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Add immutable array buffer awareness to structuredClone #11033

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06282ff
Prevent structuredClone transfer of immutable array buffers (which ar…
gibson042 Feb 15, 2025
2f4d3cb
Preserve ArrayBuffer immutability in Structured{Serialize,Deserialize}
gibson042 Feb 17, 2025
a48c69a
Comment on StructuredSerializeInternal for an immutable ArrayBuffer w…
gibson042 Feb 18, 2025
1c0cf64
fixup! Comment on StructuredSerializeInternal for an immutable ArrayB…
gibson042 Feb 18, 2025
88b5fdf
fixup! Prevent structuredClone transfer of immutable array buffers (w…
gibson042 Feb 18, 2025
56c3332
fixup! Preserve ArrayBuffer immutability in Structured{Serialize,Dese…
gibson042 Feb 18, 2025
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40 changes: 37 additions & 3 deletions source
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Original file line number Diff line number Diff line change
Expand Up @@ -3047,6 +3047,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
<li>The <dfn data-x-href="https://tc39.es/ecma262/#sec-isconstructor">IsConstructor</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.es/ecma262/#sec-isdatadescriptor">IsDataDescriptor</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.es/ecma262/#sec-isdetachedbuffer">IsDetachedBuffer</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.es/ecma262/#sec-isimmutablebuffer">IsImmutableBuffer</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.es/ecma262/#sec-issharedarraybuffer">IsSharedArrayBuffer</dfn> abstract operation</li>
<li>The <dfn data-x="js-NewObjectEnvironment" data-x-href="https://tc39.es/ecma262/#sec-newobjectenvironment">NewObjectEnvironment</dfn> abstract operation</li>
<li>The <dfn data-x-href="https://tc39.es/ecma262/#sec-normalcompletion">NormalCompletion</dfn> abstract operation</li>
Expand Down Expand Up @@ -9744,6 +9745,23 @@ interface <dfn interface>DOMStringList</dfn> {
</ol>
</li>

<li>
<p>Otherwise, if <span>IsImmutableBuffer</span>(<var>value</var>) is true, then:</p>

<ol>
<li>
<p>Set <var>serialized</var> to { [[Type]]: "ImmutableArrayBuffer", [[ArrayBufferData]]:
<var>value</var>.[[ArrayBufferData]], [[ArrayBufferByteLength]]:
<var>value</var>.[[ArrayBufferByteLength]] }.</p>

<p class="note">To support deserialization by independent processes at arbitrary points in
the future, the <em>contents</em> of <var>value</var>.[[ArrayBufferData]] need to be
preserved when <var>forStorage</var> is true. But otherwise, a pointer <em>referencing</em>
<var>value</var>.[[ArrayBufferData]] is expected to suffice.</p>
</li>
</ol>
</li>

<li>
<p>Otherwise:</p>

Expand Down Expand Up @@ -9791,7 +9809,8 @@ interface <dfn interface>DOMStringList</dfn> {
<var>memory</var>).</p></li>

<li><p><span>Assert</span>: <var>bufferSerialized</var>.[[Type]] is "ArrayBuffer",
"ResizableArrayBuffer", "SharedArrayBuffer", or "GrowableSharedArrayBuffer".</p></li>
"ImmutableArrayBuffer", "ResizableArrayBuffer", "SharedArrayBuffer", or
"GrowableSharedArrayBuffer".</p></li>

<li><p>If <var>value</var> has a [[DataView]] internal slot, then set <var>serialized</var> to
{ [[Type]]: "ArrayBufferView", [[Constructor]]: "DataView", [[ArrayBufferSerialized]]:
Expand Down Expand Up @@ -10186,6 +10205,20 @@ o.myself = o;</code></pre>
</ol>
</li>

<li>
<p>Otherwise, if <var>serialized</var>.[[Type]] is "ImmutableArrayBuffer", then:</p>

<ol>
<li><p>Set <var>value</var> to a new ArrayBuffer object in <var>targetRealm</var> whose
[[ArrayBufferData]] internal slot value is <var>serialized</var>.[[ArrayBufferData]], whose
[[ArrayBufferByteLength]] internal slot value is
<var>serialized</var>.[[ArrayBufferByteLength]], and whose [[ArrayBufferIsImmutable]] internal
slot value is undefined.</p></li>

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Is it possible for a slot to not have a value in this way?

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Technically yes, but it's obviously not great and I see now that things are moving away from it. I've updated accordingly.

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But for the record, the document.all HTMLAllCollection seems to be another example—it has an [[IsHTMLDDA]] internal slot for which no value is ever specified AFAICT.

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And in ECMAScript, Object Internal Methods and Internal Slots defines the initial value of an internal slot to be undefined.

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True although see also tc39/ecma262#3399

<li><p><span>Assert</span>: <span>IsImmutableBuffer</span>(<var>value</var>) is true.</p></li>
</ol>
</li>

<li>
<p>Otherwise, if <var>serialized</var>.[[Type]] is "ArrayBuffer", then set <var>value</var> to a
new ArrayBuffer object in <var>targetRealm</var> whose [[ArrayBufferData]] internal slot value
Expand Down Expand Up @@ -10462,8 +10495,9 @@ o.myself = o;</code></pre>
<span>[[Detached]]</span> internal slot, then throw a
<span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p></li>

<li><p>If <var>transferable</var> has an [[ArrayBufferData]] internal slot and
<span>IsSharedArrayBuffer</span>(<var>transferable</var>) is true, then throw a
<li><p>If <var>transferable</var> has an [[ArrayBufferData]] internal slot and either
<span>IsSharedArrayBuffer</span>(<var>transferable</var>) is true or
<span>IsImmutableBuffer</span>(<var>transferable</var>) is true, then throw a
<span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p></li>

<li><p>If <var>memory</var>[<var>transferable</var>] <span data-x="map exists">exists</span>,
Expand Down