gotosocial/vendor/github.com/superseriousbusiness/exif-terminator/terminator.go

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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 (
"bufio"
"bytes"
"errors"
"fmt"
"io"
jpegstructure "github.com/superseriousbusiness/go-jpeg-image-structure/v2"
pngstructure "github.com/superseriousbusiness/go-png-image-structure/v2"
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)
func Terminate(in io.Reader, fileSize int, mediaType string) (io.Reader, error) {
// To avoid keeping too much stuff
// in memory we want to pipe data
// directly to the reader.
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pipeReader, pipeWriter := io.Pipe()
// We don't know ahead of time how long
// segments might be: they could be as
// large as the file itself, so we need
// a buffer with generous overhead.
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scanner := bufio.NewScanner(in)
scanner.Buffer([]byte{}, fileSize)
var err error
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switch mediaType {
case "image/jpeg", "jpeg", "jpg":
err = terminateJpeg(scanner, pipeWriter, fileSize)
case "image/webp", "webp":
err = terminateWebp(scanner, pipeWriter)
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case "image/png", "png":
// For pngs we need to skip the header bytes, so read
// them in and check we're really dealing with a png.
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header := make([]byte, len(pngstructure.PngSignature))
if _, headerError := in.Read(header); headerError != nil {
err = headerError
break
}
if !bytes.Equal(header, pngstructure.PngSignature[:]) {
err = errors.New("could not decode png: invalid header")
break
}
err = terminatePng(scanner, pipeWriter)
default:
err = fmt.Errorf("mediaType %s cannot be processed", mediaType)
}
return pipeReader, err
}
func terminateJpeg(scanner *bufio.Scanner, writer *io.PipeWriter, expectedFileSize int) error {
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v := &jpegVisitor{
writer: writer,
expectedFileSize: expectedFileSize,
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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)
// The visitor also needs to read back the
// list of segments: for this it needs to
// know what jpeg splitter it's attached to,
// so give it a pointer to the splitter.
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v.js = js
// Jpeg visitor's 'split' function
// satisfies bufio.SplitFunc{}.
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scanner.Split(js.Split)
go scanAndClose(scanner, writer)
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return nil
}
func terminateWebp(scanner *bufio.Scanner, writer *io.PipeWriter) error {
v := &webpVisitor{
writer: writer,
}
// Webp visitor's 'split' function
// satisfies bufio.SplitFunc{}.
scanner.Split(v.split)
go scanAndClose(scanner, writer)
return nil
}
func terminatePng(scanner *bufio.Scanner, writer *io.PipeWriter) error {
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ps := pngstructure.NewPngSplitter()
// Don't bother checking CRC;
// we're overwriting it anyway.
ps.DoCheckCrc(false)
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v := &pngVisitor{
ps: ps,
writer: writer,
lastWrittenChunk: -1,
}
// Png visitor's 'split' function
// satisfies bufio.SplitFunc{}.
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scanner.Split(v.split)
go scanAndClose(scanner, writer)
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return nil
}
// scanAndClose scans through the given scanner until there's
// nothing left to scan, and then closes the writer so that the
// reader on the other side of the pipe knows that we're done.
//
// Any error encountered when scanning will be logged by terminator.
//
// Due to the nature of io.Pipe, writing won't actually work
// until the pipeReader starts being read by the caller, which
// is why this function should always be called asynchronously.
func scanAndClose(scanner *bufio.Scanner, writer *io.PipeWriter) {
var err error
defer func() {
// Always close writer, using returned
// scanner error (if any). If err is nil
// then the standard io.EOF will be used.
// (this will not overwrite existing).
writer.CloseWithError(err)
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}()
for scanner.Scan() {
}
// Set error on return.
err = scanner.Err()
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}