Buffer.isEncoding(enc)

Re: #3918

doc/api/buffer.markdown

@@ -65,6 +65,13 @@ Allocates a new buffer using an `array` of octets.
 Allocates a new buffer containing the given `str`.
 `encoding` defaults to `'utf8'`.
 
+### Class Method: Buffer.isEncoding(encoding)
+
+* `encoding` {String} The encoding string to test
+
+Returns true if the `encoding` is a valid encoding argument, or false
+otherwise.
+
 ### buf.write(string, [offset], [length], [encoding])
 
 * `string` String - data to be written to buffer

lib/buffer.js

@@ -274,6 +274,29 @@ function isArrayIsh(subject) {
 exports.SlowBuffer = SlowBuffer;
 exports.Buffer = Buffer;
 
+
+Buffer.isEncoding = function(encoding) {
+  switch (encoding && encoding.toLowerCase()) {
+    case 'hex':
+    case 'utf8':
+    case 'utf-8':
+    case 'ascii':
+    case 'binary':
+    case 'base64':
+    case 'ucs2':
+    case 'ucs-2':
+    case 'utf16le':
+    case 'utf-16le':
+    case 'raw':
+      return true;
+
+    default:
+      return false;
+  }
+};
+
+
+
 Buffer.poolSize = 8 * 1024;
 var pool;
 

test/simple/test-buffer.js

@@ -727,3 +727,24 @@ assert.equal(b.toString(), 'xxx');
 
 // issue GH-3416
 Buffer(Buffer(0), 0, 0);
+
+
+[ 'hex',
+  'utf8',
+  'utf-8',
+  'ascii',
+  'binary',
+  'base64',
+  'ucs2',
+  'ucs-2',
+  'utf16le',
+  'utf-16le' ].forEach(function(enc) {
+    assert.equal(Buffer.isEncoding(enc), true);
+  });
+
+[ 'utf9',
+  'utf-7',
+  'Unicode-FTW',
+  'new gnu gun'  ].forEach(function(enc) {
+    assert.equal(Buffer.isEncoding(enc), false);
+  });