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Fix BufferSource algorithms for shared and resizable buffers #1529

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Fix BufferSource algorithms for shared and resizable buffers #1529

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e4e9948
Fix buffer source's byte length
MattiasBuelens Oct 8, 2025
447a26c
Add byte offset to ArrayBufferView
MattiasBuelens Oct 8, 2025
b8d7401
Fix writing bytes into an ArrayBufferView backed by a SharedArrayBuffer
MattiasBuelens Oct 8, 2025
037e6ff
Simplify writing into an ArrayBufferView
MattiasBuelens Oct 8, 2025
ba8a3fa
Move assert before conversion
MattiasBuelens Oct 8, 2025
9866f09
Fix detached check
MattiasBuelens Oct 8, 2025
3140a47
Use ArrayBufferCopyAndDetach to transfer an ArrayBuffer
MattiasBuelens Oct 8, 2025
fabdef2
Rework "get a copy of the bytes held"
MattiasBuelens Oct 8, 2025
e2308a0
Use IsArrayBufferViewOutOfBounds instead
MattiasBuelens Oct 8, 2025
4a52a2f
Use SEQ-CST ordering to match ECMAScript
MattiasBuelens Oct 8, 2025
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85 changes: 50 additions & 35 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -9294,19 +9294,15 @@ a reference to the same object that the IDL value represents.
To <dfn id="dfn-get-buffer-source-copy" export lt="get a copy of the buffer source|get a copy of the bytes held by the buffer source">get a copy of the bytes held by the buffer source</dfn>
given a [=buffer source type=] instance |bufferSource|:

1. Let |jsBufferSource| be the result of [=converted to a JavaScript value|converting=]
|bufferSource| to a JavaScript value.
1. Let |jsArrayBuffer| be |jsBufferSource|.
1. Let |arrayBuffer| be |bufferSource|.
1. Let |offset| be 0.
1. Let |length| be 0.
1. If |jsBufferSource| has a \[[ViewedArrayBuffer]] [=/internal slot=], then:
1. Set |jsArrayBuffer| to |jsBufferSource|.\[[ViewedArrayBuffer]].
1. Set |offset| to |jsBufferSource|.\[[ByteOffset]].
1. Set |length| to |jsBufferSource|.\[[ByteLength]].
1. Otherwise:
1. Assert: |jsBufferSource| is an {{ArrayBuffer}} or
{{SharedArrayBuffer}} object.
1. Set |length| to |jsBufferSource|.\[[ArrayBufferByteLength]].
1. Let |length| be |bufferSource|'s [=BufferSource/byte length=].
1. If |bufferSource| is a [=buffer view type=] instance, then:
1. Set |arrayBuffer| to |bufferSource|'s [=underlying buffer=].
1. Set |offset| to |bufferSource|'s [=ArrayBufferView/byte offset=].
1. Assert: |arrayBuffer| is an {{ArrayBuffer}} or {{SharedArrayBuffer}} object.
1. Let |jsArrayBuffer| be the result of [=converted to a JavaScript value|converting=]
|arrayBuffer| to a JavaScript value.
1. If [$IsDetachedBuffer$](|jsArrayBuffer|) is true, then return the empty
[=byte sequence=].
1. Let |bytes| be a new [=byte sequence=] of [=byte sequence/length=] equal to |length|.
Expand All @@ -9316,15 +9312,40 @@ a reference to the same object that the IDL value represents.
1. Return |bytes|.
</div>

<div algorithm>
The <dfn export for="ArrayBufferView">byte offset</dfn> of an {{ArrayBufferView}}
|view| is the value returned by the following steps:

1. Let |jsView| be the result of [=converted to a JavaScript value|converting=] |view| to
a JavaScript value.
1. If [$IsArrayBufferViewOutOfBounds$](|jsView|) is true, throw a {{TypeError}} exception.
1. Return |jsView|.\[[ByteOffset]].
</div>

<div algorithm>
The <dfn export for="BufferSource">byte length</dfn> of a [=buffer source type=] instance
|bufferSource| is the value returned by the following steps:

1. Let |jsBufferSource| be the result of [=converted to a JavaScript value|converting=]
|bufferSource| to a JavaScript value.
1. If |jsBufferSource| has a \[[ViewedArrayBuffer]] internal slot, then return
|jsBufferSource|.\[[ByteLength]].
1. Return |jsBufferSource|.\[[ArrayBufferByteLength]].
1. If |jsBufferSource| has a \[[ViewedArrayBuffer]] [=/internal slot=], then:
1. If |jsBufferSource| has a \[[TypedArrayName]] [=/internal slot=]:
1. Assert: |jsBufferSource| is a [=typed array type=] instance.
1. Let |taRecord| be [$MakeTypedArrayWithBufferWitnessRecord$](|jsBufferSource|,
Seq-Cst).
1. Return [$TypedArrayByteLength$](|taRecord|).
1. Otherwise:
1. Assert: |jsBufferSource| is a {{DataView}}.
1. Let |viewRecord| be [$MakeDataViewWithBufferWitnessRecord$](|jsBufferSource|,
Seq-Cst).
1. If [$IsViewOutOfBounds$](|viewRecord|) is true, return 0.
1. Return [$GetViewByteLength$](|viewRecord|).
1. Otherwise, if [$IsSharedArrayBuffer$](|jsBufferSource|) is true, then:
1. Assert: |jsBufferSource| is a {{SharedArrayBuffer}}.
1. Return [$ArrayBufferByteLength$](|jsBufferSource|, Seq-Cst).
1. Otherwise:
1. Assert: |jsBufferSource| is an {{ArrayBuffer}}.
1. Return |jsBufferSource|.\[[ArrayBufferByteLength]].
</div>
<!-- TODO: should this be stricter around not being detached? -->

Expand All @@ -9348,10 +9369,10 @@ a reference to the same object that the IDL value represents.
<dfn id=arraybuffer-write-startingoffset export for="ArrayBuffer/write,SharedArrayBuffer/write">|startingOffset|</dfn>
(default 0):

1. Assert: |bytes|'s [=byte sequence/length=] ≤ |arrayBuffer|'s [=byte length=]
&minus; |startingOffset|.
1. Let |jsArrayBuffer| be the result of [=converted to a JavaScript value|converting=]
|arrayBuffer| to a JavaScript value.
1. Assert: |bytes|'s [=byte sequence/length=] ≤ |jsArrayBuffer|.\[[ArrayBufferByteLength]]
&minus; |startingOffset|.
1. For |i| in [=the range=] |startingOffset| to |startingOffset| + |bytes|'s [=byte
sequence/length=] &minus; 1, inclusive, perform [$SetValueInBuffer$](|jsArrayBuffer|,
|i|, Uint8, |bytes|[|i| - |startingOffset|], true, Unordered).
Expand All @@ -9362,16 +9383,12 @@ a reference to the same object that the IDL value represents.
{{ArrayBufferView}} |view|, optionally given a
<dfn export for="ArrayBufferView/write">|startingOffset|</dfn> (default 0):

1. Let |jsView| be the result of [=converted to a JavaScript value|converting=] |view| to
a JavaScript value.
1. Assert: |bytes|'s [=byte sequence/length=] ≤ |jsView|.\[[ByteLength]] &minus;
1. Assert: |bytes|'s [=byte sequence/length=] ≤ |view|'s [=byte length=] &minus;
|startingOffset|.
1. Assert: if |view| is not a {{DataView}}, then |bytes|'s [=byte sequence/length=] [=modulo=]
the [=element size=] of |view|'s type is 0.
1. Let |arrayBuffer| be the result of [=converted to an IDL value|converting=]
|jsView|.\[[ViewedArrayBuffer]] to an IDL value of type {{ArrayBuffer}}.
1. [=ArrayBuffer/Write=] |bytes| into |arrayBuffer| with
<i>[=ArrayBuffer/write/startingOffset=]</i> set to |jsView|.\[[ByteOffset]] +
1. [=ArrayBuffer/Write=] |bytes| into |view|'s [=underlying buffer=] with
<i>[=ArrayBuffer/write/startingOffset=]</i> set to |view|'s [=ArrayBufferView/byte offset=] +
|startingOffset|.
</div>

Expand Down Expand Up @@ -9429,22 +9446,20 @@ a reference to the same object that the IDL value represents.
1. Return true.
</div>

<div algorithm>
<div algorithm="ArrayBuffer/transfer">
To <dfn for="ArrayBuffer" export>transfer</dfn> an {{ArrayBuffer}} |arrayBuffer|, optionally
given a [=realm=] |targetRealm|:
given <dfn export for="ArrayBuffer/transfer">|preserveResizability|</dfn> (default false):

1. Let |jsArrayBuffer| be the result of [=converted to a JavaScript value|converting=]
|arrayBuffer| to a JavaScript value.
1. If [$IsDetachedBuffer$](|jsArrayBuffer|) is false, then [=JavaScript/throw=] a
1. If [$IsDetachedBuffer$](|jsArrayBuffer|) is true, then [=JavaScript/throw=] a
<l spec=ecmascript>{{TypeError}}</l>.
1. Let |arrayBufferData| be |jsArrayBuffer|.\[[ArrayBufferData]].
1. Let |arrayBufferByteLength| be |jsArrayBuffer|.\[[ArrayBufferByteLength]].
1. Perform [=?=] [$DetachArrayBuffer$](|jsArrayBuffer|).
1. If |targetRealm| is not given, let |targetRealm| be the [=current realm=].
1. Let |jsTransferred| be [=?=]
[$AllocateArrayBuffer$](|targetRealm|.\[[Intrinsics]].\[[{{%ArrayBuffer%}}]], 0).
1. Set |jsTransferred|.\[[ArrayBufferData]] to |arrayBufferData|.
1. Set |jsTransferred|.\[[ArrayBufferByteLength]] to |arrayBufferByteLength|.
1. If |preserveResizability| is true, then:
1. Let |jsTransferred| be [=?=] [$ArrayBufferCopyAndDetach$](|jsArrayBuffer|, undefined,
Preserve-Resizability).
1. Otherwise,
1. Let |jsTransferred| be [=?=] [$ArrayBufferCopyAndDetach$](|jsArrayBuffer|, undefined,
Fixed-Length).
1. Return the result of [=converted to an IDL value|converting=] |jsTransferred| to an IDL
value of type {{ArrayBuffer}}.

Expand Down