lib: faster blob cloning

Author: H4ad

benchmark/blob/clone.js

@@ -7,14 +7,17 @@ const assert = require('assert');
 
 const bench = common.createBenchmark(main, {
   n: [50e3],
+  bytes: [128, 1024, 1024 ** 2],
 });
 
 let _cloneResult;
 
-function main({ n }) {
+function main({ n, bytes }) {
+  const buff = Buffer.allocUnsafe(bytes);
+  const blob = new Blob(buff);
   bench.start();
   for (let i = 0; i < n; ++i)
-    _cloneResult = structuredClone(new Blob(['hello']));
+    _cloneResult = structuredClone(blob);
   bench.end(n);
 
   // Avoid V8 deadcode (elimination)

lib/internal/blob.js

@@ -200,7 +200,7 @@ class Blob {
     const length = this[kLength];
     return {
       data: { handle, type, length },
-      deserializeInfo: 'internal/blob:ClonedBlob',
+      deserializeInfo: 'internal/blob:CloneableBlob',
     };
   }
 
@@ -397,25 +397,27 @@ class Blob {
   }
 }
 
-function ClonedBlob() {
-  return ReflectConstruct(function() {
+class CloneableBlob extends Blob {
+  static {
     markTransferMode(this, true, false);
-  }, [], Blob);
+    this[kDeserialize] = () => {};
+  }
 }
-ClonedBlob.prototype[kDeserialize] = () => {};
 
-function TransferrableBlob(handle, length, type = '') {
+CloneableBlob.prototype.constructor = Blob;
+
+function TransferableBlob(handle, length, type = '') {
   markTransferMode(this, true, false);
   this[kHandle] = handle;
   this[kType] = type;
   this[kLength] = length;
 }
 
-ObjectSetPrototypeOf(TransferrableBlob.prototype, Blob.prototype);
-ObjectSetPrototypeOf(TransferrableBlob, Blob);
+ObjectSetPrototypeOf(TransferableBlob.prototype, Blob.prototype);
+ObjectSetPrototypeOf(TransferableBlob, Blob);
 
 function createBlob(handle, length, type = '') {
-  const transferredBlob = new TransferrableBlob(handle, length, type);
+  const transferredBlob = new TransferableBlob(handle, length, type);
 
   // Fix issues like: https://github.com/nodejs/node/pull/49730#discussion_r1331720053
   transferredBlob.constructor = Blob;
@@ -489,7 +491,7 @@ function createBlobFromFilePath(path, options) {
 
 module.exports = {
   Blob,
-  ClonedBlob,
+  CloneableBlob,
   createBlob,
   createBlobFromFilePath,
   isBlob,

test/parallel/test-blob.js

@@ -480,3 +480,13 @@ assert.throws(() => new Blob({}), {
   assert.ok(blob.slice(0, 1).constructor === Blob);
   assert.ok(blob.slice(0, 1) instanceof Blob);
 }
+
+(async () => {
+  const blob = new Blob(['hello']);
+
+  assert.ok(structuredClone(blob).constructor === Blob);
+  assert.ok(structuredClone(blob) instanceof Blob);
+  assert.ok(structuredClone(blob).size === blob.size);
+  assert.ok(structuredClone(blob).size === blob.size);
+  assert.ok((await structuredClone(blob).text()) === (await blob.text()));
+})().then(common.mustCall());