Tag Archives: .NET

How to enable sessions in Web API

Web API does not support native HTTP sessions. And it’s the nature of Web API, but there might be times you need HTTP sessions which resembles your bad design. Because a service framework should not support HTTP sessions as it should be a stateless element. So why do we need sessions in Web API ? I think you should not use sessions in Web API in production; eliminate HTTP sessions completely.

So the answer for the question why do we need sessions in Web API is, just to show how you can enable them. Silly though but you can use this in developing some POC and quick functional demos. Never use sessions in Web API because Web API is designed to be stateless.

First we should implement a ControllerHandler which is capable of handling sessions. In order make our ControllerHandler handle sessions we should implement IRequiresSessionState interface as well. Look at the below code.

   1: public class SessionableControllerHandler : HttpControllerHandler, IRequiresSessionState

   2: {

   3:     public SessionableControllerHandler(RouteData routeData) 

   4:         : base(routeData)

   5:     {

   6:  

   7:     }

   8: }

The next step is to create a RouteHandler as a wrapper to the ControllerHandler we created, this is because when registering routes in the RouteTable we can pass RouteHandler types not ControllerHandler types. Look at the below code for the custom RouteHandler.

   1: public class SessionStateRouteHandler : IRouteHandler

   2: {

   3:     public IHttpHandler GetHttpHandler(RequestContext requestContext)

   4:     {

   5:         return new SessionableControllerHandler(requestContext.RouteData);

   6:     }

   7: }

Then finally we have to register our RouteHandler in the RouteTable

   1: RouteTable.Routes.MapHttpRoute(

   2:     name: "DefaultApi",

   3:     routeTemplate: "api/{controller}/{id}",

   4:     defaults: new { id = RouteParameter.Optional }

   5: ).RouteHandler = new SessionStateRouteHandler();

In order to make our custom route to be used we need to put it on top of other route registrations.

AES Cryptography

Contains the code for AES encryption and decryption in C#.

   1: public byte [] EncryptText(string plainData)

   2:         {

   3:             RijndaelManaged rij = new RijndaelManaged();

   4:             

   5:             rij.GenerateKey();

   6:             _key = rij.Key;

   7:  

   8:             rij.GenerateIV();

   9:             _intializationVector = rij.IV;

  10:  

  11:             ICryptoTransform encryptor = rij.CreateEncryptor(_key, _intializationVector);

  12:  

  13:             using (MemoryStream msEncrypt = new MemoryStream())

  14:             {

  15:                 using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))

  16:                 {

  17:                     using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))

  18:                     {

  19:                         swEncrypt.Write(plainData);

  20:                     }

  21:  

  22:                     return msEncrypt.ToArray();

  23:                 }

  24:             }

  25:  

  26:         }

  27:  

  28:  

  29:         public string  DecryptText(byte [] encrytedData)

  30:         {

  31:             RijndaelManaged rij = new RijndaelManaged();

  32:  

  33:             ICryptoTransform decryptor = rij.CreateDecryptor(_key, _intializationVector);

  34:  

  35:             using (MemoryStream msDecrypt = new MemoryStream(encrytedData))

  36:             {

  37:                 using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))

  38:                 {

  39:                     using (StreamReader srDecrypt = new StreamReader(csDecrypt))

  40:                     {

  41:                         return srDecrypt.ReadToEnd();

  42:                     }

  43:                 }

  44:             }

  45:         }

  46:         

  47:     }

checked and unchecked keywords in C#

This post explains about checked and unchecked keywords in C#. In arithmetic calculations when constants are involved compiler detects the overflows in the data types. For example look at the following code.

   1: // int range is from -2,147,483,648 to 2,147,483,647

   2: int i = 2147483647 + 10;

The above will generate a compile time error. But the following won’t and it will give an output –2,147,483,639

   1: int ten = 10;       

   2: int i = 2147483647;

   3: Console.WriteLine(i + ten);

Because the compiler does not detect the overflows when non constants are are involved in the expression.

The above will not even raise an OverflowException. To make sure that the above is validated in runtime, we can use the checked keyword as a block or in line.

As a block

   1: checked

   2: {

   3:     Console.WriteLine(i + 10);

   4: }

Inline

   1: Console.WriteLine(checked(i + 10));

Since checked keyword validates against the overflows and throws an exception, it has a performance hit. So when you are sure that the expression is not going to cause an OverflowException it is better not use the checked keyword.

 

unchecked does the opposite of the checked. It mainly instructs the compiler not to do the validation for an expression. The following would generate a compile time error if it is not enclosed with the unchecked block. As checked keyword unchecked keyword can also be used in blocks and inline.

   1: unchecked

   2: {

   3:     int a = 2147483647 + 10;

   4:     Console.WriteLine(a);

   5: }

Detecting the Windows Phone Theme Background Color

We often need to detect the WP background theme color to switch the color schemes of our apps.

This is very useful when we utilize the application bar and have some metro icons in our app. In built WP apps have this feature and switch between different icons. For example when you use the Messaging app in dark background mode the icons are white and when the background is in light mode. A very simple feature but how to detect the background theme color of the WP.

Here’s the code snippet for this. PhoneBackgroundBrush is a property of the Application.Current.Resources Dictionary object.

private readonly Color _lightThemeBackground = Color.FromArgb(255, 255, 255, 255); private readonly Color _darkThemeBackground = Color.FromArgb(255, 0, 0, 0); private void DetectPhoneTheme() { SolidColorBrush theme = Application.Current.Resources["PhoneBackgroundBrush"] as SolidColorBrush; if (theme.Color == _lightThemeBackground) { btnBack.IconUri = new Uri("Images/backB.png", UriKind.Relative); BtnNext.IconUri = new Uri("Images/nextB.png", UriKind.Relative); BtnShare.IconUri = new Uri("Images/shareB.png", UriKind.Relative); } else { btnBack.IconUri = new Uri("/Images/backW.png", UriKind.Relative); BtnNext.IconUri = new Uri("/Images/nextW.png", UriKind.Relative); BtnShare.IconUri = new Uri("/Images/shareW.png", UriKind.Relative); } } private readonly Color _lightThemeBackground = Color.FromArgb(255, 255, 255, 255); private readonly Color _darkThemeBackground = Color.FromArgb(255, 0, 0, 0); private void DetectPhoneTheme() { SolidColorBrush theme = Application.Current.Resources["PhoneBackgroundBrush"] as SolidColorBrush; if (theme.Color == _lightThemeBackground) { btnBack.IconUri = new Uri("Images/backB.png", UriKind.Relative); BtnNext.IconUri = new Uri("Images/nextB.png", UriKind.Relative); BtnShare.IconUri = new Uri("Images/shareB.png", UriKind.Relative); } else { btnBack.IconUri = new Uri("/Images/backW.png", UriKind.Relative); BtnNext.IconUri = new Uri("/Images/nextW.png", UriKind.Relative); BtnShare.IconUri = new Uri("/Images/shareW.png", UriKind.Relative); } }

Adapter Pattern

Adapter pattern is often mentioned as wrapper in normal convention. It is a pattern which introduces loose coupling when creating a middle interface between two unmatched types. The name itself, self describes itself.  Rolling on the floor laughing

Think we have a class which renders a dataset on the screen. So we’ve a working class like this.

class Renderer { private readonly IDbDataAdapter _adapter; public Renderer(IDbDataAdapter dataAdaper) { _adapter = dataAdaper; } public void Render() { Console.WriteLine("Writing data...."); DataSet dataset = new DataSet(); _adapter.Fill(dataset); DataTable table = dataset.Tables.OfType<DataTable>().First<DataTable>(); foreach (DataRow row in table.Rows) { foreach (DataColumn column in table.Columns) { Console.Write(row[column].ToString()); Console.Write(" "); } Console.WriteLine(); } Console.WriteLine("/n Render complete"); } }

Severe bug is, that it renders only the first table of the DataSet, but forget about the bug as of now and let’s focus on the design. Freezing

Simply Renderer does these things.

  • It has a constructor which takes an IDbDataAdapter and set it to its readonly property.
  • The Render() calls the Fill method of the IDbDataAdapter by passing a DataSet
  • Takes the first table of the DataSet
  • Displays the data

 

So it’s obvious any class that implements IDbDataAdapter would be a perfect candidate for the Renderer class.

Now move on to the scenario. Airplane

Think we have a data object class Game.

public class Game { public string Id { get; set; } public string Name { get; set; } public string Description { get; set; } }

And we have a class for rendering the game objects on the screen.

public class GameRenderer { public string ListGames(IEnumerable<Game> games) { // do the rendering return game.ToString(); } }

We have the Render class to do the rendering work for us. So we do not need to write the same code again. Only thing we’ve to do is connecting GameRenderer to our Renderer.

But we’ve got problems. Steaming mad

  • We need an IDbDataAdapter implementation to use the Renderer.
  • Render() is a parameter less method with no return types, which has to be mapped with the ListGames(IEnumerable<Game> games) which returns a string.

We need to have a class which works between GameRenderer and Renderer. That’s the adapter class we’re going to write. (GameCollectionDBAdapter)

So our GameCollectionDBAdapter should to be an IDbDataAdapter to work with the Renderer. In the other end it should be some other type to conform with the GameRenderer.

Create a new interface called IGameColllectionRenderer. This is the interface which conforms our adapter class with the GameRenderer.

The diagram explains the things clearly.

adapter

Not neat indeed. Shifty

So now you’ve got the idea.

The rest of the code goes here.

Code for IGameColllectionRenderer

public interface IGameColllectionRenderer { string ListGames(IEnumerable<Game> games); }

Code for the GameCollectionDBAdapter which is a IDbDataAdapter and  IGameColllectionRenderer.

public class GameCollectionDBAdapter : IDbDataAdapter, IGameColllectionRenderer { private IEnumerable<Game> _games; public string ListGames(IEnumerable<Game> games) { _games = games; Renderer renderer = new Renderer(this); renderer.Render(); return _games.Count().ToString(); } public int Fill(DataSet dataSet) { DataTable table = new DataTable(); table.Columns.Add(new DataColumn() { ColumnName = "Id" }); table.Columns.Add(new DataColumn() { ColumnName = "Name" }); table.Columns.Add(new DataColumn() { ColumnName = "Description" }); foreach (Game g in _games) { DataRow row = table.NewRow(); row.ItemArray = new object[] { g.Id, g.Name, g.Description }; table.Rows.Add(row); } dataSet.Tables.Add(table); dataSet.AcceptChanges(); return _games.Count(); } }

 

Here IDbDataAdapter is not fully implemented, Fill method alone enough to run the code. But you have to have blank implementations of the other methods with throw NotImplementedException.

A slight change in your GameRenderer

public class GameRenderer { private readonly IGameColllectionRenderer _gameControllerRenderer; public GameRenderer(IGameColllectionRenderer gameCollectionRenderer) { _gameControllerRenderer = gameCollectionRenderer; } public string ListGames(IEnumerable<Game> games) { return _gameControllerRenderer.ListGames(games); } }

Finally the Main method

Thumbs up

class Program { static void Main(string[] args) { List<Game> games = new List<Game>() { new Game() { Id = "2323", Name = "Need for Sleep", Description = "A game for sleepers" }, new Game() { Id = "w4334", Name = "MK4", Description = "Ever green fighter game" } }; GameRenderer gr = new GameRenderer(new GameCollectionDBAdapter()); gr.ListGames(games); Console.ReadKey(); } }

Singleton Pattern

Singleton pattern is a simple design pattern in software practice and sometimes considered as an anti-pattern due its tight coupling nature.

A very simple non thread safe implementation of the Singleton pattern would be like this.

Singleton non thread safe

class Singleton
{
  privatestatic Singleton _instance;
  private Singleton()
  {
    Console.WriteLine(Singleton instantiated);
  }
 
publicstatic Singleton SingletonInstance
{
  get
   {
        if (_instance ==null)
            {
               // delay the object creation to demonstrate the thread saftey.
               Thread.Sleep(1500);
            _instance =new Singleton();
            }
      return     _instance;
  }
 }
}

Run the above class using Main method shown below, you can notice Singleton constructor is called twice by the both threads, since it is not thread safe. ( You can use the same Main methid implementation for all 3 Singleton implementations)

Main method implementation

class Program
{
staticvoid Main(string[] args)
{
new Thread(() => { Singleton sin1 = Singleton.SingletonInstance; }).Start();
Singleton sin2 = Singleton.SingletonInstance;
 
Console.ReadKey();
}
}

Singleton thread safe

Making the above implementation to a thread safe code is not a complex task, we can use our same old locking technique.

class Singleton
{
privatestatic Singleton _instance;
privatestaticobject _lock =newobject();
 
private Singleton()
{
Console.WriteLine(Singleton instantiated);
}
 
publicstatic Singleton SingletonInstance
{
get
{
lock (_lock)
{
if (_instance ==null)
  {
      // delay the object creation to demonstrate the thread saftey.
        Thread.Sleep(1500);
         _instance =new Singleton();
   }
return _instance;
}
}
}
}

The above is a perfect Singleton implementation in C#. But is there any other way that we can have the Singleton behavior without compensating our performance into locking. Because locking is a performance drop for sure.

Singleton C# way  – The trendy way

This is a neat and a trendy way to implement the Singleton.

We do not use locks in this implementation and it is very fast yet purely thread safe.

class Singleton
{
    privatestaticreadonly Singleton _instance;
 
    static Singleton()
    {
             _instance =new Singleton();
     }
 
    private Singleton()
   {
       Console.WriteLine(Singleton instantiated);
    }
 
   public static Singleton SingletonInstance
  {
     get
    {
      return _instance;
     }
  }
}

The magic is, static constructor.

A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed once only. It is called automatically before the first instance is created or any static members are referenced.

To remeber simply you can think that the static constructor is called when the class is loaded.

More about static constructors in this MSDN article.

Sending Email from C#

Pure code is here. You can just copy and use it, and you can understand easily from the comments.

string to = "someone@hotmail.com"; // here the username can be any address // this is the address that the reciever will reply to when he/she hits the Reply button // this doesn't have to be the same as the credential address below. string from = "username@gmail.com"; string subject = "My mail from C#"; string body = "<a href=\"http://www.microsoft.com\"> Click here </a><br/><img src=\"http://t0.gstatic.com/images?q=tbn:2LUYVF-U1KxK2M:http://img.bollywoodsargam.com/albumsbolly/Priyanka_Chopra/Priyanka_Chopra_In_Barsaat_Movie_Stills_002_18_08_2005.jpg\"/>"; System.Net.Mail.MailMessage msg = new System.Net.Mail.MailMessage(from, to, subject, body); msg.IsBodyHtml = true; // adding attachement System.Net.Mail.Attachment at = new System.Net.Mail.Attachment(@"C:\Users\Thurupathan\Desktop\myfile.zip"); msg.Attachments.Add(at); // sending from the gmail account // for the hotmail / live / outlook => smtp.live.com port => 587 System.Net.Mail.SmtpClient smtp = new System.Net.Mail.SmtpClient("smtp.gmail.com", 587); // provide credentials System.Net.NetworkCredential gmailAuthentication = new System.Net.NetworkCredential("username@gmail.com", "password"); smtp.Credentials = gmailAuthentication; // SSL enable based on the smtp.EnableSsl = true; try { smtp.Send(msg); } catch (Exception ex) { Console.WriteLine(ex.Message); }

Asynchronous Programing C# 5.0

C# 5.0 mostly bluff about the asynchronous programming. Of course it has some really kick ass features in the asynchronous programming world.

First of all, asynchronous programing is not new in C# 5.0. It’s been there from C# 1.0, so what’s the big deal now ?

In C# 5.0 they have created a whole new, very tidy and easy programing approach in asynchronous programing. It’s really very tidy.

Here’s a WPF sample application which downloads the headers of an HTTP request and displays in a TextBox. Simply we all know that if we do this without threads our UI will hang until the download operation completes. The solution we’ve been using is threading.

Here I want to make a point; conceptually we all know that using the threads for the above problem will yield the solution for UI unresponsiveness.  But it creates challenges like monitoring the threads and updating the UI, handling exceptions and code untidiness.

Again one more point, when using the threads for the above problem .NET provides various solutions. In Win Forms using the BackgroundWorker is the popular way, in WPF we go for the Dispatcher, we also have our same old IAsyncCallback and delegates mechanism, using the thread pool explicitly, creating and customizing our own threads.

As you see, almost all the above methods are cluttered every where, developers use their own way to handle the problem, not bad but it’s not good either.

And also we have our problems in updating the UI; especially when updating a UI control from a different thread. We get the Cross thread access exceptions.

Here’s the code that shows one way of how the above scenario can be implemented prior to C# 5.0 in WPF.

 private void OldAsyncTechnique()
        {
            SynchronizationContext sync = SynchronizationContext.Current;

            var req = (HttpWebRequest)WebRequest.Create("https://thuruinhttp.wordpress.com");
            req.Method = "HEAD";

            req.BeginGetResponse((asyncResult) =>
            {
                var resp = (HttpWebResponse)req.EndGetResponse(asyncResult);
                sync.Post(delegate
                {
                    TxtHeaders.Text = FormatHeaders(resp.Headers);
                }, null);
            }, null);
        }

Here I get the SynchronizationContext of the current thread, (means the main UI thread) and creates my web request. Then I call the asynchronous BeginGetResponse method of the HttpWebRequest class.

To make the code compact, I called the EndGetResponse in lamda. Using the SynchronizationContext of the UI thread I post the message to the UI control.

But this very complex and I have to pass state object parameters and all. (I have passed null here).

Note : This is not the only way to do this.

 

In C# 5.0 we have new keywords async and await. (You still can enable this in .NET 4 by installing the Async CTP, but since the VS 2012 and .NET 4.5 is released do not waste your time on doing this. You can simply upgrade yourself to .NET 4.5 world)

Here’s the code.

 private async void NewMethod()
        {
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create("https://thuruinhttp.wordpress.com");
            req.Method = "HEAD";
            HttpWebResponse res = (HttpWebResponse) await req.GetResponseAsync();
            TxtHeaders.Text = FormatHeaders(res.Headers);
        }

Simple as that. You declare the method async and make an awaitable type.

When the code hits the await keyword the method returns immediately, and once the await got the results, the method begins the execution from where it left. Simple theory.

But how it is possible, again that is simple inside C# when you compile the above code, C# compiler rewrites the above code in a fine and an efficient old way.

The real working pattern and how things happen are complex and it used the TPL heavily.

Important : Once you install .NET 4.5 you will get the GetResponseAsync() in the WebClient class. And most classes are enriched with these types of async methods in .NET 4.5. We can have our async and await functionality in our custom classed as well.

Here’s the implementation of the FormatHeaders method.

 private string FormatHeaders(WebHeaderCollection collection)
        {
            StringBuilder builder = new StringBuilder();
            foreach (var s in collection.Keys)
            {
                builder.Append(s + " : ");
                builder.Append(collection[s.ToString()].ToString());
                builder.Append(Environment.NewLine);
            }

            return builder.ToString();
        }