package pkcs12 import ( "errors" "unicode/utf16" "unicode/utf8" ) func bmpString(utf8String []byte) ([]byte, error) { // References: // https://tools.ietf.org/html/rfc7292#appendix-B.1 // http://en.wikipedia.org/wiki/Plane_(Unicode)#Basic_Multilingual_Plane // - non-BMP characters are encoded in UTF 16 by using a surrogate pair of 16-bit codes // EncodeRune returns 0xfffd if the rune does not need special encoding // - the above RFC provides the info that BMPStrings are NULL terminated. rv := make([]byte, 0, 2*len(utf8String)+2) start := 0 for start < len(utf8String) { c, size := utf8.DecodeRune(utf8String[start:]) start += size if t, _ := utf16.EncodeRune(c); t != 0xfffd { return nil, errors.New("string contains characters that cannot be encoded in UCS-2") } rv = append(rv, byte(c/256), byte(c%256)) } rv = append(rv, 0, 0) return rv, nil } func decodeBMPString(bmpString []byte) (string, error) { if len(bmpString)%2 != 0 { return "", errors.New("expected BMP byte string to be an even length") } // strip terminator if present if terminator := bmpString[len(bmpString)-2:]; terminator[0] == terminator[1] && terminator[1] == 0 { bmpString = bmpString[:len(bmpString)-2] } s := make([]uint16, 0, len(bmpString)/2) for len(bmpString) > 0 { s = append(s, uint16(bmpString[0])*265+uint16(bmpString[1])) bmpString = bmpString[2:] } return string(utf16.Decode(s)), nil }