func (editor *OggTagEditor) makeNewPages(existingCommentPages []byte, tag Tag) ([]byte, []byte, int) {
// bitstream number
var bitstream int = 31013
if len(existingCommentPages) > oggPageHeaderSize {
bitstream = utils.ReadInt32Le(existingCommentPages[14:18])
}
commentHeader, existingTagData, setupHeader := editor.splitCommentPages(existingCommentPages)
if len(commentHeader) == 0 {
commentHeader = make([]byte, 1+len(oggHeaderMagic)+4)
commentHeader[0] = 3
copy(commentHeader[1:1+len(oggHeaderMagic)], oggHeaderMagic)
utils.WriteInt32Le(0, commentHeader[len(oggHeaderMagic):len(oggHeaderMagic)+4])
}
unsupportedTagData, unsupportedFields := getUnsupportedVorbisTags(existingTagData)
newTagData, totalFields := serializeVorbisTag(tag, unsupportedFields)
tagData := make([]byte, len(commentHeader)+4+len(newTagData)+len(unsupportedTagData)+1)
copy(tagData, commentHeader)
utils.WriteInt32Le(totalFields, tagData[len(commentHeader):len(commentHeader)+4])
copy(tagData[len(commentHeader)+4:], newTagData)
copy(tagData[len(commentHeader)+4+len(newTagData):], unsupportedTagData)
tagData[len(tagData)-1] = 1
newCommentHeader, commentPages := editor.packTagDataIntoFrames(bitstream, 1, tagData)
newSetupHeader, setupPages := editor.packTagDataIntoFrames(bitstream, commentPages+1, setupHeader)
return newCommentHeader, newSetupHeader, commentPages + setupPages
}
func (editor *OggTagEditor) WriteTag(src, dst string, tag Tag) error {
err := editor.readFile(src)
if err != nil {
return err
}
idPage, commentPages, restData := editor.splitFileData(editor.file)
newCommentPages, newSetupPages, numberOfPages := editor.makeNewPages(commentPages, tag)
newPrefix := make([]byte, len(idPage)+len(newCommentPages)+len(newSetupPages))
copy(newPrefix, idPage)
copy(newPrefix[len(idPage):], newCommentPages)
copy(newPrefix[len(idPage)+len(newCommentPages):], newSetupPages)
// fix page numbers and CRCs
sequence := numberOfPages + 1
data := restData
for len(data) > oggPageHeaderSize {
pageSize := editor.getPageSize(data)
utils.WriteInt32Le(sequence, data[18:22]) // number
utils.WriteUint32Le(0, data[22:26]) // zero CRC
utils.WriteUint32Le(editor.crc(data[:pageSize]), data[22:26]) // CRC
sequence++
data = data[pageSize:]
}
return ioutil.WriteFile(dst, append(newPrefix, restData...), 0666)
}
func serializeVorbisTagTextField(text, frameName string, dst []byte, offset int) int {
fieldSize := len(frameName) + len(text) + 1
utils.WriteInt32Le(fieldSize, dst[offset:offset+4])
copy(dst[offset+4:offset+4+len(frameName)], frameName)
dst[offset+4+len(frameName)] = 0x3d // '='
copy(dst[offset+5+len(frameName):offset+4+fieldSize], text)
return offset + 4 + fieldSize
}
func (editor *OggTagEditor) fillHeader(dst []byte, bitstream, sequence, totalSize int) (int, int) {
copy(dst[0:4], oggPageMagic) // magic
dst[4] = 0 // version
dst[5] = 0 // header type
dst[6] = 0 // granule position
dst[7] = 0
dst[8] = 0
dst[9] = 0
dst[10] = 0
dst[11] = 0
dst[12] = 0
dst[13] = 0
utils.WriteInt32Le(bitstream, dst[14:18]) // bitstream serial number
utils.WriteInt32Le(sequence, dst[18:22]) // page sequence number
dst[22] = 0 // CRC checksum
dst[23] = 0
dst[24] = 0
dst[25] = 0
dataSize := totalSize
if dataSize > maxFrameDataSize {
dataSize = maxFrameDataSize
}
dst[26] = byte(dataSize / 255)
if dataSize%255 != 0 {
dst[26]++
}
headerSize := 27 + int(dst[26])
for i := 27; i < headerSize; i++ {
dst[i] = 0xFF
}
if dataSize%255 != 0 {
dst[headerSize-1] = byte(dataSize % 255)
}
return headerSize, dataSize
}
func (editor *FlacTagEditor) makeNewCommentBlock(tag Tag, existingCommentBlock []byte) []byte {
var vendorData []byte = nil
var unsupportedTagData []byte = nil
var unsupportedFields int = 0
if len(existingCommentBlock) >= 8 {
vendorSize := utils.ReadInt32Le(existingCommentBlock[4:8])
vendorData = existingCommentBlock[4 : 8+vendorSize]
unsupportedTagData, unsupportedFields = getUnsupportedVorbisTags(existingCommentBlock[8+vendorSize:])
}
newCommentData, totalFields := serializeVorbisTag(tag, unsupportedFields)
newCommentBlock := make([]byte, 4+len(vendorData)+4+len(newCommentData)+len(unsupportedTagData))
newCommentBlock[0] = commentBlockType
utils.WriteInt24Be(len(newCommentBlock)-4, newCommentBlock[1:4])
copy(newCommentBlock[4:], vendorData)
utils.WriteInt32Le(totalFields, newCommentBlock[4+len(vendorData):8+len(vendorData)])
copy(newCommentBlock[8+len(vendorData):], newCommentData)
copy(newCommentBlock[8+len(vendorData)+len(newCommentData):], unsupportedTagData)
return newCommentBlock
}