surl/app.js

const redis = require('redis');
const validUrl = require('valid-url');
const express = require('express');

const app = express();
app.use(express.json());
const port = 3000;

//redis client
const redisCli = redis.createClient({
  host: 'redis',
  port: 6379
})
redisCli.on("error", console.error);

//validation
const outpath = ['sym', '', 'manifest.json', 'admin', 'stats', 'api', 'swagger'];
const validateKey = key => !outpath.find(path=>path===key);

//random key
const getKey = length => {
  let forbidden = false;
  let key = '';
  let characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  do{
    for (let i = 0; i < length; i++ )
      key += characters.charAt(Math.floor(Math.random() * characters.length));
    forbidden = !validateKey(key);
    redisCli.hget('surl;'+key, 'url', (err, obj) => {
      if(err) console.error(err);
      if(obj) forbidden = true;
    });
  } while (forbidden);
  return key;
}

const keyLength = 4;

//validate url
const validateUrl = url => validUrl.isUri(url);

//express server
app.put('/api/v1/key', async (req, res) => {
  if (req.body.url === undefined){
    res.status(400);
    res.send({status: 400, message: 'url is undefined'});
    return
  }
  if (!validateUrl(req.body.url)){
    res.status(400);
    res.send({status: 400, message: 'url is invalid'});
    return
  }
  try{
    let key = getKey(keyLength);
    await redisCli.HMSET('surl;'+key, 'url', req.body.url, 'time', Date.now());
    res.status(201);
    res.send({status: 201, url: req.body.url, key});
  }catch (e){
    console.error(e);
    res.status(500);
    res.send({status: 500, message: 'server error'});
  }
});

app.get('/:key', (req, res) => {
  redisCli.HGET('surl;'+req.params.key, 'url', (err, obj) => {
    if(obj){
      res.redirect(302, obj);
    }else{
      res.status(404);
      res.send({status: 404, message: 'this short url does not exist'});
    }
  });
});

app.listen(port);