ASP.NET WebAPI: How to control string content returned to client?

Question

In WebAPI, say I return a string wrapped in an HTTP response:

return Request.CreateResponse(HttpStatusCode.BadRequest, \"Line1 \\r\\n Line2\");

Answer 1

This happens because your controller is returning JSON in which string values are quoted.

A simple solution is to parse the responseText as JSON and then you can use the value as intended:

$.ajax("/api/values/10", {
    error: function (xhr) {
        var error = JSON.parse(xhr.responseText);
        $("textarea").val(error);
    }
});

This correctly interprets the line breaks/carriage returns.

Alternatively you can specify the text/plain media type in your controller:

return Request.CreateResponse(
    HttpStatusCode.BadRequest, 
    "Line1 \r\n Line2", "text/plain");

Web API will then try and load an appropriate media type formatter for text/plain which unfortunately does not exist OOTB. You'll find one in WebApiContrib.

Answer 2

What you are after is a custom MediaTypeFormatter. It sounds like you wish to implement your own custom one to replace and existing or you're creating a new custom one all together depending what what Accept header you're expecting. Good news is you can swap out existing ones or come up with a new MediaType of you like. A couple places that will help get you started can be found here:

http://byterot.blogspot.com/2012/04/aspnet-web-api-series-part-5.html

http://www.asp.net/web-api/overview/formats-and-model-binding/media-formatters

Yes, I've actually done this in small part as I've swapped out some of the default formatter e.g. JSON with a faster one i.e. ServiceStack and it works great.