108 lines
3.8 KiB
Java
108 lines
3.8 KiB
Java
/*
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* Copyright 2012 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.handler.codec.compression.snappy;
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import io.netty.buffer.ByteBuf;
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import io.netty.channel.ChannelHandlerContext;
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import io.netty.handler.codec.ByteToByteEncoder;
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import static io.netty.handler.codec.compression.snappy.SnappyChecksumUtil.*;
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/**
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* Compresses a {@link ByteBuf} using the Snappy framing format.
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*
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* See http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt
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*/
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public class SnappyFramedEncoder extends ByteToByteEncoder {
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/**
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* The minimum amount that we'll consider actually attempting to compress.
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* This value is preamble + the minimum length our Snappy service will
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* compress (instead of just emitting a literal).
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*/
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private static final int MIN_COMPRESSIBLE_LENGTH = 18;
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/**
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* All streams should start with the "Stream identifier", containing chunk
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* type 0xff, a length field of 0x6, and 'sNaPpY' in ASCII.
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*/
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private static final byte[] STREAM_START = {
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-0x80, 0x06, 0x00, 0x73, 0x4e, 0x61, 0x50, 0x70, 0x59
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};
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private final Snappy snappy = new Snappy();
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private boolean started;
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@Override
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public void encode(ChannelHandlerContext ctx, ByteBuf in, ByteBuf out) throws Exception {
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if (!in.readable()) {
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return;
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}
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if (!started) {
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started = true;
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out.writeBytes(STREAM_START);
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}
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final int chunkLength = in.readableBytes();
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if (chunkLength > MIN_COMPRESSIBLE_LENGTH) {
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// If we have lots of available data, break it up into smaller chunks
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int numberOfChunks = 1 + chunkLength / Short.MAX_VALUE;
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for (int i = 0; i < numberOfChunks; i++) {
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int subChunkLength = Math.min(Short.MAX_VALUE, chunkLength);
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out.writeByte(0);
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writeChunkLength(out, subChunkLength);
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ByteBuf slice = in.slice();
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calculateAndWriteChecksum(slice, out);
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snappy.encode(slice, out, subChunkLength);
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}
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} else {
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out.writeByte(1);
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writeChunkLength(out, chunkLength);
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ByteBuf slice = in.slice();
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calculateAndWriteChecksum(slice, out);
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out.writeBytes(slice);
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}
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in.readerIndex(in.readerIndex() + chunkLength);
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}
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/**
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* Writes the 2-byte chunk length to the output buffer.
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*
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* @param out The buffer to write to
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* @param chunkLength The length to write
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*/
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private static void writeChunkLength(ByteBuf out, int chunkLength) {
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out.writeByte(chunkLength & 0x0ff);
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out.writeByte(chunkLength >> 8 & 0x0ff);
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}
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/**
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* Calculates and writes the 4-byte checksum to the output buffer
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*
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* @param slice The data to calculate the checksum for
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* @param out The output buffer to write the checksum to
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*/
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private static void calculateAndWriteChecksum(ByteBuf slice, ByteBuf out) {
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int checksum = calculateChecksum(slice);
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out.writeByte(checksum & 0x0ff);
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out.writeByte(checksum >> 8 & 0x0ff);
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out.writeByte(checksum >> 16 & 0x0ff);
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out.writeByte(checksum >> 24 & 0x0ff);
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}
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}
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