94 lines
2.4 KiB
Go
94 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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"io"
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pngstructure "github.com/superseriousbusiness/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 now has
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// any new chunks in it for us.
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chunkSlice, err := v.ps.Chunks()
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if err != nil {
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return advance, token, err
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}
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// Write each chunk by passing it
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// through our custom write func,
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// which strips out exif and fixes
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// the CRC of each chunk.
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chunks := chunkSlice.Chunks()
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for i, chunk := range chunks {
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if i <= v.lastWrittenChunk {
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// Skip already
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// written chunks.
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continue
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}
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// Write this new chunk.
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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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v.lastWrittenChunk = i
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// Zero data; here you
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// go garbage collector.
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chunk.Data = nil
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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 chunk.Type == pngstructure.EXifChunkType {
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// Replace exif data
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// with zero bytes.
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clear(chunk.Data)
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}
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// Fix CRC of each chunk.
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chunk.UpdateCrc32()
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// finally, write chunk to writer.
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_, err := chunk.WriteTo(v.writer)
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return err
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}
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