Bug 971054 - Part 4. Class to manage the service's auth token lifetime and renewal. r=florian

browser/components/translation/BingTranslator.jsm

@@ -247,6 +247,77 @@ BingRequest.prototype = {
    }
 };
 
+/**
+ * Authentication Token manager for the API
+ */
+let BingTokenManager = {
+  _currentToken: null,
+  _currentExpiryTime: 0,
+  _pendingRequest: null,
+
+  /**
+   * Get a valid, non-expired token to be used for the API calls.
+   *
+   * @returns {Promise}  A promise that resolves with the token
+   *                     string once it is obtained. The token returned
+   *                     can be the same one used in the past if it is still
+   *                     valid.
+   */
+  getToken: function() {
+    if (this._pendingRequest) {
+      return this._pendingRequest;
+    }
+
+    let remainingMs = this._currentExpiryTime - new Date();
+    // Our existing token is still good for more than a minute, let's use it.
+    if (remainingMs > 60 * 1000) {
+      return Promise.resolve(this._currentToken);
+    }
+
+    return this._getNewToken();
+  },
+
+  /**
+   * Generates a new token from the server.
+   *
+   * @returns {Promise}  A promise that resolves with the token
+   *                     string once it is obtained.
+   */
+  _getNewToken: function() {
+    let request = new RESTRequest("https://datamarket.accesscontrol.windows.net/v2/OAuth2-13");
+    request.setHeader("Content-type", "application/x-www-form-urlencoded");
+    let params = [
+      "grant_type=client_credentials",
+      "scope=" + encodeURIComponent("http://api.microsofttranslator.com"),
+      "client_id=",
+      "client_secret="
+    ];
+
+    let deferred = Promise.defer();
+    this._pendingRequest = deferred.promise;
+    request.post(params.join("&"), function(err) {
+      this._pendingRequest = null;
+
+      if (err) {
+        deferred.reject(err);
+      }
+
+      try {
+        let json = JSON.parse(this.response.body);
+        let token = json.access_token;
+        let expires_in = json.expires_in;
+        BingTokenManager._currentToken = token;
+        BingTokenManager._currentExpiryTime = new Date(Date.now() + expires_in * 1000);
+        deferred.resolve(token);
+      } catch (e) {
+        deferred.reject(e);
+      }
+    });
+
+    return deferred.promise;
+  }
+};
+
 /**
  * Escape a string to be valid XML content.
  */