buffer: add Buffer.allocUnsafeSlow(size)

Aligns the functionality of SlowBuffer with the new Buffer
constructor API. Next step is to docs-only deprecate
SlowBuffer.

Replace the internal uses of SlowBuffer with
`Buffer.allocUnsafeSlow(size)`

PR-URL: https://github.com/nodejs/node/pull/5833
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

2 files changed, 27 insertions, 7 deletions

diff --git a/lib/buffer.js b/lib/buffer.js
index f672dae558..1d0963bb50 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -133,13 +133,23 @@ Buffer.from = function(value, encodingOrOffset, length) {
 Object.setPrototypeOf(Buffer.prototype, Uint8Array.prototype);
 Object.setPrototypeOf(Buffer, Uint8Array);
 
+function assertSize(size) {
+  if (typeof size !== 'number') {
+    const err = new TypeError('"size" argument must be a number');
+    // The following hides the 'assertSize' method from the
+    // callstack. This is done simply to hide the internal
+    // details of the implementation from bleeding out to users.
+    Error.captureStackTrace(err, assertSize);
+    throw err;
+  }
+}
+
 /**
  * Creates a new filled Buffer instance.
  * alloc(size[, fill[, encoding]])
  **/
 Buffer.alloc = function(size, fill, encoding) {
-  if (typeof size !== 'number')
-    throw new TypeError('"size" argument must be a number');
+  assertSize(size);
   if (size <= 0)
     return createBuffer(size);
   if (fill !== undefined) {
@@ -161,11 +171,22 @@ Buffer.alloc = function(size, fill, encoding) {
  * instance. If `--zero-fill-buffers` is set, will zero-fill the buffer.
  **/
 Buffer.allocUnsafe = function(size) {
-  if (typeof size !== 'number')
-    throw new TypeError('"size" argument must be a number');
+  assertSize(size);
   return allocate(size);
 };
 
+/**
+ * Equivalent to SlowBuffer(num), by default creates a non-zero-filled
+ * Buffer instance that is not allocated off the pre-initialized pool.
+ * If `--zero-fill-buffers` is set, will zero-fill the buffer.
+ **/
+Buffer.allocUnsafeSlow = function(size) {
+  assertSize(size);
+  if (size > 0)
+    flags[kNoZeroFill] = 1;
+  return createBuffer(size);
+};
+
 // If --zero-fill-buffers command line argument is set, a zero-filled
 // buffer is returned.
 function SlowBuffer(length) {
diff --git a/lib/fs.js b/lib/fs.js
index 3047e5ad98..e441746366 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -3,7 +3,6 @@
 
 'use strict';
 
-const SlowBuffer = require('buffer').SlowBuffer;
 const util = require('util');
 const pathModule = require('path');
 
@@ -321,7 +320,7 @@ ReadFileContext.prototype.read = function() {
   var length;
 
   if (this.size === 0) {
-    buffer = this.buffer = SlowBuffer(kReadFileBufferLength);
+    buffer = this.buffer = Buffer.allocUnsafeSlow(kReadFileBufferLength);
     offset = 0;
     length = kReadFileBufferLength;
   } else {
@@ -389,7 +388,7 @@ function readFileAfterStat(err, st) {
     return context.close(err);
   }
 
-  context.buffer = SlowBuffer(size);
+  context.buffer = Buffer.allocUnsafeSlow(size);
   context.read();
 }