[bugfix] Don't remove jpeg orientation metadata (#663)

vendor/github.com/superseriousbusiness/exif-terminator/README.md

@@ -53,10 +53,14 @@ Exif removal is a pain in the arse. Most other libraries seem to parse the whole
 
 `exif-terminator` differs in that it removes exif data *while scanning through the image bytes*, and it doesn't do any reencoding of the image. Bytes of exif data are simply all set to 0, and the image data is piped back out again into the returned reader.
 
+The only exception is orientation data: if an image contains orientation data, this and only this data will be preserved since it's *actually useful*.
+
 ## Example
 
+You can run the following example with `go run ./example/main.go`:
+
 ```go
-package test
+package main
 
 import (
   "io"
@@ -71,6 +75,7 @@ func main() {
   if err != nil {
     panic(err)
   }
+  defer sloth.Close()
 
   // get the length of the file
   stat, err := sloth.Stat()
@@ -103,6 +108,7 @@ func main() {
 
 `exif-terminator` borrows heavily from the two [`dsoprea`](https://github.com/dsoprea) libraries credited below. In fact, it's basically a hack on top of those libraries. Thanks `dsoprea`!
 
+- [dsoprea/go-exif](https://github.com/dsoprea/go-exif): exif header reconstruction. [MIT License](https://spdx.org/licenses/MIT.html).
 - [dsoprea/go-jpeg-image-structure](https://github.com/dsoprea/go-jpeg-image-structure): jpeg structure parsing. [MIT License](https://spdx.org/licenses/MIT.html).
 - [dsoprea/go-png-image-structure](https://github.com/dsoprea/go-png-image-structure): png structure parsing. [MIT License](https://spdx.org/licenses/MIT.html).
 - [stretchr/testify](https://github.com/stretchr/testify); test framework. [MIT License](https://spdx.org/licenses/MIT.html).

vendor/github.com/superseriousbusiness/exif-terminator/jpeg.go

@@ -19,10 +19,12 @@
 package terminator
 
 import (
+	"bytes"
 	"encoding/binary"
 	"fmt"
 	"io"
 
+	exif "github.com/dsoprea/go-exif/v3"
 	jpegstructure "github.com/superseriousbusiness/go-jpeg-image-structure/v2"
 )
 
@@ -121,18 +123,129 @@ func (v *jpegVisitor) writeSegment(s *jpegstructure.Segment) error {
 		}
 	}
 
-	if s.IsExif() {
-		// if this segment is exif data, write blank bytes
-		blank := make([]byte, len(s.Data))
-		if _, err := w.Write(blank); err != nil {
+	if !s.IsExif() {
+		// if this isn't exif data just copy it over and bail
+		_, err := w.Write(s.Data)
+		return err
+	}
+
+	ifd, _, err := s.Exif()
+	if err != nil {
+		return err
+	}
+
+	// amount of bytes we've written into the exif body
+	var written int
+
+	if orientationEntries, err := ifd.FindTagWithName("Orientation"); err == nil && len(orientationEntries) == 1 {
+		// If we have an orientation entry, we don't want to completely obliterate the exif data.
+		// Instead, we want to surgically obliterate everything *except* the orientation tag, so
+		// that the image will still be rotated correctly when shown in client applications etc.
+		//
+		// To accomplish this, we're going to extract just the bytes that we need and write them
+		// in according to the exif specification, then fill in the rest of the space with empty
+		// bytes.
+		//
+		// First we need to write the exif prefix for this segment.
+		//
+		// Then we write the exif header which contains the byte order and offset of the first ifd.
+		//
+		// Then we write the ifd0 entry which contains the orientation data.
+		//
+		// After that we just fill fill fill.
+
+		newData := &bytes.Buffer{}
+
+		// 1. Write exif prefix.
+		// https://www.ozhiker.com/electronics/pjmt/jpeg_info/app_segments.html
+		prefix := []byte{'E', 'x', 'i', 'f', 0, 0}
+		if err := binary.Write(newData, ifd.ByteOrder(), &prefix); err != nil {
 			return err
 		}
-	} else {
-		// otherwise write the data
-		if _, err := w.Write(s.Data); err != nil {
+		written += 6
+
+		// 2. Write exif header, taking the existing byte order.
+		exifHeader, err := exif.BuildExifHeader(ifd.ByteOrder(), exif.ExifDefaultFirstIfdOffset)
+		if err != nil {
+			return err
+		}
+		hWritten, err := newData.Write(exifHeader)
+		if err != nil {
+			return err
+		}
+		written += hWritten
+
+		// https://web.archive.org/web/20190624045241if_/http://www.cipa.jp:80/std/documents/e/DC-008-Translation-2019-E.pdf
+		//
+		// An ifd with one orientation entry is structured like this:
+		// 		2 bytes: the number of entries in the ifd	uint16(1)
+		// 		2 bytes: the tag id							uint16(274)
+		// 		2 bytes: the tag type						uint16(3)
+		//      4 bytes: the tag count						uint32(1)
+		// 		4 bytes: the tag value offset:				uint32(one of the below with padding on the end)
+		// 			1 = Horizontal (normal)
+		// 			2 = Mirror horizontal
+		// 			3 = Rotate 180
+		// 			4 = Mirror vertical
+		// 			5 = Mirror horizontal and rotate 270 CW
+		// 			6 = Rotate 90 CW
+		// 			7 = Mirror horizontal and rotate 90 CW
+		// 			8 = Rotate 270 CW
+		orientationEntry := orientationEntries[0]
+
+		ifdCount := uint16(1) // we're only adding one entry into the ifd
+		if err := binary.Write(newData, ifd.ByteOrder(), &ifdCount); err != nil {
+			return err
+		}
+		written += 2
+
+		tagID := orientationEntry.TagId()
+		if err := binary.Write(newData, ifd.ByteOrder(), &tagID); err != nil {
+			return err
+		}
+		written += 2
+
+		tagType := orientationEntry.TagType()
+		if err := binary.Write(newData, ifd.ByteOrder(), &tagType); err != nil {
+			return err
+		}
+		written += 2
+
+		tagCount := orientationEntry.UnitCount()
+		if err := binary.Write(newData, ifd.ByteOrder(), &tagCount); err != nil {
+			return err
+		}
+		written += 4
+
+		valueOffset, err := orientationEntry.GetRawBytes()
+		if err != nil {
+			return err
+		}
+
+		vWritten, err := newData.Write(valueOffset)
+		if err != nil {
+			return err
+		}
+		written += vWritten
+
+		valuePad := make([]byte, 4-vWritten)
+		pWritten, err := newData.Write(valuePad)
+		if err != nil {
+			return err
+		}
+		written += pWritten
+
+		// write everything in
+		if _, err := io.Copy(w, newData); err != nil {
 			return err
 		}
 	}
 
+	// fill in the (remaining) exif body with blank bytes
+	blank := make([]byte, len(s.Data)-written)
+	if _, err := w.Write(blank); err != nil {
+		return err
+	}
+
 	return nil
 }

vendor/github.com/superseriousbusiness/exif-terminator/terminator.go

@@ -25,8 +25,8 @@ import (
 	"fmt"
 	"io"
 
-	jpegstructure "github.com/superseriousbusiness/go-jpeg-image-structure/v2"
 	pngstructure "github.com/dsoprea/go-png-image-structure/v2"
+	jpegstructure "github.com/superseriousbusiness/go-jpeg-image-structure/v2"
 )
 
 func Terminate(in io.Reader, fileSize int, mediaType string) (io.Reader, error) {