Support binding to form and form file parameters in minimal actions

src/Http/Http.Abstractions/src/Metadata/IFromFormMetadata.cs

@@ -0,0 +1,15 @@
+// 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.Metadata;
+
+/// <summary>
+/// Interface marking attributes that specify a parameter should be bound using a form field from the request body.
+/// </summary>
+public interface IFromFormMetadata
+{
+    /// <summary>
+    /// The form field name.
+    /// </summary>
+    string? Name { get; }
+}

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

@@ -1,3 +1,5 @@
 #nullable enable
 *REMOVED*abstract Microsoft.AspNetCore.Http.HttpResponse.ContentType.get -> string!
+Microsoft.AspNetCore.Http.Metadata.IFromFormMetadata
+Microsoft.AspNetCore.Http.Metadata.IFromFormMetadata.Name.get -> string?
 abstract Microsoft.AspNetCore.Http.HttpResponse.ContentType.get -> string?

src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

@@ -92,12 +92,14 @@ private ApiDescription CreateApiDescription(RouteEndpoint routeEndpoint, string
             {
                 DisplayName = routeEndpoint.DisplayName,
                 RouteValues =
-                    {
-                        ["controller"] = controllerName,
-                    },
+                {
+                    ["controller"] = controllerName,
+                },
             },
         };
 
+        var hasBodyOrFormFileParameter = false;
+
         foreach (var parameter in methodInfo.GetParameters())
         {
             var parameterDescription = CreateApiParameterDescription(parameter, routeEndpoint.RoutePattern);
@@ -108,23 +110,33 @@ private ApiDescription CreateApiDescription(RouteEndpoint routeEndpoint, string
             }
 
             apiDescription.ParameterDescriptions.Add(parameterDescription);
+
+            hasBodyOrFormFileParameter |=
+                parameterDescription.Source == BindingSource.Body ||
+                parameterDescription.Source == BindingSource.FormFile;
         }
 
         // Get IAcceptsMetadata.
         var acceptsMetadata = routeEndpoint.Metadata.GetMetadata<IAcceptsMetadata>();
         if (acceptsMetadata is not null)
         {
-            var acceptsRequestType = acceptsMetadata.RequestType;
-            var isOptional = acceptsMetadata.IsOptional;
-            var parameterDescription = new ApiParameterDescription
+            // Add a default body parameter if there was no explicitly defined parameter associated with
+            // either the body or a form and the user explicity defined some metadata describing the
+            // content types the endpoint consumes (such as Accepts<TRequest>(...) or [Consumes(...)]).
+            if (!hasBodyOrFormFileParameter)
             {
-                Name = acceptsRequestType is not null ? acceptsRequestType.Name : typeof(void).Name,
-                ModelMetadata = CreateModelMetadata(acceptsRequestType ?? typeof(void)),
-                Source = BindingSource.Body,
-                Type = acceptsRequestType ?? typeof(void),
-                IsRequired = !isOptional,
-            };
-            apiDescription.ParameterDescriptions.Add(parameterDescription);
+                var acceptsRequestType = acceptsMetadata.RequestType;
+                var isOptional = acceptsMetadata.IsOptional;
+                var parameterDescription = new ApiParameterDescription
+                {
+                    Name = acceptsRequestType is not null ? acceptsRequestType.Name : typeof(void).Name,
+                    ModelMetadata = CreateModelMetadata(acceptsRequestType ?? typeof(void)),
+                    Source = BindingSource.Body,
+                    Type = acceptsRequestType ?? typeof(void),
+                    IsRequired = !isOptional,
+                };
+                apiDescription.ParameterDescriptions.Add(parameterDescription);
+            }
 
             var supportedRequestFormats = apiDescription.SupportedRequestFormats;
 
@@ -148,8 +160,7 @@ private ApiDescription CreateApiDescription(RouteEndpoint routeEndpoint, string
         var (source, name, allowEmpty, paramType) = GetBindingSourceAndName(parameter, pattern);
 
         // Services are ignored because they are not request parameters.
-        // We ignore/skip body parameter because the value will be retrieved from the IAcceptsMetadata.
-        if (source == BindingSource.Services || source == BindingSource.Body)
+        if (source == BindingSource.Services)
         {
             return null;
         }
@@ -239,6 +250,10 @@ private static ParameterDescriptor CreateParameterDescriptor(ParameterInfo param
         {
             return (BindingSource.Body, parameter.Name ?? string.Empty, fromBodyAttribute.AllowEmpty, parameter.ParameterType);
         }
+        else if (attributes.OfType<IFromFormMetadata>().FirstOrDefault() is { } fromFormAttribute)
+        {
+            return (BindingSource.FormFile, fromFormAttribute.Name ?? parameter.Name ?? string.Empty, false, parameter.ParameterType);
+        }
         else if (parameter.CustomAttributes.Any(a => typeof(IFromServiceMetadata).IsAssignableFrom(a.AttributeType)) ||
                  parameter.ParameterType == typeof(HttpContext) ||
                  parameter.ParameterType == typeof(HttpRequest) ||
@@ -265,6 +280,10 @@ private static ParameterDescriptor CreateParameterDescriptor(ParameterInfo param
                 return (BindingSource.Query, parameter.Name ?? string.Empty, false, displayType);
             }
         }
+        else if (parameter.ParameterType == typeof(IFormFile) || parameter.ParameterType == typeof(IFormFileCollection))
+        {
+            return (BindingSource.FormFile, parameter.Name ?? string.Empty, false, parameter.ParameterType);
+        }
         else
         {
             return (BindingSource.Body, parameter.Name ?? string.Empty, false, parameter.ParameterType);