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The $http service is a core Angular service that facilitates communication with the remote HTTP servers via the 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 patterns this doesn't matter much, for advanced usage it is important to familiarize yourself with these APIs and the 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.

// Simple GET request example :
$http.get('/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.
  });

// Simple POST request example (passing data) :
$http.post('/someUrl', {msg:'hello word!'}).
  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, 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 between 200 and 299 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.

Writing Unit Tests that use $http

When unit testing (using ngMock), it is necessary to call $httpBackend.flush() to flush each pending request using trained responses.

$httpBackend.expectGET(...);
$http.get(...);
$httpBackend.flush();

Shortcut methods

Shortcut methods are also available. All shortcut methods require passing in the URL, and request data must be passed in for POST/PUT requests.

$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
• $http.patch

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 POST requests)
  • Content-Type: application/json
• $httpProvider.defaults.headers.put (header defaults for PUT requests)
  • Content-Type: application/json

To add or overwrite these defaults, simply add or remove a property from these configuration objects. To add headers for an HTTP method other than POST or PUT, simply add a new object with the lowercased HTTP method name as the key, e.g. `$httpProvider.defaults.headers.get = { 'My-Header' : 'value' }.

The defaults can also be set at runtime via the $http.defaults object in the same fashion. For example:

module.run(function($http) {
  $http.defaults.headers.common.Authorization = 'Basic YmVlcDpib29w'
});

In addition, you can supply a headers property in the config object passed when calling $http(config), which overrides the defaults without changing them globally.

To explicitly remove a header automatically added via $httpProvider.defaults.headers on a per request basis, Use the headers property, setting the desired header to undefined. For example:

var req = {
 method: 'POST',
 url: 'http://example.com',
 headers: {
   'Content-Type': undefined
 },
 data: { test: 'test' }
}

$http(req).success(function(){...}).error(function(){...});

Transforming Requests and Responses

Both requests and responses can be transformed using transformation functions: transformRequest and transformResponse. These properties can be a single function that returns the transformed value (function(data, headersGetter, status)) or an array of such transformation functions, which allows you to push or unshift a new transformation function into the transformation chain.

Default Transformations

The $httpProvider provider and $http service expose defaults.transformRequest and defaults.transformResponse properties. If a request does not provide its own transformations then these will be applied.

You can augment or replace the default transformations by modifying these properties by adding to or replacing the array.

Angular provides the following default transformations:

Request transformations ($httpProvider.defaults.transformRequest and $http.defaults.transformRequest):

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

Response transformations ($httpProvider.defaults.transformResponse and $http.defaults.transformResponse):

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

Overriding the Default Transformations Per Request

If you wish override the request/response transformations only for a single request then provide transformRequest and/or transformResponse properties on the configuration object passed into $http.

Note that if you provide these properties on the config object the default transformations will be overwritten. If you wish to augment the default transformations then you must include them in your local transformation array.

The following code demonstrates adding a new response transformation to be run after the default response transformations have been run.

function appendTransform(defaults, transform) {

  // We can't guarantee that the default transformation is an array
  defaults = angular.isArray(defaults) ? defaults : [defaults];

  // Append the new transformation to the defaults
  return defaults.concat(transform);
}

$http({
  url: '...',
  method: 'GET',
  transformResponse: appendTransform($http.defaults.transformResponse, function(value) {
    return doTransform(value);
  })
});

Caching

To enable caching, set the request configuration cache property to true (to use default cache) or to a custom cache object (built with $cacheFactory). When the cache is enabled, $http stores the response from the server in the specified cache. The next time the same request is made, 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 from the first request.

You can change the default cache to a new object (built with $cacheFactory) by updating the $http.defaults.cache property. All requests who set their cache property to true will now use this cache object.

If you set the default cache to false then only requests that specify their own custom cache object will be cached.

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 pre-processing of request or postprocessing of responses, it is desirable to be able to intercept requests before they are handed to the server and responses before they are handed over to the application code that initiated these requests. The interceptors leverage the promise APIs to fulfill this need for both synchronous and asynchronous pre-processing.

The interceptors are service factories that are registered with the $httpProvider by adding them to the $httpProvider.interceptors array. The factory is called and injected with dependencies (if specified) and returns the interceptor.

There are two kinds of interceptors (and two kinds of rejection interceptors):

• request: interceptors get called with a http config object. The function is free to modify the config object or create a new one. The function needs to return the config object directly, or a promise containing the config or a new config object.
• requestError: interceptor gets called when a previous interceptor threw an error or resolved with a rejection.
• response: interceptors get called with http response object. The function is free to modify the response object or create a new one. The function needs to return the response object directly, or as a promise containing the response or a new response object.
• responseError: interceptor gets called when a previous interceptor threw an error or resolved with a rejection.

// register the interceptor as a service
$provide.factory('myHttpInterceptor', function($q, dependency1, dependency2) {
  return {
    // optional method
    'request': function(config) {
      // do something on success
      return config;
    },

    // optional method
   'requestError': function(rejection) {
      // do something on error
      if (canRecover(rejection)) {
        return responseOrNewPromise
      }
      return $q.reject(rejection);
    },



    // optional method
    'response': function(response) {
      // do something on success
      return response;
    },

    // optional method
   'responseError': function(rejection) {
      // do something on error
      if (canRecover(rejection)) {
        return responseOrNewPromise
      }
      return $q.reject(rejection);
    }
  };
});

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


// alternatively, register the interceptor via an anonymous factory
$httpProvider.interceptors.push(function($q, dependency1, dependency2) {
  return {
   'request': function(config) {
       // same as above
    },

    'response': function(response) {
       // 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 website 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 a mechanism to counter XSRF. When performing XHR requests, the $http service reads a token from a cookie (by default, XSRF-TOKEN) and sets it as an 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 the first HTTP GET request. On subsequent XHR 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 sent the request. The token must be unique for each user and must be verifiable by the server (to prevent the JavaScript from making up its own tokens). We recommend that the token is a digest of your site's authentication cookie with a salt for added security.

The name of the headers can be specified using the xsrfHeaderName and xsrfCookieName properties of either $httpProvider.defaults at config-time, $http.defaults at run-time, or the per-request config object.