diff --git a/js/dos/ext/string_decoder.js b/js/dos/ext/string_decoder.js
new file mode 100644
index 0000000..99e39bb
--- /dev/null
+++ b/js/dos/ext/string_decoder.js
@@ -0,0 +1,200 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var Buffer = Require('buffer').Buffer;
+
+var isBufferEncoding = 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;
+       }
+     }
+
+
+function assertEncoding(encoding) {
+  if (encoding && !isBufferEncoding(encoding)) {
+    throw new Error('Unknown encoding: ' + encoding);
+  }
+}
+
+var StringDecoder = exports.StringDecoder = function(encoding) {
+  this.encoding = (encoding || 'utf8').toLowerCase().replace(/[-_]/, '');
+  assertEncoding(encoding);
+  switch (this.encoding) {
+    case 'utf8':
+      // CESU-8 represents each of Surrogate Pair by 3-bytes
+      this.surrogateSize = 3;
+      break;
+    case 'ucs2':
+    case 'utf16le':
+      // UTF-16 represents each of Surrogate Pair by 2-bytes
+      this.surrogateSize = 2;
+      this.detectIncompleteChar = utf16DetectIncompleteChar;
+      break;
+    case 'base64':
+      // Base-64 stores 3 bytes in 4 chars, and pads the remainder.
+      this.surrogateSize = 3;
+      this.detectIncompleteChar = base64DetectIncompleteChar;
+      break;
+    default:
+      this.write = passThroughWrite;
+      return;
+  }
+
+  this.charBuffer = new Buffer(6);
+  this.charReceived = 0;
+  this.charLength = 0;
+};
+
+
+StringDecoder.prototype.write = function(buffer) {
+  var charStr = '';
+  var offset = 0;
+
+  // if our last write ended with an incomplete multibyte character
+  while (this.charLength) {
+    // determine how many remaining bytes this buffer has to offer for this char
+    var i = (buffer.length >= this.charLength - this.charReceived) ?
+                this.charLength - this.charReceived :
+                buffer.length;
+
+    // add the new bytes to the char buffer
+    buffer.copy(this.charBuffer, this.charReceived, offset, i);
+    this.charReceived += (i - offset);
+    offset = i;
+
+    if (this.charReceived < this.charLength) {
+      // still not enough chars in this buffer? wait for more ...
+      return '';
+    }
+
+    // get the character that was split
+    charStr = this.charBuffer.slice(0, this.charLength).toString(this.encoding);
+
+    // lead surrogate (D800-DBFF) is also the incomplete character
+    var charCode = charStr.charCodeAt(charStr.length - 1);
+    if (charCode >= 0xD800 && charCode <= 0xDBFF) {
+      this.charLength += this.surrogateSize;
+      charStr = '';
+      continue;
+    }
+    this.charReceived = this.charLength = 0;
+
+    // if there are no more bytes in this buffer, just emit our char
+    if (i == buffer.length) return charStr;
+
+    // otherwise cut off the characters end from the beginning of this buffer
+    buffer = buffer.slice(i, buffer.length);
+    break;
+  }
+
+  var lenIncomplete = this.detectIncompleteChar(buffer);
+
+  var end = buffer.length;
+  if (this.charLength) {
+    // buffer the incomplete character bytes we got
+    buffer.copy(this.charBuffer, 0, buffer.length - lenIncomplete, end);
+    this.charReceived = lenIncomplete;
+    end -= lenIncomplete;
+  }
+
+  charStr += buffer.toString(this.encoding, 0, end);
+
+  var end = charStr.length - 1;
+  var charCode = charStr.charCodeAt(end);
+  // lead surrogate (D800-DBFF) is also the incomplete character
+  if (charCode >= 0xD800 && charCode <= 0xDBFF) {
+    var size = this.surrogateSize;
+    this.charLength += size;
+    this.charReceived += size;
+    this.charBuffer.copy(this.charBuffer, size, 0, size);
+    this.charBuffer.write(charStr.charAt(charStr.length - 1), this.encoding);
+    return charStr.substring(0, end);
+  }
+
+  // or just emit the charStr
+  return charStr;
+};
+
+StringDecoder.prototype.detectIncompleteChar = function(buffer) {
+  // determine how many bytes we have to check at the end of this buffer
+  var i = (buffer.length >= 3) ? 3 : buffer.length;
+
+  // Figure out if one of the last i bytes of our buffer announces an
+  // incomplete char.
+  for (; i > 0; i--) {
+    var c = buffer[buffer.length - i];
+
+    // See http://en.wikipedia.org/wiki/UTF-8#Description
+
+    // 110XXXXX
+    if (i == 1 && c >> 5 == 0x06) {
+      this.charLength = 2;
+      break;
+    }
+
+    // 1110XXXX
+    if (i <= 2 && c >> 4 == 0x0E) {
+      this.charLength = 3;
+      break;
+    }
+
+    // 11110XXX
+    if (i <= 3 && c >> 3 == 0x1E) {
+      this.charLength = 4;
+      break;
+    }
+  }
+
+  return i;
+};
+
+StringDecoder.prototype.end = function(buffer) {
+  var res = '';
+  if (buffer && buffer.length)
+    res = this.write(buffer);
+
+  if (this.charReceived) {
+    var cr = this.charReceived;
+    var buf = this.charBuffer;
+    var enc = this.encoding;
+    res += buf.slice(0, cr).toString(enc);
+  }
+
+  return res;
+};
+
+function passThroughWrite(buffer) {
+  return buffer.toString(this.encoding);
+}
+
+function utf16DetectIncompleteChar(buffer) {
+  var incomplete = this.charReceived = buffer.length % 2;
+  this.charLength = incomplete ? 2 : 0;
+  return incomplete;
+}
+
+function base64DetectIncompleteChar(buffer) {
+  var incomplete = this.charReceived = buffer.length % 3;
+  this.charLength = incomplete ? 3 : 0;
+  return incomplete;
+}