ssh remoting: Treat closed stderr as error (#19289)

Before this change we had a race condition bug: if stderr was closed
before the other two sockets, we wouldn't properly detect when the
server died, and not report or retry anything.

That's because we treated a closed stderr as a non-error.

Technically, it isn't an error (closing a connection is okay!), but
until we have a proper shutdown ceremony between all three processes, we
can treat it as an error, because that lets us to detect when the server
is gone.

On the client-side, we also always react to these errors by
reconnecting. Except when we shutdown: there we do a proper shutdown and
won't error on the proxy exit code.

So, this works, even if I wish there was a better way for the server to
communicate to the proxy that it shutdown properly. But I don't want a
fourth socket.

Release Notes:

- N/A

crates/remote_server/src/unix.rs

@@ -186,7 +186,6 @@ fn start_server(
             log::info!("accepting new connections");
             let result = select! {
                 streams = streams.fuse() => {
-                    log::warn!("stdin {:?}, stdout: {:?}, stderr: {:?}", streams.0, streams.1, streams.2);
                     let (Some(Ok(stdin_stream)), Some(Ok(stdout_stream)), Some(Ok(stderr_stream))) = streams else {
                         break;
                     };
@@ -211,8 +210,6 @@ fn start_server(
                 break;
             };
 
-            log::info!("yep! we got connections");
-
             let mut input_buffer = Vec::new();
             let mut output_buffer = Vec::new();
             loop {
@@ -253,7 +250,6 @@ fn start_server(
                         }
                     }
 
-                    // // TODO: How do we handle backpressure?
                     log_message = log_rx.next().fuse() => {
                         if let Some(log_message) = log_message {
                             if let Err(error) = stderr_stream.write_all(&log_message).await {
@@ -316,7 +312,7 @@ pub fn execute_run(
 
     let listeners = ServerListeners::new(stdin_socket, stdout_socket, stderr_socket)?;
 
-    log::debug!("starting gpui app");
+    log::info!("starting headless gpui app");
     gpui::App::headless().run(move |cx| {
         settings::init(cx);
         HeadlessProject::init(cx);
@@ -404,7 +400,7 @@ pub fn execute_proxy(identifier: String, is_reconnecting: bool) -> Result<()> {
     init_logging_proxy();
     init_panic_hook();
 
-    log::debug!("starting up. PID: {}", std::process::id());
+    log::info!("starting proxy process. PID: {}", std::process::id());
 
     let server_paths = ServerPaths::new(&identifier)?;
 
@@ -417,7 +413,7 @@ pub fn execute_proxy(identifier: String, is_reconnecting: bool) -> Result<()> {
         }
     } else {
         if let Some(pid) = server_pid {
-            log::debug!("found server already running with PID {}. Killing process and cleaning up files...", pid);
+            log::info!("proxy found server already running with PID {}. Killing process and cleaning up files...", pid);
             kill_running_server(pid, &server_paths)?;
         }
 
@@ -443,7 +439,9 @@ pub fn execute_proxy(identifier: String, is_reconnecting: bool) -> Result<()> {
         loop {
             match stream.read(&mut stderr_buffer).await {
                 Ok(0) => {
-                    return anyhow::Ok(());
+                    let error =
+                        std::io::Error::new(std::io::ErrorKind::UnexpectedEof, "stderr closed");
+                    Err(anyhow!(error))?;
                 }
                 Ok(n) => {
                     stderr.write_all(&mut stderr_buffer[..n]).await?;
@@ -463,6 +461,12 @@ pub fn execute_proxy(identifier: String, is_reconnecting: bool) -> Result<()> {
             result = stderr_task.fuse() => result,
         }
     }) {
+        if let Some(error) = forwarding_result.downcast_ref::<std::io::Error>() {
+            if error.kind() == std::io::ErrorKind::UnexpectedEof {
+                log::error!("connection to server closed due to unexpected EOF");
+                return Err(anyhow!("connection to server closed"));
+            }
+        }
         log::error!(
             "failed to forward messages: {:?}, terminating...",
             forwarding_result
@@ -518,7 +522,10 @@ fn spawn_server(paths: &ServerPaths) -> Result<()> {
         .arg(&paths.stderr_socket)
         .spawn()?;
 
-    log::debug!("server started. PID: {:?}", server_process.id());
+    log::info!(
+        "proxy spawned server process. PID: {:?}",
+        server_process.id()
+    );
 
     let mut total_time_waited = std::time::Duration::from_secs(0);
     let wait_duration = std::time::Duration::from_millis(20);