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/*
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 (
"encoding/binary"
"errors"
"io"
)
const (
riffHeader = "RIFF"
webpHeader = "WEBP"
exifFourcc = "EXIF"
xmpFourcc = "XMP "
)
var (
errNoRiffHeader = errors.New("no RIFF header")
errNoWebpHeader = errors.New("not a WEBP file")
errInvalidChunk = errors.New("invalid chunk")
)
type webpVisitor struct {
writer io.Writer
doneHeader bool
}
func (v *webpVisitor) split(data []byte, atEOF bool) (advance int, token []byte, err error) {
// parse/write the header first
if !v.doneHeader {
// const rifHeaderSize = 12
if len(data) < 12 {
if atEOF {
err = errNoRiffHeader
}
return
}
if string(data[:4]) != riffHeader {
err = errNoRiffHeader
return
}
if string(data[8:12]) != webpHeader {
err = errNoWebpHeader
return
}
if _, err = v.writer.Write(data[:12]); err != nil {
return
}
advance += 12
data = data[12:]
v.doneHeader = true
}
for {
// need enough for
// fourcc and size
if len(data) < 8 {
return
}
size := int64(binary.LittleEndian.Uint32(data[4:]))
if (size & 1) != 0 {
// odd chunk size:
// extra padding byte
size++
}
// wait until there is enough
if int64(len(data)) < 8+size {
return
}
// replace exif/xmp with blank
switch string(data[:4]) {
case exifFourcc, xmpFourcc:
clear(data[8 : 8+size])
}
if _, err = v.writer.Write(data[:8+size]); err != nil {
return
}
advance += 8 + int(size)
data = data[8+size:]
}
}
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