Add CloneAsUint8Array helper

Author: MattiasBuelens

index.bs

@@ -2341,8 +2341,8 @@ create them does not matter.
     1. [=Queue a microtask=] to perform the following steps:
      1. Set |reading| to false.
      1. Let |chunk1| and |chunk2| be |chunk|.
-     1. If |canceled1| is false and |canceled2| is false, set |chunk2| to !
-        [$StructuredDeserialize$](? [$StructuredSerialize$](|chunk|), [=the current Realm=]).
+     1. If |canceled1| is false and |canceled2| is false, set |chunk2| to ?
+        [$CloneAsUint8Array$](|chunk|).
      1. If |canceled1| is false, perform !
         [$ReadableByteStreamControllerEnqueue$](|branch1|.[=ReadableStream/[[controller]]=],
         |chunk1|).
@@ -2387,8 +2387,7 @@ create them does not matter.
      1. Set |reading| to false.
      1. If |forBranch2| is true,
       1. If |canceled1| is false,
-       1. Let |clonedChunk| be ! [$StructuredDeserialize$](? [$StructuredSerialize$](|chunk|),
-          [=the current Realm=]).
+       1. Let |clonedChunk| be ? [$CloneAsUint8Array$](|chunk|).
        1. Perform ! [$ReadableByteStreamControllerEnqueue$](|branch1|.[=ReadableStream/[[controller]]=],
           |clonedChunk|).
       1. If |canceled2| is true,
@@ -2398,8 +2397,7 @@ create them does not matter.
          |chunk|).
      1. Otherwise,
       1. If |canceled2| is false,
-       1. Let |clonedChunk| be ! [$StructuredDeserialize$](? [$StructuredSerialize$](|chunk|),
-          [=the current Realm=]).
+       1. Let |clonedChunk| be ? [$CloneAsUint8Array$](|chunk|).
        1. Perform ! [$ReadableByteStreamControllerEnqueue$](|branch2|.[=ReadableStream/[[controller]]=],
           |clonedChunk|).
       1. If |canceled1| is true,
@@ -6324,6 +6322,19 @@ The following abstract operations are a grab-bag of utilities.
     \[[ArrayBufferByteLength]] internal slot value is |arrayBufferByteLength|.
 </div>
 
+<div algorithm>
+ <dfn abstract-op lt="CloneAsUint8Array"
+ id="clone-as-uint8-array">CloneAsUint8Array(|O|)</dfn> performs the following steps:
+
+ 1. Assert: [$Type$](|O|) is Object.
+ 1. Assert: |O| has an \[[ViewedArrayBuffer]] internal slot.
+ 1. Assert: ! [$IsDetachedBuffer$](|O|.\[[ViewedArrayBuffer]]) is false.
+ 1. Let |buffer| be ? [$CloneArrayBuffer$](|O|.\[[ViewedArrayBuffer]], |O|.\[[ByteOffset]],
+    |O|.\[[ByteLength]], {{%ArrayBuffer%}}).
+ 1. Let |array| be ! [$Construct$]({{%Uint8Array%}}, « |buffer| »).
+ 1. Return |array|.
+</div>
+
 <h2 id="other-specs">Using streams in other specifications</h2>
 
 Much of this standard concerns itself with the internal machinery of streams. Other specifications

reference-implementation/lib/abstract-ops/miscellaneous.js

@@ -16,7 +16,7 @@ exports.IsNonNegativeNumber = v => {
   return true;
 };
 
-// Implements StructuredDeserialize(StructuredSerialize(view)), but only for typed arrays and DataViews
-exports.CloneArrayBufferView = view => {
-  return new view.constructor(view.buffer.slice(), view.byteOffset, view.byteLength);
+exports.CloneAsUint8Array = O => {
+  const buffer = O.buffer.slice(O.byteOffset, O.byteOffset + O.byteLength);
+  return new Uint8Array(buffer);
 };

reference-implementation/lib/abstract-ops/readable-streams.js

@@ -5,7 +5,7 @@ const { promiseResolvedWith, promiseRejectedWith, newPromise, resolvePromise, re
         setPromiseIsHandledToTrue, waitForAllPromise, transformPromiseWith, uponFulfillment, uponRejection } =
   require('../helpers/webidl.js');
 const { CopyDataBlockBytes, CreateArrayFromList, TransferArrayBuffer } = require('./ecmascript.js');
-const { CloneArrayBufferView, IsNonNegativeNumber } = require('./miscellaneous.js');
+const { CloneAsUint8Array, IsNonNegativeNumber } = require('./miscellaneous.js');
 const { EnqueueValueWithSize, ResetQueue } = require('./queue-with-sizes.js');
 const { AcquireWritableStreamDefaultWriter, IsWritableStreamLocked, WritableStreamAbort,
         WritableStreamDefaultWriterCloseWithErrorPropagation, WritableStreamDefaultWriterRelease,
@@ -501,7 +501,7 @@ function ReadableByteStreamTee(stream) {
           const chunk1 = chunk;
           let chunk2 = chunk;
           if (canceled1 === false && canceled2 === false) {
-            chunk2 = CloneArrayBufferView(chunk);
+            chunk2 = CloneAsUint8Array(chunk);
           }
 
           if (canceled1 === false) {
@@ -556,7 +556,7 @@ function ReadableByteStreamTee(stream) {
 
           if (forBranch2 === true) {
             if (canceled1 === false) {
-              const clonedChunk = CloneArrayBufferView(chunk);
+              const clonedChunk = CloneAsUint8Array(chunk);
               ReadableByteStreamControllerEnqueue(branch1._controller, clonedChunk);
             }
             if (canceled2 === true) {
@@ -565,7 +565,7 @@ function ReadableByteStreamTee(stream) {
             ReadableByteStreamControllerRespondWithNewView(branch2._controller, chunk);
           } else {
             if (canceled2 === false) {
-              const clonedChunk = CloneArrayBufferView(chunk);
+              const clonedChunk = CloneAsUint8Array(chunk);
               ReadableByteStreamControllerEnqueue(branch2._controller, clonedChunk);
             }
             if (canceled1 === true) {