creation/bytebuddy/ByteBuddyCrossClassLoaderSerializationSupport.java

/*
 * Copyright (c) 2007 Mockito contributors
 * This program is made available under the terms of the MIT License.
 */

package org.mockito.internal.creation.bytebuddy;

import org.mockito.Incubating;
import org.mockito.exceptions.base.MockitoSerializationIssue;
import org.mockito.internal.configuration.plugins.Plugins;
import org.mockito.internal.creation.settings.CreationSettings;
import org.mockito.internal.util.MockUtil;
import org.mockito.mock.MockCreationSettings;
import org.mockito.mock.MockName;
import org.mockito.mock.SerializableMode;

import java.io.*;
import java.lang.reflect.Field;
import java.util.Set;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import static org.mockito.internal.creation.bytebuddy.MockMethodInterceptor.ForWriteReplace;
import static org.mockito.internal.util.StringUtil.join;
import static org.mockito.internal.util.reflection.FieldSetter.setField;

/**
 * This is responsible for serializing a mock, it is enabled if the mock is implementing {@link Serializable}.
 *
 * <p>
 *     The way it works is to enable serialization with mode {@link SerializableMode#ACROSS_CLASSLOADERS},
 *     if the mock settings is set to be serializable the mock engine will implement the
 *     {@link CrossClassLoaderSerializableMock} marker interface.
 *     This interface defines a the {@link CrossClassLoaderSerializableMock#writeReplace()}
 *     whose signature match the one that is looked by the standard Java serialization.
 * </p>
 *
 * <p>
 *     Then in the proxy class there will be a generated <code>writeReplace</code> that will delegate to
 *     {@link ForWriteReplace#doWriteReplace(MockAccess)} of mockito, and in turn will delegate to the custom
 *     implementation of this class {@link #writeReplace(Object)}. This method has a specific
 *     knowledge on how to serialize a mockito mock that is based on ByteBuddy and will ignore other Mockito MockMakers.
 * </p>
 *
 * <p><strong>Only one instance per mock! See {@link MockMethodInterceptor}</strong></p>
 *
 * TODO check the class is mockable in the deserialization side
 *
 * @see SubclassByteBuddyMockMaker
 * @see org.mockito.internal.creation.bytebuddy.MockMethodInterceptor
 * @author Brice Dutheil
 * @since 1.10.0
 */
@Incubating
class ByteBuddyCrossClassLoaderSerializationSupport implements Serializable {
    private static final long serialVersionUID = 7411152578314420778L;
    private static final String MOCKITO_PROXY_MARKER = "ByteBuddyMockitoProxyMarker";
    private boolean instanceLocalCurrentlySerializingFlag = false;
    private final Lock mutex = new ReentrantLock();

    /**
     * Custom implementation of the <code>writeReplace</code> method for serialization.
     * <p/>
     * Here's how it's working and why :
     * <ol>
     *
     *     <li>
     *         <p>When first entering in this method, it's because some is serializing the mock, with some code like :</p>
     *
     * <pre class="code"><code class="java">
     * objectOutputStream.writeObject(mock);
     * </code></pre>
     *
     *         <p>So, {@link ObjectOutputStream} will track the <code>writeReplace</code> method in the instance and
     *         execute it, which is wanted to replace the mock by another type that will encapsulate the actual mock.
     *         At this point, the code will return an
     *         {@link CrossClassLoaderSerializableMock}.</p>
     *     </li>
     *     <li>
     *         <p>Now, in the constructor
     *         {@link CrossClassLoaderSerializationProxy#CrossClassLoaderSerializationProxy(java.lang.Object)}
     *         the mock is being serialized in a custom way (using {@link MockitoMockObjectOutputStream}) to a
     *         byte array. So basically it means the code is performing double nested serialization of the passed
     *         <code>mockitoMock</code>.</p>
     *
     *         <p>However the <code>ObjectOutputStream</code> will still detect the custom
     *         <code>writeReplace</code> and execute it.
     *         <em>(For that matter disabling replacement via {@link ObjectOutputStream#enableReplaceObject(boolean)}
     *         doesn't disable the <code>writeReplace</code> call, but just just toggle replacement in the
     *         written stream, <strong><code>writeReplace</code> is always called by
     *         <code>ObjectOutputStream</code></strong>.)</em></p>
     *
     *         <p>In order to avoid this recursion, obviously leading to a {@link StackOverflowError}, this method is using
     *         a flag that marks the mock as already being replaced, and then shouldn't replace itself again.
     *         <strong>This flag is local to this class</strong>, which means the flag of this class unfortunately needs
     *         to be protected against concurrent access, hence the reentrant lock.</p>
     *     </li>
     * </ol>
     *
     * @param mockitoMock The Mockito mock to be serialized.
     * @return A wrapper ({@link CrossClassLoaderSerializationProxy}) to be serialized by the calling ObjectOutputStream.
     * @throws java.io.ObjectStreamException
     */
    public Object writeReplace(Object mockitoMock) throws ObjectStreamException {
        // reentrant lock for critical section. could it be improved ?
        mutex.lock();
        try {
            // mark started flag // per thread, not per instance
            // temporary loosy hack to avoid stackoverflow
            if (mockIsCurrentlyBeingReplaced()) {
                return mockitoMock;
            }
            mockReplacementStarted();

            return new CrossClassLoaderSerializationProxy(mockitoMock);
        } catch (IOException ioe) {
            MockName mockName = MockUtil.getMockName(mockitoMock);
            String mockedType = MockUtil.getMockSettings(mockitoMock).getTypeToMock().getCanonicalName();
            throw new MockitoSerializationIssue(join(
                    "The mock '" + mockName + "' of type '" + mockedType + "'",
                    "The Java Standard Serialization reported an '" + ioe.getClass().getSimpleName() + "' saying :",
                    "  " + ioe.getMessage()
            ), ioe);
        } finally {
            // unmark
            mockReplacementCompleted();
            mutex.unlock();
        }
    }


    private void mockReplacementCompleted() {
        instanceLocalCurrentlySerializingFlag = false;
    }


    private void mockReplacementStarted() {
        instanceLocalCurrentlySerializingFlag = true;
    }


    private boolean mockIsCurrentlyBeingReplaced() {
        return instanceLocalCurrentlySerializingFlag;
    }

    /**
     * This is the serialization proxy that will encapsulate the real mock data as a byte array.
     * <p/>
     * <p>When called in the constructor it will serialize the mock in a byte array using a
     * custom {@link MockitoMockObjectOutputStream} that will annotate the mock class in the stream.
     * Other information are used in this class in order to facilitate deserialization.
     * </p>
     * <p/>
     * <p>Deserialization of the mock will be performed by the {@link #readResolve()} method via
     * the custom {@link MockitoMockObjectInputStream} that will be in charge of creating the mock class.</p>
     */
    public static class CrossClassLoaderSerializationProxy implements Serializable {

        private static final long serialVersionUID = -7600267929109286514L;
        private final byte[] serializedMock;
        private final Class<?> typeToMock;
        private final Set<Class<?>> extraInterfaces;

        /**
         * Creates the wrapper that be used in the serialization stream.
         *
         * <p>Immediately serializes the Mockito mock using specifically crafted {@link MockitoMockObjectOutputStream},
         * in a byte array.</p>
         *
         * @param mockitoMock The Mockito mock to serialize.
         * @throws java.io.IOException
         */
        public CrossClassLoaderSerializationProxy(Object mockitoMock) throws IOException {
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            ObjectOutputStream objectOutputStream = new MockitoMockObjectOutputStream(out);

            objectOutputStream.writeObject(mockitoMock);

            objectOutputStream.close();
            out.close();

            MockCreationSettings<?> mockSettings = MockUtil.getMockSettings(mockitoMock);
            this.serializedMock = out.toByteArray();
            this.typeToMock = mockSettings.getTypeToMock();
            this.extraInterfaces = mockSettings.getExtraInterfaces();
        }

        /**
         * Resolves the proxy to a new deserialized instance of the Mockito mock.
         * <p/>
         * <p>Uses the custom crafted {@link MockitoMockObjectInputStream} to deserialize the mock.</p>
         *
         * @return A deserialized instance of the Mockito mock.
         * @throws java.io.ObjectStreamException
         */
        private Object readResolve() throws ObjectStreamException {
            try {
                ByteArrayInputStream bis = new ByteArrayInputStream(serializedMock);
                ObjectInputStream objectInputStream = new MockitoMockObjectInputStream(bis, typeToMock, extraInterfaces);

                Object deserializedMock = objectInputStream.readObject();

                bis.close();
                objectInputStream.close();

                return deserializedMock;
            } catch (IOException ioe) {
                throw new MockitoSerializationIssue(join(
                        "Mockito mock cannot be deserialized to a mock of '" + typeToMock.getCanonicalName() + "'. The error was :",
                        "  " + ioe.getMessage(),
                        "If you are unsure what is the reason of this exception, feel free to contact us on the mailing list."
                ), ioe);
            } catch (ClassNotFoundException cce) {
                throw new MockitoSerializationIssue(join(
                        "A class couldn't be found while deserializing a Mockito mock, you should check your classpath. The error was :",
                        "  " + cce.getMessage(),
                        "If you are still unsure what is the reason of this exception, feel free to contact us on the mailing list."
                ), cce);
            }
        }
    }


    /**
     * Special Mockito aware <code>ObjectInputStream</code> that will resolve the Mockito proxy class.
     * <p/>
     * <p>
     *     This specifically crafted ObjectInoutStream has the most important role to resolve the Mockito generated
     *     class. It is doing so via the {@link #resolveClass(ObjectStreamClass)} which looks in the stream
     *     for a Mockito marker. If this marker is found it will try to resolve the mockito class otherwise it
     *     delegates class resolution to the default super behavior.
     *     The mirror method used for serializing the mock is {@link MockitoMockObjectOutputStream#annotateClass(Class)}.
     * </p>
     * <p/>
     * <p>
     *     When this marker is found, {@link ByteBuddyMockMaker#createMockType(MockCreationSettings)} methods are being used
     *     to create the mock class.
     * </p>
     */
    public static class MockitoMockObjectInputStream extends ObjectInputStream {
        private final Class<?> typeToMock;
        private final Set<Class<?>> extraInterfaces;

        public MockitoMockObjectInputStream(InputStream in, Class<?> typeToMock, Set<Class<?>> extraInterfaces) throws IOException {
            super(in);
            this.typeToMock = typeToMock;
            this.extraInterfaces = extraInterfaces;
            enableResolveObject(true); // ensure resolving is enabled
        }

        /**
         * Resolve the Mockito proxy class if it is marked as such.
         * <p/>
         * <p>Uses the fields {@link #typeToMock} and {@link #extraInterfaces} to
         * create the Mockito proxy class as the <code>ObjectStreamClass</code>
         * doesn't carry useful information for this purpose.</p>
         *
         * @param desc Description of the class in the stream, not used.
         * @return The class that will be used to deserialize the instance mock.
         * @throws java.io.IOException
         * @throws ClassNotFoundException
         */
        @Override
        protected Class<?> resolveClass(ObjectStreamClass desc) throws IOException, ClassNotFoundException {
            if (notMarkedAsAMockitoMock(readObject())) {
                return super.resolveClass(desc);
            }

            // create the Mockito mock class before it can even be deserialized
            try {
                @SuppressWarnings("unchecked")
                Class<?> proxyClass = ((ClassCreatingMockMaker) Plugins.getMockMaker()).createMockType(
                        new CreationSettings()
                                .setTypeToMock(typeToMock)
                                .setExtraInterfaces(extraInterfaces)
                                .setSerializableMode(SerializableMode.ACROSS_CLASSLOADERS));

                hackClassNameToMatchNewlyCreatedClass(desc, proxyClass);
                return proxyClass;
            } catch (ClassCastException cce) {
                throw new MockitoSerializationIssue(join(
                        "A Byte Buddy-generated mock cannot be deserialized into a non-Byte Buddy generated mock class",
                        "",
                        "The mock maker in use was: " + Plugins.getMockMaker().getClass()
                ), cce);
            }
        }

        /**
         * Hack the <code>name</code> field of the given <code>ObjectStreamClass</code> with
         * the <code>newProxyClass</code>.
         * <p/>
         * The parent ObjectInputStream will check the name of the class in the stream matches the name of the one
         * that is created in this method.
         * <p/>
         * The CGLIB classes uses a hash of the classloader and/or maybe some other data that allow them to be
         * relatively unique in a JVM.
         * <p/>
         * When names differ, which happens when the mock is deserialized in another ClassLoader, a
         * <code>java.io.InvalidObjectException</code> is thrown, so this part of the code is hacking through
         * the given <code>ObjectStreamClass</code> to change the name with the newly created class.
         *
         * @param descInstance The <code>ObjectStreamClass</code> that will be hacked.
         * @param proxyClass   The proxy class whose name will be applied.
         * @throws java.io.InvalidObjectException
         */
        private void hackClassNameToMatchNewlyCreatedClass(ObjectStreamClass descInstance, Class<?> proxyClass) throws ObjectStreamException {
            try {
                Field classNameField = descInstance.getClass().getDeclaredField("name");
                setField(descInstance, classNameField,proxyClass.getCanonicalName());
            } catch (NoSuchFieldException nsfe) {
                throw new MockitoSerializationIssue(join(
                        "Wow, the class 'ObjectStreamClass' in the JDK don't have the field 'name',",
                        "this is definitely a bug in our code as it means the JDK team changed a few internal things.",
                        "",
                        "Please report an issue with the JDK used, a code sample and a link to download the JDK would be welcome."
                ), nsfe);
            }
        }

        /**
         * Read the stream class annotation and identify it as a Mockito mock or not.
         *
         * @param marker The marker to identify.
         * @return <code>true</code> if not marked as a Mockito, <code>false</code> if the class annotation marks a Mockito mock.
         */
        private boolean notMarkedAsAMockitoMock(Object marker) {
            return !MOCKITO_PROXY_MARKER.equals(marker);
        }
    }


    /**
     * Special Mockito aware <code>ObjectOutputStream</code>.
     * <p/>
     * <p>
     * This output stream has the role of marking in the stream the Mockito class. This
     * marking process is necessary to identify the proxy class that will need to be recreated.
     * <p/>
     * The mirror method used for deserializing the mock is
     * {@link MockitoMockObjectInputStream#resolveClass(ObjectStreamClass)}.
     * </p>
     */
    private static class MockitoMockObjectOutputStream extends ObjectOutputStream {
        private static final String NOTHING = "";

        public MockitoMockObjectOutputStream(ByteArrayOutputStream out) throws IOException {
            super(out);
        }

        /**
         * Annotates (marks) the class if this class is a Mockito mock.
         *
         * @param cl The class to annotate.
         * @throws java.io.IOException
         */
        @Override
        protected void annotateClass(Class<?> cl) throws IOException {
            writeObject(mockitoProxyClassMarker(cl));
            // might be also useful later, for embedding classloader info ...maybe ...maybe not
        }

        /**
         * Returns the Mockito marker if this class is a Mockito mock.
         *
         * @param cl The class to mark.
         * @return The marker if this is a Mockito proxy class, otherwise returns a void marker.
         */
        private String mockitoProxyClassMarker(Class<?> cl) {
            if (CrossClassLoaderSerializableMock.class.isAssignableFrom(cl)) {
                return MOCKITO_PROXY_MARKER;
            } else {
                return NOTHING;
            }
        }
    }


    /**
     * Simple interface that hold a correct <code>writeReplace</code> signature that can be seen by an
     * <code>ObjectOutputStream</code>.
     * <p/>
     * It will be applied before the creation of the mock when the mock setting says it should serializable.
     */
    public interface CrossClassLoaderSerializableMock {
        Object writeReplace();
    }
}