Better JSON deserialization errors. Implements #4607, #4862

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ModelStateDictionary.cs

@@ -7,6 +7,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using Microsoft.AspNetCore.Mvc.Abstractions;
+using Microsoft.AspNetCore.Mvc.Formatters;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding
@@ -263,6 +264,11 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
 
                 return TryAddModelError(key, errorMessage);
             }
+            else if (exception is InputFormatterException && !string.IsNullOrEmpty(exception.Message))
+            {
+                // InputFormatterException is a signal that the message is safe to expose to clients
+                return TryAddModelError(key, exception.Message);
+            }
 
             ErrorCount++;
             AddModelErrorCore(key, exception);

src/Microsoft.AspNetCore.Mvc.Core/MvcOptions.cs

@@ -170,11 +170,20 @@ namespace Microsoft.AspNetCore.Mvc
         public bool AllowBindingUndefinedValueToEnumType { get; set; }
 
         /// <summary>
-        /// Gets or sets the option to determine if model binding should convert all exceptions(including ones not related to bad input)
+        /// Gets or sets the option to determine if model binding should convert all exceptions (including ones not related to bad input)
         /// that occur during deserialization in <see cref="IInputFormatter"/>s into model state errors.
         /// This option applies only to custom <see cref="IInputFormatter"/>s.
         /// Default is <see cref="InputFormatterExceptionModelStatePolicy.AllExceptions"/>.
         /// </summary>
         public InputFormatterExceptionModelStatePolicy InputFormatterExceptionModelStatePolicy { get; set; }
+
+        /// <summary>
+        /// Gets or sets a flag to determine whether, if an action receives invalid JSON in
+        /// the request body, the JSON deserialization exception message should be replaced
+        /// by a generic error message in model state.
+        /// <see langword="false"/> by default, meaning that clients may receive details about
+        /// why the JSON they posted is considered invalid.
+        /// </summary>
+        public bool SuppressJsonDeserializationExceptionMessagesInModelState { get; set; } = false;
     }
 }

src/Microsoft.AspNetCore.Mvc.Core/Properties/AssemblyInfo.cs

@@ -2,6 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Runtime.CompilerServices;
+using Microsoft.AspNetCore.Mvc.Formatters;
 
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Core.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("DynamicProxyGenAssembly2, PublicKey=0024000004800000940000000602000000240000525341310004000001000100c547cac37abd99c8db225ef2f6c8a3602f3b3606cc9891605d02baa56104f4cfc0734aa39b93bf7852f7d9266654753cc297e7d2edfe0bac1cdcf9f717241550e0a7b191195b7667bb4f64bcb8e2121380fd1d9d46ad2d92d2d15605093924cceaf74c4861eff62abf69b9291ed0a340e113be11e6a7d3113e92484cf7045cc7")]
+[assembly: TypeForwardedTo(typeof(InputFormatterException))]

src/Microsoft.AspNetCore.Mvc.Formatters.Json/Internal/MvcJsonMvcOptionsSetup.cs

@@ -69,7 +69,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters.Json.Internal
                 _jsonSerializerSettings,
                 _charPool,
                 _objectPoolProvider,
-                options.SuppressInputFormatterBuffering));
+                options.SuppressInputFormatterBuffering,
+                options.SuppressJsonDeserializationExceptionMessagesInModelState));
 
             var jsonInputLogger = _loggerFactory.CreateLogger<JsonInputFormatter>();
             options.InputFormatters.Add(new JsonInputFormatter(
@@ -77,7 +78,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters.Json.Internal
                 _jsonSerializerSettings,
                 _charPool,
                 _objectPoolProvider,
-                options.SuppressInputFormatterBuffering));
+                options.SuppressInputFormatterBuffering,
+                options.SuppressJsonDeserializationExceptionMessagesInModelState));
 
             options.FormatterMappings.SetMediaTypeMappingForFormat("json", MediaTypeHeaderValue.Parse("application/json"));
 

src/Microsoft.AspNetCore.Mvc.Formatters.Json/JsonInputFormatter.cs

@@ -28,6 +28,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         private readonly ILogger _logger;
         private readonly ObjectPoolProvider _objectPoolProvider;
         private readonly bool _suppressInputFormatterBuffering;
+        private readonly bool _suppressJsonDeserializationExceptionMessages;
 
         private ObjectPool<JsonSerializer> _jsonSerializerPool;
 
@@ -70,6 +71,32 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             ArrayPool<char> charPool,
             ObjectPoolProvider objectPoolProvider,
             bool suppressInputFormatterBuffering)
+            : this(logger, serializerSettings, charPool, objectPoolProvider, suppressInputFormatterBuffering, suppressJsonDeserializationExceptionMessages: false)
+        {
+            // This constructor by default treats JSON deserialization exceptions as safe
+            // because this is the default for applications generally
+        }
+
+        /// <summary>
+        /// Initializes a new instance of <see cref="JsonInputFormatter"/>.
+        /// </summary>
+        /// <param name="logger">The <see cref="ILogger"/>.</param>
+        /// <param name="serializerSettings">
+        /// The <see cref="JsonSerializerSettings"/>. Should be either the application-wide settings
+        /// (<see cref="MvcJsonOptions.SerializerSettings"/>) or an instance
+        /// <see cref="JsonSerializerSettingsProvider.CreateSerializerSettings"/> initially returned.
+        /// </param>
+        /// <param name="charPool">The <see cref="ArrayPool{Char}"/>.</param>
+        /// <param name="objectPoolProvider">The <see cref="ObjectPoolProvider"/>.</param>
+        /// <param name="suppressInputFormatterBuffering">Flag to buffer entire request body before deserializing it.</param>
+        /// <param name="suppressJsonDeserializationExceptionMessages">If <see langword="true"/>, JSON deserialization exception messages will replaced by a generic message in model state.</param>
+        public JsonInputFormatter(
+            ILogger logger,
+            JsonSerializerSettings serializerSettings,
+            ArrayPool<char> charPool,
+            ObjectPoolProvider objectPoolProvider,
+            bool suppressInputFormatterBuffering,
+            bool suppressJsonDeserializationExceptionMessages)
         {
             if (logger == null)
             {
@@ -96,6 +123,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             _charPool = new JsonArrayPool<char>(charPool);
             _objectPoolProvider = objectPoolProvider;
             _suppressInputFormatterBuffering = suppressInputFormatterBuffering;
+            _suppressJsonDeserializationExceptionMessages = suppressJsonDeserializationExceptionMessages;
 
             SupportedEncodings.Add(UTF8EncodingWithoutBOM);
             SupportedEncodings.Add(UTF16EncodingLittleEndian);
@@ -187,7 +215,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
                         }
 
                         var metadata = GetPathMetadata(context.Metadata, eventArgs.ErrorContext.Path);
-                        context.ModelState.TryAddModelError(key, eventArgs.ErrorContext.Error, metadata);
+                        var modelStateException = WrapExceptionForModelState(eventArgs.ErrorContext.Error);
+                        context.ModelState.TryAddModelError(key, modelStateException, metadata);
 
                         _logger.JsonInputException(eventArgs.ErrorContext.Error);
 
@@ -315,5 +344,19 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
 
             return metadata;
         }
+
+        private Exception WrapExceptionForModelState(Exception exception)
+        {
+            // It's not known that Json.NET currently ever raises error events with exceptions
+            // other than these two types, but we're being conservative and limiting which ones
+            // we regard as having safe messages to expose to clients
+            var isJsonExceptionType =
+                exception is JsonReaderException || exception is JsonSerializationException;
+            var suppressOriginalMessage =
+                _suppressJsonDeserializationExceptionMessages || !isJsonExceptionType;
+            return suppressOriginalMessage
+                ? exception
+                : new InputFormatterException(exception.Message, exception);
+        }
     }
 }

src/Microsoft.AspNetCore.Mvc.Formatters.Json/JsonPatchInputFormatter.cs

@@ -27,7 +27,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         /// The <see cref="JsonSerializerSettings"/>. Should be either the application-wide settings
         /// (<see cref="MvcJsonOptions.SerializerSettings"/>) or an instance
         /// <see cref="JsonSerializerSettingsProvider.CreateSerializerSettings"/> initially returned.
-        /// </param>/// <param name="charPool">The <see cref="ArrayPool{Char}"/>.</param>
+        /// </param>
+        /// <param name="charPool">The <see cref="ArrayPool{Char}"/>.</param>
         /// <param name="objectPoolProvider">The <see cref="ObjectPoolProvider"/>.</param>
         public JsonPatchInputFormatter(
             ILogger logger,
@@ -46,7 +47,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         /// The <see cref="JsonSerializerSettings"/>. Should be either the application-wide settings
         /// (<see cref="MvcJsonOptions.SerializerSettings"/>) or an instance
         /// <see cref="JsonSerializerSettingsProvider.CreateSerializerSettings"/> initially returned.
-        /// </param>/// <param name="charPool">The <see cref="ArrayPool{Char}"/>.</param>
+        /// </param>
+        /// <param name="charPool">The <see cref="ArrayPool{Char}"/>.</param>
         /// <param name="objectPoolProvider">The <see cref="ObjectPoolProvider"/>.</param>
         /// <param name="suppressInputFormatterBuffering">Flag to buffer entire request body before deserializing it.</param>
         public JsonPatchInputFormatter(
@@ -55,7 +57,31 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             ArrayPool<char> charPool,
             ObjectPoolProvider objectPoolProvider,
             bool suppressInputFormatterBuffering)
-            : base(logger, serializerSettings, charPool, objectPoolProvider, suppressInputFormatterBuffering)
+            : this(logger, serializerSettings, charPool, objectPoolProvider, suppressInputFormatterBuffering, suppressJsonDeserializationExceptionMessages: false)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new <see cref="JsonPatchInputFormatter"/> instance.
+        /// </summary>
+        /// <param name="logger">The <see cref="ILogger"/>.</param>
+        /// <param name="serializerSettings">
+        /// The <see cref="JsonSerializerSettings"/>. Should be either the application-wide settings
+        /// (<see cref="MvcJsonOptions.SerializerSettings"/>) or an instance
+        /// <see cref="JsonSerializerSettingsProvider.CreateSerializerSettings"/> initially returned.
+        /// </param>
+        /// <param name="charPool">The <see cref="ArrayPool{Char}"/>.</param>
+        /// <param name="objectPoolProvider">The <see cref="ObjectPoolProvider"/>.</param>
+        /// <param name="suppressInputFormatterBuffering">Flag to buffer entire request body before deserializing it.</param>
+        /// <param name="suppressJsonDeserializationExceptionMessages">If <see langword="true"/>, JSON deserialization exception messages will replaced by a generic message in model state.</param>
+        public JsonPatchInputFormatter(
+            ILogger logger,
+            JsonSerializerSettings serializerSettings,
+            ArrayPool<char> charPool,
+            ObjectPoolProvider objectPoolProvider,
+            bool suppressInputFormatterBuffering,
+            bool suppressJsonDeserializationExceptionMessages)
+            : base(logger, serializerSettings, charPool, objectPoolProvider, suppressInputFormatterBuffering, suppressJsonDeserializationExceptionMessages)
         {
             // Clear all values and only include json-patch+json value.
             SupportedMediaTypes.Clear();

test/Microsoft.AspNetCore.Mvc.Abstractions.Test/ModelBinding/ModelStateDictionaryTest.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using Microsoft.AspNetCore.Mvc.Formatters;
 using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;
 using Microsoft.Extensions.Options;
@@ -1005,7 +1006,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         [Fact]
-        public void ModelStateDictionary_NoErrorMessage_ForNonFormatException()
+        public void ModelStateDictionary_NoErrorMessage_ForUnrecognizedException()
         {
             // Arrange
             var dictionary = new ModelStateDictionary();
@@ -1021,6 +1022,28 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             Assert.Empty(error.ErrorMessage);
         }
 
+        [Fact]
+        public void ModelStateDictionary_AddsErrorMessage_ForInputFormatterException()
+        {
+            // Arrange
+            var expectedMessage = "This is an InputFormatterException";
+            var dictionary = new ModelStateDictionary();
+
+            var bindingMetadataProvider = new DefaultBindingMetadataProvider();
+            var compositeProvider = new DefaultCompositeMetadataDetailsProvider(new[] { bindingMetadataProvider });
+            var provider = new DefaultModelMetadataProvider(compositeProvider, new OptionsAccessor());
+            var metadata = provider.GetMetadataForType(typeof(int));
+
+            // Act
+            dictionary.TryAddModelError("key", new InputFormatterException(expectedMessage), metadata);
+
+            // Assert
+            var entry = Assert.Single(dictionary);
+            Assert.Equal("key", entry.Key);
+            var error = Assert.Single(entry.Value.Errors);
+            Assert.Equal(expectedMessage, error.ErrorMessage);
+        }
+
         [Fact]
         public void ModelStateDictionary_ClearEntriesThatMatchWithKey_NonEmptyKey()
         {

test/Microsoft.AspNetCore.Mvc.Core.Test/ModelBinding/Binders/BodyModelBinderTests.cs

@@ -232,10 +232,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
             // Key is the empty string because this was a top-level binding.
             var entry = Assert.Single(bindingContext.ModelState);
             Assert.Equal(string.Empty, entry.Key);
-            var errorMessage = Assert.Single(entry.Value.Errors).Exception.Message;
+            var errorMessage = Assert.Single(entry.Value.Errors).ErrorMessage;
             Assert.Equal("Bad input!!", errorMessage);
-            var formatException = Assert.IsType<FormatException>(entry.Value.Errors[0].Exception.InnerException);
-            Assert.Same(expectedFormatException, formatException);
+            Assert.Null(entry.Value.Errors[0].Exception);
         }
 
         public static TheoryData<IInputFormatter, InputFormatterExceptionModelStatePolicy> BuiltInFormattersThrowingInputFormatterException
@@ -282,9 +281,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
             // Key is the empty string because this was a top-level binding.
             var entry = Assert.Single(bindingContext.ModelState);
             Assert.Equal(string.Empty, entry.Key);
-            var errorMessage = Assert.Single(entry.Value.Errors).Exception.Message;
+            var errorMessage = Assert.Single(entry.Value.Errors).ErrorMessage;
             Assert.Equal("An error occured while deserializing input data.", errorMessage);
-            Assert.IsType<InputFormatterException>(entry.Value.Errors[0].Exception);
+            Assert.Null(entry.Value.Errors[0].Exception);
         }
 
         [Theory]
@@ -319,7 +318,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
             // Key is the empty string because this was a top-level binding.
             var entry = Assert.Single(bindingContext.ModelState);
             Assert.Equal(string.Empty, entry.Key);
-            Assert.IsType<JsonReaderException>(entry.Value.Errors[0].Exception);
+            Assert.NotEmpty(entry.Value.Errors[0].ErrorMessage);
         }
 
         public static TheoryData<IInputFormatter, InputFormatterExceptionModelStatePolicy> DerivedFormattersThrowingInputFormatterException
@@ -366,9 +365,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
             // Key is the empty string because this was a top-level binding.
             var entry = Assert.Single(bindingContext.ModelState);
             Assert.Equal(string.Empty, entry.Key);
-            var errorMessage = Assert.Single(entry.Value.Errors).Exception.Message;
+            var errorMessage = Assert.Single(entry.Value.Errors).ErrorMessage;
             Assert.Equal("An error occured while deserializing input data.", errorMessage);
-            Assert.IsType<InputFormatterException>(entry.Value.Errors[0].Exception);
+            Assert.Null(entry.Value.Errors[0].Exception);
         }
 
         [Theory]
@@ -403,7 +402,8 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
             // Key is the empty string because this was a top-level binding.
             var entry = Assert.Single(bindingContext.ModelState);
             Assert.Equal(string.Empty, entry.Key);
-            Assert.IsType<JsonReaderException>(entry.Value.Errors[0].Exception);
+            Assert.NotEmpty(entry.Value.Errors[0].ErrorMessage);
+            Assert.Null(entry.Value.Errors[0].Exception);
         }
 
         // Throwing Non-InputFormatterException

test/Microsoft.AspNetCore.Mvc.Core.Test/ValidationProblemDetailsTest.cs

@@ -1,6 +1,7 @@
 // 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;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Xunit;
 
@@ -47,5 +48,30 @@ namespace Microsoft.AspNetCore.Mvc
                     Assert.Equal(new[] { "error2", "error3" }, item.Value);
                 });
         }
+
+        [Fact]
+        public void Constructor_SerializesErrorsFromModelStateDictionary_AddsDefaultMessage()
+        {
+            // Arrange
+            var modelStateDictionary = new ModelStateDictionary();
+            var provider = new EmptyModelMetadataProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(string), nameof(string.Length));
+            modelStateDictionary.AddModelError("unsafeError",
+                new Exception("This message should not be returned to clients"),
+                metadata);
+
+            // Act
+            var problemDescription = new ValidationProblemDetails(modelStateDictionary);
+
+            // Assert
+            Assert.Equal("One or more validation errors occured.", problemDescription.Title);
+            Assert.Collection(
+                problemDescription.Errors,
+                item =>
+                {
+                    Assert.Equal("unsafeError", item.Key);
+                    Assert.Equal(new[] { "The input was not valid." }, item.Value);
+                });
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.Formatters.Json.Test/JsonInputFormatterTest.cs

@@ -331,7 +331,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             Assert.True(result.HasError);
             Assert.Equal(
                 "Could not convert string to decimal: not-an-age. Path 'Age', line 1, position 39.",
-                modelState["Age"].Errors[0].Exception.Message);
+                modelState["Age"].Errors[0].ErrorMessage);
         }
 
         [Fact]
@@ -392,7 +392,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             Assert.True(result.HasError);
             Assert.Equal(
                 "Error converting value 300 to type 'System.Byte'. Path '[1].Small', line 1, position 59.",
-                modelState["names[1].Small"].Errors[0].Exception.Message);
+                modelState["names[1].Small"].Errors[0].ErrorMessage);
         }
 
         [Fact]
@@ -508,7 +508,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             Assert.True(result.HasError);
             Assert.False(modelState.IsValid);
 
-            var modelErrorMessage = modelState.Values.First().Errors[0].Exception.Message;
+            var modelErrorMessage = modelState.Values.First().Errors[0].ErrorMessage;
             Assert.Contains("Required property 'Password' not found in JSON", modelErrorMessage);
         }
 
@@ -533,6 +533,81 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             Assert.Equal(settings.DateTimeZoneHandling, actual.DateTimeZoneHandling);
         }
 
+        [Theory]
+        [InlineData("{", "", "Unexpected end when reading JSON. Path '', line 1, position 1.")]
+        [InlineData("{\"a\":{\"b\"}}", "a", "Invalid character after parsing property name. Expected ':' but got: }. Path 'a', line 1, position 9.")]
+        [InlineData("{\"age\":\"x\"}", "age", "Could not convert string to decimal: x. Path 'age', line 1, position 10.")]
+        [InlineData("{\"login\":1}", "login", "Error converting value 1 to type 'Microsoft.AspNetCore.Mvc.Formatters.JsonInputFormatterTest+UserLogin'. Path 'login', line 1, position 10.")]
+        [InlineData("{\"login\":{\"username\":\"somevalue\"}}", "login", "Required property 'Password' not found in JSON. Path 'login', line 1, position 33.")]
+        public async Task ReadAsync_RegistersJsonInputExceptionsAsInputFormatterException(
+            string content,
+            string modelStateKey,
+            string expectedMessage)
+        {
+            // Arrange
+            var logger = GetLogger();
+            var formatter =
+                new JsonInputFormatter(logger, _serializerSettings, ArrayPool<char>.Shared, _objectPoolProvider);
+            var contentBytes = Encoding.UTF8.GetBytes(content);
+
+            var modelState = new ModelStateDictionary();
+            var httpContext = GetHttpContext(contentBytes);
+            var provider = new EmptyModelMetadataProvider();
+            var metadata = provider.GetMetadataForType(typeof(User));
+            var context = new InputFormatterContext(
+                httpContext,
+                modelName: string.Empty,
+                modelState: modelState,
+                metadata: metadata,
+                readerFactory: new TestHttpRequestStreamReaderFactory().CreateReader);
+
+            // Act
+            var result = await formatter.ReadAsync(context);
+
+            // Assert
+            Assert.True(result.HasError);
+            Assert.True(!modelState.IsValid);
+            Assert.True(modelState.ContainsKey(modelStateKey));
+
+            var modelError = modelState[modelStateKey].Errors.Single();
+            Assert.Equal(expectedMessage, modelError.ErrorMessage);
+        }
+
+        [Fact]
+        public async Task ReadAsync_WhenSuppressJsonDeserializationExceptionMessagesIsTrue_DoesNotWrapJsonInputExceptions()
+        {
+            // Arrange
+            var logger = GetLogger();
+            var formatter = new JsonInputFormatter(
+                logger, _serializerSettings, ArrayPool<char>.Shared, _objectPoolProvider,
+                suppressInputFormatterBuffering: false, suppressJsonDeserializationExceptionMessages: true);
+            var contentBytes = Encoding.UTF8.GetBytes("{");
+            var modelStateKey = string.Empty;
+
+            var modelState = new ModelStateDictionary();
+            var httpContext = GetHttpContext(contentBytes);
+            var provider = new EmptyModelMetadataProvider();
+            var metadata = provider.GetMetadataForType(typeof(User));
+            var context = new InputFormatterContext(
+                httpContext,
+                modelName: string.Empty,
+                modelState: modelState,
+                metadata: metadata,
+                readerFactory: new TestHttpRequestStreamReaderFactory().CreateReader);
+
+            // Act
+            var result = await formatter.ReadAsync(context);
+
+            // Assert
+            Assert.True(result.HasError);
+            Assert.True(!modelState.IsValid);
+            Assert.True(modelState.ContainsKey(modelStateKey));
+
+            var modelError = modelState[modelStateKey].Errors.Single();
+            Assert.IsNotType<InputFormatterException>(modelError.Exception);
+            Assert.Empty(modelError.ErrorMessage);
+        }
+
         private class TestableJsonInputFormatter : JsonInputFormatter
         {
             public TestableJsonInputFormatter(JsonSerializerSettings settings)
@@ -609,6 +684,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             public decimal Age { get; set; }
 
             public byte Small { get; set; }
+
+            public UserLogin Login { get; set; }
         }
 
         private sealed class UserLogin

test/Microsoft.AspNetCore.Mvc.Formatters.Json.Test/JsonPatchInputFormatterTest.cs

@@ -271,7 +271,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
 
             // Assert
             Assert.True(result.HasError);
-            Assert.Contains(exceptionMessage, modelState[""].Errors[0].Exception.Message);
+            Assert.Contains(exceptionMessage, modelState[""].Errors[0].ErrorMessage);
         }
 
         private static ILogger GetLogger()

test/Microsoft.AspNetCore.Mvc.FunctionalTests/InputFormatterTests.cs

@@ -97,6 +97,21 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
         }
 
+        [Fact]
+        public async Task JsonInputFormatter_SuppliedJsonDeserializationErrorMessage()
+        {
+            // Arrange
+            var content = new StringContent("{", Encoding.UTF8, "application/json");
+
+            // Act
+            var response = await Client.PostAsync("http://localhost/JsonFormatter/ReturnInput/", content);
+            var responseBody = await response.Content.ReadAsStringAsync();
+
+            // Assert
+            Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+            Assert.Equal("{\"\":[\"Unexpected end when reading JSON. Path '', line 1, position 1.\"]}", responseBody);
+        }
+
         [Theory]
         [InlineData("\"I'm a JSON string!\"")]
         [InlineData("true")]

test/Microsoft.AspNetCore.Mvc.FunctionalTests/XmlDataContractSerializerInputFormatterTest.cs

@@ -46,11 +46,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             // Assert
             Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
             var data = await response.Content.ReadAsStringAsync();
-            Assert.Contains(
-                string.Format(
-                    "There was an error deserializing the object of type {0}.",
-                    typeof(DummyClass).FullName),
-                data);
+            Assert.Contains("An error occured while deserializing input data.", data);
         }
 
         [Fact]

test/Microsoft.AspNetCore.Mvc.FunctionalTests/XmlSerializerInputFormatterTests.cs

@@ -52,7 +52,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             // Assert
             Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
             var data = await response.Content.ReadAsStringAsync();
-            Assert.Contains("There is an error in XML document", data);
+            Assert.Contains("An error occured while deserializing input data.", data);
         }
     }
 }

test/Microsoft.AspNetCore.Mvc.IntegrationTests/BodyValidationIntegrationTests.cs

@@ -485,11 +485,11 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTests
             Assert.Null(entry.Value.AttemptedValue);
             Assert.Null(entry.Value.RawValue);
             var error = Assert.Single(entry.Value.Errors);
-            Assert.NotNull(error.Exception);
+            Assert.Null(error.Exception);
 
             // Json.NET currently throws an exception starting with "No JSON content found and type 'System.Int32' is
             // not nullable." but do not tie test to a particular Json.NET build.
-            Assert.NotEmpty(error.Exception.Message);
+            Assert.NotEmpty(error.ErrorMessage);
         }
 
         private class Person5
@@ -586,11 +586,11 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTests
             Assert.Null(state.AttemptedValue);
             Assert.Null(state.RawValue);
             var error = Assert.Single(state.Errors);
-            Assert.NotNull(error.Exception);
+            Assert.Null(error.Exception);
 
             // Json.NET currently throws an Exception with a Message starting with "Could not convert string to
             // integer: not a number." but do not tie test to a particular Json.NET build.
-            Assert.NotEmpty(error.Exception.Message);
+            Assert.NotEmpty(error.ErrorMessage);
         }
 
         [Theory]

test/WebSites/FormatterWebSite/Controllers/JsonFormatterController.cs

@@ -47,7 +47,7 @@ namespace FormatterWebSite.Controllers
         {
             if (!ModelState.IsValid)
             {
-                return BadRequest();
+                return BadRequest(ModelState);
             }
 
             return Content(dummyObject.SampleInt.ToString());