Re: [whatwg/webidl] Fix `BufferSource` algorithms for shared and resizable buffers (PR #1529) from Anne van Kesteren on 2025-11-24 (public-webapps-github@w3.org from November 2025)

From: Anne van Kesteren <notifications@github.com>
Date: Sun, 23 Nov 2025 23:26:46 -0800
To: whatwg/webidl <webidl@noreply.github.com>
Cc: Subscribed <subscribed@noreply.github.com>
Message-ID: <whatwg/webidl/pull/1529/review/3498640943@github.com>
@annevk commented on this pull request.

I did an editorial pass.

>      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:

```suggestion
    1.  If |bufferSource| is a [=buffer view type=] instance:
```

> @@ -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.

```suggestion
    1.  If [$IsArrayBufferViewOutOfBounds$](|jsView|) is true, then throw a {{TypeError}} exception.
```

>  <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:

```suggestion
    1.  If |jsBufferSource| has a \[[ViewedArrayBuffer]] [=/internal slot=]:
```

>      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.

```suggestion
    1.  [=/Assert=]: |arrayBuffer| is an {{ArrayBuffer}} or {{SharedArrayBuffer}} object.
```

>  <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.

```suggestion
            1.  [=/Assert=]: |jsBufferSource| is a [=typed array type=] instance.
```

>  <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}}.

```suggestion
            1.  [=/Assert=]: |jsBufferSource| is a {{DataView}}.
```

>  <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.

```suggestion
            1.  If [$IsViewOutOfBounds$](|viewRecord|) is true, then return 0.
```

> -    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:

```suggestion
    1.  Otherwise, if [$IsSharedArrayBuffer$](|jsBufferSource|) is true:
```

> -        |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}}.

```suggestion
        1.  [=/Assert=]: |jsBufferSource| is a {{SharedArrayBuffer}}.
```

> +        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}}.

```suggestion
        1.  [=/Assert=]: |jsBufferSource| is an {{ArrayBuffer}}.
```

> @@ -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=]

```suggestion
    1.  [=/Assert=]: |bytes|'s [=byte sequence/length=] ≤ |arrayBuffer|'s [=byte length=]
```

> @@ -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;

```suggestion
    1.  [=/Assert=]: |bytes|'s [=byte sequence/length=] ≤ |view|'s [=byte length=] &minus;
```

>          <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:

```suggestion
    1.  If |preserveResizability| is true:
```

>          <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,

```suggestion
    1.  Otherwise:
```

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Received on Monday, 24 November 2025 07:26:50 UTC