Don't allocate the FormFeature eagerly

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

Author: davidfowl

src/Http/Http/src/DefaultHttpContext.cs

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

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

@@ -48,7 +48,7 @@ public FormFeature(HttpRequest request, FormOptions options)
             }
 
             _request = request;
-            _options = options;
+            _options = (request.HttpContext is DefaultHttpContext defaultHttpContext) ? defaultHttpContext.FormOptions ?? options : options;
         }
 
         private MediaTypeHeaderValue ContentType

src/Http/Http/src/HttpContextFactory.cs

@@ -42,13 +42,12 @@ public HttpContext Create(IFeatureCollection featureCollection)
                 _httpContextAccessor.HttpContext = httpContext;
             }
 
-            var formFeature = new FormFeature(httpContext.Request, _formOptions);
-            featureCollection.Set<IFormFeature>(formFeature);
+            httpContext.FormOptions = _formOptions;
 
             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/test/Features/FormFeatureTests.cs

@@ -29,6 +29,24 @@ public async Task ReadFormAsync_0ContentLength_ReturnsEmptyForm()
             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 @@ public async Task ReadFormAsync_ValueCountLimitExceeded_Throw(bool bufferRequest
             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 @@ public async Task ReadFormAsync_ValueCountLimitExceededWithFiles_Throw(bool buff
             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 @@ public CancellationToken RequestAborted
 
         protected HttpResponseHeaders HttpResponseHeaders { get; } = new HttpResponseHeaders();
 
-        HttpContext IHttpContextContainer.HttpContext
+        DefaultHttpContext IHttpContextContainer.HttpContext
         {
             get
             {