Question

I have a JSON WCF service and I have written some javascript to access the service like this,

function stuffClick2() {
        $.ajax({
            url: "http://192.168.54.98/JsonWCFService/Service1.svc/Post",
            type: "POST",
            contentType: "application/json",
            data: '{"x":"1","y":"2","message":"The answer is: "}',
            dataType: "html",
            success: function(data) { $('body').html(data); }     
        });
    }

I have written an HTML page which has the above javascript in it. The HTML page is served up using IIS.

When I access the HTML page using chrome on my PC I see these operations being sent to the WCF JSON service in this order,

OPTIONS /JsonWCFService/Service1.svc/Post HTTP/1.1
POST /JsonWCFService/Service1.svc/Post HTTP/1.1

The OPTIONS was previously failing, but I made the OPTIONS call return this header which then makes it work,

Access-Control-Allow-Origin: *

But the callback I have defined above does not work,

success: function(data) { $('body').html(data); } 

I know that the WCF service has returned something like this,

<b> The answer is 3 </b>

But when the callback is called the value of data is an empty string.

When I run the html page in a different browser (IE) which only causes a POST call, but not an OPTIONS call then it works. I notice that IE warns me that it poses a security risk and asks me whether I want to continue.

Answer 1

I ran across this issue when I was trying to implement CORS with WCF for a mobile HTML app I was making. OPTIONS is a preflight request to see if a method is available before calling it.

Here will be your problems:

1. OPTIONS is, I think, defaultly turned off by IIS. Possibly a starting point is here: http://www-jo.se/f.pfleger/cors-and-iis
2. The OPTIONS verb will make it to your actual POST method so you will want to have something in WCF filter OPTIONS to another method with the same return type that does nothing. And filter the POST verb to your actual method. If you don’t do this, you will find strange behavior of either your method being called twice or it will throw a webservice vague exception.

Im not sure if you are using CORS or not, but the principal will be the same, as it sends a OPTIONS request then a POST request.