Use a ReusableBoxFuture to store ReceiverStream

crates/rdsys-backend/Cargo.toml

@@ -14,3 +14,4 @@ tokio = { version = "1", features = ["macros"]}
 reqwest = { version = "0.11", features = ["stream"]}
 tokio-stream = "0.1.12"
 futures = "0.3.27"
+tokio-util = "0.7.7"

crates/rdsys-backend/src/lib.rs

@@ -5,12 +5,13 @@
 
 use bytes::{self, Buf, Bytes};
 use core::pin::Pin;
-use core::task::Poll;
+use core::task::{Poll, ready};
 use futures_util::{Stream, StreamExt};
 use reqwest::Client;
 use std::io::{self, BufRead};
 use tokio::sync::mpsc;
 use tokio_stream::wrappers::ReceiverStream;
+use tokio_util::sync::ReusableBoxFuture;
 
 pub mod proto;
 
@@ -42,7 +43,7 @@ impl From<io::Error> for Error {
 /// An iterable wrapper of ResourceDiff items for the streamed chunks of Bytes
 /// received from the connection to the rdsys backend
 pub struct ResourceStream {
-    rx: ReceiverStream<Bytes>,
+    inner: ReusableBoxFuture<'static, (Option<Bytes>, ReceiverStream<Bytes>)>,
     buf: Vec<u8>,
     partial: Option<bytes::buf::Reader<Bytes>>,
 }
@@ -50,13 +51,18 @@ pub struct ResourceStream {
 impl ResourceStream {
     pub fn new(rx: mpsc::Receiver<Bytes>) -> ResourceStream {
         ResourceStream {
-            rx: ReceiverStream::new(rx),
+            inner: ReusableBoxFuture::new(make_future(ReceiverStream::new(rx))),
             buf: vec![],
             partial: None,
         }
     }
 }
 
+async fn make_future(mut rx: ReceiverStream<Bytes>) -> (Option<Bytes>, ReceiverStream<Bytes>) {
+    let result = rx.next().await;
+    (result, rx)
+}
+
 impl Stream for ResourceStream {
     type Item = proto::ResourceDiff;
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut core::task::Context) -> Poll<Option<Self::Item>> {
@@ -92,8 +98,12 @@ impl Stream for ResourceStream {
             }
         }
         self.buf = buf;
-        match Pin::new(&mut self.rx).poll_next(cx) {
+        println!("HERE");
-            Poll::Ready(Some(chunk)) => {
+        let (result, rx) = ready!(self.inner.poll(cx));
+        println!("HERE2");
+        self.inner.set(make_future(rx));
+        match result {
+            Some(chunk) => {
                 let mut buffer = chunk.reader();
                 match parse(&mut buffer, &mut self.buf) {
                     Ok(Some(diff)) => {
@@ -104,8 +114,7 @@ impl Stream for ResourceStream {
                     Err(_) => return Poll::Ready(None),
                 }
             }
-            Poll::Ready(None) => Poll::Ready(None),
+            None => Poll::Ready(None),
-            Poll::Pending => Poll::Pending,
         }
     }
 }