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

[alktab]

Hello, I have this code in vb net

    Public Function encodeQrText(ByVal sallerName As String, ByVal sallerTRN As String, ByVal invoiceDateTime As String, ByVal totalWithVAT As String, ByVal VATTotal As String) As String
        Dim bytes As Byte() = Encoding.UTF8.GetBytes(sallerName)
        Dim L1 As String = bytes.Length.ToString("X")
        Dim tag1Hex As String = BitConverter.ToString(bytes)
        tag1Hex = tag1Hex.Replace("-", "")
        Dim L2 As String = sallerTRN.Length.ToString("X")
        Dim L3 As String = invoiceDateTime.Length.ToString("X")
        Dim L4 As String = totalWithVAT.Length.ToString("X")
        Dim L5 As String = VATTotal.Length.ToString("X")

        Dim hex As String = "01" & (If((L1.Length = 1), ("0" & L1), L1)) & tag1Hex & "02" & (If((L2.Length = 1), ("0" & L2), L2)) & ToHexString(sallerTRN) & "03" & (If((L3.Length = 1), ("0" & L3), L3)) + ToHexString(invoiceDateTime) & "04" & (If((L4.Length = 1), ("0" & L4), L4)) + ToHexString(totalWithVAT) & "05" & (If((L5.Length = 1), ("0" & L5), L5)) + ToHexString(VATTotal)
        Texthex.Text = hex


        Return HexToBase64(hex)
    End Function

    Private Function HexToBase64(ByVal strInput As String) As String
        Try
            Dim bytes = New Byte(strInput.Length / 2 - 1) {}
            For i = 0 To bytes.Length - 1
                bytes(i) = Convert.ToByte(strInput.Substring(i * 2, 2), 16)
            Next
            Return Convert.ToBase64String(bytes)
        Catch __unusedException1__ As Exception
            Return "-1"
        End Try
    End Function

Outputs :
AQRURVNUAg8zMDAyNTQyMzU0NTg0NTYDFDIwMjQtMDItMTdUMDM6MDA6NDJaBAMxMDAFAjE1
010454455354020F3330303235343233353435383435360314323032342D30322D31375430333A30303A34325A040331303005023135

How can it be converted to B4A

The code depends on five variables that I want to deal with inside B4A

 

[Erel]

Convert bytes to hex with ByteConverter.HexFromBytes.
Convert bytes to base64 with StringUtils.

 

[emexes]

This might be a useful starting point:

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

Waiting for debugger to connect...
Program started.
base64    AQRURVNUAg8zMDAyNTQyMzU0NTg0NTYDFDIwMjQtMDItMTdUMDM6MDA6NDJaBAMxMDAFAjE1
hex       010454455354020F3330303235343233353435383435360314323032342D30322D31375430333A30303A34325A040331303005023135
tag   length   value
1     4        TEST
2     15       300254235458456
3     20       2024-02-17T03:00:42Z
4     3        100
5     2        15

 

[emexes]

This might be a useful starting point:

Maybe this too:

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

Waiting for debugger to connect...
Program started.
AQRURVNUAg8zMDAyNTQyMzU0NTg0NTYDFDIwMjQtMDItMTdUMDM6MDA6NDJaBAMxMDAFAjE1

 

[alktab]

Convert bytes to hex with ByteConverter.HexFromBytes.
Convert bytes to base64 with StringUtils.

Thank Erel
תודה אריאל

 

[alktab]

Thank you emexes
It took me a lot of time how creative you are in thinking and thank you once again and to brother Ariel I came up with a very wonderful project God bless you