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102 lines
2.4 KiB
Go
102 lines
2.4 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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"encoding/binary"
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"errors"
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"io"
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)
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const (
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riffHeaderSize = 4 * 3
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)
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var (
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riffHeader = [4]byte{'R', 'I', 'F', 'F'}
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webpHeader = [4]byte{'W', 'E', 'B', 'P'}
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exifFourcc = [4]byte{'E', 'X', 'I', 'F'}
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xmpFourcc = [4]byte{'X', 'M', 'P', ' '}
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errNoRiffHeader = errors.New("no RIFF header")
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errNoWebpHeader = errors.New("not a WEBP file")
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)
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type webpVisitor struct {
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writer io.Writer
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doneHeader bool
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}
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func fourCC(b []byte) [4]byte {
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return [4]byte{b[0], b[1], b[2], b[3]}
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}
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func (v *webpVisitor) split(data []byte, atEOF bool) (advance int, token []byte, err error) {
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// parse/write the header first
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if !v.doneHeader {
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if len(data) < riffHeaderSize {
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// need the full header
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return
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}
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if fourCC(data) != riffHeader {
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err = errNoRiffHeader
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return
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}
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if fourCC(data[8:]) != webpHeader {
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err = errNoWebpHeader
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return
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}
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if _, err = v.writer.Write(data[:riffHeaderSize]); err != nil {
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return
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}
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advance += riffHeaderSize
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data = data[riffHeaderSize:]
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v.doneHeader = true
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}
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// need enough for fourcc and size
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if len(data) < 8 {
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return
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}
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size := int64(binary.LittleEndian.Uint32(data[4:]))
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if (size & 1) != 0 {
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// odd chunk size - extra padding byte
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size++
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}
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// wait until there is enough
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if int64(len(data)-8) < size {
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return
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}
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fourcc := fourCC(data)
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rawChunkData := data[8 : 8+size]
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if fourcc == exifFourcc || fourcc == xmpFourcc {
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// replace exif/xmp with blank
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rawChunkData = make([]byte, size)
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}
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if _, err = v.writer.Write(data[:8]); err == nil {
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if _, err = v.writer.Write(rawChunkData); err == nil {
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advance += 8 + int(size)
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}
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}
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return
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}
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