Allow ArrayBuffer as argument to writeFile and friends

[Jamesernator]

What is the problem this feature will solve?

Currently one can write a large number of types to a file. However one cannot currently write an ArrayBuffer to a file without wrapping it in a typed array.

It would be convenient to be able to write an ArrayBuffer directly to a file if one is received from some library without having to wrap directly. (The fact this isn't possible is something I forget pretty much everytime I go to write an ArrayBuffer).

What is the feature you are proposing to solve the problem?

I propose allowing fs.promises.writeFile("./some-file", someArrayBuffer) to work when someArrayBuffer is an ArrayBuffer. Typed arrays and such are already supported, so this shouldn't be particularly complicated to implement.

What alternatives have you considered?

No response

[JckXia]

Looking at the writeFile implementation in (https://github.com/nodejs/node/blob/master/lib/internal/fs/promises.js#L809), it looks like Node enforce the data to be either a TypedArray, iterable, a string (or an object that we can serialize into a string). Not sure if there's a lot of wiggle room to loosen the check against pure ArrayBuffers.

I also wonder if writing arrayBuffers directly to a file is considered to be an undefined behaviour, since they are byte arrays and their representation is dependent on the width of the view we are casting it to. (https://stackoverflow.com/questions/42416783/where-to-use-arraybuffer-vs-typed-array-in-javascript)

[Jamesernator]

Looking at the writeFile implementation in (https://github.com/nodejs/node/blob/master/lib/internal/fs/promises.js#L809), it looks like Node enforce the data to be either a TypedArray, iterable, a string (or an object that we can serialize into a string). Not sure if there's a lot of wiggle room to loosen the check against pure ArrayBuffers.

The implementation literally just casts any TypedArray into a Uint8Array: (https://github.com/nodejs/node/blob/master/lib/internal/fs/promises.js#L395). There should be no difficulty in just adding an else if (isArrayBuffer(data)) data = new Uint8Array(data).

I also wonder if writing arrayBuffers directly to a file is considered to be an undefined behaviour, since they are byte arrays and their representation is dependent on the width of the view we are casting it to. (https://stackoverflow.com/questions/42416783/where-to-use-arraybuffer-vs-typed-array-in-javascript)

The answer you link would suggest ArrayBuffer is the more correct concept to read/write files with. From the answer:

They are on the other hand used for binary data transfers between server and client, or from the user's file system via Blobs.

Which makes sense, like you actually write a chunk of bytes to a file, not a sequence of Float32 or whatever TypedArray you might happen to have. Blob (and it's subclass File), and Body do in fact expose their data via blobOrBody.arrayBuffer() not via typed arrays.

[JckXia]

Okay that makes sense, thanks for the explanation!

[benjamingr]

@nodejs/fs

[github-actions]

There has been no activity on this feature request for 5 months and it is unlikely to be implemented. It will be closed 6 months after the last non-automated comment.

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[Jamesernator]

There has been no activity on this feature request for 5 months and it is unlikely to be implemented. It will be closed 6 months after the last non-automated comment.

keepalive

[SRHerzog]

Here's a draft PR to consider. It required some work in a few different places to apply the change to most of the write functions:

• fsPromises.writeFile
• fsPromises.write
• filehandle.writeFile
• filehandle.write
• fs.writeFile
• fs.writeFileSync
• fs.write

I didn't touch any writev functions yet, they'll take some more work.