Adding libwebp: Adding clean copy of libwebp 0.4.0

This commit imports libwebp 0.4.0, including AUTHORS, COPYING, ChangeLog,
NEWS, PATENTS, README and src directories. In src, only includes header
and source files.

The patches required to build it in Qt will follow in separate
commit(s).

Task-number: QTBUG-14205
Change-Id: I747918fe2a07716f66cffb795129f7aa5e067759
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 1002 insertions, 0 deletions

diff --git a/src/3rdparty/libwebp/src/demux/demux.c b/src/3rdparty/libwebp/src/demux/demux.c
new file mode 100644
index 0000000..f66ac6d
--- /dev/null
+++ b/src/3rdparty/libwebp/src/demux/demux.c
@@ -0,0 +1,1002 @@
+// 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 "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 0
+#define DMUX_MIN_VERSION 2
+#define DMUX_REV_VERSION 0
+
+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 is_fragment_;  // this is a frame fragment (and not a full frame).
+  int frame_num_;  // the referent frame number for use in assembling fragments.
+  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;
+}
+
+// Store image bearing chunks to 'frame'.
+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) < 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);
+    const uint32_t payload_size_padded = payload_size + (payload_size & 1);
+    const size_t payload_available = (payload_size_padded > MemDataSize(mem))
+                                   ? MemDataSize(mem) : payload_size_padded;
+    const size_t chunk_size = CHUNK_HEADER_SIZE + payload_available;
+
+    if (payload_size > MAX_CHUNK_PAYLOAD) return PARSE_ERROR;
+    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;
+          frame->img_components_[0].offset_ = chunk_start_offset;
+          frame->img_components_[0].size_ = chunk_size;
+          frame->width_ = features.width;
+          frame->height_ = features.height;
+          frame->has_alpha_ |= features.has_alpha;
+          frame->frame_num_ = frame_num;
+          frame->complete_ = (status == PARSE_OK);
+          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*)calloc(1, 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;
+  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) {
+    free(frame);
+    return PARSE_ERROR;
+  }
+
+  // Store a frame only if the animation flag is set there is some data for
+  // this frame is available.
+  status = StoreFrame(dmux->num_frames_ + 1, anmf_payload_size, mem, frame);
+  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) free(frame);
+  return status;
+}
+
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+// Parse a 'FRGM' chunk and any image bearing chunks that immediately follow.
+// 'fragment_chunk_size' is the previously validated, padded chunk size.
+static ParseStatus ParseFragment(WebPDemuxer* const dmux,
+                                 uint32_t fragment_chunk_size) {
+  const int frame_num = 1;  // All fragments belong to the 1st (and only) frame.
+  const int is_fragmented = !!(dmux->feature_flags_ & FRAGMENTS_FLAG);
+  const uint32_t frgm_payload_size = fragment_chunk_size - FRGM_CHUNK_SIZE;
+  int added_fragment = 0;
+  MemBuffer* const mem = &dmux->mem_;
+  Frame* frame;
+  ParseStatus status =
+      NewFrame(mem, FRGM_CHUNK_SIZE, fragment_chunk_size, &frame);
+  if (status != PARSE_OK) return status;
+
+  frame->is_fragment_ = 1;
+  frame->x_offset_ = 2 * ReadLE24s(mem);
+  frame->y_offset_ = 2 * ReadLE24s(mem);
+
+  // Store a fragment only if the 'fragments' flag is set and there is some
+  // data available.
+  status = StoreFrame(frame_num, frgm_payload_size, mem, frame);
+  if (status != PARSE_ERROR && is_fragmented && frame->frame_num_ > 0) {
+    added_fragment = AddFrame(dmux, frame);
+    if (!added_fragment) {
+      status = PARSE_ERROR;
+    } else {
+      dmux->num_frames_ = 1;
+    }
+  }
+
+  if (!added_fragment) free(frame);
+  return status;
+}
+#endif  // WEBP_EXPERIMENTAL_FEATURES
+
+// 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*)calloc(1, 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*)calloc(1, sizeof(*frame));
+  if (frame == NULL) return PARSE_ERROR;
+
+  // For the single image case we allow parsing of a partial frame, but we need
+  // at least CHUNK_HEADER_SIZE for parsing.
+  status = StoreFrame(1, CHUNK_HEADER_SIZE, &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) free(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);
+    const uint32_t chunk_size_padded = chunk_size + (chunk_size & 1);
+
+    if (chunk_size > MAX_CHUNK_PAYLOAD) return PARSE_ERROR;
+    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;
+      }
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+      case MKFOURCC('F', 'R', 'G', 'M'): {
+        status = ParseFragment(dmux, chunk_size_padded);
+        break;
+      }
+#endif
+      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.
+// TODO(jzern): this is insufficient in the fragmented image case if the
+// expectation is that the fragments completely cover 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 int is_fragmented = !!(dmux->feature_flags_ & FRAGMENTS_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;
+#ifndef WEBP_EXPERIMENTAL_FEATURES
+  if (is_fragmented) return 0;
+#endif
+
+  while (f != NULL) {
+    const int cur_frame_set = f->frame_num_;
+    int frame_count = 0, fragment_count = 0;
+
+    // Check frame properties and if the image is composed of fragments that
+    // each fragment came from a fragment.
+    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_fragmented && !f->is_fragment_) return 0;
+      if (!is_fragmented && f->is_fragment_) return 0;
+      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 || is_fragmented),
+                            dmux->canvas_width_, dmux->canvas_height_)) {
+        return 0;
+      }
+
+      fragment_count += f->is_fragment_;
+      ++frame_count;
+    }
+    if (!is_fragmented && frame_count > 1) return 0;
+    if (fragment_count > 0 && frame_count != fragment_count) return 0;
+  }
+  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;
+}
+
+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 (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*)calloc(1, 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_;
+    free(cur_frame);
+  }
+  for (c = dmux->chunks_; c != NULL;) {
+    Chunk* const cur_chunk = c;
+    c = c->next_;
+    free(cur_chunk);
+  }
+  free(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
+
+// Find the first 'frame_num' frame. There may be multiple such frames in a
+// fragmented frame.
+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;
+}
+
+// Returns fragment 'fragment_num' and the total count.
+static const Frame* GetFragment(
+    const Frame* const frame_set, int fragment_num, int* const count) {
+  const int this_frame = frame_set->frame_num_;
+  const Frame* f = frame_set;
+  const Frame* fragment = NULL;
+  int total;
+
+  for (total = 0; f != NULL && f->frame_num_ == this_frame; f = f->next_) {
+    if (++total == fragment_num) fragment = f;
+  }
+  *count = total;
+  return fragment;
+}
+
+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 first_frame,
+                           int fragment_num, WebPIterator* const iter) {
+  const uint8_t* const mem_buf = dmux->mem_.buf_;
+  int num_fragments;
+  size_t payload_size = 0;
+  const Frame* const fragment =
+      GetFragment(first_frame, fragment_num, &num_fragments);
+  const uint8_t* const payload =
+      GetFramePayload(mem_buf, fragment, &payload_size);
+  if (payload == NULL) return 0;
+  assert(first_frame != NULL);
+
+  iter->frame_num      = first_frame->frame_num_;
+  iter->num_frames     = dmux->num_frames_;
+  iter->fragment_num   = fragment_num;
+  iter->num_fragments  = num_fragments;
+  iter->x_offset       = fragment->x_offset_;
+  iter->y_offset       = fragment->y_offset_;
+  iter->width          = fragment->width_;
+  iter->height         = fragment->height_;
+  iter->has_alpha      = fragment->has_alpha_;
+  iter->duration       = fragment->duration_;
+  iter->dispose_method = fragment->dispose_method_;
+  iter->blend_method   = fragment->blend_method_;
+  iter->complete       = fragment->complete_;
+  iter->fragment.bytes = payload;
+  iter->fragment.size  = payload_size;
+  // TODO(jzern): adjust offsets for 'FRGM's embedded in 'ANMF's
+  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, 1, 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);
+}
+
+int WebPDemuxSelectFragment(WebPIterator* iter, int fragment_num) {
+  if (iter != NULL && iter->private_ != NULL && fragment_num > 0) {
+    const WebPDemuxer* const dmux = (WebPDemuxer*)iter->private_;
+    const Frame* const frame = GetFrame(dmux, iter->frame_num);
+    if (frame == NULL) return 0;
+
+    return SynthesizeFrame(dmux, frame, fragment_num, iter);
+  }
+  return 0;
+}
+
+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;
+}
+