class used to allow making authorized requests to google API that also allows streaming the response even if a token refresh is required

SimpleAuthTransporter.js

"use strict";

var util = require("util"),
    _ = require("underscore"),
    events = require("events"),
    request = require("request"),
    AppAuthClient = require("../google/AppAuthClient"); //thin wrapper around the google oauth2client - simply initializing it with app's client id and secret

var SimpleAuthTransporter= (function () {

    var _USER_AGENT = "css-server@node";

    var SimpleAuthTransporter = function () {
        events.EventEmitter.call(this);
    };

    util.inherits(SimpleAuthTransporter, events.EventEmitter);

    SimpleAuthTransporter.prototype.request = function (options, responseCallback) {

        var tokenInfo = options.tokens;

        responseCallback = _wrapResponseCallback(responseCallback);

        if (tokenInfo) {
            if (!tokenInfo.access_token && !tokenInfo.refresh_token) {
                responseCallback(new Error("access token or refresh tokens not supplied"));
                return;
            }

            var isTokenExpired = tokenInfo.expiry_date ? tokenInfo.expiry_date <= (new Date()).getTime() : false;    //logic taken from google's api node client:  oauth2client class

            if (!tokenInfo.access_token || isTokenExpired){

                _refreshToken.call(this, options, responseCallback);
                return;
            }
        }

        _makeApiRequest.call(this, options, responseCallback) ;
    };

    function _makeApiRequest(options, responseCallback){

        options = _configure.call(this, options);

        var req = request(options,responseCallback.bind(this));

        this.emit("request", req); //give access to the request result 
    }

    function _onTokenRefresh(options, responseCallback, err, credentials){

        if (err){
           
            responseCallback(err);
            return;
        }

        this.emit("refresh", _.clone(credentials)); //allow calling code use the new token

        options.tokens = credentials;

        _makeApiRequest.call(this, options, responseCallback) ;
    }

    function _configure(options) {

        options.headers = options.headers || {};

        if (options.tokens) {
            options.headers["Authorization"] = options.tokens.token_type + " " + options.tokens.access_token;
        }

        options.headers["User-Agent"] = options.headers["User-Agent"] ? options.headers["User-Agent"] : _USER_AGENT;

        return options;
    }

    function _refreshToken(options, responseCallback) {

        var authClient = new AppAuthClient();//thin wrapper around the google oauth2client - simply initializing it with app's client id and secret
        authClient.setCredentials(_.clone(options.tokens));

        authClient.refreshAccessToken(_onTokenRefresh.bind(this, options, responseCallback));
    }

    function _wrapResponseCallback(callback){

        return function(err, res, body){

            if (err) {
                this.emit("error", err);
            }

            this.emit("response", err, res, body);

            if (callback) {
                callback(err, res, body); // res is: http://nodejs.org/api/http.html#http_http_incomingmessage
            }
        };
    }

    return SimpleAuthTransporter;
})();

module.exports = SimpleAuthTransporter;