How do I resolve an exception for exceeding maxJsonLength in JavaScriptSerializer?

Question

I have found a few answers that address this issue in the context of a large response, but none for my context of a large request. I get the following exception when posting a large file to an action method:

Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.

This is before my action methods ever get hit, so the abundance of posts that tell me to set a higher json size on my response are all useless here.

The stack trace is:

at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(JavaScriptSerializer serializer, String input, Type type, Int32 depthLimit)
at System.Web.Script.Serialization.JavaScriptSerializer.DeserializeObject(String input)
at System.Web.Mvc.JsonValueProviderFactory.GetDeserializedObject(ControllerContext controllerContext)
at System.Web.Mvc.JsonValueProviderFactory.GetValueProvider(ControllerContext controllerContext)
at System.Web.Mvc.ValueProviderFactoryCollection.<>c__DisplayClassc.<GetValueProvider>b__7(ValueProviderFactory factory)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at System.Web.Mvc.ValueProviderFactoryCollection.GetValueProvider(ControllerContext controllerContext)
at System.Web.Mvc.ControllerBase.get_ValueProvider()
at System.Web.Mvc.ControllerActionInvoker.GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor)
at System.Web.Mvc.ControllerActionInvoker.GetParameterValues(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass25.<BeginInvokeAction>b__1e(AsyncCallback asyncCallback, Object asyncState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeAction(ControllerContext controllerContext, String actionName, AsyncCallback callback, Object state)
at System.Web.Mvc.Controller.<>c__DisplayClass1d.<BeginExecuteCore>b__17(AsyncCallback asyncCallback, Object asyncState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.Controller.BeginExecuteCore(AsyncCallback callback, Object state)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.Controller.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state)
at System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state)
at System.Web.Mvc.MvcHandler.<>c__DisplayClass8.<BeginProcessRequest>b__2(AsyncCallback asyncCallback, Object asyncState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state)
at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state)
at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Answer 1

Extensive and panic stricken googling yielded one other poor dev with this problem, and the answer is simple but disappointingly invasive:

First you must build a custom JsonValueProviderFactory.

I copied dkinchen's custom code from his answer verbatim and it worked immediately.

I know this is a link answer, but the text of the link is a pretty good answer itself, I think.

Answer 2

There are three basic methods of handling this depending on your current environment :

1. Setting the MaxJsonLength property default value within your web.config. (This will only apply to web-services that handle JSON)
2. Setting the MaxJsonLength property of a JavascriptSerializer object to perform your serialization.
3. If you are using MVC4 to handle returning your JSON values, you may want to override the default JsonResult() ActionResult and change the maximum size manually.

Source & more info on how to implement these three solutions: http://rionscode.wordpress.com/2013/04/28/handling-larger-json-string-values-in-net-and-avoiding-exceptions/