Base64 decoding from asp
Wojtek Rappak
asp page?
Thanks for any help on this.
--
______________________________________________________________________________
Wojtek Rappak 88 Tyrwhitt Rd. London SE4 1QB +44 (0)181-691 2089
BKB Client/Server (UK) http://www.bkbcs.com w...@cssys.demon.co.uk
Paul Williams
> From: Wojtek Rappak [mailto:woj...@cssys.demon.co.uk]
> Is there a simple way of docoding a Base64-encoded string passed to an
> asp page?
ASP provides no base 64 decoding API. However, you can use the
following code provided you credit me in your source. You'll need to
define an application-scope dictionary called Base64DecodeTable inside
of your global.asa file.
Paul F. Williams
Criterion, Inc. (http://www.criterioninc.com)
------------- Begin Base64.inc -----------------------
<script language=JavaScript runat=Server>
function shiftLeft(data, numBits)
{
return data << numBits;
}
function shiftRight(data, numBits)
{
return data >> numBits;
}
// returns the requested byte of the integer data
// e.g. getByte( 0x00112233, 0) returns 0x00
// getByte( 0x00112233, 1) returns 0x11 etc.
function getByte(data, numByte)
{
return (data >> (24 - (8 * numByte))) & 0xff;
}
</script>
<script language=VBScript runat=Server>
' Decodes a base-64 encoded string.
Function Base64Decode (data)
' If first time running, populate decode table.
If (Base64DecodeTable.Count = 0) Then
Application.Lock
Dim value, i
value = 0
' A - Z
For i = 65 to 90
Base64DecodeTable.Add Chr(i), value
value = value + 1
Next
' a - z
For i = 97 to 122
Base64DecodeTable.Add Chr(i), value
value = value + 1
Next
' 0 - 9
For i = 48 to 57
Base64DecodeTable.Add Chr(i), value
value = value + 1
Next
Base64DecodeTable.Add "+", 62
Base64DecodeTable.Add "/", 63
' The character '=' pads the encoded stream to a
multiple of 4 characters.
' It has no actual value, but we use it as a place
holder.
Base64DecodeTable.Add "=", 0
Application.Unlock
End If
dataLength = Len(data)
If dataLength Mod 4 <> 0 Then
Base64Decode = ""
Err.Raise 6, "CornerStone", "Base-64 encoded string was
not an even multiple of 4 characters long."
Exit Function
End If
' Count the number of data groups.
numGroups = dataLength / 4
Dim result
result = ""
' Now decode each group:
For groupBegin = 1 to dataLength Step 4
Dim numDataBytes, j, k, thisChar, thisData, groupData
' Each data group encodes up to 3 actual bytes.
numDataBytes = 3
groupData = 0
For j = 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(data, groupBegin + j, 1)
thisData = Base64DecodeTable.Item(thisChar)
groupData = shiftLeft(groupData, 6) + thisData
If thisChar = "=" Then
numDataBytes = numDataBytes - 1
End If
Next
' Convert 4-byte integer into up to 3 characters
For k = 1 to NumDataBytes
result = result & Chr( getByte(groupData, k) )
Next
Next
Base64Decode = result
End Function
</script>
------------------ end Base64.inc ---------------------------
Here's an example of how to use it:
------------------- Begin Base64.asp -----------------------
<!--#INCLUDE FILE="Base64.inc"-->
<%
encodedData = Request("encodedData")
decodedData = Request("decodedData")
If encodedData <> "" Then
decodedData = Base64Decode(encodedData)
End If
%>
<HTML>
<HEAD>
<META NAME="GENERATOR" Content="Microsoft Developer Studio">
<META HTTP-EQUIV="Content-Type" content="text/html; charset=iso-8859-1">
<TITLE>Base-64 Decoding Test</TITLE>
</HEAD>
<BODY>
<br>Base-64 Decoder<br>
<form method="POST">
<table border=0>
<tr>
<td>Data to be decoded:</td>
<td><input type="text" size="30" name="encodedData"
value="<%= encodedData %>"></td>
</tr>
<tr>
<td>Result:</td>
<td><input type="text" size="30" name="decodedData"
value="<%= decodedData %>"></td>
</tr>
</table>
<input type="submit" name="Action" value="Submit">
</form>
</BODY>
</HTML>
------------------------ End Base64.asp