Change your ASP.NET Form's Action attribute with Response.Filter

Introduction

Sometimes you need to change an ASP.NET page's form's Action attribute. Sure that, there are many ways.. And this is one (simple) of them.

Using the code

Just create a class in the app_code folder, and copy and paste the following lines:

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Text.RegularExpressions;

public class cdsnetFormActionModifier : Stream
{
    private Stream _sink;
    private long _position;
    string _url;
    public cdsnetFormActionModifier(Stream sink, string url)
    {
        _sink = sink;
        _url = "$1" + url + "$3";
    }

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

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

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

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

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

    public override long Seek(long offset, System.IO.SeekOrigin direction)
    {
        return _sink.Seek(offset, direction);
    }

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

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

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

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

    public override void Write(byte[] buffer, int offset, int count)
    {
        string s = System.Text.UTF8Encoding.UTF8.GetString(buffer, offset, count);
        Regex reg = new Regex("(<form.*action=\")([^\"]*)" + 
                              "(\"[^>]*>)", RegexOptions.IgnoreCase);
        Match m = reg.Match(s);
        if (m.Success)
        {
            string form = reg.Replace(m.Value, _url);
            int iform = m.Index;
            int lform = m.Length;
            s = s.Substring(0, iform) + form + s.Substring(iform + lform);
        }
        byte[] yaz = System.Text.UTF8Encoding.UTF8.GetBytes(s);
        _sink.Write(yaz, 0, yaz.Length);
    }
}

And configure the Load event of any page you want, like below:

protected void Page_Load(object sender, EventArgs e)
{
    this.Response.Filter = 
      new cdsnetFormActionModifier(this.Response.Filter, "your_url");
}

Please change the string "your_url" with the client location of your destination page. That's all! Enjoy!