refactor(ext/fetch): refactor fetch to use new write_error method (#20029)

This is a prerequisite for fast streams work -- this particular resource
used a custom `mpsc`-style stream, and this work will allow us to unify
it with the streams in `ext/http` in time.

Instead of using Option as an internal semaphore for "correctly
completed EOF", we allow code to propagate errors into the channel which
can be picked up by downstream sinks like Hyper. EOF is signalled using
a more standard sender drop.

1 files changed, 45 insertions, 28 deletions

diff --git a/ext/fetch/lib.rs b/ext/fetch/lib.rs
index 48f6a0294..b2b71ec56 100644
--- a/ext/fetch/lib.rs
+++ b/ext/fetch/lib.rs
@@ -1,6 +1,5 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
 
-mod byte_stream;
 mod fs_fetch_handler;
 
 use std::borrow::Cow;
@@ -13,10 +12,12 @@ use std::pin::Pin;
 use std::rc::Rc;
 use std::sync::Arc;
 
+use deno_core::anyhow::Error;
 use deno_core::error::type_error;
 use deno_core::error::AnyError;
 use deno_core::futures::stream::Peekable;
 use deno_core::futures::Future;
+use deno_core::futures::FutureExt;
 use deno_core::futures::Stream;
 use deno_core::futures::StreamExt;
 use deno_core::op;
@@ -69,8 +70,6 @@ pub use reqwest;
 
 pub use fs_fetch_handler::FsFetchHandler;
 
-pub use crate::byte_stream::MpscByteStream;
-
 #[derive(Clone)]
 pub struct Options {
   pub user_agent: String,
@@ -293,7 +292,7 @@ where
         match data {
           None => {
             // If no body is passed, we return a writer for streaming the body.
-            let (stream, tx) = MpscByteStream::new();
+            let (tx, stream) = tokio::sync::mpsc::channel(1);
 
             // If the size of the body is known, we include a content-length
             // header explicitly.
@@ -302,11 +301,11 @@ where
                 request.header(CONTENT_LENGTH, HeaderValue::from(body_size))
             }
 
-            request = request.body(Body::wrap_stream(stream));
+            request = request.body(Body::wrap_stream(FetchBodyStream(stream)));
 
             let request_body_rid =
               state.resource_table.add(FetchRequestBodyResource {
-                body: AsyncRefCell::new(tx),
+                body: AsyncRefCell::new(Some(tx)),
                 cancel: CancelHandle::default(),
               });
 
@@ -604,8 +603,21 @@ impl Resource for FetchCancelHandle {
   }
 }
 
+/// Wraps a [`mpsc::Receiver`] in a [`Stream`] that can be used as a Hyper [`Body`].
+pub struct FetchBodyStream(pub mpsc::Receiver<Result<bytes::Bytes, Error>>);
+
+impl Stream for FetchBodyStream {
+  type Item = Result<bytes::Bytes, Error>;
+  fn poll_next(
+    mut self: Pin<&mut Self>,
+    cx: &mut std::task::Context<'_>,
+  ) -> std::task::Poll<Option<Self::Item>> {
+    self.0.poll_recv(cx)
+  }
+}
+
 pub struct FetchRequestBodyResource {
-  pub body: AsyncRefCell<mpsc::Sender<Option<bytes::Bytes>>>,
+  pub body: AsyncRefCell<Option<mpsc::Sender<Result<bytes::Bytes, Error>>>>,
   pub cancel: CancelHandle,
 }
 
@@ -619,38 +631,43 @@ impl Resource for FetchRequestBodyResource {
       let bytes: bytes::Bytes = buf.into();
       let nwritten = bytes.len();
       let body = RcRef::map(&self, |r| &r.body).borrow_mut().await;
+      let body = (*body).as_ref();
       let cancel = RcRef::map(self, |r| &r.cancel);
-      body
-        .send(Some(bytes))
-        .or_cancel(cancel)
-        .await?
-        .map_err(|_| {
-          type_error("request body receiver not connected (request closed)")
-        })?;
+      let body = body.ok_or(type_error(
+        "request body receiver not connected (request closed)",
+      ))?;
+      body.send(Ok(bytes)).or_cancel(cancel).await?.map_err(|_| {
+        type_error("request body receiver not connected (request closed)")
+      })?;
       Ok(WriteOutcome::Full { nwritten })
     })
   }
 
-  fn shutdown(self: Rc<Self>) -> AsyncResult<()> {
-    Box::pin(async move {
+  fn write_error(self: Rc<Self>, error: Error) -> AsyncResult<()> {
+    async move {
       let body = RcRef::map(&self, |r| &r.body).borrow_mut().await;
+      let body = (*body).as_ref();
       let cancel = RcRef::map(self, |r| &r.cancel);
-      // There is a case where hyper knows the size of the response body up
-      // front (through content-length header on the resp), where it will drop
-      // the body once that content length has been reached, regardless of if
-      // the stream is complete or not. This is expected behaviour, but it means
-      // that if you stream a body with an up front known size (eg a Blob),
-      // explicit shutdown can never succeed because the body (and by extension
-      // the receiver) will have dropped by the time we try to shutdown. As such
-      // we ignore if the receiver is closed, because we know that the request
-      // is complete in good health in that case.
-      body.send(None).or_cancel(cancel).await?.ok();
+      let body = body.ok_or(type_error(
+        "request body receiver not connected (request closed)",
+      ))?;
+      body.send(Err(error)).or_cancel(cancel).await??;
       Ok(())
-    })
+    }
+    .boxed_local()
+  }
+
+  fn shutdown(self: Rc<Self>) -> AsyncResult<()> {
+    async move {
+      let mut body = RcRef::map(&self, |r| &r.body).borrow_mut().await;
+      body.take();
+      Ok(())
+    }
+    .boxed_local()
   }
 
   fn close(self: Rc<Self>) {
-    self.cancel.cancel()
+    self.cancel.cancel();
   }
 }