登陆 数据库查找 以及redis校验验证码

```
//用于生成验证ma
const svgCaptcha = require("svg-captcha") 

//mysql  用于在数据库中查找前端输入的用户名和密码
const mysql = require('mysql');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  password: '12345678',
  database: 'sys'
});

connection.connect();

//redis数据库用于存储随机生成的验证码
//便于及时更新

const client = redis.createClient();

//redis 如果没有启动redis，会报错
//redis 启动命令 redis-server
//新建terminal 输入redis-cli

client.on("error", function (err) {
  console.log("Trror" + err);
})

//生成token  方便redis存储和替换
function getID(length) {
  return Number(Math.random().toString().substr(3, length) + Date.now()).toString(36);
}


  //验证码 
 app.get("/cap", (req, res) => {
   const cap = svgCaptcha.create();
   //cap=>{data:...,text:jsoa}
   //text:随机生成的四位验证码
   //data:传递给前端的验证码的图片
   
   
   let text = cap.text;
   res.type("svg");
   
   //生成一个ID redis保存 并传递给前端
   let captchaId = getID(10)
   client.set(captchaId, text)
   res.send({
     cap,
     captchaId
   })
   return
 })

  //前端引用图片
 //  <span dangerouslySetInnerHTML={{ __html: captcha }} onClick={() => this.getcaptcha()}></span>
 
 
 
 //登陆      
app.post("/getlogin", async (req, res) => {
   let { username, password, verification, captchaId } = req.body;
        let redisCaptcha = await new Promise((resolve) => {
          client.get(captchaId, function (err, res) {
            return resolve(res)
          })
        })

        if (verification === redisCaptcha) {
        } else {
          res.send({
            code: 0,
            message: "验证码错误或过期"
          })
          return
        }

     //数据库中查找数据
      connection.query(`SELECT * FROM table where username='${username}' &&passwrd='${password}'`, function (error, results, fields) {
          if (error) throw error;
          if (results[0]) {
            res.send({ code: 1, message: "登陆成功" })
          } else {
            res.send({ code: 0, message: "用户名或密码错误" })
            return
          }
        });

      })
```