static bool is_orientation_marker(jpeg_marker_struct* marker, SkCodec::Origin* orientation) {
if (kExifMarker != marker->marker || marker->data_length < kExifHeaderSize) {
return false;
}
const uint8_t* data = marker->data;
static const uint8_t kExifSig[] { 'E', 'x', 'i', 'f', '\0' };
if (memcmp(data, kExifSig, sizeof(kExifSig))) {
return false;
}
bool littleEndian;
if (!is_valid_endian_marker(data + 6, &littleEndian)) {
return false;
}
// Get the offset from the start of the marker.
// Account for 'E', 'x', 'i', 'f', '\0', '<fill byte>'.
uint32_t offset = get_endian_int(data + 10, littleEndian);
offset += sizeof(kExifSig) + 1;
// Require that the marker is at least large enough to contain the number of entries.
if (marker->data_length < offset + 2) {
return false;
}
uint32_t numEntries = get_endian_short(data + offset, littleEndian);
// Tag (2 bytes), Datatype (2 bytes), Number of elements (4 bytes), Data (4 bytes)
const uint32_t kEntrySize = 12;
numEntries = SkTMin(numEntries, (marker->data_length - offset - 2) / kEntrySize);
// Advance the data to the start of the entries.
data += offset + 2;
const uint16_t kOriginTag = 0x112;
const uint16_t kOriginType = 3;
for (uint32_t i = 0; i < numEntries; i++, data += kEntrySize) {
uint16_t tag = get_endian_short(data, littleEndian);
uint16_t type = get_endian_short(data + 2, littleEndian);
uint32_t count = get_endian_int(data + 4, littleEndian);
if (kOriginTag == tag && kOriginType == type && 1 == count) {
uint16_t val = get_endian_short(data + 8, littleEndian);
if (0 < val && val <= SkCodec::kLast_Origin) {
*orientation = (SkCodec::Origin) val;
return true;
}
}
}
return false;
}
// Quick check if the image contains a valid TIFF header as requested by DNG format.
bool isTiffHeaderValid() const {
const size_t kHeaderSize = 4;
SkAutoSTMalloc<kHeaderSize, unsigned char> header(kHeaderSize);
if (!fStream->read(header.get(), 0 /* offset */, kHeaderSize)) {
return false;
}
// Check if the header is valid (endian info and magic number "42").
bool littleEndian;
if (!is_valid_endian_marker(header, &littleEndian)) {
return false;
}
return 0x2A == get_endian_short(header + 2, littleEndian);
}
