SnappyFrameEncoder.java — netty Source File

Source Code

/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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:
 *
 *   https://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.netty.handler.codec.compression;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

import static io.netty.handler.codec.compression.Snappy.calculateChecksum;

/**
 * Compresses a {@link ByteBuf} using the Snappy framing format.
 *
 * See <a href="https://github.com/google/snappy/blob/master/framing_format.txt">Snappy framing format</a>.
 */
public class SnappyFrameEncoder extends MessageToByteEncoder<ByteBuf> {

    private static final short SNAPPY_SLICE_SIZE = Short.MAX_VALUE;

    /**
     * Both
     * {@value io.netty.handler.codec.compression.SnappyFrameEncoder#SNAPPY_SLICE_SIZE}
     * and {@value io.netty.handler.codec.compression.SnappyFrameEncoder#SNAPPY_SLICE_JUMBO_SIZE}
     * are valid lengths for the Snappy framing format
     */
    private static final int SNAPPY_SLICE_JUMBO_SIZE = 65535;

    /**
     * The minimum amount that we'll consider actually attempting to compress.
     * This value is preamble + the minimum length our Snappy service will
     * compress (instead of just emitting a literal).
     */
    private static final int MIN_COMPRESSIBLE_LENGTH = 18;

    /**
     * All streams should start with the "Stream identifier", containing chunk
     * type 0xff, a length field of 0x6, and 'sNaPpY' in ASCII.
     */
    private static final byte[] STREAM_START = {
        (byte) 0xff, 0x06, 0x00, 0x00, 0x73, 0x4e, 0x61, 0x50, 0x70, 0x59
    };

    public SnappyFrameEncoder() {
        this(SNAPPY_SLICE_SIZE);
    }

    /**
// ... (94 more lines)