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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"
"io"
pngstructure "github.com/dsoprea/go-png-image-structure/v2"
)
type pngVisitor struct {
ps *pngstructure.PngSplitter
writer io.Writer
lastWrittenChunk int
}
func (v *pngVisitor) split(data []byte, atEOF bool) (int, []byte, error) {
// execute the ps split function to read in data
advance, token, err := v.ps.Split(data, atEOF)
if err != nil {
return advance, token, err
}
// if we haven't written anything at all yet, then write the png header back into the writer first
if v.lastWrittenChunk == -1 {
if _, err := v.writer.Write(pngstructure.PngSignature[:]); err != nil {
return advance, token, err
}
}
// check if the splitter has any new chunks in it that we haven't written yet
chunkSlice := v.ps.Chunks()
chunks := chunkSlice.Chunks()
for i, chunk := range chunks {
// look through all the chunks in the splitter
if i > v.lastWrittenChunk {
// we've got a chunk we haven't written yet! write it...
if err := v.writeChunk(chunk); err != nil {
return advance, token, err
}
// then remove the data
chunk.Data = chunk.Data[:0]
// and update
v.lastWrittenChunk = i
}
}
return advance, token, err
}
func (v *pngVisitor) writeChunk(chunk *pngstructure.Chunk) error {
if err := binary.Write(v.writer, binary.BigEndian, chunk.Length); err != nil {
return err
}
if _, err := v.writer.Write([]byte(chunk.Type)); err != nil {
return err
}
if chunk.Type == pngstructure.EXifChunkType {
blank := make([]byte, len(chunk.Data))
if _, err := v.writer.Write(blank); err != nil {
return err
}
} else {
if _, err := v.writer.Write(chunk.Data); err != nil {
return err
}
}
if err := binary.Write(v.writer, binary.BigEndian, chunk.Crc); err != nil {
return err
}
return nil
}
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