go*: one go module for the repo, no more nested

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/github.com/rwcarlsen/goexif/exif/README.md

@@ -0,0 +1,4 @@
+
+To regenerate the regression test data, run `go generate` inside the exif
+package directory and commit the changes to *regress_expected_test.go*.
+

vendor/github.com/rwcarlsen/goexif/exif/exif.go

@@ -0,0 +1,655 @@
+// Package exif implements decoding of EXIF data as defined in the EXIF 2.2
+// specification (http://www.exif.org/Exif2-2.PDF).
+package exif
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/binary"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/rwcarlsen/goexif/tiff"
+)
+
+const (
+	jpeg_APP1 = 0xE1
+
+	exifPointer    = 0x8769
+	gpsPointer     = 0x8825
+	interopPointer = 0xA005
+)
+
+// A decodeError is returned when the image cannot be decoded as a tiff image.
+type decodeError struct {
+	cause error
+}
+
+func (de decodeError) Error() string {
+	return fmt.Sprintf("exif: decode failed (%v) ", de.cause.Error())
+}
+
+// IsShortReadTagValueError identifies a ErrShortReadTagValue error.
+func IsShortReadTagValueError(err error) bool {
+	de, ok := err.(decodeError)
+	if ok {
+		return de.cause == tiff.ErrShortReadTagValue
+	}
+	return false
+}
+
+// A TagNotPresentError is returned when the requested field is not
+// present in the EXIF.
+type TagNotPresentError FieldName
+
+func (tag TagNotPresentError) Error() string {
+	return fmt.Sprintf("exif: tag %q is not present", string(tag))
+}
+
+func IsTagNotPresentError(err error) bool {
+	_, ok := err.(TagNotPresentError)
+	return ok
+}
+
+// Parser allows the registration of custom parsing and field loading
+// in the Decode function.
+type Parser interface {
+	// Parse should read data from x and insert parsed fields into x via
+	// LoadTags.
+	Parse(x *Exif) error
+}
+
+var parsers []Parser
+
+func init() {
+	RegisterParsers(&parser{})
+}
+
+// RegisterParsers registers one or more parsers to be automatically called
+// when decoding EXIF data via the Decode function.
+func RegisterParsers(ps ...Parser) {
+	parsers = append(parsers, ps...)
+}
+
+type parser struct{}
+
+type tiffErrors map[tiffError]string
+
+func (te tiffErrors) Error() string {
+	var allErrors []string
+	for k, v := range te {
+		allErrors = append(allErrors, fmt.Sprintf("%s: %v\n", stagePrefix[k], v))
+	}
+	return strings.Join(allErrors, "\n")
+}
+
+// IsCriticalError, given the error returned by Decode, reports whether the
+// returned *Exif may contain usable information.
+func IsCriticalError(err error) bool {
+	_, ok := err.(tiffErrors)
+	return !ok
+}
+
+// IsExifError reports whether the error happened while decoding the EXIF
+// sub-IFD.
+func IsExifError(err error) bool {
+	if te, ok := err.(tiffErrors); ok {
+		_, isExif := te[loadExif]
+		return isExif
+	}
+	return false
+}
+
+// IsGPSError reports whether the error happened while decoding the GPS sub-IFD.
+func IsGPSError(err error) bool {
+	if te, ok := err.(tiffErrors); ok {
+		_, isGPS := te[loadExif]
+		return isGPS
+	}
+	return false
+}
+
+// IsInteroperabilityError reports whether the error happened while decoding the
+// Interoperability sub-IFD.
+func IsInteroperabilityError(err error) bool {
+	if te, ok := err.(tiffErrors); ok {
+		_, isInterop := te[loadInteroperability]
+		return isInterop
+	}
+	return false
+}
+
+type tiffError int
+
+const (
+	loadExif tiffError = iota
+	loadGPS
+	loadInteroperability
+)
+
+var stagePrefix = map[tiffError]string{
+	loadExif:             "loading EXIF sub-IFD",
+	loadGPS:              "loading GPS sub-IFD",
+	loadInteroperability: "loading Interoperability sub-IFD",
+}
+
+// Parse reads data from the tiff data in x and populates the tags
+// in x. If parsing a sub-IFD fails, the error is recorded and
+// parsing continues with the remaining sub-IFDs.
+func (p *parser) Parse(x *Exif) error {
+	if len(x.Tiff.Dirs) == 0 {
+		return errors.New("Invalid exif data")
+	}
+	x.LoadTags(x.Tiff.Dirs[0], exifFields, false)
+
+	// thumbnails
+	if len(x.Tiff.Dirs) >= 2 {
+		x.LoadTags(x.Tiff.Dirs[1], thumbnailFields, false)
+	}
+
+	te := make(tiffErrors)
+
+	// recurse into exif, gps, and interop sub-IFDs
+	if err := loadSubDir(x, ExifIFDPointer, exifFields); err != nil {
+		te[loadExif] = err.Error()
+	}
+	if err := loadSubDir(x, GPSInfoIFDPointer, gpsFields); err != nil {
+		te[loadGPS] = err.Error()
+	}
+
+	if err := loadSubDir(x, InteroperabilityIFDPointer, interopFields); err != nil {
+		te[loadInteroperability] = err.Error()
+	}
+	if len(te) > 0 {
+		return te
+	}
+	return nil
+}
+
+func loadSubDir(x *Exif, ptr FieldName, fieldMap map[uint16]FieldName) error {
+	r := bytes.NewReader(x.Raw)
+
+	tag, err := x.Get(ptr)
+	if err != nil {
+		return nil
+	}
+	offset, err := tag.Int64(0)
+	if err != nil {
+		return nil
+	}
+
+	_, err = r.Seek(offset, 0)
+	if err != nil {
+		return fmt.Errorf("exif: seek to sub-IFD %s failed: %v", ptr, err)
+	}
+	subDir, _, err := tiff.DecodeDir(r, x.Tiff.Order)
+	if err != nil {
+		return fmt.Errorf("exif: sub-IFD %s decode failed: %v", ptr, err)
+	}
+	x.LoadTags(subDir, fieldMap, false)
+	return nil
+}
+
+// Exif provides access to decoded EXIF metadata fields and values.
+type Exif struct {
+	Tiff *tiff.Tiff
+	main map[FieldName]*tiff.Tag
+	Raw  []byte
+}
+
+// Decode parses EXIF data from r (a TIFF, JPEG, or raw EXIF block)
+// and returns a queryable Exif object. After the EXIF data section is
+// called and the TIFF structure is 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 := io.ReadFull(r, header)
+	if err != nil {
+		return nil, fmt.Errorf("exif: error reading 4 byte header, got %d, %v", n, err)
+	}
+
+	var isTiff bool
+	var isRawExif bool
+	var assumeJPEG bool
+	switch string(header) {
+	case "II*\x00":
+		// TIFF - Little endian (Intel)
+		isTiff = true
+	case "MM\x00*":
+		// TIFF - Big endian (Motorola)
+		isTiff = true
+	case "Exif":
+		isRawExif = true
+	default:
+		// Not TIFF, assume JPEG
+		assumeJPEG = true
+	}
+
+	// Put the header bytes back into the reader.
+	r = io.MultiReader(bytes.NewReader(header), r)
+	var (
+		er  *bytes.Reader
+		tif *tiff.Tiff
+		sec *appSec
+	)
+
+	switch {
+	case isRawExif:
+		var header [6]byte
+		if _, err := io.ReadFull(r, header[:]); err != nil {
+			return nil, fmt.Errorf("exif: unexpected raw exif header read error")
+		}
+		if got, want := string(header[:]), "Exif\x00\x00"; got != want {
+			return nil, fmt.Errorf("exif: unexpected raw exif header; got %q, want %q", got, want)
+		}
+		fallthrough
+	case 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())
+	case assumeJPEG:
+		// Locate the JPEG APP1 header.
+		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
+}
+
+// LoadTags loads tags into the available fields from the tiff Directory
+// using the given tagid-fieldname mapping.  Used to load makernote and
+// other meta-data.  If showMissing is true, tags in d that are not in the
+// fieldMap will be loaded with the FieldName UnknownPrefix followed by the
+// tag ID (in hex format).
+func (x *Exif) LoadTags(d *tiff.Dir, fieldMap map[uint16]FieldName, showMissing bool) {
+	for _, tag := range d.Tags {
+		name := fieldMap[tag.Id]
+		if name == "" {
+			if !showMissing {
+				continue
+			}
+			name = FieldName(fmt.Sprintf("%v%x", UnknownPrefix, tag.Id))
+		}
+		x.main[name] = tag
+	}
+}
+
+// Get retrieves the EXIF tag for the given field name.
+//
+// If the tag is not known or not present, an error is returned. If the
+// tag name is known, the error will be a TagNotPresentError.
+func (x *Exif) Get(name FieldName) (*tiff.Tag, error) {
+	if tg, ok := x.main[name]; ok {
+		return tg, nil
+	}
+	return nil, TagNotPresentError(name)
+}
+
+// Walker is the interface used to traverse all fields of an Exif object.
+type Walker interface {
+	// Walk is called for each non-nil EXIF field. Returning a non-nil
+	// error aborts the walk/traversal.
+	Walk(name FieldName, tag *tiff.Tag) error
+}
+
+// Walk calls the Walk method of w with the name and tag for every non-nil
+// EXIF field.  If w aborts the walk with an error, that error is returned.
+func (x *Exif) Walk(w Walker) error {
+	for name, tag := range x.main {
+		if err := w.Walk(name, tag); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// DateTime returns the EXIF's "DateTimeOriginal" field, which
+// is the creation time of the photo. If not found, it tries
+// the "DateTime" (which is meant as the modtime) instead.
+// The error will be TagNotPresentErr if none of those tags
+// were found, or a generic error if the tag value was
+// not a string, or the error returned by time.Parse.
+//
+// If the EXIF lacks timezone information or GPS time, the returned
+// time's Location will be time.Local.
+func (x *Exif) DateTime() (time.Time, error) {
+	var dt time.Time
+	tag, err := x.Get(DateTimeOriginal)
+	if err != nil {
+		tag, err = x.Get(DateTime)
+		if err != nil {
+			return dt, err
+		}
+	}
+	if tag.Format() != tiff.StringVal {
+		return dt, errors.New("DateTime[Original] not in string format")
+	}
+	exifTimeLayout := "2006:01:02 15:04:05"
+	dateStr := strings.TrimRight(string(tag.Val), "\x00")
+	// TODO(bradfitz,mpl): look for timezone offset, GPS time, etc.
+	timeZone := time.Local
+	if tz, _ := x.TimeZone(); tz != nil {
+		timeZone = tz
+	}
+	return time.ParseInLocation(exifTimeLayout, dateStr, timeZone)
+}
+
+func (x *Exif) TimeZone() (*time.Location, error) {
+	// TODO: parse more timezone fields (e.g. Nikon WorldTime).
+	timeInfo, err := x.Get("Canon.TimeInfo")
+	if err != nil {
+		return nil, err
+	}
+	if timeInfo.Count < 2 {
+		return nil, errors.New("Canon.TimeInfo does not contain timezone")
+	}
+	offsetMinutes, err := timeInfo.Int(1)
+	if err != nil {
+		return nil, err
+	}
+	return time.FixedZone("", offsetMinutes*60), nil
+}
+
+func ratFloat(num, dem int64) float64 {
+	return float64(num) / float64(dem)
+}
+
+// Tries to parse a Geo degrees value from a string as it was found in some
+// EXIF data.
+// Supported formats so far:
+// - "52,00000,50,00000,34,01180" ==> 52 deg 50'34.0118"
+//   Probably due to locale the comma is used as decimal mark as well as the
+//   separator of three floats (degrees, minutes, seconds)
+//   http://en.wikipedia.org/wiki/Decimal_mark#Hindu.E2.80.93Arabic_numeral_system
+// - "52.0,50.0,34.01180" ==> 52deg50'34.0118"
+// - "52,50,34.01180"     ==> 52deg50'34.0118"
+func parseTagDegreesString(s string) (float64, error) {
+	const unparsableErrorFmt = "Unknown coordinate format: %s"
+	isSplitRune := func(c rune) bool {
+		return c == ',' || c == ';'
+	}
+	parts := strings.FieldsFunc(s, isSplitRune)
+	var degrees, minutes, seconds float64
+	var err error
+	switch len(parts) {
+	case 6:
+		degrees, err = strconv.ParseFloat(parts[0]+"."+parts[1], 64)
+		if err != nil {
+			return 0.0, fmt.Errorf(unparsableErrorFmt, s)
+		}
+		minutes, err = strconv.ParseFloat(parts[2]+"."+parts[3], 64)
+		if err != nil {
+			return 0.0, fmt.Errorf(unparsableErrorFmt, s)
+		}
+		minutes = math.Copysign(minutes, degrees)
+		seconds, err = strconv.ParseFloat(parts[4]+"."+parts[5], 64)
+		if err != nil {
+			return 0.0, fmt.Errorf(unparsableErrorFmt, s)
+		}
+		seconds = math.Copysign(seconds, degrees)
+	case 3:
+		degrees, err = strconv.ParseFloat(parts[0], 64)
+		if err != nil {
+			return 0.0, fmt.Errorf(unparsableErrorFmt, s)
+		}
+		minutes, err = strconv.ParseFloat(parts[1], 64)
+		if err != nil {
+			return 0.0, fmt.Errorf(unparsableErrorFmt, s)
+		}
+		minutes = math.Copysign(minutes, degrees)
+		seconds, err = strconv.ParseFloat(parts[2], 64)
+		if err != nil {
+			return 0.0, fmt.Errorf(unparsableErrorFmt, s)
+		}
+		seconds = math.Copysign(seconds, degrees)
+	default:
+		return 0.0, fmt.Errorf(unparsableErrorFmt, s)
+	}
+	return degrees + minutes/60.0 + seconds/3600.0, nil
+}
+
+func parse3Rat2(tag *tiff.Tag) ([3]float64, error) {
+	v := [3]float64{}
+	for i := range v {
+		num, den, err := tag.Rat2(i)
+		if err != nil {
+			return v, err
+		}
+		v[i] = ratFloat(num, den)
+		if tag.Count < uint32(i+2) {
+			break
+		}
+	}
+	return v, nil
+}
+
+func tagDegrees(tag *tiff.Tag) (float64, error) {
+	switch tag.Format() {
+	case tiff.RatVal:
+		// The usual case, according to the Exif spec
+		// (http://www.kodak.com/global/plugins/acrobat/en/service/digCam/exifStandard2.pdf,
+		// sec 4.6.6, p. 52 et seq.)
+		v, err := parse3Rat2(tag)
+		if err != nil {
+			return 0.0, err
+		}
+		return v[0] + v[1]/60 + v[2]/3600.0, nil
+	case tiff.StringVal:
+		// Encountered this weird case with a panorama picture taken with a HTC phone
+		s, err := tag.StringVal()
+		if err != nil {
+			return 0.0, err
+		}
+		return parseTagDegreesString(s)
+	default:
+		// don't know how to parse value, give up
+		return 0.0, fmt.Errorf("Malformed EXIF Tag Degrees")
+	}
+}
+
+// LatLong returns the latitude and longitude of the photo and
+// whether it was present.
+func (x *Exif) LatLong() (lat, long float64, err error) {
+	// All calls of x.Get might return an TagNotPresentError
+	longTag, err := x.Get(FieldName("GPSLongitude"))
+	if err != nil {
+		return
+	}
+	ewTag, err := x.Get(FieldName("GPSLongitudeRef"))
+	if err != nil {
+		return
+	}
+	latTag, err := x.Get(FieldName("GPSLatitude"))
+	if err != nil {
+		return
+	}
+	nsTag, err := x.Get(FieldName("GPSLatitudeRef"))
+	if err != nil {
+		return
+	}
+	if long, err = tagDegrees(longTag); err != nil {
+		return 0, 0, fmt.Errorf("Cannot parse longitude: %v", err)
+	}
+	if lat, err = tagDegrees(latTag); err != nil {
+		return 0, 0, fmt.Errorf("Cannot parse latitude: %v", err)
+	}
+	ew, err := ewTag.StringVal()
+	if err == nil && ew == "W" {
+		long *= -1.0
+	} else if err != nil {
+		return 0, 0, fmt.Errorf("Cannot parse longitude: %v", err)
+	}
+	ns, err := nsTag.StringVal()
+	if err == nil && ns == "S" {
+		lat *= -1.0
+	} else if err != nil {
+		return 0, 0, fmt.Errorf("Cannot parse longitude: %v", err)
+	}
+	return lat, long, nil
+}
+
+// String returns a pretty text representation of the decoded exif data.
+func (x *Exif) String() string {
+	var buf bytes.Buffer
+	for name, tag := range x.main {
+		fmt.Fprintf(&buf, "%s: %s\n", name, tag)
+	}
+	return buf.String()
+}
+
+// JpegThumbnail returns the jpeg thumbnail if it exists. If it doesn't exist,
+// TagNotPresentError will be returned
+func (x *Exif) JpegThumbnail() ([]byte, error) {
+	offset, err := x.Get(ThumbJPEGInterchangeFormat)
+	if err != nil {
+		return nil, err
+	}
+	start, err := offset.Int(0)
+	if err != nil {
+		return nil, err
+	}
+
+	length, err := x.Get(ThumbJPEGInterchangeFormatLength)
+	if err != nil {
+		return nil, err
+	}
+	l, err := length.Int(0)
+	if err != nil {
+		return nil, err
+	}
+
+	return x.Raw[start : start+l], nil
+}
+
+// MarshalJson implements the encoding/json.Marshaler interface providing output of
+// all EXIF fields present (names and values).
+func (x Exif) MarshalJSON() ([]byte, error) {
+	return json.Marshal(x.main)
+}
+
+type appSec struct {
+	marker byte
+	data   []byte
+}
+
+// newAppSec finds marker in r and returns the corresponding application data
+// section.
+func newAppSec(marker byte, r io.Reader) (*appSec, error) {
+	br := bufio.NewReader(r)
+	app := &appSec{marker: marker}
+	var dataLen int
+
+	// seek to marker
+	for dataLen == 0 {
+		if _, err := br.ReadBytes(0xFF); err != nil {
+			return nil, err
+		}
+		c, err := br.ReadByte()
+		if err != nil {
+			return nil, err
+		} else if c != marker {
+			continue
+		}
+
+		dataLenBytes := make([]byte, 2)
+		for k, _ := range dataLenBytes {
+			c, err := br.ReadByte()
+			if err != nil {
+				return nil, err
+			}
+			dataLenBytes[k] = c
+		}
+		dataLen = int(binary.BigEndian.Uint16(dataLenBytes)) - 2
+	}
+
+	// read section data
+	nread := 0
+	for nread < dataLen {
+		s := make([]byte, dataLen-nread)
+		n, err := br.Read(s)
+		nread += n
+		if err != nil && nread < dataLen {
+			return nil, err
+		}
+		app.data = append(app.data, s[:n]...)
+	}
+	return app, nil
+}
+
+// reader returns a reader on this appSec.
+func (app *appSec) reader() *bytes.Reader {
+	return bytes.NewReader(app.data)
+}
+
+// exifReader returns a reader on this appSec with the read cursor advanced to
+// the start of the exif's tiff encoded portion.
+func (app *appSec) exifReader() (*bytes.Reader, error) {
+	if len(app.data) < 6 {
+		return nil, errors.New("exif: failed to find exif intro marker")
+	}
+
+	// read/check for exif special mark
+	exif := app.data[:6]
+	if !bytes.Equal(exif, append([]byte("Exif"), 0x00, 0x00)) {
+		return nil, errors.New("exif: failed to find exif intro marker")
+	}
+	return bytes.NewReader(app.data[6:]), nil
+}

vendor/github.com/rwcarlsen/goexif/exif/fields.go

@@ -0,0 +1,309 @@
+package exif
+
+type FieldName string
+
+// UnknownPrefix is used as the first part of field names for decoded tags for
+// which there is no known/supported EXIF field.
+const UnknownPrefix = "UnknownTag_"
+
+// Primary EXIF fields
+const (
+	ImageWidth                 FieldName = "ImageWidth"
+	ImageLength                FieldName = "ImageLength" // Image height called Length by EXIF spec
+	BitsPerSample              FieldName = "BitsPerSample"
+	Compression                FieldName = "Compression"
+	PhotometricInterpretation  FieldName = "PhotometricInterpretation"
+	Orientation                FieldName = "Orientation"
+	SamplesPerPixel            FieldName = "SamplesPerPixel"
+	PlanarConfiguration        FieldName = "PlanarConfiguration"
+	YCbCrSubSampling           FieldName = "YCbCrSubSampling"
+	YCbCrPositioning           FieldName = "YCbCrPositioning"
+	XResolution                FieldName = "XResolution"
+	YResolution                FieldName = "YResolution"
+	ResolutionUnit             FieldName = "ResolutionUnit"
+	DateTime                   FieldName = "DateTime"
+	ImageDescription           FieldName = "ImageDescription"
+	Make                       FieldName = "Make"
+	Model                      FieldName = "Model"
+	Software                   FieldName = "Software"
+	Artist                     FieldName = "Artist"
+	Copyright                  FieldName = "Copyright"
+	ExifIFDPointer             FieldName = "ExifIFDPointer"
+	GPSInfoIFDPointer          FieldName = "GPSInfoIFDPointer"
+	InteroperabilityIFDPointer FieldName = "InteroperabilityIFDPointer"
+	ExifVersion                FieldName = "ExifVersion"
+	FlashpixVersion            FieldName = "FlashpixVersion"
+	ColorSpace                 FieldName = "ColorSpace"
+	ComponentsConfiguration    FieldName = "ComponentsConfiguration"
+	CompressedBitsPerPixel     FieldName = "CompressedBitsPerPixel"
+	PixelXDimension            FieldName = "PixelXDimension"
+	PixelYDimension            FieldName = "PixelYDimension"
+	MakerNote                  FieldName = "MakerNote"
+	UserComment                FieldName = "UserComment"
+	RelatedSoundFile           FieldName = "RelatedSoundFile"
+	DateTimeOriginal           FieldName = "DateTimeOriginal"
+	DateTimeDigitized          FieldName = "DateTimeDigitized"
+	SubSecTime                 FieldName = "SubSecTime"
+	SubSecTimeOriginal         FieldName = "SubSecTimeOriginal"
+	SubSecTimeDigitized        FieldName = "SubSecTimeDigitized"
+	ImageUniqueID              FieldName = "ImageUniqueID"
+	ExposureTime               FieldName = "ExposureTime"
+	FNumber                    FieldName = "FNumber"
+	ExposureProgram            FieldName = "ExposureProgram"
+	SpectralSensitivity        FieldName = "SpectralSensitivity"
+	ISOSpeedRatings            FieldName = "ISOSpeedRatings"
+	OECF                       FieldName = "OECF"
+	ShutterSpeedValue          FieldName = "ShutterSpeedValue"
+	ApertureValue              FieldName = "ApertureValue"
+	BrightnessValue            FieldName = "BrightnessValue"
+	ExposureBiasValue          FieldName = "ExposureBiasValue"
+	MaxApertureValue           FieldName = "MaxApertureValue"
+	SubjectDistance            FieldName = "SubjectDistance"
+	MeteringMode               FieldName = "MeteringMode"
+	LightSource                FieldName = "LightSource"
+	Flash                      FieldName = "Flash"
+	FocalLength                FieldName = "FocalLength"
+	SubjectArea                FieldName = "SubjectArea"
+	FlashEnergy                FieldName = "FlashEnergy"
+	SpatialFrequencyResponse   FieldName = "SpatialFrequencyResponse"
+	FocalPlaneXResolution      FieldName = "FocalPlaneXResolution"
+	FocalPlaneYResolution      FieldName = "FocalPlaneYResolution"
+	FocalPlaneResolutionUnit   FieldName = "FocalPlaneResolutionUnit"
+	SubjectLocation            FieldName = "SubjectLocation"
+	ExposureIndex              FieldName = "ExposureIndex"
+	SensingMethod              FieldName = "SensingMethod"
+	FileSource                 FieldName = "FileSource"
+	SceneType                  FieldName = "SceneType"
+	CFAPattern                 FieldName = "CFAPattern"
+	CustomRendered             FieldName = "CustomRendered"
+	ExposureMode               FieldName = "ExposureMode"
+	WhiteBalance               FieldName = "WhiteBalance"
+	DigitalZoomRatio           FieldName = "DigitalZoomRatio"
+	FocalLengthIn35mmFilm      FieldName = "FocalLengthIn35mmFilm"
+	SceneCaptureType           FieldName = "SceneCaptureType"
+	GainControl                FieldName = "GainControl"
+	Contrast                   FieldName = "Contrast"
+	Saturation                 FieldName = "Saturation"
+	Sharpness                  FieldName = "Sharpness"
+	DeviceSettingDescription   FieldName = "DeviceSettingDescription"
+	SubjectDistanceRange       FieldName = "SubjectDistanceRange"
+	LensMake                   FieldName = "LensMake"
+	LensModel                  FieldName = "LensModel"
+)
+
+// Windows-specific tags
+const (
+	XPTitle    FieldName = "XPTitle"
+	XPComment  FieldName = "XPComment"
+	XPAuthor   FieldName = "XPAuthor"
+	XPKeywords FieldName = "XPKeywords"
+	XPSubject  FieldName = "XPSubject"
+)
+
+// thumbnail fields
+const (
+	ThumbJPEGInterchangeFormat       FieldName = "ThumbJPEGInterchangeFormat"       // offset to thumb jpeg SOI
+	ThumbJPEGInterchangeFormatLength FieldName = "ThumbJPEGInterchangeFormatLength" // byte length of thumb
+)
+
+// GPS fields
+const (
+	GPSVersionID        FieldName = "GPSVersionID"
+	GPSLatitudeRef      FieldName = "GPSLatitudeRef"
+	GPSLatitude         FieldName = "GPSLatitude"
+	GPSLongitudeRef     FieldName = "GPSLongitudeRef"
+	GPSLongitude        FieldName = "GPSLongitude"
+	GPSAltitudeRef      FieldName = "GPSAltitudeRef"
+	GPSAltitude         FieldName = "GPSAltitude"
+	GPSTimeStamp        FieldName = "GPSTimeStamp"
+	GPSSatelites        FieldName = "GPSSatelites"
+	GPSStatus           FieldName = "GPSStatus"
+	GPSMeasureMode      FieldName = "GPSMeasureMode"
+	GPSDOP              FieldName = "GPSDOP"
+	GPSSpeedRef         FieldName = "GPSSpeedRef"
+	GPSSpeed            FieldName = "GPSSpeed"
+	GPSTrackRef         FieldName = "GPSTrackRef"
+	GPSTrack            FieldName = "GPSTrack"
+	GPSImgDirectionRef  FieldName = "GPSImgDirectionRef"
+	GPSImgDirection     FieldName = "GPSImgDirection"
+	GPSMapDatum         FieldName = "GPSMapDatum"
+	GPSDestLatitudeRef  FieldName = "GPSDestLatitudeRef"
+	GPSDestLatitude     FieldName = "GPSDestLatitude"
+	GPSDestLongitudeRef FieldName = "GPSDestLongitudeRef"
+	GPSDestLongitude    FieldName = "GPSDestLongitude"
+	GPSDestBearingRef   FieldName = "GPSDestBearingRef"
+	GPSDestBearing      FieldName = "GPSDestBearing"
+	GPSDestDistanceRef  FieldName = "GPSDestDistanceRef"
+	GPSDestDistance     FieldName = "GPSDestDistance"
+	GPSProcessingMethod FieldName = "GPSProcessingMethod"
+	GPSAreaInformation  FieldName = "GPSAreaInformation"
+	GPSDateStamp        FieldName = "GPSDateStamp"
+	GPSDifferential     FieldName = "GPSDifferential"
+)
+
+// interoperability fields
+const (
+	InteroperabilityIndex FieldName = "InteroperabilityIndex"
+)
+
+var exifFields = map[uint16]FieldName{
+	/////////////////////////////////////
+	////////// IFD 0 ////////////////////
+	/////////////////////////////////////
+
+	// image data structure for the thumbnail
+	0x0100: ImageWidth,
+	0x0101: ImageLength,
+	0x0102: BitsPerSample,
+	0x0103: Compression,
+	0x0106: PhotometricInterpretation,
+	0x0112: Orientation,
+	0x0115: SamplesPerPixel,
+	0x011C: PlanarConfiguration,
+	0x0212: YCbCrSubSampling,
+	0x0213: YCbCrPositioning,
+	0x011A: XResolution,
+	0x011B: YResolution,
+	0x0128: ResolutionUnit,
+
+	// Other tags
+	0x0132: DateTime,
+	0x010E: ImageDescription,
+	0x010F: Make,
+	0x0110: Model,
+	0x0131: Software,
+	0x013B: Artist,
+	0x8298: Copyright,
+
+	// Windows-specific tags
+	0x9c9b: XPTitle,
+	0x9c9c: XPComment,
+	0x9c9d: XPAuthor,
+	0x9c9e: XPKeywords,
+	0x9c9f: XPSubject,
+
+	// private tags
+	exifPointer: ExifIFDPointer,
+
+	/////////////////////////////////////
+	////////// Exif sub IFD /////////////
+	/////////////////////////////////////
+
+	gpsPointer:     GPSInfoIFDPointer,
+	interopPointer: InteroperabilityIFDPointer,
+
+	0x9000: ExifVersion,
+	0xA000: FlashpixVersion,
+
+	0xA001: ColorSpace,
+
+	0x9101: ComponentsConfiguration,
+	0x9102: CompressedBitsPerPixel,
+	0xA002: PixelXDimension,
+	0xA003: PixelYDimension,
+
+	0x927C: MakerNote,
+	0x9286: UserComment,
+
+	0xA004: RelatedSoundFile,
+	0x9003: DateTimeOriginal,
+	0x9004: DateTimeDigitized,
+	0x9290: SubSecTime,
+	0x9291: SubSecTimeOriginal,
+	0x9292: SubSecTimeDigitized,
+
+	0xA420: ImageUniqueID,
+
+	// picture conditions
+	0x829A: ExposureTime,
+	0x829D: FNumber,
+	0x8822: ExposureProgram,
+	0x8824: SpectralSensitivity,
+	0x8827: ISOSpeedRatings,
+	0x8828: OECF,
+	0x9201: ShutterSpeedValue,
+	0x9202: ApertureValue,
+	0x9203: BrightnessValue,
+	0x9204: ExposureBiasValue,
+	0x9205: MaxApertureValue,
+	0x9206: SubjectDistance,
+	0x9207: MeteringMode,
+	0x9208: LightSource,
+	0x9209: Flash,
+	0x920A: FocalLength,
+	0x9214: SubjectArea,
+	0xA20B: FlashEnergy,
+	0xA20C: SpatialFrequencyResponse,
+	0xA20E: FocalPlaneXResolution,
+	0xA20F: FocalPlaneYResolution,
+	0xA210: FocalPlaneResolutionUnit,
+	0xA214: SubjectLocation,
+	0xA215: ExposureIndex,
+	0xA217: SensingMethod,
+	0xA300: FileSource,
+	0xA301: SceneType,
+	0xA302: CFAPattern,
+	0xA401: CustomRendered,
+	0xA402: ExposureMode,
+	0xA403: WhiteBalance,
+	0xA404: DigitalZoomRatio,
+	0xA405: FocalLengthIn35mmFilm,
+	0xA406: SceneCaptureType,
+	0xA407: GainControl,
+	0xA408: Contrast,
+	0xA409: Saturation,
+	0xA40A: Sharpness,
+	0xA40B: DeviceSettingDescription,
+	0xA40C: SubjectDistanceRange,
+	0xA433: LensMake,
+	0xA434: LensModel,
+}
+
+var gpsFields = map[uint16]FieldName{
+	/////////////////////////////////////
+	//// GPS sub-IFD ////////////////////
+	/////////////////////////////////////
+	0x0:  GPSVersionID,
+	0x1:  GPSLatitudeRef,
+	0x2:  GPSLatitude,
+	0x3:  GPSLongitudeRef,
+	0x4:  GPSLongitude,
+	0x5:  GPSAltitudeRef,
+	0x6:  GPSAltitude,
+	0x7:  GPSTimeStamp,
+	0x8:  GPSSatelites,
+	0x9:  GPSStatus,
+	0xA:  GPSMeasureMode,
+	0xB:  GPSDOP,
+	0xC:  GPSSpeedRef,
+	0xD:  GPSSpeed,
+	0xE:  GPSTrackRef,
+	0xF:  GPSTrack,
+	0x10: GPSImgDirectionRef,
+	0x11: GPSImgDirection,
+	0x12: GPSMapDatum,
+	0x13: GPSDestLatitudeRef,
+	0x14: GPSDestLatitude,
+	0x15: GPSDestLongitudeRef,
+	0x16: GPSDestLongitude,
+	0x17: GPSDestBearingRef,
+	0x18: GPSDestBearing,
+	0x19: GPSDestDistanceRef,
+	0x1A: GPSDestDistance,
+	0x1B: GPSProcessingMethod,
+	0x1C: GPSAreaInformation,
+	0x1D: GPSDateStamp,
+	0x1E: GPSDifferential,
+}
+
+var interopFields = map[uint16]FieldName{
+	/////////////////////////////////////
+	//// Interoperability sub-IFD ///////
+	/////////////////////////////////////
+	0x1: InteroperabilityIndex,
+}
+
+var thumbnailFields = map[uint16]FieldName{
+	0x0201: ThumbJPEGInterchangeFormat,
+	0x0202: ThumbJPEGInterchangeFormatLength,
+}