WebAPI throws 415 error for HttpGet

Question

I am bamboozled right now.

I have an [HttpGet] method in my Web API 2 controller:

[HttpGet]
public LanguageResponse GetLanguages(LanguageRequest request) 
{
...
}

My url looks like this http://localhost:1234/api/MyController/GetLanguages?Id=1

When try to call it (for example, via Postman), I recieve HTTP error 415:

{"message":"The request contains an entity body but no Content-Type header. The inferred media type 'application/octet-stream' is not supported for this resource.","exceptionMessage":"No MediaTypeFormatter is available to read an object of type 'LanguagesRequest' from content with media type 'application/octet-stream'.","exceptionType":"System.Net.Http.UnsupportedMediaTypeException","stackTrace":"   at System.Net.Http.HttpContentExtensions.ReadAsAsync[T](HttpContent content, Type type, IEnumerable`1 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)"}

Which is kind of weird because I am using a GET.

If I add Content-Type:application/json, the exception will not be thrown, but then method's request parameter is set to null.

In my client code it's even worse. I cannot set the Content-Type header since I don't have Content in my HttpRequestMessage and if I set the content, it complains I am using a wrong verb.

Answer 1

The As explained in Why do we have to specify FromBody and FromUri in ASP.NET Web-API?, for a complex model to be parsed from the Uri, you'll have to use the [FromUri] attribute on the parameter you wish to be parsed from the request Uri:

[HttpGet]
public LanguageResponse GetLanguages([FromUri] LanguageRequest request) 
{
    ...
}

Otherwise the model binder will complain about the missing Content-Type header, as it needs to know how to parse the request body, which is missing or empty on a GET request anyway.

To set the content type for your client on requests that do have a body (POST, PUT, ...) see How do you set the Content-Type header for an HttpClient request?.