Android Question How to create and parse Tag, Length, Value (TLV) in .b4a and encode it in Base64

Dim Base64Input As String = "AQRURVNUAg8zMDAyNTQyMzU0NTg0NTYDFDIwMjQtMDItMTdUMDM6MDA6NDJaBAMxMDAFAjE1"

Log("base64" & TAB & Base64Input)

Dim su As StringUtils
Dim B() As Byte = su.DecodeBase64(Base64Input)

Dim bc As ByteConverter
Log("hex" & TAB & bc.HexFromBytes(B))

Log("tag" & TAB & "length" & TAB & "value")

Dim NumDone As Int = 0
Do While NumDone + 2 <= B.Length    'expecting at least tag and length bytes
    Dim FieldTag As Byte = B(NumDone)
    NumDone = NumDone + 1
  
    Dim FieldLength As Int = Bit.And(B(NumDone), 0xFF)    'translate signed -128..127 to unsigned 0..255
    NumDone = NumDone + 1
  
    If NumDone + FieldLength > B.Length Then Exit    'expecting at least FieldLength bytes

    Dim V(FieldLength) As Byte
    bc.ArrayCopy(B, NumDone, V, 0, FieldLength)
    NumDone = NumDone + FieldLength

    Dim FieldValue As String = bc.StringFromBytes(V, "UTF-8")

    'if we get to here then FieldTag+Length+Value are ok
    Log(FieldTag & TAB & FieldLength & TAB & FieldValue)
Loop

Dim EncodedQrText As String = encodeQrText( _
    "TEST", _
    "300254235458456", _
    "2024-02-17T03:00:42Z", _
    "100", _
    "15" _
)

Log(EncodedQrText)


Sub encodeQrText(sallerName As String, sallerTRN As String, invoiceDateTime As String, totalWithVAT As String, VATTotal As String) As String

    Dim hex As String = _
        StringToTagLengthValueHex(1, sallerName) & _
        StringToTagLengthValueHex(2, sallerTRN) & _
        StringToTagLengthValueHex(3, invoiceDateTime) & _
        StringToTagLengthValueHex(4, totalWithVAT) & _
        StringToTagLengthValueHex(5, VATTotal)

    Dim bc As ByteConverter
    Dim B() As Byte = bc.HexToBytes(hex)

    Dim su As StringUtils
    Return su.EncodeBase64(B)
 
End Sub


Sub StringToTagLengthValueHex(Tag As Int, Value As String) As String

    Dim bc As ByteConverter
 
    For L = Value.Length To 0 Step -1    'ensure not too long for 8-bit (unsigned) length byte 0..255
        Dim V() As Byte = bc.StringToBytes(Value.SubString2(0, L), "UTF-8")
        If V.Length <= 255 Then Exit
    Next

    Dim TL() As Byte = Array As Byte(Tag, V.Length)
 
    Return bc.HexFromBytes(TL) & bc.HexFromBytes(V)

End Sub