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

252 lines
6.5 KiB
Go

/*
exif-terminator
Copyright (C) 2022 SuperSeriousBusiness admin@gotosocial.org
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package terminator
import (
"bytes"
"encoding/binary"
"fmt"
"io"
exif "github.com/dsoprea/go-exif/v3"
jpegstructure "github.com/superseriousbusiness/go-jpeg-image-structure/v2"
)
var markerLen = map[byte]int{
0x00: 0,
0x01: 0,
0xd0: 0,
0xd1: 0,
0xd2: 0,
0xd3: 0,
0xd4: 0,
0xd5: 0,
0xd6: 0,
0xd7: 0,
0xd8: 0,
0xd9: 0,
0xda: 0,
// J2C
0x30: 0,
0x31: 0,
0x32: 0,
0x33: 0,
0x34: 0,
0x35: 0,
0x36: 0,
0x37: 0,
0x38: 0,
0x39: 0,
0x3a: 0,
0x3b: 0,
0x3c: 0,
0x3d: 0,
0x3e: 0,
0x3f: 0,
0x4f: 0,
0x92: 0,
0x93: 0,
// J2C extensions
0x74: 4,
0x75: 4,
0x77: 4,
}
type jpegVisitor struct {
js *jpegstructure.JpegSplitter
writer io.Writer
}
// HandleSegment satisfies the visitor interface{} of the jpegstructure library.
//
// We don't really care about any of the parameters, since all we're interested
// in here is the very last segment that was scanned.
func (v *jpegVisitor) HandleSegment(_ byte, _ string, _ int, _ bool) error {
// all we want to do here is get the last segment that was scanned, and then manipulate it
segmentList := v.js.Segments()
segments := segmentList.Segments()
lastSegment := segments[len(segments)-1]
return v.writeSegment(lastSegment)
}
func (v *jpegVisitor) writeSegment(s *jpegstructure.Segment) error {
w := v.writer
defer func() {
// whatever happens, when we finished then evict data from the segment;
// once we've written it we don't want it in memory anymore
s.Data = s.Data[:0]
}()
// The scan-data will have a marker-ID of (0) because it doesn't have a marker-ID or length.
if s.MarkerId != 0 {
if _, err := w.Write([]byte{0xff, s.MarkerId}); err != nil {
return err
}
sizeLen, found := markerLen[s.MarkerId]
if !found || sizeLen == 2 {
sizeLen = 2
l := uint16(len(s.Data) + sizeLen)
if err := binary.Write(w, binary.BigEndian, &l); err != nil {
return err
}
} else if sizeLen == 4 {
l := uint32(len(s.Data) + sizeLen)
if err := binary.Write(w, binary.BigEndian, &l); err != nil {
return err
}
} else if sizeLen != 0 {
return fmt.Errorf("not a supported marker-size: MARKER-ID=(0x%02x) MARKER-SIZE-LEN=(%d)", s.MarkerId, sizeLen)
}
}
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
}
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
}