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HttpRequest.Filter Property

Gets or sets the filter to use when reading the current input stream.

[Visual Basic]
Public Property Filter As Stream
[C#]
public Stream Filter {get; set;}
[C++]
public: __property Stream* get_Filter();
public: __property void set_Filter(Stream*);
[JScript]
public function get Filter() : Stream;
public function set Filter(Stream);

Property Value

A Stream object to be used as the filter.

Exceptions

Exception Type Condition
HttpException Invalid Stream object.

Example

[Visual Basic, C#] The following example creates two new classes, QQQ1 and QQQ2 that filter the InputStream. Put the classes into the Global.asa file in an ASP.Net application's directory so that all input for all aspx pages in the application will be filtered.

[Visual Basic] 

<%@ Page language="VB" %>
<%@ Import namespace="System.Text" %>
<%@ Import namespace="System.IO" %>

<script runat=server>
' This example is meant to be added to a Global.asax file.

Sub Application_BeginRequest()
   Request.Filter = New QQQ1(Request.Filter)
   Request.Filter = New QQQ2(Request.Filter)
End Sub

' The class QQQ1 changes all lower case alpha chars to upper case.
Public Class QQQ1
   Inherits Stream

   Private _sink As Stream

   Public Sub New(sink As Stream)
      _sink = sink
   End Sub

   ' All MustOverride interface members must be included.
   Public Overrides ReadOnly Property CanRead() As Boolean
      Get 
         Return True
      End Get
   End Property

   Public Overrides ReadOnly Property CanSeek() As Boolean
      Get
         Return False
      End Get
   End Property

   Public Overrides ReadOnly Property CanWrite() As Boolean
      Get
         Return False
      End Get
   End Property

   Public Overrides ReadOnly Property Length() As Long
      Get
         Return _sink.Length
      End Get
   End Property

   Public Overrides Property Position() As Long
      Get
         Return _sink.Position
      End Get
      Set 
         Throw New NotSupportedException()
      End Set
   End Property

   Public Overrides Function Read(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer) As Integer
      Dim c As Integer = _sink.Read(buffer, offset, count)
      Dim i As Integer
      For i = 0 To count - 1
         If buffer(offset+i) >= Asc("a") And buffer(offset+i) <= Asc("z") Then
            buffer(offset+i) = buffer(offset+i) - (Asc("a")-Asc("A"))
         End If
      Next i
      Return c
   End Function

   Public Overrides Function Seek(ByVal offset As Long, ByVal direction As System.IO.SeekOrigin) As Long
        Throw New NotSupportedException()
   End Function

   Public Overrides Sub SetLength(ByVal length As Long)
      Throw New NotSupportedException()
   End Sub

   Public Overrides Sub Close()
      _sink.Close()
   End Sub

   Public Overrides Sub Flush()
      _sink.Flush()
   End Sub

   Public Overrides Sub Write(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer)
      Throw New NotSupportedException()
   End Sub
End Class


' The class QQQ2 changes all E characters to asterisks.
class QQQ2 
   Inherits Stream
    
   Private _sink As Stream

   Public Sub New(sink As Stream)
      _sink = sink
   End Sub

   ' All MustOverride interface members must be included.
   Public Overrides ReadOnly Property CanRead() As Boolean
      Get  
         Return true
      End Get
   End Property

   Public Overrides ReadOnly Property CanSeek() As Boolean
      Get
         Return False
      End Get
   End Property

   Public Overrides ReadOnly Property CanWrite() As Boolean
      Get 
         Return False
      End Get
   End Property

   Public Overrides ReadOnly Property Length() As Long
      Get
         Return _sink.Length
      End Get
   End Property

   Public Overrides Property Position() As Long
      Get
         Return _sink.Position
      End Get  
      Set 
         Throw New NotSupportedException()
      End Set
   End Property

   Public Overrides Function Read(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer) As Integer
      Dim c As Integer = _sink.Read(buffer, offset, count)
      Dim i As Integer
      For i = 0 To count-1
         If buffer(i) = Asc("E") Then
            buffer(i) = Asc("*")
         End If
      Next i
      Return c
   End Function

   Public Overrides Function Seek(ByVal offset As Long, ByVal direction As System.IO.SeekOrigin) As Long
      Throw New NotSupportedException()
   End Function

   Public Overrides Sub SetLength(length As Long)
      Throw New NotSupportedException()
   End Sub

   Public Overrides Sub Close()
      _sink.Close()
   End Sub

   Public Overrides Sub Flush()
      _sink.Flush()
   End Sub

   Public Overrides Sub Write(ByVal buffer() As Byte, ByVal offset As Integer, ByVal count As Integer)
      Throw New NotSupportedException()
   End Sub
End Class


'____________________________________________________________________

' This ASP.NET page uses the request filter to modify all text sent by the 
' browser in Request.InputStream. To test the filter, use this page to take
' the POSTed output from a data entry page using a tag such as: 
' <form method="POST" action="ThisTestPage.aspx">

'<%@ PAGE LANGUAGE = VB %>
'<%@ IMPORT namespace="System.IO" %>

'<html>
'<Script runat=server>

'   Sub Page_Load()
'      Dim str As Stream, strmContents As String
'      Dim counter, strLen As Integer
 
      ' Create a Stream object.
'      str = Request.InputStream

      ' Find number of bytes in stream.
'      strLen = CInt(str.Length)

      ' Create a byte array.
'      Dim strArr(strLen) As Byte 

      ' Read stream into byte array.
'      str.Read(strArr,0,strLen) 
 
      ' Convert byte array to a text string.
'      For counter = 0 To strLen-1
'         strmContents = strmContents & Chr(strArr(counter))
'      Next counter

'      Response.Write("Contents of Filtered InputStream: " & strmContents)
'   End Sub

'</Script>
'</html>

</script>

[C#] 

<%@ Page language="c#" %>
<%@ Import namespace="System.Text" %>
<%@ Import namespace="System.IO" %>

<script runat=server>

// This code is to be added to a Global.asax file.

public void Application_BeginRequest() 
{
   Request.Filter = new QQQ1(Request.Filter);
   Request.Filter = new QQQ2(Request.Filter);
}

class QQQ1 : Stream
{
    private Stream _sink;

    public QQQ1(Stream sink)
    {
        _sink = sink;
    }

    public override bool CanRead
    {
        get { return true; }
    }

    public override bool CanSeek
    {
        get { return false; }
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override long Length
    {
        get { return _sink.Length; }
    }

    public override long Position
    {
        get { return _sink.Position; }
        set { throw new NotSupportedException(); }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
    int c = _sink.Read(buffer, offset, count);

        for (int i = 0; i < count; i++)
        {
            if (buffer[offset+i] >= 'a' && buffer[offset+i] <= 'z')
                buffer[offset+i] -= ('a'-'A');
        }

        return c;
    }

    public override long Seek(long offset, System.IO.SeekOrigin direction)
    {
        throw new NotSupportedException();
    }

    public override void SetLength(long length)
    {
        throw new NotSupportedException();
    }

    public override void Close()
    {
        _sink.Close();
    }

    public override void Flush()
    {
        _sink.Flush();
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
    throw new NotSupportedException();
    }
}

class QQQ2 : Stream
{
    private Stream _sink;

    public QQQ2(Stream sink)
    {
        _sink = sink;
    }

    public override bool CanRead
    {
        get { return true; }
    }

    public override bool CanSeek
    {
        get { return false; }
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override long Length
    {
        get { return _sink.Length; }
    }

    public override long Position
    {
        get { return _sink.Position; }
        set { throw new NotSupportedException(); }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
    int c = _sink.Read(buffer, offset, count);

        for (int i = 0; i < count; i++)
        {
            if (buffer[i] == 'E')
                buffer[i] = (byte)'*';
            else if (buffer[i] == 'e')
                buffer[i] = (byte)'#';
        }
        return c;
    }

    public override long Seek(long offset, System.IO.SeekOrigin direction)
    {
        throw new NotSupportedException();
    }

    public override void SetLength(long length)
    {
        throw new NotSupportedException();
    }

    public override void Close()
    {
        _sink.Close();
    }

    public override void Flush()
    {
        _sink.Flush();
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
    throw new NotSupportedException();
    }
}


/*____________________________________________________________________

This ASP.NET page uses the request filter to modify all text sent by the 
browser in Request.InputStream. To test the filter, use this page to take
the POSTed output from a data entry page using a tag such as: 
<form method="POST" action="ThisTestPage.aspx">


<%@ PAGE LANGUAGE = C# %>
<%@ IMPORT namespace="System.IO" %>

<html>
<Script runat=server>
   void Page_Load()
   {
 
      // Create a Stream object to capture entire InputStream from browser.
      Stream str = Request.InputStream;
   
      // Find number of bytes in stream.
      int strLen = (int)str.Length;

      // Create a byte array to hold stream.
      byte[] bArr = new byte[strLen];

      // Read stream into byte array.
      str.Read(bArr,0,strLen);
 
      // Convert byte array to a text string.
      String strmContents="";
      for(int i = 0; i < strLen; i++)
         strmContents = strmContents + (Char)bArr[i];
     
      // Display filtered stream in browser.
      Response.Write("Contents of Filtered InputStream: <br>" + strmContents);
   }
______________________________________________________________________*/

</script>

[C++, JScript] No example is available for C++ or JScript. To view a Visual Basic or C# example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 2000, Windows XP Professional, Windows Server 2003 family

See Also

HttpRequest Class | HttpRequest Members | System.Web Namespace

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