angularjs - Reading response headers when using $http of Angularjs

Question

I am using $http to make an api call which is sending some custom header like X-Foo. However I can't yet figure out how to read them. Inside the $http({...}).success(function (data, status, headers, config) {...}) function, headers is a function that should give me a hash of all headers but it only shows the header content-type. Is there a way to get the response headers ?