Why WebAPI does not use my JSONP formatter to deserialize model? - asp.net-web-api

Question

I'm very very confuse about Microsoft brand-new framework, ASP.NET MVC WebAPI. I try to create complete solution for cross-site API with JSONP data.
First, I modify their default WebApiConfig to the following code.
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
config.Routes.MapHttpRoute("DefaultApi", "api/{controller}/{action}/{id}", new {id = RouteParameter.Optional});
// Custom customization
config.Formatters.Clear();
config.Formatters.Add(new JsonpFormatter());
}
}
I use jQuery to create a request to this API website.
// jQuery will create HTTP GET the following URL
// http://localhost:3557/api/FlightAvailability/SearchFlight?callback=jQuery18206342989655677229_1353568617029&origin=JFK&destination=SLC&isOneWayFlight=false&departFlightDate=Wed%2C+28+Nov+2012+17%3A00%3A00+GMT&returnFlightDate=Wed%2C+05+Dec+2012+17%3A00%3A00+GMT&numberOfGuests=1&numberOfChildren=1&numberOfInfants=1&preferredCurrency=USD&query=%7B+Origin%3A+'JFK'+%7D&flightDate=Wed%2C+28+Nov+2012+17%3A00%3A00+GMT&_=1353568618465
$.ajax
({
url: 'http://localhost:3557/api/FlightAvailability/SearchFlight',
dataType: 'jsonp',
data: $.postify(model),
success: processResponse
});
I create action to handle above request. Everything is correct. I can call to this action but WebAPI doesn't use my JSONP formatter to deserialize my query object.
However, I try to directly call ContentNegotiator to get which formatter that handle my request. It's quite surprise that negotiatorResult is my JSONP formatter.
[HttpGet]
public List<FlightInfo> SearchFlight(FlightAvailabilityQuery query)
{
var negotiator = Configuration.Services.GetContentNegotiator();
var negotiatorResult = negotiator.Negotiate(typeof (FlightAvailabilityQuery), Request, Configuration.Formatters);
var flight = new FlightsAvailability();
var result = flight.GetAvailability(WebApiAuthentication.UserInfo.SessionService, query);
return result;
}
Why WebAPI does not use my JSONP formatter to deserialize query FlightAvailabilityQuery object?
PS. I try to break all possible line in JSONP formatter but Visual Studio doesn't hit any break point by it directly go to action method without call at my only one formatter. However, when I directly call ContentNegotiator, it hit at my break point correctly.
Update #1 - Add JSONP formatter source code
public class JsonpFormatter : JsonMediaTypeFormatter
{
private readonly JsonSerializerSettings _serializerSettings;
private string _jsonpCallbackFunction;
public JsonpFormatter()
{
JsonpParameterName = "callback";
_serializerSettings = new JsonSerializerSettings();
_serializerSettings.TypeNameHandling = TypeNameHandling.Objects;
_serializerSettings.Converters.Add(new IsoDateTimeConverter());
MediaTypeMappings.Add(new ExtendedQueryStringMapping(JsonpParameterName, "application/json"));
}
public string JsonpParameterName { get; set; }
public override bool CanReadType(Type type)
{
return true;
}
public override bool CanWriteType(Type type)
{
return true;
}
public override MediaTypeFormatter GetPerRequestFormatterInstance(Type type, HttpRequestMessage request, MediaTypeHeaderValue mediaType)
{
var formatter = new JsonpFormatter()
{
_jsonpCallbackFunction = GetJsonCallbackFunction(request)
};
// this doesn't work unfortunately
//formatter.SerializerSettings = GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings;
formatter.SerializerSettings.Converters.Add(new StringEnumConverter());
formatter.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
formatter.SerializerSettings.Formatting = Newtonsoft.Json.Formatting.Indented;
return formatter;
}
public override Task<object> ReadFromStreamAsync(Type type, Stream stream, HttpContent content, IFormatterLogger formatterLogger)
{
// Create a serializer
var serializer = JsonSerializer.Create(_serializerSettings);
// Create task reading the content
return Task.Factory.StartNew(() =>
{
using (var streamReader = new StreamReader(stream, Encoding.UTF8))
{
using (var jsonTextReader = new JsonTextReader(streamReader))
{
return serializer.Deserialize(jsonTextReader, type);
}
}
});
}
public override Task WriteToStreamAsync(Type type, object value, Stream stream, HttpContent content, TransportContext transportContext)
{
if (string.IsNullOrEmpty(_jsonpCallbackFunction))
return base.WriteToStreamAsync(type, value, stream, content, transportContext);
StreamWriter writer = null;
// write the pre-amble
try
{
writer = new StreamWriter(stream);
writer.Write(_jsonpCallbackFunction + "(");
writer.Flush();
}
catch (Exception ex)
{
try
{
if (writer != null)
writer.Dispose();
}
catch { }
var tcs = new TaskCompletionSource<object>();
tcs.SetException(ex);
return tcs.Task;
}
return base.WriteToStreamAsync(type, value, stream, content, transportContext)
.ContinueWith(innerTask =>
{
if (innerTask.Status == TaskStatus.RanToCompletion)
{
writer.Write(")");
writer.Flush();
}
}, TaskContinuationOptions.ExecuteSynchronously)
.ContinueWith(innerTask =>
{
writer.Dispose();
return innerTask;
}, TaskContinuationOptions.ExecuteSynchronously)
.Unwrap();
}
private string GetJsonCallbackFunction(HttpRequestMessage request)
{
if (request.Method != HttpMethod.Get)
return null;
var query = HttpUtility.ParseQueryString(request.RequestUri.Query);
var queryVal = query[this.JsonpParameterName];
if (string.IsNullOrEmpty(queryVal))
return null;
return queryVal;
}
}

Answer 1

Your action does not get hit because it cannot model bind your query parameter. Also JsonP is for HTTP GET only, so your formatter will not be selected for deserialization. How do you expect your FlightAvailabilityQuery being deserialized? I saw a lot of query parameters from your URL, do you want that be turned into FlightAvailabilityQuery?
The easiest way to get that is to use FromUri.
public List<FlightInfo> SearchFlight([FromUri]FlightAvailabilityQuery query)
If for some reason that does not work, you can try to add individual query parameter name on the action, such as origin, isOneWay, destination. etc. Then inside your action construct the FlightAvailabilityQuery object.
Also, if you have a lot of actions that you want to reuse this model binding logic, you can register a custom parameter binding to solve that. Please see this link for how to register a custom parameter binding to solve this.
Hope this helps!