A co-worker and I just spent some frustrating time trying to figure out how to write a base64 URL decoder in vbscript (for a facebook app). We thought someone else might have the same issues – so here you go. You need both functions to make it work:
decodedString= Base64URLDecode(encodedString) Function Base64URLDecode(stringtodecode) stringtodecode = replace(stringtodecode,"-", "+") stringtodecode = replace(stringtodecode,"_", "/") select case (len(stringtodecode) mod 4) case 0: stringtodecode = stringtodecode case 2: stringtodecode = stringtodecode +"==" case 3: stringtodecode = stringtodecode +"=" case else: Err.Raise 1, "Base64Decode", "Bad Base64 string." end select stringtodecode=Base64Decode(stringtodecode) Base64URLDecode = stringtodecode End function Function Base64Decode(base64String) 'rfc1521 ' Decodes a base-64 encoded string (BSTR type). ' 1999 - 2004 Antonin Foller, http://www.motobit.com ' 1.01 - solves problem with Access And 'Compare Database' (InStr) Const Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" Dim dataLength, sOut, groupBegin 'remove white spaces, If any base64String = Replace(base64String, vbCrLf, "") base64String = Replace(base64String, vbTab, "") base64String = Replace(base64String, " ", "") 'The source must consists from groups with Len of 4 chars dataLength = Len(base64String) If dataLength Mod 4 <> 0 Then Err.Raise 1, "Base64Decode", "Bad Base64 string." Exit Function End If ' Now decode each group: For groupBegin = 1 To dataLength Step 4 Dim numDataBytes, CharCounter, thisChar, thisData, nGroup, pOut ' Each data group encodes up To 3 actual bytes. numDataBytes = 3 nGroup = 0 For CharCounter = 0 To 3 ' Convert each character into 6 bits of data, And add it To ' an integer For temporary storage. If a character is a '=', there ' is one fewer data byte. (There can only be a maximum of 2 '=' In ' the whole string.) thisChar = Mid(base64String, groupBegin + CharCounter, 1) If thisChar = "=" Then numDataBytes = numDataBytes - 1 thisData = 0 Else thisData = InStr(1, Base64, thisChar, vbBinaryCompare) - 1 End If If thisData = -1 Then Err.Raise 2, "Base64Decode", "Bad character In Base64 string." Exit Function End If nGroup = 64 * nGroup + thisData Next 'Hex splits the long To 6 groups with 4 bits nGroup = Hex(nGroup) 'Add leading zeros nGroup = String(6 - Len(nGroup), "0") & nGroup 'Convert the 3 byte hex integer (6 chars) To 3 characters pOut = Chr(CByte("&H" & Mid(nGroup, 1, 2))) + _ Chr(CByte("&H" & Mid(nGroup, 3, 2))) + _ Chr(CByte("&H" & Mid(nGroup, 5, 2))) 'add numDataBytes characters To out string sOut = sOut & Left(pOut, numDataBytes) Next Base64Decode = sOut End Function
Advertisements