ASP Learning: An addendum to the UrlDecode method

ASP inside there is no urldecode function, as if ASPX have it, I am not clear, but the ASP inside or use a lot. I looked up the UrlDecode function written by someone else on the internet, but the function was wrong, and in some ways it was hard to understand. And there are errors, when there are obscure double-byte text will produce errors, such as "乄" after the Urlencoder "%81w", decoding can not be successful.

In fact, two-byte code here as long as the "W" also into 16 into the ASC code can be.

Knowledge Point: The cookie in the computer is also urlencode encoded, so UrlDecode is also useful for cracking cookies.

The following is the source code:

  Function UrlDecode (enstr)
  Dim destr
  Dim c,i,v
  Destr= ""
  for I=1 to Len (E NSTR)
  C=mid (enstr,i,1)
  if c= "%" then
  v=eval ("&h" +mid (enstr,i+1,2))
  If V <128 then
  DESTR=DESTR&CHR (v)
  i=i+2
  Else
  if Isvalidhex (Mid (enstr,i,3)) Then
  if Isvalidhex (Mid (enstr,i+3,3)) then
  V=eval ("&h" +mid (enstr,i+1,2) +mid (enstr,i+4,2))
  DESTR=DESTR&CHR (v)
  i=i+5
  Else
  V=eval ("&h" +mid (enstr,i+1,2) +cstr ( Hex (ASC (Mid enstr,i+3,1)))
  DESTR=DESTR&CHR (v)
  i=i+3
  End If
  else
& nbsp Destr=destr&c
  End If
  End If
  else
  if c= "+" then
  destr=destr& ""
  Else
  DESTR=DESTR&C
  End If
  End If
  next
  URLDECODE=DESTR
  End Function

function Isvalidhex (str)
Isvalidhex=true
Str=ucase (str)
If Len (str) <>3 then Isvalidhex=false:exit function
If left (str,1) <> "%" then Isvalidhex=false:exit function
C=mid (str,2,1)
If not ((c>= "0") and (c<= "9")) or ((c>= "A") and (c<= "Z")) then Isvalidhex=false:exit function
C=mid (str,3,1)
If not ((c>= "0") and (c<= "9")) or ((c>= "A") and (c<= "Z")) then Isvalidhex=false:exit function
End Function

You use this method to decode "%81w" look, it's OK.

Of course, you can also play a little bit, make it a string encryption of their own way.