Category Archives: Programming

Don’t forget that Response.End()

While adding some few enhancement on an old project, ASP.NET webform-based API, I was having problem removing the HTML tag output from the API. I have written this project five years ago and I know that you can write a response from an ASPX page without the HTML tags. I simply should use the Response.Clear() or Response.ClearContent(). Response.Clear() is not working?!?!?!

Here is the code that does not output what I want.

protected void Page_Load(object sender, EventArgs e)
{
     //Erases any buffered HTML output
     Response.Clear();
     Response.Write("Hello, API.");
}

If you view the source of the output,

Hello, API.


<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title></title>
    </head>
    <body>
<form method="post" action="NewApi.aspx" id="form1">
<div class="aspNetHidden">
                <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="YpQKYTR2RvrptiLm1lmMsAJwJ//a75ZBpZNGl/rMG5KPseJDjWPtzsRumtqz2U5cLtK9ilxYWrQxgjcxR9VyjfQzP4W4MK8Xgdd753gdoh4=" />
            </div>
<div></div>
<div class="aspNetHidden">
                <input type="hidden" name="__VIEWSTATEGENERATOR" id="__VIEWSTATEGENERATOR" value="F48D0FAC" />
            </div>
        </form>
        <!-- Visual Studio Browser Link -->
        <script type="application/json" id="__browserLink_initializationData">
    {"appName":"Chrome","requestId":"dacea9113ab74bf7a121e7e8599c93a5"}
</script>
        <script type="text/javascript" src="http://localhost:52028/b08ad1d741774013a9875e2b2003daf7/browserLink" async="async"></script>
        <!-- End Browser Link -->
    </body>
</html>

Using my old arsenal of restarting and clearing cache did not work. So I did look up my old code and sure enough I forgot to write the most important line of code. The Response.End()

The working code

protected void Page_Load(object sender, EventArgs e)
{
     //Erases any buffered HTML output
     Response.Clear();
     Response.Write("Hello, API.");
     //Sends all currently buffered output
     //and stops the execution of the page
     Response.End();
}

And I got the correct output.

Hello, API.

So, don’t forget that Response.End();

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C# Extension Methods

As defined by MSDN: Extension methods enable you to “add” methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. It was introduced in .NET 3.5 at the same time with LINQ – which in turn uses Extensions. That’s why all of a sudden, you can now use LINQ against Enumerables even though those objects where never modified.

As defined by me: A very powerful feature that sometimes new developers forget, doesn’t care or doesn’t know about it or don’t quite understand how to create one.

Consider the following scenario. To secure your application credentials at runtime, you decided to use System.Security.SecureString. The content of the SecureString is encrypted while in memory. Read the documentation about SecureString. You cannot assign a string directly to SecureString. It only has a method of AppendChar that accepts one character at a time. So to assign a string, you have to do this.

string s = "MyPassword";
System.Security.SecureString secureString = 
  new System.Security.SecureString();
foreach(char c in s)
{
    secureString.AppendChar(c);
}

Imagine you have to do this over and over in different classes in your code. So you decided to create a public static method and call it every time like this.

public static System.Security.SecureString GetSecureString(string s)
{
    System.Security.SecureString secureString = new System.Security.SecureString();
    foreach (char c in s)
    {
        secureString.AppendChar(c);
    }
    return secureString;
}
static void Main(string[] args)
{
    string unsecuredPassword = "Password123";
    var securePassword = GetSecureString(unsecuredPassword);
}

How about doing it in a more elegant way. Like for example, when you convert the string into lower case, you would do this.

string myString = "Hello World";
string lower = myString.ToLower();

And to convert to SecureString, you would do this.

string unsecuredPassword = "Password123";
var securePassword = unsecuredPassword.ToSecureString();

If you add ToSecureString() into your existing string, it will not compile. Because ToSecureString() is not a method or extension of string by default. We have to create an extension method to be able to do this.

To create an extension

  1. Create a public static class
  2. Create a public static method with the parameter you wish to extend. In this example,  the string object.
  3. Put the this keyword before the object you are extending.
  4. Don’t forget the this

See example below.


public static class StringExtension
{
   public static System.Security.SecureString ToSecureString(this String s)
   {
       System.Security.SecureString secureString = 
       new System.Security.SecureString();
       foreach(char c in s)
       {
           secureString.AppendChar(c);
       }
       return secureString;
   }
 }

And now, to use it…

    

 class Program
 {
     static void Main(string[] args)
     {
         string unsecuredPassword = "Password123";
         var securePassword = unsecuredPassword.ToSecureString();
         Console.Read();
     }
 }
        

Creating extension methods is easy after all. But don’t overdo it! Enjoy coding!

C# 5.0 Asynchronous Programming with async and await

The introduction of async and await in C# 5.0 makes asynchronous programming a breeze. In contrast with traditional asynchronous technique that is complicated. However, you need to understand how the new technique works and how to implement it properly.

First, lets see the code snippet below. A method that returns something.

        async Task<int> GetTotalCustomerAsync()
        {
            //the data to be returned
            int result = 0;
            using (SqlConnection conn = new SqlConnection("..."))
            {
                using (SqlCommand cmd = new SqlCommand("....", conn))
                {
                    //open the connection asynchronously
                    await conn.OpenAsync();
                    //execute the query
                    Object obj = await cmd.ExecuteScalarAsync();
                    //convert the result
                    if(obj!=null)
                    {
                        int.TryParse(obj.ToString(), out result);
                    }                    
                }
            }
            //return the result
            return result;
        }

Pointers:

  1. The method signature includes an async modifier
  2. The method must not return void. Except when you’re writing an async event handler.
  3. The method must return Task<TResult> or Task if it returns nothing.
  4. The method must have at least one await operator.
  5. By convention, the method ends with Async suffix. So that you will easily identify that the method is asynchronous and can be awaitable as you can see in the succeeding example.
  6. await can only be used to an asynchronous method provided by the type. e.g. SqlCommand.ExecuteNonQueryAsync(). Hence, you cannot await SqlCommand.ExecuteNonQuery();

Just follow the pointers and method signature above and you can implement an asynchronous programming technique easily. As stated in Pointers #4, there must be at least one await operator. The next question now is what if I have my own method but I can’t use the await operator inside because there is nothing asynchronous inside that I can call and I want that my method to be asynchronous? An example would be:

        double Compute()
        {
            double result = 0;
            //very extensive computation with I/O and it may take a while
            //the computed value is stored to result
            return result;
        }

        void MyMethod()
        {
            double finalResult = Compute();
        }

        //decorating with async and await like this
        //will not compile at all as noted in the pointers above
        //because Compute is not async and awaitable
        async Task MyMethod()
        {
            double finalResult = await Compute();
        }


TaskCompletionSource to the rescue. As defined by MSDN, “Represents the producer side of a Task unbound to a delegate, providing access to the consumer side through the Task property.” It is a little bit hard to understand but applying it in the example, I hope you can grasp the idea.

        Task<double> ComputeAsync()
        {
            double result = 0;

            //create a task completion source
            //the type of the result value should be the same
            //as the type in the returning Task            
            TaskCompletionSource<double> taskCompletionSource = new TaskCompletionSource<double>();

            //create and run the extenstive computation in background task
            //to complete taskCompletionSource.Task
            Task.Run(() =>
              {
                  try
                  {
                      //very extensive computation with I/O and it may take a while
                      //the computed value is stored to result
                      //....                      
                      //set the result to TaskCompletionSource
                      taskCompletionSource.SetResult(result);
                  }
                  catch (Exception ex)
                  {
                      //pass the exception to TaskCompletionSource
                      //for proper handling
                      taskCompletionSource.SetException(ex);
                  }
              }
            );
            //return the Task
            return taskCompletionSource.Task;
        }

Implementing an asynchronous programming is now easier than before. Likewise, you can make your own method to run asynchronously easily, too. However, it doesn’t mean that you have to convert all your methods to run asynchronously. In my own experience, I only convert those methods that require I/O and CPU extensive tasks that may complete for more than 50 milliseconds.