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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

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

  1. 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.
  2. 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!
}

report

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