summaryrefslogtreecommitdiff
path: root/media/libwebp/demux/demux.c
blob: 13953b1c540d9b1c9d7558563681b33cfb22eaac (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
// Copyright 2012 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
//  WebP container demux.
//

#ifdef HAVE_CONFIG_H
#include "../webp/config.h"
#endif

#include <assert.h>
#include <stdlib.h>
#include <string.h>

#include "../utils/utils.h"
#include "../webp/decode.h"     // WebPGetFeatures
#include "../webp/demux.h"
#include "../webp/format_constants.h"

#define DMUX_MAJ_VERSION 1
#define DMUX_MIN_VERSION 2
#define DMUX_REV_VERSION 2

typedef struct {
  size_t start_;        // start location of the data
  size_t end_;          // end location
  size_t riff_end_;     // riff chunk end location, can be > end_.
  size_t buf_size_;     // size of the buffer
  const uint8_t* buf_;
} MemBuffer;

typedef struct {
  size_t offset_;
  size_t size_;
} ChunkData;

typedef struct Frame {
  int x_offset_, y_offset_;
  int width_, height_;
  int has_alpha_;
  int duration_;
  WebPMuxAnimDispose dispose_method_;
  WebPMuxAnimBlend blend_method_;
  int frame_num_;
  int complete_;   // img_components_ contains a full image.
  ChunkData img_components_[2];  // 0=VP8{,L} 1=ALPH
  struct Frame* next_;
} Frame;

typedef struct Chunk {
  ChunkData data_;
  struct Chunk* next_;
} Chunk;

struct WebPDemuxer {
  MemBuffer mem_;
  WebPDemuxState state_;
  int is_ext_format_;
  uint32_t feature_flags_;
  int canvas_width_, canvas_height_;
  int loop_count_;
  uint32_t bgcolor_;
  int num_frames_;
  Frame* frames_;
  Frame** frames_tail_;
  Chunk* chunks_;  // non-image chunks
  Chunk** chunks_tail_;
};

typedef enum {
  PARSE_OK,
  PARSE_NEED_MORE_DATA,
  PARSE_ERROR
} ParseStatus;

typedef struct ChunkParser {
  uint8_t id[4];
  ParseStatus (*parse)(WebPDemuxer* const dmux);
  int (*valid)(const WebPDemuxer* const dmux);
} ChunkParser;

static ParseStatus ParseSingleImage(WebPDemuxer* const dmux);
static ParseStatus ParseVP8X(WebPDemuxer* const dmux);
static int IsValidSimpleFormat(const WebPDemuxer* const dmux);
static int IsValidExtendedFormat(const WebPDemuxer* const dmux);

static const ChunkParser kMasterChunks[] = {
  { { 'V', 'P', '8', ' ' }, ParseSingleImage, IsValidSimpleFormat },
  { { 'V', 'P', '8', 'L' }, ParseSingleImage, IsValidSimpleFormat },
  { { 'V', 'P', '8', 'X' }, ParseVP8X,        IsValidExtendedFormat },
  { { '0', '0', '0', '0' }, NULL,             NULL },
};

//------------------------------------------------------------------------------

int WebPGetDemuxVersion(void) {
  return (DMUX_MAJ_VERSION << 16) | (DMUX_MIN_VERSION << 8) | DMUX_REV_VERSION;
}

// -----------------------------------------------------------------------------
// MemBuffer

static int RemapMemBuffer(MemBuffer* const mem,
                          const uint8_t* data, size_t size) {
  if (size < mem->buf_size_) return 0;  // can't remap to a shorter buffer!

  mem->buf_ = data;
  mem->end_ = mem->buf_size_ = size;
  return 1;
}

static int InitMemBuffer(MemBuffer* const mem,
                         const uint8_t* data, size_t size) {
  memset(mem, 0, sizeof(*mem));
  return RemapMemBuffer(mem, data, size);
}

// Return the remaining data size available in 'mem'.
static WEBP_INLINE size_t MemDataSize(const MemBuffer* const mem) {
  return (mem->end_ - mem->start_);
}

// Return true if 'size' exceeds the end of the RIFF chunk.
static WEBP_INLINE int SizeIsInvalid(const MemBuffer* const mem, size_t size) {
  return (size > mem->riff_end_ - mem->start_);
}

static WEBP_INLINE void Skip(MemBuffer* const mem, size_t size) {
  mem->start_ += size;
}

static WEBP_INLINE void Rewind(MemBuffer* const mem, size_t size) {
  mem->start_ -= size;
}

static WEBP_INLINE const uint8_t* GetBuffer(MemBuffer* const mem) {
  return mem->buf_ + mem->start_;
}

// Read from 'mem' and skip the read bytes.
static WEBP_INLINE uint8_t ReadByte(MemBuffer* const mem) {
  const uint8_t byte = mem->buf_[mem->start_];
  Skip(mem, 1);
  return byte;
}

static WEBP_INLINE int ReadLE16s(MemBuffer* const mem) {
  const uint8_t* const data = mem->buf_ + mem->start_;
  const int val = GetLE16(data);
  Skip(mem, 2);
  return val;
}

static WEBP_INLINE int ReadLE24s(MemBuffer* const mem) {
  const uint8_t* const data = mem->buf_ + mem->start_;
  const int val = GetLE24(data);
  Skip(mem, 3);
  return val;
}

static WEBP_INLINE uint32_t ReadLE32(MemBuffer* const mem) {
  const uint8_t* const data = mem->buf_ + mem->start_;
  const uint32_t val = GetLE32(data);
  Skip(mem, 4);
  return val;
}

// -----------------------------------------------------------------------------
// Secondary chunk parsing

static void AddChunk(WebPDemuxer* const dmux, Chunk* const chunk) {
  *dmux->chunks_tail_ = chunk;
  chunk->next_ = NULL;
  dmux->chunks_tail_ = &chunk->next_;
}

// Add a frame to the end of the list, ensuring the last frame is complete.
// Returns true on success, false otherwise.
static int AddFrame(WebPDemuxer* const dmux, Frame* const frame) {
  const Frame* const last_frame = *dmux->frames_tail_;
  if (last_frame != NULL && !last_frame->complete_) return 0;

  *dmux->frames_tail_ = frame;
  frame->next_ = NULL;
  dmux->frames_tail_ = &frame->next_;
  return 1;
}

static void SetFrameInfo(size_t start_offset, size_t size,
                         int frame_num, int complete,
                         const WebPBitstreamFeatures* const features,
                         Frame* const frame) {
  frame->img_components_[0].offset_ = start_offset;
  frame->img_components_[0].size_ = size;
  frame->width_ = features->width;
  frame->height_ = features->height;
  frame->has_alpha_ |= features->has_alpha;
  frame->frame_num_ = frame_num;
  frame->complete_ = complete;
}

// Store image bearing chunks to 'frame'. 'min_size' is an optional size
// requirement, it may be zero.
static ParseStatus StoreFrame(int frame_num, uint32_t min_size,
                              MemBuffer* const mem, Frame* const frame) {
  int alpha_chunks = 0;
  int image_chunks = 0;
  int done = (MemDataSize(mem) < CHUNK_HEADER_SIZE ||
              MemDataSize(mem) < min_size);
  ParseStatus status = PARSE_OK;

  if (done) return PARSE_NEED_MORE_DATA;

  do {
    const size_t chunk_start_offset = mem->start_;
    const uint32_t fourcc = ReadLE32(mem);
    const uint32_t payload_size = ReadLE32(mem);
    uint32_t payload_size_padded;
    size_t payload_available;
    size_t chunk_size;

    if (payload_size > MAX_CHUNK_PAYLOAD) return PARSE_ERROR;

    payload_size_padded = payload_size + (payload_size & 1);
    payload_available = (payload_size_padded > MemDataSize(mem))
                      ? MemDataSize(mem) : payload_size_padded;
    chunk_size = CHUNK_HEADER_SIZE + payload_available;
    if (SizeIsInvalid(mem, payload_size_padded)) return PARSE_ERROR;
    if (payload_size_padded > MemDataSize(mem)) status = PARSE_NEED_MORE_DATA;

    switch (fourcc) {
      case MKFOURCC('A', 'L', 'P', 'H'):
        if (alpha_chunks == 0) {
          ++alpha_chunks;
          frame->img_components_[1].offset_ = chunk_start_offset;
          frame->img_components_[1].size_ = chunk_size;
          frame->has_alpha_ = 1;
          frame->frame_num_ = frame_num;
          Skip(mem, payload_available);
        } else {
          goto Done;
        }
        break;
      case MKFOURCC('V', 'P', '8', 'L'):
        if (alpha_chunks > 0) return PARSE_ERROR;  // VP8L has its own alpha
        // fall through
      case MKFOURCC('V', 'P', '8', ' '):
        if (image_chunks == 0) {
          // Extract the bitstream features, tolerating failures when the data
          // is incomplete.
          WebPBitstreamFeatures features;
          const VP8StatusCode vp8_status =
              WebPGetFeatures(mem->buf_ + chunk_start_offset, chunk_size,
                              &features);
          if (status == PARSE_NEED_MORE_DATA &&
              vp8_status == VP8_STATUS_NOT_ENOUGH_DATA) {
            return PARSE_NEED_MORE_DATA;
          } else if (vp8_status != VP8_STATUS_OK) {
            // We have enough data, and yet WebPGetFeatures() failed.
            return PARSE_ERROR;
          }
          ++image_chunks;
          SetFrameInfo(chunk_start_offset, chunk_size, frame_num,
                       status == PARSE_OK, &features, frame);
          Skip(mem, payload_available);
        } else {
          goto Done;
        }
        break;
 Done:
      default:
        // Restore fourcc/size when moving up one level in parsing.
        Rewind(mem, CHUNK_HEADER_SIZE);
        done = 1;
        break;
    }

    if (mem->start_ == mem->riff_end_) {
      done = 1;
    } else if (MemDataSize(mem) < CHUNK_HEADER_SIZE) {
      status = PARSE_NEED_MORE_DATA;
    }
  } while (!done && status == PARSE_OK);

  return status;
}

// Creates a new Frame if 'actual_size' is within bounds and 'mem' contains
// enough data ('min_size') to parse the payload.
// Returns PARSE_OK on success with *frame pointing to the new Frame.
// Returns PARSE_NEED_MORE_DATA with insufficient data, PARSE_ERROR otherwise.
static ParseStatus NewFrame(const MemBuffer* const mem,
                            uint32_t min_size, uint32_t actual_size,
                            Frame** frame) {
  if (SizeIsInvalid(mem, min_size)) return PARSE_ERROR;
  if (actual_size < min_size) return PARSE_ERROR;
  if (MemDataSize(mem) < min_size)  return PARSE_NEED_MORE_DATA;

  *frame = (Frame*)WebPSafeCalloc(1ULL, sizeof(**frame));
  return (*frame == NULL) ? PARSE_ERROR : PARSE_OK;
}

// Parse a 'ANMF' chunk and any image bearing chunks that immediately follow.
// 'frame_chunk_size' is the previously validated, padded chunk size.
static ParseStatus ParseAnimationFrame(
    WebPDemuxer* const dmux, uint32_t frame_chunk_size) {
  const int is_animation = !!(dmux->feature_flags_ & ANIMATION_FLAG);
  const uint32_t anmf_payload_size = frame_chunk_size - ANMF_CHUNK_SIZE;
  int added_frame = 0;
  int bits;
  MemBuffer* const mem = &dmux->mem_;
  Frame* frame;
  size_t start_offset;
  ParseStatus status =
      NewFrame(mem, ANMF_CHUNK_SIZE, frame_chunk_size, &frame);
  if (status != PARSE_OK) return status;

  frame->x_offset_       = 2 * ReadLE24s(mem);
  frame->y_offset_       = 2 * ReadLE24s(mem);
  frame->width_          = 1 + ReadLE24s(mem);
  frame->height_         = 1 + ReadLE24s(mem);
  frame->duration_       = ReadLE24s(mem);
  bits = ReadByte(mem);
  frame->dispose_method_ =
      (bits & 1) ? WEBP_MUX_DISPOSE_BACKGROUND : WEBP_MUX_DISPOSE_NONE;
  frame->blend_method_ = (bits & 2) ? WEBP_MUX_NO_BLEND : WEBP_MUX_BLEND;
  if (frame->width_ * (uint64_t)frame->height_ >= MAX_IMAGE_AREA) {
    WebPSafeFree(frame);
    return PARSE_ERROR;
  }

  // Store a frame only if the animation flag is set there is some data for
  // this frame is available.
  start_offset = mem->start_;
  status = StoreFrame(dmux->num_frames_ + 1, anmf_payload_size, mem, frame);
  if (status != PARSE_ERROR && mem->start_ - start_offset > anmf_payload_size) {
    status = PARSE_ERROR;
  }
  if (status != PARSE_ERROR && is_animation && frame->frame_num_ > 0) {
    added_frame = AddFrame(dmux, frame);
    if (added_frame) {
      ++dmux->num_frames_;
    } else {
      status = PARSE_ERROR;
    }
  }

  if (!added_frame) WebPSafeFree(frame);
  return status;
}

// General chunk storage, starting with the header at 'start_offset', allowing
// the user to request the payload via a fourcc string. 'size' includes the
// header and the unpadded payload size.
// Returns true on success, false otherwise.
static int StoreChunk(WebPDemuxer* const dmux,
                      size_t start_offset, uint32_t size) {
  Chunk* const chunk = (Chunk*)WebPSafeCalloc(1ULL, sizeof(*chunk));
  if (chunk == NULL) return 0;

  chunk->data_.offset_ = start_offset;
  chunk->data_.size_ = size;
  AddChunk(dmux, chunk);
  return 1;
}

// -----------------------------------------------------------------------------
// Primary chunk parsing

static ParseStatus ReadHeader(MemBuffer* const mem) {
  const size_t min_size = RIFF_HEADER_SIZE + CHUNK_HEADER_SIZE;
  uint32_t riff_size;

  // Basic file level validation.
  if (MemDataSize(mem) < min_size) return PARSE_NEED_MORE_DATA;
  if (memcmp(GetBuffer(mem), "RIFF", CHUNK_SIZE_BYTES) ||
      memcmp(GetBuffer(mem) + CHUNK_HEADER_SIZE, "WEBP", CHUNK_SIZE_BYTES)) {
    return PARSE_ERROR;
  }

  riff_size = GetLE32(GetBuffer(mem) + TAG_SIZE);
  if (riff_size < CHUNK_HEADER_SIZE) return PARSE_ERROR;
  if (riff_size > MAX_CHUNK_PAYLOAD) return PARSE_ERROR;

  // There's no point in reading past the end of the RIFF chunk
  mem->riff_end_ = riff_size + CHUNK_HEADER_SIZE;
  if (mem->buf_size_ > mem->riff_end_) {
    mem->buf_size_ = mem->end_ = mem->riff_end_;
  }

  Skip(mem, RIFF_HEADER_SIZE);
  return PARSE_OK;
}

static ParseStatus ParseSingleImage(WebPDemuxer* const dmux) {
  const size_t min_size = CHUNK_HEADER_SIZE;
  MemBuffer* const mem = &dmux->mem_;
  Frame* frame;
  ParseStatus status;
  int image_added = 0;

  if (dmux->frames_ != NULL) return PARSE_ERROR;
  if (SizeIsInvalid(mem, min_size)) return PARSE_ERROR;
  if (MemDataSize(mem) < min_size) return PARSE_NEED_MORE_DATA;

  frame = (Frame*)WebPSafeCalloc(1ULL, sizeof(*frame));
  if (frame == NULL) return PARSE_ERROR;

  // For the single image case we allow parsing of a partial frame, so no
  // minimum size is imposed here.
  status = StoreFrame(1, 0, &dmux->mem_, frame);
  if (status != PARSE_ERROR) {
    const int has_alpha = !!(dmux->feature_flags_ & ALPHA_FLAG);
    // Clear any alpha when the alpha flag is missing.
    if (!has_alpha && frame->img_components_[1].size_ > 0) {
      frame->img_components_[1].offset_ = 0;
      frame->img_components_[1].size_ = 0;
      frame->has_alpha_ = 0;
    }

    // Use the frame width/height as the canvas values for non-vp8x files.
    // Also, set ALPHA_FLAG if this is a lossless image with alpha.
    if (!dmux->is_ext_format_ && frame->width_ > 0 && frame->height_ > 0) {
      dmux->state_ = WEBP_DEMUX_PARSED_HEADER;
      dmux->canvas_width_ = frame->width_;
      dmux->canvas_height_ = frame->height_;
      dmux->feature_flags_ |= frame->has_alpha_ ? ALPHA_FLAG : 0;
    }
    if (!AddFrame(dmux, frame)) {
      status = PARSE_ERROR;  // last frame was left incomplete
    } else {
      image_added = 1;
      dmux->num_frames_ = 1;
    }
  }

  if (!image_added) WebPSafeFree(frame);
  return status;
}

static ParseStatus ParseVP8XChunks(WebPDemuxer* const dmux) {
  const int is_animation = !!(dmux->feature_flags_ & ANIMATION_FLAG);
  MemBuffer* const mem = &dmux->mem_;
  int anim_chunks = 0;
  ParseStatus status = PARSE_OK;

  do {
    int store_chunk = 1;
    const size_t chunk_start_offset = mem->start_;
    const uint32_t fourcc = ReadLE32(mem);
    const uint32_t chunk_size = ReadLE32(mem);
    uint32_t chunk_size_padded;

    if (chunk_size > MAX_CHUNK_PAYLOAD) return PARSE_ERROR;

    chunk_size_padded = chunk_size + (chunk_size & 1);
    if (SizeIsInvalid(mem, chunk_size_padded)) return PARSE_ERROR;

    switch (fourcc) {
      case MKFOURCC('V', 'P', '8', 'X'): {
        return PARSE_ERROR;
      }
      case MKFOURCC('A', 'L', 'P', 'H'):
      case MKFOURCC('V', 'P', '8', ' '):
      case MKFOURCC('V', 'P', '8', 'L'): {
        // check that this isn't an animation (all frames should be in an ANMF).
        if (anim_chunks > 0 || is_animation) return PARSE_ERROR;

        Rewind(mem, CHUNK_HEADER_SIZE);
        status = ParseSingleImage(dmux);
        break;
      }
      case MKFOURCC('A', 'N', 'I', 'M'): {
        if (chunk_size_padded < ANIM_CHUNK_SIZE) return PARSE_ERROR;

        if (MemDataSize(mem) < chunk_size_padded) {
          status = PARSE_NEED_MORE_DATA;
        } else if (anim_chunks == 0) {
          ++anim_chunks;
          dmux->bgcolor_ = ReadLE32(mem);
          dmux->loop_count_ = ReadLE16s(mem);
          Skip(mem, chunk_size_padded - ANIM_CHUNK_SIZE);
        } else {
          store_chunk = 0;
          goto Skip;
        }
        break;
      }
      case MKFOURCC('A', 'N', 'M', 'F'): {
        if (anim_chunks == 0) return PARSE_ERROR;  // 'ANIM' precedes frames.
        status = ParseAnimationFrame(dmux, chunk_size_padded);
        break;
      }
      case MKFOURCC('I', 'C', 'C', 'P'): {
        store_chunk = !!(dmux->feature_flags_ & ICCP_FLAG);
        goto Skip;
      }
      case MKFOURCC('E', 'X', 'I', 'F'): {
        store_chunk = !!(dmux->feature_flags_ & EXIF_FLAG);
        goto Skip;
      }
      case MKFOURCC('X', 'M', 'P', ' '): {
        store_chunk = !!(dmux->feature_flags_ & XMP_FLAG);
        goto Skip;
      }
 Skip:
      default: {
        if (chunk_size_padded <= MemDataSize(mem)) {
          if (store_chunk) {
            // Store only the chunk header and unpadded size as only the payload
            // will be returned to the user.
            if (!StoreChunk(dmux, chunk_start_offset,
                            CHUNK_HEADER_SIZE + chunk_size)) {
              return PARSE_ERROR;
            }
          }
          Skip(mem, chunk_size_padded);
        } else {
          status = PARSE_NEED_MORE_DATA;
        }
      }
    }

    if (mem->start_ == mem->riff_end_) {
      break;
    } else if (MemDataSize(mem) < CHUNK_HEADER_SIZE) {
      status = PARSE_NEED_MORE_DATA;
    }
  } while (status == PARSE_OK);

  return status;
}

static ParseStatus ParseVP8X(WebPDemuxer* const dmux) {
  MemBuffer* const mem = &dmux->mem_;
  uint32_t vp8x_size;

  if (MemDataSize(mem) < CHUNK_HEADER_SIZE) return PARSE_NEED_MORE_DATA;

  dmux->is_ext_format_ = 1;
  Skip(mem, TAG_SIZE);  // VP8X
  vp8x_size = ReadLE32(mem);
  if (vp8x_size > MAX_CHUNK_PAYLOAD) return PARSE_ERROR;
  if (vp8x_size < VP8X_CHUNK_SIZE) return PARSE_ERROR;
  vp8x_size += vp8x_size & 1;
  if (SizeIsInvalid(mem, vp8x_size)) return PARSE_ERROR;
  if (MemDataSize(mem) < vp8x_size) return PARSE_NEED_MORE_DATA;

  dmux->feature_flags_ = ReadByte(mem);
  Skip(mem, 3);  // Reserved.
  dmux->canvas_width_  = 1 + ReadLE24s(mem);
  dmux->canvas_height_ = 1 + ReadLE24s(mem);
  if (dmux->canvas_width_ * (uint64_t)dmux->canvas_height_ >= MAX_IMAGE_AREA) {
    return PARSE_ERROR;  // image final dimension is too large
  }
  Skip(mem, vp8x_size - VP8X_CHUNK_SIZE);  // skip any trailing data.
  dmux->state_ = WEBP_DEMUX_PARSED_HEADER;

  if (SizeIsInvalid(mem, CHUNK_HEADER_SIZE)) return PARSE_ERROR;
  if (MemDataSize(mem) < CHUNK_HEADER_SIZE) return PARSE_NEED_MORE_DATA;

  return ParseVP8XChunks(dmux);
}

// -----------------------------------------------------------------------------
// Format validation

static int IsValidSimpleFormat(const WebPDemuxer* const dmux) {
  const Frame* const frame = dmux->frames_;
  if (dmux->state_ == WEBP_DEMUX_PARSING_HEADER) return 1;

  if (dmux->canvas_width_ <= 0 || dmux->canvas_height_ <= 0) return 0;
  if (dmux->state_ == WEBP_DEMUX_DONE && frame == NULL) return 0;

  if (frame->width_ <= 0 || frame->height_ <= 0) return 0;
  return 1;
}

// If 'exact' is true, check that the image resolution matches the canvas.
// If 'exact' is false, check that the x/y offsets do not exceed the canvas.
static int CheckFrameBounds(const Frame* const frame, int exact,
                            int canvas_width, int canvas_height) {
  if (exact) {
    if (frame->x_offset_ != 0 || frame->y_offset_ != 0) {
      return 0;
    }
    if (frame->width_ != canvas_width || frame->height_ != canvas_height) {
      return 0;
    }
  } else {
    if (frame->x_offset_ < 0 || frame->y_offset_ < 0) return 0;
    if (frame->width_ + frame->x_offset_ > canvas_width) return 0;
    if (frame->height_ + frame->y_offset_ > canvas_height) return 0;
  }
  return 1;
}

static int IsValidExtendedFormat(const WebPDemuxer* const dmux) {
  const int is_animation = !!(dmux->feature_flags_ & ANIMATION_FLAG);
  const Frame* f = dmux->frames_;

  if (dmux->state_ == WEBP_DEMUX_PARSING_HEADER) return 1;

  if (dmux->canvas_width_ <= 0 || dmux->canvas_height_ <= 0) return 0;
  if (dmux->loop_count_ < 0) return 0;
  if (dmux->state_ == WEBP_DEMUX_DONE && dmux->frames_ == NULL) return 0;
  if (dmux->feature_flags_ & ~ALL_VALID_FLAGS) return 0;  // invalid bitstream

  while (f != NULL) {
    const int cur_frame_set = f->frame_num_;
    int frame_count = 0;

    // Check frame properties.
    for (; f != NULL && f->frame_num_ == cur_frame_set; f = f->next_) {
      const ChunkData* const image = f->img_components_;
      const ChunkData* const alpha = f->img_components_ + 1;

      if (!is_animation && f->frame_num_ > 1) return 0;

      if (f->complete_) {
        if (alpha->size_ == 0 && image->size_ == 0) return 0;
        // Ensure alpha precedes image bitstream.
        if (alpha->size_ > 0 && alpha->offset_ > image->offset_) {
          return 0;
        }

        if (f->width_ <= 0 || f->height_ <= 0) return 0;
      } else {
        // There shouldn't be a partial frame in a complete file.
        if (dmux->state_ == WEBP_DEMUX_DONE) return 0;

        // Ensure alpha precedes image bitstream.
        if (alpha->size_ > 0 && image->size_ > 0 &&
            alpha->offset_ > image->offset_) {
          return 0;
        }
        // There shouldn't be any frames after an incomplete one.
        if (f->next_ != NULL) return 0;
      }

      if (f->width_ > 0 && f->height_ > 0 &&
          !CheckFrameBounds(f, !is_animation,
                            dmux->canvas_width_, dmux->canvas_height_)) {
        return 0;
      }

      ++frame_count;
    }
  }
  return 1;
}

// -----------------------------------------------------------------------------
// WebPDemuxer object

static void InitDemux(WebPDemuxer* const dmux, const MemBuffer* const mem) {
  dmux->state_ = WEBP_DEMUX_PARSING_HEADER;
  dmux->loop_count_ = 1;
  dmux->bgcolor_ = 0xFFFFFFFF;  // White background by default.
  dmux->canvas_width_ = -1;
  dmux->canvas_height_ = -1;
  dmux->frames_tail_ = &dmux->frames_;
  dmux->chunks_tail_ = &dmux->chunks_;
  dmux->mem_ = *mem;
}

static ParseStatus CreateRawImageDemuxer(MemBuffer* const mem,
                                         WebPDemuxer** demuxer) {
  WebPBitstreamFeatures features;
  const VP8StatusCode status =
      WebPGetFeatures(mem->buf_, mem->buf_size_, &features);
  *demuxer = NULL;
  if (status != VP8_STATUS_OK) {
    return (status == VP8_STATUS_NOT_ENOUGH_DATA) ? PARSE_NEED_MORE_DATA
                                                  : PARSE_ERROR;
  }

  {
    WebPDemuxer* const dmux = (WebPDemuxer*)WebPSafeCalloc(1ULL, sizeof(*dmux));
    Frame* const frame = (Frame*)WebPSafeCalloc(1ULL, sizeof(*frame));
    if (dmux == NULL || frame == NULL) goto Error;
    InitDemux(dmux, mem);
    SetFrameInfo(0, mem->buf_size_, 1 /*frame_num*/, 1 /*complete*/, &features,
                 frame);
    if (!AddFrame(dmux, frame)) goto Error;
    dmux->state_ = WEBP_DEMUX_DONE;
    dmux->canvas_width_ = frame->width_;
    dmux->canvas_height_ = frame->height_;
    dmux->feature_flags_ |= frame->has_alpha_ ? ALPHA_FLAG : 0;
    dmux->num_frames_ = 1;
    assert(IsValidSimpleFormat(dmux));
    *demuxer = dmux;
    return PARSE_OK;

 Error:
    WebPSafeFree(dmux);
    WebPSafeFree(frame);
    return PARSE_ERROR;
  }
}

WebPDemuxer* WebPDemuxInternal(const WebPData* data, int allow_partial,
                               WebPDemuxState* state, int version) {
  const ChunkParser* parser;
  int partial;
  ParseStatus status = PARSE_ERROR;
  MemBuffer mem;
  WebPDemuxer* dmux;

  if (state != NULL) *state = WEBP_DEMUX_PARSE_ERROR;

  if (WEBP_ABI_IS_INCOMPATIBLE(version, WEBP_DEMUX_ABI_VERSION)) return NULL;
  if (data == NULL || data->bytes == NULL || data->size == 0) return NULL;

  if (!InitMemBuffer(&mem, data->bytes, data->size)) return NULL;
  status = ReadHeader(&mem);
  if (status != PARSE_OK) {
    // If parsing of the webp file header fails attempt to handle a raw
    // VP8/VP8L frame. Note 'allow_partial' is ignored in this case.
    if (status == PARSE_ERROR) {
      status = CreateRawImageDemuxer(&mem, &dmux);
      if (status == PARSE_OK) {
        if (state != NULL) *state = WEBP_DEMUX_DONE;
        return dmux;
      }
    }
    if (state != NULL) {
      *state = (status == PARSE_NEED_MORE_DATA) ? WEBP_DEMUX_PARSING_HEADER
                                                : WEBP_DEMUX_PARSE_ERROR;
    }
    return NULL;
  }

  partial = (mem.buf_size_ < mem.riff_end_);
  if (!allow_partial && partial) return NULL;

  dmux = (WebPDemuxer*)WebPSafeCalloc(1ULL, sizeof(*dmux));
  if (dmux == NULL) return NULL;
  InitDemux(dmux, &mem);

  status = PARSE_ERROR;
  for (parser = kMasterChunks; parser->parse != NULL; ++parser) {
    if (!memcmp(parser->id, GetBuffer(&dmux->mem_), TAG_SIZE)) {
      status = parser->parse(dmux);
      if (status == PARSE_OK) dmux->state_ = WEBP_DEMUX_DONE;
      if (status == PARSE_NEED_MORE_DATA && !partial) status = PARSE_ERROR;
      if (status != PARSE_ERROR && !parser->valid(dmux)) status = PARSE_ERROR;
      if (status == PARSE_ERROR) dmux->state_ = WEBP_DEMUX_PARSE_ERROR;
      break;
    }
  }
  if (state != NULL) *state = dmux->state_;

  if (status == PARSE_ERROR) {
    WebPDemuxDelete(dmux);
    return NULL;
  }
  return dmux;
}

void WebPDemuxDelete(WebPDemuxer* dmux) {
  Chunk* c;
  Frame* f;
  if (dmux == NULL) return;

  for (f = dmux->frames_; f != NULL;) {
    Frame* const cur_frame = f;
    f = f->next_;
    WebPSafeFree(cur_frame);
  }
  for (c = dmux->chunks_; c != NULL;) {
    Chunk* const cur_chunk = c;
    c = c->next_;
    WebPSafeFree(cur_chunk);
  }
  WebPSafeFree(dmux);
}

// -----------------------------------------------------------------------------

uint32_t WebPDemuxGetI(const WebPDemuxer* dmux, WebPFormatFeature feature) {
  if (dmux == NULL) return 0;

  switch (feature) {
    case WEBP_FF_FORMAT_FLAGS:     return dmux->feature_flags_;
    case WEBP_FF_CANVAS_WIDTH:     return (uint32_t)dmux->canvas_width_;
    case WEBP_FF_CANVAS_HEIGHT:    return (uint32_t)dmux->canvas_height_;
    case WEBP_FF_LOOP_COUNT:       return (uint32_t)dmux->loop_count_;
    case WEBP_FF_BACKGROUND_COLOR: return dmux->bgcolor_;
    case WEBP_FF_FRAME_COUNT:      return (uint32_t)dmux->num_frames_;
  }
  return 0;
}

// -----------------------------------------------------------------------------
// Frame iteration

static const Frame* GetFrame(const WebPDemuxer* const dmux, int frame_num) {
  const Frame* f;
  for (f = dmux->frames_; f != NULL; f = f->next_) {
    if (frame_num == f->frame_num_) break;
  }
  return f;
}

static const uint8_t* GetFramePayload(const uint8_t* const mem_buf,
                                      const Frame* const frame,
                                      size_t* const data_size) {
  *data_size = 0;
  if (frame != NULL) {
    const ChunkData* const image = frame->img_components_;
    const ChunkData* const alpha = frame->img_components_ + 1;
    size_t start_offset = image->offset_;
    *data_size = image->size_;

    // if alpha exists it precedes image, update the size allowing for
    // intervening chunks.
    if (alpha->size_ > 0) {
      const size_t inter_size = (image->offset_ > 0)
                              ? image->offset_ - (alpha->offset_ + alpha->size_)
                              : 0;
      start_offset = alpha->offset_;
      *data_size  += alpha->size_ + inter_size;
    }
    return mem_buf + start_offset;
  }
  return NULL;
}

// Create a whole 'frame' from VP8 (+ alpha) or lossless.
static int SynthesizeFrame(const WebPDemuxer* const dmux,
                           const Frame* const frame,
                           WebPIterator* const iter) {
  const uint8_t* const mem_buf = dmux->mem_.buf_;
  size_t payload_size = 0;
  const uint8_t* const payload = GetFramePayload(mem_buf, frame, &payload_size);
  if (payload == NULL) return 0;
  assert(frame != NULL);

  iter->frame_num      = frame->frame_num_;
  iter->num_frames     = dmux->num_frames_;
  iter->x_offset       = frame->x_offset_;
  iter->y_offset       = frame->y_offset_;
  iter->width          = frame->width_;
  iter->height         = frame->height_;
  iter->has_alpha      = frame->has_alpha_;
  iter->duration       = frame->duration_;
  iter->dispose_method = frame->dispose_method_;
  iter->blend_method   = frame->blend_method_;
  iter->complete       = frame->complete_;
  iter->fragment.bytes = payload;
  iter->fragment.size  = payload_size;
  return 1;
}

static int SetFrame(int frame_num, WebPIterator* const iter) {
  const Frame* frame;
  const WebPDemuxer* const dmux = (WebPDemuxer*)iter->private_;
  if (dmux == NULL || frame_num < 0) return 0;
  if (frame_num > dmux->num_frames_) return 0;
  if (frame_num == 0) frame_num = dmux->num_frames_;

  frame = GetFrame(dmux, frame_num);
  if (frame == NULL) return 0;

  return SynthesizeFrame(dmux, frame, iter);
}

int WebPDemuxGetFrame(const WebPDemuxer* dmux, int frame, WebPIterator* iter) {
  if (iter == NULL) return 0;

  memset(iter, 0, sizeof(*iter));
  iter->private_ = (void*)dmux;
  return SetFrame(frame, iter);
}

int WebPDemuxNextFrame(WebPIterator* iter) {
  if (iter == NULL) return 0;
  return SetFrame(iter->frame_num + 1, iter);
}

int WebPDemuxPrevFrame(WebPIterator* iter) {
  if (iter == NULL) return 0;
  if (iter->frame_num <= 1) return 0;
  return SetFrame(iter->frame_num - 1, iter);
}

void WebPDemuxReleaseIterator(WebPIterator* iter) {
  (void)iter;
}

// -----------------------------------------------------------------------------
// Chunk iteration

static int ChunkCount(const WebPDemuxer* const dmux, const char fourcc[4]) {
  const uint8_t* const mem_buf = dmux->mem_.buf_;
  const Chunk* c;
  int count = 0;
  for (c = dmux->chunks_; c != NULL; c = c->next_) {
    const uint8_t* const header = mem_buf + c->data_.offset_;
    if (!memcmp(header, fourcc, TAG_SIZE)) ++count;
  }
  return count;
}

static const Chunk* GetChunk(const WebPDemuxer* const dmux,
                             const char fourcc[4], int chunk_num) {
  const uint8_t* const mem_buf = dmux->mem_.buf_;
  const Chunk* c;
  int count = 0;
  for (c = dmux->chunks_; c != NULL; c = c->next_) {
    const uint8_t* const header = mem_buf + c->data_.offset_;
    if (!memcmp(header, fourcc, TAG_SIZE)) ++count;
    if (count == chunk_num) break;
  }
  return c;
}

static int SetChunk(const char fourcc[4], int chunk_num,
                    WebPChunkIterator* const iter) {
  const WebPDemuxer* const dmux = (WebPDemuxer*)iter->private_;
  int count;

  if (dmux == NULL || fourcc == NULL || chunk_num < 0) return 0;
  count = ChunkCount(dmux, fourcc);
  if (count == 0) return 0;
  if (chunk_num == 0) chunk_num = count;

  if (chunk_num <= count) {
    const uint8_t* const mem_buf = dmux->mem_.buf_;
    const Chunk* const chunk = GetChunk(dmux, fourcc, chunk_num);
    iter->chunk.bytes = mem_buf + chunk->data_.offset_ + CHUNK_HEADER_SIZE;
    iter->chunk.size  = chunk->data_.size_ - CHUNK_HEADER_SIZE;
    iter->num_chunks  = count;
    iter->chunk_num   = chunk_num;
    return 1;
  }
  return 0;
}

int WebPDemuxGetChunk(const WebPDemuxer* dmux,
                      const char fourcc[4], int chunk_num,
                      WebPChunkIterator* iter) {
  if (iter == NULL) return 0;

  memset(iter, 0, sizeof(*iter));
  iter->private_ = (void*)dmux;
  return SetChunk(fourcc, chunk_num, iter);
}

int WebPDemuxNextChunk(WebPChunkIterator* iter) {
  if (iter != NULL) {
    const char* const fourcc =
        (const char*)iter->chunk.bytes - CHUNK_HEADER_SIZE;
    return SetChunk(fourcc, iter->chunk_num + 1, iter);
  }
  return 0;
}

int WebPDemuxPrevChunk(WebPChunkIterator* iter) {
  if (iter != NULL && iter->chunk_num > 1) {
    const char* const fourcc =
        (const char*)iter->chunk.bytes - CHUNK_HEADER_SIZE;
    return SetChunk(fourcc, iter->chunk_num - 1, iter);
  }
  return 0;
}

void WebPDemuxReleaseChunkIterator(WebPChunkIterator* iter) {
  (void)iter;
}