package util import ( "strings" euni "golang.org/x/text/encoding/unicode" ) // got the logic from: https://github.com/bogem/id3v2 , thank you very much. const first7BitsMask = uint32(254 << 24) // shifting 11111110 to the end of uint32 // Converts given bytes into integer func BytesToInt(gBytes []byte) uint32 { var integer uint32 = 0 for _, b := range gBytes { integer = integer << 8 integer = integer | uint32(b) } return integer } // Decodes given integer bytes into integer, ignores the first bit // of every given byte in binary form func BytesToIntSynchsafe(gBytes []byte) uint32 { var integer uint32 = 0 for _, b := range gBytes { integer = integer << 7 integer = integer | uint32(b) } return integer } // The exact opposite of what `BytesToIntSynchsafe` does // Finally understood with the help of: https://github.com/bogem/id3v2/blob/master/size.go , // thank you very much ! func IntToBytesSynchsafe(gInt uint32) []byte { synchsafeIBytes := make([]byte, 4) // skip 4 0`ed bits gInt = gInt << 4 // int32 == 4 bytes for i := 0; i < 32/8; i++ { // get first 7 bits first7Bits := gInt & first7BitsMask // shift captured bits to the beginning first7Bits = first7Bits >> (3*8 + 1) b := byte(first7Bits) synchsafeIBytes = append(synchsafeIBytes, b) // prepare next 7 bits for the next iteration gInt = gInt << 7 } return synchsafeIBytes } // Converts given bytes into string, ignoring the first 31 non-printable ASCII characters. // (LOSSY, if given bytes contain some nasty ones) func ToStringLossy(gBytes []byte) string { var runes []rune for _, b := range gBytes { if b <= 31 { continue } runes = append(runes, rune(b)) } return strings.ToValidUTF8(string(runes), "") } // Decodes the given frame`s contents func DecodeText(fContents []byte) string { textEncoding := fContents[0] // the first byte is the encoding switch textEncoding { case 0: // ISO-8859-1 return ToStringLossy(fContents[1:]) case 1: // UTF-16 with BOM encoding := euni.UTF16(euni.BigEndian, euni.ExpectBOM) decoder := encoding.NewDecoder() decodedBytes := make([]byte, len(fContents)*2) _, _, err := decoder.Transform(decodedBytes, fContents[1:], true) if err != nil { return "" } return string(decodedBytes) case 2: // UTF-16 encoding := euni.UTF16(euni.BigEndian, euni.IgnoreBOM) decoder := encoding.NewDecoder() decodedBytes := make([]byte, len(fContents)*2) _, _, err := decoder.Transform(decodedBytes, fContents[1:], true) if err != nil { return "" } return string(decodedBytes) case 3: // UTF-8 return ToStringLossy(fContents[1:]) } return "" }