JsonMaxLength exception on deserializing large json objects

Question

Intro:

Web application, ASP.NET MVC 3, a controller action that accepts an instance of POCO model class with (potentially) large field.

Mode

Answer 1

The built-in JsonValueProviderFactory ignores the setting. So you could write a custom factory by using the built-in implementation:

public sealed class MyJsonValueProviderFactory : ValueProviderFactory
{
    private static void AddToBackingStore(Dictionary backingStore, string prefix, object value)
    {
        IDictionary d = value as IDictionary;
        if (d != null)
        {
            foreach (KeyValuePair entry in d)
            {
                AddToBackingStore(backingStore, MakePropertyKey(prefix, entry.Key), entry.Value);
            }
            return;
        }

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

        // primitive
        backingStore[prefix] = value;
    }

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

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

        JavaScriptSerializer serializer = new JavaScriptSerializer();
        serializer.MaxJsonLength = 2147483647;
        object jsonData = serializer.DeserializeObject(bodyText);
        return jsonData;
    }

    public override IValueProvider GetValueProvider(ControllerContext controllerContext)
    {
        if (controllerContext == null)
        {
            throw new ArgumentNullException("controllerContext");
        }

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

        Dictionary backingStore = new Dictionary(StringComparer.OrdinalIgnoreCase);
        AddToBackingStore(backingStore, String.Empty, jsonData);
        return new DictionaryValueProvider