buffer: improve blob read performance

meixg · sxa · commit d05758f79f96 · 2022-03-07T17:41:06.000Z
Fix: #42108 PR-URL: #42117 Fixes: #42108 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Mestery <mestery@protonmail.com>
diff --git a/lib/internal/blob.js b/lib/internal/blob.js
@@ -65,6 +65,7 @@ const {
 
 const kHandle = Symbol('kHandle');
 const kState = Symbol('kState');
+const kIndex = Symbol('kIndex');
 const kType = Symbol('kType');
 const kLength = Symbol('kLength');
 const kArrayBufferPromise = Symbol('kArrayBufferPromise');
@@ -325,17 +326,17 @@ class Blob {
 return new lazyReadableStream({
 async start() {
 this[kState] = await self.arrayBuffer();
+ this[kIndex] = 0;
 },
 
 pull(controller) {
- if (this[kState].byteLength <= kMaxChunkSize) {
- controller.enqueue(new Uint8Array(this[kState]));
+ if (this[kState].byteLength - this[kIndex] <= kMaxChunkSize) {
+ controller.enqueue(new Uint8Array(this[kState], this[kIndex]));
 controller.close();
 this[kState] = undefined;
 } else {
- const slice = this[kState].slice(0, kMaxChunkSize);
- this[kState] = this[kState].slice(kMaxChunkSize);
- controller.enqueue(new Uint8Array(slice));
+ controller.enqueue(new Uint8Array(this[kState], this[kIndex], kMaxChunkSize));
+ this[kIndex] += kMaxChunkSize;
 }
 }
 });

-Original file line number
+Diff line change
 constkHandle=Symbol('kHandle');
 constkState=Symbol('kState');
 +constkIndex=Symbol('kIndex');
 constkType=Symbol('kType');
 constkLength=Symbol('kLength');
 constkArrayBufferPromise=Symbol('kArrayBufferPromise');
 returnnewlazyReadableStream({
 asyncstart(){
 this[kState]=awaitself.arrayBuffer();
 +this[kIndex]=0;
 },
 pull(controller){
 -if(this[kState].byteLength<=kMaxChunkSize){
 -controller.enqueue(newUint8Array(this[kState]));
 +if(this[kState].byteLength-this[kIndex]<=kMaxChunkSize){
 +controller.enqueue(newUint8Array(this[kState],this[kIndex]));
 controller.close();
 this[kState]=undefined;
 }else{
 -constslice=this[kState].slice(0,kMaxChunkSize);
 -this[kState]=this[kState].slice(kMaxChunkSize);
 -controller.enqueue(newUint8Array(slice));
 +controller.enqueue(newUint8Array(this[kState],this[kIndex],kMaxChunkSize));
 +this[kIndex]+=kMaxChunkSize;
+}
+}
 });