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7.11 kB
| use std::{ | |
| fmt, | |
| pin::Pin, | |
| sync::{Arc, Mutex}, | |
| task::{Context as TaskContext, Poll}, | |
| }; | |
| use anyhow::Result; | |
| use futures::{Stream as StreamTrait, StreamExt, TryStreamExt}; | |
| use serde::{Deserialize, Deserializer, Serialize, Serializer}; | |
| /// Streams allow for streaming values from source to sink. | |
| /// | |
| /// A Stream implements both a reader (which implements the Stream trait), and a | |
| /// writer (which can be sent to another thread). As new values are written, any | |
| /// pending readers will be woken up to receive the new value. | |
| pub struct Stream<T: Clone + Send> { | |
| inner: Arc<Mutex<StreamState<T>>>, | |
| } | |
| /// The StreamState actually holds the data of a Stream. | |
| struct StreamState<T> { | |
| source: Option<Pin<Box<dyn StreamTrait<Item = T> + Send>>>, | |
| pulled: Vec<T>, | |
| } | |
| impl<T: Clone + Send> Stream<T> { | |
| /// Constructs a new Stream, and immediately closes it with only the passed | |
| /// values. | |
| pub fn new_closed(pulled: Vec<T>) -> Self { | |
| Self { | |
| inner: Arc::new(Mutex::new(StreamState { | |
| source: None, | |
| pulled, | |
| })), | |
| } | |
| } | |
| /// Creates a new Stream, which will lazily pull from the source stream. | |
| pub fn new_open( | |
| pulled: Vec<T>, | |
| source: Box<dyn StreamTrait<Item = T> + Send + 'static>, | |
| ) -> Self { | |
| Self { | |
| inner: Arc::new(Mutex::new(StreamState { | |
| source: Some(Box::into_pin(source)), | |
| pulled, | |
| })), | |
| } | |
| } | |
| /// Returns a [StreamTrait] implementation to poll values out of our Stream. | |
| pub fn read(&self) -> StreamRead<T> { | |
| StreamRead { | |
| source: self.clone(), | |
| index: 0, | |
| } | |
| } | |
| pub async fn into_single(&self) -> SingleValue<T> { | |
| let mut stream = self.read(); | |
| let Some(first) = stream.next().await else { | |
| return SingleValue::None; | |
| }; | |
| if stream.next().await.is_some() { | |
| return SingleValue::Multiple; | |
| } | |
| SingleValue::Single(first) | |
| } | |
| } | |
| impl<T: Clone + Send, E: Clone + Send> Stream<Result<T, E>> { | |
| /// Converts a TryStream into a single value when possible. | |
| pub async fn try_into_single(&self) -> Result<SingleValue<T>, E> { | |
| let mut stream = self.read(); | |
| let Some(first) = stream.try_next().await? else { | |
| return Ok(SingleValue::None); | |
| }; | |
| if stream.try_next().await?.is_some() { | |
| return Ok(SingleValue::Multiple); | |
| } | |
| Ok(SingleValue::Single(first)) | |
| } | |
| } | |
| pub enum SingleValue<T> { | |
| /// The Stream did not hold a value. | |
| None, | |
| /// The Stream held multiple values. | |
| Multiple, | |
| /// The held only a single value. | |
| Single(T), | |
| } | |
| impl<T: fmt::Debug> fmt::Debug for SingleValue<T> { | |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
| match self { | |
| SingleValue::None => f.debug_struct("SingleValue::None").finish(), | |
| SingleValue::Multiple => f.debug_struct("SingleValue::Multiple").finish(), | |
| SingleValue::Single(v) => f.debug_tuple("SingleValue::Single").field(v).finish(), | |
| } | |
| } | |
| } | |
| impl<T: Clone + Send, S: StreamTrait<Item = T> + Send + Unpin + 'static> From<S> for Stream<T> { | |
| fn from(source: S) -> Self { | |
| Self::new_open(vec![], Box::new(source)) | |
| } | |
| } | |
| impl<T: Clone + Send> Default for Stream<T> { | |
| fn default() -> Self { | |
| Self::new_closed(vec![]) | |
| } | |
| } | |
| impl<T: Clone + PartialEq + Send> PartialEq for Stream<T> { | |
| // A Stream is equal if it's the same internal pointer, or both streams are | |
| // closed with equivalent values. | |
| fn eq(&self, other: &Self) -> bool { | |
| Arc::ptr_eq(&self.inner, &other.inner) || { | |
| let left = self.inner.lock().unwrap(); | |
| let right = other.inner.lock().unwrap(); | |
| match (&*left, &*right) { | |
| ( | |
| StreamState { | |
| pulled: a, | |
| source: None, | |
| }, | |
| StreamState { | |
| pulled: b, | |
| source: None, | |
| }, | |
| ) => a == b, | |
| _ => false, | |
| } | |
| } | |
| } | |
| } | |
| impl<T: Clone + Eq + Send> Eq for Stream<T> {} | |
| impl<T: Clone + Serialize + Send> Serialize for Stream<T> { | |
| fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> { | |
| use serde::ser::Error; | |
| let lock = self.inner.lock().map_err(Error::custom)?; | |
| match &*lock { | |
| StreamState { | |
| pulled, | |
| source: None, | |
| } => pulled.serialize(serializer), | |
| _ => Err(Error::custom("cannot serialize open stream")), | |
| } | |
| } | |
| } | |
| impl<'de, T: Clone + Send + Deserialize<'de>> Deserialize<'de> for Stream<T> { | |
| fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> { | |
| let data = <Vec<T>>::deserialize(deserializer)?; | |
| Ok(Stream::new_closed(data)) | |
| } | |
| } | |
| impl<T: Clone + fmt::Debug> fmt::Debug for StreamState<T> { | |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
| f.debug_struct("StreamState") | |
| .field("pulled", &self.pulled) | |
| .finish() | |
| } | |
| } | |
| /// Implements [StreamTrait] over our Stream. | |
| pub struct StreamRead<T: Clone + Send> { | |
| index: usize, | |
| source: Stream<T>, | |
| } | |
| impl<T: Clone + Send> StreamTrait for StreamRead<T> { | |
| type Item = T; | |
| fn poll_next(self: Pin<&mut Self>, cx: &mut TaskContext<'_>) -> Poll<Option<Self::Item>> { | |
| let this = self.get_mut(); | |
| let index = this.index; | |
| let mut inner = this.source.inner.lock().unwrap(); | |
| if let Some(v) = inner.pulled.get(index) { | |
| // If the current reader can be satisfied by a value we've already pulled, then | |
| // just do that. | |
| this.index += 1; | |
| return Poll::Ready(Some(v.clone())); | |
| }; | |
| let Some(source) = &mut inner.source else { | |
| // If the source has been closed, there's nothing left to pull. | |
| return Poll::Ready(None); | |
| }; | |
| match source.poll_next_unpin(cx) { | |
| // If the source stream is ready to give us a new value, we can immediately store that | |
| // and return it to the caller. Any other readers will be able to read the value from | |
| // the already-pulled data. | |
| Poll::Ready(Some(v)) => { | |
| this.index += 1; | |
| inner.pulled.push(v.clone()); | |
| Poll::Ready(Some(v)) | |
| } | |
| // If the source stream is finished, then we can transition to the closed state | |
| // to drop the source stream. | |
| Poll::Ready(None) => { | |
| inner.source.take(); | |
| Poll::Ready(None) | |
| } | |
| // Else, we need to wait for the source stream to give us a new value. The | |
| // source stream will be responsible for waking the TaskContext. | |
| Poll::Pending => Poll::Pending, | |
| } | |
| } | |
| } | |