gtsocial-umbx

jpeg.go (8063B)

---

 /*
    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
 	expectedFileSize  int
 	writtenTotalBytes int
 }
 
 // HandleSegment satisfies the visitor interface{} of the jpegstructure library.
 //
 // We don't really care about many of the parameters, since all we're interested
 // in here is the very last segment that was scanned.
 func (v *jpegVisitor) HandleSegment(segmentMarker byte, _ string, _ int, _ bool) error {
 	// get the most recent segment scanned (ie., last in the segments list)
 	segmentList := v.js.Segments()
 	segments := segmentList.Segments()
 	mostRecentSegment := segments[len(segments)-1]
 
 	// check if we've written the expected number of bytes by EOI
 	if segmentMarker == jpegstructure.MARKER_EOI {
 		// take account of the last 2 bytes taken up by the EOI
 		eoiLength := 2
 
 		// this is the total file size we will
 		// have written including the EOI
 		willHaveWritten := v.writtenTotalBytes + eoiLength
 
 		if willHaveWritten < v.expectedFileSize {
 			// if we won't have written enough,
 			// pad the final segment before EOI
 			// so that we meet expected file size
 			missingBytes := make([]byte, v.expectedFileSize-willHaveWritten)
 			if _, err := v.writer.Write(missingBytes); err != nil {
 				return err
 			}
 		}
 	}
 
 	// process the segment
 	return v.writeSegment(mostRecentSegment)
 }
 
 func (v *jpegVisitor) writeSegment(s *jpegstructure.Segment) error {
 	var writtenSegmentData int
 	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 {
 		markerIDWritten, err := w.Write([]byte{0xff, s.MarkerId})
 		if err != nil {
 			return err
 		}
 		writtenSegmentData += markerIDWritten
 
 		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
 			}
 
 			writtenSegmentData += 2
 		} else if sizeLen == 4 {
 			l := uint32(len(s.Data) + sizeLen)
 
 			if err := binary.Write(w, binary.BigEndian, &l); err != nil {
 				return err
 			}
 
 			writtenSegmentData += 4
 		} 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
 		writtenNormalData, err := w.Write(s.Data)
 		if err != nil {
 			return err
 		}
 
 		writtenSegmentData += writtenNormalData
 		v.writtenTotalBytes += writtenSegmentData
 		return nil
 	}
 
 	ifd, _, err := s.Exif()
 	if err != nil {
 		return err
 	}
 
 	// amount of bytes we've writtenExifData into the exif body, we'll update this as we go
 	var writtenExifData 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.
 
 		newExifData := &bytes.Buffer{}
 		byteOrder := ifd.ByteOrder()
 
 		// 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(newExifData, byteOrder, &prefix); err != nil {
 			return err
 		}
 		writtenExifData += len(prefix)
 
 		// 2. Write exif header, taking the existing byte order.
 		exifHeader, err := exif.BuildExifHeader(byteOrder, exif.ExifDefaultFirstIfdOffset)
 		if err != nil {
 			return err
 		}
 		hWritten, err := newExifData.Write(exifHeader)
 		if err != nil {
 			return err
 		}
 		writtenExifData += hWritten
 
 		// 3. Write in the new ifd
 		//
 		// 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
 		//
 		// see https://web.archive.org/web/20190624045241if_/http://www.cipa.jp:80/std/documents/e/DC-008-Translation-2019-E.pdf - p24-25
 		orientationEntry := orientationEntries[0]
 
 		ifdCount := uint16(1) // we're only adding one entry into the ifd
 		if err := binary.Write(newExifData, byteOrder, &ifdCount); err != nil {
 			return err
 		}
 		writtenExifData += 2
 
 		tagID := orientationEntry.TagId()
 		if err := binary.Write(newExifData, byteOrder, &tagID); err != nil {
 			return err
 		}
 		writtenExifData += 2
 
 		tagType := uint16(orientationEntry.TagType())
 		if err := binary.Write(newExifData, byteOrder, &tagType); err != nil {
 			return err
 		}
 		writtenExifData += 2
 
 		tagCount := orientationEntry.UnitCount()
 		if err := binary.Write(newExifData, byteOrder, &tagCount); err != nil {
 			return err
 		}
 		writtenExifData += 4
 
 		valueOffset, err := orientationEntry.GetRawBytes()
 		if err != nil {
 			return err
 		}
 
 		vWritten, err := newExifData.Write(valueOffset)
 		if err != nil {
 			return err
 		}
 		writtenExifData += vWritten
 
 		valuePad := make([]byte, 4-vWritten)
 		pWritten, err := newExifData.Write(valuePad)
 		if err != nil {
 			return err
 		}
 		writtenExifData += pWritten
 
 		// write all the new data into the writer from the segment
 		writtenNewExifData, err := io.Copy(w, newExifData)
 		if err != nil {
 			return err
 		}
 
 		writtenSegmentData += int(writtenNewExifData)
 	}
 
 	// fill in any remaining exif body with blank bytes
 	blank := make([]byte, len(s.Data)-writtenExifData)
 	writtenPadding, err := w.Write(blank)
 	if err != nil {
 		return err
 	}
 
 	writtenSegmentData += writtenPadding
 	v.writtenTotalBytes += writtenSegmentData
 	return nil
 }