sdk/lib/convert/chunked_conversion.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;

typedef void _ChunkedConversionCallback<T>(T accumulated);

/**
 * A [ChunkedConversionSink] is used to transmit data more efficiently between
 * two converters during chunked conversions.
 *
 * The basic `ChunkedConversionSink` is just a [Sink], and converters should
 * work with a plain `Sink`, but may work more efficiently with certain
 * specialized types of `ChunkedConversionSink`.
 *
 * It is recommended that implementations of `ChunkedConversionSink` extends
 * this class, to inherit any further methods that may be added to the class.
 */
abstract class ChunkedConversionSink<T> implements Sink<T> {
  ChunkedConversionSink();
  factory ChunkedConversionSink.withCallback(
      void callback(List<T> accumulated)) = _SimpleCallbackSink;

  /**
   * Adds chunked data to this sink.
   *
   * This method is also used when converters are used as [StreamTransformer]s.
   */
  void add(T chunk);

  /**
   * Closes the sink.
   *
   * This signals the end of the chunked conversion. This method is called
   * when converters are used as [StreamTransformer]'s.
   */
  void close();
}

/**
 * This class accumulates all chunks and invokes a callback with a list of
 * the chunks when the sink is closed.
 *
 * This class can be used to terminate a chunked conversion.
 */
class _SimpleCallbackSink<T> extends ChunkedConversionSink<T> {
  final _ChunkedConversionCallback<List<T>> _callback;
  final List<T> _accumulated = <T>[];

  _SimpleCallbackSink(this._callback);

  void add(T chunk) { _accumulated.add(chunk); }
  void close() { _callback(_accumulated); }
}

class _EventSinkAdapter<T> implements ChunkedConversionSink<T> {
  final EventSink<T> _sink;

  _EventSinkAdapter(this._sink);

  void add(T data) => _sink.add(data);
  void close() => _sink.close();
}

/**
 * This class converts implements the logic for a chunked conversion as a
 * stream transformer.
 *
 * It is used as strategy in the [EventTransformStream].
 *
 * It also implements the [ChunkedConversionSink] interface so that it
 * can be used as output sink in a chunked conversion.
 */
class _ConverterStreamEventSink<S, T> implements EventSink<S> {
  /** The output sink for the converter. */
  final EventSink<T> _eventSink;

  /**
   * The input sink for new data. All data that is received with
   * [handleData] is added into this sink.
   */
  ChunkedConversionSink _chunkedSink;

  _ConverterStreamEventSink(Converter converter, EventSink<T> sink)
      : this._eventSink = sink,
        _chunkedSink = converter.startChunkedConversion(sink);

  void add(S o) => _chunkedSink.add(o);
  void addError(Object error, [StackTrace stackTrace]) {
    _eventSink.addError(error, stackTrace);
  }
  void close() => _chunkedSink.close();
}