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Add immutable array buffer awareness to structuredClone #11033

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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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31 changes: 29 additions & 2 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 +9745,16 @@ 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></li>
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@andreubotella andreubotella Feb 17, 2025 •
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Is value.[[ArrayBufferData]] supposed to be able to be kept alive in the serialization? Unlike for SABs, serializing immutable ArrayBuffers doesn't throw if forStorage is true, meaning that the serialization could be deserialized at some future time in a different process that doesn't share any memory with the current one.

At the very least we should have a note saying that implementations should make sure that a forStorage serialization actually serializes the buffer's contents, but a non-for-storage one might serialize a pointer to the buffer data instead.

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Is value.[[ArrayBufferData]] supposed to be able to be kept alive in the serialization? Unlike for SABs, serializing immutable ArrayBuffers doesn't throw if forStorage is true, meaning that the serialization could be deserialized at some future time in a different process that doesn't share any memory with the current one.

That's a good question. I'm not very well versed in the particulars here, but my instinct is that I've got it correct—an immutable array buffer should behave like any other non-shared array buffer when forStorage is true, such that it could be deserialized into a new immutable array buffer with identical contents by a completely independent process at some point in the future.

I like your idea of a note, and have attempted to update accordingly.

</ol>
</li>

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

Expand Down Expand Up @@ -9791,7 +9802,8 @@ 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 +10198,20 @@ 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 is present.</p></li>

<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
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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

Expand Down Expand Up @@ -10463,7 +10489,8 @@ o.myself = o;</code></pre>
<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
<span>IsSharedArrayBuffer</span>(<var>transferable</var>) is true or
either <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