// Decode parses EXIF-encoded data from r and returns a queryable Exif object.
func Decode(r io.Reader) (*Exif, error) {
sec, err := newAppSec(0xE1, r)
if err != nil {
return nil, err
}
er, err := sec.exifReader()
if err != nil {
return nil, err
}
tif, err := tiff.Decode(er)
if err != nil {
return nil, errors.New("exif: decode failed: " + err.Error())
}
// build an exif structure from the tiff
x := &Exif{
main: map[FieldName]*tiff.Tag{},
tif: tif,
}
ifd0 := tif.Dirs[0]
for _, tag := range ifd0.Tags {
name := exifFields[tag.Id]
x.main[name] = tag
}
// recurse into exif, gps, and interop sub-IFDs
if err = x.loadSubDir(er, exifIFDPointer, exifFields); err != nil {
return x, err
}
if err = x.loadSubDir(er, gpsInfoIFDPointer, gpsFields); err != nil {
return x, err
}
if err = x.loadSubDir(er, interoperabilityIFDPointer, interopFields); err != nil {
return x, err
}
return x, nil
}
// Decode parses EXIF-encoded data from r and returns a queryable Exif object.
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 n < len(header) {
return nil, errors.New("exif: short read on header")
}
if err != nil {
return nil, err
}
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 {
// Strip away JPEG APP1 header.
var sec *appSec
sec, err = newAppSec(0xE1, 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, errors.New("exif: decode failed: " + err.Error())
}
// build an exif structure from the tiff
x := &Exif{
main: map[FieldName]*tiff.Tag{},
tif: tif,
}
ifd0 := tif.Dirs[0]
for _, tag := range ifd0.Tags {
name := exifFields[tag.Id]
x.main[name] = tag
}
// recurse into exif, gps, and interop sub-IFDs
if err = x.loadSubDir(er, exifIFDPointer, exifFields); err != nil {
return x, err
}
if err = x.loadSubDir(er, gpsInfoIFDPointer, gpsFields); err != nil {
return x, err
}
if err = x.loadSubDir(er, interoperabilityIFDPointer, interopFields); err != nil {
return x, err
}
return x, nil
}
