csapi/application/index/controller/Index.php

<?php
namespace app\index\controller;
use app\index\model\ShortUrlModel;
use think\Controller;
use think\Validate;

class Index extends Controller
{
    /**
     * 短链接进入接口
     */
    public function index(){

        $params = $this->request->param();
        $rule = [
            'to'=>'require'
        ];
        $validate = new Validate($rule);
        if(!$validate->check($params)){
            header('HTTP/1.1 400 [to]');
            exit;
        }

        $shortUrlModel = new ShortUrlModel();
        $res = $shortUrlModel->where(['url_str'=>"{$params['to']}"])->find();
        if(empty($res)){
            header('HTTP/1.1 400 [url_str]');
            exit;
        }

        $url = base64_decode($res['old_url']);
        header("HTTP/1.1 301 Moved Permanently");
        header("Location: $url");
        exit;
    }
}