Unify most of our utf8 implementations. This takes the implementation

utils/string_encoding/utf16.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("utf16");
-#import("unicode_core.dart");
-#import("unicode.dart");
-
-/**
- * Decodes the UTF-16 bytes as an iterable. Thus, the consumer can only convert
- * as much of the input as needed. Determines the byte order from the BOM,
- * or uses big-endian as a default. This method always strips a leading BOM.
- * Set the [replacementCodepoint] to null to throw an IllegalArgumentException
- * rather than replace the bad value. The default value for
- * [replacementCodepoint] is U+FFFD.
- */
-IterableUtf16Decoder decodeUtf16AsIterable(List<int> bytes, [int offset = 0,
-    int length, int replacementCodepoint =
-    UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
-  return new IterableUtf16Decoder._(
-      () => new Utf16BytesToCodeUnitsDecoder(bytes, offset, length,
-      replacementCodepoint), replacementCodepoint);
-}
-
-/**
- * Decodes the UTF-16BE bytes as an iterable. Thus, the consumer can only
- * convert as much of the input as needed. This method strips a leading BOM by
- * default, but can be overridden by setting the optional parameter [stripBom]
- * to false. Set the [replacementCodepoint] to null to throw an
- * IllegalArgumentException rather than replace the bad value. The default
- * value for the [replacementCodepoint] is U+FFFD.
- */
-IterableUtf16Decoder decodeUtf16beAsIterable(List<int> bytes, [int offset = 0,
-    int length, bool stripBom = true, int replacementCodepoint =
-    UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
-  return new IterableUtf16Decoder._(
-      () => new Utf16beBytesToCodeUnitsDecoder(bytes, offset, length, stripBom,
-      replacementCodepoint), replacementCodepoint);
-}
-
-/**
- * Decodes the UTF-16LE bytes as an iterable. Thus, the consumer can only
- * convert as much of the input as needed. This method strips a leading BOM by
- * default, but can be overridden by setting the optional parameter [stripBom]
- * to false. Set the [replacementCodepoint] to null to throw an
- * IllegalArgumentException rather than replace the bad value. The default
- * value for the [replacementCodepoint] is U+FFFD.
- */
-IterableUtf16Decoder decodeUtf16leAsIterable(List<int> bytes, [int offset = 0,
-    int length, bool stripBom = true, int replacementCodepoint =
-    UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
-  return new IterableUtf16Decoder._(
-      () => new Utf16leBytesToCodeUnitsDecoder(bytes, offset, length, stripBom,
-      replacementCodepoint), replacementCodepoint);
-}
-
-/**
- * Produce a String from a sequence of UTF-16 encoded bytes. This method always
- * strips a leading BOM. Set the [replacementCodepoint] to null to throw  an
- * IllegalArgumentException rather than replace the bad value. The default
- * value for the [replacementCodepoint] is U+FFFD.
- */
-String decodeUtf16(List<int> bytes, [int offset = 0, int length,
-    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
-  Utf16BytesToCodeUnitsDecoder decoder = new Utf16BytesToCodeUnitsDecoder(bytes,
-      offset, length, replacementCodepoint);
-  List<int> codeunits = decoder.decodeRest();
-  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
-  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
-  // removing after this issue is resolved.
-  if (is16BitCodeUnit()) {
-    return new String.fromCharCodes(codeunits);
-  } else {
-    return new String.fromCharCodes(
-        utf16CodeUnitsToCodepoints(codeunits, 0, null, replacementCodepoint));
-  }
-}
-
-/**
- * Produce a String from a sequence of UTF-16BE encoded bytes. This method
- * strips a leading BOM by default, but can be overridden by setting the
- * optional parameter [stripBom] to false. Set the [replacementCodepoint] to
- * null to throw an IllegalArgumentException rather than replace the bad value.
- * The default value for the [replacementCodepoint] is U+FFFD.
- */
-String decodeUtf16be(List<int> bytes, [int offset = 0, int length,
-    bool stripBom = true,
-    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
-  List<int> codeunits = (new Utf16beBytesToCodeUnitsDecoder(bytes, offset,
-      length, stripBom, replacementCodepoint)).decodeRest();
-  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
-  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
-  // removing after this issue is resolved.
-  if (is16BitCodeUnit()) {
-    return new String.fromCharCodes(codeunits);
-  } else {
-    return new String.fromCharCodes(
-        utf16CodeUnitsToCodepoints(codeunits, 0, null, replacementCodepoint));
-  }
-}
-
-/**
- * Produce a String from a sequence of UTF-16LE encoded bytes. This method
- * strips a leading BOM by default, but can be overridden by setting the
- * optional parameter [stripBom] to false. Set the [replacementCodepoint] to
- * null to throw an IllegalArgumentException rather than replace the bad value.
- * The default value for the [replacementCodepoint] is U+FFFD.
- */
-String decodeUtf16le(List<int> bytes, [int offset = 0, int length,
-    bool stripBom = true,
-    int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
-  List<int> codeunits = (new Utf16leBytesToCodeUnitsDecoder(bytes, offset,
-      length, stripBom, replacementCodepoint)).decodeRest();
-  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
-  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
-  // removing after this issue is resolved.
-  if (is16BitCodeUnit()) {
-    return new String.fromCharCodes(codeunits);
-  } else {
-    return new String.fromCharCodes(
-        utf16CodeUnitsToCodepoints(codeunits, 0, null, replacementCodepoint));
-  }
-}
-
-/**
- * Produce a list of UTF-16 encoded bytes. This method prefixes the resulting
- * bytes with a big-endian byte-order-marker.
- */
-List<int> encodeUtf16(String str) =>
-    encodeUtf16be(str, true);
-
-/**
- * Produce a list of UTF-16BE encoded bytes. By default, this method produces
- * UTF-16BE bytes with no BOM.
- */
-List<int> encodeUtf16be(String str, [bool writeBOM = false]) {
-  List<int> utf16CodeUnits = _stringToUtf16CodeUnits(str);
-  List<int> encoding =
-      new List<int>(2 * utf16CodeUnits.length + (writeBOM ? 2 : 0));
-  int i = 0;
-  if (writeBOM) {
-    encoding[i++] = UNICODE_UTF_BOM_HI;
-    encoding[i++] = UNICODE_UTF_BOM_LO;
-  }
-  for (int unit in utf16CodeUnits) {
-    encoding[i++] = (unit & UNICODE_BYTE_ONE_MASK) >> 8;
-    encoding[i++] = unit & UNICODE_BYTE_ZERO_MASK;
-  }
-  return encoding;
-}
-
-/**
- * Produce a list of UTF-16LE encoded bytes. By default, this method produces
- * UTF-16LE bytes with no BOM.
- */
-List<int> encodeUtf16le(String str, [bool writeBOM = false]) {
-  List<int> utf16CodeUnits = _stringToUtf16CodeUnits(str);
-  List<int> encoding =
-      new List<int>(2 * utf16CodeUnits.length + (writeBOM ? 2 : 0));
-  int i = 0;
-  if (writeBOM) {
-    encoding[i++] = UNICODE_UTF_BOM_LO;
-    encoding[i++] = UNICODE_UTF_BOM_HI;
-  }
-  for (int unit in utf16CodeUnits) {
-    encoding[i++] = unit & UNICODE_BYTE_ZERO_MASK;
-    encoding[i++] = (unit & UNICODE_BYTE_ONE_MASK) >> 8;
-  }
-  return encoding;
-}
-
-/**
- * Identifies whether a List of bytes starts (based on offset) with a
- * byte-order marker (BOM).
- */
-bool hasUtf16Bom(List<int> utf32EncodedBytes, [int offset = 0, int length]) {
-  return hasUtf16beBom(utf32EncodedBytes, offset, length) ||
-      hasUtf16leBom(utf32EncodedBytes, offset, length);
-}
-
-/**
- * Identifies whether a List of bytes starts (based on offset) with a
- * big-endian byte-order marker (BOM).
- */
-bool hasUtf16beBom(List<int> utf16EncodedBytes, [int offset = 0, int length]) {
-  int end = length != null ? offset + length : utf16EncodedBytes.length;
-  return (offset + 2) <= end &&
-      utf16EncodedBytes[offset] == UNICODE_UTF_BOM_HI &&
-      utf16EncodedBytes[offset + 1] == UNICODE_UTF_BOM_LO;
-}
-
-/**
- * Identifies whether a List of bytes starts (based on offset) with a
- * little-endian byte-order marker (BOM).
- */
-bool hasUtf16leBom(List<int> utf16EncodedBytes, [int offset = 0, int length]) {
-  int end = length != null ? offset + length : utf16EncodedBytes.length;
-  return (offset + 2) <= end &&
-      utf16EncodedBytes[offset] == UNICODE_UTF_BOM_LO &&
-      utf16EncodedBytes[offset + 1] == UNICODE_UTF_BOM_HI;
-}
-
-List<int> _stringToUtf16CodeUnits(String str) {
-  // TODO is16BitCodeUnit() is used to work around a bug with frog/dartc
-  // (http://code.google.com/p/dart/issues/detail?id=1357). Consider
-  // removing after this issue is resolved.
-  if (is16BitCodeUnit()) {
-    return str.charCodes();
-  } else {
-    return codepointsToUtf16CodeUnits(str.charCodes());
-  }
-}
-
-/**
- * Return type of [decodeUtf16AsIterable] 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 IterableUtf16Decoder implements Iterable<int> {
-  final Function codeunitsProvider;
-  final int replacementCodepoint;
-
-  IterableUtf16Decoder._(ListRangeIterator<int> this.codeunitsProvider(),
-      int this.replacementCodepoint);
-
-  Utf16CodeUnitDecoder iterator() =>
-      new Utf16CodeUnitDecoder.fromListRangeIterator(codeunitsProvider(),
-          replacementCodepoint);
-}
-
-/**
- * Convert UTF-16 encoded bytes to UTF-16 code units by grouping 1-2 bytes
- * to produce the code unit (0-(2^16)-1). Relies on BOM to determine
- * endian-ness, and defaults to BE.
- */
-class Utf16BytesToCodeUnitsDecoder implements ListRangeIterator<int> {
-  final ListRangeIterator<int> utf16EncodedBytesIterator;
-  final int replacementCodepoint;
-
-  Utf16BytesToCodeUnitsDecoder._fromListRangeIterator(
-      ListRangeIterator<int> this.utf16EncodedBytesIterator,
-      int this.replacementCodepoint);
-
-  factory Utf16BytesToCodeUnitsDecoder(List<int> utf16EncodedBytes, [
-      int offset = 0, int length,
-      int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) {
-    if (length == null) {
-      length = utf16EncodedBytes.length - offset;
-    }
-    if (hasUtf16beBom(utf16EncodedBytes, offset, length)) {
-      return new Utf16beBytesToCodeUnitsDecoder(utf16EncodedBytes, offset + 2,
-          length - 2, false, replacementCodepoint);
-    } else if (hasUtf16leBom(utf16EncodedBytes, offset, length)) {
-      return new Utf16leBytesToCodeUnitsDecoder(utf16EncodedBytes, offset + 2,
-          length - 2, false, replacementCodepoint);
-    } else {
-      return new Utf16beBytesToCodeUnitsDecoder(utf16EncodedBytes, offset,
-          length, false, replacementCodepoint);
-    }
-  }
-
-  /**
-   * Provides a fast way to decode the rest of the source bytes in a single
-   * call. This method trades memory for improved speed in that it potentially
-   * over-allocates the List containing results.
-   */
-  List<int> decodeRest() {
-    List<int> codeunits = new List<int>(remaining);
-    int i = 0;
-    while (hasNext()) {
-      codeunits[i++] = next();
-    }
-    if (i == codeunits.length) {
-      return codeunits;
-    } else {
-      List<int> truncCodeunits = new List<int>(i);
-      truncCodeunits.setRange(0, i, codeunits);
-      return truncCodeunits;
-    }
-  }
-
-  bool hasNext() => utf16EncodedBytesIterator.hasNext();
-
-  int next() {
-    if (utf16EncodedBytesIterator.remaining < 2) {
-      utf16EncodedBytesIterator.next();
-      if (replacementCodepoint != null) {
-        return replacementCodepoint;
-      } else {
-        throw new IllegalArgumentException(
-            "Invalid UTF16 at ${utf16EncodedBytesIterator.position}");
-      }
-    } else {
-      return decode();
-    }
-  }
-
-  int get position() => utf16EncodedBytesIterator.position ~/ 2;
-
-  void backup([int by = 1]) {
-    utf16EncodedBytesIterator.backup(2 * by);
-  }
-
-  int get remaining() => (utf16EncodedBytesIterator.remaining + 1) ~/ 2;
-
-  void skip([int count = 1]) {
-    utf16EncodedBytesIterator.skip(2 * count);
-  }
-
-  abstract int decode();
-}
-
-/**
- * Convert UTF-16BE encoded bytes to utf16 code units by grouping 1-2 bytes
- * to produce the code unit (0-(2^16)-1).
- */
-class Utf16beBytesToCodeUnitsDecoder extends Utf16BytesToCodeUnitsDecoder {
-  Utf16beBytesToCodeUnitsDecoder(List<int> utf16EncodedBytes, [
-      int offset = 0, int length, bool stripBom = true,
-      int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) :
-      super._fromListRangeIterator((new ListRange(utf16EncodedBytes, offset,
-      length)).iterator(), replacementCodepoint) {
-    if (stripBom && hasUtf16beBom(utf16EncodedBytes, offset, length)) {
-      skip();
-    }
-  }
-
-  int decode() {
-    int hi = utf16EncodedBytesIterator.next();
-    int lo = utf16EncodedBytesIterator.next();
-    return (hi << 8) + lo;
-  }
-}
-
-/**
- * Convert UTF-16LE encoded bytes to utf16 code units by grouping 1-2 bytes
- * to produce the code unit (0-(2^16)-1).
- */
-class Utf16leBytesToCodeUnitsDecoder extends Utf16BytesToCodeUnitsDecoder {
-  Utf16leBytesToCodeUnitsDecoder(List<int> utf16EncodedBytes, [
-      int offset = 0, int length, bool stripBom = true,
-      int replacementCodepoint = UNICODE_REPLACEMENT_CHARACTER_CODEPOINT]) :
-      super._fromListRangeIterator((new ListRange(utf16EncodedBytes, offset,
-      length)).iterator(), replacementCodepoint) {
-    if (stripBom && hasUtf16leBom(utf16EncodedBytes, offset, length)) {
-      skip();
-    }
-  }
-
-  int decode() {
-    int lo = utf16EncodedBytesIterator.next();
-    int hi = utf16EncodedBytesIterator.next();
-    return (hi << 8) + lo;
-  }
-}