sdk/lib/convert/latin1.dart

// Copyright (c) 2013, 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.

part of dart.convert;

/**
 * An instance of the default implementation of the [Latin1Codec].
 *
 * This instance provides a convenient access to the most common ISO Latin 1
 * use cases.
 *
 * Examples:
 *
 *     var encoded = LATIN1.encode("blåbærgrød");
 *     var decoded = LATIN1.decode([0x62, 0x6c, 0xe5, 0x62, 0xe6,
 *                                  0x72, 0x67, 0x72, 0xf8, 0x64]);
 */
const LATIN1 = const Latin1Codec();

const int _LATIN1_MASK = 0xFF;

/**
 * A [LatinCodec] encodes strings to ISO Latin-1 (aka ISO-8859-1) bytes
 * and decodes Latin-1 bytes to strings.
 */
class Latin1Codec extends Encoding {
  final bool _allowInvalid;
  /**
   * Instantiates a new [Latin1Codec].
   *
   * If [allowInvalid] is true, the [decode] method and the converter
   * returned by [decoder] will default to allowing invalid values. Invalid
   * values are decoded into the Unicode Replacement character (U+FFFD).
   * Calls to the [decode] method can override this default.
   *
   * Encoders will not accept invalid (non Latin-1) characters.
   */
  const Latin1Codec({bool allowInvalid: false}) : _allowInvalid = allowInvalid;

  String get name => "iso-8859-1";

  /**
   * Decodes the Latin-1 [bytes] (a list of unsigned 8-bit integers) to the
   * corresponding string.
   *
   * If [bytes] contains values that are not in the range 0 .. 255, the decoder
   * will eventually throw a [FormatException].
   *
   * If [allowInvalid] is not provided, it defaults to the value used to create
   * this [Latin1Codec].
   */
  String decode(List<int> bytes, { bool allowInvalid }) {
    if (allowInvalid == null) allowInvalid = _allowInvalid;
    if (allowInvalid) {
      return const Latin1Decoder(allowInvalid: true).convert(bytes);
    } else {
      return const Latin1Decoder(allowInvalid: false).convert(bytes);
    }
  }

  Converter<String, List<int>> get encoder => const Latin1Encoder();

  Converter<List<int>, String> get decoder =>
      _allowInvalid ? const Latin1Decoder(allowInvalid: true)
                    : const Latin1Decoder(allowInvalid: false);
}

/**
 * This class converts strings of only ISO Latin-1 characters to bytes.
 */
class Latin1Encoder extends _UnicodeSubsetEncoder {
  const Latin1Encoder() : super(_LATIN1_MASK);
}

/**
 * This class converts Latin-1 bytes (lists of unsigned 8-bit integers)
 * to a string.
 */
class Latin1Decoder extends _UnicodeSubsetDecoder {
  /**
   * Instantiates a new [Latin1Decoder].
   *
   * The optional [allowInvalid] argument defines how [convert] deals
   * with invalid bytes.
   *
   * If it is `true`, [convert] replaces invalid bytes with the Unicode
   * Replacement character `U+FFFD` (�).
   * Otherwise it throws a [FormatException].
   */
  const Latin1Decoder({ bool allowInvalid: false })
      : super(allowInvalid, _LATIN1_MASK);

  /**
   * Starts a chunked conversion.
   *
   * The converter works more efficiently if the given [sink] is a
   * [StringConversionSink].
   */
  ByteConversionSink startChunkedConversion(
      ChunkedConversionSink<String> sink) {
    StringConversionSink stringSink;
    if (sink is StringConversionSink) {
      stringSink = sink;
    } else {
      stringSink = new StringConversionSink.from(sink);
    }
    // TODO(lrn): Use stringSink.asUtf16Sink() if it becomes available.
    return new _Latin1DecoderSink(_allowInvalid, stringSink);
  }
}

class _Latin1DecoderSink extends ByteConversionSinkBase {
  final bool _allowInvalid;
  StringConversionSink _sink;
  _Latin1DecoderSink(this._allowInvalid, this._sink);

  void close() {
    _sink.close();
  }

  void add(List<int> source) {
    addSlice(source, 0, source.length, false);
  }

  void _addSliceToSink(List<int> source, int start, int end, bool isLast) {
    // If _sink was a UTF-16 conversion sink, just add the slice directly with
    // _sink.addSlice(source, start, end, isLast).
    // The code below is an incredibly stupid workaround until a real
    // solution can be made.
    _sink.add(new String.fromCharCodes(source.getRange(start, end)));
    if (isLast) close();
  }

  void addSlice(List<int> source, int start, int end, bool isLast) {
    if (start < 0 || start > source.length) {
      throw new RangeError.range(start, 0, source.length);
    }
    if (end < start || end > source.length) {
      throw new RangeError.range(end, start, source.length);
    }
    for (int i = start; i < end; i++) {
      if ((source[i] & ~_LATIN1_MASK) != 0) {
        if (_allowInvalid) {
          if (i > start) _addSliceToSink(source, start, i, false);
          // Add UTF-8 encoding of U+FFFD.
          _addSliceToSink(const[0xFFFD], 0, 1, false);
          start = i + 1;
        } else {
          throw new FormatException("Source contains non-Latin-1 characters.");
        }
      }
    }
    if (start < end) {
      _addSliceToSink(source, start, end, isLast);
    } else if (isLast) {
      close();
    }
  }
}