微信小程序 支付成功回调返回服务器内容

public function couponNotify(){
        $xml = file_get_contents("php://input");
        $arr = $this->xmltoarray($xml);
        if($arr['result_code']=="SUCCESS" && $arr['return_code']=="SUCCESS"){
            $orderNum = $arr['out_trade_no'];
            //取出userid
            $userId = substr($orderNum,'0',strrpos($orderNum,"u"));//前面
            //取出couponid
            $couponId = substr($orderNum,strpos($orderNum,'u')+1,strpos($orderNum,'s')-3);
            //取出Guid
            //$gradeUid = substr($orderNum,strpos($orderNum,'s')+1,strpos($orderNum,'g')-7);
            $preg= '/s(.*?)g/';
            preg_match_all($preg,$orderNum,$res);
            $gradeUid = $res[1][0];
            if($gradeUid != null){
                $this->createProfit($gradeUid,$userId,3);//3.下单加100 1级10 二级20
            }
            $data = array(
                'transaction_id' => $arr['transaction_id'],
                'out_trade_no'=>$arr['out_trade_no'],
                'status'=>1
            );
            $isEmpty =  DB::table('my_coupon')->where('user_id',$userId)->where('coupon_id',$couponId)->where('type',3)->get();
            if($isEmpty->isEmpty()){
                DB::beginTransaction(); //开启事务
                $res1 = DB::table('zs_order')->where('user_id',$userId)->where('coupon_id',$couponId)->where('status',0)->update($data);
                $data1 = ['user_id'=>$userId,'coupon_id'=>$couponId,'type'=>3,'code'=>createCode(),'created_at'=>date("Y-m-d H:i:s")];
                $res2 = DB::table('my_coupon')->insert($data1);
                if($res1 && $res2){
                    DB::commit();  //提交
                }else{
                    DB::rollback();//回滚
                }
            }
            return '<xml><return_code><![CDATA[SUCCESS]]></return_code><return_msg><![CDATA[OK]]></return_msg></xml>';
        }
    }




    function xmltoarray($xml) {
        //禁止引用外部xml实体
        libxml_disable_entity_loader(true);
        $xmlstring = simplexml_load_string($xml, 'SimpleXMLElement', LIBXML_NOCDATA);
        $val = json_decode(json_encode($xmlstring),true);
        return $val;
    }