💡 Today I Learned

Serving some images from MVC but not all

I want some .png requests to be served by asp.net MVC, and most of them to just be served as static images.

I got it working with the IIS express, but it returned IIS level 404's when shipped to production (which uses real IIS).

In other words, the request never made it to the application. IIS looked at the url, assumed it referred to a static file, checked for the existence of the static file on disk, didn't find it, and thus quit.

If you want ALL static files to be served from MVC (rather than IIS) you add this to your web.config

<modules runAllManagedModulesForAllRequests="true">

...under <system.WebServer>

aka — THE DREADED RAMMFAR!!

But that means every request will be sent to Asp.net, which could create a whole bunch of work for you.

If you only want a subset — a folder for example — to be routed through Asp.net (and MVC), then you can use this approach:

Under this node:

<system.webServer>
    <handlers>

Add, for example:

<add name="MyImageHandler" path="HelpImg/*" verb="GET" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0"/>

name is unimportant, just a name. verb is GET, because we're only interested in getting the images. path is important... it's the folder which we are allowing. For me it was HelpImg/*

The rest of the rule is the same as this existing rule, which you should find in that handlers section already:

<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"/>

...and by the time you're reusing this technique, that other rule may have moved on a bit... so make it match with it.

Thanks to Darin Dimitrov's answers here.