Add a test to verify NewtonsoftJsonInputFormatter disposes temporary buffer (#25919)

#22342 was fixed in a patch release,
but we hadn't written a test for this at that time. This change adds a unit
test to verify this.

Fixes #22342

Author: pranavkm

src/Mvc/Mvc.NewtonsoftJson/src/NewtonsoftJsonInputFormatter.cs

@@ -123,7 +123,8 @@ public override async Task<InputFormatterResult> ReadRequestBodyAsync(
                 throw new ArgumentNullException(nameof(encoding));
             }
 
-            var request = context.HttpContext.Request;
+            var httpContext = context.HttpContext;
+            var request = httpContext.Request;
 
             var suppressInputFormatterBuffering = _options.SuppressInputFormatterBuffering;
 
@@ -153,7 +154,7 @@ public override async Task<InputFormatterResult> ReadRequestBodyAsync(
 
                 readStream = new FileBufferingReadStream(request.Body, memoryThreshold);
                 // Ensure the file buffer stream is always disposed at the end of a request.
-                request.HttpContext.Response.RegisterForDispose(readStream);
+                httpContext.Response.RegisterForDispose(readStream);
 
                 await readStream.DrainAsync(CancellationToken.None);
                 readStream.Seek(0L, SeekOrigin.Begin);

src/Mvc/Mvc.NewtonsoftJson/test/NewtonsoftJsonInputFormatterTest.cs

@@ -9,6 +9,7 @@
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
+using Microsoft.AspNetCore.WebUtilities;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.ObjectPool;
@@ -399,6 +400,39 @@ public async Task ReadAsync_DoesNotRethrowOverflowExceptions()
             Assert.Equal("The supplied value is invalid.", modelError.ErrorMessage);
         }
 
+        [Fact]
+        public async Task ReadAsync_RegistersFileStreamForDisposal()
+        {
+            // Arrange
+            var formatter = new NewtonsoftJsonInputFormatter(
+                GetLogger(),
+                _serializerSettings,
+                ArrayPool<char>.Shared,
+                _objectPoolProvider,
+                new MvcOptions(),
+                new MvcNewtonsoftJsonOptions());
+            var httpContext = new Mock<HttpContext>();
+            IDisposable registerForDispose = null;
+
+            var content = Encoding.UTF8.GetBytes("\"Hello world\"");
+            httpContext.Setup(h => h.Request.Body).Returns(new NonSeekableReadStream(content, allowSyncReads: false));
+            httpContext.Setup(h => h.Request.ContentType).Returns("application/json");
+            httpContext.Setup(h => h.Response.RegisterForDispose(It.IsAny<IDisposable>()))
+                .Callback((IDisposable disposable) => registerForDispose = disposable)
+                .Verifiable();
+
+            var formatterContext = CreateInputFormatterContext(typeof(string), httpContext.Object);
+
+            // Act
+            var result = await formatter.ReadAsync(formatterContext);
+
+            // Assert
+            Assert.Equal("Hello world", result.Model);
+            Assert.NotNull(registerForDispose);
+            Assert.IsType<FileBufferingReadStream>(registerForDispose);
+            httpContext.Verify();
+        }
+
         private class TestableJsonInputFormatter : NewtonsoftJsonInputFormatter
         {
             public TestableJsonInputFormatter(JsonSerializerSettings settings, ObjectPoolProvider objectPoolProvider)