Harden embedded server lifecycle

Cargo.lock

@@ -436,7 +436,7 @@ dependencies = [
 
 [[package]]
 name = "dosh"
-version = "1.0.0-rc47"
+version = "1.0.0-rc49"
 dependencies = [
  "anyhow",
  "base64",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "dosh"
-version = "1.0.0-rc47"
+version = "1.0.0-rc49"
 edition = "2024"
 license = "MIT"
 

examples/sdk_echo_server.rs

@@ -16,6 +16,9 @@ async fn main() -> Result<()> {
                     client.user, client.session, client.conn_id
                 );
             }
+            DoshServerEvent::Disconnected(client) => {
+                eprintln!("disconnected conn={:?}", client.conn_id);
+            }
             DoshServerEvent::Session {
                 conn_id,
                 event: SessionEvent::Stream(TransportEvent::Open(open)),

src/server.rs

@@ -16,8 +16,8 @@ use crate::transport::{
 use crate::udp::{is_transient_udp_error, is_transient_udp_send_error};
 use anyhow::{Context, Result, anyhow, bail};
 use ed25519_dalek::SigningKey;
-use std::collections::{HashMap, HashSet};
+use std::collections::{HashMap, HashSet, VecDeque};
-use std::net::SocketAddr;
+use std::net::{IpAddr, SocketAddr};
 use std::path::PathBuf;
 use std::sync::Arc;
 use std::time::{Duration, Instant};
@@ -31,10 +31,13 @@ pub struct DoshServerConfig {
     pub transport: TransportConfig,
     pub require_current_user: bool,
     pub auth_timeout: Duration,
+    pub max_pending_auth: usize,
+    pub connection_timeout: Duration,
 }
 
 impl DoshServerConfig {
     pub fn new(server: ServerConfig) -> Self {
+        let connection_timeout = Duration::from_secs(server.client_timeout_secs.max(1));
         Self {
             server,
             bind_addr: None,
@@ -42,6 +45,8 @@ impl DoshServerConfig {
             transport: TransportConfig::default(),
             require_current_user: true,
             auth_timeout: Duration::from_secs(30),
+            max_pending_auth: 1024,
+            connection_timeout,
         }
     }
 
@@ -71,6 +76,21 @@ impl DoshServerConfig {
         self.transport = transport;
         self
     }
+
+    pub fn connection_timeout(mut self, timeout: Duration) -> Self {
+        self.connection_timeout = timeout.max(ADAPTIVE_RETRANSMIT_MIN);
+        self
+    }
+
+    pub fn auth_timeout(mut self, timeout: Duration) -> Self {
+        self.auth_timeout = timeout.max(ADAPTIVE_RETRANSMIT_MIN);
+        self
+    }
+
+    pub fn max_pending_auth(mut self, max_pending: usize) -> Self {
+        self.max_pending_auth = max_pending.max(1);
+        self
+    }
 }
 
 impl Default for DoshServerConfig {
@@ -91,6 +111,7 @@ pub struct DoshAccepted {
 #[derive(Debug, Clone)]
 pub enum DoshServerEvent {
     Accepted(DoshAccepted),
+    Disconnected(DoshAccepted),
     Session {
         conn_id: [u8; 16],
         event: SessionEvent,
@@ -107,13 +128,78 @@ struct PendingServerAuth {
     created_at: Instant,
 }
 
+struct AuthRateLimiter {
+    per_minute: u32,
+    max_sources: usize,
+    buckets: HashMap<IpAddr, AuthTokenBucket>,
+}
+
+#[derive(Clone, Copy)]
+struct AuthTokenBucket {
+    tokens: f64,
+    last_refill: Instant,
+}
+
+impl AuthRateLimiter {
+    fn new(per_minute: u32, max_sources: usize) -> Self {
+        Self {
+            per_minute,
+            max_sources: max_sources.max(1),
+            buckets: HashMap::new(),
+        }
+    }
+
+    fn check(&mut self, ip: IpAddr, now: Instant) -> Result<u32, ()> {
+        if self.per_minute == 0 {
+            return Err(());
+        }
+        self.evict_full(now);
+        if !self.buckets.contains_key(&ip) && self.buckets.len() >= self.max_sources {
+            return Err(());
+        }
+        let capacity = self.per_minute as f64;
+        let refill_per_sec = capacity / 60.0;
+        let bucket = self.buckets.entry(ip).or_insert(AuthTokenBucket {
+            tokens: capacity,
+            last_refill: now,
+        });
+        let elapsed = now
+            .saturating_duration_since(bucket.last_refill)
+            .as_secs_f64();
+        bucket.tokens = (bucket.tokens + elapsed * refill_per_sec).min(capacity);
+        bucket.last_refill = now;
+        if bucket.tokens < 1.0 {
+            return Err(());
+        }
+        bucket.tokens -= 1.0;
+        Ok(bucket.tokens as u32)
+    }
+
+    fn evict_full(&mut self, now: Instant) {
+        if self.per_minute == 0 {
+            self.buckets.clear();
+            return;
+        }
+        let capacity = self.per_minute as f64;
+        let refill_per_sec = capacity / 60.0;
+        self.buckets.retain(|_, bucket| {
+            let elapsed = now
+                .saturating_duration_since(bucket.last_refill)
+                .as_secs_f64();
+            (bucket.tokens + elapsed * refill_per_sec) < capacity
+        });
+    }
+}
+
 pub struct DoshServer {
     socket: Arc<UdpSocket>,
     config: DoshServerConfig,
     host_signing: SigningKey,
+    auth_limiter: AuthRateLimiter,
     pending: HashMap<[u8; 16], PendingServerAuth>,
     transports: HashMap<[u8; 16], DoshTransport>,
     accepted: HashMap<[u8; 16], DoshAccepted>,
+    disconnected: VecDeque<DoshAccepted>,
 }
 
 impl DoshServer {
@@ -139,13 +225,19 @@ impl DoshServer {
         };
         let host_signing = load_or_create_host_key(&config.server)?;
         let socket = Arc::new(UdpSocket::bind(bind_addr).await?);
+        let auth_limiter = AuthRateLimiter::new(
+            config.server.native_auth_rate_limit_per_minute,
+            config.max_pending_auth,
+        );
         Ok(Self {
             socket,
             config,
             host_signing,
+            auth_limiter,
             pending: HashMap::new(),
             transports: HashMap::new(),
             accepted: HashMap::new(),
+            disconnected: VecDeque::new(),
         })
     }
 
@@ -165,10 +257,19 @@ impl DoshServer {
         self.transports.get_mut(conn_id)
     }
 
+    pub fn remove_connection(&mut self, conn_id: &[u8; 16]) -> Option<DoshAccepted> {
+        self.transports.remove(conn_id);
+        self.accepted.remove(conn_id)
+    }
+
     pub async fn recv(&mut self) -> Result<DoshServerEvent> {
         let mut buf = vec![0u8; 65535];
         loop {
             self.expire_pending();
+            self.expire_connections();
+            if let Some(connection) = self.disconnected.pop_front() {
+                return Ok(DoshServerEvent::Disconnected(connection));
+            }
             let (n, peer) = match tokio::time::timeout(
                 ADAPTIVE_RETRANSMIT_MIN,
                 self.socket.recv_from(&mut buf),
@@ -207,6 +308,9 @@ impl DoshServer {
         }
         if let Some(transport) = self.transports.get_mut(&packet.header.conn_id) {
             let event = transport.handle_datagram(datagram, peer).await?;
+            if let Some(accepted) = self.accepted.get_mut(&packet.header.conn_id) {
+                accepted.peer_addr = transport.peer_addr();
+            }
             return Ok(Some(DoshServerEvent::Session {
                 conn_id: packet.header.conn_id,
                 event,
@@ -270,7 +374,21 @@ impl DoshServer {
             self.send_reject(peer, [0u8; 16], &err.to_string()).await?;
             return Ok(());
         }
-        let result = self.build_server_hello(req.hello, peer);
+        self.expire_pending();
+        if self.pending.len() >= self.config.max_pending_auth {
+            self.send_reject(peer, [0u8; 16], "native auth server busy")
+                .await?;
+            return Ok(());
+        }
+        let rate_limit_remaining = match self.auth_limiter.check(peer.ip(), Instant::now()) {
+            Ok(remaining) => remaining,
+            Err(()) => {
+                self.send_reject(peer, [0u8; 16], "native auth rate limit exceeded")
+                    .await?;
+                return Ok(());
+            }
+        };
+        let result = self.build_server_hello(req.hello, peer, Some(rate_limit_remaining));
         let (pending_id, hello) = match result {
             Ok(value) => value,
             Err(err) => {
@@ -288,6 +406,7 @@ impl DoshServer {
         &mut self,
         client: native::NativeClientHello,
         peer: SocketAddr,
+        rate_limit_remaining: Option<u32>,
     ) -> Result<([u8; 16], NativeServerHello)> {
         if !self.config.server.native_auth {
             bail!("native auth disabled");
@@ -307,11 +426,14 @@ impl DoshServer {
             bail!("native auth requires a supported user key algorithm");
         }
         if self.config.require_current_user {
-            let current_user = std::env::var("USER").unwrap_or_else(|_| "unknown".to_string());
+            let current_user = local_username();
             if client.requested_user != current_user {
                 bail!("native auth user mismatch");
             }
         }
+        if self.pending.len() >= self.config.max_pending_auth {
+            bail!("native auth server busy");
+        }
 
         let (server_secret, server_public) = generate_native_ephemeral();
         let mut server = NativeServerHello {
@@ -322,7 +444,7 @@ impl DoshServer {
             chosen_aead: "chacha20poly1305".to_string(),
             server_key_epoch: 1,
             auth_challenge: crypto::random_32(),
-            rate_limit_remaining: None,
+            rate_limit_remaining,
             host_signature: Vec::new(),
         };
         sign_server_hello(&self.host_signing, &client, &mut server)?;
@@ -477,7 +599,37 @@ impl DoshServer {
         let timeout = self.config.auth_timeout;
         self.pending
             .retain(|_, pending| pending.created_at.elapsed() <= timeout);
+        self.auth_limiter.evict_full(Instant::now());
     }
+
+    fn expire_connections(&mut self) {
+        let timeout = self.config.connection_timeout;
+        let expired = self
+            .transports
+            .iter()
+            .filter_map(|(conn_id, transport)| {
+                (transport.stale_for() > timeout).then_some(*conn_id)
+            })
+            .collect::<Vec<_>>();
+        for conn_id in expired {
+            self.transports.remove(&conn_id);
+            if let Some(connection) = self.accepted.remove(&conn_id) {
+                self.disconnected.push_back(connection);
+            }
+        }
+    }
+}
+
+fn local_username() -> String {
+    local_username_from_env(|name| std::env::var(name).ok())
+}
+
+fn local_username_from_env(get: impl FnMut(&str) -> Option<String>) -> String {
+    ["USER", "USERNAME"]
+        .into_iter()
+        .filter_map(get)
+        .find(|value| !value.is_empty())
+        .unwrap_or_else(|| "unknown".to_string())
 }
 
 async fn send_udp(socket: &UdpSocket, packet: &[u8], peer: SocketAddr) -> Result<bool> {
@@ -530,6 +682,24 @@ mod tests {
     use crate::transport::TransportEvent;
     use ed25519_dalek::SigningKey;
 
+    fn native_client_hello(public: [u8; 32]) -> native::NativeClientHello {
+        native::NativeClientHello {
+            protocol_version: native::NATIVE_PROTOCOL_VERSION,
+            client_random: crypto::random_32(),
+            client_ephemeral_public: public,
+            requested_host: "127.0.0.1".to_string(),
+            requested_user: "sdk-user".to_string(),
+            requested_session: "test".to_string(),
+            requested_mode: "forward-only".to_string(),
+            terminal_size: (80, 24),
+            supported_aead: vec!["chacha20poly1305".to_string()],
+            supported_user_key_algorithms: vec!["ssh-ed25519".to_string()],
+            cached_host_key_fingerprint: None,
+            attach_ticket_envelope: None,
+            requested_env: Vec::new(),
+        }
+    }
+
     #[tokio::test]
     async fn sdk_client_and_server_exchange_service_stream() {
         let dir = tempfile::tempdir().unwrap();
@@ -752,6 +922,209 @@ mod tests {
         assert_eq!(open.target_host, "@dosh-echo");
     }
 
+    #[tokio::test]
+    async fn sdk_server_expires_disconnected_transport_and_reports_it() {
+        let dir = tempfile::tempdir().unwrap();
+        let server_config = ServerConfig {
+            host_key: dir.path().join("host_key").to_string_lossy().to_string(),
+            ..ServerConfig::default()
+        };
+        let server_config = DoshServerConfig::new(server_config)
+            .bind_addr("127.0.0.1:0".parse().unwrap())
+            .require_current_user(false)
+            .connection_timeout(Duration::from_millis(30));
+        let mut server = DoshServer::bind(server_config).await.unwrap();
+        let peer_socket = UdpSocket::bind("127.0.0.1:0").await.unwrap();
+        let peer_addr = peer_socket.local_addr().unwrap();
+        let conn_id = [81u8; 16];
+        let transport = DoshTransport::new(
+            Arc::clone(&server.socket),
+            SessionTransportConfig {
+                role: SessionRole::Server,
+                conn_id,
+                session_key: [82u8; 32],
+                peer_addr,
+                initial_send_seq: 1,
+                initial_ack: 0,
+                stream: server.config.transport.clone(),
+            },
+        );
+        let accepted = DoshAccepted {
+            conn_id,
+            user: "sdk-user".to_string(),
+            session: "mobile".to_string(),
+            services: vec!["echo".to_string()],
+            peer_addr,
+        };
+        server.transports.insert(conn_id, transport);
+        server.accepted.insert(conn_id, accepted.clone());
+
+        tokio::time::sleep(Duration::from_millis(40)).await;
+        let event = tokio::time::timeout(Duration::from_secs(1), server.recv())
+            .await
+            .expect("server did not report expired connection")
+            .unwrap();
+        match event {
+            DoshServerEvent::Disconnected(disconnected) => {
+                assert_eq!(disconnected.conn_id, conn_id);
+                assert_eq!(disconnected.session, "mobile");
+            }
+            other => panic!("unexpected expiry event {other:?}"),
+        }
+        assert!(server.connection(&conn_id).is_none());
+        assert!(server.transport(&conn_id).is_none());
+    }
+
+    #[tokio::test]
+    async fn sdk_server_updates_connection_metadata_after_authenticated_roam() {
+        let dir = tempfile::tempdir().unwrap();
+        let server_config = ServerConfig {
+            host_key: dir.path().join("host_key").to_string_lossy().to_string(),
+            ..ServerConfig::default()
+        };
+        let server_config = DoshServerConfig::new(server_config)
+            .bind_addr("127.0.0.1:0".parse().unwrap())
+            .require_current_user(false);
+        let mut server = DoshServer::bind(server_config).await.unwrap();
+        let original = UdpSocket::bind("127.0.0.1:0").await.unwrap();
+        let roaming = UdpSocket::bind("127.0.0.1:0").await.unwrap();
+        let original_addr = original.local_addr().unwrap();
+        let roaming_addr = roaming.local_addr().unwrap();
+        let conn_id = [83u8; 16];
+        let session_key = [84u8; 32];
+        let transport = DoshTransport::new(
+            Arc::clone(&server.socket),
+            SessionTransportConfig {
+                role: SessionRole::Server,
+                conn_id,
+                session_key,
+                peer_addr: original_addr,
+                initial_send_seq: 1,
+                initial_ack: 0,
+                stream: server.config.transport.clone(),
+            },
+        );
+        server.transports.insert(conn_id, transport);
+        server.accepted.insert(
+            conn_id,
+            DoshAccepted {
+                conn_id,
+                user: "sdk-user".to_string(),
+                session: "mobile".to_string(),
+                services: Vec::new(),
+                peer_addr: original_addr,
+            },
+        );
+        let ping = protocol::encode_encrypted(
+            PacketKind::Ping,
+            conn_id,
+            1,
+            0,
+            &session_key,
+            CLIENT_TO_SERVER,
+            b"",
+        )
+        .unwrap();
+        roaming
+            .send_to(&ping, server.local_addr().unwrap())
+            .await
+            .unwrap();
+
+        let event = tokio::time::timeout(Duration::from_secs(1), server.recv())
+            .await
+            .expect("server did not receive roaming ping")
+            .unwrap();
+        assert!(matches!(
+            event,
+            DoshServerEvent::Session {
+                event: SessionEvent::Ping,
+                ..
+            }
+        ));
+        assert_eq!(server.connection(&conn_id).unwrap().peer_addr, roaming_addr);
+    }
+
+    #[tokio::test]
+    async fn sdk_server_bounds_and_rate_limits_pending_authentication() {
+        let dir = tempfile::tempdir().unwrap();
+        let server_config = ServerConfig {
+            host_key: dir.path().join("host_key").to_string_lossy().to_string(),
+            native_auth_rate_limit_per_minute: 1,
+            ..ServerConfig::default()
+        };
+        let server_config = DoshServerConfig::new(server_config)
+            .bind_addr("127.0.0.1:0".parse().unwrap())
+            .require_current_user(false)
+            .max_pending_auth(1);
+        let mut server = DoshServer::bind(server_config).await.unwrap();
+        let client = UdpSocket::bind("127.0.0.1:0").await.unwrap();
+        let peer = client.local_addr().unwrap();
+        let (_, public) = native::generate_native_ephemeral();
+        let body = protocol::to_body(&NativeClientHelloBody {
+            hello: native_client_hello(public),
+        })
+        .unwrap();
+
+        server
+            .handle_client_hello(peer, body.clone())
+            .await
+            .unwrap();
+        let mut packet = [0u8; 65535];
+        let (n, _) = client.recv_from(&mut packet).await.unwrap();
+        let response = protocol::decode(&packet[..n]).unwrap();
+        assert_eq!(response.header.kind, PacketKind::NativeServerHello);
+        let hello: NativeServerHelloBody = protocol::from_body(&response.body).unwrap();
+        assert_eq!(hello.hello.rate_limit_remaining, Some(0));
+        assert_eq!(server.pending.len(), 1);
+
+        server
+            .handle_client_hello(peer, body.clone())
+            .await
+            .unwrap();
+        let (n, _) = client.recv_from(&mut packet).await.unwrap();
+        let response = protocol::decode(&packet[..n]).unwrap();
+        assert_eq!(response.header.kind, PacketKind::AttachReject);
+        let reject: AttachReject = protocol::from_body(&response.body).unwrap();
+        assert_eq!(reject.reason, "native auth server busy");
+        assert_eq!(server.pending.len(), 1);
+
+        server.pending.clear();
+        server.handle_client_hello(peer, body).await.unwrap();
+        let (n, _) = client.recv_from(&mut packet).await.unwrap();
+        let response = protocol::decode(&packet[..n]).unwrap();
+        assert_eq!(response.header.kind, PacketKind::AttachReject);
+        let reject: AttachReject = protocol::from_body(&response.body).unwrap();
+        assert_eq!(reject.reason, "native auth rate limit exceeded");
+        assert!(server.pending.is_empty());
+    }
+
+    #[test]
+    fn sdk_auth_rate_limiter_bounds_source_tracking_and_refills() {
+        let now = Instant::now();
+        let mut limiter = AuthRateLimiter::new(2, 1);
+        let first: IpAddr = "192.0.2.1".parse().unwrap();
+        let second: IpAddr = "192.0.2.2".parse().unwrap();
+
+        assert_eq!(limiter.check(first, now), Ok(1));
+        assert_eq!(limiter.check(first, now), Ok(0));
+        assert_eq!(limiter.check(first, now), Err(()));
+        assert_eq!(limiter.check(second, now), Err(()));
+        assert_eq!(limiter.check(second, now + Duration::from_secs(60)), Ok(1));
+        assert_eq!(limiter.buckets.len(), 1);
+    }
+
+    #[test]
+    fn sdk_server_username_supports_windows_environment() {
+        assert_eq!(
+            local_username_from_env(|name| match name {
+                "USER" => None,
+                "USERNAME" => Some("palav-win".to_string()),
+                _ => None,
+            }),
+            "palav-win"
+        );
+    }
+
     #[tokio::test]
     async fn bad_native_auth_does_not_consume_pending_challenge() {
         let dir = tempfile::tempdir().unwrap();
@@ -778,22 +1151,10 @@ mod tests {
         let mut server = DoshServer::bind(server_config).await.unwrap();
         let peer: SocketAddr = "127.0.0.1:9".parse().unwrap();
         let (client_secret, client_public) = native::generate_native_ephemeral();
-        let hello = native::NativeClientHello {
+        let hello = native_client_hello(client_public);
-            protocol_version: native::NATIVE_PROTOCOL_VERSION,
+        let (pending_id, server_hello) = server
-            client_random: crypto::random_32(),
+            .build_server_hello(hello.clone(), peer, None)
-            client_ephemeral_public: client_public,
+            .unwrap();
-            requested_host: "127.0.0.1".to_string(),
-            requested_user: "sdk-user".to_string(),
-            requested_session: "test".to_string(),
-            requested_mode: "forward-only".to_string(),
-            terminal_size: (80, 24),
-            supported_aead: vec!["chacha20poly1305".to_string()],
-            supported_user_key_algorithms: vec!["ssh-ed25519".to_string()],
-            cached_host_key_fingerprint: None,
-            attach_ticket_envelope: None,
-            requested_env: Vec::new(),
-        };
-        let (pending_id, server_hello) = server.build_server_hello(hello.clone(), peer).unwrap();
         let session_key = native::derive_native_session_key(
             &client_secret,
             server_hello.server_ephemeral_public,

tests/client_terminal_runtime.rs

@@ -16,6 +16,8 @@ const SESSION_KEY: [u8; 32] = [0x91; 32];
 const INPUT_BYTES: &[u8] = concat!(
     "\x1b[A",
     "\x1b[B",
+    "\x1b[I",
+    "\x1b[O",
     "\x1b[200~",
     "paste-λ-界",
     "\x1b[201~",
@@ -50,6 +52,7 @@ struct CachedCredentialWire {
 enum ServerObservation {
     BulkSent,
     Input(Vec<u8>),
+    Ping,
     Reconnected,
     RenderResynced,
     Resize(u16, u16),
@@ -148,6 +151,10 @@ fn native_client_terminal_round_trip_is_platform_complete() {
         contains(&output, b"\x1b[?1006h"),
         "SGR mouse mode was not preserved: {output:?}"
     );
+    assert!(
+        contains(&output, b"\x1b[?1004h"),
+        "focus-report mode was not preserved: {output:?}"
+    );
     assert!(
         contains(&output, b"\x1b[?25h"),
         "terminal cleanup did not restore the cursor: {output:?}"
@@ -300,6 +307,87 @@ fn idle_reconnect_restores_snapshot_and_orders_reordered_frames() {
     assert!(status.success(), "Dosh client exited with {status:?}");
 }
 
+#[test]
+fn authenticated_idle_pongs_do_not_trigger_snapshot_reconnects() {
+    let dir = tempfile::tempdir().unwrap();
+    let home = dir.path().join("home");
+    let cache = dir.path().join("credentials");
+    fs::create_dir_all(home.join(".config/dosh")).unwrap();
+    fs::create_dir_all(&cache).unwrap();
+
+    let socket = UdpSocket::bind("127.0.0.1:0").unwrap();
+    socket
+        .set_read_timeout(Some(Duration::from_millis(100)))
+        .unwrap();
+    let port = socket.local_addr().unwrap().port();
+    write_client_fixture(&home, &cache, port, 5);
+    let config_path = home.join(".config/dosh/client.toml");
+    let mut config: ClientConfig =
+        toml::from_str(&fs::read_to_string(&config_path).unwrap()).unwrap();
+    config.disconnect_status = true;
+    fs::write(&config_path, toml::to_string(&config).unwrap()).unwrap();
+
+    let (observation_tx, observation_rx) = mpsc::channel();
+    let server = thread::spawn(move || run_idle_keepalive_server(socket, observation_tx));
+
+    let pty = NativePtySystem::default();
+    let pair = pty
+        .openpty(PtySize {
+            rows: 24,
+            cols: 80,
+            pixel_width: 0,
+            pixel_height: 0,
+        })
+        .unwrap();
+    let mut reader = pair.master.try_clone_reader().unwrap();
+    let mut command = client_command(dir.path(), port);
+    command.env("HOME", home.to_string_lossy().to_string());
+    command.env("USERPROFILE", home.to_string_lossy().to_string());
+    command.env("APPDATA", home.to_string_lossy().to_string());
+    command.env("LOCALAPPDATA", home.to_string_lossy().to_string());
+    command.env("TERM", "xterm-256color");
+    let mut child = pair.slave.spawn_command(command).unwrap();
+    drop(pair.slave);
+
+    let output = Arc::new(Mutex::new(Vec::new()));
+    let reader_output = Arc::clone(&output);
+    let reader_thread = thread::spawn(move || {
+        let mut buf = [0u8; 4096];
+        loop {
+            match reader.read(&mut buf) {
+                Ok(0) | Err(_) => break,
+                Ok(n) => reader_output.lock().unwrap().extend_from_slice(&buf[..n]),
+            }
+        }
+    });
+
+    let status = child.wait().unwrap();
+    drop(pair.master);
+    reader_thread.join().unwrap();
+    server.join().unwrap();
+    assert!(status.success(), "Dosh client exited with {status:?}");
+
+    let observations: Vec<_> = observation_rx.try_iter().collect();
+    assert!(
+        observations
+            .iter()
+            .filter(|event| matches!(event, ServerObservation::Ping))
+            .count()
+            >= 2,
+        "idle session did not exercise repeated authenticated keepalives: {observations:?}"
+    );
+    assert!(
+        !observations
+            .iter()
+            .any(|event| matches!(event, ServerObservation::Reconnected)),
+        "healthy idle pongs caused a snapshot reconnect: {observations:?}"
+    );
+    assert!(
+        !contains(&output.lock().unwrap(), b"[dosh] reconnecting"),
+        "healthy idle session flashed the disconnect overlay"
+    );
+}
+
 #[test]
 fn renderer_overflow_resyncs_without_dropping_the_session() {
     const PROBE: &[u8] = b"DOSH_OVERFLOW_INPUT\r";
@@ -483,6 +571,7 @@ fn run_fake_terminal_server(socket: UdpSocket, observations: mpsc::Sender<Server
                         "\x1b[?1049h",
                         "\x1b[?1003h",
                         "\x1b[?1006h",
+                        "\x1b[?1004h",
                         "\x1b[?2004h",
                         "\x1b[2J\x1b[H",
                         "DOSH_PARITY_READY"
@@ -521,7 +610,7 @@ fn run_fake_terminal_server(socket: UdpSocket, observations: mpsc::Sender<Server
                         PacketKind::Frame,
                         20,
                         16,
-                        b"\x1b[?1003l\x1b[?1006l\x1b[?1049lDOSH_PARITY_DONE",
+                        b"\x1b[?1003l\x1b[?1006l\x1b[?1004l\x1b[?1049lDOSH_PARITY_DONE",
                         false,
                         true,
                     );
@@ -713,6 +802,87 @@ fn run_reconnect_server(
     }
 }
 
+fn run_idle_keepalive_server(socket: UdpSocket, observations: mpsc::Sender<ServerObservation>) {
+    let started = Instant::now();
+    let mut peer = None;
+    let mut attached = false;
+    let mut server_seq = 1u64;
+    let mut buf = [0u8; 65535];
+    loop {
+        if started.elapsed() >= Duration::from_secs(7)
+            && let Some(source) = peer
+        {
+            server_seq += 1;
+            send_frame(
+                &socket,
+                source,
+                PacketKind::Frame,
+                server_seq,
+                11,
+                b"DOSH_IDLE_KEEPALIVE_DONE",
+                false,
+                true,
+            );
+            break;
+        }
+
+        let (n, source) = match socket.recv_from(&mut buf) {
+            Ok(value) => value,
+            Err(err)
+                if matches!(
+                    err.kind(),
+                    std::io::ErrorKind::WouldBlock | std::io::ErrorKind::TimedOut
+                ) =>
+            {
+                continue;
+            }
+            Err(err) => panic!("idle keepalive server receive failed: {err}"),
+        };
+        let packet = protocol::decode(&buf[..n]).unwrap();
+        match packet.header.kind {
+            PacketKind::ResumeRequest => {
+                let plain =
+                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
+                let request: protocol::ResumeRequest = protocol::from_body(&plain).unwrap();
+                assert_eq!(request.session, SESSION);
+                if attached {
+                    observations.send(ServerObservation::Reconnected).unwrap();
+                }
+                attached = true;
+                peer = Some(source);
+                send_frame(
+                    &socket,
+                    source,
+                    PacketKind::ResumeOk,
+                    server_seq,
+                    10,
+                    b"DOSH_IDLE_KEEPALIVE_READY",
+                    true,
+                    false,
+                );
+            }
+            PacketKind::Ping => {
+                protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
+                observations.send(ServerObservation::Ping).unwrap();
+                server_seq += 1;
+                let pong = protocol::encode_encrypted(
+                    PacketKind::Pong,
+                    CLIENT_ID,
+                    server_seq,
+                    packet.header.seq,
+                    &SESSION_KEY,
+                    SERVER_TO_CLIENT,
+                    b"",
+                )
+                .unwrap();
+                socket.send_to(&pong, source).unwrap();
+            }
+            PacketKind::Ack => {}
+            _ => {}
+        }
+    }
+}
+
 fn run_overflow_server(
     socket: UdpSocket,
     observations: mpsc::Sender<ServerObservation>,