ASP.NET MVC returns Content-Type text/plain even if application/xml was requested in case of return type is string

[YEVHENO]

This is my controller:

[Route("")]
public class ValuesController : Controller
{
    //This always returns text/plain
    [HttpPost("/text")]
    [Produces("application/xml", "application/json")]
    public string GetText() => "Some text";

    [HttpPost("/textarray")]
    [Produces("application/xml", "application/json")]
    public IEnumerable<string> GetTextarray() => new[] { "Some text", "Some text2" };
}

GetText() always returns text/plain even if I specify "Accept: application/xml" in request header. This happens only in case of return type "string". I expect get xml instead of plain text. See sample requests below:

Request 1:
GET /text HTTP/1.1
Host: localhost:5004
Accept: application/xml

Response 1:
HTTP/1.1 200 OK
Date: Fri, 04 Dec 2015 20:13:00 GMT
Content-Type: text/plain; charset=utf-8
Server: Kestrel

Some text

Request 2:
GET /textarray HTTP/1.1
Host: localhost:5004
Accept: application/xml

Response 2:
HTTP/1.1 200 OK
Date: Fri, 04 Dec 2015 20:13:04 GMT
Content-Type: application/json; charset=utf-8
Server: Kestrel

<ArrayOfString xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><string>Some text</string><string>Some text2</string></ArrayOfString>

[dougbu]

Have you added the Microsoft.AspNet.Mvc.Formatters.Xml package to your dependencies in project.json? Without that dependency and configuration in the Startup class (or a custom output formatter), MVC does not support application/xml.

[YEVHENO]

Yes, I have added Microsoft.AspNet.Mvc.Formatters.Xml like this:

var mvc = services.AddMvc(); mvc.AddXmlSerializerFormatters();

In my controller GetTextarray() return xml if requested. I have an issue with GetText which has response type string. Only in this case MVC always returns plain text. Please see sample request/response from my first comment.

[rynowak]

I'd try adding the following to your startup code:

mvc.AddMvcOptions(options =>
{
    options.OutputFormatters.RemoveType<StringOutputFormatter>();
});

We have a formatter registered by default that treats strings as text/plain content.

You could also bypass formatters if your content is already in the format you want.

return Content(text, "application/xml");

[YEVHENO]

Removing of StringOutputFormatter helps. But then no need to return xml content like this: return Content(text, "application/xml"). Attribute [Produces("application/xml")] does it.

[YEVHENO]

My expectation was the following: Since I have marked method as [Produces("application/xml")], XmlSerializerOutputFormatter for this method should have higher priority than StringOutputFormatter. But that is not true if return type is string.

[danroth27]

We should figure out what we want to do with the StringFormatter.