Friday, 30 October 2015

Creating a socket-based echo server and client

Sockets in C# are flexible and efficient way of creating communication between a client and server. It supports many protocols and the code below shows one of the simplest scenarios for using Sockets - an echo server and client. Note that the code below will target TCP and Ipv4 protocol. Many users today have got a Ipv6 and/or Ipv4 address assigned.

Socket-based server

Create a new Console Application in Visual Studio and insert the following code into the Program.cs file.

using System;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace SynchronousSocketServer
{

    public class SynchronousSocketServer
    {

        //Incoming data from the client. 
        private static string _data;

        public static void StartListening()
        {
            //Data buffer for incoming data. 
            // ReSharper disable once RedundantAssignment

            //Establish the local endpoint for the socket.
            //Dns.GetHostName returns the name of the host running the application
            IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
            IPAddress ipAddress = ipHostInfo.AddressList.First(a =< a.AddressFamily == AddressFamily.InterNetwork);
            IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11004);

            //Create a TCP/IP socket 
            var listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

            //Bind the socket to the local endpoint and listen for incoming connections 
            try
            {
                listener.Bind(localEndPoint);
                listener.Listen(10);

                //Start listening for connections 
                while (true)
                {
                    Console.WriteLine("Waiting for connection ...");
                    //Program is suspended while waiting for an incoming connection. 
                    Socket handler = listener.Accept();
                    _data = null;

                    //An incoming connection needs to be processed. 
                    while (true)
                    {
                        var bytes = new byte[1024];
                        int bytesRec = handler.Receive(bytes);
                        _data += "\n" + Encoding.Unicode.GetString(bytes, 0, bytesRec);
                        if (_data.IndexOf("<EOF>", StringComparison.Ordinal) > -1)
                        {
                            break;
                        }
                        //Show the data on the console. 
                        byte[] msg = Encoding.Unicode.GetBytes(_data);
                        handler.Send(msg);
                    }

                    Console.WriteLine("Text received: {0}", _data);

                  
                    handler.Shutdown(SocketShutdown.Both);
                    handler.Close();
                }
            }
            catch (Exception err)
            {
                Console.WriteLine(err.ToString());
            } //try-catch 

            Console.WriteLine("\nPress ENTER to continue ...");
            Console.Read();
        }

        // ReSharper disable once UnusedParameter.Local
        static int Main(string[] args)
        {
            StartListening();
            return 0;
        }

    }

}

Socket-based client

Create a new Console application in Visual Studio. Add the following code into the Program.cs file:

using System;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace SynchronousSocketClient
{

    public class SynchronousSocketClient
    {

        public static void StartClient()
        {
            //Data buffer for incoming data. 
            byte[] bytes = new byte[1024];

            //Connect to a remote device. 
            try
            {
                //Establish the remote endpoint for the socket
                //This example uses port 11000 on the local computer 
                IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
                IPAddress ipAddress = ipHostInfo.AddressList.First(a =< a.AddressFamily == AddressFamily.InterNetwork);
                IPEndPoint remoteEndPoint = new IPEndPoint(ipAddress, 11004);

                //Create a TCP/IP socket. 
                var sender = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

                //Connect the socket to the remote endpoint. Catch any errors. 
                try
                {
                    sender.Connect(remoteEndPoint);

                    Console.WriteLine("Socket connected to {0}", sender.RemoteEndPoint);

                    while (true)
                    {
                        Console.WriteLine("Enter text, type <EOF> to exit:");

                        //Encode the data string into a byte array 
                        string enteredText = Console.ReadLine() ?? "<EOF>"; 
                        byte[] msg = Encoding.Unicode.GetBytes(enteredText);

                        //Send the data through the socket. 
                        int bytesSent = sender.Send(msg);
                        Console.WriteLine("Sent {0} bytes over the network", bytesSent);

                        //Receive the response from the remote device. 
                        int bytesReceived = sender.Receive(bytes);
                        Console.WriteLine("Echoed test = {0}", Encoding.Unicode.GetString(bytes, 0, bytesReceived));

                        if (enteredText.IndexOf(">EOF<", StringComparison.CurrentCultureIgnoreCase) < -1)
                        {
                            break;
                        }

                    }

                    //Release the socket. 
                    sender.Shutdown(SocketShutdown.Both);
                    sender.Close();
                }
                catch (ArgumentNullException err)
                {
                    Console.WriteLine("ArgumentNullException : {0}", err.Message);
                }
                catch (SocketException err)
                {
                    Console.WriteLine("SocketException : {0}", err.Message);
                }
                catch (Exception err)
                {
                    Console.WriteLine("Exception : {0}", err.Message);
                }

            }
            catch (Exception err)
            {
                Console.WriteLine(err.Message);
            } //try-catch 

        }

        // ReSharper disable once UnusedParameter.Local
        static int Main(string[] args)
        {
            StartClient();
            return 0;
        }

    }

}

Wednesday, 28 October 2015

Creating an Azure WebJob and persisting data to an Azure Storage table

This article will describe how you can create an Azure WebJob and persist some data to an Azure Storage table. First of, head over to the portal for Azure using Internet Explorer and log in using your subscription: Azure Portal Select Web Apps in the left menu and click Add. Enter a name for your Web App and select your Subscription, Resource Group and App Service plan/Location and hit Create. Afterwards, select the Web Apps in the left menu again and select the Web App you just created. Use the Settings and choose WebJobs. We are going to create a webjob here using Visual Studio, note that the WebJobs link will list your webjobs.
Next, create in VS 2013 or newer a new ASP.NET Web Application using File and New Project in the Main Menu of VS. Choose an Empty web application. Do the following next:
  • Right click the web project
  • Choose Add
  • Add ASP.NET folder
  • App_Data
    • Select Solution Explorer and choose the Solution and right-click and add a new project which is Console Application. Also create subfolder jobs, triggered and web-job-helloworldv5. We will drop the compiled contents of the Console Application project we will add next. Let's add two app settings in the Console Application app.config file:


      
      <?xml version="1.0" encoding="utf-8" ?>
      <configuration>
        <appSettings>
          <add key="StorageAccount" value="INSERT_STORAGE_ACCOUNT" />
          <add key="StorageKey" value="INSERT_STORAGE_KEY" />
        </appSettings>
          <startup> 
              <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
          </startup>
      </configuration>
      
      
      Obviously, we need to put into the two appsettings the storage account and storage primary key. In the left menu of Azure Portal select New and choose Data+Storage and choose Storage Account. This is needed to get started with Blobs, Tables and Queues and Choose Create Back in the left menu again, choose Browse and then Storage accounts (classic). Now we need the necessary connection details to this Storage Accounts. Select in the right menu Settings the link Keys. Copy the values for Storage account name and Primary Access Key. Add these two values into the two app settings earlier noted. Now we just need to make a simple WebJob and persist some data into Azure Storage Table. Let's calculate the first 100 prime numbers and then add these numbers to a Azure Storage Table. Into the Main method of Program.cs of the Console application we add the following code:
      
       static void Main(string[] args)
              {
                  Console.WriteLine("Starting prime number calculation..");
                  var primes = new List<int>(); 
                  foreach (var n in Enumerable.Range(0, 100))
                  {
                      int numberToCheck = (n*2) + 1;
                      bool isPrimes = IsPrime(numberToCheck);
                      if (isPrimes)
                      {
                          primes.Add(numberToCheck);
                      }
                  }
      
                  StoreToAzureTableStorage(primes, "primenumbersfound");
              }
      
              public static bool IsPrime(long num)
              {
                  for (long j = 2; j <= Math.Sqrt(num); j++) // you actually only need to check up to sqrt(i)
                  {
                      if (num%j == 0)
                      {
                          return false;
                      }
                  } //for
      
                  return true;
              }
      
      
      We need some plumbing code to get our CloudTableClient to work against our Azure Table:
      
      /// 
              /// Returns an instance of a Azure Cloud Table client 
              /// 
              /// 
              public static CloudTableClient GetCloudTableClient()
              {
                  string accountName = ConfigurationManager.AppSettings["StorageAccount"];
                  string accountKey = ConfigurationManager.AppSettings["StorageKey"];
      
                  if (string.IsNullOrEmpty(accountName) || string.IsNullOrEmpty(accountKey))
                      return null; 
      
                  try
                  {
                      var credentials = new StorageCredentials(accountName, accountKey); 
                      var cloudStorageAccount = new CloudStorageAccount(credentials, useHttps: true);
                      CloudTableClient client = cloudStorageAccount.CreateCloudTableClient();
                      return client;
                  }
                  catch (Exception ex)
                  {
                      return null;
                  }
              }
      
      
      Next we commit the data to our Azure Storage Table:
      
         public static void StoreToAzureTableStorage(List primes, string tableName)
              {
                  
                  try
                  {
      
                      CloudTableClient client = GetCloudTableClient();
                      CloudTable table = client.GetTableReference(tableName);
                      table.CreateIfNotExists();
      
                      foreach (int prime in primes)
                      {
                          var primeEntity = new PrimeNumberEntity(prime);
                          var insertOperation = TableOperation.Insert(primeEntity);
                          table.Execute(insertOperation);
                      }
      
      
                      var query = new TableQuery();
                      var primesFound = table.ExecuteQuery(query).OrderBy(p => int.Parse(p.RowKey)).ToList();
      
                      foreach (PrimeNumberEntity pf in primesFound)
                      {
                          Console.WriteLine(pf);
                      }
      
                  }
      
                  catch (Exception ex)
                  {
      
                      Console.WriteLine(ex);
      
                  }
      
      
                  Console.WriteLine("Done... press a key to end.");
      
              }
      
      
      We can now invoke our WebJob from the Azure portal:




      We can choose Web Apps and then our WebApp and next in the right menu WebJobs. Note that we can pin our WebApp to our Dashboard for quicker navigation using the pin symbol in Azure Portal. Now choose the WebJobs and right click and choose Run.



      We can inspect the data we inserted using Azure Storage Explorer. Download a Visual Studio 2013 solution with code above below, you will need create a Web App and a Storage account in Azure Portal and insert the necessary app settings as noted to run the example: Download VS 2013 Solution file (.zip) [69 MB]

Friday, 9 October 2015

Switchbased delay with Dispatcher in WPF

Extended my DispatcherUtil class today, with SwitchBasedDelay! Example of calling the new method, note we use a fixed Guid in this case to "group" calls into a logical switch:

 DispatcherUtil.SwitchbasedDelayedInvokeAction(Guid.Parse(@"{4E101F98-31F3-4E19-B18B-2820AEA60A1B}"), () =>
     {
      PublishEvent<ProcedureFreeTypeTextChangedEvent, ProcedureFreeTypeTextChangedEventArg>(
       new ProcedureFreeTypeTextChangedEventArg
        {
          FreshId = Context.CurrentOperationalUnit.FreshId,
          ProcedureCode = Model.ProcedureTypeFreeText,
          OperationId = Model.OperationId
        });
      }, 2000);


using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Windows.Threading;

namespace SomeAcme.SomePackage
{

    /// <summary>
    /// Contains helper methods for dispatcher operations 
    /// </summary>
    public static class DispatcherUtil
    {

        private static readonly List<DelayedAction> ActionsRegistered = new List<DelayedAction>();

        private static readonly Dictionary<Guid?, bool> SwitchDelays = new Dictionary<Guid?, bool>();

        /// <summary>
        /// Executes an action passed into this method by a timeout measured in millisecond in a switch-based manner. 
        /// </summary>
        /// <param name="keyToken">A key token (Guid) to identity the switch (basic grouping)</param>
        /// <param name="executeAction">Action to execute</param>
        /// <param name="timeOut">The timeout to wait before executing (in milliseconds)</param>
        /// <param name="priority">Priority of the dispatcher operation</param>
        /// <returns></returns>
        public static bool SwitchbasedDelayedInvokeAction(Guid keyToken, Action executeAction, int timeOut,
            DispatcherPriority priority = DispatcherPriority.Background)
        {
            if (SwitchDelays.ContainsKey(keyToken) && SwitchDelays[keyToken])
                return false; //do not execute, already in progress 

            SwitchDelays[keyToken] = true;

            DelayedInvokeAction(executeAction, timeOut, priority, keyToken);
            return true; //delayed action sent off
        }

        /// <summary>
        /// Executes an action passed into this method by a timeout measured in milliseconds
        /// </summary>
        /// <param name="executeAction">Action to execute</param>
        /// <param name="timeOut">The timeout to wait before executing (in milliseconds)</param>
        /// <param name="priority"></param>
        ///    /// <param name="keyToken">A key token to identity the switch (basic grouing). Will be used as a tag on the DispatcherTimer</param>
        public static bool DelayedInvokeAction(Action executeAction, int timeOut, DispatcherPriority priority = DispatcherPriority.Background, Guid? keyToken = null)
        {
            var delayedAction = new DelayedAction(executeAction, timeOut, keyToken);
            ActionsRegistered.Add(delayedAction);
            DispatcherTimer dtimer = new DispatcherTimer(priority);

            dtimer.Interval += new TimeSpan(0, 0, 0, 0, timeOut);
            dtimer.Tag = delayedAction.ExecuteGuid;
            dtimer.Tick += DelayedInvokeTimerTick;
            dtimer.IsEnabled = true;
            dtimer.Start();

            return true;
        }

        private static void DelayedInvokeTimerTick(object sender, EventArgs e)
        {
            var dtimer = sender as DispatcherTimer;
            if (dtimer != null)
            {
                dtimer.IsEnabled = false;
                dtimer.Stop();
                dtimer.Tick -= DelayedInvokeTimerTick; //unsubscribe
                Guid targetActionGuid = (Guid)dtimer.Tag;

                DelayedAction delayedAction = ActionsRegistered.Single(a => a.ExecuteGuid == targetActionGuid);
                delayedAction.ActionToExecute(); //now execute the action 
                ActionsRegistered.Remove(delayedAction);

                if (dtimer.Tag != null)
                {
                    Guid? keyToken = dtimer.Tag as Guid?; 
                    if (SwitchDelays.ContainsKey(keyToken))
                    {
                        SwitchDelays.Remove(keyToken); //remove the switch 
                    } //if 
                } //if 

                // ReSharper disable once RedundantAssignment
                dtimer = null; //ensure free up dispatcher timer - do not starve threading resources 
            } //if 
        }

        /// <summary>
        /// Invokes an action on the current dispatcher, used to execute operations on the GUI thread
        /// </summary>
        /// <param name="executeAction">The action to execute, pass in e.g. delegate { --code lines goes here } </param>
        /// <param name="dispatcherPriority">The priority to give the action on the thread (signal to the WPF messaging queue). Default is background.</param>
        /// <returns>Returns true when the action was dispatched</returns>
        /// <remarks>Default priority is DispatcherPriority.Background</remarks>
        public static bool InvokeAction(Action executeAction, DispatcherPriority dispatcherPriority = DispatcherPriority.Background)
        {
            Dispatcher.CurrentDispatcher.Invoke(new Action(() =>
            {
                executeAction();
            }), dispatcherPriority);
            return true;
        }

        /// <summary>
        /// Asynchronously invokes an action on the current dispatcher, used to execute operations on the GUI thread
        /// </summary>
        /// <param name="executeAction">The action to execute, pass in e.g. delegate { --code lines goes here } </param>
        /// <param name="dispatcherPriority">The priority to give the action on the thread (signal to the WPF messaging queue). Default is background.</param>
        /// <returns>Returns true when the action was dispatched</returns>
        /// <remarks>Default priority is DispatcherPriority.Background</remarks>
        public static bool BeginInvokeAction(Action executeAction, DispatcherPriority dispatcherPriority = DispatcherPriority.Background)
        {
            Dispatcher.CurrentDispatcher.BeginInvoke(new Action(() =>
            {
                executeAction();
            }), dispatcherPriority);
            return true;
        }

        public static void AsyncWorkAndUiThreadUpdate<T>(Dispatcher currentDispatcher, Func<T> threadWork, Action<T> guiUpdate)
        {
            // ReSharper disable once UnusedAnonymousMethodSignature
            ThreadPool.QueueUserWorkItem(delegate(object state)
            {
                T resultAfterThreadWork = threadWork();
                // ReSharper disable once UnusedAnonymousMethodSignature
                // ReSharper disable once UnusedAnonymousMethodSignature
                currentDispatcher.BeginInvoke(DispatcherPriority.Normal, new Action<T>(delegate {
                    guiUpdate(resultAfterThreadWork);
                }), resultAfterThreadWork);

            });
        }

    }
}



Tuesday, 6 October 2015

DispatcherUtil - Elegant WPF Dispatcher programmatic handling

Don't you hate it when you need to tweak the Dispatcher to do what you expect and respect the main GUI thread can only work with GUI controls rule? Wouldn't you like to have some code that just does the things you want to do with the Dispatcher without getting the dreaded InvalidOperationException? Well here is the DispatcherUtil I use to achieve this!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Windows.Threading;

namespace SomeAcme.SomePackage
{

    /// <summary>
    /// Contains helper methods for dispatcher operations 
    /// </summary>
    public static class DispatcherUtil
    {

        private static readonly List<DelayedAction> actionsRegistered = new List<DelayedAction>();


        /// <summary>
        /// Executes an action passed into this method by a timeout measured in milliseconds
        /// </summary>
        /// <param name="executeAction">Action to execute</param>
        /// <param name="timeOut">The timeout to wait before executing (in milliseconds)</param>
        /// <param name="priority"></param>
        public static bool DelayedInvokeAction(Action executeAction, int timeOut, DispatcherPriority priority = DispatcherPriority.Background)
        {
            var delayedAction = new DelayedAction(executeAction, timeOut);
            actionsRegistered.Add(delayedAction);
            DispatcherTimer dtimer = new DispatcherTimer(priority); 
            dtimer.Interval += new TimeSpan(0, 0, 0, 0, timeOut);
            dtimer.Tag = delayedAction.ExecuteGuid;
            dtimer.Tick += DelayedInvokeTimerTick;
            dtimer.IsEnabled = true;
            dtimer.Start();

            return true;
        }

        private static void DelayedInvokeTimerTick(object sender, EventArgs e)
        {
            var dtimer = sender as DispatcherTimer;
            if (dtimer != null)
            {
                dtimer.IsEnabled = false;
                dtimer.Stop();
                dtimer.Tick -= DelayedInvokeTimerTick; //unsubscribe
                Guid targetActionGuid = (Guid)dtimer.Tag;

                DelayedAction delayedAction = actionsRegistered.Single(a => a.ExecuteGuid == targetActionGuid);
                delayedAction.ActionToExecute(); //now execute the action 
                actionsRegistered.Remove(delayedAction); 

                if (dtimer != null)
                    dtimer = null; //ensure free up dispatcher timer - do not starve threading resources 
            } //if 
        }

        /// <summary>
        /// Invokes an action on the current dispatcher, used to execute operations on the GUI thread
        /// </summary>
        /// <param name="executeAction">The action to execute, pass in e.g. delegate { --code lines goes here } </param>
        /// <param name="dispatcherPriority">The priority to give the action on the thread (signal to the WPF messaging queue). Default is background.</param>
        /// <returns>Returns true when the action was dispatched</returns>
        /// <remarks>Default priority is DispatcherPriority.Background</remarks>
        public static bool InvokeAction(Action executeAction, DispatcherPriority dispatcherPriority = DispatcherPriority.Background)
        {
            Dispatcher.CurrentDispatcher.Invoke(new Action(() =>
            {
                executeAction();
            }), dispatcherPriority);
            return true;
        }

        /// <summary>
        /// Asynchronously invokes an action on the current dispatcher, used to execute operations on the GUI thread
        /// </summary>
        /// <param name="executeAction">The action to execute, pass in e.g. delegate { --code lines goes here } </param>
        /// <param name="dispatcherPriority">The priority to give the action on the thread (signal to the WPF messaging queue). Default is background.</param>
        /// <returns>Returns true when the action was dispatched</returns>
        /// <remarks>Default priority is DispatcherPriority.Background</remarks>
        public static bool BeginInvokeAction(Action executeAction, DispatcherPriority dispatcherPriority = DispatcherPriority.Background)
        {
            Dispatcher.CurrentDispatcher.BeginInvoke(new Action(() =>
            {
                executeAction();
            }), dispatcherPriority);
            return true;
        }

        public static void AsyncWorkAndUIThreadUpdate<T>(Dispatcher currentDispatcher, Func<T> threadWork, Action<T> guiUpdate)
        {
            ThreadPool.QueueUserWorkItem(delegate(object state)
            {
                T resultAfterThreadWork = threadWork();
                currentDispatcher.BeginInvoke(DispatcherPriority.Normal, new Action<T>(delegate(T result)
                {
                    guiUpdate(resultAfterThreadWork);
                }), resultAfterThreadWork);

            });
        }

    }
}


Enjoy the code! It has helped me many times when I want to do work in other threads or using Tasks with TPL!

Displaying math in webpages with MathJax

MathJax is a powerful Library for displaying math in webpages. It is possible to write mathematical symbols and equations with MathML syntatax or LateX syntax, and even other formats. In this article, LateX will be used. LaTeX has got all the necessary support for writing mathematical symbols and equations, note though that this does not mean everything in LateX is supported in browsers through MathJax. In this article, only simple examples will be used. First off, to use MathJax, just add a Reference to the MathJax JavaScript Library in the <HEAD>HEAD section of Your HTML page:

<html>
<head>
<script type="text/javascript"
  src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML">
</script>

<script type="text/x-mathjax-config">
MathJax.Hub.Config({
  tex2jax: {
    inlineMath: [['$','$'], ['\\(','\\)']],
    processEscapes: true
  }
});

</script>

</head>

Now we are ready to insert some mathematical symbols and Equations on our web page!
Let's first add the Quadratic Equation:

<font size="+2">
Quadratic equation:

$$ \begin{array}{*{20}c} { x = \frac{ -b \pm \sqrt {b^2 - 4ac}}{2a} } & {{\rm{when}}} & {ax^2 + bx + c = 0} \\ \end{array} $$ </font>

And let us also list the Greek alphabet: <div style="color:charcoal;width:300px;background:white"> <font size="+2"> $$ \\ Greek \hspace{2mm} Alphabet. \\ letter - small symbol - large symbol \\ alpha \hspace{1mm} \alpha \hspace{2mm} A \hspace{2mm} \cdotp beta \hspace{1mm} \beta \hspace{2mm} B \hspace{2mm} \cdotp gamma \hspace{1mm} \gamma \hspace{2mm} \Gamma \hspace{2mm} \cdotp delta \hspace{1mm} \delta \hspace{2mm} \Delta \hspace{2mm} \cdotp epsilon \hspace{1mm} \epsilon \hspace{2mm} E \hspace{2mm} \cdotp zeta \hspace{1mm} \zeta \hspace{2mm} Z \hspace{2mm} \cdotp \\ eta \hspace{1mm} \eta \hspace{2mm} H \hspace{2mm} \cdotp theta \hspace{1mm} \theta \hspace{2mm} \Theta \hspace{2mm} \cdotp iota \hspace{1mm} \iota \hspace{2mm} I \hspace{2mm} \cdotp kappa \hspace{1mm} \kappa \hspace{2mm} K \hspace{2mm} \cdotp lambda \hspace{1mm} \lambda \hspace{2mm} \Lambda \hspace{2mm} \cdotp mu \hspace{1mm} \mu \hspace{2mm} M \hspace{2mm} \cdotp nu \hspace{1mm} \nu \hspace{2mm} N \hspace{2mm} \cdotp xi \hspace{1mm} \xi \hspace{2mm} \Xi \hspace{2mm} \cdotp omicron \hspace{1mm} \omicron \hspace{2mm} O \hspace{2mm} \cdotp \\ pi \hspace{1mm} \pi \hspace{2mm} \Pi \hspace{2mm} \cdotp rho \hspace{1mm} \rho \hspace{2mm} P \hspace{2mm} \cdotp sigma \hspace{1mm} \sigma \hspace{2mm} \Sigma \hspace{2mm} \cdotp tau \hspace{1mm} \tau \hspace{2mm} T \hspace{2mm} \cdotp upsilon \hspace{1mm} \upsilon \hspace{2mm} Y \hspace{2mm} \cdotp phi \hspace{1mm} \phi \hspace{2mm} \Phi \hspace{2mm} \cdotp chi \hspace{1mm} \chi \hspace{2mm} X \hspace{2mm} \cdotp psi \hspace{1mm} \psi \hspace{2mm} \Psi \hspace{2mm} \cdotp omega \hspace{1mm} \omega \hspace{2mm} \Omega \hspace{2mm} \cdotp $$ </font> </div>
As you have noted, we use the $$ .. $$ enclosing syntax to insert our LateX code that constitute the mathematical symbols and Equations. MathJax is really powerful! You can display triple integrals, matrices and vector Equations - both elementary, Intermediate and Advanced Math can be displayed on a web page. The web site of MathJax is available here: MathJax webiste - MathJax.org Ok, so how does the code above look like?


Displayed in IFRAME next - the source is: http://toreaurstad.ddns.net/website/index2.htm

Monday, 5 October 2015

Displaying the SQL of Entity Framework Linq to Entities queries

When working with Entity Framework or EF we often blindly run Linq to Entities queries and see that we get the results we are after, ignoring the SQL we are generating behind the scenes. This is often a bad strategy, as we risk the following:
  1. The SQL can be erroneuous and give wrong results
  2. The SQL can be inefficient and slow
  3. We abstract ourselves away from SQL and use the wrong logical constructs in EF
Here is an example of an extension method that allow ourselves to display the SQL of Linq to Entities queries:

public static class IQueryableExtensions
    {

        /// 
        /// Shows the sql the IQueryable query will be generated into and executed on the DbServer
        /// 
        /// The IQueryable to analyze
        /// Set to true if this method should try decoding the parameters
        /// This is the generated SQL query in use for Entity Framework
        public static string ShowSql(this IQueryable query, bool decodeParameters = false)
        {
            var objectQuery = (ObjectQuery)query; 

            string result = ((ObjectQuery)query).ToTraceString();

            if (!decodeParameters)
                return result; 

            foreach (var p in objectQuery.Parameters)
            {
                string valueString = p.Value != null ? p.Value.ToString() : string.Empty;
                if (p.ParameterType == typeof(string) || p.ParameterType == typeof(DateTime))
                    valueString = "'" + valueString + "'";
                result = result.Replace("@" +p.Name, p.Value != null ? valueString : string.Empty); 
            }
            return result; 
        }     

}

Next, here is a simple extension method that shows how we can use this in an integration test. If you want, you can output the sql string to the Output Window, using either Console.WriteLine() or Debug.WriteLine().

    [TestFixture]
    public class IqueryableExtensionsTest
    {

        [Test]
        public void QueryableReturnsSqlAndDoesNotThrow()
        {
            using (var dbContext = SomeObjectContextFactory.SomeObjectDataContext)
            {
                var somerows= from somerow in dbContext.SomeTable
                    where somerow.SomeStatus == (int) SomeStatus.SomeStatusValue
                    && somerow.SomeOtherDateColumn >= new DateTime(2015, 2, 12)
                    select somerow;
                string sql = someRows.ShowSql();
                Assert.IsNotNull(sql);
            }
        }

    }

Friday, 2 October 2015

DistinctBy in LINQ

The operator DistinctBy is lacking in LINQ, but we can achieve it with the GroupBy operator.

using System;
using System.Collections.Generic;
using System.Linq;

namespace GroupingLinq
{
    
  

        public static class EnumerableExtensions
        {

            /// <summary>
            /// Returns a ienumerable which is distinct by a given property key selector. If a custom equality 
            /// comparer is to be used, pass this in as the comparer. By setting the comparer default to null,
            /// the default comparer is used. 
            /// </summary>
            /// <typeparam name="T">The item type in the ienumerable</typeparam>
            /// <typeparam name="TKey">The type of the key selector (property to disinct elements by)</typeparam>
            /// <param name="coll">The source ienumerable</param>
            /// <param name="keySelector">The key selector, use a member expression in a lambda expression</param>
            /// <param name="comparer">Custom comparer to use, pass in null here to specify that default comparer is used,
            /// however, this is default set to null and not required parameter</param>
            /// <returns></returns>
            public static IEnumerable<T> DistinctBy<T, TKey>(this IEnumerable<T> coll, Func<T, TKey> keySelector,
                IEqualityComparer<TKey> comparer = null)
            {
                if (coll == null)
                    throw new ArgumentNullException("coll");
                if (keySelector == null)
                    throw new ArgumentNullException("keySelector");

                var result = coll.GroupBy(keySelector, comparer).Select(g => g.First()).ToList();
                return new List<T>(result).AsEnumerable();
            }

        }
    

}

The following entertaining example which is a console application shows how we can use this operator:

class Program
    {

        static void Main(string[] args)
        {

            var cars = new []
            {
                new Car {Model = "Audi", Make = "A4", Color = "Black"},
                new Car {Model = "Audi", Make = "A8", Color = "Red"},
                new Car {Model = "Audi", Make = "TT", Color = "Black"},
                new Car {Model = "Volvo", Make = "XC90", Color = "Black"},
                new Car {Model = "Volvo", Make = "S90", Color = "Black"},
                new Car {Model = "Ferrari", Make = "F500", Color = "Yellow"},
                new Car {Model = "Ferrari", Make = "F500", Color = "Red"},
                new Car {Model = "Lada", Make = "Limousine", Color = "Rusty"}
            };

            var groupedCars = cars.DistinctBy(c => new {c.Model, c.Color});


            foreach (var gc in groupedCars)
            {
                Console.WriteLine(gc.ToString()); 
            }

            Console.WriteLine("Press any key to continue ...");
            Console.ReadKey(); 
        }




        // Define other methods and classes here

    }

The sample output is then:

Model: Audi, Make: A4, Color: Black
Model: Audi, Make: A8, Color: Red
Model: Volvo, Make: XC90, Color: Black
Model: Ferrari, Make: F500, Color: Yellow
Model: Ferrari, Make: F500, Color: Red
Model: Lada, Make: Limousine, Color: Rusty
Press any key to continue ...

In the example we used DistinctBy some Cars based on their properties Model and Color. We want in other words unique combinations of Model AND Color. I.e. we can have multiple Cars of the same Model but WITH different Color OR we can have multiple cars with same Color but then the Model but be different. Uniqueness Criterion: (Model, Color) We did not get the item "Audi TT Black" because we already got a black Audi. We did not get the "Volvo S90 Black" because we already got a black Volvo. We got both the Ferrari F500 because they got different colors. And sadly, we are stuck with the "Lada Limousine Rusty" since it was the only combination of Model and Color.

Detect USB drives in a WPF application



We can use the class System.IO.DriveInfo to retrieve all the drives on the system and look for drives where the DriveType is Removable. In addition, the removable drive (USB usually) must be ready, which is accessible as the property IsReady. First off, we define a provider to retrieve the removable drives:
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;

    namespace TestPopWpfWindow
    {

    public static class UsbDriveListProvider
    {


        public static IEnumerable<DriveInfo> GetAllRemovableDrives()
        {
            var driveInfos = DriveInfo.GetDrives().AsEnumerable();
            driveInfos = driveInfos.Where(drive => drive.DriveType == DriveType.Removable);
            return driveInfos;
        }

    }
}

Let us use the MVVM pattern also, so we define a ViewModelbase class, implementing INotifyPropertyChanged.
using System.ComponentModel;

namespace TestPopWpfWindow
{

    public class ViewModelBase : INotifyPropertyChanged
    {

        public event PropertyChangedEventHandler PropertyChanged;

        public void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }


    }
}
It is also handy to have an implemetation of ICommand:
    using System;
    using System.Windows.Input;

    namespace TestPopWpfWindow
    {

        public class RelayCommand : ICommand
        {

            private Predicate<object> _canExecute;

            private Action<object> _execute;  


            public RelayCommand(Predicate<object> canExecute, Action<object> execute)
            {
                _canExecute = canExecute;
                _execute = execute;
            }

            public bool CanExecute(object parameter)
            {
                return _canExecute(parameter); 
            }

            public event EventHandler CanExecuteChanged;

            public void Execute(object parameter)
            {
                _execute(parameter); 
            }

        }
    }

We also set the DataContext of MainWindow to an instance of a demo view model defined afterwards:
namespace TestPopWpfWindow
{

    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {

        public MainWindow()
        {
            InitializeComponent();
            DataContext = new UsbDriveInfoDemoViewModel();
        }

    }
}

We then define the view model itself and use System.Management.ManagementEventWatcher to look for changes in the drives mounted onto the system.
  using System;
    using System.Collections.Generic;
    using System.Diagnostics;
    using System.IO;
    using System.Management;
    using System.Windows;
    using System.Windows.Input;

    namespace TestPopWpfWindow
    {

        public class UsbDriveInfoDemoViewModel : ViewModelBase, IDisposable
        {

            public UsbDriveInfoDemoViewModel()
            {
                DriveInfos = new List<DriveInfo>();
                ReloadDriveInfos();
                RegisterManagementEventWatching(); 
                TargetUsbDrive = @"E:<"; 
                AccessCommand = new RelayCommand(x => true, x => MessageBox.Show("Functionality executed."));
            }

            public int UsbDriveCount { get; set; }

            private string _targetUsbDrive;

            public string TargetUsbDrive
            {
                get { return _targetUsbDrive; }
                set
                {
                    if (_targetUsbDrive != value)
                    {
                        _targetUsbDrive = value; 
                        RaisePropertyChanged("TargetUsbDrive");
                        RaisePropertyChanged("DriveInfo");
                    }
                }
            }

            public ICommand AccessCommand { get; set; }

            private void ReloadDriveInfos()
            {
                var usbDrives = UsbDriveListProvider.GetAllRemovableDrives();

                Application.Current.Dispatcher.Invoke(() =>
                {
                    DriveInfos.Clear();

                    foreach (var usbDrive in usbDrives)
                    {
                        DriveInfos.Add(usbDrive);
                    }
                    UsbDriveCount = DriveInfos.Count;
                    RaisePropertyChanged("UsbDriveCount");
                    RaisePropertyChanged("DriveInfos");
                }); 
            }

            public List<DriveInfo> DriveInfos { get; set; }

            private ManagementEventWatcher _watcher;

            private void RegisterManagementEventWatching()
            {
                _watcher = new ManagementEventWatcher();
                var query = new WqlEventQuery("SELECT * FROM Win32_VolumeChangeEvent");
                _watcher.EventArrived += watcher_EventArrived;
                _watcher.Query = query;
                _watcher.Start();
            }

            private void watcher_EventArrived(object sender, EventArrivedEventArgs e)
            {
                Debug.WriteLine(e.NewEvent);
                ReloadDriveInfos();
            }



            public void Dispose()
            {
                if (_watcher != null)
                {
                    _watcher.Stop();
                    _watcher.EventArrived -= watcher_EventArrived;
                }
            }

        }

    }

We also define a WPF multi-converter next to enable the button:
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Windows.Data;

namespace TestPopWpfWindow
{

    public class UsbDriveAvailableEnablerConverter : IMultiValueConverter
    {

        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            if (values == null || values.Count() != 2)
                return false;

            var driveInfos = values[1] as List<DriveInfo>;
            var targetDrive = values[0] as string; 
            if (driveInfos == null || !driveInfos.Any() || string.IsNullOrEmpty(targetDrive))
                return false;
            return driveInfos.Any(d => d.IsReady && d.Name == targetDrive);
        }




        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

And we define a GUI to test this code:
<Window x:Class="TestPopWpfWindow.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:TestPopWpfWindow"
        Title="MainWindow" Height="350" Width="525">

    <Window.Resources>

        <Style x:Key="usbLabel" TargetType="Label">
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsReady}" Value="False">
                    <Setter Property="Background" Value="Gray"></Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding IsReady}" Value="True">
                    <Setter Property="Background" Value="Green"></Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>

        <local:UsbDriveAvailableEnablerConverter x:Key="usbDriveAvailableEnablerConverter"></local:UsbDriveAvailableEnablerConverter>

    </Window.Resources>


    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>

        </Grid.RowDefinitions>

        <StackPanel Orientation="Vertical">
            <TextBlock Text="USB Drive-detector" FontWeight="DemiBold" HorizontalAlignment="Center" FontSize="14" Margin="2"></TextBlock>
            <TextBlock Text="Removable drives on the system" FontWeight="Normal" HorizontalAlignment="Center" Margin="2"></TextBlock>
            <TextBlock Text="Drives detected:" FontWeight="Normal" HorizontalAlignment="Center" Margin="2"></TextBlock>
            <TextBlock Text="{Binding UsbDriveCount, UpdateSourceTrigger=PropertyChanged}" FontWeight="Normal" HorizontalAlignment="Center" Margin="2"></TextBlock>

            <ItemsControl Grid.Row="0" ItemsSource="{Binding DriveInfos, UpdateSourceTrigger=PropertyChanged}"
                          Width="100" BorderBrush="Black" BorderThickness="1">
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Vertical">
                            <Label Style="{StaticResource usbLabel}" Width="32" Height="32" FontSize="18" Foreground="White" Content="{Binding Name}">
                            </Label>
                        </StackPanel>

                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>
        </StackPanel>

        <Button Grid.Row="1" Height="24" Width="130" VerticalAlignment="Top" Margin="10" Content="Access functionality" Command="{Binding AccessCommand}">
            <Button.IsEnabled>
                <MultiBinding Converter="{StaticResource usbDriveAvailableEnablerConverter}">
                    <MultiBinding.Bindings>
                        <Binding Path="TargetUsbDrive"></Binding>
                        <Binding Path="DriveInfos"></Binding>
                    </MultiBinding.Bindings>
                </MultiBinding>
            </Button.IsEnabled>
        </Button>

        <StackPanel Grid.Row="2" Orientation="Horizontal" HorizontalAlignment="Center">
            <TextBlock Margin="2" Text="Target this USB-drive:"></TextBlock>
            <TextBox Margin="2" Text="{Binding TargetUsbDrive, UpdateSourceTrigger=LostFocus}" Width="100"></TextBox>
        </StackPanel>

    </Grid>

</Window>

I have now provided the Visual Studio 2013 solution with the code above available for download here:

Download VS 2013 Solution with source code above

Thursday, 1 October 2015

ASP.NET Cache and Redis

ASP.NET Cache can utilize Redis for caching page data, but also additional kinds of data such as images and arbitrary data. This is documented in the MSDN article "ASP.NET Output Cache Provider for Azure Redis Cache": https://msdn.microsoft.com/en-us/library/azure/dn798898.aspx First off, we create a new ASP.NET Solution such as a MVC solution and select after creating it Manage Nuget Packages through right clicking the Solution Explorer.




We can also add this Nuget package using Package Manager Console and type:
Install-Package Install-Package Microsoft.Web.RedisOutputCacheProvider


Note, this will add a <caching> element into Web.Config that you now can change. The following sets up the RedisOutputCacheProvider to a Redis Server running on localhost, not using SSL and using port 6379:
      <add name="MyRedisOutputCache" type="Microsoft.Web.Redis.RedisOutputCacheProvider" host="localhost" accessKey="" applicationName="RedisCache" port="6379" ssl="false" />
   


We can monitor the activity on the local Redis server by starting a redis client and type the command:

c:\Redis>redis-cli
redis 127.0.0.1:6379> monitor
OK

Note: If your Redis Server is not running yet, start it by running redis-server

c:\Redis>redis-server
[10092] 01 Oct 15:05:45.635 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
                _._
           _.-``__ ''-._
      _.-``    `.  `_.  ''-._           Redis 2.6.12 (00000000/0) 64 bit
  .-`` .-```.  ```\/    _.,_ ''-._
 (    '      ,       .-`  | `,    )     Running in stand alone mode
 |`-._`-...-` __...-.``-._|'` _.-'|     Port: 6379
 |    `-._   `._    /     _.-'    |     PID: 10092
  `-._    `-._  `-./  _.-'    _.-'
 |`-._`-._    `-.__.-'    _.-'_.-'|
 |    `-._`-._        _.-'_.-'    |           http://redis.io
  `-._    `-._`-.__.-'_.-'    _.-'
 |`-._`-._    `-.__.-'    _.-'_.-'|
 |    `-._`-._        _.-'_.-'    |
  `-._    `-._`-.__.-'_.-'    _.-'
      `-._    `-.__.-'    _.-'
          `-._        _.-'
              `-.__.-'

[10092] 01 Oct 15:05:45.656 # Server started, Redis version 2.6.12
[10092] 01 Oct 15:05:45.659 * DB loaded from disk: 0.001 seconds
[10092] 01 Oct 15:05:45.660 * The server is now ready to accept connections on port 6379


Tips of how to run Redis as a Windows Service is available in the Code Project article "Running Redis as a Windows Service": http://www.codeproject.com/Articles/715967/Running-Redis-as-a-Windows-Service Note: If you install Redis on a Linux system, it is possible to set up Redis as a service / daemon quite easily. Check the INSTALLATION notes. Already now you will be able to cache page data quite easily, that is the HTML and javascript/CSS content of the page. To do this, just add the [OutputCache] action attribute on the MVC controller action you want to cache a page:

     [OutputCache(Duration=5)]
        public ActionResult Index()
        {
            return View();
        }



In the example above, the page data is cached with a duration of five seconds. We need to do additional measures for caching image data in Redis, this is also possible. First we define a controller action to handle the parsing of image paths and do necessary actions to Redis caching:

using System.Linq;
using System.Web.Mvc;
using RedisCacheTest.Models;

namespace RedisCacheTest.Controllers
{
    public class ImagesController : Controller
    {
       
        [OutputCache(Duration=5)]
        public ImageResult ShowImage(string id)
        {
            if (string.IsNullOrEmpty(id))
                return null; 

            string[] fileComponents = id.Split('-');
            if (!fileComponents.Any() || fileComponents.Count() != 2)
                return null;

            ImageFileExtension imageFileExtension = ImageFileExtensionPatternProvider.GetImageFileExtension()
                .FirstOrDefault(x => x.Extension == fileComponents[1]);
            if (imageFileExtension == null)
                return null; 

            ImageResult result = new ImageResult(Url.Content("~/Content/Images/" + fileComponents[0] + "." + imageFileExtension.Extension), imageFileExtension.ContentType);
            return result; 
        }

         

    }
}


namespace RedisCacheTest.Models
{

    public class ImageFileExtension
    {

        public string Extension { get; set; }

        public string ContentType { get; set; }


    }

}

namespace RedisCacheTest.Models
{

    public static class ImageFileExtensionPatternProvider
    {

        public static ImageFileExtension[] GetImageFileExtension()
        {
            return new ImageFileExtension[]
            {
                new ImageFileExtension { Extension = "gif", ContentType = "image/gif" },
                new ImageFileExtension { Extension = "png", ContentType = "image/png"  },
                new ImageFileExtension { Extension = "jpeg", ContentType = "image/jpeg"  },
                new ImageFileExtension { Extension = "jpg", ContentType = "image/jpeg" },
                new ImageFileExtension { Extension = "tif", ContentType = "image/tif" },
                new ImageFileExtension { Extension = "tiff", ContentType = "image/tif" },
                new ImageFileExtension { Extension = "bmp", ContentType = "image/bmp" },
            };
        }

    }
}

As one can see from the MVC controller action we expect images to reside in the Content/Images folder of the MVC solution and we use the Url.Content method. Our <IMG> tag will use a specific syntax for paths in the SRC attribute (shown later in the article). Note that a key point here is that we have a controller action that uses also the [OutputCache] directive. We have defined some familiar image file extension and associated ContentType values. In addition we return a new kind of ActionResult, ImageResult. This is defined next:


using System;
using System.IO;
using System.Web.Mvc;

namespace RedisCacheTest
{
    
    public class ImageResult : ActionResult 
    {

        public string ContentType { get; set; }

        public byte[] ImageBytes { get; set;  }


        public string SourceFileName { get; set; }

        public ImageResult(string sourceFileName, string contentType)
        {
            SourceFileName = sourceFileName;
            ContentType = contentType; 
        }

        public ImageResult(byte[] sourceStream, String contentType)
        {
            ImageBytes = sourceStream;
            ContentType = contentType; 
        }

        public override void ExecuteResult(ControllerContext context)
        {
            var response = context.HttpContext.Response;
            response.Clear();
            response.ContentType = ContentType;

            if (ImageBytes != null)
            {
                var stream = new MemoryStream(ImageBytes);
                stream.WriteTo(response.OutputStream);
                stream.Dispose();
            }
            else
            {
                response.TransmitFile(SourceFileName); 
            }
        }

    }
}

The class ImageResult inherits from ActionResult and will return image data in its override of ExecuteResult. We grab hold of the response from the ControllerContext.HttpContext.Response property and use methods on this response object to either TransmitFile or write directly to the stream. Next off, we need a simple MVC page to test out the Redis Cache of both page data and image data:

@using System.Globalization
@{
    ViewBag.Title = "Home Page";
}

<style type="text/css">

img {
    border: 1px solid black;
}

</style>


<h4>CROATIA Images (Cached 5 seconds)</h4>


<h5>Last update:</h5>
@Html.Label(DateTime.Now.ToString(CultureInfo.InvariantCulture))



@{
    var rnd = new Random(); 
}

@foreach (var number in Enumerable.Range(1, 1000))
{
    var imageIndex = rnd.Next(1, 7);
    var filename = Url.Action("ShowImage", "Images", new { id = Url.Encode("Croatia" + imageIndex + "-jpg") });

    <img src="@filename" width="150" />     
}


We use the syntax for images to do the action /Images/ShowImage and provide as a parameter (id) the name of the file minus its extension and then dash its extension type, in this case "-jpg". The MVC controller action will then use output caching also for image data since we have tagged the MVC controller action with [OutputCache] action filter. Here is an image of the cached web page, which will be refreshed every five seconds with some nice images from Croatia:



Of course, now our Redis server instance got more caching up to do since it also caches image data:


The contents of the Redis server can be interrogated by typing the KEYS command:

keys * 



We can even be more specific of using Redis to cache image data for example for an expiration of 60 seconds and directly use RedisNativeClient to take control of which keys to use for saving the image data. The following adjusted ImageResult action result will directly take care of loading the image data into a byte array and store it to Redis, then retrieve the byte array if the same key is already defined. I set here an expiration of 60 seconds. This makes it possible to reflect changes in images for example every 60 seconds, since the key is then set to expired. We can see that Redis is a great technology to be used to both cache HTML, javascript, CSS and image data in Redis, making it possible to quickly load media-intensive web pages and web sites. Best of all, we offload the ASP.NET application server running say a ASP.NET web site or MVC web site and retrieve data from Redis.

using System;
using System.Configuration;
using System.Diagnostics;
using System.IO;
using System.Web.Mvc;
using ServiceStack.Redis;
using System.Web;
using System.Web.Configuration;

namespace RedisCacheTest
{
    
    public class ImageResult : ActionResult 
    {

        
        public string ContentType { get; set; }

        public byte[] ImageBytes { get; set;  }


        public string SourceFileName { get; set; }

        public ImageResult(string sourceFileName, string contentType)
        {
            SourceFileName = sourceFileName;
            ContentType = contentType; 
        }

        public ImageResult(byte[] sourceStream, String contentType)
        {
            ImageBytes = sourceStream;
            ContentType = contentType; 
        }

        public override void ExecuteResult(ControllerContext context)
        {
            var response = context.HttpContext.Response;
            response.Clear();
            response.ContentType = ContentType;

            CheckImageDataPreload();

            if (ImageBytes != null)
            {
                WriteImageDataToStream(response);
            }
            else
            {
                byte[] imageData = UpdateImagePreloadData(context);
                if (imageData != null)
                {
                    ImageBytes = imageData;
                    WriteImageDataToStream(response);
                }
                else
                {
                    response.TransmitFile(SourceFileName);
                    response.Flush();
                }
            }
        }

        private void WriteImageDataToStream(HttpResponseBase response)
        {
            var stream = new MemoryStream(ImageBytes);
            stream.WriteTo(response.OutputStream);
            stream.Dispose();
        }

        private byte[] UpdateImagePreloadData(ControllerContext context)
        {
            try
            {
                var imageFileName = context.HttpContext.Server.MapPath(SourceFileName);
                byte[] imageFileContents = File.ReadAllBytes(imageFileName);

                using (var redisClient = new RedisNativeClient())
                {
                    redisClient.Set(GetRedisImageKey(), imageFileContents);
                    redisClient.Expire(GetRedisImageKey(), 60);
                    return imageFileContents;
                }
            }
            catch (Exception err)
            {
                Debug.WriteLine(err.Message);
            }
            return null; 
        }

        private void CheckImageDataPreload()
        {
            try
            {
                using (var redisClient = new RedisNativeClient())
                {
                    string redisImageKey = GetRedisImageKey();
                    var imageData = redisClient.Get(redisImageKey);
                    if (imageData != null)
                    {
                        ImageBytes = imageData;
                    }
                }
            }
            catch (Exception err)
            {
                Debug.WriteLine(err.Message);
            }
        }

        private string GetRedisImageKey()
        {
            return RedisCacheConfiguratedApplicationName + "/IMAGEBANK" + SourceFileName;
        }

        private static readonly string RedisCacheConfiguratedApplicationName = GetRedisApplicationName();

        private static string GetRedisApplicationName()
        {
            var section = ConfigurationManager.GetSection("system.web/caching/outputCache") as OutputCacheSection;
            if (section != null)
            {
                if (section.Providers != null && section.Providers.Count > 0)
                {
                    ProviderSettings providerSettings = section.Providers[0];
                    if (providerSettings.Parameters["applicationName"] != null)
                    {

                        string applicationName = providerSettings.Parameters["applicationName"];
                        return applicationName;
                    }
                }
            }
            return "RedisApplication";
        } 


    }
}

In fact, we can now remove our [OutputCache] action attribute of the ShowImage action, since we now use directly Redis through RedisNativeClient to persist the image data to Redis. Actually I have seen a benefit of this method by auto-expiring images. With Redis you usually want to cache the data which many users request. ASP.NET Cache will actually accumulate its content into the Redis cache irrespective of the last time the key in the Redis cache was entered. By using the ImageResult ActionResult here that works directly with Redis, we can auto expire image data, reducing memory pressure on Redis server. We can configure Redis to limit the maximum amount of memory that Redis can use by setting the maxmemory setting. The following redis.conf file which is a Redis configuration file for 2.6 has been adjusted to have 300 MB max memory limit:

# Redis configuration file example

# Note on units: when memory size is needed, it is possible to specify
# it in the usual form of 1k 5GB 4M and so forth:
#
# 1k => 1000 bytes
# 1kb => 1024 bytes
# 1m => 1000000 bytes
# 1mb => 1024*1024 bytes
# 1g => 1000000000 bytes
# 1gb => 1024*1024*1024 bytes
#
# units are case insensitive so 1GB 1Gb 1gB are all the same.

# By default Redis does not run as a daemon. Use 'yes' if you need it.
# Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
daemonize no

# When running daemonized, Redis writes a pid file in /var/run/redis.pid by
# default. You can specify a custom pid file location here.
pidfile /var/run/redis.pid

# Accept connections on the specified port, default is 6379.
# If port 0 is specified Redis will not listen on a TCP socket.
port 6379

# If you want you can bind a single interface, if the bind option is not
# specified all the interfaces will listen for incoming connections.
#
# bind 127.0.0.1

# Specify the path for the unix socket that will be used to listen for
# incoming connections. There is no default, so Redis will not listen
# on a unix socket when not specified.
#
# unixsocket /tmp/redis.sock
# unixsocketperm 755

# Close the connection after a client is idle for N seconds (0 to disable)
timeout 0

# TCP keepalive.
#
# If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence
# of communication. This is useful for two reasons:
#
# 1) Detect dead peers.
# 2) Take the connection alive from the point of view of network
#    equipment in the middle.
#
# On Linux, the specified value (in seconds) is the period used to send ACKs.
# Note that to close the connection the double of the time is needed.
# On other kernels the period depends on the kernel configuration.
#
# A reasonable value for this option is 60 seconds.
tcp-keepalive 0

# Specify the server verbosity level.
# This can be one of:
# debug (a lot of information, useful for development/testing)
# verbose (many rarely useful info, but not a mess like the debug level)
# notice (moderately verbose, what you want in production probably)
# warning (only very important / critical messages are logged)
loglevel notice

# Specify the log file name. Also 'stdout' can be used to force
# Redis to log on the standard output. Note that if you use standard
# output for logging but daemonize, logs will be sent to /dev/null
logfile stdout

# To enable logging to the system logger, just set 'syslog-enabled' to yes,
# and optionally update the other syslog parameters to suit your needs.
# syslog-enabled no

# Specify the syslog identity.
# syslog-ident redis

# Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.
# syslog-facility local0

# Set the number of databases. The default database is DB 0, you can select
# a different one on a per-connection basis using SELECT  where
# dbid is a number between 0 and 'databases'-1
databases 16

################################ SNAPSHOTTING  #################################
#
# Save the DB on disk:
#
#   save  
#
#   Will save the DB if both the given number of seconds and the given
#   number of write operations against the DB occurred.
#
#   In the example below the behaviour will be to save:
#   after 900 sec (15 min) if at least 1 key changed
#   after 300 sec (5 min) if at least 10 keys changed
#   after 60 sec if at least 10000 keys changed
#
#   Note: you can disable saving at all commenting all the "save" lines.
#
#   It is also possible to remove all the previously configured save
#   points by adding a save directive with a single empty string argument
#   like in the following example:
#
#   save ""

save 900 1
save 300 10
save 60 10000

# By default Redis will stop accepting writes if RDB snapshots are enabled
# (at least one save point) and the latest background save failed.
# This will make the user aware (in an hard way) that data is not persisting
# on disk properly, otherwise chances are that no one will notice and some
# distater will happen.
#
# If the background saving process will start working again Redis will
# automatically allow writes again.
#
# However if you have setup your proper monitoring of the Redis server
# and persistence, you may want to disable this feature so that Redis will
# continue to work as usually even if there are problems with disk,
# permissions, and so forth.
stop-writes-on-bgsave-error yes

# Compress string objects using LZF when dump .rdb databases?
# For default that's set to 'yes' as it's almost always a win.
# If you want to save some CPU in the saving child set it to 'no' but
# the dataset will likely be bigger if you have compressible values or keys.
rdbcompression yes

# Since version 5 of RDB a CRC64 checksum is placed at the end of the file.
# This makes the format more resistant to corruption but there is a performance
# hit to pay (around 10%) when saving and loading RDB files, so you can disable it
# for maximum performances.
#
# RDB files created with checksum disabled have a checksum of zero that will
# tell the loading code to skip the check.
rdbchecksum yes

# The filename where to dump the DB
dbfilename dump.rdb

# The working directory.
#
# The DB will be written inside this directory, with the filename specified
# above using the 'dbfilename' configuration directive.
# 
# The Append Only File will also be created inside this directory.
# 
# Note that you must specify a directory here, not a file name.
dir ./

################################# REPLICATION #################################

# Master-Slave replication. Use slaveof to make a Redis instance a copy of
# another Redis server. Note that the configuration is local to the slave
# so for example it is possible to configure the slave to save the DB with a
# different interval, or to listen to another port, and so on.
#
# slaveof  

# If the master is password protected (using the "requirepass" configuration
# directive below) it is possible to tell the slave to authenticate before
# starting the replication synchronization process, otherwise the master will
# refuse the slave request.
#
# masterauth 

# When a slave loses its connection with the master, or when the replication
# is still in progress, the slave can act in two different ways:
#
# 1) if slave-serve-stale-data is set to 'yes' (the default) the slave will
#    still reply to client requests, possibly with out of date data, or the
#    data set may just be empty if this is the first synchronization.
#
# 2) if slave-serve-stale-data is set to 'no' the slave will reply with
#    an error "SYNC with master in progress" to all the kind of commands
#    but to INFO and SLAVEOF.
#
slave-serve-stale-data yes

# You can configure a slave instance to accept writes or not. Writing against
# a slave instance may be useful to store some ephemeral data (because data
# written on a slave will be easily deleted after resync with the master) but
# may also cause problems if clients are writing to it because of a
# misconfiguration.
#
# Since Redis 2.6 by default slaves are read-only.
#
# Note: read only slaves are not designed to be exposed to untrusted clients
# on the internet. It's just a protection layer against misuse of the instance.
# Still a read only slave exports by default all the administrative commands
# such as CONFIG, DEBUG, and so forth. To a limited extend you can improve
# security of read only slaves using 'rename-command' to shadow all the
# administrative / dangerous commands.
slave-read-only yes

# Slaves send PINGs to server in a predefined interval. It's possible to change
# this interval with the repl_ping_slave_period option. The default value is 10
# seconds.
#
# repl-ping-slave-period 10

# The following option sets a timeout for both Bulk transfer I/O timeout and
# master data or ping response timeout. The default value is 60 seconds.
#
# It is important to make sure that this value is greater than the value
# specified for repl-ping-slave-period otherwise a timeout will be detected
# every time there is low traffic between the master and the slave.
#
# repl-timeout 60

# Disable TCP_NODELAY on the slave socket after SYNC?
#
# If you select "yes" Redis will use a smaller number of TCP packets and
# less bandwidth to send data to slaves. But this can add a delay for
# the data to appear on the slave side, up to 40 milliseconds with
# Linux kernels using a default configuration.
#
# If you select "no" the delay for data to appear on the slave side will
# be reduced but more bandwidth will be used for replication.
#
# By default we optimize for low latency, but in very high traffic conditions
# or when the master and slaves are many hops away, turning this to "yes" may
# be a good idea.
repl-disable-tcp-nodelay no

# The slave priority is an integer number published by Redis in the INFO output.
# It is used by Redis Sentinel in order to select a slave to promote into a
# master if the master is no longer working correctly.
#
# A slave with a low priority number is considered better for promotion, so
# for instance if there are three slaves with priority 10, 100, 25 Sentinel will
# pick the one wtih priority 10, that is the lowest.
#
# However a special priority of 0 marks the slave as not able to perform the
# role of master, so a slave with priority of 0 will never be selected by
# Redis Sentinel for promotion.
#
# By default the priority is 100.
slave-priority 100

################################## SECURITY ###################################

# Require clients to issue AUTH  before processing any other
# commands.  This might be useful in environments in which you do not trust
# others with access to the host running redis-server.
#
# This should stay commented out for backward compatibility and because most
# people do not need auth (e.g. they run their own servers).
# 
# Warning: since Redis is pretty fast an outside user can try up to
# 150k passwords per second against a good box. This means that you should
# use a very strong password otherwise it will be very easy to break.
#
# requirepass foobared

# Command renaming.
#
# It is possible to change the name of dangerous commands in a shared
# environment. For instance the CONFIG command may be renamed into something
# hard to guess so that it will still be available for internal-use tools
# but not available for general clients.
#
# Example:
#
# rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52
#
# It is also possible to completely kill a command by renaming it into
# an empty string:
#
# rename-command CONFIG ""
#
# Please note that changing the name of commands that are logged into the
# AOF file or transmitted to slaves may cause problems.

################################### LIMITS ####################################

# Set the max number of connected clients at the same time. By default
# this limit is set to 10000 clients, however if the Redis server is not
# able to configure the process file limit to allow for the specified limit
# the max number of allowed clients is set to the current file limit
# minus 32 (as Redis reserves a few file descriptors for internal uses).
#
# Once the limit is reached Redis will close all the new connections sending
# an error 'max number of clients reached'.
#
# maxclients 10000

# Don't use more memory than the specified amount of bytes.
# When the memory limit is reached Redis will try to remove keys
# accordingly to the eviction policy selected (see maxmemmory-policy).
#
# If Redis can't remove keys according to the policy, or if the policy is
# set to 'noeviction', Redis will start to reply with errors to commands
# that would use more memory, like SET, LPUSH, and so on, and will continue
# to reply to read-only commands like GET.
#
# This option is usually useful when using Redis as an LRU cache, or to set
# an hard memory limit for an instance (using the 'noeviction' policy).
#
# WARNING: If you have slaves attached to an instance with maxmemory on,
# the size of the output buffers needed to feed the slaves are subtracted
# from the used memory count, so that network problems / resyncs will
# not trigger a loop where keys are evicted, and in turn the output
# buffer of slaves is full with DELs of keys evicted triggering the deletion
# of more keys, and so forth until the database is completely emptied.
#
# In short... if you have slaves attached it is suggested that you set a lower
# limit for maxmemory so that there is some free RAM on the system for slave
# output buffers (but this is not needed if the policy is 'noeviction').
#
# maxmemory 

maxmemory 300mb

# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
# is reached. You can select among five behaviors:
# 
# volatile-lru -> remove the key with an expire set using an LRU algorithm
# allkeys-lru -> remove any key accordingly to the LRU algorithm
# volatile-random -> remove a random key with an expire set
# allkeys-random -> remove a random key, any key
# volatile-ttl -> remove the key with the nearest expire time (minor TTL)
# noeviction -> don't expire at all, just return an error on write operations
# 
# Note: with any of the above policies, Redis will return an error on write
#       operations, when there are not suitable keys for eviction.
#
#       At the date of writing this commands are: set setnx setex append
#       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
#       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
#       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
#       getset mset msetnx exec sort
#
# The default is:
#
# maxmemory-policy volatile-lru

# LRU and minimal TTL algorithms are not precise algorithms but approximated
# algorithms (in order to save memory), so you can select as well the sample
# size to check. For instance for default Redis will check three keys and
# pick the one that was used less recently, you can change the sample size
# using the following configuration directive.
#
# maxmemory-samples 3

############################## APPEND ONLY MODE ###############################

# By default Redis asynchronously dumps the dataset on disk. This mode is
# good enough in many applications, but an issue with the Redis process or
# a power outage may result into a few minutes of writes lost (depending on
# the configured save points).
#
# The Append Only File is an alternative persistence mode that provides
# much better durability. For instance using the default data fsync policy
# (see later in the config file) Redis can lose just one second of writes in a
# dramatic event like a server power outage, or a single write if something
# wrong with the Redis process itself happens, but the operating system is
# still running correctly.
#
# AOF and RDB persistence can be enabled at the same time without problems.
# If the AOF is enabled on startup Redis will load the AOF, that is the file
# with the better durability guarantees.
#
# Please check http://redis.io/topics/persistence for more information.

appendonly no

# The name of the append only file (default: "appendonly.aof")
# appendfilename appendonly.aof

# The fsync() call tells the Operating System to actually write data on disk
# instead to wait for more data in the output buffer. Some OS will really flush 
# data on disk, some other OS will just try to do it ASAP.
#
# Redis supports three different modes:
#
# no: don't fsync, just let the OS flush the data when it wants. Faster.
# always: fsync after every write to the append only log . Slow, Safest.
# everysec: fsync only one time every second. Compromise.
#
# The default is "everysec", as that's usually the right compromise between
# speed and data safety. It's up to you to understand if you can relax this to
# "no" that will let the operating system flush the output buffer when
# it wants, for better performances (but if you can live with the idea of
# some data loss consider the default persistence mode that's snapshotting),
# or on the contrary, use "always" that's very slow but a bit safer than
# everysec.
#
# More details please check the following article:
# http://antirez.com/post/redis-persistence-demystified.html
#
# If unsure, use "everysec".

# appendfsync always
appendfsync everysec
# appendfsync no

# When the AOF fsync policy is set to always or everysec, and a background
# saving process (a background save or AOF log background rewriting) is
# performing a lot of I/O against the disk, in some Linux configurations
# Redis may block too long on the fsync() call. Note that there is no fix for
# this currently, as even performing fsync in a different thread will block
# our synchronous write(2) call.
#
# In order to mitigate this problem it's possible to use the following option
# that will prevent fsync() from being called in the main process while a
# BGSAVE or BGREWRITEAOF is in progress.
#
# This means that while another child is saving, the durability of Redis is
# the same as "appendfsync none". In practical terms, this means that it is
# possible to lose up to 30 seconds of log in the worst scenario (with the
# default Linux settings).
# 
# If you have latency problems turn this to "yes". Otherwise leave it as
# "no" that is the safest pick from the point of view of durability.
no-appendfsync-on-rewrite no

# Automatic rewrite of the append only file.
# Redis is able to automatically rewrite the log file implicitly calling
# BGREWRITEAOF when the AOF log size grows by the specified percentage.
# 
# This is how it works: Redis remembers the size of the AOF file after the
# latest rewrite (if no rewrite has happened since the restart, the size of
# the AOF at startup is used).
#
# This base size is compared to the current size. If the current size is
# bigger than the specified percentage, the rewrite is triggered. Also
# you need to specify a minimal size for the AOF file to be rewritten, this
# is useful to avoid rewriting the AOF file even if the percentage increase
# is reached but it is still pretty small.
#
# Specify a percentage of zero in order to disable the automatic AOF
# rewrite feature.

auto-aof-rewrite-percentage 100
auto-aof-rewrite-min-size 64mb

################################ LUA SCRIPTING  ###############################

# Max execution time of a Lua script in milliseconds.
#
# If the maximum execution time is reached Redis will log that a script is
# still in execution after the maximum allowed time and will start to
# reply to queries with an error.
#
# When a long running script exceed the maximum execution time only the
# SCRIPT KILL and SHUTDOWN NOSAVE commands are available. The first can be
# used to stop a script that did not yet called write commands. The second
# is the only way to shut down the server in the case a write commands was
# already issue by the script but the user don't want to wait for the natural
# termination of the script.
#
# Set it to 0 or a negative value for unlimited execution without warnings.
lua-time-limit 5000

################################## SLOW LOG ###################################

# The Redis Slow Log is a system to log queries that exceeded a specified
# execution time. The execution time does not include the I/O operations
# like talking with the client, sending the reply and so forth,
# but just the time needed to actually execute the command (this is the only
# stage of command execution where the thread is blocked and can not serve
# other requests in the meantime).
# 
# You can configure the slow log with two parameters: one tells Redis
# what is the execution time, in microseconds, to exceed in order for the
# command to get logged, and the other parameter is the length of the
# slow log. When a new command is logged the oldest one is removed from the
# queue of logged commands.

# The following time is expressed in microseconds, so 1000000 is equivalent
# to one second. Note that a negative number disables the slow log, while
# a value of zero forces the logging of every command.
slowlog-log-slower-than 10000

# There is no limit to this length. Just be aware that it will consume memory.
# You can reclaim memory used by the slow log with SLOWLOG RESET.
slowlog-max-len 128

############################### ADVANCED CONFIG ###############################

# Hashes are encoded using a memory efficient data structure when they have a
# small number of entries, and the biggest entry does not exceed a given
# threshold. These thresholds can be configured using the following directives.
hash-max-ziplist-entries 512
hash-max-ziplist-value 64

# Similarly to hashes, small lists are also encoded in a special way in order
# to save a lot of space. The special representation is only used when
# you are under the following limits:
list-max-ziplist-entries 512
list-max-ziplist-value 64

# Sets have a special encoding in just one case: when a set is composed
# of just strings that happens to be integers in radix 10 in the range
# of 64 bit signed integers.
# The following configuration setting sets the limit in the size of the
# set in order to use this special memory saving encoding.
set-max-intset-entries 512

# Similarly to hashes and lists, sorted sets are also specially encoded in
# order to save a lot of space. This encoding is only used when the length and
# elements of a sorted set are below the following limits:
zset-max-ziplist-entries 128
zset-max-ziplist-value 64

# Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in
# order to help rehashing the main Redis hash table (the one mapping top-level
# keys to values). The hash table implementation Redis uses (see dict.c)
# performs a lazy rehashing: the more operation you run into an hash table
# that is rehashing, the more rehashing "steps" are performed, so if the
# server is idle the rehashing is never complete and some more memory is used
# by the hash table.
# 
# The default is to use this millisecond 10 times every second in order to
# active rehashing the main dictionaries, freeing memory when possible.
#
# If unsure:
# use "activerehashing no" if you have hard latency requirements and it is
# not a good thing in your environment that Redis can reply form time to time
# to queries with 2 milliseconds delay.
#
# use "activerehashing yes" if you don't have such hard requirements but
# want to free memory asap when possible.
activerehashing yes

# The client output buffer limits can be used to force disconnection of clients
# that are not reading data from the server fast enough for some reason (a
# common reason is that a Pub/Sub client can't consume messages as fast as the
# publisher can produce them).
#
# The limit can be set differently for the three different classes of clients:
#
# normal -> normal clients
# slave  -> slave clients and MONITOR clients
# pubsub -> clients subcribed to at least one pubsub channel or pattern
#
# The syntax of every client-output-buffer-limit directive is the following:
#
# client-output-buffer-limit    
#
# A client is immediately disconnected once the hard limit is reached, or if
# the soft limit is reached and remains reached for the specified number of
# seconds (continuously).
# So for instance if the hard limit is 32 megabytes and the soft limit is
# 16 megabytes / 10 seconds, the client will get disconnected immediately
# if the size of the output buffers reach 32 megabytes, but will also get
# disconnected if the client reaches 16 megabytes and continuously overcomes
# the limit for 10 seconds.
#
# By default normal clients are not limited because they don't receive data
# without asking (in a push way), but just after a request, so only
# asynchronous clients may create a scenario where data is requested faster
# than it can read.
#
# Instead there is a default limit for pubsub and slave clients, since
# subscribers and slaves receive data in a push fashion.
#
# Both the hard or the soft limit can be disabled by setting them to zero.
client-output-buffer-limit normal 0 0 0
client-output-buffer-limit slave 256mb 64mb 60
client-output-buffer-limit pubsub 32mb 8mb 60

# Redis calls an internal function to perform many background tasks, like
# closing connections of clients in timeot, purging expired keys that are
# never requested, and so forth.
#
# Not all tasks are perforemd with the same frequency, but Redis checks for
# tasks to perform accordingly to the specified "hz" value.
#
# By default "hz" is set to 10. Raising the value will use more CPU when
# Redis is idle, but at the same time will make Redis more responsive when
# there are many keys expiring at the same time, and timeouts may be
# handled with more precision.
#
# The range is between 1 and 500, however a value over 100 is usually not
# a good idea. Most users should use the default of 10 and raise this up to
# 100 only in environments where very low latency is required.
hz 10

# When a child rewrites the AOF file, if the following option is enabled
# the file will be fsync-ed every 32 MB of data generated. This is useful
# in order to commit the file to the disk more incrementally and avoid
# big latency spikes.
#aof-rewrite-incremental-fsync yes

################################## INCLUDES ###################################

# Include one or more other config files here.  This is useful if you
# have a standard template that goes to all Redis server but also need
# to customize a few per-server settings.  Include files can include
# other files, so use this wisely.
#
# include /path/to/local.conf
# include /path/to/other.conf


We can now check our maxmemory setting by using the following Redis command:

config get maxmemory





To sum up, we now have a powerful way of caching page content and image data to Redis!


Download Visual Studio 2013 solution discussed in this article

Redis Cache VS 2013 Solution [ZIP] | 27,5 MB Tested with Redis 2.6 Windows binaries (64-bits edition): https://github.com/MSOpenTech/redis/tree/2.6/bin/release