Sitecore Custom HTTP Handlers

We recently had a requirement that we need thumbnail for PDFs stored in Sitecore, so whenever we need to find PDFs or other media files, we can find out them by its thumbnail. In starting we thought to create a thumbnail for each media file and then store it to another location in Sitecore tree itself while uploading media. It was a good idea, but the problem in this approach would come when a user updates the media? We need to create thumbnail again... Same thing when user deletes/moves/publishes, etc. it needed to generate thumbnail all the time.

Finally we came to a perfect solution of using Custom HTTP Handler, using which we can fulfill this requirement easily.

Overview of Sitecore Custom Handlers?

Search for in your web.config. These are the custom handlers called by Sitecore to serve requests of media, xaml, icon, feed, etc. See below block in web.config:
      <handler handler="sitecore_media.ashx" trigger="~/media/" />
      <handler handler="sitecore_api.ashx" trigger="~/api/" />
      <handler handler="sitecore_xaml.ashx" trigger="~/xaml/" />
      <handler handler="sitecore_icon.ashx" trigger="~/icon/" />
      <handler handler="sitecore_feed.ashx" trigger="~/feed/" />
Sitecore.Pipelines.HttpRequest.CustomHandlers processor from httpBeginRequest dispatches requests to specialized handlers that are required. These handlers are defined in web.config under configuration/sitecore/customHandlers.

If the current request ends with the a handler’s file (e.g., sitecore_media.ashx), then Sitecore aborts the current pipeline, since this request is specifically targeting a handler directly, which are defined in system.webServer/handlers section as below, which shows that the media request will be served through Sitecore.Resources.Media.MediaRequestHandler. See below block of web.config:
      <add name="Sitecore.MediaRequestHandler" path="sitecore_media.ashx"  type="Sitecore.Resources.Media.MediaRequestHandler, Sitecore.Kernel" verb="*" />

Create own Sitecore Custom Handlers to generate thumbnails of media items

Now, we created a new custom handler for creating thumbnail and registered in handlers as below:
<configuration xmlns:patch="">

    <!-- Define Custom Handler -->
      <handler trigger="~/mediathumb/" handler="sitecore_media_thumb.ashx"  />

    <!-- Define Media Prefix -->
        <prefix value="~/mediathumb" />

  <!-- Define Web Handler -->
     <add verb="*" path="sitecore_media_thumb.ashx" type="SitecoreTactics.ThumbnailManager.PDFThumbnailRequestHandler, SitecoreTactics.ThumbnailManager" name="SitecoreTactics.PDFThumbnailRequestHandler"/>
This class will create a thumbnail of the request PDF on-the-fly using GhostScript. We will save this thumbnail as Media Cache, so on the next request, the thumbnail will not be created, but will be served from Media Cache itself, same as Sitecore serves media items.

In this case suppose, the PDF we uploaded has URL:
Now, we can get its thumbnail as JPG file using URL, which will be served by our new handler because it contains /~/mediathumb trigger.

Finally, we do not need to take care if media item is moved, deleted, published or updated. I will attach its source code very soon.... :)

What else we can do using Custom Handlers?

- In above approach, we can also generate thumbnail of different size, dimensions passed through querystring, same way Sitecore provides it for images. Read how we can Resize Sitecore Media Images on the fly.
- Even Custom Handlers can be useful to serve different kind of resources like creating sitemap (/~/sitemap/), RSS for page or its children (/~/rss/), stylesheets (/~/css/), javascripts (/~/js/), etc.

Related Posts:
- PDF Thumbnail Handler
- Show PDF Thumbnail Icons in Content Editor