Add common.buffer (#710)

* Add common.buffer

* Fix comment

src/common.js

@@ -38,6 +38,7 @@ var DEFAULT_CONFIG = {
   silent: false,
   verbose: false,
   execPath: null,
+  bufLength: 64 * 1024, // 64KB
 };
 
 var config = {
@@ -273,6 +274,17 @@ function expand(list) {
 }
 exports.expand = expand;
 
+// Normalizes Buffer creation, using Buffer.alloc if possible.
+// Also provides a good default buffer length for most use cases.
+var buffer = typeof Buffer.alloc === 'function' ?
+  function (len) {
+    return Buffer.alloc(len || config.bufLength);
+  } :
+  function (len) {
+    return new Buffer(len || config.bufLength);
+  };
+exports.buffer = buffer;
+
 // Normalizes _unlinkSync() across platforms to match Unix behavior, i.e.
 // file can be unlinked even if it's read-only, see https://github.com/joyent/node/issues/3006
 function unlinkSync(file) {

src/cp.js

@@ -45,9 +45,9 @@ function copyFileSync(srcFile, destFile, options) {
     var symlinkFull = fs.readlinkSync(srcFile);
     fs.symlinkSync(symlinkFull, destFile, isWindows ? 'junction' : null);
   } else {
-    var BUF_LENGTH = 64 * 1024;
-    var buf = new Buffer(BUF_LENGTH);
-    var bytesRead = BUF_LENGTH;
+    var buf = common.buffer();
+    var bufLength = buf.length;
+    var bytesRead = bufLength;
     var pos = 0;
     var fdr = null;
     var fdw = null;
@@ -66,8 +66,8 @@ function copyFileSync(srcFile, destFile, options) {
       common.error('copyFileSync: could not write to dest file (code=' + e.code + '):' + destFile);
     }
 
-    while (bytesRead === BUF_LENGTH) {
-      bytesRead = fs.readSync(fdr, buf, 0, BUF_LENGTH, pos);
+    while (bytesRead === bufLength) {
+      bytesRead = fs.readSync(fdr, buf, 0, bufLength, pos);
       fs.writeSync(fdw, buf, 0, bytesRead);
       pos += bytesRead;
     }

src/head.js

@@ -10,9 +10,9 @@ common.register('head', _head, {
 
 // This reads n or more lines, or the entire file, whichever is less.
 function readSomeLines(file, numLines) {
-  var BUF_LENGTH = 64 * 1024;
-  var buf = new Buffer(BUF_LENGTH);
-  var bytesRead = BUF_LENGTH;
+  var buf = common.buffer();
+  var bufLength = buf.length;
+  var bytesRead = bufLength;
   var pos = 0;
   var fdr = null;
 
@@ -24,8 +24,8 @@ function readSomeLines(file, numLines) {
 
   var numLinesRead = 0;
   var ret = '';
-  while (bytesRead === BUF_LENGTH && numLinesRead < numLines) {
-    bytesRead = fs.readSync(fdr, buf, 0, BUF_LENGTH, pos);
+  while (bytesRead === bufLength && numLinesRead < numLines) {
+    bytesRead = fs.readSync(fdr, buf, 0, bufLength, pos);
     var bufStr = buf.toString('utf8', 0, bytesRead);
     numLinesRead += bufStr.split('\n').length - 1;
     ret += bufStr;

test/common.js

@@ -188,6 +188,32 @@ test('non-string', t => {
   t.deepEqual(result, [5]);
 });
 
+//
+// common.buffer()
+//
+test('common.buffer returns buffer', t => {
+  const buf = common.buffer();
+  t.falsy(shell.error());
+  t.truthy(buf instanceof Buffer);
+  t.is(buf.length, 64 * 1024);
+});
+
+test('common.buffer with explicit length', t => {
+  const buf = common.buffer(20);
+  t.falsy(shell.error());
+  t.truthy(buf instanceof Buffer);
+  t.is(buf.length, 20);
+});
+
+test('common.buffer with different config.bufLength', t => {
+  common.config.bufLength = 20;
+  const buf = common.buffer();
+  t.falsy(shell.error());
+  t.truthy(buf instanceof Buffer);
+  t.is(buf.length, 20);
+  common.config.reset();
+});
+
 test('common.parseOptions (normal case)', t => {
   const result = common.parseOptions('-Rf', {
     R: 'recursive',