微信小程序实现Session功能及无法获取session问题的解决方法

function NetRequest({url, data, success, fail, complete, method = "POST", header = { 'Content-type': 'application/x-www-form-urlencoded' }}) {
 let session_id = wx.getStorageSync('PHPSESSID');//本地取存储的sessionID
 if (session_id != "" && session_id != null) { //本地session存在,则放到header里
  header.Cookie = session_id;
 }
 wx.request({
  url: url,
  method: method,
  data: data,
  header: header,
  success: res => {
   //发现response有Set-Cookie,说明本地的PHPSESSID需要更新或不存在:
   if(res.header["Set-Cookie"]){
    wx.setStorageSync('PHPSESSID', res.header["Set-Cookie"]);
   }
   res['statusCode'] === 200 ? success(res.data) : fail(res)
  },
  fail: fail,
  complete: complete
 })
}

wx.request({
 ......//此处省略
 success: function(res) {
 console.log(res.header);
 wx.removeStorageSync('sessionid') //必须先清除，否则res.header['Set-Cookie']会报错
 //set-cookie:PHPSESSID=ic4vj84aaavqgb800k82etisu0; path=/; domain=.zhix.net
 // 登录成功，获取第一次的sessionid,存储起来
 // 注意：Set-Cookie（开发者工具中调试全部小写）（远程调试和线上首字母大写）
 wx.setStorageSync("sessionid", res.header["Set-Cookie"]);
 }
}) 

wx.request({
 ......
 header: {
 'content-type': 'application/json', // 默认值
 'cookie': wx.getStorageSync("sessionid")
 //读取sessionid,当作cookie传入后台将PHPSESSID做session_id使用
 },
 success: function(res) {
 console.log(res)
 }
}) 

<?php
// 判断$_COOKIE['PHPSESSID']是否存在，存在则作session_id
if ($_COOKIE['PHPSESSID']) {
 session_id($_COOKIE['PHPSESSID']);
}
session_start();
echo session_id();