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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"
)
func Terminate(in io.Reader, mediaType string) (io.Reader, error) {
// To avoid keeping too much stuff
// in memory we want to pipe data
// directly to the reader.
pr, pw := io.Pipe()
// Setup scanner to terminate exif into pipe writer.
scanner, err := terminatingScanner(pw, in, mediaType)
if err != nil {
_ = pw.Close()
return nil, err
}
go func() {
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).
pw.CloseWithError(err)
}()
// Scan through input.
for scanner.Scan() {
}
// Set error on return.
err = scanner.Err()
}()
return pr, nil
}
func TerminateInto(out io.Writer, in io.Reader, mediaType string) error {
// Setup scanner to terminate exif from 'in' to 'out'.
scanner, err := terminatingScanner(out, in, mediaType)
if err != nil {
return err
}
// Scan through input.
for scanner.Scan() {
}
// Return scan errors.
return scanner.Err()
}
func terminatingScanner(out io.Writer, in io.Reader, mediaType string) (*bufio.Scanner, error) {
scanner := bufio.NewScanner(in)
// 40mb buffer size should be enough
// to scan through most file chunks
// without running into issues, they're
// usually chunked smaller than this...
scanner.Buffer(nil, 40*1024*1024)
switch mediaType {
case "image/jpeg", "jpeg", "jpg":
v := &jpegVisitor{
writer: out,
}
// Provide the visitor to the splitter so
// that it triggers on every section scan.
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.
v.js = js
// Jpeg visitor's 'split' function
// satisfies bufio.SplitFunc{}.
scanner.Split(js.Split)
case "image/webp", "webp":
// Webp visitor's 'split' function
// satisfies bufio.SplitFunc{}.
scanner.Split((&webpVisitor{
writer: out,
}).split)
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.
header := make([]byte, len(pngstructure.PngSignature))
if _, headerError := in.Read(header); headerError != nil {
return nil, headerError
} else if !bytes.Equal(header, pngstructure.PngSignature[:]) {
return nil, errors.New("could not decode png: invalid header")
}
// Don't bother checking CRC;
// we're overwriting it anyway.
ps := pngstructure.NewPngSplitter()
ps.DoCheckCrc(false)
// Png visitor's 'split' function
// satisfies bufio.SplitFunc{}.
scanner.Split((&pngVisitor{
ps: ps,
writer: out,
lastWrittenChunk: -1,
}).split)
default:
return nil, fmt.Errorf("mediaType %s cannot be processed", mediaType)
}
return scanner, nil
}
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