http://netty.io/netty-all/: Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers and clients. (The Netty Project) 
/*
 * 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:
 *
 *   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.netty.handler.codec.compression;

import com.jcraft.jzlib.Deflater;
import com.jcraft.jzlib.JZlib;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.channel.ChannelPromiseNotifier;
import io.netty.util.concurrent.EventExecutor;
import io.netty.util.internal.EmptyArrays;

import java.util.concurrent.TimeUnit;


Compresses a ByteBuf using the deflate algorithm. 
/**
 * Compresses a {@link ByteBuf} using the deflate algorithm.
 */
public class JZlibEncoder extends ZlibEncoder {

    private final int wrapperOverhead;
    private final Deflater z = new Deflater();
    private volatile boolean finished;
    private volatile ChannelHandlerContext ctx;

    
Creates a new zlib encoder with the default compression level (6), default window bits (15), default memory level (8), and the default wrapper (ZlibWrapper.ZLIB). 
Throws:
/**
     * Creates a new zlib encoder with the default compression level ({@code 6}),
     * default window bits ({@code 15}), default memory level ({@code 8}),
     * and the default wrapper ({@link ZlibWrapper#ZLIB}).
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder() {
        this(6);
    }

    
Creates a new zlib encoder with the specified compressionLevel, default window bits (15), default memory level (8), and the default wrapper (ZlibWrapper.ZLIB). 
Params:
  • compressionLevel –  1 yields the fastest compression and 9 yields the best compression. 0 means no compression. The default compression level is 6.
Throws:
/**
     * Creates a new zlib encoder with the specified {@code compressionLevel},
     * default window bits ({@code 15}), default memory level ({@code 8}),
     * and the default wrapper ({@link ZlibWrapper#ZLIB}).
     *
     * @param compressionLevel
     *        {@code 1} yields the fastest compression and {@code 9} yields the
     *        best compression.  {@code 0} means no compression.  The default
     *        compression level is {@code 6}.
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder(int compressionLevel) {
        this(ZlibWrapper.ZLIB, compressionLevel);
    }

    
Creates a new zlib encoder with the default compression level (6), default window bits (15), default memory level (8), and the specified wrapper. 
Throws:
/**
     * Creates a new zlib encoder with the default compression level ({@code 6}),
     * default window bits ({@code 15}), default memory level ({@code 8}),
     * and the specified wrapper.
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder(ZlibWrapper wrapper) {
        this(wrapper, 6);
    }

    
Creates a new zlib encoder with the specified compressionLevel, default window bits (15), default memory level (8), and the specified wrapper. 
Params:
  • compressionLevel –  1 yields the fastest compression and 9 yields the best compression. 0 means no compression. The default compression level is 6.
Throws:
/**
     * Creates a new zlib encoder with the specified {@code compressionLevel},
     * default window bits ({@code 15}), default memory level ({@code 8}),
     * and the specified wrapper.
     *
     * @param compressionLevel
     *        {@code 1} yields the fastest compression and {@code 9} yields the
     *        best compression.  {@code 0} means no compression.  The default
     *        compression level is {@code 6}.
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder(ZlibWrapper wrapper, int compressionLevel) {
        this(wrapper, compressionLevel, 15, 8);
    }

    
Creates a new zlib encoder with the specified compressionLevel, the specified windowBits, the specified memLevel, and the specified wrapper. 
Params:
  • compressionLevel –  1 yields the fastest compression and 9 yields the best compression. 0 means no compression. The default compression level is 6.
  • windowBits –  The base two logarithm of the size of the history buffer. The value should be in the range 9 to 15 inclusive. Larger values result in better compression at the expense of memory usage. The default value is 15.
  • memLevel –  How much memory should be allocated for the internal compression state. 1 uses minimum memory and 9 uses maximum memory. Larger values result in better and faster compression at the expense of memory usage. The default value is 8
Throws:
/**
     * Creates a new zlib encoder with the specified {@code compressionLevel},
     * the specified {@code windowBits}, the specified {@code memLevel}, and
     * the specified wrapper.
     *
     * @param compressionLevel
     *        {@code 1} yields the fastest compression and {@code 9} yields the
     *        best compression.  {@code 0} means no compression.  The default
     *        compression level is {@code 6}.
     * @param windowBits
     *        The base two logarithm of the size of the history buffer.  The
     *        value should be in the range {@code 9} to {@code 15} inclusive.
     *        Larger values result in better compression at the expense of
     *        memory usage.  The default value is {@code 15}.
     * @param memLevel
     *        How much memory should be allocated for the internal compression
     *        state.  {@code 1} uses minimum memory and {@code 9} uses maximum
     *        memory.  Larger values result in better and faster compression
     *        at the expense of memory usage.  The default value is {@code 8}
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder(ZlibWrapper wrapper, int compressionLevel, int windowBits, int memLevel) {

        if (compressionLevel < 0 || compressionLevel > 9) {
            throw new IllegalArgumentException(
                    "compressionLevel: " + compressionLevel +
                    " (expected: 0-9)");
        }
        if (windowBits < 9 || windowBits > 15) {
            throw new IllegalArgumentException(
                    "windowBits: " + windowBits + " (expected: 9-15)");
        }
        if (memLevel < 1 || memLevel > 9) {
            throw new IllegalArgumentException(
                    "memLevel: " + memLevel + " (expected: 1-9)");
        }
        if (wrapper == null) {
            throw new NullPointerException("wrapper");
        }
        if (wrapper == ZlibWrapper.ZLIB_OR_NONE) {
            throw new IllegalArgumentException(
                    "wrapper '" + ZlibWrapper.ZLIB_OR_NONE + "' is not " +
                    "allowed for compression.");
        }

        int resultCode = z.init(
                compressionLevel, windowBits, memLevel,
                ZlibUtil.convertWrapperType(wrapper));
        if (resultCode != JZlib.Z_OK) {
            ZlibUtil.fail(z, "initialization failure", resultCode);
        }

        wrapperOverhead = ZlibUtil.wrapperOverhead(wrapper);
    }

    
Creates a new zlib encoder with the default compression level (6), default window bits (15), default memory level (8), and the specified preset dictionary. The wrapper is always ZlibWrapper.ZLIB because it is the only format that supports the preset dictionary. 
Params:
  • dictionary –  the preset dictionary
Throws:
/**
     * Creates a new zlib encoder with the default compression level ({@code 6}),
     * default window bits ({@code 15}), default memory level ({@code 8}),
     * and the specified preset dictionary.  The wrapper is always
     * {@link ZlibWrapper#ZLIB} because it is the only format that supports
     * the preset dictionary.
     *
     * @param dictionary  the preset dictionary
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder(byte[] dictionary) {
        this(6, dictionary);
    }

    
Creates a new zlib encoder with the specified compressionLevel, default window bits (15), default memory level (8), and the specified preset dictionary. The wrapper is always ZlibWrapper.ZLIB because it is the only format that supports the preset dictionary. 
Params:
  • compressionLevel –  1 yields the fastest compression and 9 yields the best compression. 0 means no compression. The default compression level is 6.
  • dictionary –  the preset dictionary
Throws:
/**
     * Creates a new zlib encoder with the specified {@code compressionLevel},
     * default window bits ({@code 15}), default memory level ({@code 8}),
     * and the specified preset dictionary.  The wrapper is always
     * {@link ZlibWrapper#ZLIB} because it is the only format that supports
     * the preset dictionary.
     *
     * @param compressionLevel
     *        {@code 1} yields the fastest compression and {@code 9} yields the
     *        best compression.  {@code 0} means no compression.  The default
     *        compression level is {@code 6}.
     * @param dictionary  the preset dictionary
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder(int compressionLevel, byte[] dictionary) {
        this(compressionLevel, 15, 8, dictionary);
    }

    
Creates a new zlib encoder with the specified compressionLevel, the specified windowBits, the specified memLevel, and the specified preset dictionary. The wrapper is always ZlibWrapper.ZLIB because it is the only format that supports the preset dictionary. 
Params:
  • compressionLevel –  1 yields the fastest compression and 9 yields the best compression. 0 means no compression. The default compression level is 6.
  • windowBits –  The base two logarithm of the size of the history buffer. The value should be in the range 9 to 15 inclusive. Larger values result in better compression at the expense of memory usage. The default value is 15.
  • memLevel –  How much memory should be allocated for the internal compression state. 1 uses minimum memory and 9 uses maximum memory. Larger values result in better and faster compression at the expense of memory usage. The default value is 8
  • dictionary –  the preset dictionary
Throws:
/**
     * Creates a new zlib encoder with the specified {@code compressionLevel},
     * the specified {@code windowBits}, the specified {@code memLevel},
     * and the specified preset dictionary.  The wrapper is always
     * {@link ZlibWrapper#ZLIB} because it is the only format that supports
     * the preset dictionary.
     *
     * @param compressionLevel
     *        {@code 1} yields the fastest compression and {@code 9} yields the
     *        best compression.  {@code 0} means no compression.  The default
     *        compression level is {@code 6}.
     * @param windowBits
     *        The base two logarithm of the size of the history buffer.  The
     *        value should be in the range {@code 9} to {@code 15} inclusive.
     *        Larger values result in better compression at the expense of
     *        memory usage.  The default value is {@code 15}.
     * @param memLevel
     *        How much memory should be allocated for the internal compression
     *        state.  {@code 1} uses minimum memory and {@code 9} uses maximum
     *        memory.  Larger values result in better and faster compression
     *        at the expense of memory usage.  The default value is {@code 8}
     * @param dictionary  the preset dictionary
     *
     * @throws CompressionException if failed to initialize zlib
     */
    public JZlibEncoder(int compressionLevel, int windowBits, int memLevel, byte[] dictionary) {
        if (compressionLevel < 0 || compressionLevel > 9) {
            throw new IllegalArgumentException("compressionLevel: " + compressionLevel + " (expected: 0-9)");
        }
        if (windowBits < 9 || windowBits > 15) {
            throw new IllegalArgumentException(
                    "windowBits: " + windowBits + " (expected: 9-15)");
        }
        if (memLevel < 1 || memLevel > 9) {
            throw new IllegalArgumentException(
                    "memLevel: " + memLevel + " (expected: 1-9)");
        }
        if (dictionary == null) {
            throw new NullPointerException("dictionary");
        }
        int resultCode;
        resultCode = z.deflateInit(
                compressionLevel, windowBits, memLevel,
                JZlib.W_ZLIB); // Default: ZLIB format
        if (resultCode != JZlib.Z_OK) {
            ZlibUtil.fail(z, "initialization failure", resultCode);
        } else {
            resultCode = z.deflateSetDictionary(dictionary, dictionary.length);
            if (resultCode != JZlib.Z_OK) {
                ZlibUtil.fail(z, "failed to set the dictionary", resultCode);
            }
        }

        wrapperOverhead = ZlibUtil.wrapperOverhead(ZlibWrapper.ZLIB);
    }

    @Override
    public ChannelFuture close() {
        return close(ctx().channel().newPromise());
    }

    @Override
    public ChannelFuture close(final ChannelPromise promise) {
        ChannelHandlerContext ctx = ctx();
        EventExecutor executor = ctx.executor();
        if (executor.inEventLoop()) {
            return finishEncode(ctx, promise);
        } else {
            final ChannelPromise p = ctx.newPromise();
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    ChannelFuture f = finishEncode(ctx(), p);
                    f.addListener(new ChannelPromiseNotifier(promise));
                }
            });
            return p;
        }
    }

    private ChannelHandlerContext ctx() {
        ChannelHandlerContext ctx = this.ctx;
        if (ctx == null) {
            throw new IllegalStateException("not added to a pipeline");
        }
        return ctx;
    }

    @Override
    public boolean isClosed() {
        return finished;
    }

    @Override
    protected void encode(ChannelHandlerContext ctx, ByteBuf in, ByteBuf out) throws Exception {
        if (finished) {
            out.writeBytes(in);
            return;
        }

        int inputLength = in.readableBytes();
        if (inputLength == 0) {
            return;
        }

        try {
            // Configure input.
            boolean inHasArray = in.hasArray();
            z.avail_in = inputLength;
            if (inHasArray) {
                z.next_in = in.array();
                z.next_in_index = in.arrayOffset() + in.readerIndex();
            } else {
                byte[] array = new byte[inputLength];
                in.getBytes(in.readerIndex(), array);
                z.next_in = array;
                z.next_in_index = 0;
            }
            int oldNextInIndex = z.next_in_index;

            // Configure output.
            int maxOutputLength = (int) Math.ceil(inputLength * 1.001) + 12 + wrapperOverhead;
            out.ensureWritable(maxOutputLength);
            z.avail_out = maxOutputLength;
            z.next_out = out.array();
            z.next_out_index = out.arrayOffset() + out.writerIndex();
            int oldNextOutIndex = z.next_out_index;

            // Note that Z_PARTIAL_FLUSH has been deprecated.
            int resultCode;
            try {
                resultCode = z.deflate(JZlib.Z_SYNC_FLUSH);
            } finally {
                in.skipBytes(z.next_in_index - oldNextInIndex);
            }

            if (resultCode != JZlib.Z_OK) {
                ZlibUtil.fail(z, "compression failure", resultCode);
            }

            int outputLength = z.next_out_index - oldNextOutIndex;
            if (outputLength > 0) {
                out.writerIndex(out.writerIndex() + outputLength);
            }
        } finally {
            // Deference the external references explicitly to tell the VM that
            // the allocated byte arrays are temporary so that the call stack
            // can be utilized.
            // I'm not sure if the modern VMs do this optimization though.
            z.next_in = null;
            z.next_out = null;
        }
    }

    @Override
    public void close(
            final ChannelHandlerContext ctx,
            final ChannelPromise promise) {
        ChannelFuture f = finishEncode(ctx, ctx.newPromise());
        f.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture f) throws Exception {
                ctx.close(promise);
            }
        });

        if (!f.isDone()) {
            // Ensure the channel is closed even if the write operation completes in time.
            ctx.executor().schedule(new Runnable() {
                @Override
                public void run() {
                    ctx.close(promise);
                }
            }, 10, TimeUnit.SECONDS); // FIXME: Magic number
        }
    }

    private ChannelFuture finishEncode(ChannelHandlerContext ctx, ChannelPromise promise) {
        if (finished) {
            promise.setSuccess();
            return promise;
        }
        finished = true;

        ByteBuf footer;
        try {
            // Configure input.
            z.next_in = EmptyArrays.EMPTY_BYTES;
            z.next_in_index = 0;
            z.avail_in = 0;

            // Configure output.
            byte[] out = new byte[32]; // room for ADLER32 + ZLIB / CRC32 + GZIP header
            z.next_out = out;
            z.next_out_index = 0;
            z.avail_out = out.length;

            // Write the ADLER32 checksum (stream footer).
            int resultCode = z.deflate(JZlib.Z_FINISH);
            if (resultCode != JZlib.Z_OK && resultCode != JZlib.Z_STREAM_END) {
                promise.setFailure(ZlibUtil.deflaterException(z, "compression failure", resultCode));
                return promise;
            } else if (z.next_out_index != 0) {
                footer = Unpooled.wrappedBuffer(out, 0, z.next_out_index);
            } else {
                footer = Unpooled.EMPTY_BUFFER;
            }
        } finally {
            z.deflateEnd();

            // Deference the external references explicitly to tell the VM that
            // the allocated byte arrays are temporary so that the call stack
            // can be utilized.
            // I'm not sure if the modern VMs do this optimization though.
            z.next_in = null;
            z.next_out = null;
        }
        return ctx.writeAndFlush(footer, promise);
    }

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        this.ctx = ctx;
    }
}