With gravatars now becoming ubiquitous in blogs and forums, I have developed an ASP.NET Control that encapsulates their functionality in a simple, reusable component. It’s so easy to use, you can download and be using it on your ASP.NET sites within minutes.

I introduced the control in February of 2008, and updated the functionality in March of 2008.

I’ve since had a lot of interest in the source code for the control, and so this post describes how the control works, as well as providing a download containing the control, as well as the full control source and example website that uses the control.

OK, let me download it already!

Download the Control and get started. Note that the demo projects included in the ZIP were written in Visual Studio 2005, so if you’re using Visual Studio 2008, you’ll need to convert the solution. If you’ve not done a conversion before, just follow the instructions that Visual Studio provides. Please also note that the solution will not open in Express Editions, since they do not support control projects. However, you can still use the control that’s included in the ZIP file.

Unzip the .zip download, and you’ll have the following folder structure:

The root contains a small readme file, Visual Studio solution, FreshClickmedia.dll – the gravatar control assembly, Freshclickmedia.Web control project and GravatarSite website, which contains a few control examples.

Opening the solution in visual studio will give you this solution structure:

Fire up the website, and you should see something like this:

Examining the Code

    <h1>Gravatar Examples</h1>
    <h2>My email address, size of 80 pixels:</h2>
        <fcm:Gravatar ID="Gravatar1" runat="server" Email="youremailaddress@domain.com"
             OutputGravatarSiteLink="true" Size="80" />
    <h2>No email address, with default image (absolute url) specified:</h2>
        <fcm:Gravatar ID="Gravatar2" runat="server" Size="80" DefaultImage="http://farm3.static.flickr.com/2375/2552064340_192825f989_o.jpg" />
    <h2>Email address not associated with Gravatar, with no default image:</h2>
        <fcm:Gravatar ID="Gravatar3" runat="server" Email="thisemaildoesnotexist@freshclickmedia.com" Size="80"  />

The control requires an email address:

<fcm:Gravatar ID='Gravatar1' runat='server' Email='username@domain.com' />

For my email address, I get the following generated HTML:

And if we look at the generated source:

<a id="Gravatar1" href="http://www.gravatar.com" title="Get your avatar"><img width="80" height="80" src="http://www.gravatar.com/avatar.php?gravatar_id=ccf3b8c638f15d005e5d070aeb1a3923&rating=G&size=80" alt="Gravatar" /></a>

The default produces a hyperlink off to the Gravatar site with a title “Get your avatar”. The image contains the MD5 email hash, a rating of “G” (suitable for all audience types), and a size of 80.

Customisation

The control supports a number of properties supporting the customisation of its output.

Size

The size property of the control can be in the range 1 to 80. If it is outside this range, a default of 80 will be used.

MaxAllowedRating

The ‘highest’ allowed rating of image.

• A G rated gravatar is suitable for display on all websites with any audience type.
• PG rated gravatars contain may contain rude gestures, provocatively dressed individuals, the lesser swear words, or mild violence.
• R rated gravatars may contain such things as harsh profanity, intense violence, nudity, or hard drug use.
• X rated gravatars may contain hardcore sexual imagery or extremely disturbing violence.

OutputGravatarSiteLink

True by default, determines whether a hyperlink linking to the gravatar website will be output around the image.

LinkTitle

“Get your avatar” by default, allows the customisation of the ‘title’ attribute of the link (obviously doesn’t apply if OutputGravatarSiteLink property is set to false.)

DefaultImage

URL encoded URL, protocol included, of a GIF, JPEG, or PNG image that should be returned if either the requested email address has no associated gravatar, or that gravatar has a rating higher than is allowed by the “MaxAllowedRating” property.

The code snippet below shows the associated properties.

<fcm:Gravatar ID="Gravatar1" runat="server"
    Email="username@domain.com"
    DefaultImage="http://www.site.com/default.jpg"
    OutputGravatarSiteLink="true" Size="40" />

Examining the control code

The Gravatar control derives from System.Web.UI.WebControls.WebControl and overrides the Render method.

The various properties such as Email are all implemented as simple C# properties, with various attributes depending on the property.

[Bindable(true), Category("Appearance"), DefaultValue("80")]
public short Size
{
	get
	{
		return _size;
	}
	set
	{
		_size = value;
	}
}

These properties are then used in the Render method to write out HTML using the method’s HtmlTextWriter parameter.

The Render method begins by adding the default attributes to the render, ensuring that the size is within the valid range of 1 to 512, and initialises the gravatar URL:

AddAttributesToRender(output);
// if the size property has been specified, ensure it is a short, and in the range
// 1..512:
try
{
    // if it's not in the allowed range, throw an exception:
    if (Size < 1 || Size > 512)
        throw new ArgumentOutOfRangeException();
}
catch
{
    Size = 80;
}
// default the image url:
string imageUrl = "http://www.gravatar.com/avatar.php?";

If an Email address has been supplied, the MD5CryptoServiceProvider hashes the email and a StringBuilder converts this to the required format:

if( !string.IsNullOrEmpty( Email))
{
    // build up image url, including MD5 hash for supplied email:
    MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
    UTF8Encoding encoder = new UTF8Encoding();
    MD5CryptoServiceProvider md5Hasher = new MD5CryptoServiceProvider();
    byte[] hashedBytes = md5Hasher.ComputeHash(encoder.GetBytes(Email));
    StringBuilder sb = new StringBuilder(hashedBytes.Length * 2);
    for (int i = 0; i < hashedBytes.Length; i++)
    {
        sb.Append(hashedBytes[i].ToString("X2"));
    }
    // output parameters:
    imageUrl += "gravatar_id=" + sb.ToString().ToLower();
    imageUrl += "&rating=" + MaxAllowedRating.ToString();
    imageUrl += "&size=" + Size.ToString();
}

The final part of the method assigns a default image, if one has been specified, outputs the site ink, if required, outputs the required attributes and tags.

// output default parameter if specified
if (!string.IsNullOrEmpty(DefaultImage))
{
    imageUrl += "&default=" + HttpUtility.UrlEncode(DefaultImage);
}
// if we need to output the site link:
if (OutputGravatarSiteLink)
{
    output.AddAttribute(HtmlTextWriterAttribute.Href, "http://www.gravatar.com");
    output.AddAttribute(HtmlTextWriterAttribute.Title, LinkTitle);
    output.RenderBeginTag(HtmlTextWriterTag.A);
}
// output required attributes/img tag:
output.AddAttribute(HtmlTextWriterAttribute.Width, Size.ToString());
output.AddAttribute(HtmlTextWriterAttribute.Height, Size.ToString());
output.AddAttribute(HtmlTextWriterAttribute.Src, imageUrl);
output.AddAttribute(HtmlTextWriterAttribute.Alt, "Gravatar");
output.RenderBeginTag("img");
output.RenderEndTag();
// if we need to output the site link:
if (OutputGravatarSiteLink)
{
    output.RenderEndTag();
}

Using the control on your own projects

As previously mentioned, the download solution will not open properly in Express versions of Visual Studio, since it does not support control projects, but the control, included in the download is supported by all versions of Visual Studio, 2005 and later.

The easiest way to use the control is to add the control to the toolbox. To do this, ensure that you are in design mode (looking at a web page), and right click on the ‘Standard’ group header of the Toolbox. From the context menu, select “Choose Items” and browse to the assembly (Freshclickmedia.Web.dll), and click “OK” to add.

Once you’ve added the assembly, you should see the following:

From there, you can drag the control onto your page and start having fun!