Sean Kearney's Blog

Gravatar 2.0 has been out for a few weeks now and I didn't see any ASP.NET implementation listed on their site so I figured I would wip one up.

It is pretty simple to implement a Gravatar. All you need to do is set the src attribute of an img tag to a location on Gravatar's domain. The src attribute has a few parameters, but the only "tricky" one is an MD5 hash of the users email address.

Here is the code:

public class Gravatar : System.Web.UI.WebControls.Image
    {
        #region Rating property
        public enum GravatarRating {G , PG , R , X }
        private GravatarRating _Rating = GravatarRating.G;
        public GravatarRating Rating
        {
            get { return _Rating; }// get
            set { _Rating = value; }// set
        }// property

        #endregion

        #region Size property
        private int _Size=80;
        /// <summary>
        /// An optional "size" parameter may follow that specifies the desired width and height of the gravatar. Valid values are from 1 to 80 inclusive. Any size other than 80 will cause the original gravatar image to be downsampled using bicubic resampling before output.
        /// </summary>
        public int Size
        {
            get { 
                if (_Size <= 0)
                    return 80;
                if (_Size > 80)
                    return 80;
                return _Size;
            }
            set { 
                _Size = value;
                base.Width = value;
                base.Height = value;
            }// set
        }// property
        #endregion

        #region Email property
        private string _Email;
        public string Email
        {
            get { return _Email; }// get
            set { _Email = value; }// set
        }// property

        #endregion

        #region DefaultImageUrl property
        private string _DefaultImageUrl;

        public string DefaultImageUrl
        {
            get { return _DefaultImageUrl; }// get
            set { _DefaultImageUrl = value; }// set
        }// property

        #endregion

        #region Hide some members
        new private string ImageUrl { get { return String.Empty; } }
        /// Gravatar only supports a size property
        new private int Width { get { return Size; } }
        new private int Height { get { return Size; } }
        #endregion

        protected override void Render(System.Web.UI.HtmlTextWriter writer)
        {
            System.Text.StringBuilder image = new System.Text.StringBuilder();
            image.Append("http://www.gravatar.com/avatar.php?");
            image.Append("gravatar_id=");
            image.Append(MD5HashMe(Email));
            image.Append("&rating=");
            image.Append(Rating.ToString());
            image.Append("&size=");
            image.Append(Size.ToString());

            if (!String.IsNullOrEmpty(DefaultImageUrl))
            {
                image.Append("&default=");
                image.Append(System.Web.HttpUtility.UrlEncode(DefaultImageUrl));
            }

            base.ImageUrl = image.ToString();
            base.Render(writer);
        }

        private string MD5HashMe(string email)
        {
            System.Text.Encoder enc = System.Text.Encoding.Unicode.GetEncoder();
            byte[] unicodeText = new byte[email.Length * 2];
            enc.GetBytes(email.ToCharArray(), 0, email.Length, unicodeText, 0, true);

            System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
            byte[] result = md5.ComputeHash(unicodeText);

            System.Text.StringBuilder sb = new System.Text.StringBuilder();
            for (int i = 0; i < result.Length; i++)
                sb.Append(result.ToString("X2"));

            return sb.ToString();
        }

To use this control all you need to do is add the following to your .aspx page:

<%@ Register TagPrefix="CC" Assembly="CarKnee.Controls" Namespace="CarKnee.Controls" %>
<CC:Gravatar id="g" runat="server" Size="80" Email="test@example.com" Rating="G" DefaultImageUrl="http://www.google.com/intl/en_ALL/images/logo.gif" />

The code is also available for download here.