                public void visit(String name, Object value) {
-                    if (name == null) {
-                        args.add((String) value);
-                        return;
-                    }
-                    if (name.equals("javacall")) { // NOI18N
-                        javacall = (Boolean)value;
-                        return;
-                    }
-                    assert name.equals("body");
-                    body = (String) value;
-                }
-
-                @Override
-                public AnnotationVisitor visitArray(String name) {
-                    return this;
-                }
-
-                @Override
-                public void visitEnd() {
-                    if (body != null) {
-                        if (javacall) {
-                            body = FnUtils.callback(body);
-                            args.add("vm");
-                        }
-                        generateJSBody(args, body);
-                    }
-                }
-            }
-        }
-        
-        private final class LoadResource extends AnnotationVisitor {
-            public LoadResource() {
-                super(Opcodes.ASM4);
-            }
-            
-            @Override
-            public void visit(String attrName, Object value)  {
-                String relPath = (String) value;
-                if (relPath.startsWith("/")) {
-                    FnUtils.loadScript(JsClassLoader.this, relPath);
-                } else {
-                    int last = name.lastIndexOf('/');
-                    String fullPath = name.substring(0, last + 1) + relPath;
-                    FnUtils.loadScript(JsClassLoader.this, fullPath);
-                }
-            }
-        }
-    }
-    
-    private class ClassWriterEx extends ClassWriter {
-
-        public ClassWriterEx(ClassReader classReader, int flags) {
-            super(classReader, flags);
-        }
-        
-        @Override
-        protected String getCommonSuperClass(final String type1, final String type2) {
-            Class<?> c, d;
-            ClassLoader classLoader = JsClassLoader.this;
-            try {
-                c = Class.forName(type1.replace('/', '.'), false, classLoader);
-                d = Class.forName(type2.replace('/', '.'), false, classLoader);
-            } catch (Exception e) {
-                throw new RuntimeException(e.toString());
-            }
-            if (c.isAssignableFrom(d)) {
-                return type1;
-            }
-            if (d.isAssignableFrom(c)) {
-                return type2;
-            }
-            if (c.isInterface() || d.isInterface()) {
-                return "java/lang/Object";
-            } else {
-                do {
-                    c = c.getSuperclass();
-                } while (!c.isAssignableFrom(d));
-                return c.getName().replace('.', '/');
-            }
-        }        
-    }
 }
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/main/java/org/apidesign/html/boot/impl/Test.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/boot/src/main/java/org/apidesign/html/boot/impl/Test.java	Wed Nov 06 15:15:54 2013 +0100
@@ -0,0 +1,35 @@
+/**
+ * HTML via Java(tm) Language Bindings
+ * Copyright (C) 2013 Jaroslav Tulach <jaroslav.tulach@apidesign.org>
+ *
+ * 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, version 2 of the License.
+ *
+ * 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. apidesign.org
+ * designates this particular file as subject to the
+ * "Classpath" exception as provided by apidesign.org
+ * in the License file that accompanied this code.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. Look for COPYING file in the top folder.
+ * If not, see http://wiki.apidesign.org/wiki/GPLwithClassPathException
+ */
+package org.apidesign.html.boot.impl;
+
+import java.util.concurrent.Callable;
+import net.java.html.js.JavaScriptBody;
+
+/**
+ *
+ * @author Jaroslav Tulach <jtulach@netbeans.org>
+ */
+public final class Test implements Callable<Boolean> {
+    @Override @JavaScriptBody(args = {}, body = "return true;")
+    public Boolean call() {
+        return false;
+    }
+}
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/main/java/org/apidesign/html/boot/spi/Fn.java
--- a/boot/src/main/java/org/apidesign/html/boot/spi/Fn.java	Tue Nov 05 23:06:32 2013 +0100
+++ b/boot/src/main/java/org/apidesign/html/boot/spi/Fn.java	Wed Nov 06 15:15:54 2013 +0100
@@ -62,6 +62,31 @@
         return FnContext.currentPresenter() == presenter;
     }
     
+    /** Helper method to check if the provided instance is valid function.
+     * Checks if the parameter is non-null and if so, does {@link #isValid()}
+     * check.
+     * 
+     * @param fnOrNull function or <code>null</code>
+     * @return true if the parameter is non-null and valid
+     * @since 0.7
+     */
+    public static boolean isValid(Fn fnOrNull) {
+        return fnOrNull != null && fnOrNull.isValid();
+    }
+
+    /** Helper method to find current presenter and ask it to define new
+     * function by calling {@link Presenter#defineFn(java.lang.String, java.lang.String...)}.
+     * 
+     * @param caller the class who wishes to define the function
+     * @param code the body of the function (can reference <code>this</code> and <code>names</code> variables)
+     * @param names names of individual parameters
+     * @return the function object that can be {@link Fn#invoke(java.lang.Object, java.lang.Object...) invoked}
+     * @since 0.7
+     */
+    public static Fn define(Class<?> caller, String code, String... names) {
+        return FnContext.currentPresenter().defineFn(code, names);
+    }
+    
     /** The currently active presenter.
      * 
      * @return the currently active presenter or <code>null</code>
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/test/java/org/apidesign/html/boot/impl/FnTest.java
--- a/boot/src/test/java/org/apidesign/html/boot/impl/FnTest.java	Tue Nov 05 23:06:32 2013 +0100
+++ b/boot/src/test/java/org/apidesign/html/boot/impl/FnTest.java	Wed Nov 06 15:15:54 2013 +0100
@@ -21,6 +21,7 @@
 
 package org.apidesign.html.boot.impl;
 
+import java.io.Closeable;
 import java.io.Reader;
 import java.net.URL;
 import java.net.URLClassLoader;
@@ -115,7 +116,9 @@
         ClassLoader loader = FnUtils.newLoader(impl, impl, parent);
         presenter = impl;
         
+        Closeable close = FnContext.activate(impl);
         methodClass = loader.loadClass(JsMethods.class.getName());
+        close.close();
     }
 
     @BeforeMethod public void initPresenter() {
diff -r 4a93f2679691 -r 86aabecda7a3 boot/src/test/java/org/apidesign/html/boot/impl/JsClassLoaderTest.java
--- a/boot/src/test/java/org/apidesign/html/boot/impl/JsClassLoaderTest.java	Tue Nov 05 23:06:32 2013 +0100
+++ b/boot/src/test/java/org/apidesign/html/boot/impl/JsClassLoaderTest.java	Wed Nov 06 15:15:54 2013 +0100
@@ -20,6 +20,7 @@
  */
 package org.apidesign.html.boot.impl;
 
+import java.io.Closeable;
 import java.io.Reader;
 import org.apidesign.html.boot.spi.Fn;
 import java.net.URL;
@@ -115,7 +116,9 @@
         };
         
         MyCL l = new MyCL(parent);
+        Closeable close = FnContext.activate(l);
         methodClass = l.loadClass(JsMethods.class.getName());
+        close.close();
         loader = l;
     }