Message.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.jafka.message;

import static java.lang.String.format;

import java.nio.ByteBuffer;

import io.jafka.api.ICalculable;
import io.jafka.common.UnknownMagicByteException;
import io.jafka.utils.Utils;

/**
 * * A message. The format of an N byte message is the following:
 * 
 * <p>
 * magic byte is 1
 * 
 * <pre>
 * 1. 1 byte "magic" identifier to allow format changes
 * 2. 1 byte "attributes" identifier to allow annotations on the message
 * independent of the version (e.g. compression enabled, type of codec used)
 * 3. 4 byte CRC32 of the payload
 * 4. N - 6 byte payload
 * </pre>
 *
 * 
 * @author adyliu (imxylz@gmail.com)
 * @since 1.0
 */
public class Message implements ICalculable {

    private static final byte MAGIC_VERSION2 = 1;

    public static final byte CurrentMagicValue = 1;

    public static final byte MAGIC_OFFSET = 0;

    public static final byte MAGIC_LENGTH = 1;

    public static final byte ATTRIBUTE_OFFSET = MAGIC_OFFSET + MAGIC_LENGTH;

    public static final byte ATTRIBUT_ELENGTH = 1;

    /**
     * Specifies the mask for the compression code. 2 bits to hold the
     * compression codec. 0 is reserved to indicate no compression
     */
    public static final int CompressionCodeMask = 0x03; //

    public static final int NoCompression = 0;

    /**
     * Computes the CRC value based on the magic byte
     * 
     * @param magic Specifies the magic byte value. Possible values are 1
     *        (compression)
     * @return crc value
     */
    public static int crcOffset(byte magic) {
        switch (magic) {
            case MAGIC_VERSION2:
                return ATTRIBUTE_OFFSET + ATTRIBUT_ELENGTH;

        }
        throw new UnknownMagicByteException(format("Magic byte value of %d is unknown", magic));
    }

    public static final byte CrcLength = 4;

    /**
     * Computes the offset to the message payload based on the magic byte
     * 
     * @param magic Specifies the magic byte value. Possible values are 0
     *        and 1 0 for no compression 1 for compression
     * @return offset data
     */
    public static int payloadOffset(byte magic) {
        return crcOffset(magic) + CrcLength;
    }

    /**
     * Computes the size of the message header based on the magic byte
     * 
     * @param magic Specifies the magic byte value. Possible values are 0
     *        and 1 0 for no compression 1 for compression
     * @return size of header
     */
    public static int headerSize(byte magic) {
        return payloadOffset(magic);
    }

    /**
     * Size of the header for magic byte 0. This is the minimum size of any
     * message header
     */
    public static final int MinHeaderSize = headerSize((byte) 1);

    final ByteBuffer buffer;

    private final int messageSize;

    public Message(ByteBuffer buffer) {
        this.buffer = buffer;
        this.messageSize = buffer.limit();
    }

    public Message(long checksum, byte[] bytes, CompressionCodec compressionCodec) {
        this(ByteBuffer.allocate(Message.headerSize(Message.CurrentMagicValue) + bytes.length));
        buffer.put(CurrentMagicValue);
        byte attributes = 0;
        if (compressionCodec.codec > 0) {
            attributes = (byte) (attributes | (CompressionCodeMask & compressionCodec.codec));
        }
        buffer.put(attributes);
        Utils.putUnsignedInt(buffer, checksum);
        buffer.put(bytes);
        buffer.rewind();
    }

    public Message(long checksum, byte[] bytes) {
        this(checksum, bytes, CompressionCodec.NoCompressionCodec);
    }

    public Message(byte[] bytes, CompressionCodec compressionCodec) {
        this(Utils.crc32(bytes), bytes, compressionCodec);
    }

    /**
     * create no compression message
     * 
     * @param bytes message data
     * @see CompressionCodec#NoCompressionCodec
     */
    public Message(byte[] bytes) {
        this(bytes, CompressionCodec.NoCompressionCodec);
    }

    //
    public int getSizeInBytes() {
        return messageSize;
    }

    /**
     * magic code ( constant 1)
     * 
     * @return 1
     */
    public byte magic() {
        return buffer.get(MAGIC_OFFSET);
    }

    public int payloadSize() {
        return getSizeInBytes() - headerSize(magic());
    }

    public byte attributes() {
        return buffer.get(ATTRIBUTE_OFFSET);
    }

    public CompressionCodec compressionCodec() {
        byte magicByte = magic();
        switch (magicByte) {
            case 0:
                return CompressionCodec.NoCompressionCodec;
            case 1:
                return CompressionCodec.valueOf(buffer.get(ATTRIBUTE_OFFSET) & CompressionCodeMask);
        }
        throw new RuntimeException("Invalid magic byte " + magicByte);
    }

    public long checksum() {
        return Utils.getUnsignedInt(buffer, crcOffset(magic()));
    }

    /**
     * get the real data without message header
     * @return message data(without header)
     */
    public ByteBuffer payload() {
        ByteBuffer payload = buffer.duplicate();
        payload.position(headerSize(magic()));
        payload = payload.slice();
        payload.limit(payloadSize());
        payload.rewind();
        return payload;
    }

    public boolean isValid() {
        return checksum() == Utils.crc32(buffer.array(), buffer.position() + buffer.arrayOffset() + payloadOffset(magic()), payloadSize());
    }

    public int serializedSize() {
        return 4 /* int size */+ buffer.limit();
    }

    public void serializeTo(ByteBuffer serBuffer) {
        serBuffer.putInt(buffer.limit());
        serBuffer.put(buffer.duplicate());
    }

    //
    @Override
    public String toString() {
        return format("message(magic = %d, attributes = %d, crc = %d, payload = %s)",//
                magic(), attributes(), checksum(), payload());
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof Message) {
            Message m = (Message) obj;
            return getSizeInBytes() == m.getSizeInBytes()//
                    && attributes() == m.attributes()//
                    && checksum() == m.checksum()//
                    && payload() == m.payload()//
                    && magic() == m.magic();
        }
        return false;
    }

    @Override
    public int hashCode() {
        return buffer.hashCode();
    }
}