SwaggerUI broken by primitive return values + endpoint filters

[erikhejl]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

A combination of returning primitives from a minimal API delegate and adding an endpoint filter will cause the SwaggerUI page to crash. Primitive return values and endpoint filters do not cause this problem individually. This is in an application targeting .NET Core 7.

Expected Behavior

SwaggerUI page renders.

Steps To Reproduce

app.MapGet("/", () =>
{
return 1;
}).AddEndpointFilter(async (context, nextFilter) => await nextFilter(context));

Exceptions (if any)

ArgumentException: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Object' of method 'System.Threading.Tasks.ValueTask`1[System.Object] WrapObjectAsValueTask(System.Object)' (Parameter 'arg0')

System.Dynamic.Utils.ExpressionUtils.ValidateOneArgument(MethodBase method, ExpressionType nodeKind, Expression arguments, ParameterInfo pi, string methodParamName, string argumentParamName, int index)
System.Linq.Expressions.Expression.Call(MethodInfo method, Expression arg0)
Microsoft.AspNetCore.Http.RequestDelegateFactory.CreateFilterPipeline(MethodInfo methodInfo, Expression targetExpression, RequestDelegateFactoryContext factoryContext, Expression<Func<HttpContext, object>> targetFactory)
Microsoft.AspNetCore.Http.RequestDelegateFactory.CreateTargetableRequestDelegate(MethodInfo methodInfo, Expression targetExpression, RequestDelegateFactoryContext factoryContext, Expression<Func<HttpContext, object>> targetFactory)
Microsoft.AspNetCore.Http.RequestDelegateFactory.Create(Delegate handler, RequestDelegateFactoryOptions options, RequestDelegateMetadataResult metadataResult)
Microsoft.AspNetCore.Routing.RouteEndpointDataSource.CreateRouteEndpointBuilder(RouteEntry entry, RoutePattern groupPrefix, IReadOnlyList<Action<EndpointBuilder>> groupConventions, IReadOnlyList<Action<EndpointBuilder>> groupFinallyConventions)
Microsoft.AspNetCore.Routing.RouteEndpointDataSource.get_Endpoints()
Microsoft.AspNetCore.Routing.CompositeEndpointDataSource.CreateEndpointsUnsynchronized()
Microsoft.AspNetCore.Routing.CompositeEndpointDataSource.EnsureEndpointsInitialized()
Microsoft.AspNetCore.Routing.DataSourceDependentCache<T>.Initialize()
System.Threading.LazyInitializer.EnsureInitializedCore<T>(ref T target, ref bool initialized, ref object syncLock, Func<T> valueFactory)
Microsoft.AspNetCore.Routing.Matching.DataSourceDependentMatcher..ctor(EndpointDataSource dataSource, Lifetime lifetime, Func<MatcherBuilder> matcherBuilderFactory)
Microsoft.AspNetCore.Routing.Matching.DfaMatcherFactory.CreateMatcher(EndpointDataSource dataSource)
Microsoft.AspNetCore.Routing.EndpointRoutingMiddleware.InitializeCoreAsync()
Microsoft.AspNetCore.Routing.EndpointRoutingMiddleware.<Invoke>g__AwaitMatcher|8_0(EndpointRoutingMiddleware middleware, HttpContext httpContext, Task<Matcher> matcherTask)
Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

.NET Version

8.0.100

Anything else?

.NET SDK:
Version: 8.0.100
Commit: 57efcf1350
Workload version: 8.0.100-manifests.8d38d0cc

Runtime Environment:
OS Name: Windows
OS Version: 10.0.22621
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\8.0.100\

.NET workloads installed:
Workload version: 8.0.100-manifests.8d38d0cc
[wasm-tools-net6]
Installation Source: VS 17.8.34309.116
Manifest Version: 8.0.0/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.workload.mono.toolchain.net6\8.0.0\WorkloadManifest.json
Install Type: Msi

Host:
Version: 8.0.0
Architecture: x64
Commit: 5535e31a71

.NET SDKs installed:
8.0.100 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[ryanpeters-MSFT]

Has a fix been found for this? This sample code will fail, but changing the X and Y properties to string will work fine:

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();

app.MapPost("/addsmallnumbers", (AddRequest request) =>
{
    return request.X + request.Y;

}).AddEndpointFilter(async (ctx, next) => 
{
    return await next(ctx);
});

app.Run();

public class AddRequest
{
    public int X { get; set; } = default;
    public int Y { get; set; } = default;
}

[erikhejl]

It's still broken as of version 8.0.4. You can work around it by casting as (object), but this will defeat reflection based swagger generation done.

[shanerogers]

I just downloaded the lastest .net 8 sdk... I still get this issue..

[captainsafia]

I'll try to take a look at this bug and see if we can slot it in for servicing.

In the meantime, you can try seeing if compiling your application using the source generator for minimal APIs will work for you. It doesn't run into the same conversion bug we are seeing here with the Linq expressions we generated.

<PropertyGroup>
    <EnableRequestDelegateGenerator>true</EnableRequestDelegateGenerator>
</PropertyGroup>

[captainsafia]

This is fixed now in .NET 10 Preview 1 (we've already branched for .NET 9). .NET 10 preview builds aren't available yet. I'd like to wait until they are, have folks try them out to validate the fix, then backport to 8.0/9.0 once we've confirmed that this fix resolves the issue.

[UdiAzulay]

The issue only occur if the method that return int result has also an endpoint filter, without the filter, it works.
Please patch a fix for .Net 8 ASAP (as it's the only available stable release now)

[captainsafia]

Thanks for your patience here, everyone! The fix for this has been merged into all release branches and will ship in .NET 8.0.11, 9.0, and 10.