perf: optimize consumeEnd

lib/api/readable.js

@@ -6,7 +6,7 @@ const assert = require('assert')
 const { Readable } = require('stream')
 const { RequestAbortedError, NotSupportedError, InvalidArgumentError, AbortError } = require('../core/errors')
 const util = require('../core/util')
-const { ReadableStreamFrom, toUSVString } = require('../core/util')
+const { ReadableStreamFrom } = require('../core/util')
 
 let Blob
 
@@ -267,29 +267,44 @@ function consumeStart (consume) {
   }
 }
 
+const decoder = new TextDecoder()
+
+/**
+ * @see https://encoding.spec.whatwg.org/#utf-8-decode
+ * @param {Buffer} buffer
+ */
+function utf8DecodeBytes (buffer) {
+  if (buffer.length === 0) {
+    return ''
+  }
+  // 1.
+  // 2.
+  if (buffer[0] === 0xEF && buffer[1] === 0xBB && buffer[2] === 0xBF) {
+    buffer = buffer.subarray(3)
+  }
+  // 3.
+  const output = decoder.decode(buffer)
+  // 4.
+  return output
+}
+
 function consumeEnd (consume) {
   const { type, body, resolve, stream, length } = consume
 
   try {
-    if (type === 'text') {
-      resolve(toUSVString(Buffer.concat(body)))
-    } else if (type === 'json') {
-      resolve(JSON.parse(Buffer.concat(body)))
-    } else if (type === 'arrayBuffer') {
-      const dst = new Uint8Array(length)
-
-      let pos = 0
-      for (const buf of body) {
-        dst.set(buf, pos)
-        pos += buf.byteLength
-      }
-
-      resolve(dst.buffer)
-    } else if (type === 'blob') {
-      if (!Blob) {
-        Blob = require('buffer').Blob
-      }
-      resolve(new Blob(body, { type: stream[kContentType] }))
+    switch (type) {
+      case 'text':
+        resolve(utf8DecodeBytes(Buffer.concat(body, length)))
+        break
+      case 'json':
+        resolve(JSON.parse(utf8DecodeBytes(Buffer.concat(body, length))))
+        break
+      case 'arrayBuffer':
+        resolve(Buffer.concat(body, length).buffer)
+        break
+      case 'blob':
+        resolve(new (Blob ??= require('buffer').Blob)(body, { type: stream[kContentType] }))
+        break
     }
 
     consumeFinish(consume)