mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-12-05 10:02:47 +00:00
296 lines
7.9 KiB
Go
296 lines
7.9 KiB
Go
/*
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exif-terminator
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Copyright (C) 2022 SuperSeriousBusiness admin@gotosocial.org
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package terminator
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"io"
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exif "github.com/dsoprea/go-exif/v3"
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jpegstructure "github.com/superseriousbusiness/go-jpeg-image-structure/v2"
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)
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var markerLen = map[byte]int{
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0x00: 0,
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0x01: 0,
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0xd0: 0,
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0xd1: 0,
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0xd2: 0,
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0xd3: 0,
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0xd4: 0,
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0xd5: 0,
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0xd6: 0,
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0xd7: 0,
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0xd8: 0,
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0xd9: 0,
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0xda: 0,
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// J2C
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0x30: 0,
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0x31: 0,
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0x32: 0,
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0x33: 0,
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0x34: 0,
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0x35: 0,
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0x36: 0,
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0x37: 0,
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0x38: 0,
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0x39: 0,
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0x3a: 0,
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0x3b: 0,
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0x3c: 0,
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0x3d: 0,
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0x3e: 0,
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0x3f: 0,
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0x4f: 0,
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0x92: 0,
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0x93: 0,
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// J2C extensions
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0x74: 4,
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0x75: 4,
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0x77: 4,
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}
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type jpegVisitor struct {
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js *jpegstructure.JpegSplitter
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writer io.Writer
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expectedFileSize int
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writtenTotalBytes int
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}
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// HandleSegment satisfies the visitor interface{} of the jpegstructure library.
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//
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// We don't really care about many of the parameters, since all we're interested
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// in here is the very last segment that was scanned.
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func (v *jpegVisitor) HandleSegment(segmentMarker byte, _ string, _ int, _ bool) error {
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// get the most recent segment scanned (ie., last in the segments list)
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segmentList := v.js.Segments()
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segments := segmentList.Segments()
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mostRecentSegment := segments[len(segments)-1]
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// check if we've written the expected number of bytes by EOI
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if segmentMarker == jpegstructure.MARKER_EOI {
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// take account of the last 2 bytes taken up by the EOI
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eoiLength := 2
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// this is the total file size we will
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// have written including the EOI
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willHaveWritten := v.writtenTotalBytes + eoiLength
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if willHaveWritten < v.expectedFileSize {
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// if we won't have written enough,
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// pad the final segment before EOI
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// so that we meet expected file size
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missingBytes := make([]byte, v.expectedFileSize-willHaveWritten)
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if _, err := v.writer.Write(missingBytes); err != nil {
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return err
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}
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}
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}
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// process the segment
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return v.writeSegment(mostRecentSegment)
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}
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func (v *jpegVisitor) writeSegment(s *jpegstructure.Segment) error {
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var writtenSegmentData int
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w := v.writer
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defer func() {
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// whatever happens, when we finished then evict data from the segment;
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// once we've written it we don't want it in memory anymore
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s.Data = s.Data[:0]
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}()
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// The scan-data will have a marker-ID of (0) because it doesn't have a marker-ID or length.
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if s.MarkerId != 0 {
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markerIDWritten, err := w.Write([]byte{0xff, s.MarkerId})
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if err != nil {
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return err
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}
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writtenSegmentData += markerIDWritten
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sizeLen, found := markerLen[s.MarkerId]
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if !found || sizeLen == 2 {
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sizeLen = 2
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l := uint16(len(s.Data) + sizeLen)
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if err := binary.Write(w, binary.BigEndian, &l); err != nil {
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return err
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}
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writtenSegmentData += 2
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} else if sizeLen == 4 {
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l := uint32(len(s.Data) + sizeLen)
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if err := binary.Write(w, binary.BigEndian, &l); err != nil {
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return err
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}
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writtenSegmentData += 4
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} else if sizeLen != 0 {
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return fmt.Errorf("not a supported marker-size: MARKER-ID=(0x%02x) MARKER-SIZE-LEN=(%d)", s.MarkerId, sizeLen)
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}
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}
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if !s.IsExif() {
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// if this isn't exif data just copy it over and bail
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writtenNormalData, err := w.Write(s.Data)
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if err != nil {
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return err
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}
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writtenSegmentData += writtenNormalData
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v.writtenTotalBytes += writtenSegmentData
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return nil
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}
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ifd, _, err := s.Exif()
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if err != nil {
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return err
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}
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// amount of bytes we've writtenExifData into the exif body, we'll update this as we go
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var writtenExifData int
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if orientationEntries, err := ifd.FindTagWithName("Orientation"); err == nil && len(orientationEntries) == 1 {
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// If we have an orientation entry, we don't want to completely obliterate the exif data.
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// Instead, we want to surgically obliterate everything *except* the orientation tag, so
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// that the image will still be rotated correctly when shown in client applications etc.
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//
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// To accomplish this, we're going to extract just the bytes that we need and write them
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// in according to the exif specification, then fill in the rest of the space with empty
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// bytes.
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//
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// First we need to write the exif prefix for this segment.
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//
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// Then we write the exif header which contains the byte order and offset of the first ifd.
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//
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// Then we write the ifd0 entry which contains the orientation data.
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//
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// After that we just fill.
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newExifData := &bytes.Buffer{}
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byteOrder := ifd.ByteOrder()
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// 1. Write exif prefix.
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// https://www.ozhiker.com/electronics/pjmt/jpeg_info/app_segments.html
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prefix := []byte{'E', 'x', 'i', 'f', 0, 0}
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if err := binary.Write(newExifData, byteOrder, &prefix); err != nil {
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return err
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}
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writtenExifData += len(prefix)
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// 2. Write exif header, taking the existing byte order.
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exifHeader, err := exif.BuildExifHeader(byteOrder, exif.ExifDefaultFirstIfdOffset)
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if err != nil {
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return err
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}
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hWritten, err := newExifData.Write(exifHeader)
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if err != nil {
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return err
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}
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writtenExifData += hWritten
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// 3. Write in the new ifd
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//
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// An ifd with one orientation entry is structured like this:
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// 2 bytes: the number of entries in the ifd uint16(1)
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// 2 bytes: the tag id uint16(274)
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// 2 bytes: the tag type uint16(3)
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// 4 bytes: the tag count uint32(1)
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// 4 bytes: the tag value offset: uint32(one of the below with padding on the end)
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// 1 = Horizontal (normal)
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// 2 = Mirror horizontal
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// 3 = Rotate 180
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// 4 = Mirror vertical
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// 5 = Mirror horizontal and rotate 270 CW
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// 6 = Rotate 90 CW
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// 7 = Mirror horizontal and rotate 90 CW
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// 8 = Rotate 270 CW
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//
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// see https://web.archive.org/web/20190624045241if_/http://www.cipa.jp:80/std/documents/e/DC-008-Translation-2019-E.pdf - p24-25
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orientationEntry := orientationEntries[0]
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ifdCount := uint16(1) // we're only adding one entry into the ifd
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if err := binary.Write(newExifData, byteOrder, &ifdCount); err != nil {
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return err
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}
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writtenExifData += 2
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tagID := orientationEntry.TagId()
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if err := binary.Write(newExifData, byteOrder, &tagID); err != nil {
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return err
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}
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writtenExifData += 2
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tagType := uint16(orientationEntry.TagType())
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if err := binary.Write(newExifData, byteOrder, &tagType); err != nil {
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return err
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}
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writtenExifData += 2
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tagCount := orientationEntry.UnitCount()
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if err := binary.Write(newExifData, byteOrder, &tagCount); err != nil {
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return err
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}
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writtenExifData += 4
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valueOffset, err := orientationEntry.GetRawBytes()
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if err != nil {
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return err
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}
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vWritten, err := newExifData.Write(valueOffset)
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if err != nil {
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return err
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}
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writtenExifData += vWritten
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valuePad := make([]byte, 4-vWritten)
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pWritten, err := newExifData.Write(valuePad)
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if err != nil {
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return err
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}
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writtenExifData += pWritten
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// write all the new data into the writer from the segment
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writtenNewExifData, err := io.Copy(w, newExifData)
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if err != nil {
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return err
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}
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writtenSegmentData += int(writtenNewExifData)
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}
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// fill in any remaining exif body with blank bytes
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blank := make([]byte, len(s.Data)-writtenExifData)
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writtenPadding, err := w.Write(blank)
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if err != nil {
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return err
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}
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writtenSegmentData += writtenPadding
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v.writtenTotalBytes += writtenSegmentData
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return nil
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}
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