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// Copyright (c) 2016, 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.
import 'dart:async';
import 'dart:convert';
import 'package:async/async.dart';
import '../stream_channel.dart';
import 'transformer/typed.dart';
/// A [StreamChannelTransformer] transforms the events being passed to and
/// emitted by a [StreamChannel].
/// This works on the same principle as [StreamTransformer] and
/// [StreamSinkTransformer]. Each transformer defines a [bind] method that takes
/// in the original [StreamChannel] and returns the transformed version.
/// Transformers must be able to have [bind] called multiple times. If a
/// subclass implements [bind] explicitly, it should be sure that the returned
/// stream follows the second stream channel guarantee: closing the sink causes
/// the stream to close before it emits any more events. This guarantee is
/// invalidated when an asynchronous gap is added between the original stream's
/// event dispatch and the returned stream's, for example by transforming it
/// with a [StreamTransformer]. The guarantee can be easily preserved using [new
/// StreamChannel.withCloseGuarantee].
class StreamChannelTransformer<S, T> {
/// The transformer to use on the channel's stream.
final StreamTransformer<T, S> _streamTransformer;
/// The transformer to use on the channel's sink.
final StreamSinkTransformer<S, T> _sinkTransformer;
/// Creates a wrapper that coerces the type of [transformer].
/// This soundly converts a [StreamChannelTransformer] to a
/// `StreamChannelTransformer<S, T>`, regardless of its original generic type,
/// by asserting that the events emitted by the transformed channel's stream
/// are instances of `T` whenever they're provided. If they're not, the stream
/// throws a [CastError]. This also means that calls to [StreamSink.add] on
/// the transformed channel's sink may throw a [CastError] if the argument
/// type doesn't match the reified type of the sink.
static StreamChannelTransformer<S, T> typed<S, T>(
StreamChannelTransformer transformer) =>
transformer is StreamChannelTransformer<S, T>
? transformer
: new TypeSafeStreamChannelTransformer(transformer);
/// Creates a [StreamChannelTransformer] from existing stream and sink
/// transformers.
const StreamChannelTransformer(
this._streamTransformer, this._sinkTransformer);
/// Creates a [StreamChannelTransformer] from a codec's encoder and decoder.
/// All input to the inner channel's sink is encoded using [Codec.encoder],
/// and all output from its stream is decoded using [Codec.decoder].
StreamChannelTransformer.fromCodec(Codec<S, T> codec)
: this(
new StreamSinkTransformer.fromStreamTransformer(
/// Transforms the events sent to and emitted by [channel].
/// Creates a new channel. When events are passed to the returned channel's
/// sink, the transformer will transform them and pass the transformed
/// versions to `channel.sink`. When events are emitted from the
/// `channel.straem`, the transformer will transform them and pass the
/// transformed versions to the returned channel's stream.
StreamChannel<S> bind(StreamChannel<T> channel) =>
new StreamChannel<S>.withCloseGuarantee(,