Convert hex string (image) to base64 (for browser rendering) in VBScript

Question

I have a script that outputs a .bmp captcha image.

The image is built in hexadecimal, and converted to binary and sent to the browser via response.binaryWrite

Answer 1

The Microsoft.XMLDOM has built in converters for bin.base64 and bin.hex. I wrote functions that demonstrate how to use this:

Function TextToBinary(text, dataType)
  Dim dom
  Set dom = CreateObject("Microsoft.XMLDOM")
  dom.loadXML("<HELLO/>")
  dom.documentElement.nodeTypedValue = text
  dom.documentElement.dataType = dataType
  TextToBinary = dom.documentElement.nodeTypedValue
End Function

Function BinaryToText(binary, dataType)
  Dim dom
  Set dom = CreateObject("Microsoft.XMLDOM")
  dom.loadXML("<HELLO/>")
  dom.documentElement.dataType = dataType
  dom.documentElement.nodeTypedValue = binary
  dom.documentElement.removeAttribute("dt:dt")
  BinaryToText = dom.documentElement.nodeTypedValue
End Function

Function HexToBase64(strHex)
  HexToBase64 = BinaryToText(TextToBinary(strHex, "bin.hex"), "bin.base64")
End Function

Function Base64ToHex(strBase64)
  Base64ToHex = BinaryToText(TextToBinary(strBase64, "bin.base64"), "bin.hex")
End Function

Here's an example of their usage:

MsgBox HexToBase64("41")
MsgBox Base64ToHex("QQ==")

Also look at the ADODB.Stream as a means of working with binary files. It'll work with these routines.

Answer 2

I was able to get this working. Here is how.

In sendHex, I removed the &H portion, and wrapped my string in hex():

Private Sub sendHex(valHex)
    Dim iCntHex
    For iCntHex = 1 To len(valHex) Step 2
    If len( mid(valHex, iCntHex, 2)) = 1 Then 
        response.write "0"
    end if 
    response.write mid(valHex, iCntHex, 2)
    Next
End Sub

This results in a string output like this (in byte strings of 2 hexidecimal chars):

424d1e050000000000003e00000028000000340000001800000001000

I can then dump that proper hex string into a HEX to base64 function as follows (not written by me, but rather, by Richard Mueller - http://www.rlmueller.net/Base64.htm)

Function HexToBase64(strHex)
    ' Function to convert a hex string into a base64 encoded string.
    ' Constant B64 has global scope.
    Dim lngValue, lngTemp, lngChar, intLen, k, j, strWord, str64, intTerm

    intLen = Len(strHex)

    ' Pad with zeros to multiple of 3 bytes.
    intTerm = intLen Mod 6
    If (intTerm = 4) Then
        strHex = strHex & "00"
        intLen = intLen + 2
    End If
    If (intTerm = 2) Then
        strHex = strHex & "0000"
        intLen = intLen + 4
    End If

    ' Parse into groups of 3 hex bytes.
    j = 0
    strWord = ""
    HexToBase64 = ""
    For k = 1 To intLen Step 2
        j = j + 1
        strWord = strWord & Mid(strHex, k, 2)
        If (j = 3) Then
            ' Convert 3 8-bit bytes into 4 6-bit characters.
            lngValue = CCur("&H" & strWord)

            lngTemp = Fix(lngValue / 64)
            lngChar = lngValue - (64 * lngTemp)
            str64 = Mid(B64, lngChar + 1, 1)
            lngValue = lngTemp

            lngTemp = Fix(lngValue / 64)
            lngChar = lngValue - (64 * lngTemp)
            str64 = Mid(B64, lngChar + 1, 1) & str64
            lngValue = lngTemp

            lngTemp = Fix(lngValue / 64)
            lngChar = lngValue - (64 * lngTemp)
            str64 = Mid(B64, lngChar + 1, 1) & str64

            str64 = Mid(B64, lngTemp + 1, 1) & str64

            HexToBase64 = HexToBase64 & str64
            j = 0
            strWord = ""
        End If
    Next
    ' Account for padding.
    If (intTerm = 4) Then
        HexToBase64 = Left(HexToBase64, Len(HexToBase64) - 1) & "="
    End If
    If (intTerm = 2) Then
        HexToBase64 = Left(HexToBase64, Len(HexToBase64) - 2) & "=="
    End If

End Function

This converts the above to base64, and I can use the output like this (e.g. in a browser url bar) to view it as an image:

data:image/bmp;base64,Qk0eBQAAAAAAAD4AAAAo...