SSH reconnect reliability (#19398)

Release Notes:

- SSH Remoting: Fix message reliability across restarts

---------

Co-authored-by: Nathan <nathan@zed.dev>

Cargo.lock

@@ -9119,6 +9119,7 @@ name = "remote"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "async-trait",
  "collections",
  "fs",
  "futures 0.3.30",

crates/collab/src/tests/remote_editing_collaboration_tests.rs

@@ -26,7 +26,7 @@ async fn test_sharing_an_ssh_remote_project(
         .await;
 
     // Set up project on remote FS
-    let (client_ssh, server_ssh) = SshRemoteClient::fake(cx_a, server_cx);
+    let (forwarder, server_ssh) = SshRemoteClient::fake_server(server_cx);
     let remote_fs = FakeFs::new(server_cx.executor());
     remote_fs
         .insert_tree(
@@ -67,6 +67,7 @@ async fn test_sharing_an_ssh_remote_project(
         )
     });
 
+    let client_ssh = SshRemoteClient::fake_client(forwarder, cx_a).await;
     let (project_a, worktree_id) = client_a
         .build_ssh_project("/code/project1", client_ssh, cx_a)
         .await;

crates/project/src/project.rs

@@ -1243,6 +1243,10 @@ impl Project {
         self.client.clone()
     }
 
+    pub fn ssh_client(&self) -> Option<Model<SshRemoteClient>> {
+        self.ssh_client.clone()
+    }
+
     pub fn user_store(&self) -> Model<UserStore> {
         self.user_store.clone()
     }

crates/proto/proto/zed.proto

@@ -12,6 +12,7 @@ message Envelope {
     uint32 id = 1;
     optional uint32 responding_to = 2;
     optional PeerId original_sender_id = 3;
+    optional uint32 ack_id = 266;
 
     oneof payload {
         Hello hello = 4;
@@ -295,7 +296,9 @@ message Envelope {
         OpenServerSettings open_server_settings = 263;
 
         GetPermalinkToLine get_permalink_to_line = 264;
-        GetPermalinkToLineResponse get_permalink_to_line_response = 265;  // current max
+        GetPermalinkToLineResponse get_permalink_to_line_response = 265;
+
+        FlushBufferedMessages flush_buffered_messages = 267;
     }
 
     reserved 87 to 88;
@@ -2521,3 +2524,6 @@ message GetPermalinkToLine {
 message GetPermalinkToLineResponse {
     string permalink = 1;
 }
+
+message FlushBufferedMessages {}
+message FlushBufferedMessagesResponse {}

crates/proto/src/macros.rs

@@ -32,6 +32,7 @@ macro_rules! messages {
                         responding_to,
                         original_sender_id,
                         payload: Some(envelope::Payload::$name(self)),
+                        ack_id: None,
                     }
                 }
 

crates/proto/src/proto.rs

@@ -372,6 +372,7 @@ messages!(
     (OpenServerSettings, Foreground),
     (GetPermalinkToLine, Foreground),
     (GetPermalinkToLineResponse, Foreground),
+    (FlushBufferedMessages, Foreground),
 );
 
 request_messages!(
@@ -498,6 +499,7 @@ request_messages!(
     (RemoveWorktree, Ack),
     (OpenServerSettings, OpenBufferResponse),
     (GetPermalinkToLine, GetPermalinkToLineResponse),
+    (FlushBufferedMessages, Ack),
 );
 
 entity_messages!(

crates/remote/Cargo.toml

@@ -19,6 +19,7 @@ test-support = ["fs/test-support"]
 
 [dependencies]
 anyhow.workspace = true
+async-trait.workspace = true
 collections.workspace = true
 fs.workspace = true
 futures.workspace = true

crates/remote/src/ssh_session.rs

@@ -6,6 +6,7 @@ use crate::{
     proxy::ProxyLaunchError,
 };
 use anyhow::{anyhow, Context as _, Result};
+use async_trait::async_trait;
 use collections::HashMap;
 use futures::{
     channel::{
@@ -31,6 +32,7 @@ use smol::{
 };
 use std::{
     any::TypeId,
+    collections::VecDeque,
     ffi::OsStr,
     fmt,
     ops::ControlFlow,
@@ -276,7 +278,7 @@ async fn run_cmd(command: &mut process::Command) -> Result<String> {
     }
 }
 
-struct ChannelForwarder {
+pub struct ChannelForwarder {
     quit_tx: UnboundedSender<()>,
     forwarding_task: Task<(UnboundedSender<Envelope>, UnboundedReceiver<Envelope>)>,
 }
@@ -347,7 +349,7 @@ const MAX_RECONNECT_ATTEMPTS: usize = 3;
 enum State {
     Connecting,
     Connected {
-        ssh_connection: SshRemoteConnection,
+        ssh_connection: Box<dyn SshRemoteProcess>,
         delegate: Arc<dyn SshClientDelegate>,
         forwarder: ChannelForwarder,
 
@@ -357,7 +359,7 @@ enum State {
     HeartbeatMissed {
         missed_heartbeats: usize,
 
-        ssh_connection: SshRemoteConnection,
+        ssh_connection: Box<dyn SshRemoteProcess>,
         delegate: Arc<dyn SshClientDelegate>,
         forwarder: ChannelForwarder,
 
@@ -366,7 +368,7 @@ enum State {
     },
     Reconnecting,
     ReconnectFailed {
-        ssh_connection: SshRemoteConnection,
+        ssh_connection: Box<dyn SshRemoteProcess>,
         delegate: Arc<dyn SshClientDelegate>,
         forwarder: ChannelForwarder,
 
@@ -392,11 +394,11 @@ impl fmt::Display for State {
 }
 
 impl State {
-    fn ssh_connection(&self) -> Option<&SshRemoteConnection> {
+    fn ssh_connection(&self) -> Option<&dyn SshRemoteProcess> {
         match self {
-            Self::Connected { ssh_connection, .. } => Some(ssh_connection),
+            Self::Connected { ssh_connection, .. } => Some(ssh_connection.as_ref()),
-            Self::HeartbeatMissed { ssh_connection, .. } => Some(ssh_connection),
+            Self::HeartbeatMissed { ssh_connection, .. } => Some(ssh_connection.as_ref()),
-            Self::ReconnectFailed { ssh_connection, .. } => Some(ssh_connection),
+            Self::ReconnectFailed { ssh_connection, .. } => Some(ssh_connection.as_ref()),
             _ => None,
         }
     }
@@ -541,23 +543,19 @@ impl SshRemoteClient {
             let (proxy, proxy_incoming_tx, proxy_outgoing_rx) =
                 ChannelForwarder::new(incoming_tx, outgoing_rx, &mut cx);
 
-            let (ssh_connection, ssh_proxy_process) = Self::establish_connection(
+            let (ssh_connection, io_task) = Self::establish_connection(
                 unique_identifier,
                 false,
                 connection_options,
+                proxy_incoming_tx,
+                proxy_outgoing_rx,
+                connection_activity_tx,
                 delegate.clone(),
                 &mut cx,
             )
             .await?;
 
-            let multiplex_task = Self::multiplex(
+            let multiplex_task = Self::monitor(this.downgrade(), io_task, &cx);
-                this.downgrade(),
-                ssh_proxy_process,
-                proxy_incoming_tx,
-                proxy_outgoing_rx,
-                connection_activity_tx,
-                &mut cx,
-            );
 
             if let Err(error) = client.ping(HEARTBEAT_TIMEOUT).await {
                 log::error!("failed to establish connection: {}", error);
@@ -703,30 +701,24 @@ impl SshRemoteClient {
                 };
             }
 
-            if let Err(error) = ssh_connection.master_process.kill() {
+            if let Err(error) = ssh_connection.kill().await.context("Failed to kill ssh process") {
                 failed!(error, attempts, ssh_connection, delegate, forwarder);
             };
 
-            if let Err(error) = ssh_connection
+            let connection_options = ssh_connection.connection_options();
-                .master_process
-                .status()
-                .await
-                .context("Failed to kill ssh process")
-            {
-                failed!(error, attempts, ssh_connection, delegate, forwarder);
-            }
-
-            let connection_options = ssh_connection.socket.connection_options.clone();
 
             let (incoming_tx, outgoing_rx) = forwarder.into_channels().await;
             let (forwarder, proxy_incoming_tx, proxy_outgoing_rx) =
                 ChannelForwarder::new(incoming_tx, outgoing_rx, &mut cx);
             let (connection_activity_tx, connection_activity_rx) = mpsc::channel::<()>(1);
 
-            let (ssh_connection, ssh_process) = match Self::establish_connection(
+            let (ssh_connection, io_task) = match Self::establish_connection(
                 identifier,
                 true,
                 connection_options,
+                proxy_incoming_tx,
+                proxy_outgoing_rx,
+                connection_activity_tx,
                 delegate.clone(),
                 &mut cx,
             )
@@ -738,16 +730,9 @@ impl SshRemoteClient {
                 }
             };
 
-            let multiplex_task = Self::multiplex(
+            let multiplex_task = Self::monitor(this.clone(), io_task, &cx);
-                this.clone(),
-                ssh_process,
-                proxy_incoming_tx,
-                proxy_outgoing_rx,
-                connection_activity_tx,
-                &mut cx,
-            );
 
-            if let Err(error) = client.ping(HEARTBEAT_TIMEOUT).await {
+            if let Err(error) = client.resync(HEARTBEAT_TIMEOUT).await {
                 failed!(error, attempts, ssh_connection, delegate, forwarder);
             };
 
@@ -911,18 +896,17 @@ impl SshRemoteClient {
     }
 
     fn multiplex(
-        this: WeakModel<Self>,
         mut ssh_proxy_process: Child,
         incoming_tx: UnboundedSender<Envelope>,
         mut outgoing_rx: UnboundedReceiver<Envelope>,
         mut connection_activity_tx: Sender<()>,
         cx: &AsyncAppContext,
-    ) -> Task<Result<()>> {
+    ) -> Task<Result<Option<i32>>> {
         let mut child_stderr = ssh_proxy_process.stderr.take().unwrap();
         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 {
+        cx.background_executor().spawn(async move {
             let mut stdin_buffer = Vec::new();
             let mut stdout_buffer = Vec::new();
             let mut stderr_buffer = Vec::new();
@@ -1001,8 +985,14 @@ impl SshRemoteClient {
                     }
                 }
             }
-        });
+        })
+    }
 
+    fn monitor(
+        this: WeakModel<Self>,
+        io_task: Task<Result<Option<i32>>>,
+        cx: &AsyncAppContext,
+    ) -> Task<Result<()>> {
         cx.spawn(|mut cx| async move {
             let result = io_task.await;
 
@@ -1061,21 +1051,40 @@ impl SshRemoteClient {
         cx.notify();
     }
 
+    #[allow(clippy::too_many_arguments)]
     async fn establish_connection(
         unique_identifier: String,
         reconnect: bool,
         connection_options: SshConnectionOptions,
+        proxy_incoming_tx: UnboundedSender<Envelope>,
+        proxy_outgoing_rx: UnboundedReceiver<Envelope>,
+        connection_activity_tx: Sender<()>,
         delegate: Arc<dyn SshClientDelegate>,
         cx: &mut AsyncAppContext,
-    ) -> Result<(SshRemoteConnection, Child)> {
+    ) -> Result<(Box<dyn SshRemoteProcess>, Task<Result<Option<i32>>>)> {
+        #[cfg(any(test, feature = "test-support"))]
+        if let Some(fake) = fake::SshRemoteConnection::new(&connection_options) {
+            let io_task = fake::SshRemoteConnection::multiplex(
+                fake.connection_options(),
+                proxy_incoming_tx,
+                proxy_outgoing_rx,
+                connection_activity_tx,
+                cx,
+            )
+            .await;
+            return Ok((fake, io_task));
+        }
+
         let ssh_connection =
             SshRemoteConnection::new(connection_options, delegate.clone(), cx).await?;
 
         let platform = ssh_connection.query_platform().await?;
         let remote_binary_path = delegate.remote_server_binary_path(platform, cx)?;
-        ssh_connection
+        if !reconnect {
-            .ensure_server_binary(&delegate, &remote_binary_path, platform, cx)
+            ssh_connection
-            .await?;
+                .ensure_server_binary(&delegate, &remote_binary_path, platform, cx)
+                .await?;
+        }
 
         let socket = ssh_connection.socket.clone();
         run_cmd(socket.ssh_command(&remote_binary_path).arg("version")).await?;
@@ -1100,7 +1109,15 @@ impl SshRemoteClient {
             .spawn()
             .context("failed to spawn remote server")?;
 
-        Ok((ssh_connection, ssh_proxy_process))
+        let io_task = Self::multiplex(
+            ssh_proxy_process,
+            proxy_incoming_tx,
+            proxy_outgoing_rx,
+            connection_activity_tx,
+            &cx,
+        );
+
+        Ok((Box::new(ssh_connection), io_task))
     }
 
     pub fn subscribe_to_entity<E: 'static>(&self, remote_id: u64, entity: &Model<E>) {
@@ -1112,7 +1129,7 @@ impl SshRemoteClient {
             .lock()
             .as_ref()
             .and_then(|state| state.ssh_connection())
-            .map(|ssh_connection| ssh_connection.socket.ssh_args())
+            .map(|ssh_connection| ssh_connection.ssh_args())
     }
 
     pub fn proto_client(&self) -> AnyProtoClient {
@@ -1127,7 +1144,6 @@ impl SshRemoteClient {
         self.connection_options.clone()
     }
 
-    #[cfg(not(any(test, feature = "test-support")))]
     pub fn connection_state(&self) -> ConnectionState {
         self.state
             .lock()
@@ -1136,37 +1152,69 @@ impl SshRemoteClient {
             .unwrap_or(ConnectionState::Disconnected)
     }
 
-    #[cfg(any(test, feature = "test-support"))]
-    pub fn connection_state(&self) -> ConnectionState {
-        ConnectionState::Connected
-    }
-
     pub fn is_disconnected(&self) -> bool {
         self.connection_state() == ConnectionState::Disconnected
     }
 
     #[cfg(any(test, feature = "test-support"))]
-    pub fn fake(
+    pub fn simulate_disconnect(&self, cx: &mut AppContext) -> Task<()> {
-        client_cx: &mut gpui::TestAppContext,
+        use gpui::BorrowAppContext;
+
+        let port = self.connection_options().port.unwrap();
+
+        let disconnect =
+            cx.update_global(|c: &mut fake::GlobalConnections, _cx| c.take(port).into_channels());
+        cx.spawn(|mut cx| async move {
+            let (input_rx, output_tx) = disconnect.await;
+            let (forwarder, _, _) = ChannelForwarder::new(input_rx, output_tx, &mut cx);
+            cx.update_global(|c: &mut fake::GlobalConnections, _cx| c.replace(port, forwarder))
+                .unwrap()
+        })
+    }
+
+    #[cfg(any(test, feature = "test-support"))]
+    pub fn fake_server(
         server_cx: &mut gpui::TestAppContext,
-    ) -> (Model<Self>, Arc<ChannelClient>) {
+    ) -> (ChannelForwarder, Arc<ChannelClient>) {
-        use gpui::Context;
+        server_cx.update(|cx| {
+            let (outgoing_tx, outgoing_rx) = mpsc::unbounded::<Envelope>();
+            let (incoming_tx, incoming_rx) = mpsc::unbounded::<Envelope>();
 
-        let (server_to_client_tx, server_to_client_rx) = mpsc::unbounded();
+            // We use the forwarder on the server side (in production we only use one on the client side)
-        let (client_to_server_tx, client_to_server_rx) = mpsc::unbounded();
+            // the idea is that we can simulate a disconnect/reconnect by just messing with the forwarder.
+            let (forwarder, _, _) =
+                ChannelForwarder::new(incoming_tx, outgoing_rx, &mut cx.to_async());
 
-        (
+            let client = ChannelClient::new(incoming_rx, outgoing_tx, cx);
-            client_cx.update(|cx| {
+            (forwarder, client)
-                let client = ChannelClient::new(server_to_client_rx, client_to_server_tx, cx);
+        })
-                cx.new_model(|_| Self {
+    }
-                    client,
+
-                    unique_identifier: "fake".to_string(),
+    #[cfg(any(test, feature = "test-support"))]
-                    connection_options: SshConnectionOptions::default(),
+    pub async fn fake_client(
-                    state: Arc::new(Mutex::new(None)),
+        forwarder: ChannelForwarder,
-                })
+        client_cx: &mut gpui::TestAppContext,
-            }),
+    ) -> Model<Self> {
-            server_cx.update(|cx| ChannelClient::new(client_to_server_rx, server_to_client_tx, cx)),
+        use gpui::BorrowAppContext;
-        )
+        client_cx
+            .update(|cx| {
+                let port = cx.update_default_global(|c: &mut fake::GlobalConnections, _cx| {
+                    c.push(forwarder)
+                });
+
+                Self::new(
+                    "fake".to_string(),
+                    SshConnectionOptions {
+                        host: "<fake>".to_string(),
+                        port: Some(port),
+                        ..Default::default()
+                    },
+                    Arc::new(fake::Delegate),
+                    cx,
+                )
+            })
+            .await
+            .unwrap()
     }
 }
 
@@ -1176,6 +1224,13 @@ impl From<SshRemoteClient> for AnyProtoClient {
     }
 }
 
+#[async_trait]
+trait SshRemoteProcess: Send + Sync {
+    async fn kill(&mut self) -> Result<()>;
+    fn ssh_args(&self) -> Vec<String>;
+    fn connection_options(&self) -> SshConnectionOptions;
+}
+
 struct SshRemoteConnection {
     socket: SshSocket,
     master_process: process::Child,
@@ -1190,6 +1245,25 @@ impl Drop for SshRemoteConnection {
     }
 }
 
+#[async_trait]
+impl SshRemoteProcess for SshRemoteConnection {
+    async fn kill(&mut self) -> Result<()> {
+        self.master_process.kill()?;
+
+        self.master_process.status().await?;
+
+        Ok(())
+    }
+
+    fn ssh_args(&self) -> Vec<String> {
+        self.socket.ssh_args()
+    }
+
+    fn connection_options(&self) -> SshConnectionOptions {
+        self.socket.connection_options.clone()
+    }
+}
+
 impl SshRemoteConnection {
     #[cfg(not(unix))]
     async fn new(
@@ -1472,8 +1546,10 @@ type ResponseChannels = Mutex<HashMap<MessageId, oneshot::Sender<(Envelope, ones
 pub struct ChannelClient {
     next_message_id: AtomicU32,
     outgoing_tx: mpsc::UnboundedSender<Envelope>,
-    response_channels: ResponseChannels,             // Lock
+    buffer: Mutex<VecDeque<Envelope>>,
-    message_handlers: Mutex<ProtoMessageHandlerSet>, // Lock
+    response_channels: ResponseChannels,
+    message_handlers: Mutex<ProtoMessageHandlerSet>,
+    max_received: AtomicU32,
 }
 
 impl ChannelClient {
@@ -1485,8 +1561,10 @@ impl ChannelClient {
         let this = Arc::new(Self {
             outgoing_tx,
             next_message_id: AtomicU32::new(0),
+            max_received: AtomicU32::new(0),
             response_channels: ResponseChannels::default(),
             message_handlers: Default::default(),
+            buffer: Mutex::new(VecDeque::new()),
         });
 
         Self::start_handling_messages(this.clone(), incoming_rx, cx);
@@ -1507,6 +1585,25 @@ impl ChannelClient {
                     let Some(this) = this.upgrade() else {
                         return anyhow::Ok(());
                     };
+                    if let Some(ack_id) = incoming.ack_id {
+                        let mut buffer = this.buffer.lock();
+                        while buffer.front().is_some_and(|msg| msg.id <= ack_id) {
+                            buffer.pop_front();
+                        }
+                    }
+                    if let Some(proto::envelope::Payload::FlushBufferedMessages(_)) = &incoming.payload {
+                        {
+                            let buffer = this.buffer.lock();
+                            for envelope in buffer.iter() {
+                                this.outgoing_tx.unbounded_send(envelope.clone()).ok();
+                            }
+                        }
+                        let response = proto::Ack{}.into_envelope(0, Some(incoming.id), None);
+                        this.send_dynamic(response).ok();
+                        continue;
+                    }
+
+                    this.max_received.store(incoming.id, SeqCst);
 
                     if let Some(request_id) = incoming.responding_to {
                         let request_id = MessageId(request_id);
@@ -1583,6 +1680,23 @@ impl ChannelClient {
         }
     }
 
+    pub async fn resync(&self, timeout: Duration) -> Result<()> {
+        smol::future::or(
+            async {
+                self.request(proto::FlushBufferedMessages {}).await?;
+                for envelope in self.buffer.lock().iter() {
+                    self.outgoing_tx.unbounded_send(envelope.clone()).ok();
+                }
+                Ok(())
+            },
+            async {
+                smol::Timer::after(timeout).await;
+                Err(anyhow!("Timeout detected"))
+            },
+        )
+        .await
+    }
+
     pub async fn ping(&self, timeout: Duration) -> Result<()> {
         smol::future::or(
             async {
@@ -1612,7 +1726,8 @@ impl ChannelClient {
         let mut response_channels_lock = self.response_channels.lock();
         response_channels_lock.insert(MessageId(envelope.id), tx);
         drop(response_channels_lock);
-        let result = self.outgoing_tx.unbounded_send(envelope);
+
+        let result = self.send_buffered(envelope);
         async move {
             if let Err(error) = &result {
                 log::error!("failed to send message: {}", error);
@@ -1629,6 +1744,12 @@ impl ChannelClient {
 
     pub fn send_dynamic(&self, mut envelope: proto::Envelope) -> Result<()> {
         envelope.id = self.next_message_id.fetch_add(1, SeqCst);
+        self.send_buffered(envelope)
+    }
+
+    pub fn send_buffered(&self, mut envelope: proto::Envelope) -> Result<()> {
+        envelope.ack_id = Some(self.max_received.load(SeqCst));
+        self.buffer.lock().push_back(envelope.clone());
         self.outgoing_tx.unbounded_send(envelope)?;
         Ok(())
     }
@@ -1659,3 +1780,165 @@ impl ProtoClient for ChannelClient {
         false
     }
 }
+
+#[cfg(any(test, feature = "test-support"))]
+mod fake {
+    use std::path::PathBuf;
+
+    use anyhow::Result;
+    use async_trait::async_trait;
+    use futures::{
+        channel::{
+            mpsc::{self, Sender},
+            oneshot,
+        },
+        select_biased, FutureExt, SinkExt, StreamExt,
+    };
+    use gpui::{AsyncAppContext, BorrowAppContext, Global, SemanticVersion, Task};
+    use rpc::proto::Envelope;
+
+    use super::{
+        ChannelForwarder, SshClientDelegate, SshConnectionOptions, SshPlatform, SshRemoteProcess,
+    };
+
+    pub(super) struct SshRemoteConnection {
+        connection_options: SshConnectionOptions,
+    }
+
+    impl SshRemoteConnection {
+        pub(super) fn new(
+            connection_options: &SshConnectionOptions,
+        ) -> Option<Box<dyn SshRemoteProcess>> {
+            if connection_options.host == "<fake>" {
+                return Some(Box::new(Self {
+                    connection_options: connection_options.clone(),
+                }));
+            }
+            return None;
+        }
+        pub(super) async fn multiplex(
+            connection_options: SshConnectionOptions,
+            mut client_tx: mpsc::UnboundedSender<Envelope>,
+            mut client_rx: mpsc::UnboundedReceiver<Envelope>,
+            mut connection_activity_tx: Sender<()>,
+            cx: &mut AsyncAppContext,
+        ) -> Task<Result<Option<i32>>> {
+            let (server_tx, server_rx) = cx
+                .update(|cx| {
+                    cx.update_global(|conns: &mut GlobalConnections, _| {
+                        conns.take(connection_options.port.unwrap())
+                    })
+                })
+                .unwrap()
+                .into_channels()
+                .await;
+
+            let (forwarder, mut proxy_tx, mut proxy_rx) =
+                ChannelForwarder::new(server_tx, server_rx, cx);
+
+            cx.update(|cx| {
+                cx.update_global(|conns: &mut GlobalConnections, _| {
+                    conns.replace(connection_options.port.unwrap(), forwarder)
+                })
+            })
+            .unwrap();
+
+            cx.background_executor().spawn(async move {
+                loop {
+                    select_biased! {
+                        server_to_client = proxy_rx.next().fuse() => {
+                            let Some(server_to_client) = server_to_client else {
+                                return Ok(Some(1))
+                            };
+                            connection_activity_tx.try_send(()).ok();
+                            client_tx.send(server_to_client).await.ok();
+                        }
+                        client_to_server = client_rx.next().fuse() => {
+                            let Some(client_to_server) = client_to_server else {
+                                return Ok(None)
+                            };
+                            proxy_tx.send(client_to_server).await.ok();
+
+                        }
+                    }
+                }
+            })
+        }
+    }
+
+    #[async_trait]
+    impl SshRemoteProcess for SshRemoteConnection {
+        async fn kill(&mut self) -> Result<()> {
+            Ok(())
+        }
+
+        fn ssh_args(&self) -> Vec<String> {
+            Vec::new()
+        }
+
+        fn connection_options(&self) -> SshConnectionOptions {
+            self.connection_options.clone()
+        }
+    }
+
+    #[derive(Default)]
+    pub(super) struct GlobalConnections(Vec<Option<ChannelForwarder>>);
+    impl Global for GlobalConnections {}
+
+    impl GlobalConnections {
+        pub(super) fn push(&mut self, forwarder: ChannelForwarder) -> u16 {
+            self.0.push(Some(forwarder));
+            self.0.len() as u16 - 1
+        }
+
+        pub(super) fn take(&mut self, port: u16) -> ChannelForwarder {
+            self.0
+                .get_mut(port as usize)
+                .expect("no fake server for port")
+                .take()
+                .expect("fake server is already borrowed")
+        }
+        pub(super) fn replace(&mut self, port: u16, forwarder: ChannelForwarder) {
+            let ret = self
+                .0
+                .get_mut(port as usize)
+                .expect("no fake server for port")
+                .replace(forwarder);
+            if ret.is_some() {
+                panic!("fake server is already replaced");
+            }
+        }
+    }
+
+    pub(super) struct Delegate;
+
+    impl SshClientDelegate for Delegate {
+        fn ask_password(
+            &self,
+            _: String,
+            _: &mut AsyncAppContext,
+        ) -> oneshot::Receiver<Result<String>> {
+            unreachable!()
+        }
+        fn remote_server_binary_path(
+            &self,
+            _: SshPlatform,
+            _: &mut AsyncAppContext,
+        ) -> Result<PathBuf> {
+            unreachable!()
+        }
+        fn get_server_binary(
+            &self,
+            _: SshPlatform,
+            _: &mut AsyncAppContext,
+        ) -> oneshot::Receiver<Result<(PathBuf, SemanticVersion)>> {
+            unreachable!()
+        }
+        fn set_status(&self, _: Option<&str>, _: &mut AsyncAppContext) {
+            unreachable!()
+        }
+        fn set_error(&self, _: String, _: &mut AsyncAppContext) {
+            unreachable!()
+        }
+    }
+}

crates/remote_server/src/remote_editing_tests.rs

@@ -641,6 +641,47 @@ async fn test_open_server_settings(cx: &mut TestAppContext, server_cx: &mut Test
     })
 }
 
+#[gpui::test(iterations = 10)]
+async fn test_reconnect(cx: &mut TestAppContext, server_cx: &mut TestAppContext) {
+    let (project, _headless, fs) = init_test(cx, server_cx).await;
+
+    let (worktree, _) = project
+        .update(cx, |project, cx| {
+            project.find_or_create_worktree("/code/project1", true, cx)
+        })
+        .await
+        .unwrap();
+
+    let worktree_id = worktree.read_with(cx, |worktree, _| worktree.id());
+    let buffer = project
+        .update(cx, |project, cx| {
+            project.open_buffer((worktree_id, Path::new("src/lib.rs")), cx)
+        })
+        .await
+        .unwrap();
+
+    buffer.update(cx, |buffer, cx| {
+        assert_eq!(buffer.text(), "fn one() -> usize { 1 }");
+        let ix = buffer.text().find('1').unwrap();
+        buffer.edit([(ix..ix + 1, "100")], None, cx);
+    });
+
+    let client = cx.read(|cx| project.read(cx).ssh_client().unwrap());
+    client
+        .update(cx, |client, cx| client.simulate_disconnect(cx))
+        .detach();
+
+    project
+        .update(cx, |project, cx| project.save_buffer(buffer.clone(), cx))
+        .await
+        .unwrap();
+
+    assert_eq!(
+        fs.load("/code/project1/src/lib.rs".as_ref()).await.unwrap(),
+        "fn one() -> usize { 100 }"
+    );
+}
+
 fn init_logger() {
     if std::env::var("RUST_LOG").is_ok() {
         env_logger::try_init().ok();
@@ -651,9 +692,9 @@ async fn init_test(
     cx: &mut TestAppContext,
     server_cx: &mut TestAppContext,
 ) -> (Model<Project>, Model<HeadlessProject>, Arc<FakeFs>) {
-    let (ssh_remote_client, ssh_server_client) = SshRemoteClient::fake(cx, server_cx);
     init_logger();
 
+    let (forwarder, ssh_server_client) = SshRemoteClient::fake_server(server_cx);
     let fs = FakeFs::new(server_cx.executor());
     fs.insert_tree(
         "/code",
@@ -694,8 +735,9 @@ async fn init_test(
             cx,
         )
     });
-    let project = build_project(ssh_remote_client, cx);
 
+    let ssh = SshRemoteClient::fake_client(forwarder, cx).await;
+    let project = build_project(ssh, cx);
     project
         .update(cx, {
             let headless = headless.clone();