fs: refactor "options" processing as a function

As it is, the "options" processing is repeated in all the functions
which need it. That introduces checks which are inconsistent with
other functions and produces slightly different error messages.

This patch moves the basic "options" validation and processing to a
seperate function.

PR-URL: nodejs/node#7165
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Nicu Micleușanu <micnic90@gmail.com>
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

fs-file-sync-fd.js

@@ -18,9 +18,24 @@ var util = require('util');
 
 var fsFileSyncFD = {};
 
-function throwOptionsError(options) {
-  throw new TypeError('Expected options to be either an object or a string, ' +
-    'but got ' + typeof options + ' instead');
+function getOptions(options, defaultOptions) {
+  if (options === null || options === undefined ||
+      typeof options === 'function') {
+    return defaultOptions;
+  }
+
+  if (typeof options === 'string') {
+    defaultOptions = util._extend({}, defaultOptions);
+    defaultOptions.encoding = options;
+    options = defaultOptions;
+  } else if (typeof options !== 'object') {
+    throw new TypeError('"options" must be a string or an object, got ' +
+                        typeof options + ' instead.');
+  }
+
+  if (options.encoding !== 'buffer')
+    assertEncoding(options.encoding);
+  return options;
 }
 
 function assertEncoding(encoding) {
@@ -70,20 +85,9 @@ function tryReadSync(fd, isUserFd, buffer, pos, len) {
 }
 
 fsFileSyncFD.readFileSync = function(path, options) {
-  if (!options) {
-    options = { encoding: null, flag: 'r' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, flag: 'r' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
-
-  var encoding = options.encoding;
-  assertEncoding(encoding);
-
-  var flag = options.flag || 'r';
+  options = getOptions(options, { flag: 'r' });
   var isUserFd = isFd(path); // file descriptor ownership
-  var fd = isUserFd ? path : fs.openSync(path, flag, 438 /*=0o666*/);
+  var fd = isUserFd ? path : fs.openSync(path, options.flag || 'r', 438);
 
   var st = tryStatSync(fd, isUserFd);
   var size = st.isFile() ? st.size : 0;
@@ -127,22 +131,14 @@ fsFileSyncFD.readFileSync = function(path, options) {
     buffer = buffer.slice(0, pos);
   }
 
-  if (encoding) buffer = buffer.toString(encoding);
+  if (options.encoding) buffer = buffer.toString(options.encoding);
   return buffer;
 };
 
 fsFileSyncFD.writeFileSync = function(path, data, options) {
-  if (!options) {
-    options = { encoding: 'utf8', mode: 438 /*=0o666*/, flag: 'w' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, mode: 438 /*=0o666*/, flag: 'w' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
-
-  assertEncoding(options.encoding);
-
+  options = getOptions(options, { encoding: 'utf8', mode: 438, flag: 'w' });
   var flag = options.flag || 'w';
+
   var isUserFd = isFd(path); // file descriptor ownership
   var fd = isUserFd ? path : fs.openSync(path, flag, options.mode);
 
@@ -167,13 +163,7 @@ fsFileSyncFD.writeFileSync = function(path, data, options) {
 };
 
 fsFileSyncFD.appendFileSync = function(path, data, options) {
-  if (!options) {
-    options = { encoding: 'utf8', mode: 438 /*=0o666*/, flag: 'a' };
-  } else if (typeof options === 'string') {
-    options = { encoding: options, mode: 438 /*=0o666*/, flag: 'a' };
-  } else if (typeof options !== 'object') {
-    throwOptionsError(options);
-  }
+  options = getOptions(options, { encoding: 'utf8', mode: 438, flag: 'a' });
 
   if (!options.flag)
     options = util._extend({ flag: 'a' }, options);