using System;

using System.IO;

using System.Net;

using System.Net.Http.Formatting;

using System.Net.Http.Headers;

using System.Threading.Tasks;

using System.Web;

using System.Net.Http;

namespace WebApiTest

{

/// <summary>

/// Handles JsonP requests when requests are fired with

/// text/javascript or application/json and contain

/// a callback= (configurable) query string parameter

///

/// Based on Christian Weyers implementation

/// https://github.com/thinktecture/Thinktecture.Web.Http/blob/master/Thinktecture.Web.Http/Formatters/JsonpFormatter.cs

/// </summary>

public class JsonpFormatter : JsonMediaTypeFormatter

{

public JsonpFormatter()

{

SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/json"));

SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/javascript"));

//MediaTypeMappings.Add(new UriPathExtensionMapping("jsonp", "application/json"));

JsonpParameterName = "callback";

}

/// <summary>

/// Name of the query string parameter to look for

/// the jsonp function name

/// </summary>

public string JsonpParameterName { get; set; }

/// <summary>

/// Captured name of the Jsonp function that the JSON call

/// is wrapped in. Set in GetPerRequestFormatter Instance

/// </summary>

private string JsonpCallbackFunction;

public override bool CanWriteType(Type type)

{

return true;

}

/// <summary>

/// Override this method to capture the Request object

/// and look for the query string parameter and

/// create a new instance of this formatter.

///

/// This is the only place in a formatter where the

/// Request object is available.

/// </summary>

/// <param name="type"></param>

/// <param name="request"></param>

/// <param name="mediaType"></param>

/// <returns></returns>

public override MediaTypeFormatter GetPerRequestFormatterInstance(Type type, HttpRequestMessage request,

MediaTypeHeaderValue mediaType)

{

var formatter = new JsonpFormatter()

{

JsonpCallbackFunction = GetJsonCallbackFunction(request)

};

return formatter;

}

/// <summary>

/// Override to wrap existing JSON result with the

/// JSONP function call

/// </summary>

/// <param name="type"></param>

/// <param name="value"></param>

/// <param name="stream"></param>

/// <param name="contentHeaders"></param>

/// <param name="transportContext"></param>

/// <returns></returns>

public override Task WriteToStreamAsync(Type type, object value, Stream stream, HttpContentHeaders contentHeaders,

TransportContext transportContext)

{

if (!string.IsNullOrEmpty(JsonpCallbackFunction))

{

return Task.Factory.StartNew(() =>

{

var writer = new StreamWriter(stream);

writer.Write(JsonpCallbackFunction + "(");

writer.Flush();

base.WriteToStreamAsync(type, value, stream, contentHeaders, transportContext).Wait();

writer.Write(")");

writer.Flush();

});

}

else

{

return base.WriteToStreamAsync(type, value, stream, contentHeaders, transportContext);

}

}

/// <summary>

/// Retrieves the Jsonp Callback function

/// from the query string

/// </summary>

/// <returns></returns>

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;

}

}

}