Add support for endpoint filters in minimal APIs

src/Http/Http.Abstractions/src/IRouteHandlerFilter.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.AspNetCore.Http;
+
+/// <summary>
+/// Provides an interface for implementing a filter targetting a route handler.
+/// </summary>
+public interface IRouteHandlerFilter
+{
+    /// <summary>
+    /// Implements the core logic associated with the filter given a <see cref="RouteHandlerFilterContext"/>
+    /// and the next filter to call in the pipeline.
+    /// </summary>
+    /// <param name="context">The <see cref="RouteHandlerFilterContext"/> associated with the current request/response.</param>
+    /// <param name="next">The next filter in the pipeline.</param>
+    /// <returns>An awaitable result of calling the handler and apply
+    /// any modifications made by filters in the pipeline.</returns>
+    ValueTask<object?> InvokeAsync(RouteHandlerFilterContext context, Func<RouteHandlerFilterContext, ValueTask<object?>> next);
+}

src/Http/Http.Abstractions/src/PublicAPI.Unshipped.txt

@@ -1,10 +1,16 @@
 #nullable enable
 *REMOVED*abstract Microsoft.AspNetCore.Http.HttpResponse.ContentType.get -> string!
 Microsoft.AspNetCore.Http.EndpointMetadataCollection.GetRequiredMetadata<T>() -> T!
+Microsoft.AspNetCore.Http.RouteHandlerFilterContext.RouteHandlerFilterContext(Microsoft.AspNetCore.Http.HttpContext! httpContext, params object![]! parameters) -> void
+Microsoft.AspNetCore.Http.IRouteHandlerFilter.InvokeAsync(Microsoft.AspNetCore.Http.RouteHandlerFilterContext! context, System.Func<Microsoft.AspNetCore.Http.RouteHandlerFilterContext!, System.Threading.Tasks.ValueTask<object?>>! next) -> System.Threading.Tasks.ValueTask<object?>
 Microsoft.AspNetCore.Http.Metadata.IFromFormMetadata
 Microsoft.AspNetCore.Http.Metadata.IFromFormMetadata.Name.get -> string?
 Microsoft.AspNetCore.Routing.RouteValueDictionary.RouteValueDictionary(Microsoft.AspNetCore.Routing.RouteValueDictionary? dictionary) -> void
 Microsoft.AspNetCore.Routing.RouteValueDictionary.RouteValueDictionary(System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string!, object?>>? values) -> void
 Microsoft.AspNetCore.Routing.RouteValueDictionary.RouteValueDictionary(System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string!, string?>>? values) -> void
 abstract Microsoft.AspNetCore.Http.HttpResponse.ContentType.get -> string?
 Microsoft.AspNetCore.Http.Metadata.ISkipStatusCodePagesMetadata
+Microsoft.AspNetCore.Http.RouteHandlerFilterContext
+Microsoft.AspNetCore.Http.RouteHandlerFilterContext.HttpContext.get -> Microsoft.AspNetCore.Http.HttpContext!
+Microsoft.AspNetCore.Http.RouteHandlerFilterContext.Parameters.get -> System.Collections.Generic.IList<object?>!
+Microsoft.AspNetCore.Http.IRouteHandlerFilter

src/Http/Http.Abstractions/src/RouteHandlerFilterContext.cs

@@ -0,0 +1,35 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.AspNetCore.Http;
+
+/// <summary>
+/// Provides an abstraction for wrapping the <see cref="HttpContext"/> and parameters
+/// provided to a route handler.
+/// </summary>
+public class RouteHandlerFilterContext
+{
+    /// <summary>
+    /// Creates a new instance of the <see cref="RouteHandlerFilterContext"/> for a given request.
+    /// </summary>
+    /// <param name="httpContext">The <see cref="HttpContext"/> associated with the current request.</param>
+    /// <param name="parameters">A list of parameters provided in the current request.</param>
+    public RouteHandlerFilterContext(HttpContext httpContext, params object[] parameters)
+    {
+        HttpContext = httpContext;
+        Parameters = parameters;
+    }
+
+    /// <summary>
+    /// The <see cref="HttpContext"/> associated with the current request being processed by the filter.
+    /// </summary>
+    public HttpContext HttpContext { get; }
+
+    /// <summary>
+    /// A list of parameters provided in the current request to the filter.
+    /// <remarks>
+    /// This list is not read-only to premit modifying of existing parameters by filters.
+    /// </remarks>
+    /// </summary>
+    public IList<object?> Parameters { get; }
+}

src/Http/Http.Extensions/src/PublicAPI.Unshipped.txt

@@ -1,3 +1,5 @@
 #nullable enable
 Microsoft.Extensions.DependencyInjection.RouteHandlerJsonServiceExtensions
 static Microsoft.Extensions.DependencyInjection.RouteHandlerJsonServiceExtensions.ConfigureRouteHandlerJsonOptions(this Microsoft.Extensions.DependencyInjection.IServiceCollection! services, System.Action<Microsoft.AspNetCore.Http.Json.JsonOptions!>! configureOptions) -> Microsoft.Extensions.DependencyInjection.IServiceCollection!
+Microsoft.AspNetCore.Http.RequestDelegateFactoryOptions.RouteHandlerFilters.get -> System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Http.IRouteHandlerFilter!>?
+Microsoft.AspNetCore.Http.RequestDelegateFactoryOptions.RouteHandlerFilters.init -> void

src/Http/Http.Extensions/src/RequestDelegateFactory.cs

@@ -39,6 +39,7 @@ public static partial class RequestDelegateFactory
     private static readonly MethodInfo ResultWriteResponseAsyncMethod = typeof(RequestDelegateFactory).GetMethod(nameof(ExecuteResultWriteResponse), BindingFlags.NonPublic | BindingFlags.Static)!;
     private static readonly MethodInfo StringResultWriteResponseAsyncMethod = typeof(RequestDelegateFactory).GetMethod(nameof(ExecuteWriteStringResponseAsync), BindingFlags.NonPublic | BindingFlags.Static)!;
     private static readonly MethodInfo StringIsNullOrEmptyMethod = typeof(string).GetMethod(nameof(string.IsNullOrEmpty), BindingFlags.Static | BindingFlags.Public)!;
+    private static readonly MethodInfo WrapObjectAsValueTaskMethod = typeof(RequestDelegateFactory).GetMethod(nameof(WrapObjectAsValueTask), BindingFlags.NonPublic | BindingFlags.Static)!;
 
     // Call WriteAsJsonAsync<object?>() to serialize the runtime return type rather than the declared return type.
     // https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-polymorphism
@@ -71,12 +72,21 @@ public static partial class RequestDelegateFactory
     private static readonly MemberExpression FormFilesExpr = Expression.Property(FormExpr, typeof(IFormCollection).GetProperty(nameof(IFormCollection.Files))!);
     private static readonly MemberExpression StatusCodeExpr = Expression.Property(HttpResponseExpr, typeof(HttpResponse).GetProperty(nameof(HttpResponse.StatusCode))!);
     private static readonly MemberExpression CompletedTaskExpr = Expression.Property(null, (PropertyInfo)GetMemberInfo<Func<Task>>(() => Task.CompletedTask));
+    private static readonly NewExpression CompletedValueTaskExpr = Expression.New(typeof(ValueTask<object>).GetConstructor(new[] { typeof(Task) })!, CompletedTaskExpr);
 
     private static readonly ParameterExpression TempSourceStringExpr = ParameterBindingMethodCache.TempSourceStringExpr;
     private static readonly BinaryExpression TempSourceStringNotNullExpr = Expression.NotEqual(TempSourceStringExpr, Expression.Constant(null));
     private static readonly BinaryExpression TempSourceStringNullExpr = Expression.Equal(TempSourceStringExpr, Expression.Constant(null));
     private static readonly UnaryExpression TempSourceStringIsNotNullOrEmptyExpr = Expression.Not(Expression.Call(StringIsNullOrEmptyMethod, TempSourceStringExpr));
 
+    private static readonly ConstructorInfo RouteHandlerFilterContextConstructor = typeof(RouteHandlerFilterContext).GetConstructor(new[] { typeof(HttpContext), typeof(object[]) })!;
+    private static readonly ParameterExpression FilterContextExpr = Expression.Parameter(typeof(RouteHandlerFilterContext), "context");
+    private static readonly MemberExpression FilterContextParametersExpr = Expression.Property(FilterContextExpr, typeof(RouteHandlerFilterContext).GetProperty(nameof(RouteHandlerFilterContext.Parameters))!);
+    private static readonly MemberExpression FilterContextHttpContextExpr = Expression.Property(FilterContextExpr, typeof(RouteHandlerFilterContext).GetProperty(nameof(RouteHandlerFilterContext.HttpContext))!);
+    private static readonly MemberExpression FilterContextHttpContextResponseExpr = Expression.Property(FilterContextHttpContextExpr, typeof(HttpContext).GetProperty(nameof(HttpContext.Response))!);
+    private static readonly MemberExpression FilterContextHttpContextStatusCodeExpr = Expression.Property(FilterContextHttpContextResponseExpr, typeof(HttpResponse).GetProperty(nameof(HttpResponse.StatusCode))!);
+    private static readonly ParameterExpression InvokedFilterContextExpr = Expression.Parameter(typeof(RouteHandlerFilterContext), "filterContext");
+
     private static readonly string[] DefaultAcceptsContentType = new[] { "application/json" };
     private static readonly string[] FormFileContentType = new[] { "multipart/form-data" };
 
@@ -102,6 +112,7 @@ public static RequestDelegateResult Create(Delegate handler, RequestDelegateFact
         };
 
         var factoryContext = CreateFactoryContext(options);
+
         var targetableRequestDelegate = CreateTargetableRequestDelegate(handler.Method, targetExpression, factoryContext);
 
         return new RequestDelegateResult(httpContext => targetableRequestDelegate(handler.Target, httpContext), factoryContext.Metadata);
@@ -155,6 +166,7 @@ private static FactoryContext CreateFactoryContext(RequestDelegateFactoryOptions
             RouteParameters = options?.RouteParameterNames?.ToList(),
             ThrowOnBadRequest = options?.ThrowOnBadRequest ?? false,
             DisableInferredFromBody = options?.DisableInferBodyFromParameters ?? false,
+            Filters = options?.RouteHandlerFilters?.ToList()
         };
 
     private static Func<object?, HttpContext, Task> CreateTargetableRequestDelegate(MethodInfo methodInfo, Expression? targetExpression, FactoryContext factoryContext)
@@ -176,10 +188,31 @@ private static FactoryContext CreateFactoryContext(RequestDelegateFactoryOptions
         // }
 
         var arguments = CreateArguments(methodInfo.GetParameters(), factoryContext);
+        var returnType = methodInfo.ReturnType;
+        factoryContext.MethodCall = CreateMethodCall(methodInfo, targetExpression, arguments);
+
+        // If there are filters registered on the route handler, then we update the method call and
+        // return type associated with the request to allow for the filter invocation pipeline.
+        if (factoryContext.Filters is { Count: > 0 })
+        {
+            var filterPipeline = CreateFilterPipeline(methodInfo, targetExpression, factoryContext);
+            Expression<Func<RouteHandlerFilterContext, ValueTask<object?>>> invokePipeline = (context) => filterPipeline(context);
+            returnType = typeof(ValueTask<object?>);
+            // var filterContext = new RouteHandlerFilterContext(httpContext, new[] { (object)name_local, (object)int_local });
+            // invokePipeline.Invoke(filterContext);
+            factoryContext.MethodCall = Expression.Block(
+                new[] { InvokedFilterContextExpr },
+                Expression.Assign(
+                    InvokedFilterContextExpr,
+                    Expression.New(RouteHandlerFilterContextConstructor,
+                        new Expression[] { HttpContextExpr, Expression.NewArrayInit(typeof(object), factoryContext.BoxedArgs) })),
+                    Expression.Invoke(invokePipeline, InvokedFilterContextExpr)
+                );
+        }
 
         var responseWritingMethodCall = factoryContext.ParamCheckExpressions.Count > 0 ?
-            CreateParamCheckingResponseWritingMethodCall(methodInfo, targetExpression, arguments, factoryContext) :
-            CreateResponseWritingMethodCall(methodInfo, targetExpression, arguments);
+            CreateParamCheckingResponseWritingMethodCall(returnType, factoryContext) :
+            AddResponseWritingToMethodCall(factoryContext.MethodCall, returnType);
 
         if (factoryContext.UsingTempSourceString)
         {
@@ -189,6 +222,35 @@ private static FactoryContext CreateFactoryContext(RequestDelegateFactoryOptions
         return HandleRequestBodyAndCompileRequestDelegate(responseWritingMethodCall, factoryContext);
     }
 
+    private static Func<RouteHandlerFilterContext, ValueTask<object?>> CreateFilterPipeline(MethodInfo methodInfo, Expression? target, FactoryContext factoryContext)
+    {
+        Debug.Assert(factoryContext.Filters is not null);
+        // httpContext.Response.StatusCode >= 400
+        // ? Task.CompletedTask
+        // : handler((string)context.Parameters[0], (int)context.Parameters[1])
+        var filteredInvocation = Expression.Lambda<Func<RouteHandlerFilterContext, ValueTask<object?>>>(
+            Expression.Condition(
+                Expression.GreaterThanOrEqual(FilterContextHttpContextStatusCodeExpr, Expression.Constant(400)),
+                CompletedValueTaskExpr,
+                Expression.Block(
+                    new[] { TargetExpr },
+                    Expression.Call(WrapObjectAsValueTaskMethod,
+                        target is null
+                            ? Expression.Call(methodInfo, factoryContext.ContextArgAccess)
+                            : Expression.Call(target, methodInfo, factoryContext.ContextArgAccess))
+                )),
+            FilterContextExpr).Compile();
+
+        for (var i = factoryContext.Filters.Count - 1; i >= 0; i--)
+        {
+            var currentFilter = factoryContext.Filters![i];
+            var nextFilter = filteredInvocation;
+            filteredInvocation = (RouteHandlerFilterContext context) => currentFilter.InvokeAsync(context, nextFilter);
+
+        }
+        return filteredInvocation;
+    }
+
     private static Expression[] CreateArguments(ParameterInfo[]? parameters, FactoryContext factoryContext)
     {
         if (parameters is null || parameters.Length == 0)
@@ -201,6 +263,16 @@ private static Expression[] CreateArguments(ParameterInfo[]? parameters, Factory
         for (var i = 0; i < parameters.Length; i++)
         {
             args[i] = CreateArgument(parameters[i], factoryContext);
+            // Register expressions containing the boxed and unboxed variants
+            // of the route handler's arguments for use in RouteHandlerFilterContext
+            // construction and route handler invocation.
+            // (string)context.Parameters[0];
+            factoryContext.ContextArgAccess.Add(
+                Expression.Convert(
+                    Expression.Property(FilterContextParametersExpr, "Item", Expression.Constant(i)),
+                parameters[i].ParameterType));
+            // (object)name_local
+            factoryContext.BoxedArgs.Add(Expression.Convert(args[i], typeof(object)));
         }
 
         if (factoryContext.HasInferredBody && factoryContext.DisableInferredFromBody)
@@ -381,16 +453,14 @@ target is null ?
             Expression.Call(methodInfo, arguments) :
             Expression.Call(target, methodInfo, arguments);
 
-    private static Expression CreateResponseWritingMethodCall(MethodInfo methodInfo, Expression? target, Expression[] arguments)
+    private static ValueTask<object?> WrapObjectAsValueTask(object? obj)
     {
-        var callMethod = CreateMethodCall(methodInfo, target, arguments);
-        return AddResponseWritingToMethodCall(callMethod, methodInfo.ReturnType);
+        return ValueTask.FromResult<object?>(obj);
     }
 
     // If we're calling TryParse or validating parameter optionality and
     // wasParamCheckFailure indicates it failed, set a 400 StatusCode instead of calling the method.
-    private static Expression CreateParamCheckingResponseWritingMethodCall(
-        MethodInfo methodInfo, Expression? target, Expression[] arguments, FactoryContext factoryContext)
+    private static Expression CreateParamCheckingResponseWritingMethodCall(Type returnType, FactoryContext factoryContext)
     {
         // {
         //     string tempSourceString;
@@ -440,17 +510,40 @@ private static Expression CreateParamCheckingResponseWritingMethodCall(
 
         localVariables[factoryContext.ExtraLocals.Count] = WasParamCheckFailureExpr;
 
-        var set400StatusAndReturnCompletedTask = Expression.Block(
-                Expression.Assign(StatusCodeExpr, Expression.Constant(400)),
-                CompletedTaskExpr);
-
-        var methodCall = CreateMethodCall(methodInfo, target, arguments);
-
-        var checkWasParamCheckFailure = Expression.Condition(WasParamCheckFailureExpr,
-            set400StatusAndReturnCompletedTask,
-            AddResponseWritingToMethodCall(methodCall, methodInfo.ReturnType));
+        // If filters have been registered, we set the `wasParamCheckFailure` property
+        // but do not return from the invocation to allow the filters to run.
+        if (factoryContext.Filters is { Count: > 0 })
+        {
+            // if (wasParamCheckFailure)
+            // {
+            //   httpContext.Response.StatusCode = 400;
+            // }
+            // return RequestDelegateFactory.ExecuteObjectReturn(invocationPipeline.Invoke(context) as object);
+            var checkWasParamCheckFailureWithFilters = Expression.Block(
+                Expression.IfThen(
+                    WasParamCheckFailureExpr,
+                    Expression.Assign(StatusCodeExpr, Expression.Constant(400))),
+                AddResponseWritingToMethodCall(factoryContext.MethodCall!, returnType)
+            );
 
-        checkParamAndCallMethod[factoryContext.ParamCheckExpressions.Count] = checkWasParamCheckFailure;
+            checkParamAndCallMethod[factoryContext.ParamCheckExpressions.Count] = checkWasParamCheckFailureWithFilters;
+        }
+        else
+        {
+            // wasParamCheckFailure ? {
+            //  httpContext.Response.StatusCode = 400;
+            //  return Task.CompletedTask;
+            // } : {
+            //  return RequestDelegateFactory.ExecuteObjectReturn(invocationPipeline.Invoke(context) as object);
+            // }
+            var checkWasParamCheckFailure = Expression.Condition(
+                WasParamCheckFailureExpr,
+                Expression.Block(
+                    Expression.Assign(StatusCodeExpr, Expression.Constant(400)),
+                    CompletedTaskExpr),
+                AddResponseWritingToMethodCall(factoryContext.MethodCall!, returnType));
+            checkParamAndCallMethod[factoryContext.ParamCheckExpressions.Count] = checkWasParamCheckFailure;
+        }
 
         return Expression.Block(localVariables, checkParamAndCallMethod);
     }
@@ -1596,6 +1689,11 @@ private class FactoryContext
 
         public bool ReadForm { get; set; }
         public ParameterInfo? FirstFormRequestBodyParameter { get; set; }
+        // Properties for constructing and managing filters
+        public List<Expression> ContextArgAccess { get; } = new();
+        public Expression? MethodCall { get; set; }
+        public List<Expression> BoxedArgs { get; } = new();
+        public List<IRouteHandlerFilter>? Filters { get; init; }
     }
 
     private static class RequestDelegateFactoryConstants

src/Http/Http.Extensions/src/RequestDelegateFactoryOptions.cs

@@ -31,4 +31,9 @@ public sealed class RequestDelegateFactoryOptions
     /// Prevent the <see cref="RequestDelegateFactory" /> from inferring a parameter should be bound from the request body without an attribute that implements <see cref="IFromBodyMetadata"/>.
     /// </summary>
     public bool DisableInferBodyFromParameters { get; init; }
+
+    /// <summary>
+    /// The list of filters that must run in the pipeline for a given route handler.
+    /// </summary>
+    public IReadOnlyList<IRouteHandlerFilter>? RouteHandlerFilters { get; init; }
 }