Add Route Short Circuit middleware

Background and Motivation

Browsers and bots often probe servers for well known paths like favicon.ico. Normally the middleware pipeline runs to completion before rejecting a request as 404.

Services can reduce resource usage and log noise by filtering out known requests early in the pipeline. We can provide a middleware to do this efficiently.

Proposed API

Project/Assembly: Microsoft.AspNetCore.Routing

namespace Microsoft.Extensions.DependencyInjection;

+ public static class RouteShortCircuitIServiceCollectionExtensions
{
+     public static IServiceCollection AddRouteShortCircuit(this IServiceCollection services, Action<RouteShortCircuitOptions> configure) { }
}

namespace Microsoft.AspNetCore.Builder;

+ public static class RouteShortCircuitIApplicationBuilderExtensions
+ {
+     public static IApplicationBuilder UseRouteShortCircuit(this IApplicationBuilder builder) { }
+ }

namespace Microsoft.AspNetCore.Routing;

+ public class RouteShortCircuitOptions
+ {
+     // Exact path matches, empty by default
+     public ISet<string> Paths { get; } = new HashSet<string>(StringComparer.OridinalIgnoreCase);
+     // Any path that starts with these, empty by default
+     public ISet<string> PathsStartWith { get; } = new HashSet<string>(StringComparer.OridinalIgnoreCase);
+     public RequestDelegate OnRejected { get; set; }
+ }

Usage Examples

services.AddRouteShortCircuit(options =>
{
    options.Paths.Add("/favicon.ico");
    options.OnRejected(context => { /* metrics */ });
});
...
app.UseRouteShortCircuit();

Alternative:

Build this into UseRouting (https://github.com/dotnet/aspnetcore/issues/43642) and have it terminate immediately with a 404 if such an endpoint is matched.

We could also allow short circuiting to specify an endpoint/delegate to execute to produce a custom response.

Project/Assembly: Microsoft.AspNetCore.Routing

namespace Microsoft.Extensions.DependencyInjection;

+ public static class RouteShortCircuitEndpointConventionBuilderExtensions
{
+     public static IEndpointConventionBuilder ShortCircuit(this IEndpointConventionBuilder builder) { }
}

[tekian]

Oh I see what you mean. We’d advise to add routing as one of the first middlewares, claiming and assuming that the overhead to compute a route is negligent even for cases where we want to short circuit. And we’d sequence the rest of the middlewares after it, even those that are agnostic of the path.

[Kahbazi]

@Tratcher Did you mean to write IEndpointRouteBuilder as argument for MapShortCircuit?