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- // Copyright 2019 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #include "media/parsers/webp_parser.h"
- #include <limits.h>
- #include <stddef.h>
- #include <string.h>
- #include "base/bits.h"
- #include "base/check_op.h"
- #include "base/numerics/safe_conversions.h"
- #include "build/build_config.h"
- #include "media/parsers/vp8_parser.h"
- #if !defined(ARCH_CPU_LITTLE_ENDIAN)
- #error Big-Endian architecture not supported.
- #endif
- namespace media {
- namespace {
- // The byte position storing the size of the file.
- constexpr size_t kFileSizeBytePosition = 4u;
- // The byte position in which the WebP image data begins.
- constexpr size_t kWebPFileBeginBytePosition = 8u;
- // The byte position storing the size of the VP8 frame.
- constexpr size_t kVp8FrameSizePosition = 16u;
- // The 12 bytes that include the FourCC "WEBPVP8 " plus the VP8 chunk size info.
- constexpr size_t kWebPFileHeaderByteSize = 12u;
- // A valid WebP image header and VP8 chunk header require 20 bytes.
- // The VP8 Key Frame's payload also begins at byte 20.
- constexpr size_t kWebPFileAndVp8ChunkHeaderSizeInBytes = 20u;
- // The max WebP file size is (2^32 - 10) per the WebP spec:
- // https://developers.google.com/speed/webp/docs/riff_container#webp_file_header
- constexpr uint32_t kMaxWebPFileSize = (1ull << 32) - 10u;
- constexpr size_t kSizeOfUint32t = sizeof(uint32_t);
- } // namespace
- bool IsLossyWebPImage(base::span<const uint8_t> encoded_data) {
- if (encoded_data.size() < kWebPFileAndVp8ChunkHeaderSizeInBytes)
- return false;
- DCHECK(encoded_data.data());
- return !memcmp(encoded_data.data(), "RIFF", 4) &&
- !memcmp(encoded_data.data() + kWebPFileBeginBytePosition, "WEBPVP8 ",
- 8);
- }
- std::unique_ptr<Vp8FrameHeader> ParseWebPImage(
- base::span<const uint8_t> encoded_data) {
- if (!IsLossyWebPImage(encoded_data))
- return nullptr;
- static_assert(CHAR_BIT == 8, "Size of a char is not 8 bits.");
- static_assert(kSizeOfUint32t == 4u, "Size of uint32_t is not 4 bytes.");
- // Try to acquire the WebP file size. IsLossyWebPImage() has ensured
- // that we have enough data to read the file size.
- DCHECK_GE(encoded_data.size(), kFileSizeBytePosition + kSizeOfUint32t);
- // No need to worry about endianness because we assert little-endianness.
- const uint32_t file_size = *reinterpret_cast<const uint32_t*>(
- encoded_data.data() + kFileSizeBytePosition);
- // Check that |file_size| is even, per the WebP spec:
- // https://developers.google.com/speed/webp/docs/riff_container#webp_file_header
- if (file_size % 2 != 0)
- return nullptr;
- // Check that |file_size| <= 2^32 - 10, per the WebP spec:
- // https://developers.google.com/speed/webp/docs/riff_container#webp_file_header
- if (file_size > kMaxWebPFileSize)
- return nullptr;
- // Check that the file size in the header matches the encoded data's size.
- if (base::strict_cast<size_t>(file_size) !=
- encoded_data.size() - kWebPFileBeginBytePosition) {
- return nullptr;
- }
- // Try to acquire the VP8 key frame size and validate that it fits within the
- // encoded data's size.
- DCHECK_GE(encoded_data.size(), kVp8FrameSizePosition + kSizeOfUint32t);
- const uint32_t vp8_frame_size = *reinterpret_cast<const uint32_t*>(
- encoded_data.data() + kVp8FrameSizePosition);
- // Check that the VP8 frame size is bounded by the WebP size.
- if (base::strict_cast<size_t>(file_size) - kWebPFileHeaderByteSize <
- base::strict_cast<size_t>(vp8_frame_size)) {
- return nullptr;
- }
- // Check that the size of the encoded data is consistent.
- const size_t vp8_padded_frame_size =
- base::bits::AlignUp(size_t{vp8_frame_size}, size_t{2});
- if (encoded_data.size() - kWebPFileAndVp8ChunkHeaderSizeInBytes !=
- vp8_padded_frame_size) {
- return nullptr;
- }
- // Check that the last byte is 0 if |vp8_frame_size| is odd per WebP specs:
- // https://developers.google.com/speed/webp/docs/riff_container#riff_file_format
- if (vp8_frame_size % 2 &&
- encoded_data.data()[encoded_data.size() - 1] != 0u) {
- return nullptr;
- }
- // Attempt to parse the VP8 frame.
- Vp8Parser vp8_parser;
- auto result = std::make_unique<Vp8FrameHeader>();
- if (vp8_parser.ParseFrame(
- encoded_data.data() + kWebPFileAndVp8ChunkHeaderSizeInBytes,
- base::strict_cast<size_t>(vp8_frame_size), result.get())) {
- return result;
- }
- return nullptr;
- }
- } // namespace media
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