Cannot set content-type to 'application/json' in jQuery.ajax

Question

When I have this code

$.ajax({
    type: 'POST',
    //contentType: "application/json",
    url: 'http://localhost:16329/Hello',
    data: { name: 'norm' },
    dataType: 'json'
});

in Fiddler I can see following raw request

POST http://localhost:16329/Hello HTTP/1.1
Host: localhost:16329
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:10.0.2) Gecko/20100101 Firefox/10.0.2
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: ru-ru,ru;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Referer: http://localhost:14693/WebSite1/index.html
Content-Length: 9
Origin: http://localhost:14693
Pragma: no-cache
Cache-Control: no-cache

name=norm

But what I'm trying is to set content-type from application/x-www-form-urlencoded to application/json. But this code

$.ajax({
    type: "POST",
    contentType: "application/json",
    url: 'http://localhost:16329/Hello',
    data: { name: 'norm' },
    dataType: "json"
});

Generates strange request (which I can see in Fiddler)

OPTIONS http://localhost:16329/Hello HTTP/1.1
Host: localhost:16329
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:10.0.2) Gecko/20100101 Firefox/10.0.2
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: ru-ru,ru;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
Origin: http://localhost:14693
Access-Control-Request-Method: POST
Access-Control-Request-Headers: content-type
Pragma: no-cache
Cache-Control: no-cache

Why is that? What is OPTIONS when it should be POST there? And where is my content-type set to application/json? And request parameters has gone for some reason.

UPDATE 1

On server side I have really simple RESTful service.

[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class RestfulService : IRestfulService
{
    [WebInvoke(
        Method = "POST",
        UriTemplate = "Hello",
        ResponseFormat = WebMessageFormat.Json)]
    public string HelloWorld(string name)
    {
        return "hello, " + name;
    }
}

But for some reason I can't call this method with parameters.

UPDATE 2

Sorry for not answering so long.

I've added these headers to my server response

 Access-Control-Allow-Origin: *
 Access-Control-Allow-Headers: Content-Type
 Access-Control-Allow-Methods: POST, GET, OPTIONS

It didn't help, I have Method not allowed error from server.

Here is what my fiddler says

So, now I can be sure that my server accepts POST, GET, OPTIONS (if response headers work like I expect). But why "Method not allowed"?

In WebView response from server (you can see Raw response on picture above) looks like this

Answer 1

It would seem that removing http:// from the url option ensures the the correct HTTP POST header is sent.

I dont think you need to fully qualify the name of the host, just use a relative URL as below.

   $.ajax({
      type: "POST",
      contentType: "application/json",
      url: '/Hello',
      data: { name: 'norm' },
      dataType: "json"
   });

An example of mine that works:

        $.ajax({
            type: "POST",
            url: siteRoot + "api/SpaceGame/AddPlayer",
            async: false,
            data: JSON.stringify({ Name: playersShip.name, Credits: playersShip.credits }),
            contentType: "application/json",
            complete: function (data) {
            console.log(data);
            wait = false;
        }
    });

Possibly related: jQuery $.ajax(), $.post sending "OPTIONS" as REQUEST_METHOD in Firefox

Edit: After some more research I found out the OPTIONS header is used to find out if the request from the originating domain is allowed. Using fiddler, I added the following to the response headers from my server.

 Access-Control-Allow-Origin: *
 Access-Control-Allow-Headers: Content-Type
 Access-Control-Allow-Methods: POST, GET, OPTIONS

Once the browser received this response it then sent off the correct POST request with json data. It would seem that the default form-urlencoded content type is considered safe and so does not undergo the extra cross domain checks.

It looks like you will need to add the previously mentioned headers to your servers response to the OPTIONS request. You should of course configure them to allow requests from specific domains rather then all.

I used the following jQuery to test this.

$.ajax({
   type: "POST",
   url: "http://myDomain.com/path/AddPlayer",
   data: JSON.stringify({
      Name: "Test",
       Credits: 0
   }),
   //contentType: "application/json",
   dataType: 'json',
   complete: function(data) {
       $("content").html(data);
  }
});​

References:

• http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
• http://enable-cors.org/
• https://developer.mozilla.org/en/http_access_control