com.github.stokito.gag.agent.RouletteGenerator Maven / Gradle / Ivy

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Dynamic bytecode instrumentation Java agent for GAG. GAG is an annotations library that provides a rich set of annotations for developers to express themselves.

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/**
 * Copyright 2010 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.github.stokito.gag.agent;

import com.github.stokito.gag.annotation.enforceable.Roulette;
import com.github.stokito.gag.instrument.AnnotationStateError;
import com.github.stokito.gag.instrument.ClassGenerator;
import com.github.stokito.gag.instrument.info.AnnoInfo;
import com.github.stokito.gag.instrument.info.ClassInfo;
import com.github.stokito.gag.instrument.info.MethodInfo;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Type;

import static org.objectweb.asm.Opcodes.*;

public class RouletteGenerator extends ClassGenerator {

    private static final Type ROULETTE_TYPE = Type.getType(Roulette.class);

    @Override
    protected boolean canInstrument(ClassInfo classInfo) {
        return classInfo.hasMethodAnnoAnywhere(ROULETTE_TYPE);
    }

    @Override
    public MethodVisitor visitMethod(int access, String name, String desc, String sig,
                                     String[] exceptions) {

        MethodVisitor mv = writer().visitMethod(access, name, desc, sig, exceptions);
        mv.visitCode();

        MethodInfo method = classInfo().getMethod(name, desc);
        AnnoInfo anno = method.getAnnoFor(ROULETTE_TYPE);
        if (anno != null) {

            Double probability = (Double) anno.getValue("probability");
            if (probability < 0.0 || probability > 1.0) {
                throw new AnnotationStateError(
                        "Probability (" + probability + ") needs to be between 0 and 1");
            }

            Type exception = (Type) anno.getValue("exception");

            // TODO: Figure out how to get the default value from the annotation itself.
            if (exception == null) {
                exception = Type.getType(RuntimeException.class);
            }

            String message = (String) anno.getValue("message");

            Label okay = new Label();

            mv.visitTypeInsn(NEW, "java/util/Random");
            mv.visitInsn(DUP);
            mv.visitMethodInsn(INVOKESPECIAL, "java/util/Random", "", "()V");

            mv.visitMethodInsn(INVOKEVIRTUAL, "java/util/Random", "nextDouble", "()D");
            mv.visitLdcInsn(probability);
            mv.visitInsn(DCMPG);
            mv.visitJumpInsn(IFGT, okay);

            mv.visitTypeInsn(NEW, exception.getInternalName());
            mv.visitInsn(DUP);
            mv.visitLdcInsn(message);
            mv.visitMethodInsn(INVOKESPECIAL, exception.getInternalName(), "",
                    "(Ljava/lang/String;)V");
            mv.visitInsn(ATHROW);

            mv.visitLabel(okay);

            setInstrumented(true);
        }

        mv.visitEnd();
        return mv;
    }
}