/Visigo.Sharepoint.FormsBasedAuthentication/Visigo.Sharepoint.FormsBasedAuthentication/Layouts/FBA/ImageHipChallenge.ashx

<%@ WebHandler Language="C#" Class="Visigo.Sharepoint.FormsBasedAuthentication.HIP.ImageHipChallengeHandler" %>

using System;

using System.Web;

using System.Drawing;

using System.Drawing.Imaging;

using System.Drawing.Drawing2D;

using System.Collections.Specialized;

using System.Security.Cryptography;



namespace Visigo.Sharepoint.FormsBasedAuthentication.HIP

{

    /// <summary>Provides cryptographically-strong pseudo-random numbers.</summary>

    internal class RandomNumbers

    {

        /// <summary>Random number generator.</summary>

        private RNGCryptoServiceProvider _rand = new RNGCryptoServiceProvider();



        /// <summary>Used by NextRandom and NextRandomDouble.</summary>

        /// <remarks>

        /// RNGCryptoServiceProvider is not thread-safe.  Therefore, we only call to on a single thread.

        /// As a result, we can resuse the same byte arrays for every call.

        /// </remarks>

        private byte[] _rd4 = new byte[4], _rd8 = new byte[8];



        /// <summary>Gets a random non-negative integer less than max.</summary>

        /// <param name="max">The upper-bound for the random number.</param>

        /// <returns>The generated random number.</returns>

        public int Next(int max)

        {

            if (max <= 0) throw new ArgumentOutOfRangeException("max");

            _rand.GetBytes(_rd4);

            int val = BitConverter.ToInt32(_rd4, 0) % max;

            if (val < 0) val = -val;

            return val;

        }



        /// <summary>Gets a random number between min and max, inclusive.</summary>

        /// <param name="min">The minimum possible value.</param>

        /// <param name="max">The maximum possible value.</param>

        /// <returns>The randomly generated number.</returns>

        public int Next(int min, int max)

        {

            if (min > max) throw new ArgumentOutOfRangeException("max");

            return Next(max - min + 1) + min;

        }



        /// <summary>Gets a randomly generated double between 0.0 and 1.1.</summary>

        /// <returns>The random number.</returns>

        public double NextDouble()

        {

            _rand.GetBytes(_rd8);

            return BitConverter.ToUInt64(_rd8, 0) / (double)UInt64.MaxValue;

        }

    }

    

	/// <summary>Handles requests for dynamic images from the ImageHipChallenge control.</summary>

	public class ImageHipChallengeHandler : IHttpHandler

	{

        /// <summary>Default value for the RenderUrl property.</summary>

        private const string RENDERURL_DEFAULT = "ImageHipChallenge.ashx";

        /// <summary>Query string key for the image width.</summary>

        internal const string WIDTH_KEY = "w";

        /// <summary>Query string key for the image height.</summary>

        internal const string HEIGHT_KEY = "h";

        /// <summary>Query string key for challenge ID.</summary>

        internal const string ID_KEY = "id";        

        private RandomNumbers _rand = new RandomNumbers();

        

		/// <summary>Maximum width of an image to generate.</summary>

		private const int MAX_IMAGE_WIDTH = 600;

		/// <summary>Maximum height of an image to generate.</summary>

		private const int MAX_IMAGE_HEIGHT = 600;



		/// <summary>Gets whether this handler is reusable.</summary>

		/// <remarks>This handler is not thread-safe (uses non thread-safe member variables), so it is not reusable.</remarks>

		public bool IsReusable { get { return false; } }



        /// <summary>Gets a random non-negative integer less than max.</summary>

        /// <param name="max">The upper-bound for the random number.</param>

        /// <returns>The generated random number.</returns>

        protected int NextRandom(int max) { return _rand.Next(max); }



        /// <summary>Gets a random number between min and max, inclusive.</summary>

        /// <param name="min">The minimum possible value.</param>

        /// <param name="max">The maximum possible value.</param>

        /// <returns>The randomly generated number.</returns>

        protected int NextRandom(int min, int max) { return _rand.Next(min, max); }



        /// <summary>Gets a randomly generated double between 0.0 and 1.1.</summary>

        /// <returns>The random number.</returns>

        protected double NextRandomDouble() { return _rand.NextDouble(); }



        /// <summary>Gets the challenge text for a particular ID.</summary>

        /// <param name="challengeId">The ID of the challenge text to retrieve.</param>

        /// <returns>The text associated with the specified ID; null if no text exists.</returns>

        internal static string GetChallengeText(Guid challengeId)

        {

            HttpContext ctx = HttpContext.Current;

            return (string)ctx.Cache[challengeId.ToString()];

        }

                

		/// <summary>Processes the image request and generates the appropriate image.</summary>

		/// <param name="context">The current HttpContext.</param>

		public void ProcessRequest(HttpContext context)

		{

			// Retrieve query parameters and challenge text

            NameValueCollection queryString = context.Request.QueryString;

            int width = Convert.ToInt32(queryString[WIDTH_KEY]);

            if (width <= 0 || width > MAX_IMAGE_WIDTH) throw new ArgumentOutOfRangeException(WIDTH_KEY);

            int height = Convert.ToInt32(queryString[HEIGHT_KEY]);

            if (height <= 0 || height > MAX_IMAGE_HEIGHT) throw new ArgumentOutOfRangeException(HEIGHT_KEY);

            string text = GetChallengeText(new Guid(queryString[ID_KEY]));



            if (text != null)

            {

                // We successfully retrieved the information, so generate the image and send it to the client.

                HttpResponse resp = context.Response;

                resp.Clear();

                resp.ContentType = "image/jpeg";

                using (Bitmap bmp = GenerateImage(text, new Size(width, height)))

                {

                    bmp.Save(resp.OutputStream, ImageFormat.Jpeg);

                }

            }

		}



		/// <summary>Generates the challenge image.</summary>

		/// <param name="text">The text to be rendered into the image.</param>

		/// <param name="size">The size of the image to generate.</param>

		/// <returns>A dynamically-generated challenge image.</returns>

		public Bitmap GenerateImage(string text, Size size)

		{

			// Create the new Bitmap of the specified size and render to it

			Bitmap bmp = new Bitmap(size.Width, size.Height);

			using (Graphics g = Graphics.FromImage(bmp))

			{

				// Draw the background as a random linear gradient

				using(Brush b = new LinearGradientBrush(

						  new Rectangle(0,0,size.Width,size.Height),

						  Color.FromArgb(NextRandom(256),NextRandom(256),NextRandom(256)),

						  Color.FromArgb(NextRandom(256),NextRandom(256),NextRandom(256)),

						  (float)(NextRandomDouble()*360),false))

				{

					g.FillRectangle(b, 0, 0, bmp.Width, bmp.Height);

				}



				// Select a font family and create the default sized font.  We then need to shrink

				// the font size until the text fits.

				FontFamily ff = _families[NextRandom(_families.Length)];

				int emSize = (int)(size.Width*2 / text.Length);

				Font f = new Font(ff, emSize);

				try

				{

					// Make sure that the font size we have will fit with the selected text.

					SizeF measured = new SizeF(0,0);

					SizeF workingSize = new SizeF(size.Width, size.Height);

					while (emSize > 2 &&

						(measured = g.MeasureString(text, f)).Width > workingSize.Width ||

						measured.Height > workingSize.Height)

					{

						f.Dispose();

						f = new Font(ff, emSize -= 2);

					}



					// Select a color and draw the string into the center of the image

					using(StringFormat fmt = new StringFormat())

					{

						fmt.Alignment = fmt.LineAlignment = StringAlignment.Center;

						using(Brush b = new LinearGradientBrush(

								  new Rectangle(0,0,size.Width/2,size.Height/2),

								  Color.FromArgb(NextRandom(256),NextRandom(256),NextRandom(256)),

								  Color.FromArgb(NextRandom(256),NextRandom(256),NextRandom(256)),

								  (float)(NextRandomDouble()*360),false))

						{

							g.DrawString(text, f, b, new Rectangle(0,0,bmp.Width,bmp.Height), fmt);

						}

					}

				}

				finally

				{

					// Clean up

					f.Dispose();

				}

			}

			

			// Distort the final image and return it.  This distortion amount is fairly arbitrary.

			DistortImage(bmp, NextRandom(5, 10) * (NextRandom(2) == 1 ? 1 : -1) );

			return bmp;

		}



		/// <summary>Distorts the image.</summary>

		/// <param name="b">The image to be transformed.</param>

		/// <param name="distortion">An amount of distortion.</param>

		private static void DistortImage(Bitmap b, double distortion)

		{

			int width = b.Width, height = b.Height;



			// Copy the image so that we're always using the original for source color

			using (Bitmap copy = (Bitmap)b.Clone())

			{

				// Iterate over every pixel

				for (int y = 0; y < height; y++)

				{

					for (int x = 0; x < width; x++)

					{

						// Adds a simple wave

						int newX = (int)(x + (distortion * Math.Sin(Math.PI * y / 64.0)));

						int newY = (int)(y + (distortion * Math.Cos(Math.PI * x / 64.0)));

						if (newX < 0 || newX >= width) newX = 0;

						if (newY < 0 || newY >= height) newY = 0;

						b.SetPixel(x, y, copy.GetPixel(newX, newY));

					}

				}

			}

		}



		/// <summary>List of fonts that can be used for rendering text.</summary>

		/// <remarks>This list can be changed to include any families available on the current system.</remarks>

		private static FontFamily [] _families = { 

													 new FontFamily("Times New Roman")

												 };

	}

}