Fix EmptyBodyBehavior with empty content-type

Author: BrennanConroy

src/Mvc/Mvc.Core/src/ModelBinding/Binders/BodyModelBinder.cs

@@ -143,6 +143,11 @@ public async Task BindModelAsync(ModelBindingContext bindingContext)
 
             if (formatter == null)
             {
+                if (AllowEmptyBody && httpContext.Request.ContentLength == 0)
+                {
+                    return;
+                }
+
                 _logger.NoInputFormatterSelected(formatterContext);
 
                 var message = Resources.FormatUnsupportedContentType(httpContext.Request.ContentType);

src/Mvc/test/Mvc.FunctionalTests/InputFormatterTests.cs

@@ -188,6 +188,20 @@ public async Task BodyIsRequiredByDefault()
                 });
         }
 
+        [Fact]
+        public async Task BodyIsRequiredByDefaultFailsWithEmptyBody()
+        {
+            var content = new ByteArrayContent(Array.Empty<byte>());
+            Assert.Null(content.Headers.ContentType);
+            Assert.Equal(0, content.Headers.ContentLength);
+
+            // Act
+            var response = await Client.PostAsync($"Home/{nameof(HomeController.DefaultBody)}", content);
+
+            // Assert
+            await response.AssertStatusCodeAsync(HttpStatusCode.UnsupportedMediaType);
+        }
+
         [Fact]
         public async Task OptionalFromBodyWorks()
         {
@@ -197,5 +211,20 @@ public async Task OptionalFromBodyWorks()
             // Assert
             await response.AssertStatusCodeAsync(HttpStatusCode.OK);
         }
+
+        [Fact]
+        public async Task OptionalFromBodyWorksWithEmptyRequest()
+        {
+            // Arrange
+            var content = new ByteArrayContent(Array.Empty<byte>());
+            Assert.Null(content.Headers.ContentType);
+            Assert.Equal(0, content.Headers.ContentLength);
+
+            // Act
+            var response = await Client.PostAsync($"Home/{nameof(HomeController.OptionalBody)}", content);
+
+            // Assert
+            await response.AssertStatusCodeAsync(HttpStatusCode.OK);
+        }
     }
 }