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  assert(data != NULL);
  assert(data_size != NULL);
  assert(chunk_size != NULL);
  assert(is_lossless != NULL);

  if (*data_size < CHUNK_HEADER_SIZE) {
    return VP8_STATUS_NOT_ENOUGH_DATA;  // Insufficient data.
  }

  if (is_vp8 || is_vp8l) {
    // Bitstream contains VP8/VP8L header.
    const uint32_t size = get_le32(data + TAG_SIZE);
    if ((riff_size >= minimal_size) && (size > riff_size - minimal_size)) {
      return VP8_STATUS_BITSTREAM_ERROR;  // Inconsistent size information.
    }
    if (have_all_data && (size > *data_size - CHUNK_HEADER_SIZE)) {
      return VP8_STATUS_NOT_ENOUGH_DATA;  // Truncated bitstream.
    }
    // Skip over CHUNK_HEADER_SIZE bytes from VP8/VP8L Header.
    *chunk_size = size;
    *data_ptr += CHUNK_HEADER_SIZE;
    *data_size -= CHUNK_HEADER_SIZE;
    *is_lossless = is_vp8l;
  } else {
    // Raw VP8/VP8L bitstream (no header).
    *is_lossless = VP8LCheckSignature(data, *data_size);
    *chunk_size = *data_size;
  }

  return VP8_STATUS_OK;
}

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

// Fetch '*width', '*height', '*has_alpha' and fill out 'headers' based on
// 'data'. All the output parameters may be NULL. If 'headers' is NULL only the
// minimal amount will be read to fetch the remaining parameters.
// If 'headers' is non-NULL this function will attempt to locate both alpha
// data (with or without a VP8X chunk) and the bitstream chunk (VP8/VP8L).
// Note: The following chunk sequences (before the raw VP8/VP8L data) are
// considered valid by this function:
// RIFF + VP8(L)
// RIFF + VP8X + (optional chunks) + VP8(L)
// ALPH + VP8 <-- Not a valid WebP format: only allowed for internal purpose.
// VP8(L)     <-- Not a valid WebP format: only allowed for internal purpose.
static VP8StatusCode ParseHeadersInternal(const uint8_t* data,
                                          size_t data_size,
                                          int* const width,
                                          int* const height,
                                          int* const has_alpha,
                                          int* const has_animation,
                                          int* const format,
                                          WebPHeaderStructure* const headers) {
  int canvas_width = 0;
  int canvas_height = 0;
  int image_width = 0;
  int image_height = 0;
  int found_riff = 0;
  int found_vp8x = 0;
  int animation_present = 0;
  int fragments_present = 0;
  const int have_all_data = (headers != NULL) ? headers->have_all_data : 0;

  VP8StatusCode status;
  WebPHeaderStructure hdrs;

  if (data == NULL || data_size < RIFF_HEADER_SIZE) {
    return VP8_STATUS_NOT_ENOUGH_DATA;
  }
  memset(&hdrs, 0, sizeof(hdrs));
  hdrs.data = data;
  hdrs.data_size = data_size;

  // Skip over RIFF header.
  status = ParseRIFF(&data, &data_size, have_all_data, &hdrs.riff_size);
  if (status != VP8_STATUS_OK) {
    return status;   // Wrong RIFF header / insufficient data.
  }
  found_riff = (hdrs.riff_size > 0);

  // Skip over VP8X.
  {
    uint32_t flags = 0;
    status = ParseVP8X(&data, &data_size, &found_vp8x,
                       &canvas_width, &canvas_height, &flags);
    if (status != VP8_STATUS_OK) {
      return status;  // Wrong VP8X / insufficient data.
    }
    animation_present = !!(flags & ANIMATION_FLAG);
    fragments_present = !!(flags & FRAGMENTS_FLAG);
    if (!found_riff && found_vp8x) {
      // Note: This restriction may be removed in the future, if it becomes
      // necessary to send VP8X chunk to the decoder.
      return VP8_STATUS_BITSTREAM_ERROR;
    }
    if (has_alpha != NULL) *has_alpha = !!(flags & ALPHA_FLAG);
    if (has_animation != NULL) *has_animation = animation_present;
    if (format != NULL) *format = 0;   // default = undefined

    image_width = canvas_width;
    image_height = canvas_height;
    if (found_vp8x && (animation_present || fragments_present) &&
        headers == NULL) {
      status = VP8_STATUS_OK;
      goto ReturnWidthHeight;  // Just return features from VP8X header.
    }
  }

  if (data_size < TAG_SIZE) {
    status = VP8_STATUS_NOT_ENOUGH_DATA;
    goto ReturnWidthHeight;
  }

  // Skip over optional chunks if data started with "RIFF + VP8X" or "ALPH".
  if ((found_riff && found_vp8x) ||
      (!found_riff && !found_vp8x && !memcmp(data, "ALPH", TAG_SIZE))) {
    status = ParseOptionalChunks(&data, &data_size, hdrs.riff_size,
                                 &hdrs.alpha_data, &hdrs.alpha_data_size);
    if (status != VP8_STATUS_OK) {
      goto ReturnWidthHeight;  // Invalid chunk size / insufficient data.
    }
  }

  // Skip over VP8/VP8L header.
  status = ParseVP8Header(&data, &data_size, have_all_data, hdrs.riff_size,
                          &hdrs.compressed_size, &hdrs.is_lossless);
  if (status != VP8_STATUS_OK) {
    goto ReturnWidthHeight;  // Wrong VP8/VP8L chunk-header / insufficient data.
  }
  if (hdrs.compressed_size > MAX_CHUNK_PAYLOAD) {
    return VP8_STATUS_BITSTREAM_ERROR;
  }

  if (format != NULL && !(animation_present || fragments_present)) {
    *format = hdrs.is_lossless ? 2 : 1;
  }

  if (!hdrs.is_lossless) {
    if (data_size < VP8_FRAME_HEADER_SIZE) {
      status = VP8_STATUS_NOT_ENOUGH_DATA;
      goto ReturnWidthHeight;
    }
    // Validates raw VP8 data.
    if (!VP8GetInfo(data, data_size, (uint32_t)hdrs.compressed_size,
                    &image_width, &image_height)) {
      return VP8_STATUS_BITSTREAM_ERROR;
    }
  } else {
    if (data_size < VP8L_FRAME_HEADER_SIZE) {
      status = VP8_STATUS_NOT_ENOUGH_DATA;
      goto ReturnWidthHeight;
    }
    // Validates raw VP8L data.
    if (!VP8LGetInfo(data, data_size, &image_width, &image_height, has_alpha)) {
      return VP8_STATUS_BITSTREAM_ERROR;
    }
  }
  // Validates image size coherency.
  if (found_vp8x) {
    if (canvas_width != image_width || canvas_height != image_height) {
      return VP8_STATUS_BITSTREAM_ERROR;
    }
  }
  if (headers != NULL) {
    *headers = hdrs;
    headers->offset = data - headers->data;
    assert((uint64_t)(data - headers->data) < MAX_CHUNK_PAYLOAD);
    assert(headers->offset == headers->data_size - data_size);
  }
 ReturnWidthHeight:
  if (status == VP8_STATUS_OK ||
      (status == VP8_STATUS_NOT_ENOUGH_DATA && found_vp8x && headers == NULL)) {
    if (has_alpha != NULL) {
      // If the data did not contain a VP8X/VP8L chunk the only definitive way
      // to set this is by looking for alpha data (from an ALPH chunk).
      *has_alpha |= (hdrs.alpha_data != NULL);
    }
    if (width != NULL) *width = image_width;
    if (height != NULL) *height = image_height;
    return VP8_STATUS_OK;
  } else {
    return status;
  }
}

VP8StatusCode WebPParseHeaders(WebPHeaderStructure* const headers) {
  VP8StatusCode status;
  int has_animation = 0;
  assert(headers != NULL);
  // fill out headers, ignore width/height/has_alpha.
  status = ParseHeadersInternal(headers->data, headers->data_size,
                                NULL, NULL, NULL, &has_animation,
                                NULL, headers);
  if (status == VP8_STATUS_OK || status == VP8_STATUS_NOT_ENOUGH_DATA) {