1 /*
2 * Copyright 2022 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.netty5.handler.codec;
17
18 import io.netty5.buffer.BufferUtil;
19 import io.netty5.buffer.api.Buffer;
20 import io.netty5.channel.ChannelHandlerContext;
21
22 import java.nio.ByteOrder;
23
24 import static io.netty5.util.internal.ObjectUtil.checkPositive;
25 import static io.netty5.util.internal.ObjectUtil.checkPositiveOrZero;
26 import static java.util.Objects.requireNonNull;
27
28 /**
29 * A decoder that splits the received {@link Buffer}s dynamically by the
30 * value of the length field in the message. It is particularly useful when you
31 * decode a binary message which has an integer header field that represents the
32 * length of the message body or the whole message.
33 * <p>
34 * {@link LengthFieldBasedFrameDecoder} has many configuration parameters so
35 * that it can decode any message with a length field, which is often seen in
36 * proprietary client-server protocols. Here are some example that will give
37 * you the basic idea on which option does what.
38 *
39 * <h3>2 bytes length field at offset 0, do not strip header</h3>
40 * <p>
41 * The value of the length field in this example is <tt>12 (0x0C)</tt> which
42 * represents the length of "HELLO, WORLD". By default, the decoder assumes
43 * that the length field represents the number of the bytes that follows the
44 * length field. Therefore, it can be decoded with the simplistic parameter
45 * combination.
46 * <pre>
47 * <b>lengthFieldOffset</b> = <b>0</b>
48 * <b>lengthFieldLength</b> = <b>2</b>
49 * lengthAdjustment = 0
50 * initialBytesToStrip = 0 (= do not strip header)
51 *
52 * BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes)
53 * +--------+----------------+ +--------+----------------+
54 * | Length | Actual Content |----->| Length | Actual Content |
55 * | 0x000C | "HELLO, WORLD" | | 0x000C | "HELLO, WORLD" |
56 * +--------+----------------+ +--------+----------------+
57 * </pre>
58 *
59 * <h3>2 bytes length field at offset 0, strip header</h3>
60 * <p>
61 * Because we can get the length of the content by calling
62 * {@link Buffer#readableBytes()}, you might want to strip the length
63 * field by specifying <tt>initialBytesToStrip</tt>. In this example, we
64 * specified <tt>2</tt>, that is same with the length of the length field, to
65 * strip the first two bytes.
66 * <pre>
67 * lengthFieldOffset = 0
68 * lengthFieldLength = 2
69 * lengthAdjustment = 0
70 * <b>initialBytesToStrip</b> = <b>2</b> (= the length of the Length field)
71 *
72 * BEFORE DECODE (14 bytes) AFTER DECODE (12 bytes)
73 * +--------+----------------+ +----------------+
74 * | Length | Actual Content |----->| Actual Content |
75 * | 0x000C | "HELLO, WORLD" | | "HELLO, WORLD" |
76 * +--------+----------------+ +----------------+
77 * </pre>
78 *
79 * <h3>2 bytes length field at offset 0, do not strip header, the length field
80 * represents the length of the whole message</h3>
81 * <p>
82 * In most cases, the length field represents the length of the message body
83 * only, as shown in the previous examples. However, in some protocols, the
84 * length field represents the length of the whole message, including the
85 * message header. In such a case, we specify a non-zero
86 * <tt>lengthAdjustment</tt>. Because the length value in this example message
87 * is always greater than the body length by <tt>2</tt>, we specify <tt>-2</tt>
88 * as <tt>lengthAdjustment</tt> for compensation.
89 * <pre>
90 * lengthFieldOffset = 0
91 * lengthFieldLength = 2
92 * <b>lengthAdjustment</b> = <b>-2</b> (= the length of the Length field)
93 * initialBytesToStrip = 0
94 *
95 * BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes)
96 * +--------+----------------+ +--------+----------------+
97 * | Length | Actual Content |----->| Length | Actual Content |
98 * | 0x000E | "HELLO, WORLD" | | 0x000E | "HELLO, WORLD" |
99 * +--------+----------------+ +--------+----------------+
100 * </pre>
101 *
102 * <h3>3 bytes length field at the end of 5 bytes header, do not strip header</h3>
103 * <p>
104 * The following message is a simple variation of the first example. An extra
105 * header value is prepended to the message. <tt>lengthAdjustment</tt> is zero
106 * again because the decoder always takes the length of the prepended data into
107 * account during frame length calculation.
108 * <pre>
109 * <b>lengthFieldOffset</b> = <b>2</b> (= the length of Header 1)
110 * <b>lengthFieldLength</b> = <b>3</b>
111 * lengthAdjustment = 0
112 * initialBytesToStrip = 0
113 *
114 * BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes)
115 * +----------+----------+----------------+ +----------+----------+----------------+
116 * | Header 1 | Length | Actual Content |----->| Header 1 | Length | Actual Content |
117 * | 0xCAFE | 0x00000C | "HELLO, WORLD" | | 0xCAFE | 0x00000C | "HELLO, WORLD" |
118 * +----------+----------+----------------+ +----------+----------+----------------+
119 * </pre>
120 *
121 * <h3>3 bytes length field at the beginning of 5 bytes header, do not strip header</h3>
122 * <p>
123 * This is an advanced example that shows the case where there is an extra
124 * header between the length field and the message body. You have to specify a
125 * positive <tt>lengthAdjustment</tt> so that the decoder counts the extra
126 * header into the frame length calculation.
127 * <pre>
128 * lengthFieldOffset = 0
129 * lengthFieldLength = 3
130 * <b>lengthAdjustment</b> = <b>2</b> (= the length of Header 1)
131 * initialBytesToStrip = 0
132 *
133 * BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes)
134 * +----------+----------+----------------+ +----------+----------+----------------+
135 * | Length | Header 1 | Actual Content |----->| Length | Header 1 | Actual Content |
136 * | 0x00000C | 0xCAFE | "HELLO, WORLD" | | 0x00000C | 0xCAFE | "HELLO, WORLD" |
137 * +----------+----------+----------------+ +----------+----------+----------------+
138 * </pre>
139 *
140 * <h3>2 bytes length field at offset 1 in the middle of 4 bytes header,
141 * strip the first header field and the length field</h3>
142 * <p>
143 * This is a combination of all the examples above. There are the prepended
144 * header before the length field and the extra header after the length field.
145 * The prepended header affects the <tt>lengthFieldOffset</tt> and the extra
146 * header affects the <tt>lengthAdjustment</tt>. We also specified a non-zero
147 * <tt>initialBytesToStrip</tt> to strip the length field and the prepended
148 * header from the frame. If you don't want to strip the prepended header, you
149 * could specify <tt>0</tt> for <tt>initialBytesToSkip</tt>.
150 * <pre>
151 * lengthFieldOffset = 1 (= the length of HDR1)
152 * lengthFieldLength = 2
153 * <b>lengthAdjustment</b> = <b>1</b> (= the length of HDR2)
154 * <b>initialBytesToStrip</b> = <b>3</b> (= the length of HDR1 + LEN)
155 *
156 * BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)
157 * +------+--------+------+----------------+ +------+----------------+
158 * | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
159 * | 0xCA | 0x000C | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |
160 * +------+--------+------+----------------+ +------+----------------+
161 * </pre>
162 *
163 * <h3>2 bytes length field at offset 1 in the middle of 4 bytes header,
164 * strip the first header field and the length field, the length field
165 * represents the length of the whole message</h3>
166 * <p>
167 * Let's give another twist to the previous example. The only difference from
168 * the previous example is that the length field represents the length of the
169 * whole message instead of the message body, just like the third example.
170 * We have to count the length of HDR1 and Length into <tt>lengthAdjustment</tt>.
171 * Please note that we don't need to take the length of HDR2 into account
172 * because the length field already includes the whole header length.
173 * <pre>
174 * lengthFieldOffset = 1
175 * lengthFieldLength = 2
176 * <b>lengthAdjustment</b> = <b>-3</b> (= the length of HDR1 + LEN, negative)
177 * <b>initialBytesToStrip</b> = <b> 3</b>
178 *
179 * BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)
180 * +------+--------+------+----------------+ +------+----------------+
181 * | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
182 * | 0xCA | 0x0010 | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |
183 * +------+--------+------+----------------+ +------+----------------+
184 * </pre>
185 *
186 * @see LengthFieldPrepender
187 */
188 public class LengthFieldBasedFrameDecoder extends ByteToMessageDecoder { // TODO rename
189
190 private final ByteOrder byteOrder;
191 private final int maxFrameLength;
192 private final int lengthFieldOffset;
193 private final int lengthFieldLength;
194 private final int lengthFieldEndOffset;
195 private final int lengthAdjustment;
196 private final int initialBytesToStrip;
197 private final boolean failFast;
198
199 private long tooLongFrameLength;
200 private long bytesToDiscard;
201 private int currentFrameLength = -1;
202
203 /**
204 * Creates a new instance.
205 *
206 * @param maxFrameLength the maximum length of the frame. If the length of the frame is
207 * greater than this value, {@link TooLongFrameException} will be
208 * thrown.
209 * @param lengthFieldOffset the offset of the length field
210 * @param lengthFieldLength the length of the length field
211 */
212 public LengthFieldBasedFrameDecoder(int maxFrameLength, int lengthFieldOffset, int lengthFieldLength) {
213 this(maxFrameLength, lengthFieldOffset, lengthFieldLength, 0, 0);
214 }
215
216 /**
217 * Creates a new instance.
218 *
219 * @param maxFrameLength the maximum length of the frame. If the length of the frame is
220 * greater than this value, {@link TooLongFrameException} will be
221 * thrown.
222 * @param lengthFieldOffset the offset of the length field
223 * @param lengthFieldLength the length of the length field
224 * @param lengthAdjustment the compensation value to add to the value of the length field
225 * @param initialBytesToStrip the number of first bytes to strip out from the decoded frame
226 */
227 public LengthFieldBasedFrameDecoder(
228 int maxFrameLength, int lengthFieldOffset, int lengthFieldLength,
229 int lengthAdjustment, int initialBytesToStrip) {
230 this(maxFrameLength,
231 lengthFieldOffset, lengthFieldLength, lengthAdjustment,
232 initialBytesToStrip, true);
233 }
234
235 /**
236 * Creates a new instance.
237 *
238 * @param maxFrameLength the maximum length of the frame. If the length of the frame is
239 * greater than this value, {@link TooLongFrameException} will be
240 * thrown.
241 * @param lengthFieldOffset the offset of the length field
242 * @param lengthFieldLength the length of the length field
243 * @param lengthAdjustment the compensation value to add to the value of the length field
244 * @param initialBytesToStrip the number of first bytes to strip out from the decoded frame
245 * @param failFast If <tt>true</tt>, a {@link TooLongFrameException} is thrown as
246 * soon as the decoder notices the length of the frame will exceed
247 * <tt>maxFrameLength</tt> regardless of whether the entire frame
248 * has been read. If <tt>false</tt>, a {@link TooLongFrameException}
249 * is thrown after the entire frame that exceeds <tt>maxFrameLength</tt>
250 * has been read.
251 */
252 public LengthFieldBasedFrameDecoder(
253 int maxFrameLength, int lengthFieldOffset, int lengthFieldLength,
254 int lengthAdjustment, int initialBytesToStrip, boolean failFast) {
255 this(ByteOrder.BIG_ENDIAN, maxFrameLength, lengthFieldOffset, lengthFieldLength,
256 lengthAdjustment, initialBytesToStrip, failFast);
257 }
258
259 /**
260 * Creates a new instance.
261 *
262 * @param byteOrder the {@link ByteOrder} of the length field
263 * @param maxFrameLength the maximum length of the frame. If the length of the frame is
264 * greater than this value, {@link TooLongFrameException} will be
265 * thrown.
266 * @param lengthFieldOffset the offset of the length field
267 * @param lengthFieldLength the length of the length field
268 * @param lengthAdjustment the compensation value to add to the value of the length field
269 * @param initialBytesToStrip the number of first bytes to strip out from the decoded frame
270 * @param failFast If <tt>true</tt>, a {@link TooLongFrameException} is thrown as
271 * soon as the decoder notices the length of the frame will exceed
272 * <tt>maxFrameLength</tt> regardless of whether the entire frame
273 * has been read. If <tt>false</tt>, a {@link TooLongFrameException}
274 * is thrown after the entire frame that exceeds <tt>maxFrameLength</tt>
275 * has been read.
276 */
277 public LengthFieldBasedFrameDecoder(
278 ByteOrder byteOrder, int maxFrameLength, int lengthFieldOffset, int lengthFieldLength,
279 int lengthAdjustment, int initialBytesToStrip, boolean failFast) {
280 requireNonNull(byteOrder, "byteOrder");
281 checkPositive(maxFrameLength, "maxFrameLength");
282 checkPositiveOrZero(lengthFieldOffset, "lengthFieldOffset");
283 checkPositiveOrZero(initialBytesToStrip, "initialBytesToStrip");
284
285 if (lengthFieldOffset > maxFrameLength - lengthFieldLength) {
286 throw new IllegalArgumentException(
287 "maxFrameLength (" + maxFrameLength + ") " +
288 "must be equal to or greater than " +
289 "lengthFieldOffset (" + lengthFieldOffset + ") + " +
290 "lengthFieldLength (" + lengthFieldLength + ").");
291 }
292
293 this.byteOrder = byteOrder;
294 this.maxFrameLength = maxFrameLength;
295 this.lengthFieldOffset = lengthFieldOffset;
296 this.lengthFieldLength = lengthFieldLength;
297 this.lengthAdjustment = lengthAdjustment;
298 lengthFieldEndOffset = lengthFieldOffset + lengthFieldLength;
299 this.initialBytesToStrip = initialBytesToStrip;
300 this.failFast = failFast;
301 }
302
303 @Override
304 protected final void decode(ChannelHandlerContext ctx, Buffer in) throws Exception {
305 final Object decoded = decode0(ctx, in);
306 if (decoded != null) {
307 ctx.fireChannelRead(decoded);
308 }
309 }
310
311 private void discardTooLongFrame(Buffer in) {
312 final int bytesToDiscardNow = (int) Math.min(bytesToDiscard, in.readableBytes());
313 in.skipReadableBytes(bytesToDiscardNow);
314
315 bytesToDiscard -= bytesToDiscardNow;
316
317 failOnLengthExceededIfNecessary(false);
318 }
319
320 private static void failOnNegativeLengthField(Buffer buffer, long frameLength, int lengthFieldEndOffset) {
321 buffer.skipReadableBytes(lengthFieldEndOffset);
322 throw new CorruptedFrameException("negative pre-adjustment length field: " + frameLength);
323 }
324
325 private static void failOnFrameLengthLessThanLengthFieldEndOffset(
326 Buffer buffer, long frameLength, int lengthFieldEndOffset) {
327 buffer.skipReadableBytes(lengthFieldEndOffset);
328 throw new CorruptedFrameException(
329 "Adjusted frame length (" + frameLength + ") is less " +
330 "than lengthFieldEndOffset: " + lengthFieldEndOffset);
331 }
332
333 private void handleFrameLengthExceeded(Buffer buffer, long frameLength) {
334 final long discard = frameLength - buffer.readableBytes();
335 tooLongFrameLength = frameLength;
336
337 if (discard < 0) {
338 // buffer contains more bytes then the frameLength so we can discard all now
339 buffer.skipReadableBytes((int) frameLength);
340 } else {
341 // Enter the discard mode and discard everything received so far.
342 bytesToDiscard = discard;
343 buffer.skipReadableBytes(buffer.readableBytes());
344 }
345 failOnLengthExceededIfNecessary(true);
346 }
347
348 private static void failOnFrameLengthLessThanInitialBytesToStrip(
349 Buffer buffer, int frameLength, int initialBytesToStrip) {
350 buffer.skipReadableBytes(frameLength);
351 throw new CorruptedFrameException(
352 "Adjusted frame length (" + frameLength + ") is less " +
353 "than initialBytesToStrip: " + initialBytesToStrip);
354 }
355
356 /**
357 * Create a frame out of the {@link Buffer} and return it.
358 *
359 * @param ctx the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
360 * @param buffer the {@link Buffer} from which to read data
361 * @return the {@link Buffer} which represent the frame or {@code null} if no frame could be created.
362 */
363 protected Object decode0(ChannelHandlerContext ctx, Buffer buffer) throws Exception {
364 if (currentFrameLength == -1) { // new frame
365 if (bytesToDiscard > 0) {
366 discardTooLongFrame(buffer);
367 }
368
369 if (buffer.readableBytes() < lengthFieldEndOffset) {
370 return null;
371 }
372
373 final int actualLengthFieldOffset = buffer.readerOffset() + lengthFieldOffset;
374 long frameLength = getUnadjustedFrameLength(buffer, actualLengthFieldOffset, lengthFieldLength, byteOrder);
375
376 if (frameLength < 0) {
377 failOnNegativeLengthField(buffer, frameLength, lengthFieldEndOffset);
378 }
379
380 frameLength += lengthAdjustment + lengthFieldEndOffset;
381
382 if (frameLength < lengthFieldEndOffset) {
383 failOnFrameLengthLessThanLengthFieldEndOffset(buffer, frameLength, lengthFieldEndOffset);
384 }
385
386 if (frameLength > maxFrameLength) {
387 handleFrameLengthExceeded(buffer, frameLength);
388 return null;
389 }
390
391 // never overflows because it's less than maxFrameLength
392 currentFrameLength = (int) frameLength;
393 }
394
395 if (buffer.readableBytes() < currentFrameLength) { // frameLengthInt exist, just check buf
396 return null;
397 }
398
399 if (initialBytesToStrip > currentFrameLength) {
400 failOnFrameLengthLessThanInitialBytesToStrip(buffer, currentFrameLength, initialBytesToStrip);
401 }
402
403 buffer.skipReadableBytes(initialBytesToStrip);
404
405 // extract frame
406 final Buffer frame = extractFrame(ctx, buffer, currentFrameLength - initialBytesToStrip);
407 currentFrameLength = -1; // start processing the next frame
408 return frame;
409 }
410
411 /**
412 * Decodes the specified region of the buffer into an unadjusted frame length. The default implementation is
413 * capable of decoding the specified region into an unsigned 8/16/24/32/64 bit integer. Override this method to
414 * decode the length field encoded differently. Note that this method must not modify the state of the specified
415 * buffer (e.g. {@code readerOffset}, {@code writerOffset}, and the content of the buffer.)
416 *
417 * @throws DecoderException if failed to decode the specified region
418 */
419 protected long getUnadjustedFrameLength(Buffer buffer, int offset, int length, ByteOrder byteOrder) {
420 final boolean reverseBytes = byteOrder == ByteOrder.LITTLE_ENDIAN;
421
422 switch (length) {
423 case 1:
424 return buffer.getUnsignedByte(offset);
425 case 2:
426 final int shortLength = buffer.getUnsignedShort(offset);
427 return reverseBytes? BufferUtil.reverseUnsignedShort(shortLength) : shortLength;
428 case 3:
429 final int mediumLength = buffer.getUnsignedMedium(offset);
430 return reverseBytes? BufferUtil.reverseUnsignedMedium(mediumLength) : mediumLength;
431 case 4:
432 final long intLength = buffer.getUnsignedInt(offset);
433 return reverseBytes? BufferUtil.reverseUnsignedInt(intLength) : intLength;
434 case 8:
435 final long longLength = buffer.getLong(offset);
436 return reverseBytes? Long.reverseBytes(longLength) : longLength;
437 default:
438 throw new DecoderException("unsupported lengthFieldLength: " + length + " (expected: 1, 2, 3, 4, or 8)");
439 }
440 }
441
442 private void failOnLengthExceededIfNecessary(boolean firstDetectionOfTooLongFrame) {
443 if (bytesToDiscard == 0) {
444 // Reset to the initial state and tell the handlers that
445 // the frame was too large.
446 final long tooLongFrameLength = this.tooLongFrameLength;
447 this.tooLongFrameLength = 0;
448
449 if (!failFast || firstDetectionOfTooLongFrame) {
450 failOnLengthExceeded(tooLongFrameLength);
451 }
452 } else {
453 // Keep discarding and notify handlers if necessary.
454 if (failFast && firstDetectionOfTooLongFrame) {
455 failOnLengthExceeded(tooLongFrameLength);
456 }
457 }
458 }
459
460 private void failOnLengthExceeded(long frameLength) {
461 if (frameLength > 0) {
462 throw new TooLongFrameException(
463 "Adjusted frame length exceeds " + maxFrameLength + ": " + frameLength + " - discarded");
464 } else {
465 throw new TooLongFrameException("Adjusted frame length exceeds " + maxFrameLength + " - discarding");
466 }
467 }
468
469 /**
470 * Extract the sub-region of the specified buffer. This method must modify the state of the buffer to continue
471 * after the frame (e.g. by splitting the buffer or by increasing {@code readerOffset}).
472 */
473 protected Buffer extractFrame(@SuppressWarnings("unused") ChannelHandlerContext ctx, Buffer buffer, int length) {
474 return buffer.readSplit(length);
475 }
476
477 }