com.google.monitoring.runtime.instrumentation.adapters.VerifyingClassAdapter.java Source code

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Here is the source code for com.google.monitoring.runtime.instrumentation.adapters.VerifyingClassAdapter.java

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/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.monitoring.runtime.instrumentation.adapters;

import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.commons.CodeSizeEvaluator;

import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * This is a class writer that gets used in place of the existing
 * {@link org.objectweb.asm.ClassWriter},
 * and verifies properties of the class getting written.
 * <p>
 * Currently, it only checks to see if the methods are of the correct length
 * for Java methods (&lt;64K).
 *
 * @author jeremymanson@google.com (Jeremy Manson)
 */
public class VerifyingClassAdapter extends ClassVisitor {
    private static final Logger logger = Logger.getLogger(VerifyingClassAdapter.class.getName());

    /**
     * An enum which indicates whether the class in question is verified.
     */
    public enum State {
        PASS, UNKNOWN, FAIL_TOO_LONG;
    }

    final ClassWriter cw;
    final byte[] original;
    final String className;
    String message;
    State state;

    /**
     * @param cw        A class writer that is wrapped by this class adapter
     * @param original  the original bytecode
     * @param className the name of the class being examined.
     */
    public VerifyingClassAdapter(final ClassWriter cw, final byte[] original, final String className) {
        super(Opcodes.ASM5, cw);
        state = State.UNKNOWN;
        message = "The class has not finished being examined";
        this.cw = cw;
        this.original = original;
        this.className = className.replace('/', '.');
    }

    /**
     * {@inheritDoc}
     * <p>
     * In addition, the returned {@link org.objectweb.asm.MethodVisitor}
     * will throw an exception if the method is greater than 64K in length.
     */
    @Override
    public MethodVisitor visitMethod(final int access, final String name, final String desc, final String signature,
            final String[] exceptions) {
        final MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions);
        return new CodeSizeEvaluator(mv) {
            @Override
            public void visitEnd() {
                super.visitEnd();
                if (getMaxSize() > 64 * 1024) {
                    state = State.FAIL_TOO_LONG;
                    message = "the method " + name + " was too long.";
                }
            }
        };
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visitEnd() {
        super.visitEnd();
        if (state == State.UNKNOWN) {
            state = State.PASS;
        }
    }

    /**
     * Gets the verification state of this class.
     *
     * @return true iff the class passed inspection.
     */
    public boolean isVerified() {
        return state == State.PASS;
    }

    /**
     * Returns the byte array that contains the byte code for this class.
     *
     * @return a byte array.
     */
    public byte[] toByteArray() {
        if (state != State.PASS) {
            logger.log(Level.WARNING, "Failed to instrument class " + className + " because " + message);
            return original;
        }
        return cw.toByteArray();
    }
}