feat(http): set custom default cache in $http.defaults.cache

When we need more control over http caching, we may want to provide
a custom cache to be used in all http requests by default.

To skip default cache, set {cache: false} in request configuration.
To use other cache, set {cache: cache} as before.

See angular#2079

src/ng/http.js

@@ -306,6 +306,9 @@ function $HttpProvider() {
      * cache, but the cache is not populated yet, only one request to the server will be made and
      * the remaining requests will be fulfilled using the response for the first request.
      *
+     * A custom default cache built with $cacheFactory can be provided in $http.defaults.cache.
+     * To skip it, set configuration property `cache` to `false`.
+     * 
      *
      * # Response interceptors
      *
@@ -733,8 +736,10 @@ function $HttpProvider() {
       promise.then(removePendingReq, removePendingReq);
 
 
-      if (config.cache && config.method == 'GET') {
-        cache = isObject(config.cache) ? config.cache : defaultCache;
+      if ((config.cache || defaults.cache) && config.cache !== false && config.method == 'GET') {
+        cache = isObject(config.cache) ? config.cache 
+              : isObject(defaults.cache) ? defaults.cache 
+              : defaultCache;
       }
 
       if (cache) {

test/ng/httpSpec.js

@@ -923,6 +923,77 @@ describe('$http', function() {
             expect(callback).toHaveBeenCalledOnce();
           })
       );
+
+      describe('$http.defaults.cache', function () {
+
+        it('should be undefined by default', function() {
+          expect($http.defaults.cache).toBeUndefined()
+        });
+
+        it('should cache requests when no cache given in request config', function() {
+          $http.defaults.cache = cache;
+
+          // First request fills the cache from server response.
+          $httpBackend.expect('GET', '/url').respond(200, 'content');
+          $http({method: 'GET', url: '/url'}); // Notice no cache given in config.
+          $httpBackend.flush();
+
+          // Second should be served from cache, without sending request to server. 
+          $http({method: 'get', url: '/url'}).success(callback);
+          $rootScope.$digest();
+
+          expect(callback).toHaveBeenCalledOnce();
+          expect(callback.mostRecentCall.args[0]).toBe('content');
+
+          // Invalidate cache entry.
+          $http.defaults.cache.remove("/url");
+
+          // After cache entry removed, a request should be sent to server.
+          $httpBackend.expect('GET', '/url').respond(200, 'content');
+          $http({method: 'GET', url: '/url'});
+          $httpBackend.flush();
+        });
+
+        it('should have less priority than explicitly given cache', inject(function($cacheFactory) {
+          var localCache = $cacheFactory('localCache');
+          $http.defaults.cache = cache;
+
+          // Fill local cache.
+          $httpBackend.expect('GET', '/url').respond(200, 'content-local-cache');
+          $http({method: 'GET', url: '/url', cache: localCache});
+          $httpBackend.flush();
+
+          // Fill default cache.
+          $httpBackend.expect('GET', '/url').respond(200, 'content-default-cache');
+          $http({method: 'GET', url: '/url'});
+          $httpBackend.flush();
+
+          // Serve request from default cache when no local given.
+          $http({method: 'get', url: '/url'}).success(callback);
+          $rootScope.$digest();
+          expect(callback).toHaveBeenCalledOnce();
+          expect(callback.mostRecentCall.args[0]).toBe('content-default-cache');
+          callback.reset();
+
+          // Serve request from local cache when it is given (but default filled too).
+          $http({method: 'get', url: '/url', cache: localCache}).success(callback);
+          $rootScope.$digest();
+          expect(callback).toHaveBeenCalledOnce();
+          expect(callback.mostRecentCall.args[0]).toBe('content-local-cache');
+        }));
+
+        it('should be skipped if {cache: false} is passed in request config', function() {
+          $http.defaults.cache = cache;
+
+          $httpBackend.expect('GET', '/url').respond(200, 'content');
+          $http({method: 'GET', url: '/url'});
+          $httpBackend.flush();
+
+          $httpBackend.expect('GET', '/url').respond();
+          $http({method: 'GET', url: '/url', cache: false});
+          $httpBackend.flush();
+        });
+      });
     });