Visual Basic Internet Routines
UrlUnescape: Encoding and Decoding URL Escape Characters
     
Posted:   Monday July 09, 2001
Updated:   Monday December 26, 2011
     
Applies to:   VB4-32, VB5, VB6
Developed with:   VB6, Windows 2000
OS restrictions:   See prerequisites below
Author:   VBnet - Randy Birch
     

Related:  

UrlCanonicalize: Proper URL Path Encoding and Decoding
UrlCreateFromPath: Proper URL Path Conversion from a DOS Path
UrlGetPart: Determine the Constituent Parts of a URL
     
 Prerequisites
Shlwapi.dll version 5.00 or greater, Windows XP, 2000, Windows NT4 with IE 5 or later, Windows 98, or Windows 95 with IE 5 or later. 

Part of the Windows shell provides a series or Shell Lightweight Utility APIs to target specific shell functionality. UrlEscape and UrlUnescape are used to encode (and decode) a URL containing escape sequences, converting unsafe characters, such as spaces, into their corresponding escape sequences. Unsafe characters are those characters that may be altered during transport across the internet. UrlEscape converts unsafe characters into their equivalent "%xy" escape sequences; UrlUnescape converts them back.

When a URL containing spaces or other escape characters is passed to UrlEscape, the returned string has the escape characters inserted into the string. A URL that might contain unsafe spaces, such as  "\vbnet code library\" is converted to the browser-kind "\vbnet%20code%20library\".  Passing an encoded string to UrlUnescape converts the escape characters back to user-friendly form. 

Several flags are provided to customize the behaviour of UrlEscape and UrlUnescape: 
Flag Description Applies To
URL_ESCAPE_SPACES_ONLY Only escape space characters. This flag cannot be combined with URL_ESCAPE_PERCENT or URL_ESCAPE_SEGMENT_ONLY. UrlEscape
URL_ESCAPE_PERCENT Escape the % character. By default, this character is not escaped. UrlEscape
URL_ESCAPE_SEGMENT_ONLY Escape the sections following the server component, but not the extra information sections following a # or ? character. UrlEscape
URL_DONT_ESCAPE_EXTRA_INFO Don't convert the # or ? character, or any characters following them in the string. UrlEscape, UrlUnescape
URL_UNESCAPE_INPLACE Use pszURL to return the converted string instead of pszUnescaped. UrlUnescape

The string passed to UrlEscape and UrlUnescape can be any URL or file string; they do not require a http:// or file:// prefix to work.

 BAS Module Code
None.

 Form Code
To a form add two command buttons (Command1, Command2), and three text boxes (Text1, Text2, Text2), along with the following code:

Option Explicit
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Copyright 1996-2011 VBnet/Randy Birch, All Rights Reserved.
' Some pages may also contain other copyrights by the author.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Distribution: You can freely use this code in your own
'               applications, but you may not reproduce 
'               or publish this code on any web site,
'               online service, or distribute as source 
'               on any media without express permission.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Private Const MAX_PATH                   As Long = 260
Private Const ERROR_SUCCESS              As Long = 0

'Treat entire URL param as one URL segment
Private Const URL_ESCAPE_SEGMENT_ONLY    As Long = &H2000
Private Const URL_ESCAPE_PERCENT         As Long = &H1000
Private Const URL_UNESCAPE_INPLACE       As Long = &H100000

'escape #'s in paths
Private Const URL_INTERNAL_PATH          As Long = &H800000
Private Const URL_DONT_ESCAPE_EXTRA_INFO As Long = &H2000000
Private Const URL_ESCAPE_SPACES_ONLY     As Long = &H4000000
Private Const URL_DONT_SIMPLIFY          As Long = &H8000000

'Converts unsafe characters,
'such as spaces, into their
'corresponding escape sequences.
Private Declare Function UrlEscape Lib "shlwapi" _
   Alias "UrlEscapeA" _
  (ByVal pszURL As String, _
   ByVal pszEscaped As String, _
   pcchEscaped As Long, _
   ByVal dwFlags As Long) As Long

'Converts escape sequences back into
'ordinary characters.
Private Declare Function UrlUnescape Lib "shlwapi" _
   Alias "UrlUnescapeA" _
  (ByVal pszURL As String, _
   ByVal pszUnescaped As String, _
   pcchUnescaped As Long, _
   ByVal dwFlags As Long) As Long


Private Sub Form_Load()

  'fake address - don't try to navigate to it
   Text1.Text = "http://vbnet.mvps.org/vbnet code lib/net code/ip address.htm"
   Text2.Text = ""
   Text3.Text = ""
   Command1.Caption = "Encode"
   Command2.Caption = "Decode"
   
End Sub


Private Sub Command1_Click()

   Dim sUrl As String
   Dim buff As String

  'use the original string in Text1 for
  'demo, and show encoded results in Text2
   sUrl = Text1.Text
   buff = EncodeUrl(sUrl)
   
   Text2.Text = buff
   

End Sub


Private Sub Command2_Click()

   Dim sUrl As String
   Dim buff As String

  'use the encoded string in text2 for
  'demo, and show decoded results in Text3
   sUrl = Text2.Text
   buff = DecodeUrl(sUrl)
   
   Text3.Text = buff 
   
End Sub


Private Function EncodeUrl(ByVal sUrl As String) As String

   Dim buff As String
   Dim dwSize As Long
   Dim dwFlags As Long
   
   If Len(sUrl) > 0 Then
      
      buff = Space$(MAX_PATH)
      dwSize = Len(buff)
      dwFlags = URL_DONT_SIMPLIFY
      
      If UrlEscape(sUrl, _
                   buff, _
                   dwSize, _
                   dwFlags) = ERROR_SUCCESS Then
                   
         EncodeUrl = Left$(buff, dwSize)
      
      End If  'UrlEscape
   End If  'Len(sUrl)

End Function


Private Function DecodeUrl(ByVal sUrl As String) As String

   Dim buff As String
   Dim dwSize As Long
   Dim dwFlags As Long
   
   If Len(sUrl) > 0 Then
      
      buff = Space$(MAX_PATH)
      dwSize = Len(buff)
      dwFlags = URL_DONT_SIMPLIFY
      
      If UrlUnescape(sUrl, _
                   buff, _
                   dwSize, _
                   dwFlags) = ERROR_SUCCESS Then
                   
         DecodeUrl = Left$(buff, dwSize)
      
      End If  'UrlUnescape
   End If  'Len(sUrl)

End Function
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