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

//
// $Id$
//
// Narya library - tools for developing networked games
// Copyright (C) 2002-2007 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.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.ReflectPermission;

import java.util.Date;
import java.util.HashMap;

import static com.threerings.NaryaLog.log;

/**
 * Used to read and write a single field of a {@link Streamable} instance.
 */
public abstract class FieldMarshaller
{
    /**
     * Reads the contents of the supplied field from the supplied stream and sets it in the
     * supplied object.
     */
    public abstract void readField (Field field, Object target, ObjectInputStream in)
        throws Exception;

    /**
     * Writes the contents of the supplied field in the supplied object to the supplied stream.
     */
    public abstract void writeField (Field field, Object source, ObjectOutputStream out)
        throws Exception;

    /**
     * Returns a field marshaller appropriate for the supplied field or null if no marshaller
     * exists for the type contained by the field in question.
     */
    public static FieldMarshaller getFieldMarshaller (Field field)
    {
        if (_marshallers == null) {
            createMarshallers();
        }

        // if necessary (we're running in a sandbox), look for custom field accessors
        if (useFieldAccessors()) {
            Method reader = null, writer = null;
            try {
                reader = field.getDeclaringClass().getMethod(
                    getReaderMethodName(field.getName()), READER_ARGS);
                writer = field.getDeclaringClass().getMethod(
                    getWriterMethodName(field.getName()), WRITER_ARGS);
                return new MethodFieldMarshaller(reader, writer);
            } catch (NoSuchMethodException nsme) {
                // no problem
            }
            // To get to this code path, either an exception was thrown when fetching reader or
            // when fetching writer... either way writer is guaranteed to be null.
            if (reader != null) {
                log.warning("Class contains a custom field reader, but not a writer",
                            "class", field.getDeclaringClass().getName(), "field", field.getName(),
                            "reader", reader);
                // fall through to using reflection on the fields...
            }
        }

        Class<?> ftype = field.getType();
        if (ftype.isInterface()) {
            // if the class is a pure interface, use Object.
            ftype = Object.class;
        }

        // if we have an exact match, use that
        FieldMarshaller fm = _marshallers.get(ftype);

        // otherwise if the class is a streamable, use the streamable marshaller
        if (fm == null && Streamer.isStreamable(ftype)) {
            fm = _marshallers.get(Streamable.class);
        }

        return fm;
    }

    /**
     * Returns the name of the custom reader method which will be used if it exists to stream a
     * field with the supplied name.
     */
    public static final String getReaderMethodName (String field)
    {
        return "readField_" + field;
    }

    /**
     * Returns the name of the custom writer method which will be used if it exists to stream a
     * field with the supplied name.
     */
    public static final String getWriterMethodName (String field)
    {
        return "writeField_" + field;
    }

    /**
     * Returns true if we should use the generated field marshaller methods that allow us to work
     * around our inability to read and write protected and private fields of a {@link Streamable}.
     */
    protected static boolean useFieldAccessors ()
    {
        try {
            SecurityManager security = System.getSecurityManager();
            if (security != null) {
                security.checkPermission(new ReflectPermission("suppressAccessChecks"));
            }
            return false;
        } catch (SecurityException se) {
            return true;
        }
    }

    /**
     * Used to marshall and unmarshall classes for which we have a basic {@link Streamer}.
     */
    protected static class StreamerMarshaller extends FieldMarshaller
    {
        public StreamerMarshaller (Streamer streamer)
        {
            _streamer = streamer;
        }

        @Override
        public void readField (Field field, Object target, ObjectInputStream in)
            throws Exception
        {
            if (in.readBoolean()) {
                Object value = _streamer.createObject(in);
                _streamer.readObject(value, in, true);
                field.set(target, value);
            } else {
                field.set(target, null);
            }
        }

        @Override
        public void writeField (Field field, Object source, ObjectOutputStream out)
            throws Exception
        {
            Object value = field.get(source);
            if (value == null) {
                out.writeBoolean(false);
            } else {
                out.writeBoolean(true);
                _streamer.writeObject(value, out, true);
            }
        }

        @Override
        public String toString ()
        {
            return "StreamerMarshaller:" + _streamer.toString();
        }

        /** The streamer we use to read and write our field. */
        protected Streamer _streamer;
    }

    /**
     * Uses custom accessor methods to read and write a field.
     */
    protected static class MethodFieldMarshaller extends FieldMarshaller
    {
        public MethodFieldMarshaller (Method reader, Method writer)
        {
            _reader = reader;
            _writer = writer;
        }

        @Override
        public void readField (Field field, Object target, ObjectInputStream in)
            throws Exception
        {
            _reader.invoke(target, in);
        }

        @Override
        public void writeField (Field field, Object source, ObjectOutputStream out)
            throws Exception
        {
            _writer.invoke(source, out);
        }

        protected Method _reader, _writer;
    }

    /**
     * Creates instances of all known field marshaller types and populates the {@link
     * #_marshallers} table with them. This is called the first time a marshaller is requested.
     */
    protected static void createMarshallers ()
    {
        // create our table
        _marshallers = new HashMap<Class<?>, FieldMarshaller>();

        // create a generic marshaller for streamable instances
        FieldMarshaller gmarsh = new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.set(target, in.readObject());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeObject(field.get(source));
            }
        };
        _marshallers.put(Streamable.class, gmarsh);

        // use the same generic marshaller for fields declared to by type Object or Object[] with
        // the expectation that they will contain only primitive types or Streamables; the runtime
        // will fail informatively if we attempt to store non-Streamable objects in that field
        _marshallers.put(Object.class, gmarsh);
        _marshallers.put(Object[].class, gmarsh);

        // create marshallers for the primitive types
        _marshallers.put(Boolean.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setBoolean(target, in.readBoolean());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeBoolean(field.getBoolean(source));
            }
        });
        _marshallers.put(Byte.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setByte(target, in.readByte());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeByte(field.getByte(source));
            }
        });
        _marshallers.put(Character.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setChar(target, in.readChar());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeChar(field.getChar(source));
            }
        });
        _marshallers.put(Short.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setShort(target, in.readShort());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeShort(field.getShort(source));
            }
        });
        _marshallers.put(Integer.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setInt(target, in.readInt());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeInt(field.getInt(source));
            }
        });
        _marshallers.put(Long.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setLong(target, in.readLong());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeLong(field.getLong(source));
            }
        });
        _marshallers.put(Float.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setFloat(target, in.readFloat());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeFloat(field.getFloat(source));
            }
        });
        _marshallers.put(Double.TYPE, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.setDouble(target, in.readDouble());
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeDouble(field.getDouble(source));
            }
        });
        _marshallers.put(Date.class, new FieldMarshaller() {
            @Override
            public void readField (Field field, Object target, ObjectInputStream in)
                throws Exception {
                field.set(target, new Date(in.readLong()));
            }
            @Override
            public void writeField (Field field, Object source, ObjectOutputStream out)
                throws Exception {
                out.writeLong(((Date)field.get(source)).getTime());
            }
        });

        // create field marshallers for all of the basic types
        int bscount = BasicStreamers.BSTREAMER_TYPES.length;
        for (int ii = 0; ii < bscount; ii++) {
            _marshallers.put(BasicStreamers.BSTREAMER_TYPES[ii],
                             new StreamerMarshaller(BasicStreamers.BSTREAMER_INSTANCES[ii]));
        }
    }

    /** Contains a mapping from field type to field marshaller instance for that type. */
    protected static HashMap<Class<?>, FieldMarshaller> _marshallers;

    /** Defines the signature to a custom field reader method. */
    protected static final Class<?>[] READER_ARGS = { ObjectInputStream.class };

    /** Defines the signature to a custom field writer method. */
    protected static final Class<?>[] WRITER_ARGS = { ObjectOutputStream.class };
}