[perf] Use FastBuffer instead of Buffer#subarray()

`Buffer.prototype.subarray()` performance is subpar on
Node.js < 16.15.0.

Author: lpinca

lib/buffer-util.js

@@ -2,6 +2,8 @@
 
 const { EMPTY_BUFFER } = require('./constants');
 
+const FastBuffer = Buffer[Symbol.species];
+
 /**
  * Merges an array of buffers into a new buffer.
  *
@@ -23,7 +25,9 @@ function concat(list, totalLength) {
     offset += buf.length;
   }
 
-  if (offset < totalLength) return target.subarray(0, offset);
+  if (offset < totalLength) {
+    return new FastBuffer(target.buffer, target.byteOffset, offset);
+  }
 
   return target;
 }

lib/permessage-deflate.js

@@ -6,6 +6,7 @@ const bufferUtil = require('./buffer-util');
 const Limiter = require('./limiter');
 const { kStatusCode } = require('./constants');
 
+const FastBuffer = Buffer[Symbol.species];
 const TRAILER = Buffer.from([0x00, 0x00, 0xff, 0xff]);
 const kPerMessageDeflate = Symbol('permessage-deflate');
 const kTotalLength = Symbol('total-length');
@@ -437,7 +438,9 @@ class PerMessageDeflate {
         this._deflate[kTotalLength]
       );
 
-      if (fin) data = data.subarray(0, data.length - 4);
+      if (fin) {
+        data = new FastBuffer(data.buffer, data.byteOffset, data.length - 4);
+      }
 
       //
       // Ensure that the callback will not be called again in

lib/receiver.js

@@ -12,6 +12,7 @@ const {
 const { concat, toArrayBuffer, unmask } = require('./buffer-util');
 const { isValidStatusCode, isValidUTF8 } = require('./validation');
 
+const FastBuffer = Buffer[Symbol.species];
 const GET_INFO = 0;
 const GET_PAYLOAD_LENGTH_16 = 1;
 const GET_PAYLOAD_LENGTH_64 = 2;
@@ -97,8 +98,13 @@ class Receiver extends Writable {
 
     if (n < this._buffers[0].length) {
       const buf = this._buffers[0];
-      this._buffers[0] = buf.subarray(n);
-      return buf.subarray(0, n);
+      this._buffers[0] = new FastBuffer(
+        buf.buffer,
+        buf.byteOffset + n,
+        buf.length - n
+      );
+
+      return new FastBuffer(buf.buffer, buf.byteOffset, n);
     }
 
     const dst = Buffer.allocUnsafe(n);
@@ -111,7 +117,11 @@ class Receiver extends Writable {
         dst.set(this._buffers.shift(), offset);
       } else {
         dst.set(new Uint8Array(buf.buffer, buf.byteOffset, n), offset);
-        this._buffers[0] = buf.subarray(n);
+        this._buffers[0] = new FastBuffer(
+          buf.buffer,
+          buf.byteOffset + n,
+          buf.length - n
+        );
       }
 
       n -= buf.length;
@@ -562,7 +572,11 @@ class Receiver extends Writable {
           );
         }
 
-        const buf = data.subarray(2);
+        const buf = new FastBuffer(
+          data.buffer,
+          data.byteOffset + 2,
+          data.length - 2
+        );
 
         if (!this._skipUTF8Validation && !isValidUTF8(buf)) {
           return error(