package v2 ////////////////////////////////////// //(ᗜˬᗜ)~⭐//Under construction//(ᗜ‸ᗜ)// ////////////////////////////////////// import ( "bytes" "fmt" "io" "strconv" "github.com/Unbewohnte/id3ed/util" ) // ID3v2.x header structure type Header struct { Identifier string Version string Unsynchronisated bool Compressed bool Size int64 // size of the whole tag - 10 header bytes } // Reads and structuralises ID3v2 header func GetHeader(rs io.ReadSeeker) (*Header, error) { var header Header rs.Seek(0, io.SeekStart) identifier, err := util.Read(rs, 3) if err != nil { return nil, err } // check if ID3v2 is used if !bytes.Equal([]byte(ID3v2IDENTIFIER), identifier) { return nil, fmt.Errorf("no ID3v2 identifier found") } header.Identifier = string(identifier) // version majorVersionByte, err := util.Read(rs, 1) if err != nil { return nil, err } revisionNumberByte, err := util.Read(rs, 1) if err != nil { return nil, err } majorVersion, err := util.BytesToInt(majorVersionByte) if err != nil { return nil, err } revisionNumber, err := util.BytesToInt(revisionNumberByte) if err != nil { return nil, err } header.Version = fmt.Sprintf("%d%d", -majorVersion, revisionNumber) // flags flags, err := util.Read(rs, 1) if err != nil { return nil, err } bits := fmt.Sprintf("%08b", flags) // 1 byte is 8 bits if bits[0] == 1 { header.Unsynchronisated = true } else { header.Unsynchronisated = false } if bits[1] == 1 { header.Compressed = true } else { header.Compressed = false } // size sizeBytes, err := util.Read(rs, 4) if err != nil { return nil, err } // represent each byte in size as binary and get rid from the first useless bit, // then concatenate filtered parts var filteredSizeStr string for _, b := range sizeBytes { // the first bit is always 0, so filter it out filteredPart := fmt.Sprintf("%08b", b)[1:] // byte is 8 bits filteredSizeStr += filteredPart } // converting filtered binary size into usable int64 size, err := strconv.ParseInt(filteredSizeStr, 2, 64) if err != nil { return nil, err } header.Size = int64(size) return &header, nil }