// Parse decodes all Nikon makernote data found in x and adds it to x.
func (_ *nikonV3) Parse(x *exif.Exif) error {
m, err := x.Get(exif.MakerNote)
if err != nil {
return nil
} else if bytes.Compare(m.Val[:6], []byte("Nikon\000")) != 0 {
return nil
}
// Nikon v3 maker note is a self-contained IFD (offsets are relative
// to the start of the maker note)
mkNotes, err := tiff.Decode(bytes.NewReader(m.Val[10:]))
if err != nil {
return err
}
x.LoadTags(mkNotes.Dirs[0], makerNoteNikon3Fields, false)
return nil
}
// Decode parses EXIF-encoded data from r and returns a queryable Exif
// object. After the exif data section is called and the tiff structure
// decoded, each registered parser is called (in order of registration). If
// one parser returns an error, decoding terminates and the remaining
// parsers are not called.
// The error can be inspected with functions such as IsCriticalError to
// determine whether the returned object might still be usable.
func Decode(r io.Reader) (*Exif, error) {
// EXIF data in JPEG is stored in the APP1 marker. EXIF data uses the TIFF
// format to store data.
// If we're parsing a TIFF image, we don't need to strip away any data.
// If we're parsing a JPEG image, we need to strip away the JPEG APP1
// marker and also the EXIF header.
header := make([]byte, 4)
n, err := r.Read(header)
if err != nil {
return nil, err
}
if n < len(header) {
return nil, errors.New("exif: short read on header")
}
var isTiff bool
switch string(header) {
case "II*\x00":
// TIFF - Little endian (Intel)
isTiff = true
case "MM\x00*":
// TIFF - Big endian (Motorola)
isTiff = true
default:
// Not TIFF, assume JPEG
}
// Put the header bytes back into the reader.
r = io.MultiReader(bytes.NewReader(header), r)
var (
er *bytes.Reader
tif *tiff.Tiff
)
if isTiff {
// Functions below need the IFDs from the TIFF data to be stored in a
// *bytes.Reader. We use TeeReader to get a copy of the bytes as a
// side-effect of tiff.Decode() doing its work.
b := &bytes.Buffer{}
tr := io.TeeReader(r, b)
tif, err = tiff.Decode(tr)
er = bytes.NewReader(b.Bytes())
} else {
// Locate the JPEG APP1 header.
var sec *appSec
sec, err = newAppSec(jpeg_APP1, r)
if err != nil {
return nil, err
}
// Strip away EXIF header.
er, err = sec.exifReader()
if err != nil {
return nil, err
}
tif, err = tiff.Decode(er)
}
if err != nil {
return nil, decodeError{cause: err}
}
er.Seek(0, 0)
raw, err := ioutil.ReadAll(er)
if err != nil {
return nil, decodeError{cause: err}
}
// build an exif structure from the tiff
x := &Exif{
main: map[FieldName]*tiff.Tag{},
Tiff: tif,
Raw: raw,
}
for i, p := range parsers {
if err := p.Parse(x); err != nil {
if _, ok := err.(tiffErrors); ok {
return x, err
}
// This should never happen, as Parse always returns a tiffError
// for now, but that could change.
return x, fmt.Errorf("exif: parser %v failed (%v)", i, err)
}
}
return x, nil
}