Move UTF-8 decoder to utils.

dart/frog/leg/scanner/byte_strings.dart

Index: dart/frog/leg/scanner/byte_strings.dart
===================================================================
--- dart/frog/leg/scanner/byte_strings.dart	(revision 3230)
+++ dart/frog/leg/scanner/byte_strings.dart	(working copy)
@@ -15,73 +15,8 @@
 
   abstract String get charset();
 
-  String toString() {
-    var list;
-    try {
-      list = bytes.getRange(offset, length);
-    } catch (var ignored) {
-      // An exception may occur when running this on node. This is
-      // because [bytes] really is a buffer (or typed array).
-      list = new List<int>(length);
-      for (int i = 0; i < length; i++) {
-        list[i] = bytes[i + offset];
-      }
-    }
-    return new String.fromCharCodes(decodeUtf8(list));
-  }
+  String toString() => new Utf8Decoder(bytes, offset, length).toString();
 
-  static int decodeTrailing(int byte) {
-    if (byte < 0x80 || 0xBF < byte) {
-      throw new MalformedInputException('Cannot decode UTF-8 $byte');
-    } else {
-      return byte & 0x3F;
-    }
-  }
-
-  static List<int> decodeUtf8(List<int> bytes) {
-    List<int> result = new List<int>();
-    for (int i = 0; i < bytes.length; i++) {
-      if (bytes[i] < 0x80) {
-        result.add(bytes[i]);
-      } else if (bytes[i] < 0xC2) {
-        throw new MalformedInputException('Cannot decode UTF-8 @ $i');
-      } else if (bytes[i] < 0xE0) {
-        int char = (bytes[i++] & 0x1F) << 6;
-        char += decodeTrailing(bytes[i]);
-        if (char < 0x80) {
-          throw new MalformedInputException('Cannot decode UTF-8 @ ${i-1}');
-        } else {
-          result.add(char);
-        }
-      } else if (bytes[i] < 0xF0) {
-        int char = (bytes[i++] & 0x0F) << 6;
-        char += decodeTrailing(bytes[i++]);
-        char <<= 6;
-        char += decodeTrailing(bytes[i]);
-        if (char < 0x800 || (0xD800 <= char && char <= 0xDFFF)) {
-          throw new MalformedInputException('Cannot decode UTF-8 @ ${i-2}');
-        } else {
-          result.add(char);
-        }
-      } else if (bytes[i] < 0xF8) {
-        int char = (bytes[i++] & 0x07) << 6;
-        char += decodeTrailing(bytes[i++]);
-        char <<= 6;
-        char += decodeTrailing(bytes[i++]);
-        char <<= 6;
-        char += decodeTrailing(bytes[i]);
-        if (char < 0x10000) {
-          throw new MalformedInputException('Cannot decode UTF-8 @ ${i-3}');
-        } else {
-          result.add(char);
-        }
-      } else {
-        throw new MalformedInputException('Cannot decode UTF-8 @ $i');
-      }
-    }
-    return result;
-  }
-
   bool operator ==(other) {
     throw "should be overridden in subclass";
   }