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1   /*
2    * Copyright 2014 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.handler.codec.compression;
17  
18  import io.netty.buffer.ByteBuf;
19  import io.netty.channel.ChannelFuture;
20  import io.netty.channel.ChannelHandlerContext;
21  import io.netty.channel.ChannelPipeline;
22  import io.netty.channel.ChannelPromise;
23  import io.netty.handler.codec.MessageToByteEncoder;
24  import io.netty.util.concurrent.EventExecutor;
25  import io.netty.util.concurrent.PromiseNotifier;
26  
27  import static io.netty.handler.codec.compression.Bzip2Constants.BASE_BLOCK_SIZE;
28  import static io.netty.handler.codec.compression.Bzip2Constants.END_OF_STREAM_MAGIC_1;
29  import static io.netty.handler.codec.compression.Bzip2Constants.END_OF_STREAM_MAGIC_2;
30  import static io.netty.handler.codec.compression.Bzip2Constants.MAGIC_NUMBER;
31  import static io.netty.handler.codec.compression.Bzip2Constants.MAX_BLOCK_SIZE;
32  import static io.netty.handler.codec.compression.Bzip2Constants.MIN_BLOCK_SIZE;
33  
34  /**
35   * Compresses a {@link ByteBuf} using the Bzip2 algorithm.
36   *
37   * See <a href="https://en.wikipedia.org/wiki/Bzip2">Bzip2</a>.
38   */
39  public class Bzip2Encoder extends MessageToByteEncoder<ByteBuf> {
40      /**
41       * Current state of stream.
42       */
43      private enum State {
44          INIT,
45          INIT_BLOCK,
46          WRITE_DATA,
47          CLOSE_BLOCK
48      }
49  
50      private State currentState = State.INIT;
51  
52      /**
53       * A writer that provides bit-level writes.
54       */
55      private final Bzip2BitWriter writer = new Bzip2BitWriter();
56  
57      /**
58       * The declared maximum block size of the stream (before final run-length decoding).
59       */
60      private final int streamBlockSize;
61  
62      /**
63       * The merged CRC of all blocks compressed so far.
64       */
65      private int streamCRC;
66  
67      /**
68       * The compressor for the current block.
69       */
70      private Bzip2BlockCompressor blockCompressor;
71  
72      /**
73       * (@code true} if the compressed stream has been finished, otherwise {@code false}.
74       */
75      private volatile boolean finished;
76  
77      /**
78       * Used to interact with its {@link ChannelPipeline} and other handlers.
79       */
80      private volatile ChannelHandlerContext ctx;
81  
82      /**
83       * Creates a new bzip2 encoder with the maximum (900,000 byte) block size.
84       */
85      public Bzip2Encoder() {
86          this(MAX_BLOCK_SIZE);
87      }
88  
89      /**
90       * Creates a new bzip2 encoder with the specified {@code blockSizeMultiplier}.
91       * @param blockSizeMultiplier
92       *        The Bzip2 block size as a multiple of 100,000 bytes (minimum {@code 1}, maximum {@code 9}).
93       *        Larger block sizes require more memory for both compression and decompression,
94       *        but give better compression ratios. {@code 9} will usually be the best value to use.
95       */
96      public Bzip2Encoder(final int blockSizeMultiplier) {
97          if (blockSizeMultiplier < MIN_BLOCK_SIZE || blockSizeMultiplier > MAX_BLOCK_SIZE) {
98              throw new IllegalArgumentException(
99                      "blockSizeMultiplier: " + blockSizeMultiplier + " (expected: 1-9)");
100         }
101         streamBlockSize = blockSizeMultiplier * BASE_BLOCK_SIZE;
102     }
103 
104     @Override
105     protected void encode(ChannelHandlerContext ctx, ByteBuf in, ByteBuf out) throws Exception {
106         if (finished) {
107             out.writeBytes(in);
108             return;
109         }
110 
111         for (;;) {
112             switch (currentState) {
113                 case INIT:
114                     out.ensureWritable(4);
115                     out.writeMedium(MAGIC_NUMBER);
116                     out.writeByte('0' + streamBlockSize / BASE_BLOCK_SIZE);
117                     currentState = State.INIT_BLOCK;
118                     // fall through
119                 case INIT_BLOCK:
120                     blockCompressor = new Bzip2BlockCompressor(writer, streamBlockSize);
121                     currentState = State.WRITE_DATA;
122                     // fall through
123                 case WRITE_DATA:
124                     if (!in.isReadable()) {
125                         return;
126                     }
127                     Bzip2BlockCompressor blockCompressor = this.blockCompressor;
128                     final int length = Math.min(in.readableBytes(), blockCompressor.availableSize());
129                     final int bytesWritten = blockCompressor.write(in, in.readerIndex(), length);
130                     in.skipBytes(bytesWritten);
131                     if (!blockCompressor.isFull()) {
132                         if (in.isReadable()) {
133                             break;
134                         } else {
135                             return;
136                         }
137                     }
138                     currentState = State.CLOSE_BLOCK;
139                     // fall through
140                 case CLOSE_BLOCK:
141                     closeBlock(out);
142                     currentState = State.INIT_BLOCK;
143                     break;
144                 default:
145                     throw new IllegalStateException();
146             }
147         }
148     }
149 
150     /**
151      * Close current block and update {@link #streamCRC}.
152      */
153     private void closeBlock(ByteBuf out) {
154         final Bzip2BlockCompressor blockCompressor = this.blockCompressor;
155         if (!blockCompressor.isEmpty()) {
156             blockCompressor.close(out);
157             final int blockCRC = blockCompressor.crc();
158             streamCRC = (streamCRC << 1 | streamCRC >>> 31) ^ blockCRC;
159         }
160     }
161 
162     /**
163      * Returns {@code true} if and only if the end of the compressed stream has been reached.
164      */
165     public boolean isClosed() {
166         return finished;
167     }
168 
169     /**
170      * Close this {@link Bzip2Encoder} and so finish the encoding.
171      *
172      * The returned {@link ChannelFuture} will be notified once the operation completes.
173      */
174     public ChannelFuture close() {
175         return close(ctx().newPromise());
176     }
177 
178     /**
179      * Close this {@link Bzip2Encoder} and so finish the encoding.
180      * The given {@link ChannelFuture} will be notified once the operation
181      * completes and will also be returned.
182      */
183     public ChannelFuture close(final ChannelPromise promise) {
184         ChannelHandlerContext ctx = ctx();
185         EventExecutor executor = ctx.executor();
186         if (executor.inEventLoop()) {
187             return finishEncode(ctx, promise);
188         } else {
189             executor.execute(new Runnable() {
190                 @Override
191                 public void run() {
192                     ChannelFuture f = finishEncode(ctx(), promise);
193                     PromiseNotifier.cascade(f, promise);
194                 }
195             });
196             return promise;
197         }
198     }
199 
200     @Override
201     public void close(final ChannelHandlerContext ctx, final ChannelPromise promise) throws Exception {
202         ChannelFuture f = finishEncode(ctx, ctx.newPromise());
203         EncoderUtil.closeAfterFinishEncode(ctx, f, promise);
204     }
205 
206     private ChannelFuture finishEncode(final ChannelHandlerContext ctx, ChannelPromise promise) {
207         if (finished) {
208             promise.setSuccess();
209             return promise;
210         }
211         finished = true;
212 
213         final ByteBuf footer = ctx.alloc().buffer();
214         closeBlock(footer);
215 
216         final int streamCRC = this.streamCRC;
217         final Bzip2BitWriter writer = this.writer;
218         try {
219             writer.writeBits(footer, 24, END_OF_STREAM_MAGIC_1);
220             writer.writeBits(footer, 24, END_OF_STREAM_MAGIC_2);
221             writer.writeInt(footer, streamCRC);
222             writer.flush(footer);
223         } finally {
224             blockCompressor = null;
225         }
226         return ctx.writeAndFlush(footer, promise);
227     }
228 
229     private ChannelHandlerContext ctx() {
230         ChannelHandlerContext ctx = this.ctx;
231         if (ctx == null) {
232             throw new IllegalStateException("not added to a pipeline");
233         }
234         return ctx;
235     }
236 
237     @Override
238     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
239         this.ctx = ctx;
240     }
241 }