Optionally preserve exif data

exifcopy.go

@@ -0,0 +1,171 @@
+// https://stackoverflow.com/a/76779756
+package main
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"os"
+)
+
+const (
+	soi       = 0xD8
+	eoi       = 0xD9
+	sos       = 0xDA
+	exif      = 0xE1
+	copyright = 0xEE
+	comment   = 0xFE
+)
+
+func isMetaTagType(tagType byte) bool {
+	// Adapt as needed
+	return tagType == exif || tagType == copyright || tagType == comment
+}
+
+func copySegments(dst *bufio.Writer, src *bufio.Reader, filterSegment func(tagType byte) bool) error {
+	var buf [2]byte
+	_, err := io.ReadFull(src, buf[:])
+	if err != nil {
+		return err
+	}
+	if buf != [2]byte{0xFF, soi} {
+		return errors.New("expected SOI")
+	}
+	for {
+		_, err := io.ReadFull(src, buf[:])
+		if err != nil {
+			return err
+		}
+		if buf[0] != 0xFF {
+			return errors.New("invalid tag type")
+		}
+		if buf[1] == eoi {
+			// Hacky way to check for EOF
+			_, err := src.Read(buf[:1])
+			if err != nil && err != io.EOF {
+				return err
+			}
+			// don't return an error as some cameras add the exif data at the end.
+			// if n > 0 {
+			// 	return errors.New("EOF expected after EOI")
+			// }
+			return nil
+		}
+		sos := buf[1] == 0xDA
+		filter := filterSegment(buf[1])
+		if filter {
+			_, err = dst.Write(buf[:])
+			if err != nil {
+				return err
+			}
+		}
+
+		_, err = io.ReadFull(src, buf[:])
+		if err != nil {
+			return err
+		}
+		if filter {
+			_, err = dst.Write(buf[:])
+			if err != nil {
+				return err
+			}
+		}
+
+		// Note: Includes the length, but not the tag, so subtract 2
+		tagLength := ((uint16(buf[0]) << 8) | uint16(buf[1])) - 2
+		if filter {
+			_, err = io.CopyN(dst, src, int64(tagLength))
+		} else {
+			_, err = src.Discard(int(tagLength))
+		}
+		if err != nil {
+			return err
+		}
+		if sos {
+			// Find next tag `FF xx` in the stream where `xx != 0` to skip ECS
+			// See https://stackoverflow.com/questions/2467137/parsing-jpeg-file-format-format-of-entropy-coded-segments-ecs
+			for {
+				bytes, err := src.Peek(2)
+				if err != nil {
+					return err
+				}
+				if bytes[0] == 0xFF {
+					data, rstMrk := bytes[1] == 0, bytes[1] >= 0xD0 && bytes[1] <= 0xD7
+					if !data && !rstMrk {
+						break
+					}
+				}
+				if filter {
+					err = dst.WriteByte(bytes[0])
+					if err != nil {
+						return err
+					}
+				}
+				_, err = src.Discard(1)
+				if err != nil {
+					return err
+				}
+			}
+		}
+	}
+}
+
+func copyMetadata(outImagePath, imagePath, metadataImagePath string) error {
+	outFile, err := os.Create(outImagePath)
+	if err != nil {
+		return err
+	}
+	defer outFile.Close()
+	writer := bufio.NewWriter(outFile)
+
+	imageFile, err := os.Open(imagePath)
+	if err != nil {
+		return err
+	}
+	defer imageFile.Close()
+	imageReader := bufio.NewReader(imageFile)
+
+	metaFile, err := os.Open(metadataImagePath)
+	if err != nil {
+		return err
+	}
+	defer metaFile.Close()
+	metaReader := bufio.NewReader(metaFile)
+
+	_, err = writer.Write([]byte{0xFF, soi})
+	if err != nil {
+		return err
+	}
+
+	// Copy metadata segments
+	// It seems that they need to come first!
+	err = copySegments(writer, metaReader, isMetaTagType)
+	if err != nil {
+		return err
+	}
+	// Copy all non-metadata segments
+	err = copySegments(writer, imageReader, func(tagType byte) bool {
+		return !isMetaTagType(tagType)
+	})
+	if err != nil {
+		return err
+	}
+
+	_, err = writer.Write([]byte{0xFF, eoi})
+	if err != nil {
+		return err
+	}
+
+	// Flush the writer, otherwise the last couple buffered writes (including the EOI) won't get written!
+	return writer.Flush()
+}
+
+func exifCopy(fromPath, toPath string) error {
+	copyPath := toPath + "~"
+	err := os.Rename(toPath, copyPath)
+	if err != nil {
+		return err
+	}
+	defer os.Remove(copyPath)
+	return copyMetadata(toPath, copyPath, fromPath)
+}

goptimize.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"image"
 	"image/gif"
 	"image/jpeg"
 	"image/png"
@@ -30,12 +31,21 @@ func Goptimize(file string) {
 		return
 	}
 
-	// open original, rotate if necessary
+	var src image.Image
-	src, err := imaging.Open(file, imaging.AutoOrientation(true))
 
-	if err != nil {
+	if !copyExif {
-		fmt.Printf("Error: %v (%s)\n", err, file)
+		// rotate if necessary
-		return
+		src, err = imaging.Open(file, imaging.AutoOrientation(true))
+		if err != nil {
+			fmt.Printf("Error: %v (%s)\n", err, file)
+			return
+		}
+	} else {
+		src, err = imaging.Open(file)
+		if err != nil {
+			fmt.Printf("Error: %v (%s)\n", err, file)
+			return
+		}
 	}
 
 	format, err := imaging.FormatFromFilename(file)
@@ -127,6 +137,13 @@ func Goptimize(file string) {
 		} else if jpegoptim != "" {
 			RunOptimizer(tmpFilename, false, jpegoptim, "-f", "-s", "-o")
 		}
+
+		if copyExif {
+			if err := exifCopy(file, tmpFilename); err != nil {
+				fmt.Printf("Error copying exif data: %v (%s)\n", err, file)
+				return
+			}
+		}
 	} else if format.String() == "PNG" {
 		if pngquant != "" {
 			RunOptimizer(tmpFilename, true, pngquant, "-f", "--output")

main.go

@@ -24,6 +24,7 @@ var (
 	optipng          string
 	pngquant         string
 	gifsicle         string
+	copyExif         bool
 	threads          = 1
 	version          = "dev"
 )
@@ -60,6 +61,7 @@ func main() {
 	flag.StringVarP(&maxSizes, "max", "m", "", "downscale to a maximum width & height in pixels (<width>x<height>)")
 	flag.StringVarP(&outputDir, "out", "o", "", "output directory (default overwrites original)")
 	flag.BoolVarP(&preserveModTimes, "preserve", "p", true, "preserve file modification times")
+	flag.BoolVarP(&copyExif, "exif", "e", false, "copy exif data")
 	flag.BoolVarP(&update, "update", "u", false, "update to latest release")
 	flag.BoolVarP(&multiThreaded, "threaded", "t", false, "run multi-threaded (use all CPU cores)")
 	flag.BoolVarP(&showversion, "version", "v", false, "show version number")