forked from tajtiattila/metadata
/
exif.go
203 lines (172 loc) · 4 KB
/
exif.go
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// Package exif implements an JPEG/Exif decoder and encoder.
package exif
import (
"encoding/binary"
"errors"
"fmt"
"io"
xjpeg "github.com/robertkaelin/metadata/jpeg"
)
var (
NotFound = errors.New("exif: exif data not found")
ErrDecode = errors.New("exif: jpeg decode error")
ErrEncode = errors.New("exif: jpeg encode error")
)
// Exif represents Exif format metadata in JPEG/Exif files.
type Exif struct {
// ByteOrder is the byte order used for decoding and encoding
binary.ByteOrder
// Main image TIFF metadata
IFD0 []Entry
// Main image sub-IFDs
Exif, GPS, Interop []Entry
// thumbnail
IFD1 []Entry // Metadata
Thumb []byte // Raw image data, typically JPEG
}
// FormatError holds warnings encountered by Decode or DecodeBytes if
// (part of) the Exif succesfully decoded
// but corrupt or invalid data were encountered.
//
// Clients only interested only in reading the Exif
// may safely ignore a FormatError.
type FormatError []string
func (e FormatError) Error() string {
var extra string
if len(e) > 1 {
extra = "..."
}
return "exif: " + e[0] + extra
}
func (e *FormatError) warnf(format string, arg ...interface{}) {
*e = append(*e, fmt.Sprintf(format, arg...))
}
// IsFormat returns a boolean indicating whether the error is
// a format error in Exif.
func IsFormat(err error) bool {
_, is := err.(FormatError)
return is
}
// Decode decodes Exif data from r.
func Decode(r io.Reader) (*Exif, error) {
raw, err := exifFromReader(r)
if err != nil {
return nil, err
}
return DecodeBytes(raw)
}
var (
jfifChunkHeader = []byte("\xff\xe0--JFIF\x00")
jfxxChunkHeader = []byte("\xff\xe0--JFXX\x00")
exifChunkHeader = []byte("\xff\xe1--Exif\x00\x00")
)
// Copy copies the data from r to w, replacing the
// Exif metadata in r with x. If x is nil, no
// Exif metadata is written to w. The original Exif
// metadata in r is always discarded.
// Other content such as raw image data is written
// to w unmodified.
func Copy(w io.Writer, r io.Reader, x *Exif) error {
j, err := xjpeg.NewScanner(r)
if err != nil {
return err
}
var exifdata []byte
if x != nil {
var err error
exifdata, err = x.encodeBytes([]byte("Exif\x00\x00"))
if err != nil {
return err
}
}
var segments [][]byte
var jfifChunk, jfxxChunk []byte
var hasExif bool
has := 0
for has < 3 && j.Next() {
seg, err := j.ReadSegment()
if err != nil {
return err
}
switch {
case jfifChunk == nil && cmpChunkHeader(seg, jfifChunkHeader):
jfifChunkHeader = seg
has++
case jfxxChunk == nil && cmpChunkHeader(seg, jfxxChunkHeader):
jfxxChunkHeader = seg
has++
case !hasExif && cmpChunkHeader(seg, exifChunkHeader):
hasExif = true
has++
default:
// unrecognised or duplicate segment
segments = append(segments, seg)
}
}
if err := j.Err(); err != nil {
return err
}
// write segments in standard jpeg/jfif header order
ww := errw{w: w}
ww.write(segments[0])
ww.write(jfifChunk)
ww.write(jfxxChunk)
if exifdata != nil {
err := xjpeg.WriteChunk(w, 0xe1, exifdata)
if err != nil {
return err
}
}
// write other segments in jpeg (DCT, COM, APP1/XMP...)
for _, seg := range segments[1:] {
ww.write(seg)
}
if ww.err != nil {
return ww.err
}
// copy bytes unread so far, such as actual image data
_, err = io.Copy(w, j.Reader())
return err
}
type errw struct {
w io.Writer
err error
}
func (w *errw) write(p []byte) {
_, w.err = w.w.Write(p)
}
// gets raw exif as []byte
func exifFromReader(r io.Reader) ([]byte, error) {
j, err := xjpeg.NewScanner(r)
if err != nil {
return nil, err
}
prefix := exifChunkHeader[4:]
for j.NextChunk() {
if !j.IsChunk(0xe1, prefix) {
continue
}
_, p, err := j.ReadChunk()
if err != nil {
return nil, err
}
// trim exif header
return p[len(prefix):], nil
}
err = j.Err()
if err != nil {
return nil, err
}
return nil, NotFound
}
func cmpChunkHeader(p, h []byte) bool {
if len(p) < len(h) {
return false
}
for i := range h {
if !(i == 2 || i == 3 || p[i] == h[i]) {
return false
}
}
return true
}