Don't allocate the FormFeature eagerly (#6511)

- Expose FormOptions on DefaultHttpContext
- Use those options on DefaultHttpContext when the FormFeature is initialized

src/Http/Http/src/DefaultHttpContext.cs

@@ -62,6 +62,8 @@ namespace Microsoft.AspNetCore.Http
             _websockets?.Uninitialize();
         }
 
+        public FormOptions FormOptions { get; set; }
+
         private IItemsFeature ItemsFeature =>
             _features.Fetch(ref _features.Cache.Items, _newItemsFeature);
 

src/Http/Http/src/Features/FormFeature.cs

@@ -15,8 +15,6 @@ namespace Microsoft.AspNetCore.Http.Features
 {
     public class FormFeature : IFormFeature
     {
-        private static readonly FormOptions DefaultFormOptions = new FormOptions();
-
         private readonly HttpRequest _request;
         private readonly FormOptions _options;
         private Task<IFormCollection> _parsedFormTask;
@@ -32,7 +30,7 @@ namespace Microsoft.AspNetCore.Http.Features
             Form = form;
         }
         public FormFeature(HttpRequest request)
-            : this(request, DefaultFormOptions)
+            : this(request, FormOptions.Default)
         {
         }
 

src/Http/Http/src/Features/FormOptions.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.IO;
@@ -8,6 +8,8 @@ namespace Microsoft.AspNetCore.Http.Features
 {
     public class FormOptions
     {
+        internal static readonly FormOptions Default = new FormOptions();
+
         public const int DefaultMemoryBufferThreshold = 1024 * 64;
         public const int DefaultBufferBodyLengthLimit = 1024 * 1024 * 128;
         public const int DefaultMultipartBoundaryLengthLimit = 128;

src/Http/Http/src/HttpContextFactory.cs

@@ -42,13 +42,12 @@ namespace Microsoft.AspNetCore.Http
                 _httpContextAccessor.HttpContext = httpContext;
             }
 
-            var formFeature = new FormFeature(httpContext.Request, _formOptions);
+            httpContext.FormOptions = _formOptions;
-            featureCollection.Set<IFormFeature>(formFeature);
 
             return httpContext;
         }
 
-        private static HttpContext CreateHttpContext(IFeatureCollection featureCollection)
+        private static DefaultHttpContext CreateHttpContext(IFeatureCollection featureCollection)
         {
             if (featureCollection is IHttpContextContainer container)
             {

src/Http/Http/src/IHttpContextContainer.cs

@@ -6,6 +6,6 @@ namespace Microsoft.AspNetCore.Http
 {
     public interface IHttpContextContainer
     {
-        HttpContext HttpContext { get; }
+        DefaultHttpContext HttpContext { get; }
     }
 }

src/Http/Http/src/Internal/DefaultHttpRequest.cs

@@ -17,7 +17,7 @@ namespace Microsoft.AspNetCore.Http.Internal
         // Lambdas hoisted to static readonly fields to improve inlining https://github.com/dotnet/roslyn/issues/13624
         private readonly static Func<IFeatureCollection, IHttpRequestFeature> _nullRequestFeature = f => null;
         private readonly static Func<IFeatureCollection, IQueryFeature> _newQueryFeature = f => new QueryFeature(f);
-        private readonly static Func<HttpRequest, IFormFeature> _newFormFeature = r => new FormFeature(r);
+        private readonly static Func<DefaultHttpRequest, IFormFeature> _newFormFeature = r => new FormFeature(r, r._context.FormOptions ?? FormOptions.Default);
         private readonly static Func<IFeatureCollection, IRequestCookiesFeature> _newRequestCookiesFeature = f => new RequestCookiesFeature(f);
         private readonly static Func<IFeatureCollection, IRouteValuesFeature> _newRouteValuesFeature = f => new RouteValuesFeature();
         private readonly static Func<HttpContext, IRequestBodyPipeFeature> _newRequestBodyPipeFeature = context => new RequestBodyPipeFeature(context);

src/Http/Http/test/Features/FormFeatureTests.cs

@@ -29,6 +29,24 @@ namespace Microsoft.AspNetCore.Http.Features
             Assert.Same(FormCollection.Empty, formCollection);
         }
 
+        [Fact]
+        public async Task FormFeatureReadsOptionsFromDefaultHttpContext()
+        {
+            var context = new DefaultHttpContext();
+            context.Request.ContentType = "application/x-www-form-urlencoded; charset=utf-8";
+            context.FormOptions = new FormOptions
+            {
+                ValueCountLimit = 1
+            };
+
+            var formContent = Encoding.UTF8.GetBytes("foo=bar&baz=2");
+            context.Request.Body = new NonSeekableReadStream(formContent);
+
+            var exception = await Assert.ThrowsAsync<InvalidDataException>(() => context.Request.ReadFormAsync());
+
+            Assert.Equal("Form value count limit 1 exceeded.", exception.Message);
+        }
+
         [Theory]
         [InlineData(true)]
         [InlineData(false)]
@@ -391,7 +409,7 @@ namespace Microsoft.AspNetCore.Http.Features
             IFormFeature formFeature = new FormFeature(context.Request, new FormOptions() { BufferBody = bufferRequest, ValueCountLimit = 2 });
             context.Features.Set<IFormFeature>(formFeature);
 
-            var exception = await Assert.ThrowsAsync<InvalidDataException> (() => context.Request.ReadFormAsync());
+            var exception = await Assert.ThrowsAsync<InvalidDataException>(() => context.Request.ReadFormAsync());
             Assert.Equal("Form value count limit 2 exceeded.", exception.Message);
         }
 
@@ -416,7 +434,7 @@ namespace Microsoft.AspNetCore.Http.Features
             IFormFeature formFeature = new FormFeature(context.Request, new FormOptions() { BufferBody = bufferRequest, ValueCountLimit = 2 });
             context.Features.Set<IFormFeature>(formFeature);
 
-            var exception = await Assert.ThrowsAsync<InvalidDataException> (() => context.Request.ReadFormAsync());
+            var exception = await Assert.ThrowsAsync<InvalidDataException>(() => context.Request.ReadFormAsync());
             Assert.Equal("Form value count limit 2 exceeded.", exception.Message);
         }
 

src/Servers/Kestrel/Core/src/Internal/Http/HttpProtocol.cs

@@ -277,7 +277,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
 
         protected HttpResponseHeaders HttpResponseHeaders { get; } = new HttpResponseHeaders();
 
-        HttpContext IHttpContextContainer.HttpContext
+        DefaultHttpContext IHttpContextContainer.HttpContext
         {
             get
             {