/*

 * Copyright (c) 1996, 2010, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.io;

import java.io.ObjectStreamClass.WeakClassKey;

import java.lang.ref.ReferenceQueue;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.concurrent.ConcurrentHashMap;

import java.util.concurrent.ConcurrentMap;

import static java.io.ObjectStreamClass.processQueue;

import java.io.SerialCallbackContext;

/**

 * An ObjectOutputStream writes primitive data types and graphs of Java objects

 * to an OutputStream.  The objects can be read (reconstituted) using an

 * ObjectInputStream.  Persistent storage of objects can be accomplished by

 * using a file for the stream.  If the stream is a network socket stream, the

 * objects can be reconstituted on another host or in another process.

 *

 * <p>Only objects that support the java.io.Serializable interface can be

 * written to streams.  The class of each serializable object is encoded

 * including the class name and signature of the class, the values of the

 * object's fields and arrays, and the closure of any other objects referenced

 * from the initial objects.

 *

 * <p>The method writeObject is used to write an object to the stream.  Any

 * object, including Strings and arrays, is written with writeObject. Multiple

 * objects or primitives can be written to the stream.  The objects must be

 * read back from the corresponding ObjectInputstream with the same types and

 * in the same order as they were written.

 *

 * <p>Primitive data types can also be written to the stream using the

 * appropriate methods from DataOutput. Strings can also be written using the

 * writeUTF method.

 *

 * <p>The default serialization mechanism for an object writes the class of the

 * object, the class signature, and the values of all non-transient and

 * non-static fields.  References to other objects (except in transient or

 * static fields) cause those objects to be written also. Multiple references

 * to a single object are encoded using a reference sharing mechanism so that

 * graphs of objects can be restored to the same shape as when the original was

 * written.

 *

 * <p>For example to write an object that can be read by the example in

 * ObjectInputStream:

 * <br>

 * <pre>

 *      FileOutputStream fos = new FileOutputStream("t.tmp");

 *      ObjectOutputStream oos = new ObjectOutputStream(fos);

 *

 *      oos.writeInt(12345);

 *      oos.writeObject("Today");

 *      oos.writeObject(new Date());

 *

 *      oos.close();

 * </pre>

 *

 * <p>Classes that require special handling during the serialization and

 * deserialization process must implement special methods with these exact

 * signatures:

 * <br>

 * <pre>

 * private void readObject(java.io.ObjectInputStream stream)

 *     throws IOException, ClassNotFoundException;

 * private void writeObject(java.io.ObjectOutputStream stream)

 *     throws IOException

 * private void readObjectNoData()

 *     throws ObjectStreamException;

 * </pre>

 *

 * <p>The writeObject method is responsible for writing the state of the object

 * for its particular class so that the corresponding readObject method can

 * restore it.  The method does not need to concern itself with the state

 * belonging to the object's superclasses or subclasses.  State is saved by

 * writing the individual fields to the ObjectOutputStream using the

 * writeObject method or by using the methods for primitive data types

 * supported by DataOutput.

 *

 * <p>Serialization does not write out the fields of any object that does not

 * implement the java.io.Serializable interface.  Subclasses of Objects that

 * are not serializable can be serializable. In this case the non-serializable

 * class must have a no-arg constructor to allow its fields to be initialized.

 * In this case it is the responsibility of the subclass to save and restore

 * the state of the non-serializable class. It is frequently the case that the

 * fields of that class are accessible (public, package, or protected) or that

 * there are get and set methods that can be used to restore the state.

 *

 * <p>Serialization of an object can be prevented by implementing writeObject

 * and readObject methods that throw the NotSerializableException.  The

 * exception will be caught by the ObjectOutputStream and abort the

 * serialization process.

 *

 * <p>Implementing the Externalizable interface allows the object to assume

 * complete control over the contents and format of the object's serialized

 * form.  The methods of the Externalizable interface, writeExternal and

 * readExternal, are called to save and restore the objects state.  When

 * implemented by a class they can write and read their own state using all of

 * the methods of ObjectOutput and ObjectInput.  It is the responsibility of

 * the objects to handle any versioning that occurs.

 *

 * <p>Enum constants are serialized differently than ordinary serializable or

 * externalizable objects.  The serialized form of an enum constant consists

 * solely of its name; field values of the constant are not transmitted.  To

 * serialize an enum constant, ObjectOutputStream writes the string returned by

 * the constant's name method.  Like other serializable or externalizable

 * objects, enum constants can function as the targets of back references

 * appearing subsequently in the serialization stream.  The process by which

 * enum constants are serialized cannot be customized; any class-specific

 * writeObject and writeReplace methods defined by enum types are ignored

 * during serialization.  Similarly, any serialPersistentFields or

 * serialVersionUID field declarations are also ignored--all enum types have a

 * fixed serialVersionUID of 0L.

 *

 * <p>Primitive data, excluding serializable fields and externalizable data, is

 * written to the ObjectOutputStream in block-data records. A block data record

 * is composed of a header and data. The block data header consists of a marker

 * and the number of bytes to follow the header.  Consecutive primitive data

 * writes are merged into one block-data record.  The blocking factor used for

 * a block-data record will be 1024 bytes.  Each block-data record will be

 * filled up to 1024 bytes, or be written whenever there is a termination of

 * block-data mode.  Calls to the ObjectOutputStream methods writeObject,

 * defaultWriteObject and writeFields initially terminate any existing

 * block-data record.

 *

 * @author      Mike Warres

 * @author      Roger Riggs

 * @see java.io.DataOutput

 * @see java.io.ObjectInputStream

 * @see java.io.Serializable

 * @see java.io.Externalizable

 * @see <a href="../../../platform/serialization/spec/output.html">Object Serialization Specification, Section 2, Object Output Classes</a>

 * @since       JDK1.1

 */

public class ObjectOutputStream

    extends OutputStream implements ObjectOutput, ObjectStreamConstants

{

    private static class Caches {

        /** cache of subclass security audit results */

        static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =

            new ConcurrentHashMap<>();

        /** queue for WeakReferences to audited subclasses */

        static final ReferenceQueue<Class<?>> subclassAuditsQueue =

            new ReferenceQueue<>();

    }

    /** filter stream for handling block data conversion */

    private final BlockDataOutputStream bout;

    /** obj -> wire handle map */

    private final HandleTable handles;

    /** obj -> replacement obj map */

    private final ReplaceTable subs;

    /** stream protocol version */

    private int protocol = PROTOCOL_VERSION_2;

    /** recursion depth */

    private int depth;

    /** buffer for writing primitive field values */

    private byte[] primVals;

    /** if true, invoke writeObjectOverride() instead of writeObject() */

    private final boolean enableOverride;

    /** if true, invoke replaceObject() */

    private boolean enableReplace;

    // values below valid only during upcalls to writeObject()/writeExternal()

    /**

     * Context during upcalls to class-defined writeObject methods; holds

     * object currently being serialized and descriptor for current class.

     * Null when not during writeObject upcall.

     */

    private SerialCallbackContext curContext;

    /** current PutField object */

    private PutFieldImpl curPut;

    /** custom storage for debug trace info */

    private final DebugTraceInfoStack debugInfoStack;

    /**

     * value of "sun.io.serialization.extendedDebugInfo" property,

     * as true or false for extended information about exception's place

     */

    private static final boolean extendedDebugInfo =

        java.security.AccessController.doPrivileged(

            new sun.security.action.GetBooleanAction(

                "sun.io.serialization.extendedDebugInfo")).booleanValue();

    /**

     * Creates an ObjectOutputStream that writes to the specified OutputStream.

     * This constructor writes the serialization stream header to the

     * underlying stream; callers may wish to flush the stream immediately to

     * ensure that constructors for receiving ObjectInputStreams will not block

     * when reading the header.

     *

     * <p>If a security manager is installed, this constructor will check for

     * the "enableSubclassImplementation" SerializablePermission when invoked

     * directly or indirectly by the constructor of a subclass which overrides

     * the ObjectOutputStream.putFields or ObjectOutputStream.writeUnshared

     * methods.

     *

     * @param   out output stream to write to

     * @throws  IOException if an I/O error occurs while writing stream header

     * @throws  SecurityException if untrusted subclass illegally overrides

     *          security-sensitive methods

     * @throws  NullPointerException if <code>out</code> is <code>null</code>

     * @since   1.4

     * @see     ObjectOutputStream#ObjectOutputStream()

     * @see     ObjectOutputStream#putFields()

     * @see     ObjectInputStream#ObjectInputStream(InputStream)

     */

    public ObjectOutputStream(OutputStream out) throws IOException {

        verifySubclass();

        bout = new BlockDataOutputStream(out);

        handles = new HandleTable(10, (float) 3.00);

        subs = new ReplaceTable(10, (float) 3.00);

        enableOverride = false;

        writeStreamHeader();

        bout.setBlockDataMode(true);

        if (extendedDebugInfo) {

            debugInfoStack = new DebugTraceInfoStack();

        } else {

            debugInfoStack = null;

        }

    }

    /**

     * Provide a way for subclasses that are completely reimplementing

     * ObjectOutputStream to not have to allocate private data just used by

     * this implementation of ObjectOutputStream.

     *

     * <p>If there is a security manager installed, this method first calls the

     * security manager's <code>checkPermission</code> method with a

     * <code>SerializablePermission("enableSubclassImplementation")</code>

     * permission to ensure it's ok to enable subclassing.

     *

     * @throws  SecurityException if a security manager exists and its

     *          <code>checkPermission</code> method denies enabling

     *          subclassing.

     * @see SecurityManager#checkPermission

     * @see java.io.SerializablePermission

     */

    protected ObjectOutputStream() throws IOException, SecurityException {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);

        }

        bout = null;

        handles = null;

        subs = null;

        enableOverride = true;

        debugInfoStack = null;

    }

    /**

     * Specify stream protocol version to use when writing the stream.

     *

     * <p>This routine provides a hook to enable the current version of

     * Serialization to write in a format that is backwards compatible to a

     * previous version of the stream format.

     *

     * <p>Every effort will be made to avoid introducing additional

     * backwards incompatibilities; however, sometimes there is no

     * other alternative.

     *

     * @param   version use ProtocolVersion from java.io.ObjectStreamConstants.

     * @throws  IllegalStateException if called after any objects

     *          have been serialized.

     * @throws  IllegalArgumentException if invalid version is passed in.

     * @throws  IOException if I/O errors occur

     * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1

     * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_2

     * @since   1.2

     */

    public void useProtocolVersion(int version) throws IOException {

        if (handles.size() != 0) {

            // REMIND: implement better check for pristine stream?

            throw new IllegalStateException("stream non-empty");

        }

        switch (version) {

            case PROTOCOL_VERSION_1:

            case PROTOCOL_VERSION_2:

                protocol = version;

                break;

            default:

                throw new IllegalArgumentException(

                    "unknown version: " + version);

        }

    }

    /**

     * Write the specified object to the ObjectOutputStream.  The class of the

     * object, the signature of the class, and the values of the non-transient

     * and non-static fields of the class and all of its supertypes are

     * written.  Default serialization for a class can be overridden using the

     * writeObject and the readObject methods.  Objects referenced by this

     * object are written transitively so that a complete equivalent graph of

     * objects can be reconstructed by an ObjectInputStream.

     *

     * <p>Exceptions are thrown for problems with the OutputStream and for

     * classes that should not be serialized.  All exceptions are fatal to the

     * OutputStream, which is left in an indeterminate state, and it is up to

     * the caller to ignore or recover the stream state.

     *

     * @throws  InvalidClassException Something is wrong with a class used by

     *          serialization.

     * @throws  NotSerializableException Some object to be serialized does not

     *          implement the java.io.Serializable interface.

     * @throws  IOException Any exception thrown by the underlying

     *          OutputStream.

     */

    public final void writeObject(Object obj) throws IOException {

        if (enableOverride) {

            writeObjectOverride(obj);

            return;

        }

        try {

            writeObject0(obj, false);

        } catch (IOException ex) {

            if (depth == 0) {

                writeFatalException(ex);

            }

            throw ex;

        }

    }

    /**

     * Method used by subclasses to override the default writeObject method.

     * This method is called by trusted subclasses of ObjectInputStream that

     * constructed ObjectInputStream using the protected no-arg constructor.

     * The subclass is expected to provide an override method with the modifier

     * "final".

     *

     * @param   obj object to be written to the underlying stream

     * @throws  IOException if there are I/O errors while writing to the

     *          underlying stream

     * @see #ObjectOutputStream()

     * @see #writeObject(Object)

     * @since 1.2

     */

    protected void writeObjectOverride(Object obj) throws IOException {

    }

    /**

     * Writes an "unshared" object to the ObjectOutputStream.  This method is

     * identical to writeObject, except that it always writes the given object

     * as a new, unique object in the stream (as opposed to a back-reference

     * pointing to a previously serialized instance).  Specifically:

     * <ul>

     *   <li>An object written via writeUnshared is always serialized in the

     *       same manner as a newly appearing object (an object that has not

     *       been written to the stream yet), regardless of whether or not the

     *       object has been written previously.

     *

     *   <li>If writeObject is used to write an object that has been previously

     *       written with writeUnshared, the previous writeUnshared operation

     *       is treated as if it were a write of a separate object.  In other

     *       words, ObjectOutputStream will never generate back-references to

     *       object data written by calls to writeUnshared.

     * </ul>

     * While writing an object via writeUnshared does not in itself guarantee a

     * unique reference to the object when it is deserialized, it allows a

     * single object to be defined multiple times in a stream, so that multiple

     * calls to readUnshared by the receiver will not conflict.  Note that the

     * rules described above only apply to the base-level object written with

     * writeUnshared, and not to any transitively referenced sub-objects in the

     * object graph to be serialized.

     *

     * <p>ObjectOutputStream subclasses which override this method can only be

     * constructed in security contexts possessing the

     * "enableSubclassImplementation" SerializablePermission; any attempt to

     * instantiate such a subclass without this permission will cause a

     * SecurityException to be thrown.

     *

     * @param   obj object to write to stream

     * @throws  NotSerializableException if an object in the graph to be

     *          serialized does not implement the Serializable interface

     * @throws  InvalidClassException if a problem exists with the class of an

     *          object to be serialized

     * @throws  IOException if an I/O error occurs during serialization

     * @since 1.4

     */

    public void writeUnshared(Object obj) throws IOException {

        try {

            writeObject0(obj, true);

        } catch (IOException ex) {

            if (depth == 0) {

                writeFatalException(ex);

            }

            throw ex;

        }

    }

    /**

     * Write the non-static and non-transient fields of the current class to

     * this stream.  This may only be called from the writeObject method of the

     * class being serialized. It will throw the NotActiveException if it is

     * called otherwise.

     *

     * @throws  IOException if I/O errors occur while writing to the underlying

     *          <code>OutputStream</code>

     */

    public void defaultWriteObject() throws IOException {

        if ( curContext == null ) {

            throw new NotActiveException("not in call to writeObject");

        }

        Object curObj = curContext.getObj();

        ObjectStreamClass curDesc = curContext.getDesc();

        bout.setBlockDataMode(false);

        defaultWriteFields(curObj, curDesc);

        bout.setBlockDataMode(true);

    }

    /**

     * Retrieve the object used to buffer persistent fields to be written to

     * the stream.  The fields will be written to the stream when writeFields

     * method is called.

     *

     * @return  an instance of the class Putfield that holds the serializable

     *          fields

     * @throws  IOException if I/O errors occur

     * @since 1.2

     */

    public ObjectOutputStream.PutField putFields() throws IOException {

        if (curPut == null) {

            if (curContext == null) {

                throw new NotActiveException("not in call to writeObject");

            }

            Object curObj = curContext.getObj();

            ObjectStreamClass curDesc = curContext.getDesc();

            curPut = new PutFieldImpl(curDesc);

        }

        return curPut;

    }

    /**

     * Write the buffered fields to the stream.

     *

     * @throws  IOException if I/O errors occur while writing to the underlying

     *          stream

     * @throws  NotActiveException Called when a classes writeObject method was

     *          not called to write the state of the object.

     * @since 1.2

     */

    public void writeFields() throws IOException {

        if (curPut == null) {

            throw new NotActiveException("no current PutField object");

        }

        bout.setBlockDataMode(false);

        curPut.writeFields();

        bout.setBlockDataMode(true);

    }

    /**

     * Reset will disregard the state of any objects already written to the

     * stream.  The state is reset to be the same as a new ObjectOutputStream.

     * The current point in the stream is marked as reset so the corresponding

     * ObjectInputStream will be reset at the same point.  Objects previously

     * written to the stream will not be refered to as already being in the

     * stream.  They will be written to the stream again.

     *

     * @throws  IOException if reset() is invoked while serializing an object.

     */

    public void reset() throws IOException {

        if (depth != 0) {

            throw new IOException("stream active");

        }

        bout.setBlockDataMode(false);

        bout.writeByte(TC_RESET);

        clear();

        bout.setBlockDataMode(true);

    }

    /**

     * Subclasses may implement this method to allow class data to be stored in

     * the stream. By default this method does nothing.  The corresponding

     * method in ObjectInputStream is resolveClass.  This method is called

     * exactly once for each unique class in the stream.  The class name and

     * signature will have already been written to the stream.  This method may

     * make free use of the ObjectOutputStream to save any representation of

     * the class it deems suitable (for example, the bytes of the class file).

     * The resolveClass method in the corresponding subclass of

     * ObjectInputStream must read and use any data or objects written by

     * annotateClass.

     *

     * @param   cl the class to annotate custom data for

     * @throws  IOException Any exception thrown by the underlying

     *          OutputStream.

     */

    protected void annotateClass(Class<?> cl) throws IOException {

    }

    /**

     * Subclasses may implement this method to store custom data in the stream

     * along with descriptors for dynamic proxy classes.

     *

     * <p>This method is called exactly once for each unique proxy class