Detect static file request from .NET core middleware

Question

I'm writing some middleware to parse the sub-domain of a given request URL to determine the website theme. I want to ignore static file requests in order to reduce unnecessary database lookups, and I'm wondering if there's a cleaner way to do it.

This is what I've tried so far:

var staticFileExtensions = new List<string> { ".css", ".js", ".png", ".ico" };
if (staticFileExtensions.Any(x => httpContext.Request.Path.Value.EndsWith(x)))
{
    await _next(httpContext);
}
else
{
    var hostParts = httpContext.Request.Host.Host.Split('.').ToList();
    if (httpContext.Request.Path.StartsWithSegments(new PathString("/healthcheck"))
    || (hostParts.Count == 6 && _whitelistedDomains.Contains(hostParts[0])))
    {
        httpContext.Items.Add("account", hostParts[0]);
        await _next(httpContext);
    }
    else
    {
        httpContext.Response.StatusCode = (int)HttpStatusCode.NotFound;
    }
}

This is where I've added it to Startup.cs:

app.UseStaticFiles();
app.UseSpaStaticFiles();
app.UseDomainWhitelisting();

It feels as though there should be a cleaner way to detect which requests to ignore, or maybe I'm missing something?

Riccardo Bassilichi · Accepted Answer · 2020-12-10T06:45:23.353

8

You can use conditional middleware based on request. Something like:

app.UseMiddlewareOne();

app.UseWhen(context => context.Request.Path.StartsWithSegments("/api"), appBuilder =>
{
    appBuilder.UseMiddlewareTwo();
});

app.UseMiddlewareThree();

Source: https://www.devtrends.co.uk/blog/conditional-middleware-based-on-request-in-asp.net-core

edited Dec 10 '20 at 06:45

answered Dec 10 '20 at 06:24

Riccardo Bassilichi

939
12
21

score 5 · Answer 2 · answered Nov 17 '21 at 22:25

This is quite old question but I cam to it when I had similar problem, I could solve the issue and determine static files request by checking if request is ended with extension.

if(string.IsNullOrEmpty(System.IO.Path.GetExtension(httpContext.Request.Path)))
 //this is normal request
else
 //this can be a file as it ends with some extension (ex*.png)

Alex from Jitbit · Answer 3 · 2023-07-23T14:25:34.633

You don't need to.

Any middleware that is registered AFTER the call to UseStaticFiles will not execute, if the request ended up serving a static file.

I just verified this behavior on .NET 6 and 7 under both IIS and Kestrel hosting on both Windows and Linux.

That's probably because the static-files middleware never calls _next(context) delegate, thus aborting the whole pipeline. This is called terminal middleware because it short circuits a request. I wish MS docs mentioned it somewhere, but we can always look at the source codes...

Aaaah-nd yep, just as I thought, source code confirms this: https://source.dot.net/#Microsoft.AspNetCore.StaticFiles/StaticFileMiddleware.cs,79

P.S. In other words, to solve the OP's problem - just make sure you call UseStaticFiles before executing your domain logic middleware.

Detect static file request from .NET core middleware

3 Answers3