Unify most of our utf8 implementations. This takes the implementation

lib/utf/utf8.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-#library("utf8");
-#import("unicode_core.dart");
-#import("unicode.dart");
-#source("utf8_impl.dart");
+final int _UTF8_ONE_BYTE_MAX = 0x7f;
+final int _UTF8_TWO_BYTE_MAX = 0x7ff;
+final int _UTF8_THREE_BYTE_MAX = 0xffff;
+
+final int _UTF8_LO_SIX_BIT_MASK = 0x3f;
+
+final int _UTF8_FIRST_BYTE_OF_TWO_BASE = 0xc0;
+final int _UTF8_FIRST_BYTE_OF_THREE_BASE = 0xe0;
+final int _UTF8_FIRST_BYTE_OF_FOUR_BASE = 0xf0;
+final int _UTF8_FIRST_BYTE_OF_FIVE_BASE = 0xf8;
+final int _UTF8_FIRST_BYTE_OF_SIX_BASE = 0xfc;
+
+final int _UTF8_FIRST_BYTE_OF_TWO_MASK = 0x1f;
+final int _UTF8_FIRST_BYTE_OF_THREE_MASK = 0xf;
+final int _UTF8_FIRST_BYTE_OF_FOUR_MASK = 0x7;
+
+final int _UTF8_FIRST_BYTE_BOUND_EXCL = 0xfe;
+final int _UTF8_SUBSEQUENT_BYTE_BASE = 0x80;
+
+/**
+ * Decodes the UTF-8 bytes as an iterable. Thus, the consumer can only convert
+ * as much of the input as needed. Set the replacementCharacter to null to
+ * throw an IllegalArgumentException rather than replace the bad value.
+ */
+IterableUtf8Decoder decodeUtf8AsIterable(List<int> bytes, [int offset = 0,
+    int length,
+    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
+  return new IterableUtf8Decoder(bytes, offset, length, replacementCodepoint);
+}
+
+/**
+ * Produce a String from a List of UTF-8 encoded bytes. The parameters
+ * can set an offset into a list of bytes (as int), limit the length of the
+ * values to be decoded, and override the default Unicode replacement character.
+ * Set the replacementCharacter to null to throw an IllegalArgumentException
+ * rather than replace the bad value.
+ */
+String decodeUtf8(List<int> bytes, [int offset = 0, int length,
+    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
+  return codepointsToString(
+      (new Utf8Decoder(bytes, offset, length, replacementCodepoint))
+      .decodeRest());
+}
+
+/**
+ * Produce a sequence of UTF-8 encoded bytes from the provided string.
+ */
+List<int> encodeUtf8(String str) =>
+  codepointsToUtf8(stringToCodepoints(str));
+
+int _addToEncoding(int offset, int bytes, int value, List<int> buffer) {
+  while (bytes > 0) {
+    buffer[offset + bytes] = _UTF8_SUBSEQUENT_BYTE_BASE |
+        (value & _UTF8_LO_SIX_BIT_MASK);
+    value = value >> 6;
+    bytes--;
+  }
+  return value;
+}
+
+/**
+ * Encode code points as UTF-8 code units.
+ */
+List<int> codepointsToUtf8(
+    List<int> codepoints, [int offset = 0, int length]) {
+  _ListRange<int> source = new _ListRange(codepoints, offset, length);
+
+  int encodedLength = 0;
+  for (int value in source) {
+    if (value < 0 || value > UNICODE_VALID_RANGE_MAX) {
+      encodedLength += 3;
+    } else if (value <= _UTF8_ONE_BYTE_MAX) {
+      encodedLength++;
+    } else if (value <= _UTF8_TWO_BYTE_MAX) {
+      encodedLength += 2;
+    } else if (value <= _UTF8_THREE_BYTE_MAX) {
+      encodedLength += 3;
+    } else if (value <= UNICODE_VALID_RANGE_MAX) {
+      encodedLength += 4;
+    }
+  }
+
+  List<int> encoded = new List<int>(encodedLength);
+  int insertAt = 0;
+  for (int value in source) {
+    if (value < 0 || value > UNICODE_VALID_RANGE_MAX) {
+      encoded.setRange(insertAt, 3, [0xef, 0xbf, 0xbd]);
+      insertAt += 3;
+    } else if (value <= _UTF8_ONE_BYTE_MAX) {
+      encoded[insertAt] = value;
+      insertAt++;
+    } else if (value <= _UTF8_TWO_BYTE_MAX) {
+      encoded[insertAt] = _UTF8_FIRST_BYTE_OF_TWO_BASE | (
+          _UTF8_FIRST_BYTE_OF_TWO_MASK &
+          _addToEncoding(insertAt, 1, value, encoded));
+      insertAt += 2;
+    } else if (value <= _UTF8_THREE_BYTE_MAX) {
+      encoded[insertAt] = _UTF8_FIRST_BYTE_OF_THREE_BASE | (
+          _UTF8_FIRST_BYTE_OF_THREE_MASK &
+          _addToEncoding(insertAt, 2, value, encoded));
+      insertAt += 3;
+    } else if (value <= UNICODE_VALID_RANGE_MAX) {
+      encoded[insertAt] = _UTF8_FIRST_BYTE_OF_FOUR_BASE | (
+          _UTF8_FIRST_BYTE_OF_FOUR_MASK &
+          _addToEncoding(insertAt, 3, value, encoded));
+      insertAt += 4;
+    }
+  }
+  return encoded;
+}
+
+// Because UTF-8 specifies byte order, we do not have to follow the pattern
+// used by UTF-16 & UTF-32 regarding byte order.
+List<int> utf8ToCodepoints(
+    List<int> utf8EncodedBytes, [int offset = 0, int length,
+    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
+  return new Utf8Decoder(utf8EncodedBytes, offset, length,
+      replacementCodepoint).decodeRest();
+}
+
+/**
+ * Return type of [decodeUtf8AsIterable] and variants. The Iterable type
+ * provides an iterator on demand and the iterator will only translate bytes
+ * as requested by the user of the iterator. (Note: results are not cached.)
+ */
+class IterableUtf8Decoder implements Iterable<int> {
+  final List<int> bytes;
+  final int offset;
+  final int length;
+  final int replacementCodepoint;
+
+  IterableUtf8Decoder(List<int> this.bytes, [int this.offset = 0,
+      int this.length = null,
+      int this.replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]);
+
+  Utf8Decoder iterator() => new Utf8Decoder(bytes, offset, length,
+          replacementCodepoint);
+}
+
+/**
+ * Provides an iterator of Unicode codepoints from UTF-8 encoded bytes. The
+ * parameters can set an offset into a list of bytes (as int), limit the length
+ * of the values to be decoded, and override the default Unicode replacement
+ * character. Set the replacementCharacter to null to throw an
+ * IllegalArgumentException rather than replace the bad value. The return value
+ * from this method can be used as an Iterable (e.g. in a for-loop).
+ */
+class Utf8Decoder implements Iterator<int> {
+  final _ListRangeIterator<int> utf8EncodedBytesIterator;
+  final int replacementCodepoint;
+
+  Utf8Decoder(List<int> utf8EncodedBytes, [int offset = 0, int length,
+      int this.replacementCodepoint =
+      UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) :
+      utf8EncodedBytesIterator = (new _ListRange(utf8EncodedBytes, offset,
+          length)).iterator();
+
+
+  Utf8Decoder._fromListRangeIterator(_ListRange<int> source, [
+      int this.replacementCodepoint =
+      UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) :
+      utf8EncodedBytesIterator = source.iterator();
+
+  /** Decode the remaininder of the characters in this decoder
+    * into a [List<int>].
+    */
+  List<int> decodeRest() {
+    List<int> codepoints = new List<int>(utf8EncodedBytesIterator.remaining);
+    int i = 0;
+    while (hasNext()) {
+      codepoints[i++] = next();
+    }
+    if (i == codepoints.length) {
+      return codepoints;
+    } else {
+      List<int> truncCodepoints = new List<int>(i);
+      truncCodepoints.setRange(0, i, codepoints);
+      return truncCodepoints;
+    }
+  }
+
+  bool hasNext() => utf8EncodedBytesIterator.hasNext();
+
+  int next() {
+    int value = utf8EncodedBytesIterator.next();
+    int additionalBytes = 0;
+
+    if (value < 0) {
+      if (replacementCodepoint != null) {
+        return replacementCodepoint;
+      } else {
+        throw new IllegalArgumentException(
+            "Invalid UTF8 at ${utf8EncodedBytesIterator.position}");
+      }
+    } else if (value <= _UTF8_ONE_BYTE_MAX) {
+      return value;
+    } else if (value < _UTF8_FIRST_BYTE_OF_TWO_BASE) {
+      if (replacementCodepoint != null) {
+        return replacementCodepoint;
+      } else {
+        throw new IllegalArgumentException(
+            "Invalid UTF8 at ${utf8EncodedBytesIterator.position}");
+      }
+    } else if (value < _UTF8_FIRST_BYTE_OF_THREE_BASE) {
+      value -= _UTF8_FIRST_BYTE_OF_TWO_BASE;
+      additionalBytes = 1;
+    } else if (value < _UTF8_FIRST_BYTE_OF_FOUR_BASE) {
+      value -= _UTF8_FIRST_BYTE_OF_THREE_BASE;
+      additionalBytes = 2;
+    } else if (value < _UTF8_FIRST_BYTE_OF_FIVE_BASE) {
+      value -= _UTF8_FIRST_BYTE_OF_FOUR_BASE;
+      additionalBytes = 3;
+    } else if (value < _UTF8_FIRST_BYTE_OF_SIX_BASE) {
+      value -= _UTF8_FIRST_BYTE_OF_FIVE_BASE;
+      additionalBytes = 4;
+    } else if (value < _UTF8_FIRST_BYTE_BOUND_EXCL) {
+      value -= _UTF8_FIRST_BYTE_OF_SIX_BASE;
+      additionalBytes = 5;
+    } else if (replacementCodepoint != null) {
+      return replacementCodepoint;
+    } else {
+      throw new IllegalArgumentException(
+          "Invalid UTF8 at ${utf8EncodedBytesIterator.position}");
+    }
+    int j = 0;
+    while (j < additionalBytes && utf8EncodedBytesIterator.hasNext()) {
+      int nextValue = utf8EncodedBytesIterator.next();
+      if (nextValue > _UTF8_ONE_BYTE_MAX &&
+          nextValue < _UTF8_FIRST_BYTE_OF_TWO_BASE) {
+        value = ((value << 6) | (nextValue & _UTF8_LO_SIX_BIT_MASK));
+      } else {
+        // if sequence-starting code unit, reposition cursor to start here
+        if (nextValue >= _UTF8_FIRST_BYTE_OF_TWO_BASE) {
+          utf8EncodedBytesIterator.backup();
+        }
+        break;
+      }
+      j++;
+    }
+    bool validSequence = (j == additionalBytes && (
+        value < UNICODE_UTF16_RESERVED_LO ||
+        value > UNICODE_UTF16_RESERVED_HI));
+    bool nonOverlong =
+        (additionalBytes == 1 && value > _UTF8_ONE_BYTE_MAX) ||
+        (additionalBytes == 2 && value > _UTF8_TWO_BYTE_MAX) ||
+        (additionalBytes == 3 && value > _UTF8_THREE_BYTE_MAX);
+    bool inRange = value <= UNICODE_VALID_RANGE_MAX;
+    if (validSequence && nonOverlong && inRange) {
+      return value;
+    } else if (replacementCodepoint != null) {
+      return replacementCodepoint;
+    } else {
+      throw new IllegalArgumentException(
+          "Invalid UTF8 at ${utf8EncodedBytesIterator.position - j}");
+    }
+  }
+}