feat($http): add $xhrFactory service to enable creation of custom xhr objects

Closes #2318

Author: sjurba

src/AngularPublic.js

@@ -72,6 +72,7 @@
   $HttpParamSerializerProvider,
   $HttpParamSerializerJQLikeProvider,
   $HttpBackendProvider,
+  $xhrFactoryProvider,
   $LocationProvider,
   $LogProvider,
   $ParseProvider,
@@ -233,6 +234,7 @@ function publishExternalAPI(angular) {
         $httpParamSerializer: $HttpParamSerializerProvider,
         $httpParamSerializerJQLike: $HttpParamSerializerJQLikeProvider,
         $httpBackend: $HttpBackendProvider,
+        $xhrFactory: $xhrFactoryProvider,
         $location: $LocationProvider,
         $log: $LogProvider,
         $parse: $ParseProvider,

src/ng/httpBackend.js

@@ -1,14 +1,41 @@
 'use strict';
 
-function createXhr() {
-    return new window.XMLHttpRequest();
+/**
+ * @ngdoc service
+ * @name $xhrFactory
+ *
+ * @description
+ * Factory function used to create XMLHttpRequest objects.
+ *
+ * Decorate this service to create your own custom XMLHttpRequest objects.
+ *
+ * ```
+ * .config(function($provide) {
+ *   $provide.decorator('$xhrFactory', function() {
+ *     return function createXhr(method, url) {
+ *       return new window.XMLHttpRequest({mozSystem: true});
+ *     };
+ *   });
+ * });
+ * ```
+ *
+ * @param {string} method HTTP method of the request (GET, POST, PUT, ..)
+ * @param {string} url URL of the request.
+ */
+function $xhrFactoryProvider() {
+  this.$get = function() {
+    return function createXhr() {
+      return new window.XMLHttpRequest();
+    };
+  };
 }
 
 /**
  * @ngdoc service
  * @name $httpBackend
  * @requires $window
  * @requires $document
+ * @requires $xhrFactory
  *
  * @description
  * HTTP backend used by the {@link ng.$http service} that delegates to
@@ -21,8 +48,8 @@ function createXhr() {
  * $httpBackend} which can be trained with responses.
  */
 function $HttpBackendProvider() {
-  this.$get = ['$browser', '$window', '$document', function($browser, $window, $document) {
-    return createHttpBackend($browser, createXhr, $browser.defer, $window.angular.callbacks, $document[0]);
+  this.$get = ['$browser', '$window', '$document', '$xhrFactory', function($browser, $window, $document, $xhrFactory) {
+    return createHttpBackend($browser, $xhrFactory, $browser.defer, $window.angular.callbacks, $document[0]);
   }];
 }
 
@@ -46,7 +73,7 @@ function createHttpBackend($browser, createXhr, $browserDefer, callbacks, rawDoc
       });
     } else {
 
-      var xhr = createXhr();
+      var xhr = createXhr(method, url);
 
       xhr.open(method, url, true);
       forEach(headers, function(value, key) {

test/ng/httpBackendSpec.js

@@ -231,6 +231,13 @@ describe('$httpBackend', function() {
     expect(MockXhr.$$lastInstance.withCredentials).toBe(true);
   });
 
+  it('should call $xhrFactory with method and url', function() {
+    var mockXhrFactory = jasmine.createSpy('mockXhrFactory').andCallFake(createMockXhr);
+    $backend = createHttpBackend($browser, mockXhrFactory, $browser.defer, callbacks, fakeDocument);
+    $backend('GET', '/some-url', 'some-data', noop);
+    expect(mockXhrFactory).toHaveBeenCalledWith('GET', '/some-url');
+  });
+
 
   describe('responseType', function() {