最近我在使用SAP云平台的机器学习API做和SAP系统的集成，因为SAP Cloud Platform Leonardo上的机器学期API，每次消费时需要传一个Access Token，故在每次实际调用API前，我需要先发一个请求去获取Access Token. 该请求的响应，除了返回实际的token外，还有一个过期时间，expires_in字段：
根据OAuth 2.0标准定义，expires_in字段代表服务器颁发的该token，距离过期时间还剩的秒数。
我的代码如下：
const request = require('request-promise-native');
var config = require('../config.js');
var TOKEN = undefined;
var EXPIRES_IN = undefined;
var TOKEN_FETCHED_SINCE = undefined;
function isCurrentDateExpired(){
var current = new Date();
var diffInMilliSeconds = current - TOKEN_FETCHED_SINCE;
var diffInSecond = Math.ceil(diffInMilliSeconds/1000);
var expired = diffInSecond >= EXPIRES_IN ? true:false;
// for debug;
// expired = true;
return expired;
}
async function getAccessToken(){
if( TOKEN === undefined || isCurrentDateExpired()){
var raw = new Buffer(config.username + ":" + config.password);
const accessToken = await request({
method: 'GET',
headers: {
'Authorization': 'Basic ' + raw.toString('base64')
},
url: config.ACCESS_TOKEN,
json: false
});
var oToken = JSON.parse(accessToken);
EXPIRES_IN = oToken.expires_in;
TOKEN = oToken.access_token;
TOKEN_FETCHED_SINCE = new Date();
return oToken.access_token;
}
else{
return TOKEN;
}
}
var request1 = getAccessToken();
var freshNewToken, secondTimeToken;
request1.then(function(o){
// console.log("token1: " + o);
freshNewToken = o;
});
function test2(){
var b = getAccessToken();
b.then(function(o){
// console.log("token2: " + o);
secondTimeToken = o;
console.log("they should be equal: " + (freshNewToken == secondTimeToken));
});
}
setTimeout( test2, 6000);
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