// FileTime returns the best guess of the file's creation time (or modtime).
// If the file doesn't have its own metadata indication the creation time (such as in EXIF),
// FileTime uses the modification time from the file system.
// It there was a valid EXIF but an error while trying to get a date from it,
// it logs the error and tries the other methods.
func FileTime(f io.ReaderAt) (time.Time, error) {
var ct time.Time
defaultTime := func() (time.Time, error) {
if osf, ok := f.(*os.File); ok {
fi, err := osf.Stat()
if err != nil {
return ct, fmt.Errorf("Failed to find a modtime: stat: %v", err)
}
return fi.ModTime(), nil
}
return ct, errors.New("All methods failed to find a creation time or modtime.")
}
size, ok := findSize(f)
if !ok {
size = 256 << 10 // enough to get the EXIF
}
r := io.NewSectionReader(f, 0, size)
var tiffErr error
ex, err := exif.Decode(r)
if err != nil {
tiffErr = err
if exif.IsShortReadTagValueError(err) {
return ct, io.ErrUnexpectedEOF
}
if exif.IsCriticalError(err) || exif.IsExifError(err) {
return defaultTime()
}
}
ct, err = ex.DateTime()
if err != nil {
return defaultTime()
}
// If the EXIF file only had local timezone, but it did have
// GPS, then lookup the timezone and correct the time.
if ct.Location() == time.Local {
if exif.IsGPSError(tiffErr) {
log.Printf("Invalid EXIF GPS data: %v", tiffErr)
return ct, nil
}
if lat, long, err := ex.LatLong(); err == nil {
if loc := lookupLocation(latlong.LookupZoneName(lat, long)); loc != nil {
if t, err := exifDateTimeInLocation(ex, loc); err == nil {
return t, nil
}
}
} else if !exif.IsTagNotPresentError(err) {
log.Printf("Invalid EXIF GPS data: %v", err)
}
}
return ct, nil
}
func showEXIF(file string) {
f, err := os.Open(file)
if err != nil {
panic(err.Error())
}
defer f.Close()
ex, err := exif.Decode(f)
if err != nil {
if exif.IsCriticalError(err) {
log.Fatalf("exif.Decode, critical error: %v", err)
}
log.Printf("exif.Decode, warning: %v", err)
}
fmt.Printf("%v\n", ex)
if exif.IsExifError(err) {
// the error happened while decoding the EXIF sub-IFD, so as DateTime is
// part of it, we have to assume (until there's a better "decode effort"
// strategy in goexif) that it's not usable.
return
}
ct, err := ex.DateTime()
fmt.Printf("exif.DateTime = %v, %v\n", ct, err)
}