why is the httphandler not running

Question

I have written an httpHandler for an ASP.NET MVC4 site that generates an an image. The ProcessRequest function is not being called. Any thoughts on why?

MVC4, IIS Express, Windows 8 Pro

Web.config > system.webServer

 <system.webServer>
    <validation validateIntegratedModeConfiguration="false" />
    <handlers>
      <remove name="TextImage" />
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" />
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness32" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness64" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
      <add name="TextImage" path="textimage/*.png" verb="*" resourceType="Unspecified" type="MultiStepUI.TextImageHandler, MultiStepUI_MOBETTER" />
    </handlers>
  </system.webServer>

usage

<img src="/textimage/step1.png?q=Step 1&c=404040&w=30&h=250&z=12" />

Answer 1

The answer can be found on the web if one just knows what to look for.

MVC routing engine tries to map all requests to a controller - which is not what we want in this case. In addition to registering the handler in Web.config we need to tell the MVC route engine to ignore the httpHandler path so that the ASP.NET engine can handle its routing.

I've chosen to use the example from Phil Haack

To combat link rot this is an excerpt from the article

By default, ASP.NET Routing ignores requests for files that do not exist on disk. I explained the reason for this in a previous post on upcoming routing changes. Long story short, we didn’t want routing to attempt to route requests for static files such as images. Unfortunately, this caused us a headache when we remembered that many features of ASP.NET make requests for .axd files which do not exist on disk.

To fix this, we included a new extension method on RouteCollection, IgnoreRoute, that creates a Route mapped to the StopRoutingHandler route handler (class that implements IRouteHandler). Effectively, any request that matches an “ignore route” will be ignored by routing and normal ASP.NET handling will occur based on existing http handler mappings. Hence in our default template, you’ll notice we have the following route defined.

routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

This handles the standard .axd requests. However, there are other cases where you might have requests for files that don’t exist on disk. For example, if you register an HTTP Handler directly to a type that implements IHttpHandler. Not to mention requests for favicon.ico that the browser makes automatically. ASP.NET Routing attempts to route these requests to a controller. One solution to this is to add an appropriate ignore route to indicate that routing should ignore these requests. Unfortunately, we can’t do something like this:

{*path}.aspx/{*pathinfo}

We only allow one catch-all route and it must happen at the end of the URL. However, you can take the following approach. In this example, I added the following two routes.

routes.IgnoreRoute("{*allaspx}", new {allaspx=@".*\.aspx(/.*)?"});
routes.IgnoreRoute("{*favicon}", new {favicon=@"(.*/)?favicon.ico(/.*)?"});

What I’m doing here is a technique Eilon showed me which is to map all URLs to these routes, but then restrict which routes to ignore via the constraints dictionary. So in this case, these routes will match (and thus ignore) all requests for favicon.ico (no matter which directory) as well as requests for a .aspx file. Since we told routing to ignore these requests, normal ASP.NET processing of these requests will occur.