No safe way to create an ArrayBuffer from a &[u8]

[tomaka]

Motivation

I'm trying to use an existing JS library (from NPM). One of the methods in this library's API expects to get passed an ArrayBuffer object. Therefore, I need to be able to generate an ArrayBuffer from the Rust code.

It is already possible to do so by doing:

let arr = unsafe { Uint8Array::view(my_buf) };
let arr_clone = Uint8Array::new(arr).buffer();

However that requires using unsafe code.

Proposed Solution

Add an ArrayBuffer::from_data(&[u8]) function in order to move the safety issues within wasm-bindgen.
Similarly, we can also add similar from_data methods to the Uint8Array types and similar.

[alexcrichton]

Thanks for the report! This is somewhat fundamental though because ArrayBuffer represents a mutable chunk of memory which can be safely passed to things like Int8Array::new, so if we had a safe constructor it could then be unsafely actually mutated behind the scenes.

If you're interested in just the ArrayBuffer that backs wasm memory you should be able to safely acquire that via wasm_bindgen::memory(), casting that to WebAssembly::Memory, and then using buffer()

[tomaka]

so if we had a safe constructor it could then be unsafely actually mutated behind the scenes.

My suggestion would be to clone the data, not to hold a reference the &[u8].
In other words, something similar to Slice::to_vec() in the standard library.

[alexcrichton]

Oh sure yeah, that'd definitely be safe, but that can be built with a function that uses unsafe internally, right? Is this a feature request to add such a function that uses unsafe internally to wasm-bindgen itself?

[tomaka]

Is this a feature request to add such a function that uses unsafe internally to wasm-bindgen itself?

Exactly!

[Pauan]

This has been implemented, you can now do Uint8Array::from(my_buf).buffer()