Error posting JSON to Web API 2 : The request entity's media type 'text/plain' is not supported for this resource

Question

I have this class :

public class MyClass
{
    public MyClass() { Secret = "Don't tell me"; }
    public string Name { get; set; }
    public int Age { get; set; }
    public string Description { get; set; }
    private string Secret { get; set; }
}

And this WEB API method :

        // POST api/fixture
    public HttpResponseMessage Post(MyClass value)
    {
        return new HttpResponseMessage(HttpStatusCode.Created);
    }

I've set Web API to return JSON instead of XML and I haven't done any other change to the default config. I'm trying to test this method with the RESTClient extension of Firefox. Here is my request :

POST localhost:XXXX/api/fixture
Content-Type: application/json
Accept: application/json
Content-Length: 60

{
 value : { "Name":"Cosby","Age":"13","Description":"OK" }
}

However I'm getting this error :

{"Message":"The request entity's media type 'text/plain' is not supported for this resource.","ExceptionMessage":"No MediaTypeFormatter is available to read an object of type 'MyClass' from content with media type 'text/plain'.","ExceptionType":"System.Net.Http.UnsupportedMediaTypeException","StackTrace":" at System.Net.Http.HttpContentExtensions.ReadAsAsync[T](HttpContent content, Type type, IEnumerable1 formatters, IFormatterLogger formatterLogger, CancellationToken cancellationToken)\r\n at System.Net.Http.HttpContentExtensions.ReadAsAsync(HttpContent content, Type type, IEnumerable1 formatters, IFormatterLogger formatterLogger, CancellationToken cancellationToken)\r\n at System.Web.Http.ModelBinding.FormatterParameterBinding.ReadContentAsync(HttpRequestMessage request, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger, CancellationToken cancellationToken)"}

Edit:

I don't understand because it seems that the method is not even called. If I debug, I see that the constructor is called and then no other method is called. No exception is raised.

I've been on this issue for a lot of time now. I've found that this problem usually happens when Content-Type is not set properly but it doesn't seem to be my case since the request is not even processed.

Any idea ?

Thanks

You don't need to obfuscate your port number in your question. We don't know where localhost is. Anyways, are you positive that your exception occurs with that POST message? The exception makes it sound like you're posting a content type of text/plain rather than application/json. — mason

mason mason · Accepted Answer · 2014-09-19T14:22:59

You were sending the content-type of application/json in the body, rather than as a header. So your POST request was defaulting to text/plain. The RestClient extension has a separate place to enter the header.

If you ever have a question about what's being sent over the wire, check the Network tab in your browser's developer tools, or use a tool such as Fiddler to see the network traffic.

Error posting JSON to Web API 2 : The request entity's media type 'text/plain' is not supported for this resource

5 Answers