Ch5, Lab 1 - validate running before server ready

caphsob

Hi all,

I'm attempting to complete the lab for ch-5 ("Implement a RESTful JSON GET").

I've create the server using express but when I run node validate I get an error stating " Unable to connect to server on port: ....".

It looks like the validate() checks are running before the express server is actually ready. I added a delay to validate.js to wait 1000ms before the validate() function runs just to test it out. When I do this, the code passes successfully so it looks like I've missed something out on my code - but I'm not sure what? Can anyone point me in the right direction?

I've set my npm start correctly. Running in VS Code, Windows 10.

My Code:-

---

const express = require('express');
const model = require('./model');

const app = express();

app.get('/boat/:id', (req, res) => {

 model.boat.read(req.params.id, (err, data) => {

    if (err) {

      if (err.code == 'E_NOT_FOUND') {
        res.sendStatus(404);
      } else {
        res.sendStatus(500);
      }

    } else {
      res.send(data);
    }

  })
});

app.use(function (req,res,next){
    res.status(404).send('Unable to find the requested resource!');
});

app.listen(process.env.PORT, () => {
    console.log(`Listening on ${process.env.PORT}`)
});

---

Thanks!

caphsob

One extra note, this worked fine for me using Fastify - it's just the Express version I can't seem to get working without introducing a delay before validate()

jhonny111s

the function should be async, then you wait until finished or maybe return a promise.

const data = require('../../data')

router.get('/', async (req, res) => {
  const randomString = await data();
  res.send(randomString)
})

jhonny111s

check this: https://forum.linuxfoundation.org/discussion/857729/lab-3-1-deliver-data-from-a-library-api#latest

davidmarkclements

@caphsob I've checked your code against validate.js and it seems to work just fine. This may be related to your host machine and there's perhaps a race condition. I'm going to update the start function in validate.js to:

async function start () {
  const server = net.createServer().listen()
  await once(server, 'listening')
  const { port } = server.address()
  server.close()
  await once(server, 'close')
  await writeFile(join(__dirname, 'model.js'), testingModel())
  const sp = spawn(process.platform === 'win32' ? 'npm.cmd' : 'npm', ['start'], { env: { ...process.env, PORT: port }, stdio: ['ignore', 'ignore', 'inherit'] })
  const [ err ] = await Promise.race([once(sp, 'spawn'), once(sp, 'error')])

  try {
    if (err) throw err
    await validate({ port })
  } catch (err) {
    if (err.code === 'ERR_ASSERTION') {
      console.log('⛔️ ' + err.message)
      process.exit(1)
    }
    throw err
  } finally {
    await writeFile(join(__dirname, 'model.js'), model())
    try { sp.kill() } catch {}
  }
}

This being the key line:

  const [ err ] = await Promise.race([once(sp, 'spawn'), once(sp, 'error')])

The spawn event was only added fairly recently, so this will be part of our major update to Node v16 (but you can try this out with Node 14/Node 16 and see if it works).

@jhonny111s avoid recommending async functions be used with Express, the training material goes into detail as to why this is a bad idea.