blob: 5aa60548c232e904cc54b582375608890f201068 [file] [log] [blame]
// Copyright (c) 2015, 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:collection';
import 'package:collection/collection.dart';
import 'cancelable_operation.dart';
import 'result/result.dart';
import 'subscription_stream.dart';
import 'stream_completer.dart';
import 'stream_splitter.dart';
/// An asynchronous pull-based interface for accessing stream events.
///
/// Wraps a stream and makes individual events available on request.
///
/// You can request (and reserve) one or more events from the stream,
/// and after all previous requests have been fulfilled, stream events
/// go towards fulfilling your request.
///
/// For example, if you ask for [next] two times, the returned futures
/// will be completed by the next two unrequested events from the stream.
///
/// The stream subscription is paused when there are no active
/// requests.
///
/// Some streams, including broadcast streams, will buffer
/// events while paused, so waiting too long between requests may
/// cause memory bloat somewhere else.
///
/// This is similar to, but more convenient than, a [StreamIterator].
/// A `StreamIterator` requires you to manually check when a new event is
/// available and you can only access the value of that event until you
/// check for the next one. A `StreamQueue` allows you to request, for example,
/// three events at a time, either individually, as a group using [take]
/// or [skip], or in any combination.
///
/// You can also ask to have the [rest] of the stream provided as
/// a new stream. This allows, for example, taking the first event
/// out of a stream and continuing to use the rest of the stream as a stream.
///
/// Example:
///
/// var events = StreamQueue<String>(someStreamOfLines);
/// var first = await events.next;
/// while (first.startsWith('#')) {
/// // Skip comments.
/// first = await events.next;
/// }
///
/// if (first.startsWith(MAGIC_MARKER)) {
/// var headerCount =
/// first.parseInt(first.substring(MAGIC_MARKER.length + 1));
/// handleMessage(headers: await events.take(headerCount),
/// body: events.rest);
/// return;
/// }
/// // Error handling.
///
/// When you need no further events the `StreamQueue` should be closed
/// using [cancel]. This releases the underlying stream subscription.
class StreamQueue<T> {
// This class maintains two queues: one of events and one of requests.
// The active request (the one in front of the queue) is called with
// the current event queue when it becomes active, every time a
// new event arrives, and when the event source closes.
//
// If the request returns `true`, it's complete and will be removed from the
// request queue.
// If the request returns `false`, it needs more events, and will be called
// again when new events are available. It may trigger a call itself by
// calling [_updateRequests].
// The request can remove events that it uses, or keep them in the event
// queue until it has all that it needs.
//
// This model is very flexible and easily extensible.
// It allows requests that don't consume events (like [hasNext]) or
// potentially a request that takes either five or zero events, determined
// by the content of the fifth event.
final Stream<T> _source;
/// Subscription on [_source] while listening for events.
///
/// Set to subscription when listening, and set to `null` when the
/// subscription is done (and [_isDone] is set to true).
StreamSubscription<T>? _subscription;
/// Whether the event source is done.
bool _isDone = false;
/// Whether a closing operation has been performed on the stream queue.
///
/// Closing operations are [cancel] and [rest].
bool _isClosed = false;
/// The number of events dispatched by this queue.
///
/// This counts error events. It doesn't count done events, or events
/// dispatched to a stream returned by [rest].
int get eventsDispatched => _eventsReceived - _eventQueue.length;
/// The number of events received by this queue.
var _eventsReceived = 0;
/// Queue of events not used by a request yet.
final QueueList<Result<T>> _eventQueue = QueueList();
/// Queue of pending requests.
///
/// Access through methods below to ensure consistency.
final Queue<_EventRequest> _requestQueue = Queue();
/// Create a `StreamQueue` of the events of [source].
factory StreamQueue(Stream<T> source) => StreamQueue._(source);
// Private generative constructor to avoid subclasses.
StreamQueue._(this._source) {
// Start listening immediately if we could otherwise lose events.
if (_source.isBroadcast) {
_ensureListening();
_pause();
}
}
/// Asks if the stream has any more events.
///
/// Returns a future that completes with `true` if the stream has any
/// more events, whether data or error.
/// If the stream closes without producing any more events, the returned
/// future completes with `false`.
///
/// Can be used before using [next] to avoid getting an error in the
/// future returned by `next` in the case where there are no more events.
/// Another alternative is to use `take(1)` which returns either zero or
/// one events.
Future<bool> get hasNext {
if (!_isClosed) {
var hasNextRequest = _HasNextRequest<T>();
_addRequest(hasNextRequest);
return hasNextRequest.future;
}
throw _failClosed();
}
/// Look at the next [count] data events without consuming them.
///
/// Works like [take] except that the events are left in the queue.
/// If one of the next [count] events is an error, the returned future
/// completes with this error, and the error is still left in the queue.
Future<List<T>> lookAhead(int count) {
if (count < 0) throw RangeError.range(count, 0, null, 'count');
if (!_isClosed) {
var request = _LookAheadRequest<T>(count);
_addRequest(request);
return request.future;
}
throw _failClosed();
}
/// Requests the next (yet unrequested) event from the stream.
///
/// When the requested event arrives, the returned future is completed with
/// the event.
/// If the event is a data event, the returned future completes
/// with its value.
/// If the event is an error event, the returned future completes with
/// its error and stack trace.
/// If the stream closes before an event arrives, the returned future
/// completes with a [StateError].
///
/// It's possible to have several pending [next] calls (or other requests),
/// and they will be completed in the order they were requested, by the
/// first events that were not consumed by previous requeusts.
Future<T> get next {
if (!_isClosed) {
var nextRequest = _NextRequest<T>();
_addRequest(nextRequest);
return nextRequest.future;
}
throw _failClosed();
}
/// Looks at the next (yet unrequested) event from the stream.
///
/// Like [next] except that the event is not consumed.
/// If the next event is an error event, it stays in the queue.
Future<T> get peek {
if (!_isClosed) {
var nextRequest = _PeekRequest<T>();
_addRequest(nextRequest);
return nextRequest.future;
}
throw _failClosed();
}
/// Returns a stream of all the remaning events of the source stream.
///
/// All requested [next], [skip] or [take] operations are completed
/// first, and then any remaining events are provided as events of
/// the returned stream.
///
/// Using `rest` closes this stream queue. After getting the
/// `rest` the caller may no longer request other events, like
/// after calling [cancel].
Stream<T> get rest {
if (_isClosed) {
throw _failClosed();
}
var request = _RestRequest<T>(this);
_isClosed = true;
_addRequest(request);
return request.stream;
}
/// Skips the next [count] *data* events.
///
/// The [count] must be non-negative.
///
/// When successful, this is equivalent to using [take]
/// and ignoring the result.
///
/// If an error occurs before `count` data events have been skipped,
/// the returned future completes with that error instead.
///
/// If the stream closes before `count` data events,
/// the remaining unskipped event count is returned.
/// If the returned future completes with the integer `0`,
/// then all events were succssfully skipped. If the value
/// is greater than zero then the stream ended early.
Future<int> skip(int count) {
if (count < 0) throw RangeError.range(count, 0, null, 'count');
if (!_isClosed) {
var request = _SkipRequest<T>(count);
_addRequest(request);
return request.future;
}
throw _failClosed();
}
/// Requests the next [count] data events as a list.
///
/// The [count] must be non-negative.
///
/// Equivalent to calling [next] `count` times and
/// storing the data values in a list.
///
/// If an error occurs before `count` data events has
/// been collected, the returned future completes with
/// that error instead.
///
/// If the stream closes before `count` data events,
/// the returned future completes with the list
/// of data collected so far. That is, the returned
/// list may have fewer than [count] elements.
Future<List<T>> take(int count) {
if (count < 0) throw RangeError.range(count, 0, null, 'count');
if (!_isClosed) {
var request = _TakeRequest<T>(count);
_addRequest(request);
return request.future;
}
throw _failClosed();
}
/// Requests a transaction that can conditionally consume events.
///
/// The transaction can create copies of this queue at the current position
/// using [StreamQueueTransaction.newQueue]. Each of these queues is
/// independent of one another and of the parent queue. The transaction
/// finishes when one of two methods is called:
///
/// * [StreamQueueTransaction.commit] updates the parent queue's position to
/// match that of one of the copies.
///
/// * [StreamQueueTransaction.reject] causes the parent queue to continue as
/// though [startTransaction] hadn't been called.
///
/// Until the transaction finishes, this queue won't emit any events.
///
/// See also [withTransaction] and [cancelable].
///
/// ```dart
/// /// Consumes all empty lines from the beginning of [lines].
/// Future consumeEmptyLines(StreamQueue<String> lines) async {
/// while (await lines.hasNext) {
/// var transaction = lines.startTransaction();
/// var queue = transaction.newQueue();
/// if ((await queue.next).isNotEmpty) {
/// transaction.reject();
/// return;
/// } else {
/// transaction.commit(queue);
/// }
/// }
/// }
/// ```
StreamQueueTransaction<T> startTransaction() {
if (_isClosed) throw _failClosed();
var request = _TransactionRequest(this);
_addRequest(request);
return request.transaction;
}
/// Passes a copy of this queue to [callback], and updates this queue to match
/// the copy's position if [callback] returns `true`.
///
/// This queue won't emit any events until [callback] returns. If it returns
/// `false`, this queue continues as though [withTransaction] hadn't been
/// called. If it throws an error, this updates this queue to match the copy's
/// position and throws the error from the returned `Future`.
///
/// Returns the same value as [callback].
///
/// See also [startTransaction] and [cancelable].
///
/// ```dart
/// /// Consumes all empty lines from the beginning of [lines].
/// Future consumeEmptyLines(StreamQueue<String> lines) async {
/// while (await lines.hasNext) {
/// // Consume a line if it's empty, otherwise return.
/// if (!await lines.withTransaction(
/// (queue) async => (await queue.next).isEmpty)) {
/// return;
/// }
/// }
/// }
/// ```
Future<bool> withTransaction(Future<bool> Function(StreamQueue<T>) callback) {
var transaction = startTransaction();
/// Avoid async/await to ensure that [startTransaction] is called
/// synchronously and so ends up in the right place in the request queue.
var queue = transaction.newQueue();
return callback(queue).then((result) {
if (result) {
transaction.commit(queue);
} else {
transaction.reject();
}
return result;
}, onError: (Object error) {
transaction.commit(queue);
throw error;
});
}
/// Passes a copy of this queue to [callback], and updates this queue to match
/// the copy's position once [callback] completes.
///
/// If the returned [CancelableOperation] is canceled, this queue instead
/// continues as though [cancelable] hadn't been called. Otherwise, it emits
/// the same value or error as [callback].
///
/// See also [startTransaction] and [withTransaction].
///
/// ```dart
/// final _stdinQueue = StreamQueue(stdin);
///
/// /// Returns an operation that completes when the user sends a line to
/// /// standard input.
/// ///
/// /// If the operation is canceled, stops waiting for user input.
/// CancelableOperation<String> nextStdinLine() =>
/// _stdinQueue.cancelable((queue) => queue.next);
/// ```
CancelableOperation<S> cancelable<S>(
Future<S> Function(StreamQueue<T>) callback) {
var transaction = startTransaction();
var completer = CancelableCompleter<S>(onCancel: () {
transaction.reject();
});
var queue = transaction.newQueue();
completer.complete(callback(queue).whenComplete(() {
if (!completer.isCanceled) transaction.commit(queue);
}));
return completer.operation;
}
/// Cancels the underlying event source.
///
/// If [immediate] is `false` (the default), the cancel operation waits until
/// all previously requested events have been processed, then it cancels the
/// subscription providing the events.
///
/// If [immediate] is `true`, the source is instead canceled
/// immediately. Any pending events are completed as though the underlying
/// stream had closed.
///
/// The returned future completes with the result of calling
/// `cancel`.
///
/// After calling `cancel`, no further events can be requested.
/// None of [lookAhead], [next], [peek], [rest], [skip], [take] or [cancel]
/// may be called again.
Future? cancel({bool immediate = false}) {
if (_isClosed) throw _failClosed();
_isClosed = true;
if (!immediate) {
var request = _CancelRequest<T>(this);
_addRequest(request);
return request.future;
}
if (_isDone && _eventQueue.isEmpty) return Future.value();
return _cancel();
}
// ------------------------------------------------------------------
// Methods that may be called from the request implementations to
// control the event stream.
/// Matches events with requests.
///
/// Called after receiving an event or when the event source closes.
///
/// May be called by requests which have returned `false` (saying they
/// are not yet done) so they can be checked again before any new
/// events arrive.
/// Any request returing `false` from `update` when `isDone` is `true`
/// *must* call `_updateRequests` when they are ready to continue
/// (since no further events will trigger the call).
void _updateRequests() {
while (_requestQueue.isNotEmpty) {
if (_requestQueue.first.update(_eventQueue, _isDone)) {
_requestQueue.removeFirst();
} else {
return;
}
}
if (!_isDone) {
_pause();
}
}
/// Extracts a stream from the event source and makes this stream queue
/// unusable.
///
/// Can only be used by the very last request (the stream queue must
/// be closed by that request).
/// Only used by [rest].
Stream<T> _extractStream() {
assert(_isClosed);
if (_isDone) {
return Stream<T>.empty();
}
_isDone = true;
var subscription = _subscription;
if (subscription == null) {
return _source;
}
_subscription = null;
var wasPaused = subscription.isPaused;
var result = SubscriptionStream<T>(subscription);
// Resume after creating stream because that pauses the subscription too.
// This way there won't be a short resumption in the middle.
if (wasPaused) subscription.resume();
return result;
}
/// Requests that the event source pauses events.
///
/// This is called automatically when the request queue is empty.
///
/// The event source is restarted by the next call to [_ensureListening].
void _pause() {
_subscription!.pause();
}
/// Ensures that we are listening on events from the event source.
///
/// Starts listening for the first time or resumes after a [_pause].
///
/// Is called automatically if a request requires more events.
void _ensureListening() {
if (_isDone) return;
if (_subscription == null) {
_subscription = _source.listen((data) {
_addResult(Result.value(data));
}, onError: (Object error, StackTrace stackTrace) {
_addResult(Result.error(error, stackTrace));
}, onDone: () {
_subscription = null;
_close();
});
} else {
_subscription!.resume();
}
}
/// Cancels the underlying event source.
Future? _cancel() {
if (_isDone) return null;
_subscription ??= _source.listen(null);
var future = _subscription!.cancel();
_close();
return future;
}
// ------------------------------------------------------------------
// Methods called by the event source to add events or say that it's
// done.
/// Called when the event source adds a new data or error event.
/// Always calls [_updateRequests] after adding.
void _addResult(Result<T> result) {
_eventsReceived++;
_eventQueue.add(result);
_updateRequests();
}
/// Called when the event source is done.
/// Always calls [_updateRequests] after adding.
void _close() {
_isDone = true;
_updateRequests();
}
// ------------------------------------------------------------------
// Internal helper methods.
/// Returns an error for when a request is made after cancel.
///
/// Returns a [StateError] with a message saying that either
/// [cancel] or [rest] have already been called.
Error _failClosed() {
return StateError('Already cancelled');
}
/// Adds a new request to the queue.
///
/// If the request queue is empty and the request can be completed
/// immediately, it skips the queue.
void _addRequest(_EventRequest<T> request) {
if (_requestQueue.isEmpty) {
if (request.update(_eventQueue, _isDone)) return;
_ensureListening();
}
_requestQueue.add(request);
}
}
/// A transaction on a [StreamQueue], created by [StreamQueue.startTransaction].
///
/// Copies of the parent queue may be created using [newQueue]. Calling [commit]
/// moves the parent queue to a copy's position, and calling [reject] causes it
/// to continue as though [StreamQueue.startTransaction] was never called.
class StreamQueueTransaction<T> {
/// The parent queue on which this transaction is active.
final StreamQueue<T> _parent;
/// The splitter that produces copies of the parent queue's stream.
final StreamSplitter<T> _splitter;
/// Queues created using [newQueue].
final _queues = <StreamQueue>{};
/// Whether [commit] has been called.
var _committed = false;
/// Whether [reject] has been called.
var _rejected = false;
StreamQueueTransaction._(this._parent, Stream<T> source)
: _splitter = StreamSplitter(source);
/// Creates a new copy of the parent queue.
///
/// This copy starts at the parent queue's position when
/// [StreamQueue.startTransaction] was called. Its position can be committed
/// to the parent queue using [commit].
StreamQueue<T> newQueue() {
var queue = StreamQueue(_splitter.split());
_queues.add(queue);
return queue;
}
/// Commits a queue created using [newQueue].
///
/// The parent queue's position is updated to be the same as [queue]'s.
/// Further requests on all queues created by this transaction, including
/// [queue], will complete as though [cancel] were called with `immediate:
/// true`.
///
/// Throws a [StateError] if [commit] or [reject] have already been called, or
/// if there are pending requests on [queue].
void commit(StreamQueue<T> queue) {
_assertActive();
if (!_queues.contains(queue)) {
throw ArgumentError("Queue doesn't belong to this transaction.");
} else if (queue._requestQueue.isNotEmpty) {
throw StateError("A queue with pending requests can't be committed.");
}
_committed = true;
// Remove all events from the parent queue that were consumed by the
// child queue.
for (var j = 0; j < queue.eventsDispatched; j++) {
_parent._eventQueue.removeFirst();
}
_done();
}
/// Rejects this transaction without updating the parent queue.
///
/// The parent will continue as though [StreamQueue.startTransaction] hadn't
/// been called. Further requests on all queues created by this transaction
/// will complete as though [cancel] were called with `immediate: true`.
///
/// Throws a [StateError] if [commit] or [reject] have already been called.
void reject() {
_assertActive();
_rejected = true;
_done();
}
// Cancels all [_queues], removes the [_TransactionRequest] from [_parent]'s
// request queue, and runs the next request.
void _done() {
_splitter.close();
for (var queue in _queues) {
queue._cancel();
}
// If this is the active request in the queue, mark it as finished.
var currentRequest = _parent._requestQueue.first;
if (currentRequest is _TransactionRequest &&
currentRequest.transaction == this) {
_parent._requestQueue.removeFirst();
_parent._updateRequests();
}
}
/// Throws a [StateError] if [accept] or [reject] has already been called.
void _assertActive() {
if (_committed) {
throw StateError('This transaction has already been accepted.');
} else if (_rejected) {
throw StateError('This transaction has already been rejected.');
}
}
}
/// Request object that receives events when they arrive, until fulfilled.
///
/// Each request that cannot be fulfilled immediately is represented by
/// an `_EventRequest` object in the request queue.
///
/// Events from the source stream are sent to the first request in the
/// queue until it reports itself as [isComplete].
///
/// When the first request in the queue `isComplete`, either when becoming
/// the first request or after receiving an event, its [close] methods is
/// called.
///
/// The [close] method is also called immediately when the source stream
/// is done.
abstract class _EventRequest<T> {
/// Handle available events.
///
/// The available events are provided as a queue. The `update` function
/// should only remove events from the front of the event queue, e.g.,
/// using [removeFirst].
///
/// Returns `true` if the request is completed, or `false` if it needs
/// more events.
/// The call may keep events in the queue until the requeust is complete,
/// or it may remove them immediately.
///
/// If the method returns true, the request is considered fulfilled, and
/// will never be called again.
///
/// This method is called when a request reaches the front of the request
/// queue, and if it returns `false`, it's called again every time a new event
/// becomes available, or when the stream closes.
/// If the function returns `false` when the stream has already closed
/// ([isDone] is true), then the request must call
/// [StreamQueue._updateRequests] itself when it's ready to continue.
bool update(QueueList<Result<T>> events, bool isDone);
}
/// Request for a [StreamQueue.next] call.
///
/// Completes the returned future when receiving the first event,
/// and is then complete.
class _NextRequest<T> implements _EventRequest<T> {
/// Completer for the future returned by [StreamQueue.next].
final _completer = Completer<T>();
_NextRequest();
Future<T> get future => _completer.future;
@override
bool update(QueueList<Result<T>> events, bool isDone) {
if (events.isNotEmpty) {
events.removeFirst().complete(_completer);
return true;
}
if (isDone) {
_completer.completeError(StateError('No elements'), StackTrace.current);
return true;
}
return false;
}
}
/// Request for a [StreamQueue.peek] call.
///
/// Completes the returned future when receiving the first event,
/// and is then complete, but doesn't consume the event.
class _PeekRequest<T> implements _EventRequest<T> {
/// Completer for the future returned by [StreamQueue.next].
final _completer = Completer<T>();
_PeekRequest();
Future<T> get future => _completer.future;
@override
bool update(QueueList<Result<T>> events, bool isDone) {
if (events.isNotEmpty) {
events.first.complete(_completer);
return true;
}
if (isDone) {
_completer.completeError(StateError('No elements'), StackTrace.current);
return true;
}
return false;
}
}
/// Request for a [StreamQueue.skip] call.
class _SkipRequest<T> implements _EventRequest<T> {
/// Completer for the future returned by the skip call.
final _completer = Completer<int>();
/// Number of remaining events to skip.
///
/// The request [isComplete] when the values reaches zero.
///
/// Decremented when an event is seen.
/// Set to zero when an error is seen since errors abort the skip request.
int _eventsToSkip;
_SkipRequest(this._eventsToSkip);
/// The future completed when the correct number of events have been skipped.
Future<int> get future => _completer.future;
@override
bool update(QueueList<Result<T>> events, bool isDone) {
while (_eventsToSkip > 0) {
if (events.isEmpty) {
if (isDone) break;
return false;
}
_eventsToSkip--;
var event = events.removeFirst();
if (event.isError) {
_completer.completeError(
event.asError!.error, event.asError!.stackTrace);
return true;
}
}
_completer.complete(_eventsToSkip);
return true;
}
}
/// Common superclass for [_TakeRequest] and [_LookAheadRequest].
abstract class _ListRequest<T> implements _EventRequest<T> {
/// Completer for the future returned by the take call.
final _completer = Completer<List<T>>();
/// List collecting events until enough have been seen.
final _list = <T>[];
/// Number of events to capture.
///
/// The request [isComplete] when the length of [_list] reaches
/// this value.
final int _eventsToTake;
_ListRequest(this._eventsToTake);
/// The future completed when the correct number of events have been captured.
Future<List<T>> get future => _completer.future;
}
/// Request for a [StreamQueue.take] call.
class _TakeRequest<T> extends _ListRequest<T> {
_TakeRequest(int eventsToTake) : super(eventsToTake);
@override
bool update(QueueList<Result<T>> events, bool isDone) {
while (_list.length < _eventsToTake) {
if (events.isEmpty) {
if (isDone) break;
return false;
}
var event = events.removeFirst();
if (event.isError) {
event.asError!.complete(_completer);
return true;
}
_list.add(event.asValue!.value);
}
_completer.complete(_list);
return true;
}
}
/// Request for a [StreamQueue.lookAhead] call.
class _LookAheadRequest<T> extends _ListRequest<T> {
_LookAheadRequest(int eventsToTake) : super(eventsToTake);
@override
bool update(QueueList<Result<T>> events, bool isDone) {
while (_list.length < _eventsToTake) {
if (events.length == _list.length) {
if (isDone) break;
return false;
}
var event = events.elementAt(_list.length);
if (event.isError) {
event.asError!.complete(_completer);
return true;
}
_list.add(event.asValue!.value);
}
_completer.complete(_list);
return true;
}
}
/// Request for a [StreamQueue.cancel] call.
///
/// The request needs no events, it just waits in the request queue
/// until all previous events are fulfilled, then it cancels the stream queue
/// source subscription.
class _CancelRequest<T> implements _EventRequest<T> {
/// Completer for the future returned by the `cancel` call.
final _completer = Completer<void>();
/// When the event is completed, it needs to cancel the active subscription
/// of the `StreamQueue` object, if any.
final StreamQueue _streamQueue;
_CancelRequest(this._streamQueue);
/// The future completed when the cancel request is completed.
Future get future => _completer.future;
@override
bool update(QueueList<Result<T>> events, bool isDone) {
if (_streamQueue._isDone) {
_completer.complete();
} else {
_streamQueue._ensureListening();
_completer.complete(_streamQueue._extractStream().listen(null).cancel());
}
return true;
}
}
/// Request for a [StreamQueue.rest] call.
///
/// The request is always complete, it just waits in the request queue
/// until all previous events are fulfilled, then it takes over the
/// stream events subscription and creates a stream from it.
class _RestRequest<T> implements _EventRequest<T> {
/// Completer for the stream returned by the `rest` call.
final _completer = StreamCompleter<T>();
/// The [StreamQueue] object that has this request queued.
///
/// When the event is completed, it needs to cancel the active subscription
/// of the `StreamQueue` object, if any.
final StreamQueue<T> _streamQueue;
_RestRequest(this._streamQueue);
/// The stream which will contain the remaining events of [_streamQueue].
Stream<T> get stream => _completer.stream;
@override
bool update(QueueList<Result<T>> events, bool isDone) {
if (events.isEmpty) {
if (_streamQueue._isDone) {
_completer.setEmpty();
} else {
_completer.setSourceStream(_streamQueue._extractStream());
}
} else {
// There are prefetched events which needs to be added before the
// remaining stream.
var controller = StreamController<T>();
for (var event in events) {
event.addTo(controller);
}
controller
.addStream(_streamQueue._extractStream(), cancelOnError: false)
.whenComplete(controller.close);
_completer.setSourceStream(controller.stream);
}
return true;
}
}
/// Request for a [StreamQueue.hasNext] call.
///
/// Completes the [future] with `true` if it sees any event,
/// but doesn't consume the event.
/// If the request is closed without seeing an event, then
/// the [future] is completed with `false`.
class _HasNextRequest<T> implements _EventRequest<T> {
final _completer = Completer<bool>();
Future<bool> get future => _completer.future;
@override
bool update(QueueList<Result<T>> events, bool isDone) {
if (events.isNotEmpty) {
_completer.complete(true);
return true;
}
if (isDone) {
_completer.complete(false);
return true;
}
return false;
}
}
/// Request for a [StreamQueue.startTransaction] call.
///
/// This request isn't complete until the user calls
/// [StreamQueueTransaction.commit] or [StreamQueueTransaction.reject], at which
/// point it manually removes itself from the request queue and calls
/// [StreamQueue._updateRequests].
class _TransactionRequest<T> implements _EventRequest<T> {
/// The transaction created by this request.
late final StreamQueueTransaction<T> transaction;
/// The controller that passes events to [transaction].
final _controller = StreamController<T>(sync: true);
/// The number of events passed to [_controller] so far.
var _eventsSent = 0;
_TransactionRequest(StreamQueue<T> parent) {
transaction = StreamQueueTransaction._(parent, _controller.stream);
}
@override
bool update(QueueList<Result<T>> events, bool isDone) {
while (_eventsSent < events.length) {
events[_eventsSent++].addTo(_controller);
}
if (isDone && !_controller.isClosed) _controller.close();
return transaction._committed || transaction._rejected;
}
}