TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string or an instance of Buffer or URL. Received null

[pubmikeb]

• Version: v16.0.0-v8-canary202104037284782541
• Platform: Windows 10 20H1, x64
• Subsystem: environment

What steps will reproduce the bug?

For file uploading to the cloud, I'm using Multer ("multer": "^2.0.0-rc.2"). With Node.js 15.3.0 everything is working great, after upgrading to 16.0.0 (starting end of March 2021) I'm getting the following error:

node:internal/process/promises:245
          triggerUncaughtException(err, true /* fromPromise */);
          ^

TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string or an instance of Buffer or URL. Received null
    at TempWriteStream.WriteStream (node:internal/fs/streams:360:5)
    at new TempWriteStream (C:\Users\User\IdeaProjects\TMS\node_modules\fs-temp\lib\write-stream.js:6:15)
    at Object.createWriteStream (C:\Users\User\IdeaProjects\TMS\node_modules\fs-temp\lib\temp.js:121:10)
    at Busboy.<anonymous> (C:\Users\User\IdeaProjects\TMS\node_modules\multer\lib\read-body.js:70:27)
    at Busboy.emit (node:events:369:20)
    at Busboy.emit (C:\Users\User\IdeaProjects\TMS\node_modules\busboy\lib\main.js:37:33)
    at PartStream.<anonymous> (C:\Users\User\IdeaProjects\TMS\node_modules\busboy\lib\types\multipart.js:214:13)
    at PartStream.emit (node:events:369:20)
    at HeaderParser.<anonymous> (C:\Users\User\IdeaProjects\TMS\node_modules\dicer\lib\Dicer.js:50:16)
    at HeaderParser.emit (node:events:369:20) {
  code: 'ERR_INVALID_ARG_TYPE'
}

Process finished with exit code 1

When I'm rolling back to 15.3.0 no error occurs.

After some investigation, I've found out that the source of the issue is await asyncUpload(req, res);.
The code snippet:

const _upload = multer({
	limits: {
		fileSize: CONFIG_STORAGE.uploader.maxFileSizeInBytes
	}
}).single("file");

const asyncUpload = promisify(_upload);
await asyncUpload(req, res);

What's for sure, this issue happens on Node.js 16.0.0+ starting end of March, on Feb. nightly builds everything used to be OK.

[Ayase-252]

Yes, it is introduced in #35187 as a semver-major change 2 weeks ago, and will arrive at v16 (see change log #37678).

Since it is a semver-major and is expected to break something. IMO, It seems to require some changes in multer to support Node.js v16.

[ExE-Boss]

Actually, this bug is in fs‑temp, which passes null as the path parameter: https://github.com/LinusU/fs-temp/blob/c892a4786eb7e6669076649ad9c6e2cb3631a037/lib/write-stream.js#L6

[pubmikeb]

So, do I understand it correctly that it's a Node.js issue and not Multer?

[ExE-Boss]

It’s a fs‑temp issue, which is a third‑party package that Multer depends on.

[RaisinTen]

Closing as it's not a bug in Node.js. It's a bug in fs-temp and it should be reported here: https://github.com/LinusU/fs-temp/issues.