ASP .NET Hacks, Tips and Tricks

Get Google Search Results in RSS Format

2009-01-10T04:05:00.000+05:00

Here is my attempt to transform Google Search Results into a RSS feed. This functionality is missing from Google. Test it out and provide some feedback. I have published the feed as a web service at

http://www.ecubicle.net/gsearch_rss.asmx

There is a single function called GetSearchResults with the following signature

GetSearchResults(byval searchPage As string, byval gQuery As String, byval numOfResults As String)

searchPage provides the google search page that runs in multiples of 10 with 10 results each page (default on Google). The value for first page is 0

gQuery is google query. You can use any set of Google operators here to tune the query

numOfResults is the number of results to return per page. Default is 15.

The returned XML is RSS 2.0 compliant. As such, any feed reader can also read the returned XML document.

Using in a Feed Reader

To call this in a feedreader, here is the GET syntax for the web service

http://www.ecubicle.net/gsearch_rss.asmx/GetSearchResults?searchPage=0&gQuery=tutorial+asp+net&numOfResults=15

In the above, replace the parameter values shown in red with the your query values.

Read Google Maps KML using LINQ in ASP .NET to Show Driving Directions

2009-01-05T10:21:00.003+05:00

We can use LINQ to query the Google Maps KML File. The magic piece is the Google Maps URL to retrieve KML.

http://maps.google.ca/?q=From 25 King St. West, Toronto, ON to Niagara Falls, Ontario&output=kml

Dim fromAddress = "25 King St. West, Toronto, ON"
Dim toAddress = "Niagara Falls, ON"
Dim urlString As String = "http://maps.google.ca/?q=From " & fromAddress & " to " & toAddress & "&output=kml&view=text"
Dim xmlDataSource2 As New XmlDataSource()
xmlDataSource2.DataFile = urlString

Dim xdoc As XDocument = XDocument.Parse(xmlDataSource2.GetXmlDocument().InnerXml)
Dim ns As XNamespace = XNamespace.Get("http://earth.google.com/kml/2.0")
Dim ele = xdoc.Element(ns + "kml").Element(ns + "Document").Elements(ns + "Placemark").Elements(ns + "name")

GridView1.DataSource = ele.Take(ele.Count - 1)
GridView1.DataBind()

Youtube Downloading - Web Service

2009-01-05T02:40:00.002+05:00

Here is an interesting web service that allows applications to download youtube videos. Applications that require interaction with youtube can obviously use the YouTube API's to provide exhaustive youtube functionality right from their web sites. However, the only API function that is missed is the ability to download from Youtube.

The Youtube web service provides this missing functionality.

The service is located at http://www.ecubicle.net/youtubedownloader.asmx

What the service does is provide the download URL for any video on Youtube. .NET applications can then use any method to access the download URL and download the file. For example, WebClient.DownloadFile() method can be used to download the file directly if the returned URL is passed to DownloadFile.

Very interesting.

Command Window in Visual Studio 2008

2008-07-10T04:15:00.001+06:00

As we develop applications in a particular IDE, it becomes imperative that we come to terms with the technical details of the IDE itself. Features like shortcuts can prove big time saves when working in huge projects. In this post, I want to discover the command window feature in Visual Studio 2005 and 2008.

Command window allows working with the IDE using commands, instead of using the mouse and the IDE menu. Some times it is just quicker to pop open the command window and perform routine tasks, such as opening and saving files, creating aliases for other windows, reading and setting the value of a variable during debugging.

Once in a while my IDE would get messed up and I would lose my solution explorer. By having an alias for it, I simply open up the command window and get straight to any window that I need. Now, solution explorer does have its shortcut (Ctrl-Alt-L), but I am not very keen about these "3keyed shortcuts". For those of us that are used to the more traditional Dos Prompt Style, command window makes us feel right at home with its command features.

Command window can be accessed using the shortcut Ctrl-Alt-A.

Lets get down and dirty and see some useful features that have helped me. I am sure you would find them useful as well.

Creating Aliases

Aliases allow us to define a shorter name for a command. So, for example, we can define an alias to open up Server Explorer using the alias syntax like this:

alias se View.ServerExplorer

Now, lets have a look at our created alias. Simply type alias and press Enter to see a list of all aliases defined in the environment.

The alias command gives us a list as show in the image above. Notice our newly created alias highlighted.

To run this alias, simply type se on an empty line in the command window and the Server Explorer opens up for us.

To delete an alias, type in: alias se /delete as shown below.

Command window has other useful uses as well. I will leave those for another post.

FTPing with ASP .NET

2008-07-07T22:50:00.001+06:00

The framework provides us with various techniques to connect with FTP servers and interact with them. In this post, I will go over some of the ways and we will see how to add functionality to a FTP client.

Here is a limited class for our FTP. It has three methods: listFiles, makeDirectory and deleteDirectory.

 1 Imports Microsoft.VisualBasic
 2 Imports System.IO
 3 Imports System.Net
 4 
 5 
 6 Public Class ftpclientcode
 7     Protected myftprequest As FtpWebRequest
 8     Protected myftpresponse As FtpWebResponse
 9     Private _myserver As String
10     Private _myuser As String
11     Private _mypw As String
12 
13     Public Sub New(ByVal myserver As String, ByVal myuser As String, ByVal mypw As String)
14         _myserver = myserver
15         _myuser = myuser
16         _mypw = mypw
17         myftprequest = WebRequest.Create(_myserver)
18         myftprequest.Credentials = New NetworkCredential(_myuser, _mypw)
19 
20     End Sub
21 
22 
23     Public Function ListFiles() As Stream
24         myftprequest.Method = WebRequestMethods.Ftp.ListDirectory
25         myftpresponse = myftprequest.GetResponse()
26         Return myftpresponse.GetResponseStream()
27 
28     End Function
29 
30     Public Sub MakeDirectory(ByVal mydirname As String)
31 
32         myftprequest.Method = WebRequestMethods.Ftp.MakeDirectory
33         myftpresponse = myftprequest.GetResponse()
34 
35     End Sub
36 
37     Public Shared Sub Close()
38         ' myftpresponse.Close()
39 
40     End Sub
41 
42     Public Sub DeleteDirectory(ByVal mydirname As String)
43         myftprequest.Method = WebRequestMethods.Ftp.RemoveDirectory
44         myftpresponse = myftprequest.GetResponse()
45 
46     End Sub
47 
48 
49 End Class

And here is the Default.aspx page to work with our class

 1 Imports System.Net
 2 Imports System.IO
 3 
 4 Partial Class _Default
 5     Inherits System.Web.UI.Page
 6 
 7     Private servername As String = "localhost"
 8     Private myusername As String = "rafayali"
 9     Private mypassword As String = "******"
10 
11 
12     Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
13         Dim myftp As New ftpclientcode("ftp://" & servername, myusername, mypassword)
14         Label1.Text = ""
15         Dim datastream As Stream = myftp.ListFiles()
16         Dim reader As New StreamReader(datastream)
17         While Not reader.EndOfStream
18             'Response.Write(reader.ReadLine() & "<br/>")
19             Label1.Text = Label1.Text & "&nbsp;&nbsp;?&nbsp;&nbsp;&nbsp;" & reader.ReadLine() & "<br/>"
20         End While
21         'myftp.Close()
22     End Sub
23 
24     Protected Sub createdir_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles createdir.Click
25         Panel1.Visible = False
26         Panel2.Visible = False
27         Panel3.Visible = True
28         TextBox1.Focus()
29     End Sub
30 
31     Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles createbutton.Click
32         Panel3.Visible = False
33         Panel1.Visible = True
34         Panel2.Visible = True
35         Dim myftp As New ftpclientcode("ftp://" & servername & "/" & TextBox1.Text, myusername, mypassword)
36         Try
37             myftp.MakeDirectory(TextBox1.Text)
38             Page_Load(sender, e)
39         Catch ex As Exception
40             Response.Write(ex.Message.ToString())
41         Finally
42             'myftp.Close()
43         End Try
44     End Sub
45 
46     Protected Sub cancelbutton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cancelbutton.Click, Button2.Click
47         Panel1.Visible = True
48         Panel2.Visible = True
49         Panel3.Visible = False
50         Panel4.Visible = False
51     End Sub
52 
53     Protected Sub removedir_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles removedir.Click
54         Panel1.Visible = False
55         Panel2.Visible = False
56         Panel4.Visible = True
57         TextBox2.Focus()
58     End Sub
59 
60     Protected Sub Button1_Click1(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
61         Panel4.Visible = False
62         Panel1.Visible = True
63         Panel2.Visible = True
64 
65         Dim myftp As New ftpclientcode("ftp://" & servername & "/" & TextBox2.Text, myusername, mypassword)
66         Try
67             myftp.DeleteDirectory(TextBox2.Text)
68 
69         Catch ex As Exception
70             Response.Write(ex.Message.ToString())
71 
72         End Try
73         Page_Load(sender, e)
74     End Sub
75 
76     Protected Sub Page_Unload(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Unload
77 
78 
79     End Sub
80 End Class
81

Web.Config Code Snippets

2008-07-07T09:00:00.001+06:00

I was going through some old projects yesterday and came across some interesting web.config settings that I thought would be a good read. So, without further ado, here are some useful code snippets.

Set The Upload File Size to 128KB for a Particular Page

1 <configuration>
2   <location path="myFileUploadPage.aspx">
3     <system.web>
4       <httpRuntime maxRequestLength="128"/>
5     </system.web>
6   </location>
7 </configuration>

Bringing an Application Offline

1 <configuration>
2 <system.web>
3  <httpRuntime enable="false" />
4 </system.web>
5 </configuration>

Encrypting Database Passwords using MD5

2008-07-07T08:35:00.001+06:00

Today, I will show you a very basic technique to encrypt database passwords for storage using MD5 algorithm. MD5 is a one-way algorithm; decrypting is almost next to impossible. One very important characteristic of this algorithm is that a particular text value would always result in the same encrypted value. Therefore, even though the encrypted value cannot be decrypted directly, we do have a way to verify such passwords.

Let us get down straight to code and see for ourselves:

 1 Dim connectionString As String = "Data Source=.\SQLEXPRESS;AttachDbFilename=D:\rafay\projects\certification\encrypt\App_Data\members.mdf;Integrated Security=True;User Instance=True"
 2 
 3         Dim sqlStatement As String = "INSERT INTO users VALUES(@myuser,@mypassword)"
 4         Using objConn As SqlConnection = New SqlConnection(connectionString)
 5             Using objComm As SqlCommand = New SqlCommand(sqlStatement, objConn)
 6                 Dim userNameParameter As New SqlParameter("@myuser", Data.SqlDbType.NVarChar, 15)
 7                 userNameParameter.Value = "Test"
 8 
 9                 Dim passwordParameter As New SqlParameter("@mypassword", Data.SqlDbType.Binary, 16)
10                 passwordParameter.Value = encryptPasswordWithMD5("TestAccountPassword")
11 
12                 Dim objCommParameterArray() As SqlParameter = {userNameParameter, passwordParameter}
13                 objComm.Parameters.AddRange(objCommParameterArray)
14 
15                 objConn.Open()
16                 Dim result As Integer = objComm.ExecuteNonQuery()
17             End Using
18         End Using
19

This is our very basic example of connecting to SQL Server Express database file called members.mdf. We set up a sql statement and two parameters for username and password. The important part to look at is that the password is first encrypted using our helper function called encryptPasswordWithMD5. Another thing to note is that the database field for password is defined as a binary type of length 16. Once the parameters are defined and their values set, a parameter array is formed and then added to the SQLCommand object. The record is finally inserted with a call to ExecuteNonQuery.

Let us now have a look at our encryptPasswordWithMD5 function.

 1 Private Function encryptPasswordWithMD5(ByVal stringToEncrypt As String) As Byte()
 2         Dim MD5Encrypter As New MD5CryptoServiceProvider()
 3         Dim stringBytes() As Byte = convertStringToBytes(stringToEncrypt)
 4         Dim bufferToHoldEncryptedData() As Byte = Nothing
 5 
 6         bufferToHoldEncryptedData = MD5Encrypter.ComputeHash(stringBytes)
 7 
 8         Return bufferToHoldEncryptedData
 9     End Function
10 
11     Private Function convertStringToBytes(ByVal stringToConvert As String) As Byte()
12         Return Text.Encoding.UTF8.GetBytes(stringToConvert)
13     End Function

Line 3 of the code above is of particular interest. Since the ComputeHash method of MD5CryptoServiceProvider class takes in a byte value, our very first task is to convert the password string into a byte. This is accomplished using our second helper function convertStringToBytes (also defined in the listing above). What convertStringToBytes does is to take a string value and return the bytes using GetBytes method of the Encoding class in System.Text namespace. Once this is done, we calculate the hash and store in a buffer and return this buffer.

So, how do we actually verify the credentials since there is no way to decrypt? Well, since MD5 always results in the same hash for the same text, we can encode the text again and compare this against the value in the database. Code sample follows:

 1 Public Function checkPassword(ByVal userName As String, ByVal myPassword As String) As Boolean
 2         Dim connectionString As String = "Data Source=.\SQLEXPRESS;AttachDbFilename=D:\rafay\projects\certification\encrypt\App_Data\members.mdf;Integrated Security=True;User Instance=True"
 3         Dim result As Integer = 0
 4         Dim sqlStatement As String = "SELECT count(*) from users Where myuser=@myuser AND mypassword=@mypassword"
 5         Using objConn As SqlConnection = New SqlConnection(connectionString)
 6             Using objComm As SqlCommand = New SqlCommand(sqlStatement, objConn)
 7                 Dim userNameParameter As New SqlParameter("@myuser", Data.SqlDbType.NVarChar, 15)
 8                 userNameParameter.Value = userName
 9 
10                 Dim passwordParameter As New SqlParameter("@mypassword", Data.SqlDbType.Binary, 16)
11                 passwordParameter.Value = encryptPasswordWithMD5(myPassword)
12 
13                 Dim objCommParameterArray() As SqlParameter = {userNameParameter, passwordParameter}
14                 objComm.Parameters.AddRange(objCommParameterArray)
15 
16                 objConn.Open()
17                 result = CInt(objComm.ExecuteScalar())
18             End Using
19         End Using
20         If result > 0 Then
21             Return True
22         Else
23             Return False
24         End If
25     End Function
26 End Class

In the first code above, I have hardcoded the username and password values. These would naturally need to be changed and the source of input would be probably be a CreateUserWizard or another composite control with various textboxes. The values were hardcoded for simplicity.

ASP .NET Cheat Sheets

2008-07-07T02:15:00.001+06:00

Here I have collected various cheat sheets for download. I do not recall the exact sources from where they were downloaded. If you download a sheet and know the source, let me know and I will mention it in this post.

Regular Expressions Cheat Sheet (pdf)

Page Life Cycle (pdf)

ASP .NET 2.0 Life Cycle (png)

ASP .NET Tips and Tricks (ppt): Microsoft ASP .NET Team presentation

VS 2005 Code Snippets (pdf)

Health Monitoring Class Diagram (bmp): Scott Mitchell's article on Health Monitoring at 4GuysFromRolla

ASP .NET Membership Database Schema (png)

Visual Basic 2005 Default Key Bindings (pdf)

Visual Basic 2008 Default Key Bindings (pdf)

Health Monitoring Event Codes (png)

I will update these listings, if and, when I come across new sheets. If you know of any, please let me know and I will link them here.

This post is accessible from the sidebar in the future.

Compressing ViewState

2008-07-04T04:28:00.001+06:00

Viewstate is a client-side "state management" method. Viewstate allows page and control data to be preserved between postbacks.

When client side HTML is generated for the page, the current state and data of the page is serialized into base64-encoded strings and stored as hidden field(s) in the page. Viewstate is page specific; that is, once you navigate away from the page, the viewstate is lost.

Hangman Game - An Exercise in Learning

2008-07-04T03:28:00.001+06:00

With ample time on hand past Saturday, I decided to dig up some past tutorials just to refresh some material that may have slipped my mind. I have found that going through old stuff once in a while is a handy way to polish ASP .NET skills - or any programming environment for that matter. So, the first time that caught my eye was a Hangman tutorial by Scott Mitchell at 4GuysFromRolla. 4GuysFromRolla is a great place to learn about ASP .NET; I do a tutorial every night or every week (depending on the complexity and the series) to stay current with this ever changing dynamic platform.

I decided to use the Hangman tutorial and re-code it using different classes and logic. Here are parts and pieces of the changed code that I would like to share with the readers here. I have kept the method names same as the one found on 4GuysFromRolla for easy comparison.

 1 Protected Sub generateLetterBoard()
 2         'generates the letters from A-Z and creates linkbuttons 
 3         'called in page_PreInit() 
 4 
 5         Dim i As Integer = 0
 6         Dim j As Integer = 65
 7 
 8         For i = 0 To 25
 9             If j < 92 Then
10                 Dim myLinkButton As New LinkButton()
11                 myLinkButton.ID = ChrW(j).ToString()
12                 myLinkButton.Text = ChrW(j).ToString()
13                 myLinkButton.CommandArgument = ChrW(j).ToString()
14                 AddHandler myLinkButton.Command, AddressOf LetterGuessed
15                 form1.Controls.Add(myLinkButton)
16             End If
17             j = j + 1
18         Next
19     End Sub

As you can see, instead of creating link buttons singularly in the source view, I took the approach of dynamically creating the link buttons. What the above snippet does is it declares a variable to loop 26 times for each alphabet in the English language. The inner loop then executes to display letters; letters are extracted from their ASCII values (65 represents an uppercase A, 90 represents an uppercase Z). The inner loop, then, create a link button, and assigns its Text, ID, and CommandArgument properties. It then adds an event handler to handle the Command event. Command event is raised each time that a link button is clicked. Finally, the link button is added to the form's controls collection.

Here is an ASCII chart for reference (taken from http://www.cdrummond.qc.ca/cegep/informat/Professeurs/Alain/files/ascii.htm).

The second piece of code that I changed was getRandomWordFromTextFile() method. Here's the implementation:

 1 Protected Function getRandomWordFromTextFile(ByVal filePath As String) As String
 2         'Dim myFileStream As New FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read)
 3         'Dim words As New ArrayList()
 4         'Dim myStreamReader As New StreamReader(myFileStream)
 5 
 6         'While myStreamReader.Peek > -1
 7         '    words.Add(myStreamReader.ReadLine())
 8         'End While
 9 
10         'myFileStream.Close()
11         'myStreamReader.Close()
12 
13         'Dim randomNumberGenerator As New Random()
14         'Dim randomNumber As Integer = randomNumberGenerator.Next(words.Count)
15         'Dim chosenWord As String = words(randomNumber)
16         'Return chosenWord
17 
18         'THE FOLLOWING USES OLEDBDATAADAPTER TO READ THE TEXT FILE AND RETURN RANDOM WORD
19 
20         Dim ds As DataSet
21         Dim chosenWord As String = ""
22 
23         If Not Page.IsPostBack Then
24             Dim objConn As New OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=" & filePath & ";extended properties='text;hdr=yes;'")
25             Dim objAdapter As New OleDbDataAdapter("SELECT * FROM WORDS.txt", objConn)
26             ds = New DataSet()
27             objAdapter.Fill(ds)
28             Dim randomNumberGenerator As New Random()
29             Dim randomNumber As Integer = randomNumberGenerator.Next(ds.Tables(0).Rows.Count)
30             chosenWord = ds.Tables(0).Rows(randomNumber).Item(0).ToString()
31 
32         End If
33 
34         Return chosenWord
35       
36 
37 
38     End Function

Instead of using a TextReader, I opted for an OleDBDataAdapter to perform the task of connecting to the text file. A random value is then extracted from the dataset; random row is selected and the value in the first column is set as the Hangman word.

The remainder of the code is similar.

MSDN Hackable URLs

2008-07-04T03:09:00.001+06:00

An extremely useful tip to know is that the new MSDN2 urls are hackable. What this means is that you can access them via a namespace.class convention.

So, for example, lets assume we need documentation for System.Data.OLEDB namespace. We have a lot of options; the first one usually being Google.

With the MSDN2, we can also try this:

http://msdn2.microsoft.com/en-us/library/system.data.oledb.aspx

The URL above would take you straight to the documentation. So, what if we wanted to look up OleDbCommand Class? Well, we can just follow the namespace.class convention to look it up using the following URL:

http://msdn2.microsoft.com/en-us/library/system.data.oledb.oledbcommand.aspx

Pretty Neat, huh? A small but rather neat trick by Microsoft to make life easy when searching for documentation.

Making an application go offline: App_Offline.htm

2008-06-30T10:59:00.006+06:00

The easiest way an application can be made to go offline is by adding a little known file to your ASP .NET project. The file is called App_Offline.htm and needs to be placed in the root of the application. Just by including this file within your project:

the application shuts down
all requests then return the app_offline.htm file's contents

There is one thing to watch out for; and that is the size of this file. If the size is less than 512 bytes, the Friendly Error Messages must be turned off in IE for this to work (image shown below).

Otherwise, the file can be enlarged to this size by placing arbitrary data in it. Since it is a simple html file, I do not see a reason to include sample code. The file can hold any content you wish to show users when an application goes offline.

There are other methods to shut down an application as well; for example, using the web.config:

1 <configuration>
2 <system.web>
3 <httpRuntime enable="false" />
4 </system.web>
5 </configuration>
6

Or, by using this statement in your code-behind:

System.Web.HttpRuntime.ShutDownAppDomain()

It must also be remembered that the application is also shut down when one of the following occur:

web.config file is changed
global.asax file is changed
change in the App_Code directory
change in the \bin directory
when a directory is deleted

Cookieless sessions and dynamic hyperlinks

2008-06-29T07:31:00.007+06:00

When using cookieless Forms Authentication where session values are embedded and maintained in the URL, the session value must be continuously maintained within the URL for each page request. Otherwise, the session is lost. Once this session value is lost, the user (who has logged in and authenticated) gets logged out and has to pass through the authentication mechanism once more.

This maintenance of session values in the URL is automatically taken care of by ASP .NET for us in all situations where the URL DOES NOT START with either http:// or /. That means, most cases are covered.

However, there are cases when this does not hold true. I came across one such case recently.

The requirement was to run through the Site Map file and dynamically create hyperlinks within different panel controls on a page. The requirement was simple enough and all that I had to do was to use the SiteMap Class's methods to retrieve child nodes from the CurrentNode and create hyperlink server controls in code. So, the code to create the hyperlink looked something like this:

1 Dim contentHyperlink as new hyperlink()
2 contentHyperlink.navigateUrl=mySiteMapNodeCollectionObject.url
3 panel1.controls.add(contentHyperlink)

However, in this case, ASP .NET does not maintain the session id for us in the URL. If you take a moment to look at the page source, you would find that all URLS are absolute in the dynamically generated hyperlinks. As stated previously, if a URL is absolute (that is, starts with http://), session values would not be appended to the URL automatically.

To resolve this issue, we need to change the navigateUrl property assignment like this:

contentHyperlink.navigateUrl=Response.ApplyAppPathModifier(mySiteMapNodeCollectionObject.url)

What ApplyAppPathModifier does is it takes the hyperlink and embeds session value in it. The method takes virtual path as its parameter and only works if you are using cookieless session. That is, the web.config must declare session configuration as follows:

For a complete reference, visit MSDN

Show Footer in ASP .NET

2008-06-29T00:26:00.014+06:00

Here is a useful tip if you want to show a uniform footer in all pages, including any subdirectories, from a central location.

Add a new Global Application Class (Global.asax) to your application.

If you have Visual Studio, the IDE generates commonly used Application and Session events. Now which event to use?

Application_Start and End do not serve our purpose since we want the footer to show on each and every request, not only when the application is starting or ending. Application_Error, obviously is there to tap into any unhandled exceptions at the page level.

Lets have a re-look at what our requirements are:

We would like to be able to display a footer message with each and every request under any subfolder of our site. Think of how shared web hosting companies display banner ads on every user's web pages. As soon as you create a page with them, the banner ad is automatically appended to your page - without you having to write a single line of code to do that. Yes, we would like our application to have the exact same capability.

ASP .NET makes this really simple for us. What we need to do is to add a new event declaration and definition in global.asax. Note, new does not mean that we are raising a custom event. What it means is that we need to add an event that has not automatically been added for us by the IDE when we added Global.asax.

The event we are interested in is: Application_EndRequest.

Let's get into code right away and then I will discuss some salient features of this event:

 1 Sub Application_EndRequest(ByVal sender As Object, ByVal e As EventArgs)
 2        With Response
 3             .Write(String.Format("<div width='{0}' style='{1}'>", Unit.Percentage(100), "text-align:center;"))
 4             .Write(String.Format("<img src='{0}' alt='{1}'  />", "footer2.jpg", "Footer"))
 5             .Write("<div>")
 6         End With
 7 End Sub

Application_EndRequest, as the name suggests, is the last event where we have an opportunity to modify what is sent to the client.

What this does is add an image tag and set its source (src) property to the name of the image that we want to display.