Very strange behavior, multer freezes when used in testing with mock Date

Here’s a simple standalone example demonstrating this problem. The await upload(ctx) function call freezes indefinitely when using in testing with a mock Date. If you run this code you’ll see before printed to the console but not after.

sinon.useFakeTimers({ shouldAdvanceTime: false }) is the trigger of the problem. If you change false to true, then it works. Both before and after will appear on the console immediately.

Why does multer depend on the time advancing, rather than having a static fixed time? It doesn’t seem like the time should cause any change in the behavior of multer.

This demo shows it using koa and koa-multer, but the same problem exists when using express and multer directly.

const Koa = require('koa')
const multer = require('koa-multer')
const request = require('supertest')
const sinon = require('sinon')

const pathToFile = '/tmp/file.txt'

let app = new Koa()

app.use(async (ctx) => {
	const upload = multer().single('file')
	await upload(ctx)
})

app = app.listen();

(async function run() {
	sinon.useFakeTimers({ shouldAdvanceTime: false })
	console.log('before')
	await request(app)
		.post('/')
		.attach('file', pathToFile)
	console.log('after')
})()

[helio-frota]

hi, I was able to reproduce the issue. Branch created here https://github.com/helio-frota/hold-my-file/tree/multer-558

But after search for it, this I found: https://github.com/sinonjs/sinon/issues/1925#issuecomment-429106284

So it seems to be an issue related to the sinon/lolex usage only. So I think this issue can be closed 👍

[rightaway]

No problem. Maybe it’s an issue in the underlying busboy rather than multer itself, but I guess you’ll be able to see that. 😃