Backport 39275 to release/6.0 (#41993)

* Backport 39275 to release/6.0

* Cache appcontext switch value

* PR feedback

Author: brunolins16

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

@@ -23,6 +23,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
     /// </summary>
     public class NewtonsoftJsonInputFormatter : TextInputFormatter, IInputFormatterExceptionPolicy
     {
+        internal const string EnableSkipHandledError = "Microsoft.AspNetCore.Mvc.NewtonsoftJson.EnableSkipHandledError";
+
         private readonly IArrayPool<char> _charPool;
         private readonly ILogger _logger;
         private readonly ObjectPoolProvider _objectPoolProvider;
@@ -79,6 +81,8 @@ public NewtonsoftJsonInputFormatter(
             _options = options;
             _jsonOptions = jsonOptions;
 
+            SkipHandledErrorEnabled = AppContext.TryGetSwitch(EnableSkipHandledError, out var enabled) && enabled;
+
             SupportedEncodings.Add(UTF8EncodingWithoutBOM);
             SupportedEncodings.Add(UTF16EncodingLittleEndian);
 
@@ -109,6 +113,9 @@ public virtual InputFormatterExceptionPolicy ExceptionPolicy
         /// </remarks>
         protected JsonSerializerSettings SerializerSettings { get; }
 
+        // internal for testing
+        internal bool SkipHandledErrorEnabled { get; set; }
+
         /// <inheritdoc />
         public override async Task<InputFormatterResult> ReadRequestBodyAsync(
             InputFormatterContext context,
@@ -232,6 +239,13 @@ public override async Task<InputFormatterResult> ReadRequestBodyAsync(
 
             void ErrorHandler(object? sender, Newtonsoft.Json.Serialization.ErrorEventArgs eventArgs)
             {
+                // Skipping error, if it's already marked as handled
+                // This allows user code to implement its own error handling
+                if (eventArgs.ErrorContext.Handled && SkipHandledErrorEnabled)
+                {
+                    return;
+                }
+
                 successful = false;
 
                 // When ErrorContext.Path does not include ErrorContext.Member, add Member to form full path.

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

@@ -487,6 +487,47 @@ public async Task ReadAsync_WithReadJsonWithRequestCulture_DeserializesUsingRequ
             }
         }
 
+        [Fact]
+        public async Task ReadAsync_AllowUserCodeToHandleDeserializationErrors()
+        {
+            // Arrange
+            var serializerSettings = new JsonSerializerSettings
+            {
+                Error = (sender, eventArgs) =>
+                {
+                    eventArgs.ErrorContext.Handled = true;
+                }
+            };
+            var formatter = new NewtonsoftJsonInputFormatter(
+                GetLogger(),
+                serializerSettings,
+                ArrayPool<char>.Shared,
+                _objectPoolProvider,
+                new MvcOptions(),
+                new MvcNewtonsoftJsonOptions())
+            {
+                SkipHandledErrorEnabled = true
+            };
+
+            var content = $"{{'id': 'should be integer', 'name': 'test location'}}";
+            var contentBytes = Encoding.UTF8.GetBytes(content);
+            var httpContext = new DefaultHttpContext();
+            httpContext.Features.Set<IHttpResponseFeature>(new TestResponseFeature());
+            httpContext.Request.Body = new NonSeekableReadStream(contentBytes, allowSyncReads: false);
+            httpContext.Request.ContentType = "application/json";
+
+            var formatterContext = CreateInputFormatterContext(typeof(Location), httpContext);
+
+            // Act
+            var result = await formatter.ReadAsync(formatterContext);
+
+            // Assert
+            Assert.False(result.HasError);
+            var location = (Location)result.Model;
+            Assert.Equal(0, location?.Id);
+            Assert.Equal("test location", location?.Name);
+        }
+
         private class TestableJsonInputFormatter : NewtonsoftJsonInputFormatter
         {
             public TestableJsonInputFormatter(JsonSerializerSettings settings, ObjectPoolProvider objectPoolProvider)