buffer,string_decoder: consolidate encoding validation logic

Buffer.isEncoding and string_decoder.normalizeEncoding shared
quite a bit of logic. This moves the primary logic into
internal/util. The userland modules that monkey patch Buffer.isEncoding
should still work.

PR-URL: https://github.com/nodejs/node/pull/7207
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

1 files changed, 7 insertions, 28 deletions

diff --git a/lib/string_decoder.js b/lib/string_decoder.js
index 6eb71efc07..005c07ed9e 100644
--- a/lib/string_decoder.js
+++ b/lib/string_decoder.js
@@ -1,38 +1,17 @@
 'use strict';
 
 const Buffer = require('buffer').Buffer;
+const internalUtil = require('internal/util');
+const isEncoding = Buffer[internalUtil.kIsEncodingSymbol];
 
 // Do not cache `Buffer.isEncoding` when checking encoding names as some
 // modules monkey-patch it to support additional encodings
 function normalizeEncoding(enc) {
-  if (!enc) return 'utf8';
-  var low;
-  for (;;) {
-    switch (enc) {
-      case 'utf8':
-      case 'utf-8':
-        return 'utf8';
-      case 'ucs2':
-      case 'utf16le':
-      case 'ucs-2':
-      case 'utf-16le':
-        return 'utf16le';
-      case 'base64':
-      case 'ascii':
-      case 'latin1':
-      case 'binary':
-      case 'hex':
-        return enc;
-      default:
-        if (low) {
-          if (!Buffer.isEncoding(enc))
-            throw new Error('Unknown encoding: ' + enc);
-          return enc;
-        }
-        low = true;
-        enc = ('' + enc).toLowerCase();
-    }
-  }
+  const nenc = internalUtil.normalizeEncoding(enc);
+  if (typeof nenc !== 'string' &&
+      (Buffer.isEncoding === isEncoding || !Buffer.isEncoding(enc)))
+    throw new Error(`Unknown encoding: ${enc}`);
+  return nenc || enc;
 }
 
 // StringDecoder provides an interface for efficiently splitting a series of