Bump release candidate to rc5

Cargo.lock

@@ -436,7 +436,7 @@ dependencies = [
 
 [[package]]
 name = "dosh"
-version = "0.1.17"
+version = "1.0.0-rc5"
 dependencies = [
  "anyhow",
  "base64",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "dosh"
-version = "0.1.17"
+version = "1.0.0-rc5"
 edition = "2024"
 license = "MIT"
 

Makefile

@@ -27,6 +27,7 @@ reconnect-check:
 
 hostile-network-check:
 	cargo test --test hostile_network -- --nocapture
+	DOSH_BADNET_SOAK_SECONDS=$${DOSH_BADNET_SOAK_SECONDS:-300} cargo test --test hostile_network bad_network_tui_work_soak_30m -- --ignored --nocapture
 
 persistence-check:
 	cargo test --test integration_smoke session_survives_server_restart_same_shell_and_screen -- --nocapture

scripts/bench-local.sh

@@ -67,6 +67,7 @@ cleanup() {
     kill "$server_pid" 2>/dev/null || true
     wait "$server_pid" 2>/dev/null || true
   fi
+  pkill -f "$server_bin hold --runtime-dir $home/sessions/run" 2>/dev/null || true
   rm -rf "$home"
 }
 trap cleanup EXIT INT TERM
@@ -86,6 +87,7 @@ scrollback = 5000
 auth_ttl_secs = 30
 attach_ticket_ttl_secs = 3600
 allow_attach_tickets = true
+persist_sessions = false
 client_timeout_secs = 60
 retransmit_window = 256
 default_input_mode = "read-write"

src/bin/dosh-client.rs

@@ -36,6 +36,7 @@ use dosh::transport::{
     DoshTransport, SessionEvent, SessionRole, SessionTransportConfig, TransportConfig,
     TransportEvent,
 };
+use dosh::udp::is_transient_udp_send_error;
 use serde::{Deserialize, Serialize};
 use sha2::{Digest, Sha256};
 use std::collections::BTreeMap;
@@ -63,6 +64,8 @@ const STREAM_INITIAL_WINDOW: usize = 1024 * 1024;
 const MAX_PENDING_USER_INPUT_BYTES: usize = 1024 * 1024;
 const STARTUP_INPUT_HOLD: Duration = Duration::from_millis(750);
 const POST_SUBMIT_ALL_INPUT_HOLD: Duration = Duration::from_millis(120);
+const STALE_TERMINAL_INPUT_AFTER: Duration = Duration::from_secs(2);
+const POST_RECONNECT_STALE_INPUT_GRACE: Duration = Duration::from_secs(2);
 
 /// Sentinel `target_host` the server uses on a server-initiated `StreamOpen` that
 /// represents an SSH-agent connection (rather than a TCP target). The client
@@ -3524,6 +3527,14 @@ fn resolve_addr(host: &str, port: u16) -> Result<SocketAddr> {
         .ok_or_else(|| anyhow!("no UDP address resolved for {host}:{port}"))
 }
 
+async fn send_terminal_udp(socket: &UdpSocket, packet: &[u8], addr: SocketAddr) -> Result<bool> {
+    match socket.send_to(packet, addr).await {
+        Ok(_) => Ok(true),
+        Err(err) if is_transient_udp_send_error(&err) => Ok(false),
+        Err(err) => Err(err).with_context(|| format!("send UDP packet to {addr}")),
+    }
+}
+
 #[allow(clippy::too_many_arguments)]
 async fn try_native_auth(
     socket: &UdpSocket,
@@ -4322,6 +4333,7 @@ async fn run_terminal(
     let mut pending_user_input_bytes = 0usize;
     let mut startup_input_hold_until: Option<Instant> = None;
     let mut startup_gate_mode = StartupGateMode::HoldControl;
+    let mut stale_terminal_input_suppress_until: Option<Instant> = None;
     if let Some(frame) = first_frame {
         if !forward_only {
             render_frame(&frame)?;
@@ -4337,7 +4349,13 @@ async fn run_terminal(
         && cred.mode != "view-only"
         && !forward_only
     {
-        send_input(&socket, addr, &cred, &mut send_seq, bytes).await?;
+        if !send_input(&socket, addr, &cred, &mut send_seq, bytes.clone()).await? {
+            queue_stale_pending_user_input(
+                &mut pending_user_input,
+                &mut pending_user_input_bytes,
+                bytes,
+            )?;
+        }
         startup_input_hold_until = Some(Instant::now() + STARTUP_INPUT_HOLD);
         startup_gate_mode = StartupGateMode::HoldAll;
     }
@@ -4373,10 +4391,19 @@ async fn run_terminal(
             biased;
             stdin_msg = stdin_rx.recv() => {
                 match stdin_msg {
-                    Some(bytes) => {
+                    Some(mut bytes) => {
                         if input_matches_escape(&bytes, escape_key.as_deref()) {
                             break;
                         }
+                        if should_strip_stale_terminal_reports(
+                            last_packet_at.elapsed(),
+                            stale_terminal_input_suppress_until,
+                        ) {
+                            bytes = strip_stale_mouse_reports(&bytes);
+                            if bytes.is_empty() {
+                                continue;
+                            }
+                        }
                         if cred.mode != "view-only" && cred.mode != "forward-only" {
                             if let Some(deadline) = startup_input_hold_until {
                                 if !predictor.alternate_screen
@@ -4411,8 +4438,15 @@ async fn run_terminal(
                                 && let Some((send_now, mut hold_for_later)) =
                                     split_after_command_submit(&bytes)
                             {
-                                predictor.observe_input(&send_now)?;
-                                send_input(&socket, addr, &cred, &mut send_seq, send_now).await?;
+                                if send_input(&socket, addr, &cred, &mut send_seq, send_now.clone()).await? {
+                                    predictor.observe_input(&send_now)?;
+                                } else {
+                                    queue_stale_pending_user_input(
+                                        &mut pending_user_input,
+                                        &mut pending_user_input_bytes,
+                                        send_now,
+                                    )?;
+                                }
                                 startup_input_hold_until = Some(
                                     Instant::now()
                                         + post_submit_hold_duration(&hold_for_later),
@@ -4431,15 +4465,23 @@ async fn run_terminal(
                                     )?;
                                     continue;
                                 } else if !hold_for_later.is_empty() {
-                                    predictor.observe_input(&hold_for_later)?;
-                                    send_input(
+                                    let sent = send_input(
                                         &socket,
                                         addr,
                                         &cred,
                                         &mut send_seq,
-                                        std::mem::take(&mut hold_for_later),
+                                        hold_for_later.clone(),
                                     )
                                     .await?;
+                                    if sent {
+                                        predictor.observe_input(&hold_for_later)?;
+                                    } else {
+                                        queue_stale_pending_user_input(
+                                            &mut pending_user_input,
+                                            &mut pending_user_input_bytes,
+                                            std::mem::take(&mut hold_for_later),
+                                        )?;
+                                    }
                                 }
                                 continue;
                             }
@@ -4460,6 +4502,9 @@ async fn run_terminal(
                                 .await?
                                 {
                                     refresh_live_addr(&mut addr, &cred)?;
+                                    arm_stale_terminal_input_suppression(
+                                        &mut stale_terminal_input_suppress_until,
+                                    );
                                     if !forward_only {
                                         render_frame(&frame)?;
                                         predictor.observe_output(&frame.bytes);
@@ -4477,8 +4522,15 @@ async fn run_terminal(
                                     .await?;
                                 }
                             } else {
-                                predictor.observe_input(&bytes)?;
-                                send_input(&socket, addr, &cred, &mut send_seq, bytes).await?;
+                                if send_input(&socket, addr, &cred, &mut send_seq, bytes.clone()).await? {
+                                    predictor.observe_input(&bytes)?;
+                                } else {
+                                    queue_stale_pending_user_input(
+                                        &mut pending_user_input,
+                                        &mut pending_user_input_bytes,
+                                        bytes,
+                                    )?;
+                                }
                             }
                         }
                     }
@@ -4512,6 +4564,9 @@ async fn run_terminal(
                     .await?
                 {
                     refresh_live_addr(&mut addr, &cred)?;
+                    arm_stale_terminal_input_suppression(
+                        &mut stale_terminal_input_suppress_until,
+                    );
                     if !forward_only {
                         render_frame(&frame)?;
                         predictor.observe_output(&frame.bytes);
@@ -4562,6 +4617,9 @@ async fn run_terminal(
                             .await?
                             {
                                 refresh_live_addr(&mut addr, &cred)?;
+                                arm_stale_terminal_input_suppression(
+                                    &mut stale_terminal_input_suppress_until,
+                                );
                                 if !forward_only {
                                     render_frame(&frame)?;
                                     predictor.observe_output(&frame.bytes);
@@ -4667,7 +4725,7 @@ async fn run_terminal(
                             CLIENT_TO_SERVER,
                             b"",
                         )?;
-                        socket.send_to(&ack, addr).await?;
+                        let _ = send_terminal_udp(&socket, &ack, addr).await?;
                     }
                     PacketKind::AttachReject => {
                         let reject: AttachReject = protocol::from_body(&packet.body)?;
@@ -4683,6 +4741,9 @@ async fn run_terminal(
                             .await?
                             {
                                 refresh_live_addr(&mut addr, &cred)?;
+                                arm_stale_terminal_input_suppression(
+                                    &mut stale_terminal_input_suppress_until,
+                                );
                                 if !forward_only {
                                     render_frame(&frame)?;
                                     predictor.observe_output(&frame.bytes);
@@ -5075,6 +5136,9 @@ async fn run_terminal(
                     .await?
                     {
                         refresh_live_addr(&mut addr, &cred)?;
+                        arm_stale_terminal_input_suppression(
+                            &mut stale_terminal_input_suppress_until,
+                        );
                         if !forward_only {
                             render_frame(&frame)?;
                             predictor.observe_output(&frame.bytes);
@@ -5102,7 +5166,7 @@ async fn run_terminal(
                         b"",
                     )?;
                     send_seq += 1;
-                    socket.send_to(&packet, addr).await?;
+                    let _ = send_terminal_udp(&socket, &packet, addr).await?;
                 }
                 // Re-evaluate the prediction display policy on every timer tick so
                 // a latency spike (or recovery) flips speculation on/off promptly
@@ -5416,6 +5480,23 @@ fn queue_pending_user_input_with_filter(
     Ok(())
 }
 
+fn requeue_pending_user_input_front(
+    pending: &mut VecDeque<PendingUserInput>,
+    pending_bytes: &mut usize,
+    input: PendingUserInput,
+) -> Result<()> {
+    let next = pending_bytes
+        .checked_add(input.bytes.len())
+        .ok_or_else(|| anyhow!("pending input buffer overflow"))?;
+    anyhow::ensure!(
+        next <= MAX_PENDING_USER_INPUT_BYTES,
+        "pending input buffer full while disconnected"
+    );
+    *pending_bytes = next;
+    pending.push_front(input);
+    Ok(())
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct PendingUserInput {
     bytes: Vec<u8>,
@@ -5463,6 +5544,18 @@ fn should_flush_terminal_input_after_contact(
     !forward_only && !pending_empty && mode != "view-only" && mode != "forward-only"
 }
 
+fn should_strip_stale_terminal_reports(
+    silent_for: Duration,
+    suppress_until: Option<Instant>,
+) -> bool {
+    silent_for >= STALE_TERMINAL_INPUT_AFTER
+        || suppress_until.is_some_and(|deadline| Instant::now() < deadline)
+}
+
+fn arm_stale_terminal_input_suppression(suppress_until: &mut Option<Instant>) {
+    *suppress_until = Some(Instant::now() + POST_RECONNECT_STALE_INPUT_GRACE);
+}
+
 async fn flush_pending_user_input(
     socket: &UdpSocket,
     addr: SocketAddr,
@@ -5486,8 +5579,19 @@ async fn flush_pending_user_input(
         if bytes.is_empty() {
             continue;
         }
-        predictor.observe_input(&bytes)?;
-        send_input(socket, addr, cred, send_seq, bytes).await?;
+        if send_input(socket, addr, cred, send_seq, bytes.clone()).await? {
+            predictor.observe_input(&bytes)?;
+        } else {
+            requeue_pending_user_input_front(
+                pending,
+                pending_bytes,
+                PendingUserInput {
+                    bytes,
+                    strip_mouse_reports: false,
+                },
+            )?;
+            break;
+        }
     }
     Ok(())
 }
@@ -5513,6 +5617,7 @@ fn stale_mouse_report_len(bytes: &[u8], offset: usize) -> Option<usize> {
     match bytes.get(offset).copied()? {
         0x1b if bytes.get(offset + 1) == Some(&b'[') => match bytes.get(offset + 2).copied() {
             Some(b'M') if offset + 6 <= bytes.len() => Some(6),
+            Some(b'I' | b'O') => Some(3),
             Some(b'<') => mouse_report_params_len(bytes, offset + 3, 2).map(|len| len + 3),
             Some(byte) if byte.is_ascii_digit() => {
                 mouse_report_params_len(bytes, offset + 2, 2).map(|len| len + 2)
@@ -5521,13 +5626,15 @@ fn stale_mouse_report_len(bytes: &[u8], offset: usize) -> Option<usize> {
         },
         0x9b => match bytes.get(offset + 1).copied() {
             Some(b'M') if offset + 5 <= bytes.len() => Some(5),
+            Some(b'I' | b'O') => Some(2),
             Some(b'<') => mouse_report_params_len(bytes, offset + 2, 2).map(|len| len + 2),
             Some(byte) if byte.is_ascii_digit() => {
                 mouse_report_params_len(bytes, offset + 1, 2).map(|len| len + 1)
             }
             _ => None,
         },
-        byte if byte.is_ascii_digit() => mouse_report_params_len(bytes, offset, 1),
+        byte if byte.is_ascii_digit() => mouse_report_params_len(bytes, offset, 1)
+            .or_else(|| orphan_mouse_suffix_len(bytes, offset)),
         _ => None,
     }
 }
@@ -5549,6 +5656,21 @@ fn mouse_report_params_len(bytes: &[u8], offset: usize, min_semicolons: usize) -
     None
 }
 
+fn orphan_mouse_suffix_len(bytes: &[u8], offset: usize) -> Option<usize> {
+    if offset != 0 {
+        return None;
+    }
+    let mut cursor = offset;
+    while let Some(byte) = bytes.get(cursor).copied() {
+        match byte {
+            b'0'..=b'9' => cursor += 1,
+            b'M' | b'm' if cursor > offset => return Some(cursor + 1 - offset),
+            _ => return None,
+        }
+    }
+    None
+}
+
 fn stale_mouse_report_maybe_incomplete(bytes: &[u8], offset: usize) -> bool {
     let Some(rest) = bytes.get(offset..) else {
         return false;
@@ -5557,19 +5679,21 @@ fn stale_mouse_report_maybe_incomplete(bytes: &[u8], offset: usize) -> bool {
         [0x1b] | [0x1b, b'['] | [0x1b, b'[', b'<'] => true,
         [0x1b, b'[', b'M', ..] if rest.len() < 6 => true,
         [0x1b, b'[', b'<', params @ ..] | [0x1b, b'[', params @ ..]
-            if params_are_mouse_prefix(params) =>
+            if params_are_mouse_prefix(params, 2) =>
         {
             true
         }
         [0x9b] | [0x9b, b'<'] => true,
         [0x9b, b'M', ..] if rest.len() < 5 => true,
-        [0x9b, b'<', params @ ..] | [0x9b, params @ ..] if params_are_mouse_prefix(params) => true,
-        params if params_are_mouse_prefix(params) => true,
+        [0x9b, b'<', params @ ..] | [0x9b, params @ ..] if params_are_mouse_prefix(params, 2) => {
+            true
+        }
+        params if params_are_mouse_prefix(params, 2) => true,
         _ => false,
     }
 }
 
-fn params_are_mouse_prefix(params: &[u8]) -> bool {
+fn params_are_mouse_prefix(params: &[u8], min_semicolons: usize) -> bool {
     let mut semicolons = 0usize;
     let mut saw_digit = false;
     for byte in params {
@@ -5579,7 +5703,7 @@ fn params_are_mouse_prefix(params: &[u8]) -> bool {
             _ => return false,
         }
     }
-    saw_digit && semicolons >= 1
+    saw_digit && semicolons >= min_semicolons
 }
 
 async fn flush_startup_input_if_ready(
@@ -5619,7 +5743,7 @@ async fn send_input(
     cred: &CachedCredential,
     send_seq: &mut u64,
     bytes: Vec<u8>,
-) -> Result<()> {
+) -> Result<bool> {
     let body = protocol::to_body(&Input { bytes })?;
     let packet = protocol::encode_encrypted(
         PacketKind::Input,
@@ -5631,8 +5755,7 @@ async fn send_input(
         &body,
     )?;
     *send_seq += 1;
-    socket.send_to(&packet, addr).await?;
-    Ok(())
+    send_terminal_udp(socket, &packet, addr).await
 }
 
 async fn send_stream_open(
@@ -5975,7 +6098,7 @@ async fn send_stream_packet(
         body,
     )?;
     *send_seq += 1;
-    socket.send_to(&packet, addr).await?;
+    let _ = send_terminal_udp(socket, &packet, addr).await?;
     Ok(())
 }
 
@@ -6739,7 +6862,7 @@ async fn send_resize(
         &body,
     )?;
     *send_seq += 1;
-    socket.send_to(&packet, addr).await?;
+    let _ = send_terminal_udp(socket, &packet, addr).await?;
     Ok(())
 }
 
@@ -6759,7 +6882,7 @@ async fn send_ack(
         b"",
     )?;
     *send_seq += 1;
-    socket.send_to(&packet, addr).await?;
+    let _ = send_terminal_udp(socket, &packet, addr).await?;
     Ok(())
 }
 
@@ -6774,7 +6897,7 @@ async fn detach_once(socket: &UdpSocket, cred: &CachedCredential, seq: u64) -> R
         CLIENT_TO_SERVER,
         b"",
     )?;
-    socket.send_to(&packet, addr).await?;
+    let _ = send_terminal_udp(socket, &packet, addr).await?;
     Ok(())
 }
 
@@ -7128,6 +7251,7 @@ mod tests {
     use dosh::config::{ClientConfig, CommandExtension, HostConfig};
     use dosh::native::EnvVar;
     use dosh::protocol::{self, Frame, PacketKind};
+    use dosh::udp::is_transient_udp_send_error;
     use ed25519_dalek::{SigningKey, VerifyingKey};
     use std::collections::{HashMap, VecDeque};
     use std::fs;
@@ -8353,6 +8477,41 @@ mod tests {
         assert_eq!(pending_bytes, MAX_PENDING_USER_INPUT_BYTES);
     }
 
+    #[test]
+    fn transient_udp_send_errors_are_not_terminal_fatal() {
+        #[cfg(unix)]
+        {
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::ENETUNREACH)
+            ));
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::EHOSTUNREACH)
+            ));
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::EADDRNOTAVAIL)
+            ));
+            assert!(!is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(libc::EINVAL)
+            ));
+        }
+
+        #[cfg(windows)]
+        {
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10051)
+            )); // WSAENETUNREACH
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10065)
+            )); // WSAEHOSTUNREACH
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10049)
+            )); // WSAEADDRNOTAVAIL
+            assert!(!is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(10022)
+            )); // WSAEINVAL
+        }
+    }
+
     #[test]
     fn stale_mouse_reports_are_stripped_from_pending_input() {
         let input = b"\x1b[<35;152;1Mhello\x1b[<0;107;10m";
@@ -8366,6 +8525,32 @@ mod tests {
         assert_eq!(strip_stale_mouse_reports(b"152;1Mls\r"), b"ls\r");
     }
 
+    #[test]
+    fn split_stale_mouse_suffixes_are_stripped_from_pending_input() {
+        assert_eq!(strip_stale_mouse_reports(b"1M35;149;1Mls\r"), b"ls\r");
+        assert_eq!(strip_stale_mouse_reports(b"10m"), b"");
+    }
+
+    #[test]
+    fn numeric_semicolon_input_survives_stale_filter() {
+        assert_eq!(strip_stale_mouse_reports(b"123;"), b"123;");
+        assert_eq!(strip_stale_mouse_reports(b"12;34"), b"12;34");
+        assert_eq!(strip_stale_mouse_reports(b"echo 1;"), b"echo 1;");
+    }
+
+    #[test]
+    fn incomplete_three_field_mouse_prefix_is_suppressed() {
+        assert_eq!(strip_stale_mouse_reports(b"35;152;"), b"");
+        assert_eq!(strip_stale_mouse_reports(b"\x1b[<35;152;"), b"");
+        assert_eq!(strip_stale_mouse_reports(b"\x9b35;152;"), b"");
+    }
+
+    #[test]
+    fn stale_focus_reports_are_stripped_from_pending_input() {
+        assert_eq!(strip_stale_mouse_reports(b"\x1b[Ihello\x1b[O"), b"hello");
+        assert_eq!(strip_stale_mouse_reports(b"\x9bIhello\x9bO"), b"hello");
+    }
+
     #[test]
     fn non_mouse_escape_input_survives_stale_filter() {
         assert_eq!(strip_stale_mouse_reports(b"\x1b[A"), b"\x1b[A");

src/bin/dosh-server.rs

@@ -28,6 +28,7 @@ use dosh::protocol::{
     TicketAttachBody, TicketAttachEnvelope, TicketAttachOkEnvelope,
 };
 use dosh::pty::{PtyHandle, PtyOutput, adopt_pty_from_fd, spawn_pty_session};
+use dosh::udp::is_transient_udp_send_error;
 use sha2::{Digest, Sha256};
 use std::collections::{BTreeMap, HashMap, HashSet, VecDeque};
 use std::fs;
@@ -432,6 +433,7 @@ struct PendingStreamOpen {
     attempts: u32,
 }
 
+#[derive(Clone)]
 struct PendingNativeAuth {
     client: dosh::native::NativeClientHello,
     server: NativeServerHello,
@@ -863,6 +865,7 @@ async fn handle_packet(
         | PacketKind::StreamEof
         | PacketKind::StreamWindowAdjust
         | PacketKind::RekeyAck
+        | PacketKind::Detach
             if find_client_decrypt_key(state, &packet.header).is_err() =>
         {
             send_reject_to_client(socket, peer, packet.header.conn_id, "unknown client").await
@@ -980,7 +983,7 @@ async fn handle_native_client_hello(
     };
     let body = protocol::to_body(&NativeServerHelloBody { hello })?;
     let out = protocol::encode_plain(PacketKind::NativeServerHello, pending_id, 1, 0, &body)?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -991,8 +994,8 @@ async fn handle_native_user_auth(
     packet: &protocol::Packet,
 ) -> Result<()> {
     let pending = {
-        let mut locked = state.lock().expect("server state poisoned");
-        locked.pending_native.remove(&packet.header.conn_id)
+        let locked = state.lock().expect("server state poisoned");
+        locked.pending_native.get(&packet.header.conn_id).cloned()
     };
     let Some(pending) = pending else {
         return send_reject_to_client(socket, peer, packet.header.conn_id, "unknown native auth")
@@ -1008,11 +1011,38 @@ async fn handle_native_user_auth(
         .await;
     }
     if pending.created_at.elapsed() > Duration::from_secs(30) {
+        state
+            .lock()
+            .expect("server state poisoned")
+            .pending_native
+            .remove(&packet.header.conn_id);
         return send_reject_to_client(socket, peer, packet.header.conn_id, "native auth expired")
             .await;
     }
-    let body = protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER)?;
-    let req: NativeUserAuthBody = protocol::from_body(&body)?;
+    let body = match protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER) {
+        Ok(body) => body,
+        Err(_) => {
+            return send_reject_to_client(
+                socket,
+                peer,
+                packet.header.conn_id,
+                "native auth decrypt failed",
+            )
+            .await;
+        }
+    };
+    let req: NativeUserAuthBody = match protocol::from_body(&body) {
+        Ok(req) => req,
+        Err(_) => {
+            return send_reject_to_client(
+                socket,
+                peer,
+                packet.header.conn_id,
+                "invalid native auth body",
+            )
+            .await;
+        }
+    };
     if pending.client.requested_mode == "doctor" {
         let check_result = {
             let locked = state.lock().expect("server state poisoned");
@@ -1048,6 +1078,11 @@ async fn handle_native_user_auth(
                 .await;
             }
         };
+        state
+            .lock()
+            .expect("server state poisoned")
+            .pending_native
+            .remove(&packet.header.conn_id);
         let body = protocol::to_body(&check)?;
         let out = protocol::encode_encrypted(
             PacketKind::NativeAuthCheckOk,
@@ -1058,7 +1093,7 @@ async fn handle_native_user_auth(
             SERVER_TO_CLIENT,
             &body,
         )?;
-        socket.send_to(&out, peer).await?;
+        let _ = send_udp(socket, &out, peer).await?;
         return Ok(());
     }
 
@@ -1228,6 +1263,11 @@ async fn handle_native_user_auth(
     if let Some((listener, path)) = agent_listener {
         spawn_agent_forward(state, socket, client_id, listener, path);
     }
+    state
+        .lock()
+        .expect("server state poisoned")
+        .pending_native
+        .remove(&packet.header.conn_id);
 
     let ok = NativeAuthOk {
         client_id,
@@ -1251,7 +1291,7 @@ async fn handle_native_user_auth(
         SERVER_TO_CLIENT,
         &body,
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1359,7 +1399,7 @@ async fn handle_bootstrap_attach(
         SERVER_TO_CLIENT,
         &body,
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1494,7 +1534,7 @@ async fn handle_ticket_attach(
     };
     let body = protocol::to_body(&envelope)?;
     let out = protocol::encode_plain(PacketKind::AttachOk, client_id, 1, 0, &body)?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1512,7 +1552,7 @@ async fn send_reject_to_client(
         reason: reason.to_string(),
     })?;
     let out = protocol::encode_plain(PacketKind::AttachReject, client_id, 0, 0, &body)?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1578,7 +1618,7 @@ async fn handle_resume(
         SERVER_TO_CLIENT,
         &body,
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
@@ -1690,12 +1730,19 @@ async fn handle_ping(
         SERVER_TO_CLIENT,
         b"",
     )?;
-    socket.send_to(&out, peer).await?;
+    let _ = send_udp(socket, &out, peer).await?;
     Ok(())
 }
 
 async fn handle_detach(state: &Arc<Mutex<ServerState>>, packet: &protocol::Packet) -> Result<()> {
+    let (key, _) = find_client_decrypt_key(state, &packet.header)?;
+    let _ = protocol::decrypt_body(packet, &key, CLIENT_TO_SERVER)?;
     let mut locked = state.lock().expect("server state poisoned");
+    if let Some(client) = locked.client_mut(&packet.header.conn_id) {
+        if !client.replay.accept(packet.header.seq) {
+            return Ok(());
+        }
+    }
     locked.remove_client_everywhere(&packet.header.conn_id);
     Ok(())
 }
@@ -1705,6 +1752,14 @@ fn remove_client(state: &Arc<Mutex<ServerState>>, client_id: [u8; 16]) {
     locked.remove_client_everywhere(&client_id);
 }
 
+async fn send_udp(socket: &UdpSocket, packet: &[u8], peer: SocketAddr) -> Result<bool> {
+    match socket.send_to(packet, peer).await {
+        Ok(_) => Ok(true),
+        Err(err) if is_transient_udp_send_error(&err) => Ok(false),
+        Err(err) => Err(err).with_context(|| format!("send UDP packet to {peer}")),
+    }
+}
+
 async fn handle_ack(
     state: &Arc<Mutex<ServerState>>,
     peer: SocketAddr,
@@ -3020,7 +3075,7 @@ async fn send_stream_open_to_client(
         found
     };
     if let Some((endpoint, packet)) = send {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3114,7 +3169,7 @@ async fn queue_or_send_stream_data_to_client(
         send
     };
     if let Some((endpoint, packet)) = send {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3189,7 +3244,7 @@ async fn flush_stream_pending_data_to_client(
         let Some((endpoint, packet)) = send else {
             return Ok(());
         };
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
 }
 
@@ -3333,7 +3388,7 @@ async fn send_stream_packet_to_client(
         found
     };
     if let Some((endpoint, packet)) = send {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3435,7 +3490,7 @@ async fn broadcast_output(
         }
     }
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3488,7 +3543,7 @@ async fn broadcast_session_exit(
         persist::remove_runtime_dir(&sessions_dir, &session_name);
     }
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3595,7 +3650,7 @@ async fn retransmit_pending(
         sends
     };
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -3691,7 +3746,7 @@ async fn maybe_rekey_clients(
         sends
     };
     for (endpoint, packet) in sends {
-        socket.send_to(&packet, endpoint).await?;
+        let _ = send_udp(socket, &packet, endpoint).await?;
     }
     Ok(())
 }
@@ -4058,6 +4113,63 @@ mod tests {
         assert!(locked.lookup_client(&client_id).is_none());
     }
 
+    #[tokio::test]
+    async fn forged_plaintext_detach_does_not_remove_client() {
+        let (pty_tx, _pty_rx) = mpsc::unbounded_channel();
+        let mut state = ServerState::new(ServerConfig::default(), [0u8; 32], pty_tx);
+        state
+            .ensure_session("work", 80, 24, "forward-only", &[])
+            .unwrap();
+        let client_id = [21u8; 16];
+        let session_key = [22u8; 32];
+        state.insert_client("work", client_id, test_client_state(session_key));
+        let state = Arc::new(Mutex::new(state));
+        let mut packet = protocol::decode(
+            &protocol::encode_plain(PacketKind::Detach, client_id, 1, 0, b"").unwrap(),
+        )
+        .unwrap();
+        packet.header.session_key_id = protocol::session_key_id(&session_key);
+
+        assert!(handle_detach(&state, &packet).await.is_err());
+
+        let locked = state.lock().unwrap();
+        assert!(
+            locked.lookup_client(&client_id).is_some(),
+            "plaintext detach with a copied key id must not remove a live client"
+        );
+    }
+
+    #[tokio::test]
+    async fn authenticated_detach_removes_client() {
+        let (pty_tx, _pty_rx) = mpsc::unbounded_channel();
+        let mut state = ServerState::new(ServerConfig::default(), [0u8; 32], pty_tx);
+        state
+            .ensure_session("work", 80, 24, "forward-only", &[])
+            .unwrap();
+        let client_id = [23u8; 16];
+        let session_key = [24u8; 32];
+        state.insert_client("work", client_id, test_client_state(session_key));
+        let state = Arc::new(Mutex::new(state));
+        let packet = protocol::decode(
+            &protocol::encode_encrypted(
+                PacketKind::Detach,
+                client_id,
+                1,
+                0,
+                &session_key,
+                CLIENT_TO_SERVER,
+                b"",
+            )
+            .unwrap(),
+        )
+        .unwrap();
+
+        handle_detach(&state, &packet).await.unwrap();
+
+        let locked = state.lock().unwrap();
+        assert!(locked.lookup_client(&client_id).is_none());
+    }
+
     #[tokio::test]
     async fn duplicate_stream_open_for_open_stream_resends_ok() {
         let (pty_tx, _pty_rx) = mpsc::unbounded_channel();
@@ -4536,4 +4648,25 @@ mod tests {
         };
         remote_bind_allowed(&config, "0.0.0.0").unwrap();
     }
+
+    #[cfg(unix)]
+    #[test]
+    fn server_udp_send_classifier_treats_network_roaming_errors_as_transient() {
+        for code in [
+            libc::EADDRNOTAVAIL,
+            libc::ECONNREFUSED,
+            libc::ECONNRESET,
+            libc::EHOSTDOWN,
+            libc::EHOSTUNREACH,
+            libc::ENETDOWN,
+            libc::ENETRESET,
+            libc::ENETUNREACH,
+            libc::ETIMEDOUT,
+        ] {
+            assert!(
+                is_transient_udp_send_error(&std::io::Error::from_raw_os_error(code)),
+                "expected errno {code} to be transient"
+            );
+        }
+    }
 }

src/lib.rs

@@ -23,3 +23,4 @@ pub mod pty;
 pub mod server;
 pub mod ssh_agent;
 pub mod transport;
+pub mod udp;

src/protocol.rs

@@ -280,7 +280,7 @@ pub fn decode(input: &[u8]) -> Result<Packet> {
 
 pub fn decrypt_body(packet: &Packet, key: &[u8; 32], direction: u32) -> Result<Vec<u8>> {
     if packet.header.flags & 1 == 0 {
-        return Ok(packet.body.clone());
+        bail!("packet body is not encrypted");
     }
     let nonce = crypto::nonce_from(direction, packet.header.seq);
     let aad = packet.header.aad();

src/server.rs

@@ -13,6 +13,7 @@ use crate::transport::{
     DoshTransport, SessionEvent, SessionRole, SessionTransportConfig, TransportConfig,
     service_name_from_target,
 };
+use crate::udp::is_transient_udp_send_error;
 use anyhow::{Context, Result, anyhow, bail};
 use ed25519_dalek::SigningKey;
 use std::collections::{HashMap, HashSet};
@@ -97,6 +98,7 @@ pub enum DoshServerEvent {
     Ignored,
 }
 
+#[derive(Debug, Clone)]
 struct PendingServerAuth {
     client: native::NativeClientHello,
     server: NativeServerHello,
@@ -255,7 +257,7 @@ impl DoshServer {
         };
         let body = protocol::to_body(&NativeServerHelloBody { hello })?;
         let out = protocol::encode_plain(PacketKind::NativeServerHello, pending_id, 1, 0, &body)?;
-        self.socket.send_to(&out, peer).await?;
+        let _ = send_udp(&self.socket, &out, peer).await?;
         Ok(())
     }
 
@@ -327,7 +329,7 @@ impl DoshServer {
         peer: SocketAddr,
         packet: &protocol::Packet,
     ) -> Result<DoshServerEvent> {
-        let Some(pending) = self.pending.remove(&packet.header.conn_id) else {
+        let Some(pending) = self.pending.get(&packet.header.conn_id).cloned() else {
             self.send_reject(peer, packet.header.conn_id, "unknown native auth")
                 .await?;
             return Ok(DoshServerEvent::Ignored);
@@ -338,13 +340,28 @@ impl DoshServer {
             return Ok(DoshServerEvent::Ignored);
         }
         if pending.created_at.elapsed() > self.config.auth_timeout {
+            self.pending.remove(&packet.header.conn_id);
             self.send_reject(peer, packet.header.conn_id, "native auth expired")
                 .await?;
             return Ok(DoshServerEvent::Ignored);
         }
 
-        let body = protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER)?;
-        let req: NativeUserAuthBody = protocol::from_body(&body)?;
+        let body = match protocol::decrypt_body(packet, &pending.session_key, CLIENT_TO_SERVER) {
+            Ok(body) => body,
+            Err(_) => {
+                self.send_reject(peer, packet.header.conn_id, "native auth decrypt failed")
+                    .await?;
+                return Ok(DoshServerEvent::Ignored);
+            }
+        };
+        let req: NativeUserAuthBody = match protocol::from_body(&body) {
+            Ok(req) => req,
+            Err(_) => {
+                self.send_reject(peer, packet.header.conn_id, "invalid native auth body")
+                    .await?;
+                return Ok(DoshServerEvent::Ignored);
+            }
+        };
         let services = match self.verify_auth_and_services(&pending, &req.auth) {
             Ok(services) => services,
             Err(err) => {
@@ -353,6 +370,7 @@ impl DoshServer {
                 return Ok(DoshServerEvent::Ignored);
             }
         };
+        self.pending.remove(&packet.header.conn_id);
 
         let conn_id = crypto::random_16();
         let key_id = protocol::session_key_id(&pending.session_key);
@@ -381,7 +399,7 @@ impl DoshServer {
             SERVER_TO_CLIENT,
             &body,
         )?;
-        self.socket.send_to(&out, peer).await?;
+        let _ = send_udp(&self.socket, &out, peer).await?;
 
         let transport = DoshTransport::new(
             Arc::clone(&self.socket),
@@ -428,7 +446,7 @@ impl DoshServer {
             reason: reason.to_string(),
         })?;
         let out = protocol::encode_plain(PacketKind::AttachReject, conn_id, 0, 0, &body)?;
-        self.socket.send_to(&out, peer).await?;
+        let _ = send_udp(&self.socket, &out, peer).await?;
         Ok(())
     }
 
@@ -439,6 +457,14 @@ impl DoshServer {
     }
 }
 
+async fn send_udp(socket: &UdpSocket, packet: &[u8], peer: SocketAddr) -> Result<bool> {
+    match socket.send_to(packet, peer).await {
+        Ok(_) => Ok(true),
+        Err(err) if is_transient_udp_send_error(&err) => Ok(false),
+        Err(err) => Err(err).with_context(|| format!("send UDP packet to {peer}")),
+    }
+}
+
 fn validate_requested_services(
     allowed_services: &HashSet<String>,
     requests: &[ForwardingRequest],
@@ -477,6 +503,7 @@ mod tests {
     use super::*;
     use crate::client::DoshClient;
     use crate::config::{ClientConfig, HostsConfig};
+    use crate::protocol::{CLIENT_TO_SERVER, NativeUserAuthBody};
     use crate::transport::TransportEvent;
     use ed25519_dalek::SigningKey;
 
@@ -588,4 +615,91 @@ mod tests {
             }
         }
     }
+
+    #[tokio::test]
+    async fn bad_native_auth_does_not_consume_pending_challenge() {
+        let dir = tempfile::tempdir().unwrap();
+        let host_key = dir.path().join("host_key");
+        let authorized_keys = dir.path().join("authorized_keys");
+        let signing = SigningKey::from_bytes(&[93u8; 32]);
+        let keypair = ssh_key::private::Ed25519Keypair::from(&signing);
+        let private =
+            ssh_key::PrivateKey::new(ssh_key::private::KeypairData::from(keypair), "").unwrap();
+        std::fs::write(
+            &authorized_keys,
+            format!("{}\n", private.public_key().to_openssh().unwrap()),
+        )
+        .unwrap();
+
+        let server_config = ServerConfig {
+            host_key: host_key.to_string_lossy().to_string(),
+            authorized_keys: vec![authorized_keys.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 peer: SocketAddr = "127.0.0.1:9".parse().unwrap();
+        let (client_secret, client_public) = native::generate_native_ephemeral();
+        let hello = native::NativeClientHello {
+            protocol_version: native::NATIVE_PROTOCOL_VERSION,
+            client_random: crypto::random_32(),
+            client_ephemeral_public: client_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(),
+        };
+        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,
+            &hello,
+            &server_hello,
+        )
+        .unwrap();
+        let auth = native::sign_user_auth(&signing, &hello, &server_hello, Vec::new()).unwrap();
+        let body = protocol::to_body(&NativeUserAuthBody { auth }).unwrap();
+        let bad = protocol::encode_encrypted(
+            PacketKind::NativeUserAuth,
+            pending_id,
+            2,
+            1,
+            &[7u8; 32],
+            CLIENT_TO_SERVER,
+            &body,
+        )
+        .unwrap();
+        let bad = protocol::decode(&bad).unwrap();
+
+        assert!(matches!(
+            server.handle_user_auth(peer, &bad).await.unwrap(),
+            DoshServerEvent::Ignored
+        ));
+        assert!(server.pending.contains_key(&pending_id));
+
+        let valid = protocol::encode_encrypted(
+            PacketKind::NativeUserAuth,
+            pending_id,
+            2,
+            1,
+            &session_key,
+            CLIENT_TO_SERVER,
+            &body,
+        )
+        .unwrap();
+        let valid = protocol::decode(&valid).unwrap();
+        assert!(matches!(
+            server.handle_user_auth(peer, &valid).await.unwrap(),
+            DoshServerEvent::Accepted(_)
+        ));
+        assert!(!server.pending.contains_key(&pending_id));
+    }
 }

src/transport.rs

@@ -19,6 +19,7 @@ use crate::protocol::{
     self, CLIENT_TO_SERVER, PacketKind, ReplayWindow, SERVER_TO_CLIENT, StreamClose, StreamData,
     StreamOpen, StreamOpenOk, StreamOpenReject, StreamWindowAdjust,
 };
+use crate::udp::is_transient_udp_send_error;
 use anyhow::{Result, anyhow, bail};
 use std::collections::{BTreeMap, HashMap, HashSet, VecDeque};
 use std::net::SocketAddr;
@@ -348,8 +349,8 @@ impl StreamMux {
         &mut self,
         adjust: StreamWindowAdjust,
     ) -> Result<Vec<OutgoingStreamPacket>> {
-        self.ack_data(adjust.stream_id, adjust.received_offset);
-        self.add_credit(adjust.stream_id, adjust.bytes as usize);
+        let acked_bytes = self.ack_data(adjust.stream_id, adjust.received_offset);
+        self.add_credit(adjust.stream_id, acked_bytes);
         self.flush_pending_data(adjust.stream_id)
     }
 
@@ -556,9 +557,9 @@ impl StreamMux {
         (chunks, consumed, *expected)
     }
 
-    fn ack_data(&mut self, stream_id: u64, received_offset: u64) {
+    fn ack_data(&mut self, stream_id: u64, received_offset: u64) -> usize {
         let Some(sent) = self.sent_data.get_mut(&stream_id) else {
-            return;
+            return 0;
         };
         let acked_offsets = sent
             .iter()
@@ -567,12 +568,16 @@ impl StreamMux {
                 (end <= received_offset).then_some(*offset)
             })
             .collect::<Vec<_>>();
+        let mut acked_bytes = 0usize;
         for offset in acked_offsets {
-            sent.remove(&offset);
+            if let Some(chunk) = sent.remove(&offset) {
+                acked_bytes = acked_bytes.saturating_add(chunk.bytes.len());
+            }
         }
         if sent.is_empty() {
             self.sent_data.remove(&stream_id);
         }
+        acked_bytes
     }
 
     fn add_credit(&mut self, stream_id: u64, bytes: usize) {
@@ -732,11 +737,17 @@ impl DoshTransport {
             if packet.header.conn_id != self.conn_id {
                 continue;
             }
+            let plain = match protocol::decrypt_body(
+                &packet,
+                &self.session_key,
+                self.role.recv_direction(),
+            ) {
+                Ok(plain) => plain,
+                Err(_) => continue,
+            };
             if !self.replay.accept(packet.header.seq) {
                 continue;
             }
-            let plain =
-                protocol::decrypt_body(&packet, &self.session_key, self.role.recv_direction())?;
             self.peer_addr = peer;
             self.ack_seq = self.ack_seq.max(packet.header.seq);
             self.last_contact = Instant::now();
@@ -751,14 +762,21 @@ impl DoshTransport {
         datagram: &[u8],
         peer: SocketAddr,
     ) -> Result<SessionEvent> {
-        let packet = protocol::decode(datagram)?;
+        let packet = match protocol::decode(datagram) {
+            Ok(packet) => packet,
+            Err(_) => return Ok(SessionEvent::Ignored),
+        };
         if packet.header.conn_id != self.conn_id {
             return Ok(SessionEvent::Ignored);
         }
+        let plain =
+            match protocol::decrypt_body(&packet, &self.session_key, self.role.recv_direction()) {
+                Ok(plain) => plain,
+                Err(_) => return Ok(SessionEvent::Ignored),
+            };
         if !self.replay.accept(packet.header.seq) {
             return Ok(SessionEvent::Ignored);
         }
-        let plain = protocol::decrypt_body(&packet, &self.session_key, self.role.recv_direction())?;
         self.peer_addr = peer;
         self.ack_seq = self.ack_seq.max(packet.header.seq);
         self.last_contact = Instant::now();
@@ -815,7 +833,12 @@ impl DoshTransport {
 
     async fn send_kind(&mut self, kind: PacketKind, body: &[u8]) -> Result<()> {
         let encoded = self.encode_kind(kind, body)?;
-        self.socket.send_to(&encoded, self.peer_addr).await?;
+        if let Err(err) = self.socket.send_to(&encoded, self.peer_addr).await {
+            if is_transient_udp_send_error(&err) {
+                return Ok(());
+            }
+            return Err(err.into());
+        }
         Ok(())
     }
 
@@ -980,6 +1003,30 @@ mod tests {
         assert_eq!(data.bytes, b"!");
     }
 
+    #[test]
+    fn cumulative_window_adjust_restores_credit_even_if_delta_was_lost() {
+        let mut mux = StreamMux::new(TransportConfig {
+            initial_window: 5,
+            retransmit_after: Duration::from_secs(1),
+            ..TransportConfig::default()
+        });
+        mux.open_stream(1, "@dosh-test", 0).unwrap();
+        mux.handle_open_ok(StreamOpenOk { stream_id: 1 }).unwrap();
+        assert_eq!(mux.send_data(1, b"hello".to_vec()).unwrap().len(), 1);
+        assert_eq!(mux.send_credit[&1], 0);
+
+        let flushed = mux
+            .handle_window_adjust(StreamWindowAdjust {
+                stream_id: 1,
+                received_offset: 5,
+                bytes: 0,
+            })
+            .unwrap();
+        assert!(flushed.is_empty());
+        assert_eq!(mux.send_credit[&1], 5);
+        assert_eq!(mux.send_data(1, b"!".to_vec()).unwrap().len(), 1);
+    }
+
     #[test]
     fn handle_packet_decodes_and_dispatches_stream_packets() {
         let mut mux = StreamMux::new(TransportConfig::default());
@@ -1096,4 +1143,61 @@ mod tests {
         assert!(matches!(server.recv().await.unwrap(), SessionEvent::Ping));
         assert_eq!(server.peer_addr(), roaming_addr);
     }
+
+    #[tokio::test]
+    async fn unauthenticated_datagram_does_not_poison_replay_window() {
+        let socket = UdpSocket::bind("127.0.0.1:0").await.unwrap();
+        let peer: SocketAddr = "127.0.0.1:9".parse().unwrap();
+        let key = [11u8; 32];
+        let wrong_key = [12u8; 32];
+        let conn_id = [4u8; 16];
+        let mut transport = DoshTransport::new_owned(
+            socket,
+            SessionTransportConfig {
+                role: SessionRole::Client,
+                conn_id,
+                session_key: key,
+                peer_addr: peer,
+                initial_send_seq: 1,
+                initial_ack: 0,
+                stream: TransportConfig::default(),
+            },
+        );
+        let bad = protocol::encode_encrypted(
+            PacketKind::Pong,
+            conn_id,
+            9,
+            0,
+            &wrong_key,
+            SERVER_TO_CLIENT,
+            b"",
+        )
+        .unwrap();
+        let valid = protocol::encode_encrypted(
+            PacketKind::Pong,
+            conn_id,
+            9,
+            0,
+            &key,
+            SERVER_TO_CLIENT,
+            b"",
+        )
+        .unwrap();
+
+        assert!(matches!(
+            transport
+                .handle_datagram(b"not a dosh packet", peer)
+                .await
+                .unwrap(),
+            SessionEvent::Ignored
+        ));
+        assert!(matches!(
+            transport.handle_datagram(&bad, peer).await.unwrap(),
+            SessionEvent::Ignored
+        ));
+        assert!(matches!(
+            transport.handle_datagram(&valid, peer).await.unwrap(),
+            SessionEvent::Pong
+        ));
+    }
 }

src/udp.rs

@@ -0,0 +1,98 @@
+//! UDP error classification shared by Dosh clients, servers, and embedders.
+
+pub fn is_transient_udp_send_error(err: &std::io::Error) -> bool {
+    matches!(
+        err.kind(),
+        std::io::ErrorKind::Interrupted
+            | std::io::ErrorKind::TimedOut
+            | std::io::ErrorKind::WouldBlock
+    ) || err.raw_os_error().is_some_and(is_transient_udp_os_error)
+}
+
+#[cfg(unix)]
+fn is_transient_udp_os_error(code: i32) -> bool {
+    matches!(
+        code,
+        libc::EADDRNOTAVAIL
+            | libc::ECONNREFUSED
+            | libc::ECONNRESET
+            | libc::EHOSTDOWN
+            | libc::EHOSTUNREACH
+            | libc::ENETDOWN
+            | libc::ENETRESET
+            | libc::ENETUNREACH
+            | libc::ETIMEDOUT
+    )
+}
+
+#[cfg(windows)]
+fn is_transient_udp_os_error(code: i32) -> bool {
+    matches!(
+        code,
+        10049  // WSAEADDRNOTAVAIL
+            | 10050 // WSAENETDOWN
+            | 10051 // WSAENETUNREACH
+            | 10052 // WSAENETRESET
+            | 10054 // WSAECONNRESET
+            | 10060 // WSAETIMEDOUT
+            | 10061 // WSAECONNREFUSED
+            | 10064 // WSAEHOSTDOWN
+            | 10065 // WSAEHOSTUNREACH
+    )
+}
+
+#[cfg(not(any(unix, windows)))]
+fn is_transient_udp_os_error(_code: i32) -> bool {
+    false
+}
+
+#[cfg(test)]
+mod tests {
+    use super::is_transient_udp_send_error;
+
+    #[test]
+    fn classifies_portable_transient_send_errors() {
+        for kind in [
+            std::io::ErrorKind::Interrupted,
+            std::io::ErrorKind::TimedOut,
+            std::io::ErrorKind::WouldBlock,
+        ] {
+            assert!(is_transient_udp_send_error(&std::io::Error::from(kind)));
+        }
+        assert!(!is_transient_udp_send_error(&std::io::Error::from(
+            std::io::ErrorKind::PermissionDenied,
+        )));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn classifies_unix_network_churn_as_transient() {
+        for code in [
+            libc::EADDRNOTAVAIL,
+            libc::ECONNREFUSED,
+            libc::ECONNRESET,
+            libc::EHOSTDOWN,
+            libc::EHOSTUNREACH,
+            libc::ENETDOWN,
+            libc::ENETRESET,
+            libc::ENETUNREACH,
+            libc::ETIMEDOUT,
+        ] {
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(code)
+            ));
+        }
+    }
+
+    #[cfg(windows)]
+    #[test]
+    fn classifies_windows_network_churn_as_transient() {
+        for code in [
+            10049, 10050, 10051, 10052, 10054, 10060, 10061, 10064, 10065,
+        ] {
+            assert!(is_transient_udp_send_error(
+                &std::io::Error::from_raw_os_error(code)
+            ));
+        }
+    }
+}

tests/hostile_network.rs

@@ -258,7 +258,8 @@ fn relay_loop(
     let mut upstream = new_upstream();
     let mut client_addr: Option<SocketAddr> = None;
     let mut rng = StdRng::seed_from_u64(seed);
-    let mut held: Option<(Vec<u8>, bool)> = None; // (packet, is_c2s) held for reorder
+    let mut held_c2s: Option<Vec<u8>> = None;
+    let mut held_s2c: Option<Vec<u8>> = None;
     let mut buf = [0u8; 65535];
 
     loop {
@@ -288,10 +289,9 @@ fn relay_loop(
                         &upstream,
                         server_addr,
                         packet,
-                        true,
                         &controls,
                         &mut rng,
-                        &mut held,
+                        &mut held_c2s,
                     );
                 }
             }
@@ -310,7 +310,12 @@ fn relay_loop(
                     let drop_pct = controls.drop_s2c_percent.load(Ordering::SeqCst);
                     if drop_pct == 0 || rng.gen_range(0..100) >= drop_pct {
                         forward_with_effects(
-                            &front, dst, packet, false, &controls, &mut rng, &mut held,
+                            &front,
+                            dst,
+                            packet,
+                            &controls,
+                            &mut rng,
+                            &mut held_s2c,
                         );
                     }
                 }
@@ -336,23 +341,22 @@ fn forward_with_effects(
     out: &UdpSocket,
     dst: SocketAddr,
     packet: Vec<u8>,
-    is_c2s: bool,
     controls: &RelayControls,
     rng: &mut StdRng,
-    held: &mut Option<(Vec<u8>, bool)>,
+    held: &mut Option<Vec<u8>>,
 ) {
     // Reorder: if armed, hold this packet and release the previously held one
     // afterward (so two consecutive packets swap order).
     if controls.reorder_next.swap(false, Ordering::SeqCst) {
-        if let Some((prev, _)) = held.take() {
+        if let Some(prev) = held.take() {
             let _ = out.send_to(&packet, dst);
             let _ = out.send_to(&prev, dst);
             return;
         }
-        *held = Some((packet, is_c2s));
+        *held = Some(packet);
         return;
     }
-    if let Some((prev, _)) = held.take() {
+    if let Some(prev) = held.take() {
         let _ = out.send_to(&prev, dst);
     }
 
@@ -767,6 +771,46 @@ fn wait_for_text(socket: &UdpSocket, key: &[u8; 32], needle: &str, millis: u64)
     acc.contains(needle)
 }
 
+fn wait_for_text_with_ack(
+    socket: &UdpSocket,
+    relay: &Relay,
+    client_id: [u8; 16],
+    seq: &mut u64,
+    key: &[u8; 32],
+    needle: &str,
+    millis: u64,
+) -> bool {
+    let prev = socket.read_timeout().unwrap();
+    socket
+        .set_read_timeout(Some(Duration::from_millis(100)))
+        .unwrap();
+    let deadline = Instant::now() + Duration::from_millis(millis);
+    let mut acc = String::new();
+    while Instant::now() < deadline {
+        if let Some((_header, frame)) = recv_frame(socket, key) {
+            acc.push_str(&String::from_utf8_lossy(&frame.bytes));
+            let ack = protocol::encode_encrypted(
+                PacketKind::Ack,
+                client_id,
+                *seq,
+                frame.output_seq,
+                key,
+                CLIENT_TO_SERVER,
+                b"",
+            )
+            .unwrap();
+            *seq += 1;
+            socket.send_to(&ack, relay.front_addr()).unwrap();
+            if acc.contains(needle) {
+                socket.set_read_timeout(prev).unwrap();
+                return true;
+            }
+        }
+    }
+    socket.set_read_timeout(prev).unwrap();
+    acc.contains(needle)
+}
+
 #[test]
 fn session_survives_packet_loss_and_reorder() {
     let dir = tempfile::tempdir().unwrap();
@@ -820,6 +864,94 @@ fn session_survives_packet_loss_and_reorder() {
     );
 }
 
+#[test]
+#[ignore = "30-minute hostile-network TUI soak; run with `DOSH_BADNET_SOAK_SECONDS=1800 cargo test --test hostile_network bad_network_tui_work_soak_30m -- --ignored --nocapture`"]
+fn bad_network_tui_work_soak_30m() {
+    let soak_secs = std::env::var("DOSH_BADNET_SOAK_SECONDS")
+        .ok()
+        .and_then(|value| value.parse::<u64>().ok())
+        .unwrap_or(30 * 60);
+    let dir = tempfile::tempdir().unwrap();
+    let port = free_udp_port();
+    let config = write_server_config(&dir, port);
+    let mut server = start_server(&dir, &config);
+    let relay = Relay::spawn(port, 0xBADC0DEu64);
+    let (socket, bootstrap, ok) = attach_through_relay(&config, &relay);
+
+    relay.set_drop_c2s(15);
+    relay.set_drop_s2c(20);
+    relay.set_dup(10);
+
+    let deadline = Instant::now() + Duration::from_secs(soak_secs);
+    let mut seq = 2u64;
+    let mut iteration = 0u64;
+    while Instant::now() < deadline {
+        if iteration.is_multiple_of(2) {
+            relay.arm_reorder();
+        }
+        if iteration > 0 && iteration.is_multiple_of(7) {
+            let _ = relay.rebind_upstream();
+        }
+        if iteration > 0 && iteration.is_multiple_of(11) {
+            relay.set_drop_s2c(100);
+            thread::sleep(Duration::from_millis(750));
+            relay.set_drop_s2c(20);
+        }
+
+        let marker = format!("DOSH_BADNET_TUI_{iteration}");
+        let command = format!(
+            "stty -echo; \
+             printf '\\033[?1049h\\033[?2026h\\033[?25l'; \
+             for i in 1 2 3 4 5 6; do \
+               printf '\\033[%s;4H{} ⠀⠁⠃⠇⡇⣇⣧⣷⣿ █▇▆▅▄▃▂▁ %s\\033[0m' \"$i\" \"$i\"; \
+             done; \
+             printf '\\033[?25h\\033[?2026l\\033[?1049l'\n",
+            marker
+        );
+
+        let step_deadline = Instant::now() + Duration::from_secs(8);
+        let mut seen = false;
+        let mut attempts = 0;
+        while Instant::now() < step_deadline && attempts < 12 {
+            send_input(
+                &socket,
+                &relay,
+                ok.client_id,
+                seq,
+                0,
+                &bootstrap.session_key,
+                command.as_bytes(),
+            );
+            seq += 1;
+            attempts += 1;
+            if wait_for_text_with_ack(
+                &socket,
+                &relay,
+                ok.client_id,
+                &mut seq,
+                &bootstrap.session_key,
+                &marker,
+                500,
+            ) {
+                seen = true;
+                break;
+            }
+        }
+        assert!(
+            seen,
+            "TUI marker {marker} did not arrive during hostile-network soak"
+        );
+
+        iteration += 1;
+        thread::sleep(Duration::from_millis(500));
+    }
+
+    relay.clear_impairments();
+    drop(relay);
+    let _ = server.kill();
+    let _ = server.wait();
+}
+
 #[test]
 fn duplicated_and_replayed_input_is_applied_at_most_once() {
     let dir = tempfile::tempdir().unwrap();

tests/protocol_auth.rs

@@ -58,6 +58,19 @@ fn encrypted_packet_round_trips() {
     assert_eq!(plain, b"hello");
 }
 
+#[test]
+fn plaintext_packet_never_decrypts_as_authenticated_body() {
+    let key = crypto::random_32();
+    let mut decoded = protocol::decode(
+        &protocol::encode_plain(PacketKind::Input, crypto::random_16(), 1, 0, b"hello").unwrap(),
+    )
+    .unwrap();
+    decoded.header.session_key_id = protocol::session_key_id(&key);
+
+    let err = protocol::decrypt_body(&decoded, &key, CLIENT_TO_SERVER).unwrap_err();
+    assert!(err.to_string().contains("not encrypted"));
+}
+
 #[test]
 fn encrypted_packet_rejects_wrong_session_key_id_before_decrypt() {
     let key = crypto::random_32();