Subversion Repositories mkgmap

/*
 * Copyright (C) 2007 Steve Ratcliffe
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 as
 *  published by the Free Software Foundation.
 *
 *  This program 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 for more details.
 *
 *
 * Author: Steve Ratcliffe
 * Create date: Dec 19, 2007
 */
package uk.me.parabola.imgfmt.mps;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

import uk.me.parabola.imgfmt.fs.ImgChannel;
import uk.me.parabola.io.StructuredOutputStream;

/**
 * All the blocks in the file have a type and a length.
 *
 * @author Steve Ratcliffe
 */
public abstract class Block {
        private final int type;
        private final ByteArrayOutputStream output = new ByteArrayOutputStream();

        protected Block(int type) {
                this.type = type;
        }

        public void write(ImgChannel chan) throws IOException {
                // First write the body to the byte buffer so that we know its length.
                writeBody(new StructuredOutputStream(output));

                ByteBuffer buf = ByteBuffer.allocate(16);
                buf.order(ByteOrder.LITTLE_ENDIAN);
                buf.put((byte) type);
                char len = getLength();
                buf.putChar(len);

                // write the header.
                buf.flip();
                chan.write(buf);

                // write the body.
                buf = ByteBuffer.allocate(len);
                buf.put(output.toByteArray());
                buf.flip();
                chan.write(buf);
        }

        /**
         * Writes the body to the output stream given.
         *
         * @param out The stream to write to.
         */
        protected abstract void writeBody(StructuredOutputStream out) throws IOException;

        /**
         * This is only valid after everything is written to the block.
         *
         * @return The length of the block (or the amount written already).
         */
        private char getLength() {
                int len = output.toByteArray().length;
                assert len <= 0xffff;
                return (char) len;
        }
}