Github GitHub - Jack-Works/proposal-readonly-arraybuffer

3 years ago

source link: https://github.com/Jack-Works/proposal-readonly-arraybuffer/
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Freeze ArrayBuffer and Readonly view to ArrayBuffer

Status

Champion(s): Jack Works

Author(s): Jack Works

Stage: 0

Related proposal: Fixed view of ArrayBuffer

Presentations

For stage 1 on 2021/04

Motivation

Security

We can have frozen objects (via Object.freeze) but not for binary data today.

Performance

Developers might copy the whole ArrayBuffer if they want to prevent external code to modify that ArrayBuffer. The copy brings the performance lost.
Engines can safely share the memory across different Realms/processes if the ArrayBuffer is read-only.

Target

Add a new way to freeze the ArrayBuffer.
1. One-way. Once it froze, there is no way back.
2. All views to the frozen ArrayBuffer are read-only too.
3. If it is sent across Realms/processes, it is still frozen.
Add a new way to create a read-only view to a read-write ArrayBuffer.
1. Cannot construct the read-write view from readOnlyView.buffer

Possible API design

// Mutate this, not copy & return a new one.
ArrayBuffer.prototype.freeze(): ArrayBuffer
ArrayBuffer.prototype.isFrozen(): boolean

// One of the following:
new TypedArray(buffer, { readonly: true })
new TypedArray(arrayBuffer.frozenView)
TypedArray.prototype.freeze(), TypedArray.prototype.isFrozen()

Freeze ArrayBuffer

const buffer = new ArrayBuffer(8)
const view = new Int32Array(buffer)

view[0] = 42 // OK
buffer.freeze()

view[0] = 42 // TypeError
buffer.isFrozen() // true

Readonly view to ArrayBuffer

const buffer = new ArrayBuffer(8)

// This one?
function createROInt32Array(buffer) {
    return new Int32Array(buffer, { readonly: true })
}
// This one?
function createROInt32Array(buffer) {
    const view = new Int32Array(buffer)
    view.freeze()
    return view
}
// Or this one?
function createROInt32Array(buffer) {
    const view = new Int32Array(buffer.frozenView)
    // view.buffer === buffer.frozenView
    // view.buffer.buffer === view.buffer
    return view
}

const roView = createROInt32Array(buffer)
const rwView = new Int32Array(buffer)

roView[0] = 42 // TypeError
rwView[0] = 42 // OK

const tryEscape = roView.buffer
const newView = new Int32Array(tryEscape)
newView[0] = 42 // still TypeError

roView.buffer !== rwView

Integrate with Tuple & Records?

const buffer = new ArrayBuffer(8)
fillBuffer(buffer)
buffer.freeze()

const data = #{
    binary: buffer
    // yay!
}

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