MVC model validation in default configuration is very slow if models contain delegate properties

[imb590]

If a MVC model contains a delegate-typed field, then by default Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ObjectModelValidator tries to validate every field of the delegate, eventually retrieving all assembly types and going on to validate properties of those Type objects.

The following code demonstrates the problem:

using System;
using System.Net.Http;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

using var host = new WebHostBuilder()
    .UseKestrel()
    .UseUrls("http://localhost:5000")
    .ConfigureServices(s =>
    {
        s.AddLogging(l => l.AddConsole().AddSimpleConsole(c =>
        {
            c.TimestampFormat = "hh:mm:ss.fff ";
            c.SingleLine = true;
        }).SetMinimumLevel(LogLevel.Trace));
        s.AddMvc().AddControllersAsServices();
    })
    .UseStartup<Startup>()
    .Build();

await host.StartAsync();

using var client = new HttpClient();
var response = await client.GetStringAsync("http://localhost:5000?value=test");
Console.WriteLine($"Got response: {response}");
response = await client.GetStringAsync("http://localhost:5000?value=test");
Console.WriteLine($"Got response: {response}");

class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        app.UseRouting();
        app.UseEndpoints(routes =>
        {
            routes.MapControllers();
        });
    }
}

public class TestController : Controller
{
    [HttpGet("/")]
    public string Test([FromQuery]ModelWithDelegateType model)
    {
        return model.Value;
    }
}

public class ModelWithDelegateType
{
    public string Value { get; set; } = string.Empty;

    public Action Delegate { get; } = () => { };
}

The request is quite slow even for this small assembly (about 100ms on my machine), most of which is spent in Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationVisitor, as seen in the 100ms time gap in logs:

04:35:14.835 dbug: Microsoft.AspNetCore.Mvc.ModelBinding.ParameterBinder[26] Attempting to validate the bound parameter 'model' of type 'ModelWithDelegateType' ...
04:35:14.938 dbug: Microsoft.AspNetCore.Mvc.ModelBinding.ParameterBinder[27] Done attempting to validate the bound parameter 'model' of type 'ModelWithDelegateType'.

When assembly is larger, the validation takes more than a second.

This is on ASP.NET Core with SDK 5.0.205 and runtime 5.0.8.

[imb590]

Looks like the following fixes the problem:

public class DelegateValidationMetadataProvider : IValidationMetadataProvider
{
    public void CreateValidationMetadata(ValidationMetadataProviderContext context)
    {
        var isDelegate = typeof(Delegate).IsAssignableFrom(context.Key.ModelType);
        if (isDelegate)
        {
            context.ValidationMetadata.ValidateChildren = false;
        }
    }
}

...

.AddMvc(options => options.ModelMetadataDetailsProviders.Add(new DelegateValidationMetadataProvider()))

It would be nice to have that out of the box though.

[davidfowl]

I took a look at this behavior and you can disable this option to fix the performance:

s.AddMvc(o => o.SuppressImplicitRequiredAttributeForNonNullableReferenceTypes = true);

With nullable reference types turned on, MVC will generate am implicit [Required] attribute for any non nullable reference types.