Doesn't seem to work with node 10 fs.promises

[slikts]

import  { promises } from 'fs'
mock({
  test: 'file content',
})
await promises.readFile('test', { encoding: 'utf8' })

Produces: EBADF, bad file descriptor

While fs.readFileSync('test', 'utf8') works correctly.

node: 10.6.0
mock-fs: 4.6.0

[wibobm]

The last version of Node this worked on was 10.4.1

[SwinX]

Confirming this may be reproduced on [email protected] and [email protected]. Any insight about what's causing this issue and when it will be fixed?

[shadymoses]

I'm getting a similar issue. I can successfully read the mock files using fs.readFileSync, but if I convert my operation to be async:

const fs = require('fs').promises
// inside async function
const content = await fs.readFile(file, 'utf8')

it always throws:

Error: ENOENT: no such file or directory, open 'src/client.jsx'

I'm using [email protected], [email protected] and [email protected].

[maxwellgerber]

So a little insight into what's causing the issue:

mock-fs works by overloading Node's process.bindings for the internal C++ FS module. So, you call require('fs').someMethod and that someMethod calls process.bindings('fs').someMethodInternal in turn. After a mock is spun up, the fs module calls into mock-fs instead of the C++ code, allowing us to alter the behavior. Because the lib is tightly coupled to internal APIs, there's no guarantee that it will continue to function on new versions.

[NOTE: This is being phased out entirely in Node 11 due to the deprecation of bindings]

The fs.promises module isn't a wrapper around the original fs module. It does its own thing, and interacts with the underlying process bindings differently. The lib hasn't been updated to handle this new behavior, which is why people get errors when using fs.promises but not with util.promisify(fs.someFunction).

You can see the javascript-land code for fs.promises here.

The biggest change is that there's a symbol passed in to the callback param of the Binding function called kUsePromises. Conceivably, we could check for that symbol inside mock-fs here and respond appropriately. I haven't spent enough time on it to say whether or not some other issues might come up.

Feel free to take a crack at it and open a PR!

[shadymoses]

@maxwellgerber Thanks for the info! If I can find some free time soon I'll look into that.

The weird thing is that I have another test suite that's using fs.promises to walk a directory and extract paths of files matching specific types. It's using readdir and stat from fs.promises and it's passing with mock-fs. It only seems to fail on read or write attempts.

[tschaub]

This should be addressed on the 4.8.0 release (thanks @huochunpeng, see #260).