Handle Max JSON Length Property In C#

Recently, I faced this problem. When the data from my client side is more than 5 MB, it does not hit my MVC Controller; instead, it steps out and shows an error because it has exceeded the max JSON length.

But finally, I got the solution. So, I thought I should share it so that more people can benefit. There are basically 3 steps to do that.

Step1 

Set in the webconfig file,

<add key="aspnet:MaxJsonDeserializerMembers" value="550000"/>

Step2

Add the below code in app_start folder, or just download the attached file and paste it in your app_start folder.

public sealed class CustomJsonValueProviderFactory : ValueProviderFactory
    {
        public override IValueProvider GetValueProvider(ControllerContext controllerContext)
        {
            if (controllerContext == null)
            {
                throw new ArgumentNullException("controllerContext");
            }

            var jsonData = GetDeserializedObject(controllerContext);
            if (jsonData == null)
            {
                return null;
            }

            var backingStore = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
            var backingStoreWrapper = new EntryLimitedDictionary(backingStore);
            AddToBackingStore(backingStoreWrapper, String.Empty, jsonData);
            return new DictionaryValueProvider<object>(backingStore, CultureInfo.CurrentCulture);
        }

        private static void AddToBackingStore(EntryLimitedDictionary backingStore, string prefix, object value)
        {
            var d = value as IDictionary<string, object>;
            if (d != null)
            {
                foreach (var entry in d)
                {
                    AddToBackingStore(backingStore, MakePropertyKey(prefix, entry.Key), entry.Value);
                }
                return;
            }

            var l = value as IList;
            if (l != null)
            {
                for (var i = 0; i < l.Count; i++)
                {
                    AddToBackingStore(backingStore, MakeArrayKey(prefix, i), l[i]);
                }
                return;
            }

            // primitive
            backingStore.Add(prefix, value);
        }

        private static object GetDeserializedObject(ControllerContext controllerContext)
        {
            if (
                !controllerContext.HttpContext.Request.ContentType.StartsWith("application/json",
                    StringComparison.OrdinalIgnoreCase))
            {
                // not JSON request
                return null;
            }

            var reader = new StreamReader(controllerContext.HttpContext.Request.InputStream);
            var bodyText = reader.ReadToEnd();
            if (String.IsNullOrEmpty(bodyText))
            {
                // no JSON data
                return null;
            }

            var serializer = new JavaScriptSerializer {MaxJsonLength = int.MaxValue};

            var jsonData = serializer.DeserializeObject(bodyText);
            return jsonData;
        }

        private static string MakeArrayKey(string prefix, int index)
        {
            return prefix + "[" + index.ToString(CultureInfo.InvariantCulture) + "]";
        }

        private static string MakePropertyKey(string prefix, string propertyName)
        {
            return (String.IsNullOrEmpty(prefix)) ? propertyName : prefix + "." + propertyName;
        }

        private class EntryLimitedDictionary
        {
            private readonly IDictionary<string, object> _innerDictionary;
            private int _itemCount;

            public EntryLimitedDictionary(IDictionary<string, object> innerDictionary)
            {
                _innerDictionary = innerDictionary;
            }

            public void Add(string key, object value)
            {
                if (++_itemCount > MaximumDepth)
                {
                    throw new InvalidOperationException(
                        "The length of the string exceeds the value set on the maxJsonLength property.");
                }

                _innerDictionary.Add(key, value);
            }

            private static int GetMaximumDepth()
            {
                var appSettings = ConfigurationManager.AppSettings;

                var valueArray = appSettings.GetValues("aspnet:MaxJsonDeserializerMembers");
                if (valueArray != null && valueArray.Length > 0)
                {
                    int result;
                    if (Int32.TryParse(valueArray[0], out result))
                    {
                        return result;
                    }
                }

                return 1000; // Fallback default
            }

            private static readonly int MaximumDepth = GetMaximumDepth();
        }
    }

Step 3

Add the following code in global.asax under protected void Application_Start() for a better appearance. I have removed the other code.

protected void Application_Start()
{

  // Increase max Json length
foreach (var factory in ValueProviderFactories.Factories)
{
   if (factory is JsonValueProviderFactory)
   {
   ValueProviderFactories.Factories.Remove(factory as JsonValueProviderFactory);
   break;
   }
}
ValueProviderFactories.Factories.Add(new CustomJsonValueProviderFactory());

}

Thats all.