Allowing empty input

Author: brunolins16

src/Mvc/Mvc.Abstractions/src/ModelBinding/BindingInfo.cs

@@ -246,10 +246,15 @@ public bool TryApplyBindingInfo(ModelMetadata modelMetadata)
             PropertyFilterProvider = modelMetadata.PropertyFilterProvider;
         }
 
-        if (EmptyBodyBehavior == EmptyBodyBehavior.Default && modelMetadata.IsEmptyBodyAllowed != null)
+        // If the EmptyBody behavior is not configured will be infer
+        // as Allow when the ModelMetadata.IsRequired is false or HasDefaultValue
+        // https://github.com/dotnet/aspnetcore/issues/39754
+        if (EmptyBodyBehavior == EmptyBodyBehavior.Default &&
+            BindingSource == BindingSource.Body &&
+                (!modelMetadata.IsRequired || modelMetadata.HasDefaultValue))
         {
             isBindingInfoPresent = true;
-            EmptyBodyBehavior = modelMetadata.IsEmptyBodyAllowed == true ? EmptyBodyBehavior.Allow : EmptyBodyBehavior.Disallow;
+            EmptyBodyBehavior = EmptyBodyBehavior.Allow;
         }
 
         return isBindingInfoPresent;

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelMetadata.cs

@@ -500,9 +500,10 @@ internal IReadOnlyDictionary<ModelMetadata, ModelMetadata> BoundConstructorPrope
     internal virtual string? ValidationModelName { get; }
 
     /// <summary>
-    /// Gets or sets the value which decides if empty bodies are treated as valid inputs.
+    /// Gets the value that indicates if the parameter has a default value set.
+    /// This is only available when <see cref="MetadataKind"/> is <see cref="ModelMetadataKind.Parameter"/> otherwise it will be false.
     /// </summary>
-    internal virtual bool? IsEmptyBodyAllowed { get; set; }
+    internal bool HasDefaultValue { get; private set; }
 
     /// <summary>
     /// Throws if the ModelMetadata is for a record type with validation on properties.
@@ -615,6 +616,7 @@ private void InitializeTypeInformation()
         IsNullableValueType = Nullable.GetUnderlyingType(ModelType) != null;
         IsReferenceOrNullableType = !ModelType.IsValueType || IsNullableValueType;
         UnderlyingOrModelType = Nullable.GetUnderlyingType(ModelType) ?? ModelType;
+        HasDefaultValue = MetadataKind == ModelMetadataKind.Parameter && Identity.ParameterInfo!.HasDefaultValue;
 
         var collectionType = ClosedGenericMatcher.ExtractGenericInterface(ModelType, typeof(ICollection<>));
         IsCollectionType = collectionType != null;

src/Mvc/Mvc.Core/src/ApplicationModels/InferParameterBindingInfoConvention.cs

@@ -88,6 +88,12 @@ internal void InferParameterBindingSources(ActionModel action)
             message += Environment.NewLine + parameters;
             throw new InvalidOperationException(message);
         }
+        else if (fromBodyParameters.Count == 1 &&
+                  fromBodyParameters[0].BindingInfo!.EmptyBodyBehavior == EmptyBodyBehavior.Default &&
+                  IsOptionalParameter(fromBodyParameters[0]))
+        {
+            fromBodyParameters[0].BindingInfo!.EmptyBodyBehavior = EmptyBodyBehavior.Allow;
+        }
     }
 
     // Internal for unit testing.
@@ -132,4 +138,30 @@ private bool IsComplexTypeParameter(ParameterModel parameter)
 
         return metadata.IsComplexType;
     }
+
+    private bool IsOptionalParameter(ParameterModel parameter)
+    {
+        if (parameter.ParameterInfo.HasDefaultValue)
+        {
+            return true;
+        }
+
+        if (_modelMetadataProvider is ModelMetadataProvider modelMetadataProvider)
+        {
+            var metadata = modelMetadataProvider.GetMetadataForParameter(parameter.ParameterInfo);
+            return !metadata.IsRequired;
+        }
+        else
+        {
+            // Cannot be determine if the parameter is optional since the provider
+            // does not provides an option to getMetadata from the parameter info
+            // so, we will use the Nullability context
+
+            // Waiting for PR https://github.com/dotnet/aspnetcore/pull/39804
+            // No need for information from attributes on the parameter. Just use its type.
+            // var metadata = _modelMetadataProvider.GetMetadataForType(parameter.ParameterInfo.ParameterType);
+            // return metadata.NullabilityState != NullabilityState.NotNull;
+            return false;
+        }
+    }
 }

src/Mvc/Mvc.Core/src/Infrastructure/MvcCoreMvcOptionsSetup.cs

@@ -123,8 +123,6 @@ internal static void ConfigureAdditionalModelMetadataDetailsProviders(IList<IMet
         modelMetadataDetailsProviders.Add(new DefaultBindingMetadataProvider());
         modelMetadataDetailsProviders.Add(new DefaultValidationMetadataProvider());
 
-        modelMetadataDetailsProviders.Add(new NullableEmptyBodyBindingMetadataProvider());
-
         modelMetadataDetailsProviders.Add(new BindingSourceMetadataProvider(typeof(CancellationToken), BindingSource.Special));
         modelMetadataDetailsProviders.Add(new BindingSourceMetadataProvider(typeof(IFormFile), BindingSource.FormFile));
         modelMetadataDetailsProviders.Add(new BindingSourceMetadataProvider(typeof(IFormCollection), BindingSource.FormFile));

src/Mvc/Mvc.Core/src/ModelBinding/Metadata/DefaultModelMetadata.cs

@@ -474,9 +474,6 @@ public override bool? HasValidators
     /// <inheritdoc />
     internal override string? ValidationModelName => ValidationMetadata.ValidationModelName;
 
-    /// <inheritdoc />
-    internal override bool? IsEmptyBodyAllowed => BindingMetadata.IsEmptyBodyAllowed;
-
     internal static bool CalculateHasValidators(HashSet<DefaultModelMetadata> visited, ModelMetadata metadata)
     {
         RuntimeHelpers.EnsureSufficientExecutionStack();

src/Mvc/Mvc.Core/src/ModelBinding/Metadata/NullableEmptyBodyBindingMetadataProvider.cs

@@ -1,7 +1,4 @@
 #nullable enable
-Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.NullableEmptyBodyBindingMetadataProvider
-Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.NullableEmptyBodyBindingMetadataProvider.CreateBindingMetadata(Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.BindingMetadataProviderContext! context) -> void
-Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.NullableEmptyBodyBindingMetadataProvider.NullableEmptyBodyBindingMetadataProvider() -> void
 Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.SystemTextJsonValidationMetadataProvider
 Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.SystemTextJsonValidationMetadataProvider.CreateDisplayMetadata(Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DisplayMetadataProviderContext! context) -> void
 Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.SystemTextJsonValidationMetadataProvider.CreateValidationMetadata(Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ValidationMetadataProviderContext! context) -> void