buffer: add isSharedArrayBuffer checks

Fixes: https://github.com/nodejs/node/issues/8440
PR-URL: https://github.com/nodejs/node/pull/8510
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/buffer.js

@@ -2,7 +2,7 @@
 'use strict';
 
 const binding = process.binding('buffer');
-const { isArrayBuffer } = process.binding('util');
+const { isArrayBuffer, isSharedArrayBuffer } = process.binding('util');
 const bindingObj = {};
 const internalUtil = require('internal/util');
 
@@ -103,7 +103,7 @@ Buffer.from = function(value, encodingOrOffset, length) {
   if (typeof value === 'number')
     throw new TypeError('"value" argument must not be a number');
 
-  if (isArrayBuffer(value))
+  if (isArrayBuffer(value) || isSharedArrayBuffer(value))
     return fromArrayBuffer(value, encodingOrOffset, length);
 
   if (typeof value === 'string')
@@ -264,7 +264,8 @@ function fromObject(obj) {
   }
 
   if (obj) {
-    if (isArrayBuffer(obj.buffer) || 'length' in obj) {
+    if (isArrayBuffer(obj.buffer) || 'length' in obj ||
+        isSharedArrayBuffer(obj)) {
       if (typeof obj.length !== 'number' || obj.length !== obj.length) {
         return new FastBuffer();
       }
@@ -351,8 +352,10 @@ function base64ByteLength(str, bytes) {
 
 function byteLength(string, encoding) {
   if (typeof string !== 'string') {
-    if (ArrayBuffer.isView(string) || isArrayBuffer(string))
+    if (ArrayBuffer.isView(string) || isArrayBuffer(string) ||
+        isSharedArrayBuffer(string)) {
       return string.byteLength;
+    }
 
     string = '' + string;
   }

src/node_util.cc

@@ -20,6 +20,7 @@ using v8::Value;
 
 #define VALUE_METHOD_MAP(V)                                                   \
   V(isArrayBuffer, IsArrayBuffer)                                             \
+  V(isSharedArrayBuffer, IsSharedArrayBuffer)                                 \
   V(isDataView, IsDataView)                                                   \
   V(isDate, IsDate)                                                           \
   V(isMap, IsMap)                                                             \

test/parallel/test-buffer-sharedarraybuffer.js

@@ -0,0 +1,29 @@
+/*global SharedArrayBuffer*/
+'use strict';
+// Flags: --harmony-sharedarraybuffer
+
+require('../common');
+const assert = require('assert');
+const Buffer = require('buffer').Buffer;
+
+const sab = new SharedArrayBuffer(24);
+const arr1 = new Uint16Array(sab);
+const arr2 = new Uint16Array(12);
+arr2[0] = 5000;
+arr1[0] = 5000;
+arr1[1] = 4000;
+arr2[1] = 4000;
+
+const arr_buf = Buffer.from(arr1.buffer);
+const ar_buf = Buffer.from(arr2.buffer);
+
+assert.deepStrictEqual(arr_buf, ar_buf, 0);
+
+arr1[1] = 6000;
+arr2[1] = 6000;
+
+assert.deepStrictEqual(arr_buf, ar_buf, 0);
+
+// Checks for calling Buffer.byteLength on a SharedArrayBuffer
+
+assert.strictEqual(Buffer.byteLength(sab), sab.byteLength, 0);