Can't set Content-Type header on HttpResponseMessage headers?

Question

I'm using the ASP.NET WebApi to create a RESTful API. I'm creating a PUT method within one of my controllers, and the code looks like this:

public HttpResponseMessage Put(int idAssessment, int idCaseStudy, string value) {     var response = Request.CreateResponse();     if (!response.Headers.Contains("Content-Type")) {         response.Headers.Add("Content-Type", "text/plain");     }      response.StatusCode = HttpStatusCode.OK;     return response; } 

When I PUT to that location with the browser via AJAX, it gives me this Exception:

Misused header name. Make sure request headers are used with HttpRequestMessage, response headers with HttpResponseMessage, and content headers with HttpContent objects.

But isn't Content-Type a perfectly valid header for a response? Why am I getting this exception?

Answer 1

Have a look at the HttpContentHeaders.ContentType Property:

response.Content.Headers.ContentType = new MediaTypeHeaderValue("text/plain"); 

---

if (response.Content == null) {     response.Content = new StringContent("");     // The media type for the StringContent created defaults to text/plain. } 

Answer 2

Something is missing in ASP Web API: the EmptyContent type. It will allow sending an empty body while still allowing all content-specific headers.

Put the following class somewhere in your code :

public class EmptyContent : HttpContent {     protected override Task SerializeToStreamAsync(Stream stream, TransportContext context)     {         return Task.CompletedTask;     }     protected override bool TryComputeLength(out long length)     {         length = 0L;         return true;     } } 

Then use it as you wish. You now have a content object for your extra headers.

response.Content = new EmptyContent(); response.Content.Headers.LastModified = file.DateUpdatedUtc; 

Why use EmptyContent instead of new StringContent(string.Empty)?

• StringContent is a heavy class that executes lots of codes (because it inherits ByteArrayContent)
  • so let's save a few nanoseconds
• StringContent will add an extra useless/problematic header: Content-Type: plain/text; charset=...
  • so let's save a few network bytes