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go-exif
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exif.go: Use simple byte comparison to match signature

for/master
Dustin Oprea 2020-05-05 00:58:01 -04:00
parent 3e77768f35
commit df264b321a
1 changed files with 18 additions and 55 deletions
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73
v2/exif.go
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@ -29,23 +29,8 @@ const (
var (
exifLogger = log.NewLogger("exif.exif")
BigEndianBoBytes = [2]byte{'M', 'M'}
LittleEndianBoBytes = [2]byte{'I', 'I'}
ByteOrderLookup = map[[2]byte]binary.ByteOrder{
BigEndianBoBytes: binary.BigEndian,
LittleEndianBoBytes: binary.LittleEndian,
}
ByteOrderLookupR = map[binary.ByteOrder][2]byte{
binary.BigEndian: BigEndianBoBytes,
binary.LittleEndian: LittleEndianBoBytes,
}
ExifFixedBytesLookup = map[binary.ByteOrder][2]byte{
binary.LittleEndian: [2]byte{0x2a, 0x00},
binary.BigEndian: [2]byte{0x00, 0x2a},
}
ExifBigEndianSignature = [4]byte{'M', 'M', 0x00, 0x2a}
ExifLittleEndianSignature = [4]byte{'I', 'I', 0x2a, 0x00}
)
var (
@ -136,42 +121,20 @@ func ParseExifHeader(data []byte) (eh ExifHeader, err error) {
// CIPA DC-008-2016; JEITA CP-3451D
// -> http://www.cipa.jp/std/documents/e/DC-008-Translation-2016-E.pdf
if len(data) < 2 {
exifLogger.Warningf(nil, "Not enough data for EXIF header (1): (%d)", len(data))
if len(data) < 8 {
exifLogger.Warningf(nil, "Not enough data for EXIF header: (%d)", len(data))
return eh, ErrNoExif
}
byteOrderBytes := [2]byte{data[0], data[1]}
byteOrder, found := ByteOrderLookup[byteOrderBytes]
if found == false {
// exifLogger.Warningf(nil, "EXIF byte-order not recognized: [%v]", byteOrderBytes)
if bytes.Equal(data[:4], ExifBigEndianSignature[:]) == true {
eh.ByteOrder = binary.BigEndian
} else if bytes.Equal(data[:4], ExifLittleEndianSignature[:]) == true {
eh.ByteOrder = binary.LittleEndian
} else {
return eh, ErrNoExif
}
if len(data) < 4 {
exifLogger.Warningf(nil, "Not enough data for EXIF header (2): (%d)", len(data))
return eh, ErrNoExif
}
fixedBytes := [2]byte{data[2], data[3]}
expectedFixedBytes := ExifFixedBytesLookup[byteOrder]
if fixedBytes != expectedFixedBytes {
// exifLogger.Warningf(nil, "EXIF header fixed-bytes should be [%v] but are: [%v]", expectedFixedBytes, fixedBytes)
return eh, ErrNoExif
}
if len(data) < 2 {
exifLogger.Warningf(nil, "Not enough data for EXIF header (3): (%d)", len(data))
return eh, ErrNoExif
}
firstIfdOffset := byteOrder.Uint32(data[4:8])
eh = ExifHeader{
ByteOrder: byteOrder,
FirstIfdOffset: firstIfdOffset,
}
eh.FirstIfdOffset = eh.ByteOrder.Uint32(data[4:8])
return eh, nil
}
@ -214,7 +177,7 @@ func Collect(ifdMapping *IfdMapping, tagIndex *TagIndex, exifData []byte) (eh Ex
return eh, index, nil
}
// BuildExifHeader constructs the bytes that go in the very beginning.
// BuildExifHeader constructs the bytes that go at the front of the stream.
func BuildExifHeader(byteOrder binary.ByteOrder, firstIfdOffset uint32) (headerBytes []byte, err error) {
defer func() {
if state := recover(); state != nil {
@ -224,14 +187,14 @@ func BuildExifHeader(byteOrder binary.ByteOrder, firstIfdOffset uint32) (headerB
b := new(bytes.Buffer)
// This is the point in the data that all offsets are relative to.
boBytes := ByteOrderLookupR[byteOrder]
_, err = b.WriteString(string(boBytes[:]))
log.PanicIf(err)
var signatureBytes []byte
if byteOrder == binary.BigEndian {
signatureBytes = ExifBigEndianSignature[:]
} else {
signatureBytes = ExifLittleEndianSignature[:]
}
fixedBytes := ExifFixedBytesLookup[byteOrder]
_, err = b.Write(fixedBytes[:])
_, err = b.Write(signatureBytes)
log.PanicIf(err)
err = binary.Write(b, byteOrder, firstIfdOffset)