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go-exif
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exif: Dropped requirement for incorrect/non-standard EXIF prefix.

pull/3/head
Dustin Oprea 2018-06-06 05:32:14 -04:00
parent d05c9b4c81
commit 2eb57331ff
2 changed files with 7 additions and 25 deletions
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24
exif.go
View File

@ -15,7 +15,7 @@ import (
const (
// ExifAddressableAreaStart is the absolute offset in the file that all
// offsets are relative to.
ExifAddressableAreaStart = uint32(0x6)
ExifAddressableAreaStart = uint32(0x0)
// ExifDefaultFirstIfdOffset is essentially the number of bytes in addition
// to `ExifAddressableAreaStart` that you have to move in order to escape
@ -29,8 +29,6 @@ const (
var (
exifLogger = log.NewLogger("exif.exif")
ExifHeaderPrefixBytes = []byte("Exif\000\000")
// EncodeDefaultByteOrder is the default byte-order for encoding operations.
EncodeDefaultByteOrder = binary.BigEndian
@ -135,16 +133,12 @@ func ParseExifHeader(data []byte) (eh ExifHeader, err error) {
}
}()
if bytes.Compare(data[:6], ExifHeaderPrefixBytes) != 0 {
log.Panic(ErrNotExif)
}
// Good reference:
//
// CIPA DC-008-2016; JEITA CP-3451D
// -> http://www.cipa.jp/std/documents/e/DC-008-Translation-2016-E.pdf
byteOrderBytes := [2]byte { data[6], data[7] }
byteOrderBytes := [2]byte { data[0], data[1] }
byteOrder, found := ByteOrderLookup[byteOrderBytes]
if found == false {
@ -152,18 +146,13 @@ func ParseExifHeader(data []byte) (eh ExifHeader, err error) {
log.Panic(ErrNotExif)
}
fixedBytes := [2]byte { data[8], data[9] }
fixedBytes := [2]byte { data[2], data[3] }
if fixedBytes != ExifFixedBytes {
exifLogger.Warningf(nil, "EXIF header fixed-bytes should be 0x002a but are: [%v]", fixedBytes)
log.Panic(ErrNotExif)
}
firstIfdOffset := uint32(0)
if byteOrder == binary.BigEndian {
firstIfdOffset = binary.BigEndian.Uint32(data[10:14])
} else {
firstIfdOffset = binary.LittleEndian.Uint32(data[10:14])
}
firstIfdOffset := byteOrder.Uint32(data[4:8])
eh = ExifHeader{
ByteOrder: byteOrder,
@ -221,10 +210,7 @@ func BuildExifHeader(byteOrder binary.ByteOrder, firstIfdOffset uint32) (headerB
b := new(bytes.Buffer)
_, err = b.Write(ExifHeaderPrefixBytes)
log.PanicIf(err)
// NOTE: This is the point in the data that all offsets are relative to.
// This is the point in the data that all offsets are relative to.
boBytes := ByteOrderLookupR[byteOrder]
_, err = b.WriteString(string(boBytes[:]))
log.PanicIf(err)

8
test_common.go
View File

@ -30,11 +30,7 @@ func init() {
filepath := path.Join(assetsPath, "NDM_8901.jpg.exif")
exifData, err := ioutil.ReadFile(filepath)
var err error
testExifData, err = ioutil.ReadFile(filepath)
log.PanicIf(err)
// TODO(dustin): !! We're currently built to expect the JPEG EXIF header-prefix, but our test-data doesn't have that.So, artificially prefix it, for now.
testExifData = make([]byte, len(exifData) + len(ExifHeaderPrefixBytes))
copy(testExifData[0:], ExifHeaderPrefixBytes)
copy(testExifData[len(ExifHeaderPrefixBytes):], exifData)
}