gotosocial/vendor/codeberg.org/superseriousbusiness/exif-terminator/webp.go

101 lines
2.4 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 (
"encoding/binary"
"errors"
"io"
)
const (
riffHeaderSize = 4 * 3
)
var (
riffHeader = [4]byte{'R', 'I', 'F', 'F'}
webpHeader = [4]byte{'W', 'E', 'B', 'P'}
exifFourcc = [4]byte{'E', 'X', 'I', 'F'}
xmpFourcc = [4]byte{'X', 'M', 'P', ' '}
errNoRiffHeader = errors.New("no RIFF header")
errNoWebpHeader = errors.New("not a WEBP file")
)
type webpVisitor struct {
writer io.Writer
doneHeader bool
}
func fourCC(b []byte) [4]byte {
return [4]byte{b[0], b[1], b[2], b[3]}
}
func (v *webpVisitor) split(data []byte, atEOF bool) (advance int, token []byte, err error) {
// parse/write the header first
if !v.doneHeader {
if len(data) < riffHeaderSize {
// need the full header
return
}
if fourCC(data) != riffHeader {
err = errNoRiffHeader
return
}
if fourCC(data[8:]) != webpHeader {
err = errNoWebpHeader
return
}
if _, err = v.writer.Write(data[:riffHeaderSize]); err != nil {
return
}
advance += riffHeaderSize
data = data[riffHeaderSize:]
v.doneHeader = true
}
// 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
}
fourcc := fourCC(data)
rawChunkData := data[8 : 8+size]
if fourcc == exifFourcc || fourcc == xmpFourcc {
// replace exif/xmp with blank
rawChunkData = make([]byte, size)
}
if _, err = v.writer.Write(data[:8]); err == nil {
if _, err = v.writer.Write(rawChunkData); err == nil {
advance += 8 + int(size)
}
}
return
}