fix($http): fix and cleanup $http and friends

$http:
- use promises internally
- get rid of XhrFuture that was previously used internally
- get rid of $browser.defer calls for async stuff (serving from cache),
  promises will take care of asynchronicity
- fix transformation bugs (when caching requested + multiple request
  pending + error is returned)
- get rid of native header parsing and instead just lazily parse the
  header string

$httpBackend:
- don't return raw/mock XMLHttpRequest object (we don't use it for
  anything anymore)
- call the callback with response headers string

mock $httpBackend:
- unify response api for expect and when
- call the callback with response headers string
- changed the expect/when failure error message so that EXPECTED and GOT
  values are aligned

Conflicts:

	src/service/http.js
	test/service/compilerSpec.js
	test/service/httpSpec.js

2 files changed, 326 insertions, 394 deletions

diff --git a/src/service/http.js b/src/service/http.js
index e6a42b65..bd8e6e65 100644
--- a/src/service/http.js
+++ b/src/service/http.js
@@ -4,11 +4,13 @@
  * Parse headers into key value object
  *
  * @param {string} headers Raw headers as a string
- * @returns {Object} Parsed headers as key valu object
+ * @returns {Object} Parsed headers as key value object
  */
 function parseHeaders(headers) {
   var parsed = {}, key, val, i;
 
+  if (!headers) return parsed;
+
   forEach(headers.split('\n'), function(line) {
     i = line.indexOf(':');
     key = lowercase(trim(line.substr(0, i)));
@@ -26,6 +28,34 @@ function parseHeaders(headers) {
   return parsed;
 }
 
+
+/**
+ * Returns a function that provides access to parsed headers.
+ *
+ * Headers are lazy parsed when first requested.
+ * @see parseHeaders
+ *
+ * @param {(string|Object)} headers Headers to provide access to.
+ * @returns {function(string=)} Returns a getter function which if called with:
+ *
+ *   - if called with single an argument returns a single header value or null
+ *   - if called with no arguments returns an object containing all headers.
+ */
+function headersGetter(headersString) {
+  var headers = isObject(headersString) ? headersString : undefined;
+
+  return function(name) {
+    if (!headers) headers =  parseHeaders(headersString);
+
+    if (name) {
+      return headers[lowercase(name)] || null;
+    }
+
+    return headers;
+  };
+}
+
+
 /**
  * Chain all given functions
  *
@@ -36,7 +66,7 @@ function parseHeaders(headers) {
  * @param {*=} param Optional parameter to be passed to all transform functions.
  * @returns {*} Transformed data.
  */
-function transform(data, fns, param) {
+function transformData(data, fns, param) {
   if (isFunction(fns))
     return fns(data);
 
@@ -48,13 +78,18 @@ function transform(data, fns, param) {
 }
 
 
+function isSuccess(status) {
+  return 200 <= status && status < 300;
+}
+
+
 function $HttpProvider() {
   var JSON_START = /^\s*(\[|\{[^\{])/,
       JSON_END = /[\}\]]\s*$/,
       PROTECTION_PREFIX = /^\)\]\}',?\n/;
 
   var $config = this.defaults = {
-    // transform in-coming reponse data
+    // transform incoming response data
     transformResponse: function(data) {
       if (isString(data)) {
         // strip json vulnerability protection prefix
@@ -65,7 +100,7 @@ function $HttpProvider() {
       return data;
     },
 
-    // transform out-going request data
+    // transform outgoing request data
     transformRequest: function(d) {
       return isObject(d) ? toJson(d) : d;
     },
@@ -81,431 +116,328 @@ function $HttpProvider() {
     }
   };
 
-  var responseInterceptors = this.responseInterceptors = [];
+  var providerResponseInterceptors = this.responseInterceptors = [];
 
   this.$get = ['$httpBackend', '$browser', '$exceptionHandler', '$cacheFactory', '$rootScope', '$q', '$injector',
       function($httpBackend, $browser, $exceptionHandler, $cacheFactory, $rootScope, $q, $injector) {
 
-  var defaultCache = $cacheFactory('$http');
+    var defaultCache = $cacheFactory('$http'),
+        responseInterceptors = [];
 
-  forEach(responseInterceptors, function(interceptor, index) {
-    if (isString(interceptor)) {
-      responseInterceptors[index] = $injector.get(interceptor);
-    }
-  });
+    forEach(providerResponseInterceptors, function(interceptor) {
+      responseInterceptors.push(isString(interceptor) ? $injector.get(interceptor) : interceptor);
+    });
 
 
-  /**
-   * @ngdoc function
-   * @name angular.module.ng.$http
-   * @requires $httpBacked
-   * @requires $browser
-   * @requires $exceptionHandler
-   * @requires $cacheFactory
-   *
-   * @param {object} config Object describing the request to be made and how it should be processed.
-   *    The object has following properties:
-   *
-   *    - **method** – `{string}` – HTTP method (e.g. 'GET', 'POST', etc)
-   *    - **url** – `{string}` – Absolute or relative URL of the resource that is being requested.
-   *    - **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.
-   *    - **cache** – `{boolean|Cache}` – If true, a default $http cache will be used to cache the
-   *      GET request, otherwise if a cache instance built with $cacheFactory, this cache will be
-   *      used for caching.
-   *
-   * @returns {HttpPromise} Returns a promise object with the standard `then` method and two http
-   *   specific methods: `success` and `error`. The `then` method takes two arguments a success and
-   *   an error callback which will be called with a response object. The `success` and `error`
-   *   methods take a single argument - a function that will be called when the request succeeds or
-   *   fails respectively. The arguments passed into these functions are destructured representation
-   *   of the response object passed into the `then` method. The response object has these
-   *   properties:
-   *
-   *   - **data** – `{string|Object}` – The response body transformed with the transform functions.
-   *   - **status** – `{number}` – HTTP status code of the response.
-   *   - **headers** – `{function([headerName])}` – Header getter function.
-   *   - **config** – `{Object}` – The configuration object that was used to generate the request.
-   *
-   * @property {Array.<Object>} pendingRequests Array of config objects for pending requests.
-   *   This is primarily meant to be used for debugging purposes.
-   *
-   * @description
-   * $http is a service through which XHR and JSONP requests can be made.
-   */
-  function $http(config) {
-    var req = new XhrFuture().send(config),
-        deferredResp = $q.defer(),
-        promise = deferredResp.promise;
-
-    forEach(responseInterceptors, function(interceptor) {
-      promise = interceptor(promise);
-    });
+    /**
+     * @ngdoc function
+     * @name angular.module.ng.$http
+     * @requires $httpBacked
+     * @requires $browser
+     * @requires $exceptionHandler //TODO(i): still needed?
+     * @requires $cacheFactory
+     *
+     * @param {object} config Object describing the request to be made and how it should be processed.
+     *    The object has following properties:
+     *
+     *    - **method** – `{string}` – HTTP method (e.g. 'GET', 'POST', etc)
+     *    - **url** – `{string}` – Absolute or relative URL of the resource that is being requested.
+     *    - **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.
+     *    - **cache** – `{boolean|Cache}` – If true, a default $http cache will be used to cache the
+     *      GET request, otherwise if a cache instance built with $cacheFactory, this cache will be
+     *      used for caching.
+     *
+     * @returns {HttpPromise} Returns a promise object with the standard `then` method and two http
+     *   specific methods: `success` and `error`. The `then` method takes two arguments a success and
+     *   an error callback which will be called with a response object. The `success` and `error`
+     *   methods take a single argument - a function that will be called when the request succeeds or
+     *   fails respectively. The arguments passed into these functions are destructured representation
+     *   of the response object passed into the `then` method. The response object has these
+     *   properties:
+     *
+     *   - **data** – `{string|Object}` – The response body transformed with the transform functions.
+     *   - **status** – `{number}` – HTTP status code of the response.
+     *   - **headers** – `{function([headerName])}` – Header getter function.
+     *   - **config** – `{Object}` – The configuration object that was used to generate the request.
+     *
+     * @property {Array.<Object>} pendingRequests Array of config objects for pending requests.
+     *   This is primarily meant to be used for debugging purposes.
+     *
+     * @description
+     * $http is a service through which XHR and JSONP requests can be made.
+     */
+    function $http(config) {
+      config.method = uppercase(config.method);
 
-    promise.success = function(fn) {
-      promise.then(function(response) {
-        fn(response.data, response.status, response.headers, config);
-      });
-      return promise;
-    };
+      var reqTransformFn = config.transformRequest || $config.transformRequest,
+          respTransformFn = config.transformResponse || $config.transformResponse,
+          reqData = transformData(config.data, reqTransformFn),
+          defHeaders = $config.headers,
+          reqHeaders = extend({'X-XSRF-TOKEN': $browser.cookies()['XSRF-TOKEN']},
+              defHeaders.common, defHeaders[lowercase(config.method)], config.headers),
+          promise;
 
-    promise.error = function(fn) {
-      promise.then(null, function(response) {
-        fn(response.data, response.status, response.headers, config);
-      });
-      return promise;
-    };
 
-    req.on('success', function(data, status, headers) {
-      deferredResp.resolve({data: data, status: status, headers: headers, config: config});
-    }).on('error', function(data, status, headers) {
-      deferredResp.reject({data: data, status: status, headers: headers, config: config});
-    });
+      // send request
+      promise = sendReq(config, reqData, reqHeaders);
+
 
-    return promise;
-  }
-
-  $http.pendingRequests = [];
-
-  /**
-   * @ngdoc method
-   * @name angular.module.ng.$http#get
-   * @methodOf angular.module.ng.$http
-   *
-   * @description
-   * Shortcut method to perform `GET` request
-   *
-   * @param {string} url Relative or absolute URL specifying the destination of the request
-   * @param {Object=} config Optional configuration object
-   * @returns {HttpPromise} Future object
-   */
-
-  /**
-   * @ngdoc method
-   * @name angular.module.ng.$http#delete
-   * @methodOf angular.module.ng.$http
-   *
-   * @description
-   * Shortcut method to perform `DELETE` request
-   *
-   * @param {string} url Relative or absolute URL specifying the destination of the request
-   * @param {Object=} config Optional configuration object
-   * @returns {HttpPromise} Future object
-   */
-
-  /**
-   * @ngdoc method
-   * @name angular.module.ng.$http#head
-   * @methodOf angular.module.ng.$http
-   *
-   * @description
-   * Shortcut method to perform `HEAD` request
-   *
-   * @param {string} url Relative or absolute URL specifying the destination of the request
-   * @param {Object=} config Optional configuration object
-   * @returns {XhrFuture} Future object
-   */
-
-  /**
-   * @ngdoc method
-   * @name angular.module.ng.$http#patch
-   * @methodOf angular.module.ng.$http
-   *
-   * @description
-   * Shortcut method to perform `PATCH` request
-   *
-   * @param {string} url Relative or absolute URL specifying the destination of the request
-   * @param {Object=} config Optional configuration object
-   * @returns {HttpPromise} Future object
-   */
-
-  /**
-   * @ngdoc method
-   * @name angular.module.ng.$http#jsonp
-   * @methodOf angular.module.ng.$http
-   *
-   * @description
-   * Shortcut method to perform `JSONP` request
-   *
-   * @param {string} url Relative or absolute URL specifying the destination of the request.
-   *                     Should contain `JSON_CALLBACK` string.
-   * @param {Object=} config Optional configuration object
-   * @returns {XhrFuture} Future object
-   */
-  createShortMethods('get', 'delete', 'head', 'patch', 'jsonp');
-
-  /**
-   * @ngdoc method
-   * @name angular.module.ng.$http#post
-   * @methodOf angular.module.ng.$http
-   *
-   * @description
-   * Shortcut method to perform `POST` request
-   *
-   * @param {string} url Relative or absolute URL specifying the destination of the request
-   * @param {*} data Request content
-   * @param {Object=} config Optional configuration object
-   * @returns {HttpPromise} Future object
-   */
-
-  /**
-   * @ngdoc method
-   * @name angular.module.ng.$http#put
-   * @methodOf angular.module.ng.$http
-   *
-   * @description
-   * Shortcut method to perform `PUT` request
-   *
-   * @param {string} url Relative or absolute URL specifying the destination of the request
-   * @param {*} data Request content
-   * @param {Object=} config Optional configuration object
-   * @returns {XhrFuture} Future object
-   */
-  createShortMethodsWithData('post', 'put');
-
-  return $http;
-
-  function createShortMethods(names) {
-    forEach(arguments, function(name) {
-      $http[name] = function(url, config) {
-        return $http(extend(config || {}, {
-          method: name,
-          url: url
-        }));
+      // transform future response
+      promise = promise.then(transformResponse, transformResponse);
+
+      // apply interceptors
+      forEach(responseInterceptors, function(interceptor) {
+        promise = interceptor(promise);
+      });
+
+      promise.success = function(fn) {
+        promise.then(function(response) {
+          fn(response.data, response.status, response.headers, config);
+        });
+        return promise;
       };
-    });
-  }
-
-  function createShortMethodsWithData(name) {
-    forEach(arguments, function(name) {
-      $http[name] = function(url, data, config) {
-        return $http(extend(config || {}, {
-          method: name,
-          url: url,
-          data: data
-        }));
+
+      promise.error = function(fn) {
+        promise.then(null, function(response) {
+          fn(response.data, response.status, response.headers, config);
+        });
+        return promise;
       };
-    });
-  }
-
-  /**
-   * Represents Request object, returned by $http()
-   *
-   * !!! ACCESSES CLOSURE VARS:
-   * $httpBackend, $browser, $config, $log, $rootScope, defaultCache, $http.pendingRequests
-   */
-  function XhrFuture() {
-    var rawRequest, parsedHeaders,
-        cfg = {}, callbacks = [],
-        defHeaders = $config.headers,
-        self = this;
+
+      return promise;
+
+      function transformResponse(response) {
+        // make a copy since the response must be cacheable
+        var resp = extend({}, response, {
+          data: transformData(response.data, respTransformFn, response.headers)
+        });
+        return (isSuccess(response.status))
+          ? resp
+          : $q.reject(resp);
+      }
+    }
+
+    $http.pendingRequests = [];
 
     /**
-     * Callback registered to $httpBackend():
-     *  - caches the response if desired
-     *  - calls fireCallbacks()
-     *  - clears the reference to raw request object
+     * @ngdoc method
+     * @name angular.module.ng.$http#get
+     * @methodOf angular.module.ng.$http
+     *
+     * @description
+     * Shortcut method to perform `GET` request
+     *
+     * @param {string} url Relative or absolute URL specifying the destination of the request
+     * @param {Object=} config Optional configuration object
+     * @returns {HttpPromise} Future object
      */
-    function done(status, response) {
-      // aborted request or jsonp
-      if (!rawRequest) parsedHeaders = {};
-
-      if (cfg.cache && cfg.method == 'GET') {
-        var cache = isObject(cfg.cache) && cfg.cache || defaultCache;
-        if (200 <= status && status < 300) {
-          parsedHeaders = parsedHeaders || parseHeaders(rawRequest.getAllResponseHeaders());
-          cache.put(cfg.url, [status, response, parsedHeaders]);
-        } else {
-          // remove future object from cache
-          cache.remove(cfg.url);
-        }
-      }
 
-      fireCallbacks(response, status);
-      // TODO(i): we can't null the rawRequest because we might need to be able to call
-      // rawRequest.getAllResponseHeaders from a promise
-      // rawRequest = null;
-    }
+    /**
+     * @ngdoc method
+     * @name angular.module.ng.$http#delete
+     * @methodOf angular.module.ng.$http
+     *
+     * @description
+     * Shortcut method to perform `DELETE` request
+     *
+     * @param {string} url Relative or absolute URL specifying the destination of the request
+     * @param {Object=} config Optional configuration object
+     * @returns {HttpPromise} Future object
+     */
 
     /**
-     * Fire all registered callbacks for given status code
+     * @ngdoc method
+     * @name angular.module.ng.$http#head
+     * @methodOf angular.module.ng.$http
      *
-     * This method when:
-     *  - serving response from real request
-     *  - serving response from cache
+     * @description
+     * Shortcut method to perform `HEAD` request
      *
-     * It does:
-     *  - transform the response
-     *  - call proper callbacks
-     *  - log errors
-     *  - apply the $scope
-     *  - clear parsed headers
+     * @param {string} url Relative or absolute URL specifying the destination of the request
+     * @param {Object=} config Optional configuration object
+     * @returns {XhrFuture} Future object
      */
-    function fireCallbacks(response, status) {
-      var strStatus = status + '';
-
-      // transform the response
-      response = transform(response, cfg.transformResponse || $config.transformResponse, rawRequest);
-
-      var idx; // remove from pending requests
-      if ((idx = indexOf($http.pendingRequests, cfg)) !== -1)
-        $http.pendingRequests.splice(idx, 1);
-
-      // normalize internal statuses to 0
-      status = Math.max(status, 0);
-      forEach(callbacks, function(callback) {
-        if (callback.regexp.test(strStatus)) {
-          try {
-            // use local var to call it without context
-            var fn = callback.fn;
-            fn(response, status, headers);
-          } catch(e) {
-            $exceptionHandler(e);
-          }
-        }
-      });
 
-      $rootScope.$apply();
-      parsedHeaders = null;
-    }
+    /**
+     * @ngdoc method
+     * @name angular.module.ng.$http#patch
+     * @methodOf angular.module.ng.$http
+     *
+     * @description
+     * Shortcut method to perform `PATCH` request
+     *
+     * @param {string} url Relative or absolute URL specifying the destination of the request
+     * @param {Object=} config Optional configuration object
+     * @returns {HttpPromise} Future object
+     */
 
     /**
-     * This is the third argument in any user callback
-     * @see parseHeaders
+     * @ngdoc method
+     * @name angular.module.ng.$http#jsonp
+     * @methodOf angular.module.ng.$http
      *
-     * Return single header value or all headers parsed as object.
-     * Headers all lazy parsed when first requested.
+     * @description
+     * Shortcut method to perform `JSONP` request
      *
-     * @param {string=} name Name of header
-     * @returns {string|Object}
+     * @param {string} url Relative or absolute URL specifying the destination of the request.
+     *                     Should contain `JSON_CALLBACK` string.
+     * @param {Object=} config Optional configuration object
+     * @returns {XhrFuture} Future object
      */
-    function headers(name) {
-      if (name) {
-        return parsedHeaders ?
-          parsedHeaders[lowercase(name)] || null :
-          rawRequest.getResponseHeader(name);
-      }
+    createShortMethods('get', 'delete', 'head', 'patch', 'jsonp');
 
-      parsedHeaders = parsedHeaders || parseHeaders(rawRequest.getAllResponseHeaders());
+    /**
+     * @ngdoc method
+     * @name angular.module.ng.$http#post
+     * @methodOf angular.module.ng.$http
+     *
+     * @description
+     * Shortcut method to perform `POST` request
+     *
+     * @param {string} url Relative or absolute URL specifying the destination of the request
+     * @param {*} data Request content
+     * @param {Object=} config Optional configuration object
+     * @returns {HttpPromise} Future object
+     */
 
-      return parsedHeaders;
+    /**
+     * @ngdoc method
+     * @name angular.module.ng.$http#put
+     * @methodOf angular.module.ng.$http
+     *
+     * @description
+     * Shortcut method to perform `PUT` request
+     *
+     * @param {string} url Relative or absolute URL specifying the destination of the request
+     * @param {*} data Request content
+     * @param {Object=} config Optional configuration object
+     * @returns {XhrFuture} Future object
+     */
+    createShortMethodsWithData('post', 'put');
+
+
+    return $http;
+
+
+    function createShortMethods(names) {
+      forEach(arguments, function(name) {
+        $http[name] = function(url, config) {
+          return $http(extend(config || {}, {
+            method: name,
+            url: url
+          }));
+        };
+      });
     }
 
+
+    function createShortMethodsWithData(name) {
+      forEach(arguments, function(name) {
+        $http[name] = function(url, data, config) {
+          return $http(extend(config || {}, {
+            method: name,
+            url: url,
+            data: data
+          }));
+        };
+      });
+    }
+
+
     /**
-     * Retry the request
+     * Makes the request
      *
-     * @param {Object=} config Optional config object to extend the original configuration
-     * @returns {HttpPromise}
+     * !!! ACCESSES CLOSURE VARS:
+     * $httpBackend, $config, $log, $rootScope, defaultCache, $http.pendingRequests
      */
-    this.retry = function(config) {
-      if (rawRequest) throw 'Can not retry request. Abort pending request first.';
+    function sendReq(config, reqData, reqHeaders) {
+      var deferred = $q.defer(),
+          promise = deferred.promise,
+          cache,
+          cachedResp;
 
-      extend(cfg, config);
-      cfg.method = uppercase(cfg.method);
+      $http.pendingRequests.push(config);
+      promise.then(removePendingReq, removePendingReq);
 
-      var data = transform(cfg.data, cfg.transformRequest || $config.transformRequest),
-          headers = extend({'X-XSRF-TOKEN': $browser.cookies()['XSRF-TOKEN']},
-                           defHeaders.common, defHeaders[lowercase(cfg.method)], cfg.headers);
 
-      var cache = isObject(cfg.cache) && cfg.cache || defaultCache,
-          fromCache;
+      if (config.cache && config.method == 'GET') {
+        cache = isObject(config.cache) ? config.cache : defaultCache;
+      }
 
-      if (cfg.cache && cfg.method == 'GET') {
-        fromCache = cache.get(cfg.url);
-        if (fromCache) {
-          if (fromCache instanceof XhrFuture) {
-            // cached request has already been sent, but there is no reponse yet,
+      if (cache) {
+        cachedResp = cache.get(config.url);
+        if (cachedResp) {
+          if (cachedResp.then) {
+            // cached request has already been sent, but there is no response yet,
             // we need to register callback and fire callbacks when the request is back
             // note, we have to get the values from cache and perform transformations on them,
             // as the configurations don't have to be same
-            fromCache.on('always', function() {
-              var requestFromCache = cache.get(cfg.url);
-              parsedHeaders = requestFromCache[2];
-              fireCallbacks(requestFromCache[1], requestFromCache[0]);
-            });
+            cachedResp.then(removePendingReq, removePendingReq);
+            return cachedResp;
           } else {
-            // serving from cache - still needs to be async
-            $browser.defer(function() {
-              parsedHeaders = fromCache[2];
-              fireCallbacks(fromCache[1], fromCache[0]);
-            });
+            // serving from cache
+            if (isArray(cachedResp)) {
+              resolvePromise(cachedResp[1], cachedResp[0], copy(cachedResp[2]));
+            } else {
+              resolvePromise(cachedResp, 200, {});
+            }
           }
         } else {
-          // put future object into cache
-          cache.put(cfg.url, self);
+          // put the promise for the non-transformed response into cache as a placeholder
+          cache.put(config.url, promise);
         }
       }
 
-      // really send the request
-      if (!cfg.cache || cfg.method !== 'GET' || !fromCache) {
-        rawRequest = $httpBackend(cfg.method, cfg.url, data, done, headers, cfg.timeout);
+      // if we won't have the response in cache, send the request to the backend
+      if (!cachedResp) {
+        $httpBackend(config.method, config.url, reqData, done, reqHeaders, config.timeout);
       }
 
-      $http.pendingRequests.push(cfg);
-      return self;
-    };
+      return promise;
 
-    // just alias so that in stack trace we can see send() instead of retry()
-    this.send = this.retry;
 
-    /**
-     * Abort the request
-     */
-    this.abort = function() {
-      if (rawRequest) {
-        rawRequest.abort();
+      /**
+       * Callback registered to $httpBackend():
+       *  - caches the response if desired
+       *  - resolves the raw $http promise
+       *  - calls $apply
+       */
+      function done(status, response, headersString) {
+        if (cache) {
+          if (isSuccess(status)) {
+            cache.put(config.url, [status, response, parseHeaders(headersString)]);
+          } else {
+            // remove promise from the cache
+            cache.remove(config.url);
+          }
+        }
+
+        resolvePromise(response, status, headersString);
+        $rootScope.$apply();
       }
-      return this;
-    };
 
-    /**
-     * Register a callback function based on status code
-     * Note: all matched callbacks will be called, preserving registered order !
-     *
-     * Internal statuses:
-     *  `-2` = jsonp error
-     *  `-1` = timeout
-     *   `0` = aborted
-     *
-     * @example
-     *   .on('2xx', function(){});
-     *   .on('2x1', function(){});
-     *   .on('404', function(){});
-     *   .on('20x,3xx', function(){});
-     *   .on('success', function(){});
-     *   .on('error', function(){});
-     *   .on('always', function(){});
-     *   .on('timeout', function(){});
-     *   .on('abort', function(){});
-     *
-     * @param {string} pattern Status code pattern with "x" for any number
-     * @param {function(*, number, function)} callback Function to be called when response arrives
-     * @returns {XhrFuture}
-     */
-    this.on = function(pattern, callback) {
-      var alias = {
-        success: '2xx',
-        error: '-2,-1,0,4xx,5xx',
-        always: 'xxx,xx,x',
-        timeout: '-1',
-        abort: '0'
-      };
 
-      callbacks.push({
-        fn: callback,
-        // create regexp from given pattern
-        regexp: new RegExp('^(' + (alias[pattern] || pattern).replace(/,/g, '|').
-                                                              replace(/x/g, '.') + ')$')
-      });
+      /**
+       * Resolves the raw $http promise.
+       */
+      function resolvePromise(response, status, headers) {
+        // normalize internal statuses to 0
+        status = Math.max(status, 0);
 
-      return this;
-    };
+        (isSuccess(status) ? deferred.resolve : deferred.reject)({
+          data: response,
+          status: status,
+          headers: headersGetter(headers),
+          config: config
+        });
+      }
 
-    /**
-     * Configuration object of the request
-     */
-    this.config = cfg;
-  }
-}];
-}
 
+      function removePendingReq() {
+        var idx = indexOf($http.pendingRequests, config);
+        if (idx !== -1) $http.pendingRequests.splice(idx, 1);
+      }
+    }
+  }];
+}
diff --git a/src/service/httpBackend.js b/src/service/httpBackend.js
index c64519d9..c3114814 100644
--- a/src/service/httpBackend.js
+++ b/src/service/httpBackend.js
@@ -14,6 +14,11 @@ var XHR = window.XMLHttpRequest || function() {
  * @requires $document
  *
  * @description
+ * HTTP backend used by the {@link angular.module.ng.$http service} that delegates to
+ * XMLHttpRequest object.
+ *
+ * During testing this implementation is swapped with {@link angular.module.ngMock.$httpBackend mock
+ * $httpBackend} which can be trained with responses.
  */
 function $HttpBackendProvider() {
   this.$get = ['$browser', '$window', '$document', function($browser, $window, $document) {
@@ -46,24 +51,21 @@ function createHttpBackend($browser, XHR, $browserDefer, callbacks, body, locati
       var xhr = new XHR();
       xhr.open(method, url, true);
       forEach(headers, function(value, key) {
-          if (value) xhr.setRequestHeader(key, value);
+        if (value) xhr.setRequestHeader(key, value);
       });
 
       var status;
-      xhr.send(post || '');
 
-      // IE6, IE7 bug - does sync when serving from cache
-      if (xhr.readyState == 4) {
-        $browserDefer(function() {
-          completeRequest(callback, status || xhr.status, xhr.responseText);
-        }, 0);
-      } else {
-        xhr.onreadystatechange = function() {
-          if (xhr.readyState == 4) {
-            completeRequest(callback, status || xhr.status, xhr.responseText);
-          }
-        };
-      }
+      // In IE6 and 7, this might be called synchronously when xhr.send below is called and the
+      // response is in the cache
+      xhr.onreadystatechange = function() {
+        if (xhr.readyState == 4) {
+          completeRequest(
+              callback, status || xhr.status, xhr.responseText, xhr.getAllResponseHeaders());
+        }
+      };
+
+      xhr.send(post || '');
 
       if (timeout > 0) {
         $browserDefer(function() {
@@ -71,23 +73,21 @@ function createHttpBackend($browser, XHR, $browserDefer, callbacks, body, locati
           xhr.abort();
         }, timeout);
       }
-
-      return xhr;
     }
 
-    function completeRequest(callback, status, response) {
+
+    function completeRequest(callback, status, response, headersString) {
       // URL_MATCH is defined in src/service/location.js
       var protocol = (url.match(URL_MATCH) || ['', locationProtocol])[1];
 
       // fix status code for file protocol (it's always 0)
-      status = protocol == 'file' ? (response ? 200 : 404) : status;
+      status = (protocol == 'file') ? (response ? 200 : 404) : status;
 
       // normalize IE bug (http://bugs.jquery.com/ticket/1450)
       status = status == 1223 ? 204 : status;
 
-      callback(status, response);
+      callback(status, response, headersString);
       $browser.$$completeOutstandingRequest(noop);
     }
   };
 }
-