Use a channel to read stdout

crates/puffin-build/src/daemon.rs

@@ -7,6 +7,7 @@ use tokio::fs::File;
 use tokio::io::{self, BufReader};
 use tokio::io::{AsyncWriteExt, Lines};
 use tokio::process::{Child, ChildStdin, ChildStdout, Command};
+use tokio::sync::mpsc::{Receiver, Sender};
 use tracing::{debug, error};
 
 use crate::{BuildKind, Pep517Backend};
@@ -126,9 +127,23 @@ impl HookErrorKind {
         }
     }
 }
+
+async fn read_stdout_into_channel(
+    mut lines: Lines<BufReader<ChildStdout>>,
+    sender: Sender<String>,
+) -> () {
+    // We do not handle any errors here. If there's an IO error or the receiver is dropped,
+    // we will just exit. The receiver will report the daemon as closed if it attempts to
+    // read after this channel exits.
+    while let Ok(Some(line)) = lines.next_line().await {
+        if let Err(_) = sender.send(line).await {
+            return;
+        }
+    }
+}
 #[derive(Debug)]
 struct DaemonIO {
-    stdout: Lines<BufReader<ChildStdout>>,
+    stdout: Receiver<String>,
     stdin: ChildStdin,
     handle: Child,
 }
@@ -143,8 +158,14 @@ impl DaemonIO {
         // Take standard input
         let stdin = handle.stdin.take().expect("stdin is available");
 
+        // Create a channel to read standard output continuously
+        let (sender, receiver) = tokio::sync::mpsc::channel(20);
+
+        // We let this handle drop, as we don't care about its result
+        tokio::spawn(read_stdout_into_channel(stdout, sender));
+
         Self {
-            stdout,
+            stdout: receiver,
             stdin,
             handle,
         }
@@ -159,6 +180,11 @@ impl DaemonIO {
         self.stdin.flush().await?;
         Ok(())
     }
+
+    async fn recv(&mut self) -> Option<String> {
+        self.stdout.recv().await
+    }
+
     async fn close(mut self) -> Result<Option<Output>, DaemonError> {
         if !self.exited()? {
             // Send a shutdown command if it's not closed yet
@@ -195,7 +221,6 @@ impl Pep517Daemon {
 
     /// Ensure the daemon is started and ready.
     /// If the daemon is not started, [`Self::start`] will be called.
-    ///
     async fn ensure_started(&mut self) -> Result<&mut DaemonIO, DaemonError> {
         let started = {
             if let Some(io) = self.io.as_mut() {
@@ -250,11 +275,14 @@ impl Pep517Daemon {
 
     /// Reads a single response from the daemon.
     async fn receive_one(&mut self) -> Result<DaemonResponse, DaemonError> {
-        let stdout = &mut self.io.as_mut().unwrap().stdout;
-        if let Some(line) = stdout.next_line().await? {
-            Ok(DaemonResponse::try_from_str(line.as_str())?)
+        if let Some(io) = self.io.as_mut() {
+            if let Some(line) = io.recv().await {
+                Ok(DaemonResponse::try_from_str(line.as_str())?)
+            } else {
+                self.close().await?;
+                Err(DaemonError::Closed)
+            }
         } else {
-            self.close().await?;
             Err(DaemonError::Closed)
         }
     }
@@ -292,7 +320,7 @@ impl Pep517Daemon {
         hook_name: &str,
         mut args: Vec<&str>,
     ) -> Result<String, DaemonError> {
-        let mut io = self.ensure_started().await?;
+        let io = self.ensure_started().await?;
 
         // Always send run and the backend name
         let mut commands = vec!["run", backend.backend.as_str()];
@@ -434,7 +462,7 @@ impl Pep517Daemon {
         // If there's an error on close, we should raise that instead of complaining it was never called
         self.closed = true;
 
-        if let Some(mut io) = self.io.take() {
+        if let Some(io) = self.io.take() {
             io.close().await
         } else {
             Ok(None)

crates/puffin-build/src/lib.rs

@@ -366,7 +366,6 @@ impl SourceBuild {
         if let Some(pep517_backend) = &pep517_backend {
             if pep517_backend != &default_backend {
                 let environment = create_pep517_build_environment(
-                    &source_tree,
                     &venv,
                     pep517_backend,
                     &mut pep517_daemon,
@@ -537,12 +536,11 @@ impl SourceBuildTrait for SourceBuild {
 }
 /// Not a method because we call it before the builder is completely initialized
 async fn create_pep517_build_environment(
-    source_tree: &Path,
     venv: &Virtualenv,
     pep517_backend: &Pep517Backend,
     pep517_daemon: &mut Pep517Daemon,
     build_context: &impl BuildContext,
-    package_id: &str,
+    _package_id: &str,
     build_kind: BuildKind,
 ) -> Result<(), Error> {
     let extra_requires = pep517_daemon