Replace string in Response 1

[MrGandalf]

Hi,

Can anyone tell me how I can replace a string in the Response? And in which event to do this.

I have a 3party tool that injects some javascript function into the page. I want to filter this function.

Thanks in advance.

 

[NoCoolHandle]

Response.write("Some sttring".replace("sttring","String"))

 

[MrGandalf]

That's not what I mean. I want to replace a string that is already in the Response object.

 

[BoulderBum]

You'd want to make an HttpModule and hook into the PreSendRequestContent event (or some other event).

http://msdn.microsoft.com/library/d...us/cpguide/html/cpconhandlingpublicevents.asp

This will let you intercept the request for manipulation before it's sent to the client. Just be sure that it's added after the third-party utility so it processes the request after the third-party tool executes.

 

[MrGandalf]

Ok, let us asume I have intercept the Request. And there is a string: "I'm a string" in that Request. I want to replace that string "I'm NOT a string anymore".

What is the syntax to do this? Thus Request. what?

 

[TipGiver]

Hi,

I do not know how to do this or even if it is possible! Although you could use a label (asp control). Then you have to do: label1.text="I'm NOT a string anymore"


Hope i helped

 

[BoulderBum]

Okay, so part of the original suggestion was flawed: in the PreSendRequestContent event, the response stream is actually write-only so you'd need a slightly different strategy.

The trick still involves an HttpModule, but you'd actually hook the Init event and plug in a different response filter object:

// ---------------------------------------------
public void Init (HttpApplication app)
{
 app.ReleaseRequestState += new EventHandler(InstallResponseFilter);
}

// ---------------------------------------------
private void InstallResponseFilter(object sender, EventArgs e) 
{
 HttpResponse response = HttpContext.Current.Response;

 if(response.ContentType == "text/html")
       response.Filter = new PageFilter (response.Filter);
}

The filter itself would store up the buffered response output until it's complete and ready to send, then before sending, you'd run a string replace function. Here's the code for the filter:

using System;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;
using System.Web;

namespace AspNetResources.Web
{
/// <summary>
/// PageFilter does all the dirty work of tinkering the 
/// outgoing HTML stream. This is a good place to
/// enforce some compilancy with web standards.
/// </summary>
public class PageFilter : Stream
{
    Stream          responseStream;
    long            position;
    StringBuilder   responseHtml;

public PageFilter (Stream inputStream)
{
    responseStream = inputStream;
    responseHtml = new StringBuilder ();
}

#region Filter overrides
public override bool CanRead
{
    get { return true;}
}

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

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

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

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

public override long Length
{
    get { return 0; }
}

public override long Position
{
    get { return position; }
    set { position = value; }
}

public override long Seek(long offset, SeekOrigin origin)
{
    return responseStream.Seek (offset, origin);
}

public override void SetLength(long length)
{
    responseStream.SetLength (length);
}

public override int Read(byte[] buffer, int offset, int count)
{
    return responseStream.Read (buffer, offset, count);
}
#endregion

#region Dirty work
public override void Write(byte[] buffer, int offset, int count)
{
    string strBuffer = System.Text.UTF8Encoding.UTF8.«
                              GetString (buffer, offset, count);

    // ---------------------------------
    // Wait for the closing </html> tag
    // ---------------------------------
    Regex eof = new Regex ("</html>", RegexOptions.IgnoreCase);

    if (!eof.IsMatch (strBuffer))
    {
        responseHtml.Append (strBuffer);
    }
    else
    {
        responseHtml.Append (strBuffer);
        string  finalHtml = responseHtml.ToString ();

        [b]
        //here's where you'd manipulate the response.
        finalHtml = finalHtml.Replace( "blah", "whatever" ); [/b]

        byte[] data = System.Text.UTF8Encoding.UTF8.«
                              GetBytes (finalHtml);
        
        responseStream.Write (data, 0, data.Length);            
    }
}
#endregion

This goes into greater detail:

http://www.aspnetresources.com/articles/HttpFilters.aspx.

 

[MrGandalf]

Thanks Boulderbon,

I will test it and let you know. It seems doable.

 

[MrGandalf]

Tx, BoulderBum. It works.