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1   /*
2    * Copyright 2012 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;
17  
18  import io.netty.buffer.ByteBuf;
19  import io.netty.buffer.ByteBufAllocator;
20  import io.netty.buffer.CompositeByteBuf;
21  import io.netty.buffer.Unpooled;
22  import io.netty.channel.ChannelConfig;
23  import io.netty.channel.ChannelHandlerContext;
24  import io.netty.channel.ChannelInboundHandlerAdapter;
25  import io.netty.channel.socket.ChannelInputShutdownEvent;
26  import io.netty.util.internal.ObjectUtil;
27  import io.netty.util.internal.StringUtil;
28  
29  import java.util.List;
30  
31  import static io.netty.util.internal.ObjectUtil.checkPositive;
32  import static java.lang.Integer.MAX_VALUE;
33  
34  /**
35   * {@link ChannelInboundHandlerAdapter} which decodes bytes in a stream-like fashion from one {@link ByteBuf} to an
36   * other Message type.
37   *
38   * For example here is an implementation which reads all readable bytes from
39   * the input {@link ByteBuf} and create a new {@link ByteBuf}.
40   *
41   * <pre>
42   *     public class SquareDecoder extends {@link ByteToMessageDecoder} {
43   *         {@code @Override}
44   *         public void decode({@link ChannelHandlerContext} ctx, {@link ByteBuf} in, List&lt;Object&gt; out)
45   *                 throws {@link Exception} {
46   *             out.add(in.readBytes(in.readableBytes()));
47   *         }
48   *     }
49   * </pre>
50   *
51   * <h3>Frame detection</h3>
52   * <p>
53   * Generally frame detection should be handled earlier in the pipeline by adding a
54   * {@link DelimiterBasedFrameDecoder}, {@link FixedLengthFrameDecoder}, {@link LengthFieldBasedFrameDecoder},
55   * or {@link LineBasedFrameDecoder}.
56   * <p>
57   * If a custom frame decoder is required, then one needs to be careful when implementing
58   * one with {@link ByteToMessageDecoder}. Ensure there are enough bytes in the buffer for a
59   * complete frame by checking {@link ByteBuf#readableBytes()}. If there are not enough bytes
60   * for a complete frame, return without modifying the reader index to allow more bytes to arrive.
61   * <p>
62   * To check for complete frames without modifying the reader index, use methods like {@link ByteBuf#getInt(int)}.
63   * One <strong>MUST</strong> use the reader index when using methods like {@link ByteBuf#getInt(int)}.
64   * For example calling <tt>in.getInt(0)</tt> is assuming the frame starts at the beginning of the buffer, which
65   * is not always the case. Use <tt>in.getInt(in.readerIndex())</tt> instead.
66   * <h3>Pitfalls</h3>
67   * <p>
68   * Be aware that sub-classes of {@link ByteToMessageDecoder} <strong>MUST NOT</strong>
69   * annotated with {@link @Sharable}.
70   * <p>
71   * Some methods such as {@link ByteBuf#readBytes(int)} will cause a memory leak if the returned buffer
72   * is not released or added to the <tt>out</tt> {@link List}. Use derived buffers like {@link ByteBuf#readSlice(int)}
73   * to avoid leaking memory.
74   */
75  public abstract class ByteToMessageDecoder extends ChannelInboundHandlerAdapter {
76  
77      /**
78       * Cumulate {@link ByteBuf}s by merge them into one {@link ByteBuf}'s, using memory copies.
79       */
80      public static final Cumulator MERGE_CUMULATOR = new Cumulator() {
81          @Override
82          public ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in) {
83              if (!cumulation.isReadable() && in.isContiguous()) {
84                  // If cumulation is empty and input buffer is contiguous, use it directly
85                  cumulation.release();
86                  return in;
87              }
88              try {
89                  final int required = in.readableBytes();
90                  if (required > cumulation.maxWritableBytes() ||
91                          (required > cumulation.maxFastWritableBytes() && cumulation.refCnt() > 1) ||
92                          cumulation.isReadOnly()) {
93                      // Expand cumulation (by replacing it) under the following conditions:
94                      // - cumulation cannot be resized to accommodate the additional data
95                      // - cumulation can be expanded with a reallocation operation to accommodate but the buffer is
96                      //   assumed to be shared (e.g. refCnt() > 1) and the reallocation may not be safe.
97                      return expandCumulation(alloc, cumulation, in);
98                  }
99                  cumulation.writeBytes(in, in.readerIndex(), required);
100                 in.readerIndex(in.writerIndex());
101                 return cumulation;
102             } finally {
103                 // We must release in in all cases as otherwise it may produce a leak if writeBytes(...) throw
104                 // for whatever release (for example because of OutOfMemoryError)
105                 in.release();
106             }
107         }
108     };
109 
110     /**
111      * Cumulate {@link ByteBuf}s by add them to a {@link CompositeByteBuf} and so do no memory copy whenever possible.
112      * Be aware that {@link CompositeByteBuf} use a more complex indexing implementation so depending on your use-case
113      * and the decoder implementation this may be slower then just use the {@link #MERGE_CUMULATOR}.
114      */
115     public static final Cumulator COMPOSITE_CUMULATOR = new Cumulator() {
116         @Override
117         public ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in) {
118             if (!cumulation.isReadable()) {
119                 cumulation.release();
120                 return in;
121             }
122             CompositeByteBuf composite = null;
123             try {
124                 if (cumulation instanceof CompositeByteBuf && cumulation.refCnt() == 1) {
125                     composite = (CompositeByteBuf) cumulation;
126                     // Writer index must equal capacity if we are going to "write"
127                     // new components to the end
128                     if (composite.writerIndex() != composite.capacity()) {
129                         composite.capacity(composite.writerIndex());
130                     }
131                 } else {
132                     composite = alloc.compositeBuffer(Integer.MAX_VALUE).addFlattenedComponents(true, cumulation);
133                 }
134                 composite.addFlattenedComponents(true, in);
135                 in = null;
136                 return composite;
137             } finally {
138                 if (in != null) {
139                     // We must release if the ownership was not transferred as otherwise it may produce a leak
140                     in.release();
141                     // Also release any new buffer allocated if we're not returning it
142                     if (composite != null && composite != cumulation) {
143                         composite.release();
144                     }
145                 }
146             }
147         }
148     };
149 
150     private static final byte STATE_INIT = 0;
151     private static final byte STATE_CALLING_CHILD_DECODE = 1;
152     private static final byte STATE_HANDLER_REMOVED_PENDING = 2;
153 
154     ByteBuf cumulation;
155     private Cumulator cumulator = MERGE_CUMULATOR;
156     private boolean singleDecode;
157     private boolean first;
158 
159     /**
160      * This flag is used to determine if we need to call {@link ChannelHandlerContext#read()} to consume more data
161      * when {@link ChannelConfig#isAutoRead()} is {@code false}.
162      */
163     private boolean firedChannelRead;
164 
165     /**
166      * A bitmask where the bits are defined as
167      * <ul>
168      *     <li>{@link #STATE_INIT}</li>
169      *     <li>{@link #STATE_CALLING_CHILD_DECODE}</li>
170      *     <li>{@link #STATE_HANDLER_REMOVED_PENDING}</li>
171      * </ul>
172      */
173     private byte decodeState = STATE_INIT;
174     private int discardAfterReads = 16;
175     private int numReads;
176 
177     protected ByteToMessageDecoder() {
178         ensureNotSharable();
179     }
180 
181     /**
182      * If set then only one message is decoded on each {@link #channelRead(ChannelHandlerContext, Object)}
183      * call. This may be useful if you need to do some protocol upgrade and want to make sure nothing is mixed up.
184      *
185      * Default is {@code false} as this has performance impacts.
186      */
187     public void setSingleDecode(boolean singleDecode) {
188         this.singleDecode = singleDecode;
189     }
190 
191     /**
192      * If {@code true} then only one message is decoded on each
193      * {@link #channelRead(ChannelHandlerContext, Object)} call.
194      *
195      * Default is {@code false} as this has performance impacts.
196      */
197     public boolean isSingleDecode() {
198         return singleDecode;
199     }
200 
201     /**
202      * Set the {@link Cumulator} to use for cumulate the received {@link ByteBuf}s.
203      */
204     public void setCumulator(Cumulator cumulator) {
205         this.cumulator = ObjectUtil.checkNotNull(cumulator, "cumulator");
206     }
207 
208     /**
209      * Set the number of reads after which {@link ByteBuf#discardSomeReadBytes()} are called and so free up memory.
210      * The default is {@code 16}.
211      */
212     public void setDiscardAfterReads(int discardAfterReads) {
213         checkPositive(discardAfterReads, "discardAfterReads");
214         this.discardAfterReads = discardAfterReads;
215     }
216 
217     /**
218      * Returns the actual number of readable bytes in the internal cumulative
219      * buffer of this decoder. You usually do not need to rely on this value
220      * to write a decoder. Use it only when you must use it at your own risk.
221      * This method is a shortcut to {@link #internalBuffer() internalBuffer().readableBytes()}.
222      */
223     protected int actualReadableBytes() {
224         return internalBuffer().readableBytes();
225     }
226 
227     /**
228      * Returns the internal cumulative buffer of this decoder. You usually
229      * do not need to access the internal buffer directly to write a decoder.
230      * Use it only when you must use it at your own risk.
231      */
232     protected ByteBuf internalBuffer() {
233         if (cumulation != null) {
234             return cumulation;
235         } else {
236             return Unpooled.EMPTY_BUFFER;
237         }
238     }
239 
240     @Override
241     public final void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
242         if (decodeState == STATE_CALLING_CHILD_DECODE) {
243             decodeState = STATE_HANDLER_REMOVED_PENDING;
244             return;
245         }
246         ByteBuf buf = cumulation;
247         if (buf != null) {
248             // Directly set this to null so we are sure we not access it in any other method here anymore.
249             cumulation = null;
250             numReads = 0;
251             int readable = buf.readableBytes();
252             if (readable > 0) {
253                 ctx.fireChannelRead(buf);
254                 ctx.fireChannelReadComplete();
255             } else {
256                 buf.release();
257             }
258         }
259         handlerRemoved0(ctx);
260     }
261 
262     /**
263      * Gets called after the {@link ByteToMessageDecoder} was removed from the actual context and it doesn't handle
264      * events anymore.
265      */
266     protected void handlerRemoved0(ChannelHandlerContext ctx) throws Exception { }
267 
268     @Override
269     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
270         if (msg instanceof ByteBuf) {
271             CodecOutputList out = CodecOutputList.newInstance();
272             try {
273                 first = cumulation == null;
274                 cumulation = cumulator.cumulate(ctx.alloc(),
275                         first ? Unpooled.EMPTY_BUFFER : cumulation, (ByteBuf) msg);
276                 callDecode(ctx, cumulation, out);
277             } catch (DecoderException e) {
278                 throw e;
279             } catch (Exception e) {
280                 throw new DecoderException(e);
281             } finally {
282                 try {
283                     if (cumulation != null && !cumulation.isReadable()) {
284                         numReads = 0;
285                         cumulation.release();
286                         cumulation = null;
287                     } else if (++numReads >= discardAfterReads) {
288                         // We did enough reads already try to discard some bytes so we not risk to see a OOME.
289                         // See https://github.com/netty/netty/issues/4275
290                         numReads = 0;
291                         discardSomeReadBytes();
292                     }
293 
294                     int size = out.size();
295                     firedChannelRead |= out.insertSinceRecycled();
296                     fireChannelRead(ctx, out, size);
297                 } finally {
298                     out.recycle();
299                 }
300             }
301         } else {
302             ctx.fireChannelRead(msg);
303         }
304     }
305 
306     /**
307      * Get {@code numElements} out of the {@link List} and forward these through the pipeline.
308      */
309     static void fireChannelRead(ChannelHandlerContext ctx, List<Object> msgs, int numElements) {
310         if (msgs instanceof CodecOutputList) {
311             fireChannelRead(ctx, (CodecOutputList) msgs, numElements);
312         } else {
313             for (int i = 0; i < numElements; i++) {
314                 ctx.fireChannelRead(msgs.get(i));
315             }
316         }
317     }
318 
319     /**
320      * Get {@code numElements} out of the {@link CodecOutputList} and forward these through the pipeline.
321      */
322     static void fireChannelRead(ChannelHandlerContext ctx, CodecOutputList msgs, int numElements) {
323         for (int i = 0; i < numElements; i ++) {
324             ctx.fireChannelRead(msgs.getUnsafe(i));
325         }
326     }
327 
328     @Override
329     public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
330         numReads = 0;
331         discardSomeReadBytes();
332         if (!firedChannelRead && !ctx.channel().config().isAutoRead()) {
333             ctx.read();
334         }
335         firedChannelRead = false;
336         ctx.fireChannelReadComplete();
337     }
338 
339     protected final void discardSomeReadBytes() {
340         if (cumulation != null && !first && cumulation.refCnt() == 1) {
341             // discard some bytes if possible to make more room in the
342             // buffer but only if the refCnt == 1  as otherwise the user may have
343             // used slice().retain() or duplicate().retain().
344             //
345             // See:
346             // - https://github.com/netty/netty/issues/2327
347             // - https://github.com/netty/netty/issues/1764
348             cumulation.discardSomeReadBytes();
349         }
350     }
351 
352     @Override
353     public void channelInactive(ChannelHandlerContext ctx) throws Exception {
354         channelInputClosed(ctx, true);
355     }
356 
357     @Override
358     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
359         if (evt instanceof ChannelInputShutdownEvent) {
360             // The decodeLast method is invoked when a channelInactive event is encountered.
361             // This method is responsible for ending requests in some situations and must be called
362             // when the input has been shutdown.
363             channelInputClosed(ctx, false);
364         }
365         super.userEventTriggered(ctx, evt);
366     }
367 
368     private void channelInputClosed(ChannelHandlerContext ctx, boolean callChannelInactive) {
369         CodecOutputList out = CodecOutputList.newInstance();
370         try {
371             channelInputClosed(ctx, out);
372         } catch (DecoderException e) {
373             throw e;
374         } catch (Exception e) {
375             throw new DecoderException(e);
376         } finally {
377             try {
378                 if (cumulation != null) {
379                     cumulation.release();
380                     cumulation = null;
381                 }
382                 int size = out.size();
383                 fireChannelRead(ctx, out, size);
384                 if (size > 0) {
385                     // Something was read, call fireChannelReadComplete()
386                     ctx.fireChannelReadComplete();
387                 }
388                 if (callChannelInactive) {
389                     ctx.fireChannelInactive();
390                 }
391             } finally {
392                 // Recycle in all cases
393                 out.recycle();
394             }
395         }
396     }
397 
398     /**
399      * Called when the input of the channel was closed which may be because it changed to inactive or because of
400      * {@link ChannelInputShutdownEvent}.
401      */
402     void channelInputClosed(ChannelHandlerContext ctx, List<Object> out) throws Exception {
403         if (cumulation != null) {
404             callDecode(ctx, cumulation, out);
405             // If callDecode(...) removed the handle from the pipeline we should not call decodeLast(...) as this would
406             // be unexpected.
407             if (!ctx.isRemoved()) {
408                 // Use Unpooled.EMPTY_BUFFER if cumulation become null after calling callDecode(...).
409                 // See https://github.com/netty/netty/issues/10802.
410                 ByteBuf buffer = cumulation == null ? Unpooled.EMPTY_BUFFER : cumulation;
411                 decodeLast(ctx, buffer, out);
412             }
413         } else {
414             decodeLast(ctx, Unpooled.EMPTY_BUFFER, out);
415         }
416     }
417 
418     /**
419      * Called once data should be decoded from the given {@link ByteBuf}. This method will call
420      * {@link #decode(ChannelHandlerContext, ByteBuf, List)} as long as decoding should take place.
421      *
422      * @param ctx           the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
423      * @param in            the {@link ByteBuf} from which to read data
424      * @param out           the {@link List} to which decoded messages should be added
425      */
426     protected void callDecode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) {
427         try {
428             while (in.isReadable()) {
429                 final int outSize = out.size();
430 
431                 if (outSize > 0) {
432                     fireChannelRead(ctx, out, outSize);
433                     out.clear();
434 
435                     // Check if this handler was removed before continuing with decoding.
436                     // If it was removed, it is not safe to continue to operate on the buffer.
437                     //
438                     // See:
439                     // - https://github.com/netty/netty/issues/4635
440                     if (ctx.isRemoved()) {
441                         break;
442                     }
443                 }
444 
445                 int oldInputLength = in.readableBytes();
446                 decodeRemovalReentryProtection(ctx, in, out);
447 
448                 // Check if this handler was removed before continuing the loop.
449                 // If it was removed, it is not safe to continue to operate on the buffer.
450                 //
451                 // See https://github.com/netty/netty/issues/1664
452                 if (ctx.isRemoved()) {
453                     break;
454                 }
455 
456                 if (out.isEmpty()) {
457                     if (oldInputLength == in.readableBytes()) {
458                         break;
459                     } else {
460                         continue;
461                     }
462                 }
463 
464                 if (oldInputLength == in.readableBytes()) {
465                     throw new DecoderException(
466                             StringUtil.simpleClassName(getClass()) +
467                                     ".decode() did not read anything but decoded a message.");
468                 }
469 
470                 if (isSingleDecode()) {
471                     break;
472                 }
473             }
474         } catch (DecoderException e) {
475             throw e;
476         } catch (Exception cause) {
477             throw new DecoderException(cause);
478         }
479     }
480 
481     /**
482      * Decode the from one {@link ByteBuf} to an other. This method will be called till either the input
483      * {@link ByteBuf} has nothing to read when return from this method or till nothing was read from the input
484      * {@link ByteBuf}.
485      *
486      * @param ctx           the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
487      * @param in            the {@link ByteBuf} from which to read data
488      * @param out           the {@link List} to which decoded messages should be added
489      * @throws Exception    is thrown if an error occurs
490      */
491     protected abstract void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception;
492 
493     /**
494      * Decode the from one {@link ByteBuf} to an other. This method will be called till either the input
495      * {@link ByteBuf} has nothing to read when return from this method or till nothing was read from the input
496      * {@link ByteBuf}.
497      *
498      * @param ctx           the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
499      * @param in            the {@link ByteBuf} from which to read data
500      * @param out           the {@link List} to which decoded messages should be added
501      * @throws Exception    is thrown if an error occurs
502      */
503     final void decodeRemovalReentryProtection(ChannelHandlerContext ctx, ByteBuf in, List<Object> out)
504             throws Exception {
505         decodeState = STATE_CALLING_CHILD_DECODE;
506         try {
507             decode(ctx, in, out);
508         } finally {
509             boolean removePending = decodeState == STATE_HANDLER_REMOVED_PENDING;
510             decodeState = STATE_INIT;
511             if (removePending) {
512                 fireChannelRead(ctx, out, out.size());
513                 out.clear();
514                 handlerRemoved(ctx);
515             }
516         }
517     }
518 
519     /**
520      * Is called one last time when the {@link ChannelHandlerContext} goes in-active. Which means the
521      * {@link #channelInactive(ChannelHandlerContext)} was triggered.
522      *
523      * By default this will just call {@link #decode(ChannelHandlerContext, ByteBuf, List)} but sub-classes may
524      * override this for some special cleanup operation.
525      */
526     protected void decodeLast(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
527         if (in.isReadable()) {
528             // Only call decode() if there is something left in the buffer to decode.
529             // See https://github.com/netty/netty/issues/4386
530             decodeRemovalReentryProtection(ctx, in, out);
531         }
532     }
533 
534     static ByteBuf expandCumulation(ByteBufAllocator alloc, ByteBuf oldCumulation, ByteBuf in) {
535         int oldBytes = oldCumulation.readableBytes();
536         int newBytes = in.readableBytes();
537         int totalBytes = oldBytes + newBytes;
538         ByteBuf newCumulation = alloc.buffer(alloc.calculateNewCapacity(totalBytes, MAX_VALUE));
539         ByteBuf toRelease = newCumulation;
540         try {
541             // This avoids redundant checks and stack depth compared to calling writeBytes(...)
542             newCumulation.setBytes(0, oldCumulation, oldCumulation.readerIndex(), oldBytes)
543                 .setBytes(oldBytes, in, in.readerIndex(), newBytes)
544                 .writerIndex(totalBytes);
545             in.readerIndex(in.writerIndex());
546             toRelease = oldCumulation;
547             return newCumulation;
548         } finally {
549             toRelease.release();
550         }
551     }
552 
553     /**
554      * Cumulate {@link ByteBuf}s.
555      */
556     public interface Cumulator {
557         /**
558          * Cumulate the given {@link ByteBuf}s and return the {@link ByteBuf} that holds the cumulated bytes.
559          * The implementation is responsible to correctly handle the life-cycle of the given {@link ByteBuf}s and so
560          * call {@link ByteBuf#release()} if a {@link ByteBuf} is fully consumed.
561          */
562         ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in);
563     }
564 }