text/plain Media Type not being accepted for WebApi v2

Question

This problem started off with IE9, where for POST requests, the contentType has to be text/plain, and application/json will not work.

I've added the moonscript and proceeded to use contentType: text/plain. I've also added the custom media type to the api, as shown on numerous forms below:

• http://www.stormbase.net/2015/09/21/webapi-post-plaintext/
• how to post plain text to ASP.NET Web API endpoint?

And added the insertion of the text/plain media type to the WebApiConfig

config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
config.Formatters.JsonFormatter.SerializerSettings.Formatting = Newtonsoft.Json.Formatting.Indented;

// allows 'text/plain' as a supported media type
config.Formatters.Add(new TextMediaTypeFormatter());

However, when posting in IE9 (using emulation), I am still receiving a 415 Unsupported Media Type

Key Value Response HTTP/1.1 415 Unsupported Media Type

$.ajax({
    type: "POST",
    url: hope_forms.viivApiUrl + 'newsletter',
    contentType: 'text/plain',
    data: JSON.stringify(model),
    success: function (data) {
           .....
    },
    error: function (responseText) {
           console.log(responseText)
           modal.showModal('Something went wrong, please try again.');
   }                    
});

Addition:

Here's the full blown WebApiConfig in the event that something is out of order:

var cors = new EnableCorsAttribute("*", "*", "*");
config.EnableCors(cors);

config.Routes.MapHttpRoute(
    name: "DefaultApi",
    routeTemplate: "api/{controller}/{id}",
    defaults: new { id = RouteParameter.Optional }
);

// Uncomment the following line of code to enable query support for actions with an IQueryable or IQueryable<T> return type.
// To avoid processing unexpected or malicious queries, use the validation settings on QueryableAttribute to validate incoming queries.
// For more information, visit http://go.microsoft.com/fwlink/?LinkId=279712.
//config.EnableQuerySupport();

config.EnableSystemDiagnosticsTracing();


//config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
config.Formatters.JsonFormatter.SerializerSettings.Formatting = Newtonsoft.Json.Formatting.Indented;

// allows 'text/plain' as a supported media type
config.Formatters.Add(new TextMediaTypeFormatter());

I also changed the ajaxTransport xhr wrapper to use this instead: https://github.com/gfdev/javascript-jquery-transport-xdr

---

Note:

As of today, 09/21, I've switched all my POST requests to GET, but I still would like a work-around to get these types back to POST.

Answer 1

I think you've run into the strange XDomainRequest issue that cropped up in 2014 according to this MSDN blog

Note: As of 2014, XDomainRequest doesn’t appear to send any Content-Type header at all. It’s not clear to me when this changed.

Here's a previous SO question on the topic as well which actually references that blog.

This is also backed up by the documentation for the jQuery extension you are using. In the Readme.md

XDomainRequest have some limitations:

• there is no Content-Type header in request

So if you check HttpContext.Request.ContentType I'm betting it's going to be null / empty in which case you should be able to assign the response type of "text/plain" and pray to the gods it works.

Basically IE < 10 support for XDomainRequest (and even XDomainRequest itself) is garbage. It has been basically ditched to my understanding and IE 10 implemented CORS support for XHR requests