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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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/*
 * 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 org.apache.cassandra.net;

import java.nio.ByteBuffer;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler;
import net.jpountz.lz4.LZ4Compressor;
import net.jpountz.lz4.LZ4Factory;
import net.jpountz.xxhash.XXHash32;
import net.jpountz.xxhash.XXHashFactory;
import org.apache.cassandra.io.compress.BufferType;
import org.apache.cassandra.utils.ByteBufferUtil;
import org.apache.cassandra.utils.memory.BufferPool;

import static java.lang.Integer.reverseBytes;
import static java.lang.Math.min;
import static org.apache.cassandra.net.LegacyLZ4Constants.*;

/**
 * LZ4 {@link FrameEncoder} implementation for compressed legacy (3.0, 3.11) connections.
 *
 * Netty's provided implementation - {@link io.netty.handler.codec.compression.Lz4FrameEncoder} couldn't be reused
 * for two reasons:
 *   1. It notifies flushes as successful when they may not be, by flushing an empty buffer ahead
 *      of the compressed buffer
 *   2. It has very poor performance when coupled with xxHash, which we use for legacy connections -
 *      allocating a single-byte array and making a JNI call for every byte of the payload
 *
 * Please see {@link FrameDecoderLegacyLZ4} for the description of the on-wire format of the LZ4 blocks
 * used by this encoder.
 */
@ChannelHandler.Sharable
class FrameEncoderLegacyLZ4 extends FrameEncoder
{
    static final FrameEncoderLegacyLZ4 instance =
        new FrameEncoderLegacyLZ4(XXHashFactory.fastestInstance().hash32(),
                                  LZ4Factory.fastestInstance().fastCompressor());

    private final XXHash32 xxhash;
    private final LZ4Compressor compressor;

    private FrameEncoderLegacyLZ4(XXHash32 xxhash, LZ4Compressor compressor)
    {
        this.xxhash = xxhash;
        this.compressor = compressor;
    }

    @Override
    ByteBuf encode(boolean isSelfContained, ByteBuffer payload)
    {
        ByteBuffer frame = null;
        try
        {
            frame = bufferPool.getAtLeast(calculateMaxFrameLength(payload), BufferType.OFF_HEAP);

            int   frameOffset = 0;
            int payloadOffset = 0;

            int payloadLength = payload.remaining();
            while (payloadOffset < payloadLength)
            {
                int blockLength = min(DEFAULT_BLOCK_LENGTH, payloadLength - payloadOffset);
                frameOffset += compressBlock(frame, frameOffset, payload, payloadOffset, blockLength);
                payloadOffset += blockLength;
            }

            frame.limit(frameOffset);
            bufferPool.putUnusedPortion(frame);

            return GlobalBufferPoolAllocator.wrap(frame);
        }
        catch (Throwable t)
        {
            if (null != frame)
                bufferPool.put(frame);
            throw t;
        }
        finally
        {
            bufferPool.put(payload);
        }
    }

    private int compressBlock(ByteBuffer frame, int frameOffset, ByteBuffer payload, int payloadOffset, int blockLength)
    {
        int frameBytesRemaining = frame.limit() - (frameOffset + HEADER_LENGTH);
        int compressedLength = compressor.compress(payload, payloadOffset, blockLength, frame, frameOffset + HEADER_LENGTH, frameBytesRemaining);
        if (compressedLength >= blockLength)
        {
            ByteBufferUtil.copyBytes(payload, payloadOffset, frame, frameOffset + HEADER_LENGTH, blockLength);
            compressedLength = blockLength;
        }
        int checksum = xxhash.hash(payload, payloadOffset, blockLength, XXHASH_SEED) & XXHASH_MASK;
        writeHeader(frame, frameOffset, compressedLength, blockLength, checksum);
        return HEADER_LENGTH + compressedLength;
    }

    private static final byte TOKEN_NON_COMPRESSED = 0x15;
    private static final byte TOKEN_COMPRESSED     = 0x25;

    private static void writeHeader(ByteBuffer frame, int frameOffset, int compressedLength, int uncompressedLength, int checksum)
    {
        byte token = compressedLength == uncompressedLength
                   ? TOKEN_NON_COMPRESSED
                   : TOKEN_COMPRESSED;

        frame.putLong(frameOffset + MAGIC_NUMBER_OFFSET,        MAGIC_NUMBER                    );
        frame.put    (frameOffset + TOKEN_OFFSET,               token                           );
        frame.putInt (frameOffset + COMPRESSED_LENGTH_OFFSET,   reverseBytes(compressedLength)  );
        frame.putInt (frameOffset + UNCOMPRESSED_LENGTH_OFFSET, reverseBytes(uncompressedLength));
        frame.putInt (frameOffset + CHECKSUM_OFFSET,            reverseBytes(checksum)          );
    }

    private int calculateMaxFrameLength(ByteBuffer payload)
    {
        int payloadLength = payload.remaining();
        int blockCount = payloadLength / DEFAULT_BLOCK_LENGTH + (payloadLength % DEFAULT_BLOCK_LENGTH != 0 ? 1 : 0);
        return compressor.maxCompressedLength(payloadLength) + HEADER_LENGTH * blockCount;
    }
}