feat($http): accept function as headers value

So we can request with dynamic header value.

module.factory('Res', [
  '$resource'
  '$routeParams'
  'globalConfig'

function($resource, $routeParams, globalConfig) {
  resource('/url/:id', {id: "@id"}, {
    patch: {
      method: 'patch',
      headers: {
        'Authorization': function() {
          return "token " + globalConfig.token;
        }
      }
    }
  });
}]);

src/ng/http.js

@@ -535,7 +535,9 @@ function $HttpProvider() {
      *    - **params** – `{Object.<string|Object>}` – Map of strings or objects which will be turned to
      *      `?key1=value1&key2=value2` after the url. If the value is not a string, it will be JSONified.
      *    - **data** – `{string|Object}` – Data to be sent as the request message data.
-     *    - **headers** – `{Object}` – Map of strings representing HTTP headers to send to the server.
+     *    - **headers** – `{Object}` – Map of strings or functions which return strings representing
+     *      HTTP headers to send to the server. If the return value of a function is null, the header will
+     *      not be sent.
      *    - **xsrfHeaderName** – `{string}` – Name of HTTP header to populate with the XSRF token.
      *    - **xsrfCookieName** – `{string}` – Name of cookie containing the XSRF token.
      *    - **transformRequest** – `{function(data, headersGetter)|Array.<function(data, headersGetter)>}` –
@@ -736,6 +738,10 @@ function $HttpProvider() {
 
         defHeaders = extend({}, defHeaders.common, defHeaders[lowercase(config.method)]);
 
+        // execute if header value is function
+        execHeaders(defHeaders);
+        execHeaders(reqHeaders);
+
         // using for-in instead of forEach to avoid unecessary iteration after header has been found
         defaultHeadersIteration:
         for (defHeaderName in defHeaders) {
@@ -751,6 +757,21 @@ function $HttpProvider() {
         }
 
         return reqHeaders;
+
+        function execHeaders(headers) {
+          var headerContent;
+
+          forEach(headers, function(headerFn, header) {
+            if (isFunction(headerFn)) {
+              headerContent = headerFn();
+              if (headerContent != null) {
+                headers[header] = headerContent;
+              } else {
+                delete headers[header];
+              }
+            }
+          });
+        }
       }
     }
 

test/ng/httpSpec.js

@@ -784,6 +784,28 @@ describe('$http', function() {
 
         $httpBackend.flush();
       }));
+
+      it('should send execute result if header value is function', inject(function() {
+        var headerConfig = {'Accept': function() { return 'Rewritten'; }};
+
+        function checkHeaders(headers) {
+          return headers['Accept'] == 'Rewritten';
+        }
+
+        $httpBackend.expect('GET', '/url', undefined, checkHeaders).respond('');
+        $httpBackend.expect('POST', '/url', undefined, checkHeaders).respond('');
+        $httpBackend.expect('PUT', '/url', undefined, checkHeaders).respond('');
+        $httpBackend.expect('PATCH', '/url', undefined, checkHeaders).respond('');
+        $httpBackend.expect('DELETE', '/url', undefined, checkHeaders).respond('');
+
+        $http({url: '/url', method: 'GET', headers: headerConfig});
+        $http({url: '/url', method: 'POST', headers: headerConfig});
+        $http({url: '/url', method: 'PUT', headers: headerConfig});
+        $http({url: '/url', method: 'PATCH', headers: headerConfig});
+        $http({url: '/url', method: 'DELETE', headers: headerConfig});
+
+        $httpBackend.flush();
+      }));
     });