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