do arnie

vendor/code.superseriousbusiness.org/exif-terminator/webp.go

@@ -0,0 +1,109 @@
+/*
+   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 (
+	"encoding/binary"
+	"errors"
+	"io"
+)
+
+const (
+	riffHeader = "RIFF"
+	webpHeader = "WEBP"
+	exifFourcc = "EXIF"
+	xmpFourcc  = "XMP "
+)
+
+var (
+	errNoRiffHeader = errors.New("no RIFF header")
+	errNoWebpHeader = errors.New("not a WEBP file")
+	errInvalidChunk = errors.New("invalid chunk")
+)
+
+type webpVisitor struct {
+	writer     io.Writer
+	doneHeader bool
+}
+
+func (v *webpVisitor) split(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	// parse/write the header first
+	if !v.doneHeader {
+
+		// const rifHeaderSize = 12
+		if len(data) < 12 {
+			if atEOF {
+				err = errNoRiffHeader
+			}
+			return
+		}
+
+		if string(data[:4]) != riffHeader {
+			err = errNoRiffHeader
+			return
+		}
+
+		if string(data[8:12]) != webpHeader {
+			err = errNoWebpHeader
+			return
+		}
+
+		if _, err = v.writer.Write(data[:12]); err != nil {
+			return
+		}
+
+		advance += 12
+		data = data[12:]
+		v.doneHeader = true
+	}
+
+	for {
+		// need enough for
+		// fourcc and size
+		if len(data) < 8 {
+			return
+		}
+
+		size := int64(binary.LittleEndian.Uint32(data[4:]))
+
+		if (size & 1) != 0 {
+			// odd chunk size:
+			// extra padding byte
+			size++
+		}
+
+		// wait until there is enough
+		if int64(len(data)) < 8+size {
+			return
+		}
+
+		// replace exif/xmp with blank
+		switch string(data[:4]) {
+		case exifFourcc, xmpFourcc:
+			clear(data[8 : 8+size])
+		}
+
+		if _, err = v.writer.Write(data[:8+size]); err != nil {
+			return
+		}
+
+		advance += 8 + int(size)
+		data = data[8+size:]
+	}
+}