string_decoder: added support for UTF-16LE

Fixes #3223.

lib/string_decoder.js

@@ -21,22 +21,32 @@
 
 var StringDecoder = exports.StringDecoder = function(encoding) {
   this.encoding = (encoding || 'utf8').toLowerCase().replace(/[-_]/, '');
-  if (this.encoding === 'utf8') {
+  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;
+    default:
+      this.write = passThroughWrite;
+      return;
+  }
+
   this.charBuffer = new Buffer(6);
   this.charReceived = 0;
   this.charLength = 0;
-  }
 };
 
 
 StringDecoder.prototype.write = function(buffer) {
-  // If not utf8...
-  if (this.encoding !== 'utf8') {
-    return buffer.toString(this.encoding);
-  }
-
   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
@@ -55,17 +65,15 @@ StringDecoder.prototype.write = function(buffer) {
     }
 
     // get the character that was split
-    charStr = this.charBuffer.slice(0, this.charLength).toString();
+    charStr = this.charBuffer.slice(0, this.charLength).toString(this.encoding);
 
     // lead surrogate (D800-DBFF) is also the incomplete character
-    if (this.charLength === 3) {
-      var charCode = charStr.charCodeAt(0);
+    var charCode = charStr.charCodeAt(charStr.length - 1);
     if (charCode >= 0xD800 && charCode <= 0xDBFF) {
+      this.charLength += this.surrogateSize;
       charStr = '';
-        this.charLength += 3; // size of trail surrogate (DC00-DFFF)
       continue;
     }
-    }
     this.charReceived = this.charLength = 0;
 
     // if there are no more bytes in this buffer, just emit our char
@@ -76,7 +84,35 @@ StringDecoder.prototype.write = function(buffer) {
     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;
 
@@ -106,28 +142,15 @@ StringDecoder.prototype.write = function(buffer) {
     }
   }
 
-  var end = buffer.length;
-  if (this.charLength) {
-    // buffer the incomplete character bytes we got
-    buffer.copy(this.charBuffer, 0, buffer.length - i, buffer.length);
-    this.charReceived = i;
-    end -= i;
-  }
-
-  charStr += buffer.toString('utf8', 0, end);
-
-  // lead surrogate (D800-DBFF) is also the incomplete character
-  end = charStr.length - 1;
-  var charCode = charStr.charCodeAt(end);
-  if (charCode >= 0xD800 && charCode <= 0xDBFF) {
-    // CESU-8 represents each of Surrogate Pair by 3-bytes
-    this.charLength += 3
-    this.charReceived += 3
-    this.charBuffer.copy(this.charBuffer, 3, 0, 3);
-    this.charBuffer.write(charStr.charAt(end));
-    return charStr.substring(0, end);
-  }
-
-  // or just emit the charStr
-  return charStr;
+  return i;
 };
+
+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;
+}

test/simple/test-string-decoder.js

@@ -89,6 +89,42 @@ s += decoder.write(buffer.slice(0, 6));
 assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
 
 
+// UCS-2
+decoder = new StringDecoder('ucs2');
+buffer = new Buffer('ab', 'ucs2');
+assert.equal(decoder.write(buffer), 'ab'); // 2 complete chars
+buffer = new Buffer('abc', 'ucs2');
+assert.equal(decoder.write(buffer.slice(0, 3)), 'a'); // 'a' and first of 'b'
+assert.equal(decoder.write(buffer.slice(3, 6)), 'bc'); // second of 'b' and 'c'
+
+
+// UTF-16LE
+buffer = new Buffer('3DD84DDC', 'hex'); // THUMBS UP SIGN (in CESU-8)
+var s = '';
+s += decoder.write(buffer.slice(0, 1));
+s += decoder.write(buffer.slice(1, 2)); // complete lead surrogate
+assert.equal(s, '');
+s += decoder.write(buffer.slice(2, 3));
+s += decoder.write(buffer.slice(3, 4)); // complete trail surrogate
+assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
+
+var s = '';
+s += decoder.write(buffer.slice(0, 2)); // complete lead surrogate
+assert.equal(s, '');
+s += decoder.write(buffer.slice(2, 4)); // complete trail surrogate
+assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
+
+var s = '';
+s += decoder.write(buffer.slice(0, 3)); // complete lead surrogate
+assert.equal(s, '');
+s += decoder.write(buffer.slice(3, 4)); // complete trail surrogate
+assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
+
+var s = '';
+s += decoder.write(buffer.slice(0, 4));
+assert.equal(s, '\uD83D\uDC4D'); // THUMBS UP SIGN (in UTF-16)
+
+
 // A mixed ascii and non-ascii string
 // Test stolen from deps/v8/test/cctest/test-strings.cc
 // U+02E4 -> CB A4