Add HTTP headers to static files in ASP.​NET Core

Usually, static files like JavaScript, CSS, images and so on, are cached on the client after the first request. But sometimes, you need to disable the cache or to add a special cache handling.

To provide static files in a ASP.NET Core application, you use the StaticFileMiddleware:


This extension method has two overloads. One of them needs a StaticFileOptions instance, which is our friend in this case. This options has a property called OnPrepareResponse of type Action<StaticFileResponseContext>. Inside this Action, you have access to the HttpContext and many more. Let's see how it looks like to set the cache life time to 12 hours:

app.UseStaticFiles(new StaticFileOptions()
    OnPrepareResponse = context =>
        context.Context.Response.Headers["Cache-Control"] = 
                "private, max-age=43200";

        context.Context.Response.Headers["Expires"] = 

With the StaticFileResponseContext, you also have access to the file of the currently handled file. With this info, it is possible to manipulate the HTTP headers just for a specific file or file type.

This approach ensures, that the client doesn't use pretty much outdated files, but use cached versions while working with it. We use this in a ASP.NET Core single page application, which uses many JavaScript, and HTML template files. In combination with continuous deployment, we need to ensure the Application uses the latest files.