stream: use Buffer.from when constructor is a Buffer

When using BYOB streams, it's possible for the constructor in
readableByteStreamControllerConvertPullIntoDescriptor to be a node
Buffer. If it is, use `Buffer.from` over `new ctor`.
Fixes#49245
PR-URL: #49250
Reviewed-By: Debadree Chatterjee <debadree333@gmail.com>
Reviewed-By: LiviaMedeiros <livia@cirno.name>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

Author: KhafraDev

lib/internal/webstreams/readablestream.js

@@ -132,6 +132,8 @@ const {
  writableStreamDefaultWriterWrite,
 }=require('internal/webstreams/writablestream');
 
+const{ Buffer }=require('buffer');
+
 constassert=require('internal/assert');
 
 constkCancel=Symbol('kCancel');
@@ -1905,6 +1907,11 @@ function readableByteStreamControllerConvertPullIntoDescriptor(desc) {
 thrownewERR_INVALID_STATE.RangeError('The buffer size is invalid');
 assert(!(bytesFilled%elementSize));
 consttransferredBuffer=transferArrayBuffer(buffer);
+
+if(ctor===Buffer){
+returnBuffer.from(transferredBuffer,byteOffset,bytesFilled/elementSize);
+}
+
 returnnewctor(transferredBuffer,byteOffset,bytesFilled/elementSize);
 }
 

test/parallel/test-whatwg-readablebytestreambyob.js

@@ -0,0 +1,62 @@
+'use strict';
+
+constcommon=require('../common');
+
+const{
+ open,
+}=require('fs/promises');
+
+const{
+ Buffer,
+}=require('buffer');
+
+classSource{
+asyncstart(controller){
+this.file=awaitopen(__filename);
+this.controller=controller;
+}
+
+asyncpull(controller){
+constbyobRequest=controller.byobRequest;
+constview=byobRequest.view;
+
+const{
+ bytesRead,
+}=awaitthis.file.read({
+buffer: view,
+offset: view.byteOffset,
+length: view.byteLength
+});
+
+if(bytesRead===0){
+awaitthis.file.close();
+this.controller.close();
+}
+
+byobRequest.respond(bytesRead);
+}
+
+gettype(){return'bytes';}
+
+getautoAllocateChunkSize(){return1024;}
+}
+
+(async()=>{
+constsource=newSource();
+conststream=newReadableStream(source);
+
+const{ emitWarning }=process;
+
+process.emitWarning=common.mustNotCall();
+
+try{
+constreader=stream.getReader({mode: 'byob'});
+
+letresult;
+do{
+result=awaitreader.read(Buffer.alloc(100));
+}while(!result.done);
+}finally{
+process.emitWarning=emitWarning;
+}
+})().then(common.mustCall());