Fix flakey SSH connection (#19439)

Fixes a bug due to the `select!` macro tossing futures that had
partially read messages, causing us to desync our message reading with
the input stream.

Release Notes:

- N/A

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: conrad <conrad@zed.dev>

crates/remote/src/protocol.rs

@@ -2,7 +2,6 @@ use anyhow::Result;
 use futures::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
 use prost::Message as _;
 use rpc::proto::Envelope;
-use std::mem::size_of;
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct MessageId(pub u32);
@@ -30,8 +29,10 @@ pub async fn read_message<S: AsyncRead + Unpin>(
 ) -> Result<Envelope> {
     buffer.resize(MESSAGE_LEN_SIZE, 0);
     stream.read_exact(buffer).await?;
+
     let len = message_len_from_buffer(buffer);
-    read_message_with_len(stream, buffer, len).await
+    let result = read_message_with_len(stream, buffer, len).await;
+    result
 }
 
 pub async fn write_message<S: AsyncWrite + Unpin>(

crates/remote/src/ssh_session.rs

@@ -13,8 +13,7 @@ use futures::{
         oneshot,
     },
     future::BoxFuture,
-    select_biased, AsyncReadExt as _, AsyncWriteExt as _, Future, FutureExt as _, SinkExt,
-    StreamExt as _,
+    select_biased, AsyncReadExt as _, Future, FutureExt as _, SinkExt, StreamExt as _,
 };
 use gpui::{
     AppContext, AsyncAppContext, Context, EventEmitter, Model, ModelContext, SemanticVersion, Task,
@@ -922,64 +921,57 @@ impl SshRemoteClient {
         let mut child_stdout = ssh_proxy_process.stdout.take().unwrap();
         let mut child_stdin = ssh_proxy_process.stdin.take().unwrap();
 
-        let io_task = cx.background_executor().spawn(async move {
         let mut stdin_buffer = Vec::new();
         let mut stdout_buffer = Vec::new();
         let mut stderr_buffer = Vec::new();
         let mut stderr_offset = 0;
 
-            loop {
-                stdout_buffer.resize(MESSAGE_LEN_SIZE, 0);
-                stderr_buffer.resize(stderr_offset + 1024, 0);
-
-                select_biased! {
-                    outgoing = outgoing_rx.next().fuse() => {
-                        let Some(outgoing) = outgoing else {
-                            return anyhow::Ok(None);
-                        };
-
+        let stdin_task = cx.background_executor().spawn(async move {
+            while let Some(outgoing) = outgoing_rx.next().await {
                 write_message(&mut child_stdin, &mut stdin_buffer, outgoing).await?;
             }
+            anyhow::Ok(())
+        });
 
-                    result = child_stdout.read(&mut stdout_buffer).fuse() => {
-                        match result {
-                            Ok(0) => {
-                                child_stdin.close().await?;
-                                outgoing_rx.close();
-                                let status = ssh_proxy_process.status().await?;
-                                // If we don't have a code, we assume process
-                                // has been killed and treat it as non-zero exit
-                                // code
-                                return Ok(status.code().or_else(|| Some(1)));
+        let stdout_task = cx.background_executor().spawn({
+            let mut connection_activity_tx = connection_activity_tx.clone();
+            async move {
+                loop {
+                    stdout_buffer.resize(MESSAGE_LEN_SIZE, 0);
+                    let len = child_stdout.read(&mut stdout_buffer).await?;
+
+                    if len == 0 {
+                        return anyhow::Ok(());
                     }
-                            Ok(len) => {
-                                if len < stdout_buffer.len() {
+
+                    if len < MESSAGE_LEN_SIZE {
                         child_stdout.read_exact(&mut stdout_buffer[len..]).await?;
                     }
 
                     let message_len = message_len_from_buffer(&stdout_buffer);
-                                match read_message_with_len(&mut child_stdout, &mut stdout_buffer, message_len).await {
-                                    Ok(envelope) => {
+                    let envelope =
+                        read_message_with_len(&mut child_stdout, &mut stdout_buffer, message_len)
+                            .await?;
                     connection_activity_tx.try_send(()).ok();
                     incoming_tx.unbounded_send(envelope).ok();
                 }
-                                    Err(error) => {
-                                        log::error!("error decoding message {error:?}");
-                                    }
-                                }
-                            }
-                            Err(error) => {
-                                Err(anyhow!("error reading stdout: {error:?}"))?;
-                            }
-                        }
             }
+        });
+
+        let stderr_task: Task<anyhow::Result<()>> = cx.background_executor().spawn(async move {
+            loop {
+                stderr_buffer.resize(stderr_offset + 1024, 0);
+
+                let len = child_stderr
+                    .read(&mut stderr_buffer[stderr_offset..])
+                    .await?;
 
-                    result = child_stderr.read(&mut stderr_buffer[stderr_offset..]).fuse() => {
-                        match result {
-                            Ok(len) => {
                 stderr_offset += len;
                 let mut start_ix = 0;
-                                while let Some(ix) = stderr_buffer[start_ix..stderr_offset].iter().position(|b| b == &b'\n') {
+                while let Some(ix) = stderr_buffer[start_ix..stderr_offset]
+                    .iter()
+                    .position(|b| b == &b'\n')
+                {
                     let line_ix = start_ix + ix;
                     let content = &stderr_buffer[start_ix..line_ix];
                     start_ix = line_ix + 1;
@@ -994,20 +986,25 @@ impl SshRemoteClient {
 
                 connection_activity_tx.try_send(()).ok();
             }
-                            Err(error) => {
-                                Err(anyhow!("error reading stderr: {error:?}"))?;
-                            }
-                        }
-                    }
-                }
-            }
         });
 
         cx.spawn(|mut cx| async move {
-            let result = io_task.await;
+            let result = futures::select! {
+                result = stdin_task.fuse() => {
+                    result.context("stdin")
+                }
+                result = stdout_task.fuse() => {
+                    result.context("stdout")
+                }
+                result = stderr_task.fuse() => {
+                    result.context("stderr")
+                }
+            };
 
             match result {
-                Ok(Some(exit_code)) => {
+                Ok(_) => {
+                    let exit_code = ssh_proxy_process.status().await?.code().unwrap_or(1);
+
                     if let Some(error) = ProxyLaunchError::from_exit_code(exit_code) {
                         match error {
                             ProxyLaunchError::ServerNotRunning => {
@@ -1025,7 +1022,6 @@ impl SshRemoteClient {
                         })?;
                     }
                 }
-                Ok(None) => {}
                 Err(error) => {
                     log::warn!("ssh io task died with error: {:?}. reconnecting...", error);
                     this.update(&mut cx, |this, cx| {
@@ -1033,6 +1029,7 @@ impl SshRemoteClient {
                     })?;
                 }
             }
+
             Ok(())
         })
     }
@@ -1206,6 +1203,7 @@ impl SshRemoteConnection {
         delegate: Arc<dyn SshClientDelegate>,
         cx: &mut AsyncAppContext,
     ) -> Result<Self> {
+        use futures::AsyncWriteExt as _;
         use futures::{io::BufReader, AsyncBufReadExt as _};
         use smol::{fs::unix::PermissionsExt as _, net::unix::UnixListener};
         use util::ResultExt as _;

crates/remote_server/src/unix.rs

@@ -12,6 +12,7 @@ use language::LanguageRegistry;
 use node_runtime::{NodeBinaryOptions, NodeRuntime};
 use paths::logs_dir;
 use project::project_settings::ProjectSettings;
+
 use remote::proxy::ProxyLaunchError;
 use remote::ssh_session::ChannelClient;
 use remote::{
@@ -213,19 +214,27 @@ fn start_server(
 
             let mut input_buffer = Vec::new();
             let mut output_buffer = Vec::new();
+
+            let (mut stdin_msg_tx, mut stdin_msg_rx) = mpsc::unbounded::<Envelope>();
+            cx.background_executor().spawn(async move {
+                while let Ok(msg) = read_message(&mut stdin_stream, &mut input_buffer).await {
+                    if let Err(_) = stdin_msg_tx.send(msg).await {
+                        break;
+                    }
+                }
+            }).detach();
+
             loop {
+
                 select_biased! {
                     _ = app_quit_rx.next().fuse() => {
                         return anyhow::Ok(());
                     }
 
-                    stdin_message = read_message(&mut stdin_stream, &mut input_buffer).fuse() => {
-                        let message = match stdin_message {
-                            Ok(message) => message,
-                            Err(error) => {
-                                log::warn!("error reading message on stdin: {}. exiting.", error);
+                    stdin_message = stdin_msg_rx.next().fuse() => {
+                        let Some(message) = stdin_message else {
+                            log::warn!("error reading message on stdin. exiting.");
                             break;
-                            }
                         };
                         if let Err(error) = incoming_tx.unbounded_send(message) {
                             log::error!("failed to send message to application: {:?}. exiting.", error);