/* 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 ( riffHeaderSize = 4 * 3 ) var ( riffHeader = [4]byte{'R', 'I', 'F', 'F'} webpHeader = [4]byte{'W', 'E', 'B', 'P'} exifFourcc = [4]byte{'E', 'X', 'I', 'F'} xmpFourcc = [4]byte{'X', 'M', 'P', ' '} errNoRiffHeader = errors.New("no RIFF header") errNoWebpHeader = errors.New("not a WEBP file") ) type webpVisitor struct { writer io.Writer doneHeader bool } func fourCC(b []byte) [4]byte { return [4]byte{b[0], b[1], b[2], b[3]} } func (v *webpVisitor) split(data []byte, atEOF bool) (advance int, token []byte, err error) { // parse/write the header first if !v.doneHeader { if len(data) < riffHeaderSize { // need the full header return } if fourCC(data) != riffHeader { err = errNoRiffHeader return } if fourCC(data[8:]) != webpHeader { err = errNoWebpHeader return } if _, err = v.writer.Write(data[:riffHeaderSize]); err != nil { return } advance += riffHeaderSize data = data[riffHeaderSize:] v.doneHeader = true } // 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 } fourcc := fourCC(data) rawChunkData := data[8 : 8+size] if fourcc == exifFourcc || fourcc == xmpFourcc { // replace exif/xmp with blank rawChunkData = make([]byte, size) } if _, err = v.writer.Write(data[:8]); err == nil { if _, err = v.writer.Write(rawChunkData); err == nil { advance += 8 + int(size) } } return }