120 lines
3.6 KiB
Go
120 lines
3.6 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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"bufio"
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"bytes"
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"errors"
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"fmt"
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"io"
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jpegstructure "github.com/superseriousbusiness/go-jpeg-image-structure/v2"
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pngstructure "github.com/dsoprea/go-png-image-structure/v2"
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)
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func Terminate(in io.Reader, fileSize int, mediaType string) (io.Reader, error) {
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// to avoid keeping too much stuff in memory we want to pipe data directly
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pipeReader, pipeWriter := io.Pipe()
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// we don't know ahead of time how long segments might be: they could be as large as
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// the file itself, so unfortunately we need to allocate a buffer here that'scanner as large
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// as the file
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scanner := bufio.NewScanner(in)
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scanner.Buffer([]byte{}, fileSize)
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var err error
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switch mediaType {
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case "image/jpeg", "jpeg", "jpg":
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err = terminateJpeg(scanner, pipeWriter)
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case "image/png", "png":
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// for pngs we need to skip the header bytes, so read them in
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// and check we're really dealing with a png here
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header := make([]byte, len(pngstructure.PngSignature))
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if _, headerError := in.Read(header); headerError != nil {
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err = headerError
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break
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}
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if !bytes.Equal(header, pngstructure.PngSignature[:]) {
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err = errors.New("could not decode png: invalid header")
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break
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}
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err = terminatePng(scanner, pipeWriter)
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default:
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err = fmt.Errorf("mediaType %s cannot be processed", mediaType)
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}
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return pipeReader, err
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}
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func terminateJpeg(scanner *bufio.Scanner, writer io.WriteCloser) error {
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// jpeg visitor is where the spicy hack of streaming the de-exifed data is contained
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v := &jpegVisitor{
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writer: writer,
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}
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// provide the visitor to the splitter so that it triggers on every section scan
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js := jpegstructure.NewJpegSplitter(v)
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// the visitor also needs to read back the list of segments: for this it needs
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// to know what jpeg splitter it's attached to, so give it a pointer to the splitter
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v.js = js
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// use the jpeg splitters 'split' function, which satisfies the bufio.SplitFunc interface
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scanner.Split(js.Split)
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scanAndClose(scanner, writer)
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return nil
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}
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func terminatePng(scanner *bufio.Scanner, writer io.WriteCloser) error {
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ps := pngstructure.NewPngSplitter()
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v := &pngVisitor{
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ps: ps,
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writer: writer,
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lastWrittenChunk: -1,
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}
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// use the png visitor's 'split' function, which satisfies the bufio.SplitFunc interface
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scanner.Split(v.split)
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scanAndClose(scanner, writer)
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return nil
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}
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func scanAndClose(scanner *bufio.Scanner, writer io.WriteCloser) {
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// scan asynchronously until there's nothing left to scan, and then close the writer
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// so that the reader on the other side knows that we're done
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//
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// due to the nature of io.Pipe, writing won't actually work
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// until the pipeReader starts being read by the caller, which
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// is why we do this asynchronously
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go func() {
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defer writer.Close()
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for scanner.Scan() {
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}
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if scanner.Err() != nil {
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logger.Error(scanner.Err())
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}
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}()
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}
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