MetaMessage.java

/*
 * Copyright (c) 1999, 2013, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.sound.midi;


/**
 * A <code>MetaMessage</code> is a <code>{@link MidiMessage}</code> that is not meaningful to synthesizers, but
 * that can be stored in a MIDI file and interpreted by a sequencer program.
 * (See the discussion in the <code>MidiMessage</code>
 * class description.)  The Standard MIDI Files specification defines
 * various types of meta-events, such as sequence number, lyric, cue point,
 * and set tempo.  There are also meta-events
 * for such information as lyrics, copyrights, tempo indications, time and key
 * signatures, markers, etc.  For more information, see the Standard MIDI Files 1.0
 * specification, which is part of the Complete MIDI 1.0 Detailed Specification
 * published by the MIDI Manufacturer's Association
 * (<a href = http://www.midi.org>http://www.midi.org</a>).
 *
 * <p>
 * When data is being transported using MIDI wire protocol,
 * a <code>{@link ShortMessage}</code> with the status value <code>0xFF</code> represents
 * a system reset message.  In MIDI files, this same status value denotes a <code>MetaMessage</code>.
 * The types of meta-message are distinguished from each other by the first byte
 * that follows the status byte <code>0xFF</code>.  The subsequent bytes are data
 * bytes.  As with system exclusive messages, there are an arbitrary number of
 * data bytes, depending on the type of <code>MetaMessage</code>.
 *
 * @see MetaEventListener
 *
 * @author David Rivas
 * @author Kara Kytle
 */

public class MetaMessage extends MidiMessage {


    // Status byte defines

    /**
     * Status byte for <code>MetaMessage</code> (0xFF, or 255), which is used
     * in MIDI files.  It has the same value as SYSTEM_RESET, which
     * is used in the real-time "MIDI wire" protocol.
     * @see MidiMessage#getStatus
     */
    public static final int META                                                = 0xFF; // 255

    // Instance variables

    /**
     * The length of the actual message in the data array.
     * This is used to determine how many bytes of the data array
     * is the message, and how many are the status byte, the
     * type byte, and the variable-length-int describing the
     * length of the message.
     */
    private int dataLength = 0;


    /**
     * Constructs a new <code>MetaMessage</code>. The contents of
     * the message are not set here; use
     * {@link #setMessage(int, byte[], int) setMessage}
     * to set them subsequently.
     */
    public MetaMessage() {
        // Default meta message data: just the META status byte value
        this(new byte[]{(byte) META, 0});
    }

    /**
     * Constructs a new {@code MetaMessage} and sets the message parameters.
     * The contents of the message can be changed by using
     * the {@code setMessage} method.
     *
     * @param type   meta-message type (must be less than 128)
     * @param data   the data bytes in the MIDI message
     * @param length an amount of bytes in the {@code data} byte array;
     *     it should be non-negative and less than or equal to
     *     {@code data.length}
     * @throws InvalidMidiDataException if the parameter values do not specify
     *     a valid MIDI meta message
     * @see #setMessage(int, byte[], int)
     * @see #getType()
     * @see #getData()
     * @since 1.7
     */
    public MetaMessage(int type, byte[] data, int length)
            throws InvalidMidiDataException {
        super(null);
        setMessage(type, data, length); // can throw InvalidMidiDataException
    }


    /**
     * Constructs a new <code>MetaMessage</code>.
     * @param data an array of bytes containing the complete message.
     * The message data may be changed using the <code>setMessage</code>
     * method.
     * @see #setMessage
     */
    protected MetaMessage(byte[] data) {
        super(data);
        //$$fb 2001-10-06: need to calculate dataLength. Fix for bug #4511796
        if (data.length>=3) {
            dataLength=data.length-3;
            int pos=2;
            while (pos<data.length && (data[pos] & 0x80)!=0) {
                dataLength--; pos++;
            }
        }
    }


    /**
     * Sets the message parameters for a <code>MetaMessage</code>.
     * Since only one status byte value, <code>0xFF</code>, is allowed for meta-messages,
     * it does not need to be specified here.  Calls to <code>{@link MidiMessage#getStatus getStatus}</code> return
     * <code>0xFF</code> for all meta-messages.
     * <p>
     * The <code>type</code> argument should be a valid value for the byte that
     * follows the status byte in the <code>MetaMessage</code>.  The <code>data</code> argument
     * should contain all the subsequent bytes of the <code>MetaMessage</code>.  In other words,
     * the byte that specifies the type of <code>MetaMessage</code> is not considered a data byte.
     *
     * @param type              meta-message type (must be less than 128)
     * @param data              the data bytes in the MIDI message
     * @param length    the number of bytes in the <code>data</code>
     * byte array
     * @throws                  InvalidMidiDataException  if the
     * parameter values do not specify a valid MIDI meta message
     */
    public void setMessage(int type, byte[] data, int length) throws InvalidMidiDataException {

        if (type >= 128 || type < 0) {
            throw new InvalidMidiDataException("Invalid meta event with type " + type);
        }
        if ((length > 0 && length > data.length) || length < 0) {
            throw new InvalidMidiDataException("length out of bounds: "+length);
        }

        this.length = 2 + getVarIntLength(length) + length;
        this.dataLength = length;
        this.data = new byte[this.length];
        this.data[0] = (byte) META;        // status value for MetaMessages (meta events)
        this.data[1] = (byte) type;        // MetaMessage type
        writeVarInt(this.data, 2, length); // write the length as a variable int
        if (length > 0) {
            System.arraycopy(data, 0, this.data, this.length - this.dataLength, this.dataLength);
        }
    }


    /**
     * Obtains the type of the <code>MetaMessage</code>.
     * @return an integer representing the <code>MetaMessage</code> type
     */
    public int getType() {
        if (length>=2) {
            return data[1] & 0xFF;
        }
        return 0;
    }



    /**
     * Obtains a copy of the data for the meta message.  The returned
     * array of bytes does not include the status byte or the message
     * length data.  The length of the data for the meta message is
     * the length of the array.  Note that the length of the entire
     * message includes the status byte and the meta message type
     * byte, and therefore may be longer than the returned array.
     * @return array containing the meta message data.
     * @see MidiMessage#getLength
     */
    public byte[] getData() {
        byte[] returnedArray = new byte[dataLength];
        System.arraycopy(data, (length - dataLength), returnedArray, 0, dataLength);
        return returnedArray;
    }


    /**
     * Creates a new object of the same class and with the same contents
     * as this object.
     * @return a clone of this instance
     */
    public Object clone() {
        byte[] newData = new byte[length];
        System.arraycopy(data, 0, newData, 0, newData.length);

        MetaMessage event = new MetaMessage(newData);
        return event;
    }

    // HELPER METHODS

    private int getVarIntLength(long value) {
        int length = 0;
        do {
            value = value >> 7;
            length++;
        } while (value > 0);
        return length;
    }

    private final static long mask = 0x7F;

    private void writeVarInt(byte[] data, int off, long value) {
        int shift=63; // number of bitwise left-shifts of mask
        // first screen out leading zeros
        while ((shift > 0) && ((value & (mask << shift)) == 0)) shift-=7;
        // then write actual values
        while (shift > 0) {
            data[off++]=(byte) (((value & (mask << shift)) >> shift) | 0x80);
            shift-=7;
        }
        data[off] = (byte) (value & mask);
    }

}