Why are Content, Scripts served as static and other directories not?

Question

So this is a bit of asp.net I feel like way too many people don't understand. That is to say, I don't understand it and I've asked a bunch of people/googled and no one else seems to know the specifics either.

By default ASP.Net applications will serve files in Content and Scripts directories as static content. In fact, if I create other directories, I think it will serve static content in these as well.

However, the contents of some directories won't be served - the typical Asp.Net Mvc Controllers directory for example. In addition, you can always configure routes in asp.net (or OWIN handlers) that will pick up certain routes but not either.

Nothing seems to be configured anywhere. I have my suspicions, but I'm really not clear on what exactly is the rule for what gets served as static content and what gets processed by asp.net?

Answer 1

I've always found this graphic helpful: https://web.archive.org/web/20211021221111/https://www.4guysfromrolla.com/images/step2.gif

Specifically, the HttpHandlers mentioned in that graphic correspond to this section of the Web.Config file in your .NET web project's root directory:

<system.webServer>
    <handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>

The path attribute of that tag can be used to configure only certain directories being handled by a certain class. At that point, IIS will hand off the HTTP request to the appropriate class, with the proper context and thread etc. My guess is that if you are running IIS with multiple frameworks, each has a distinct path associated with its add-handler tag.

Additionally, IIS has its own default settings for what file extensions are mapped to what handler classes. These can also be modified in the IIS management interface, so it's possible that your super-helpful ops team added that for you there even if it's missing from your web.config. At the end of the day, though, it's a relationship between url-HttpHandler class that determines static-file versus dynamic.

Edit:

There's another set of tags, outlined at this ServerFault answer:

https://serverfault.com/questions/175499/serving-cs-csproj-files-on-iis7-5

That describes a <add fileExtension=".cs" allowed="false" /> tag that operates on the file extension as opposed to a pattern on the entire path. This is what disallows files ending in .cs, and .csproj from being served. Additionally, since you're operating on an installation of IISExpress, you should know that it uses a different configuration file than the standard machine.config. The path for that file is described at this answer:

Where is the IIS Express configuration / metabase file found?

All this gets muddied a little by the notion of self-hosting, aka no IIS. Nancy does this, I believe, and ServiceStack can as well. I have no experience doing that, but the way they handle paths is probably a little different.