perf(fetch): improve body mixin methods

benchmarks/fetch/body-arraybuffer.mjs

@@ -0,0 +1,24 @@
+import { group, bench, run } from 'mitata'
+import { Response } from '../../lib/web/fetch/response.js'
+
+const settings = {
+  small: 2 << 8,
+  middle: 2 << 12,
+  long: 2 << 16
+}
+
+for (const [name, length] of Object.entries(settings)) {
+  const buffer = Buffer.allocUnsafe(length).map(() => (Math.random() * 100) | 0)
+  group(`${name} (length ${length})`, () => {
+    bench('Response#arrayBuffer', async () => {
+      return await new Response(buffer).arrayBuffer()
+    })
+
+    // for comparison
+    bench('Response#text', async () => {
+      return await new Response(buffer).text()
+    })
+  })
+}
+
+await run()

lib/web/fetch/body.js

@@ -318,7 +318,8 @@ function bodyMixinMethods (instance) {
       // given a byte sequence bytes: return a new ArrayBuffer
       // whose contents are bytes.
       return consumeBody(this, (bytes) => {
-        return new Uint8Array(bytes).buffer
+        // Note: arrayBuffer already cloned.
+        return bytes.buffer
       }, instance)
     },
 
@@ -432,7 +433,7 @@ async function consumeBody (object, convertBytesToJSValue, instance) {
   // 5. If object’s body is null, then run successSteps with an
   //    empty byte sequence.
   if (object[kState].body == null) {
-    successSteps(new Uint8Array())
+    successSteps(Buffer.allocUnsafe(0))
     return promise.promise
   }
 

lib/web/fetch/util.js

@@ -1069,8 +1069,7 @@ async function fullyReadBody (body, processBody, processBodyError) {
 
   // 5. Read all bytes from reader, given successSteps and errorSteps.
   try {
-    const result = await readAllBytes(reader)
-    successSteps(result)
+    successSteps(await readAllBytes(reader))
   } catch (e) {
     errorSteps(e)
   }
@@ -1128,6 +1127,10 @@ async function readAllBytes (reader) {
 
     if (done) {
       // 1. Call successSteps with bytes.
+      if (bytes.length === 1) {
+        const { buffer, byteOffset, byteLength } = bytes[0]
+        return Buffer.from(buffer.slice(byteOffset, byteOffset + byteLength), 0, byteLength)
+      }
       return Buffer.concat(bytes, byteLength)
     }