How to cache static files in ASP.NET Core?

Question

I can't seem to enable caching of static files in ASP.NET Core 2.2. I have the following in my Configure:

public void Configure(IApplicationBuilder app, IHostingEnvironment env) {
  if (env.IsDevelopment()) {
    app.UseDeveloperExceptionPage();
    app.UseCors(...);
  }
  else {
    app.UseHsts();
  }

  app.UseHttpsRedirection();
  app.UseAuthentication();
  app.UseSignalR(routes => { routes.MapHub<NotifyHub>("/..."); });

  app.UseResponseCompression();
  app.UseStaticFiles();
  app.UseSpaStaticFiles(new StaticFileOptions() {
    OnPrepareResponse = (ctx) => {
      ctx.Context.Response.Headers[HeaderNames.CacheControl] = "public, max-age=31557600"; // cache for 1 year
    }
  });
  app.UseMvc();

  app.UseSpa(spa => {
    spa.Options.SourcePath = "ClientApp";
    if (env.IsDevelopment()) {
      spa.UseVueCli(npmScript: "serve", port: 8080);
    }
  });
}

When I try and Audit the production site on HTTPS using chrome I keep getting "Serve static assets with an efficient cache policy":

In the network tab there is no mention of caching in the headers, when I press F5 it seems everything is served from disk cache. But, how can I be sure my caching setting is working if the audit is showing its not?

Answer 1

This is working in ASP.NET Core 2.2 to 3.1:

I know this is a bit similar to Fredrik's answer but you don't have to type literal strings in order to get the cache control header

app.UseStaticFiles(new StaticFileOptions()
{
    HttpsCompression = Microsoft.AspNetCore.Http.Features.HttpsCompressionMode.Compress,               
    OnPrepareResponse = (context) =>
    {
        var headers = context.Context.Response.GetTypedHeaders();
        headers.CacheControl = new Microsoft.Net.Http.Headers.CacheControlHeaderValue
        {
            Public = true,
            MaxAge = TimeSpan.FromDays(30)
        };
    }
});