$http (service in module ng )

The $http service is a core Angular service that facilitates communication with the remote HTTP servers via browser's XMLHttpRequest object or via JSONP.

For unit testing applications that use $http service, see $httpBackend mock.

For a higher level of abstraction, please check out the $resource service.

The $http API is based on the deferred/promise APIs exposed by the $q service. While for simple usage patters this doesn't matter much, for advanced usage, it is important to familiarize yourself with these apis and guarantees they provide.

General usage

The $http service is a function which takes a single argument — a configuration object — that is used to generate an http request and returns a promise with two $http specific methods: success and error.

  $http({method: 'GET', url: '/someUrl'}).
    success(function(data, status, headers, config) {
      // this callback will be called asynchronously
      // when the response is available
    }).
    error(function(data, status, headers, config) {
      // called asynchronously if an error occurs
      // or server returns response with an error status.
    });

Since the returned value of calling the $http function is a Promise object, you can also use the then method to register callbacks, and these callbacks will receive a single argument – an object representing the response. See the api signature and type info below for more details.

A response status code that falls in the [200, 300) range is considered a success status and will result in the success callback being called. Note that if the response is a redirect, XMLHttpRequest will transparently follow it, meaning that the error callback will not be called for such responses.

Shortcut methods

Since all invocation of the $http service require definition of the http method and url and POST and PUT requests require response body/data to be provided as well, shortcut methods were created to simplify using the api:

  $http.get('/someUrl').success(successCallback);
  $http.post('/someUrl', data).success(successCallback);

Complete list of shortcut methods:

• $http.get
• $http.head
• $http.post
• $http.put
• $http.delete
• $http.jsonp

Setting HTTP Headers

The $http service will automatically add certain http headers to all requests. These defaults can be fully configured by accessing the $httpProvider.defaults.headers configuration object, which currently contains this default configuration:

• $httpProvider.defaults.headers.common (headers that are common for all requests):
  • Accept: application/json, text/plain, * / *
• $httpProvider.defaults.headers.post: (header defaults for HTTP POST requests)
  • Content-Type: application/json
• $httpProvider.defaults.headers.put (header defaults for HTTP PUT requests)
  • Content-Type: application/json

To add or overwrite these defaults, simply add or remove a property from this configuration objects. To add headers for an HTTP method other than POST or PUT, simply add a new object with name equal to the lower-cased http method name, e.g. $httpProvider.defaults.headers.get['My-Header']='value'.

Additionally, the defaults can be set at runtime via the $http.defaults object in a similar fassion as described above.

Transforming Requests and Responses

Both requests and responses can be transformed using transform functions. By default, Angular applies these transformations:

Request transformations:

• if the data property of the request config object contains an object, serialize it into JSON format.

Response transformations:

• if XSRF prefix is detected, strip it (see Security Considerations section below)
• if json response is detected, deserialize it using a JSON parser

To override these transformation locally, specify transform functions as transformRequest and/or transformResponse properties of the config object. To globally override the default transforms, override the $httpProvider.defaults.transformRequest and $httpProvider.defaults.transformResponse properties of the $httpProvider.

Caching

To enable caching set the configuration property cache to true. When the cache is enabled, $http stores the response from the server in local cache. Next time the response is served from the cache without sending a request to the server.

Note that even if the response is served from cache, delivery of the data is asynchronous in the same way that real requests are.

If there are multiple GET requests for the same url that should be cached using the same 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.

Response interceptors

Before you start creating interceptors, be sure to understand the $q and deferred/promise APIs.

For purposes of global error handling, authentication or any kind of synchronous or asynchronous preprocessing of received responses, it is desirable to be able to intercept responses for http requests before they are handed over to the application code that initiated these requests. The response interceptors leverage the promise apis to fulfil this need for both synchronous and asynchronous preprocessing.

The interceptors are service factories that are registered with the $httpProvider by adding them to the $httpProvider.responseInterceptors array. The factory is called and injected with dependencies (if specified) and returns the interceptor — a function that takes a promise and returns the original or a new promise.

  // register the interceptor as a service
  $provide.factory('myHttpInterceptor', function($q, dependency1, dependency2) {
    return function(promise) {
      return promise.then(function(response) {
        // do something on success
      }, function(response) {
        // do something on error
        if (canRecover(response)) {
          return responseOrNewPromise
        }
        return $q.reject(response);
      });
    }
  });

  $httpProvider.responseInterceptors.push('myHttpInterceptor');


  // register the interceptor via an anonymous factory
  $httpProvider.responseInterceptors.push(function($q, dependency1, dependency2) {
    return function(promise) {
      // same as above
    }
  });

Security Considerations

When designing web applications, consider security threats from:

• JSON Vulnerability
• XSRF

Both server and the client must cooperate in order to eliminate these threats. Angular comes pre-configured with strategies that address these issues, but for this to work backend server cooperation is required.

JSON Vulnerability Protection

A JSON Vulnerability allows third party web-site to turn your JSON resource URL into JSONP request under some conditions. To counter this your server can prefix all JSON requests with following string ")]}',\n". Angular will automatically strip the prefix before processing it as JSON.

For example if your server needs to return:

['one','two']

which is vulnerable to attack, your server can return:

)]}',
['one','two']

Angular will strip the prefix, before processing the JSON.

Cross Site Request Forgery (XSRF) Protection

XSRF is a technique by which an unauthorized site can gain your user's private data. Angular provides following mechanism to counter XSRF. When performing XHR requests, the $http service reads a token from a cookie called XSRF-TOKEN and sets it as the HTTP header X-XSRF-TOKEN. Since only JavaScript that runs on your domain could read the cookie, your server can be assured that the XHR came from JavaScript running on your domain. The header will not be set for cross-domain requests.

To take advantage of this, your server needs to set a token in a JavaScript readable session cookie called XSRF-TOKEN on first HTTP GET request. On subsequent non-GET requests the server can verify that the cookie matches X-XSRF-TOKEN HTTP header, and therefore be sure that only JavaScript running on your domain could have read the token. The token must be unique for each user and must be verifiable by the server (to prevent the JavaScript making up its own tokens). We recommend that the token is a digest of your site's authentication cookie with salt for added security.

$http(config);