func Parse(r io.Reader) (eIFD, gIFD, ioIFD tiff.IFD, err error) {
rars := tiff.NewReadAtReadSeeker(r)
var two [2]byte
if _, err = rars.Read(two[:]); err != nil {
return
}
if _, err = rars.Seek(0, 0); err != nil {
return
}
switch string(two[:]) {
case "MM", "II": // likely a tiff
var t tiff.TIFF
if t, err = tiff.Parse(rars, nil, nil); err != nil {
return
}
for _, tIFD := range t.IFDs() {
if tIFD.HasField(ExifIFDTagID) {
eFld := tIFD.GetField(ExifIFDTagID)
offset := eFld.Type().Valuer()(eFld.Value().Bytes(), eFld.Value().Order()).Uint()
if eIFD, err = tiff.ParseIFD(t.R(), offset, ExifTagSpace, nil); err != nil {
return
}
if tIFD.HasField(GPSIFDTagID) {
gFld := tIFD.GetField(GPSIFDTagID)
offset = gFld.Type().Valuer()(gFld.Value().Bytes(), gFld.Value().Order()).Uint()
if gIFD, err = tiff.ParseIFD(t.R(), offset, GPSTagSpace, nil); err != nil {
log.Printf("exif: GPS IFD found, but had trouble retrieving it from offset %d: %v\n", offset, err)
}
}
if tIFD.HasField(InteroperabilityIFDTagID) {
ioFld := tIFD.GetField(InteroperabilityIFDTagID)
offset = ioFld.Type().Valuer()(ioFld.Value().Bytes(), ioFld.Value().Order()).Uint()
if ioIFD, err = tiff.ParseIFD(t.R(), offset, IOPTagSpace, nil); err != nil {
log.Printf("exif: IOP IFD found, but had trouble retrieving it from offset %d: %v\n", offset, err)
}
}
return
}
}
err = fmt.Errorf("exif: no exif ifd found in tiff")
return
case "\xff\xd8": // likely a jpeg
err = fmt.Errorf("exif: still working on jpeg support")
return
}
// Anything else is currently unsupported.
err = fmt.Errorf("exif: unsupported header: %q", two[:])
return
}
func validateTIFF(t tiff.TIFF) error {
if len(t.IFDs()) == 0 {
return fmt.Errorf("tiff/image: no IFDs present in tiff to process")
}
if t.IFDs()[0] == nil {
return fmt.Errorf("tiff/image: IFD 0 is nil")
}
if t.IFDs()[0].NumEntries() == 0 || len(t.IFDs()[0].Fields()) == 0 {
return fmt.Errorf("tiff/image: no entries found in IFD 0")
}
return nil
}
// For now, findAlternates will only check against two concepts. One, is the
// "Make" tag and the other checks the presence of tags.
func findAlternateTIFFHandler(t tiff.TIFF) TIFFHandler {
ifd0 := t.IFDs()[0]
// Do tag presence check first. This is useful for identifying
// tiff files that conform to a certain specification that uses
// a tag to identify that specification. For example, tiff/ep
// uses the "TIFF/EPStandardID" tag (id 37398) to indicate the
// version number of tiff/ep in use for this tiff file. DNG has
// the "DNGVersion" tag (id 50706) for the same. And Leaf .MOS
// files do not indicate make/model, but they do have a custom
// private tag that they use for certain data (tag id 34310).
// The idea here is that a tiff/ep package or dng package or
// leaf mos package would be able to better handle processing
// the tiff than the generic package.
for _, tagID := range ListRegisteredTagPresenceIDs() {
if ifd0.HasField(tagID) {
hndlr := GetHandlerByTagPresence(tagID)
if hndlr != nil && hndlr.CanHandle(t) {
return hndlr
}
}
}
// Check for a specific make next
// Tag ID 271 is a baseline tag for the "Make" or maker or
// manufacturer of a device that created this tiff. The idea
// here is that a separate manufacturer package may be more
// directly aware of how to process a specific tiff as opposed
// to playing guessing games in a generic package.
if ifd0.HasField(271) {
f := ifd0.GetField(271)
maker := string(bytes.TrimRight(f.Value().Bytes(), " \x00"))
hndlr := GetHandlerByMake(maker)
if hndlr != nil && hndlr.CanHandle(t) {
return hndlr
}
}
return nil
}
func getDecoder(t tiff.TIFF) (dec Decoder, err error) {
if err = validateTIFF(t); err != nil {
return
}
// Look for alternates that can handle the whole tiff.
if handlr := findAlternateTIFFHandler(t); handlr != nil {
return handlr.Decoder(t)
}
// Look for alternates that can handle specific IFDs.
for _, ifd := range t.IFDs() {
if handlr := findAlternateIFDHandler(ifd); handlr != nil {
return handlr.Decoder(ifd, t.R())
}
}
// If no alternates are found... do our own thing as best we can, which
// means baseline support only.
ifd0 := t.IFDs()[0]
if !new(BaselineHandler).CanHandle(ifd0) {
return nil, fmt.Errorf("tiff/image: no handlers available for this tiff")
}
return new(BaselineHandler).Decoder(ifd0, t.R())
}