buffer: fix ArrayBuffer checks

This commit fixes detection of ArrayBuffers from different V8 contexts.
This is especially a problem for environments like nw.js where the
node and browser V8 contexts are not shared.

PR-URL: #8453
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

 Conflicts:
	test/parallel/test-buffer-alloc.js

lib/buffer.js

@@ -88,7 +88,7 @@ Buffer.from = function(value, encodingOrOffset, length) {
   if (typeof value === 'number')
     throw new TypeError('"value" argument must not be a number');
 
-  if (value instanceof ArrayBuffer)
+  if (isArrayBuffer(value))
     return fromArrayBuffer(value, encodingOrOffset, length);
 
   if (typeof value === 'string')
@@ -212,9 +212,6 @@ function fromArrayLike(obj) {
 }
 
 function fromArrayBuffer(obj, byteOffset, length) {
-  if (!isArrayBuffer(obj))
-    throw new TypeError('argument is not an ArrayBuffer');
-
   byteOffset >>>= 0;
 
   const maxLength = obj.byteLength - byteOffset;
@@ -245,7 +242,7 @@ function fromObject(obj) {
   }
 
   if (obj) {
-    if (obj.buffer instanceof ArrayBuffer || 'length' in obj) {
+    if (isArrayBuffer(obj.buffer) || 'length' in obj) {
       if (typeof obj.length !== 'number' || obj.length !== obj.length) {
         return new FastBuffer();
       }
@@ -332,7 +329,7 @@ function base64ByteLength(str, bytes) {
 
 function byteLength(string, encoding) {
   if (typeof string !== 'string') {
-    if (ArrayBuffer.isView(string) || string instanceof ArrayBuffer)
+    if (ArrayBuffer.isView(string) || isArrayBuffer(string))
       return string.byteLength;
 
     string = '' + string;

test/parallel/test-buffer-alloc.js

@@ -1,6 +1,7 @@
 'use strict';
 const common = require('../common');
 const assert = require('assert');
+const vm = require('vm');
 
 const Buffer = require('buffer').Buffer;
 const SlowBuffer = require('buffer').SlowBuffer;
@@ -1078,3 +1079,8 @@ assert.throws(() => {
 
 // Regression test
 assert.doesNotThrow(() => Buffer.from(new ArrayBuffer()));
+
+// Test that ArrayBuffer from a different context is detected correctly
+const arrayBuf = vm.runInNewContext('new ArrayBuffer()');
+assert.doesNotThrow(() => Buffer.from(arrayBuf));
+assert.doesNotThrow(() => Buffer.from({ buffer: arrayBuf }));

test/parallel/test-buffer-bytelength.js

@@ -4,6 +4,7 @@ require('../common');
 const assert = require('assert');
 const Buffer = require('buffer').Buffer;
 const SlowBuffer = require('buffer').SlowBuffer;
+const vm = require('vm');
 
 // coerce values to string
 assert.strictEqual(Buffer.byteLength(32, 'latin1'), 2);
@@ -87,3 +88,7 @@ assert.strictEqual(Buffer.byteLength('Il était tué', 'binary'), 12);
 ['ucs2', 'ucs-2', 'utf16le', 'utf-16le'].forEach(function(encoding) {
   assert.strictEqual(24, Buffer.byteLength('Il était tué', encoding));
 });
+
+// Test that ArrayBuffer from a different context is detected correctly
+const arrayBuf = vm.runInNewContext('new ArrayBuffer()');
+assert.strictEqual(Buffer.byteLength(arrayBuf), 0);