narya/src/java/com/threerings/io/ObjectInputStream.java

//
// $Id$
//
// Narya library - tools for developing networked games
// Copyright (C) 2002-2004 Three Rings Design, Inc., All Rights Reserved
// http://www.threerings.net/code/narya/
//
// This library is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published
// by the Free Software Foundation; either version 2.1 of the License, or
// (at your option) any later version.
//
// This library 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
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

package com.threerings.io;

import java.io.InputStream;
import java.io.DataInputStream;
import java.io.IOException;
import java.util.HashMap;

import com.samskivert.util.HashIntMap;
import com.samskivert.util.StringUtil;

import static com.threerings.NaryaLog.log;

/**
 * Used to read {@link Streamable} objects from an {@link InputStream}.
 * Other common object types are supported as well (@see {@link
 * ObjectOutputStream}).
 *
 * @see Streamable
 */
public class ObjectInputStream extends DataInputStream
{
    /**
     * Constructs an object input stream which will read its data from the
     * supplied source stream.
     */
    public ObjectInputStream (InputStream source)
    {
        super(source);
    }

    /**
     * Customizes the class loader used to instnatiate objects read from
     * the input stream.
     */
    public void setClassLoader (ClassLoader loader)
    {
        _loader = loader;
    }

    /**
     * Configures this object input stream with a mapping from an old
     * class name to a new one. Serialized instances of the old class name
     * will use the new class name when unserializing.
     */
    public void addTranslation (String oldname, String newname)
    {
        if (_translations == null) {
            _translations = new HashMap();
        }
        _translations.put(oldname, newname);
    }

    /**
     * Reads a {@link Streamable} instance or one of the supported object
     * types from the input stream.
     */
    public Object readObject ()
        throws IOException, ClassNotFoundException
    {
        ClassMapping cmap;

        // create our classmap if necessary
        if (_classmap == null) {
            _classmap = new HashIntMap();
        }

        try {
            // read in the class code for this instance
            short code = readShort();

            // a zero code indicates a null value
            if (code == 0) {
                if (STREAM_DEBUG) {
                    log.info(hashCode() + ": Read null.");
                }
                return null;

            // if the code is negative, that means that we've never
            // seen it before and class metadata follows
            } else if (code < 0) {
                // first swap the code into positive-land
                code *= -1;

                // read in the class metadata
                String cname = readUTF();
                // if we have a translation (used to cope when serialized
                // classes are renamed) use it
                if (_translations != null) {
                    String tname = (String)_translations.get(cname);
                    if (tname != null) {
                        cname = tname;
                    }
                }

                // create a class mapping record, and cache it
                Class sclass = Class.forName(cname, true, _loader);
                Streamer streamer = Streamer.getStreamer(sclass);
                if (STREAM_DEBUG) {
                    log.info(hashCode() + ": New class '" + cname + "'.");
                }

                // sanity check
                if (streamer == null) {
                    String errmsg = "Aiya! Unable to create streamer for " +
                        "newly seen class [code=" + code +
                        ", class=" + cname + "]";
                    throw new RuntimeException(errmsg);
                }

                cmap = new ClassMapping(code, sclass, streamer);
                _classmap.put(code, cmap);

            } else {
                cmap = (ClassMapping)_classmap.get(code);

                // sanity check
                if (cmap == null) {
                    // this will help with debugging
                    log.warning("Internal stream error, no class metadata " +
                                "[code=" + code + ", ois=" + this + "].");
                    Thread.dumpStack();
                    log.warning("ObjectInputStream mappings " +
                                StringUtil.toString(_classmap.entrySet()) +
                                ".");
                    String errmsg = "Read object code for which we " +
                        "have no registered class metadata [code=" + code + "]";
                    throw new RuntimeException(errmsg);
                }
            }

            // create an instance of the appropriate object
            Object target = cmap.streamer.createObject(this);
            readBareObject(target, cmap.streamer, true);
            return target;

        } catch (OutOfMemoryError oome) {
            throw (IOException)
                new IOException("Malformed object data").initCause(oome);
        }
    }

    /**
     * Reads an object from the input stream that was previously written
     * with {@link ObjectOutputStream#writeBareObject}.
     *
     * @param object the object to be populated from data on the stream.
     * It cannot be <code>null</code>.
     */
    public void readBareObject (Object object)
        throws IOException, ClassNotFoundException
    {
        readBareObject(object, Streamer.getStreamer(object.getClass()), true);
    }

    /**
     * Reads an object from the input stream that was previously written
     * with {@link ObjectOutputStream#writeBareObject}.
     */
    protected void readBareObject (
            Object object, Streamer streamer, boolean useReader)
        throws IOException, ClassNotFoundException
    {
        _current = object;
        _streamer = streamer;
        try {
            _streamer.readObject(object, this, useReader);

        } finally {
            // clear out our current object references
            _current = null;
            _streamer = null;
        }
    }

    /**
     * Reads the fields of the specified {@link Streamable} instance from
     * the input stream using the default object streaming mechanisms (a
     * call is not made to <code>readObject()</code>, even if such a
     * method exists).
     */
    public void defaultReadObject ()
        throws IOException, ClassNotFoundException
    {
        // sanity check
        if (_current == null) {
            throw new RuntimeException(
                "defaultReadObject() called illegally.");
        }

        // read the instance data
        _streamer.readObject(_current, this, false);
    }

    /**
     * Generates a string representation of this instance.
     */
    public String toString ()
    {
        return "[hash=" + hashCode() + ", mappings=" + _classmap.size() +
            ", current=" + StringUtil.safeToString(_current) +
            ", streamer=" + _streamer + "]";
    }

    /** Used to map classes to numeric codes and the {@link Streamer}
     * instance used to write them. */
    protected HashIntMap _classmap;

    /** The object currently being read from the stream. */
    protected Object _current;

    /** The streamer being used currently. */
    protected Streamer _streamer;

    /** The class loader we use to instantiate objects. */
    protected ClassLoader _loader = getClass().getClassLoader();

    /** An optional set of class name translations to use when
     * unserializing objects. */
    protected HashMap _translations;

    /** Used to activate verbose debug logging. */
    protected static final boolean STREAM_DEBUG = false;
}