Bound every wait that could last for ever

Nine orphaned test processes were found still running from the day before,
three of them spinning on a core each for twenty hours. The code they ran
is several changes old and the mesh test passes twenty times over now, so
the wedge itself is gone — but nothing in the way it was waited on was
bounded, which is why a wedge lasted a day instead of failing a run.

The harness enforced its deadline only between probes. A probe that never
returned — one call into a wedged runtime, which is exactly what a status
request is — waited for ever inside the deadline it was supposed to obey.
The probe is now bounded too, so the same wedge fails the test in thirty
seconds.

Shutdown claimed to be bounded and was not. The plugins had a grace
period; the network runtimes, the accept loop, the plugin request loop and
the endpoint close did not, and a peer that stops reading is enough to
hold any of them open. Each now gets a grace period and is aborted after
it. The overlay packet loop was not stopped at all: it ends when the
device reports end of stream, which a live interface never does, so it
outlived the interface it was reading. And a plugin's grace period
abandoned the future without stopping the task behind it, so the helper
is public and `wg-quic` uses it on its own runtime.

The local control socket was unbounded in both directions. A wedged agent
left `tsunagi status` hanging with nothing on screen and no way out but
Ctrl-C; it now says the agent did not answer, after five seconds, and
falls back to the state store as it already did for a socket that refuses
a connection. On the serving side, a connection that sends no request no
longer holds a task open.

Tests cover the mechanism — a task that stops on its own is not aborted,
one that ignores the grace is cut off and drops what it held — and both
sides of the change in behaviour: a probe that never answers fails its
deadline, and a silent agent is reported rather than waited out.

Also: the binary opts out of rustdoc, since it shares a name with the
library and `cargo doc` cannot put both in one directory.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/tsunagi-cli/Cargo.toml

@@ -10,6 +10,10 @@ repository.workspace = true
 [[bin]]
 name = "tsunagi"
 path = "src/main.rs"
+# The binary and the library share a name, which `cargo doc` cannot map to
+# two directories. The command line is documented by `--help`, not rustdoc,
+# so the library keeps the name and this opts out.
+doc = false
 
 [dependencies]
 tsunagi = { path = "../tsunagi", version = "0.1.0", features = ["tun-device", "dns-publish"] }

crates/tsunagi-wg-quic/src/plugin.rs

@@ -45,6 +45,7 @@ use crate::device::{PeerSummary, WireguardDevice};
 use crate::keys::{WgPublicKey, WgSecretKey};
 use crate::store::WgKeyStore;
 use tsunagi::state::Ipv4Range;
+use tsunagi::task::{TASK_GRACE, wind_down};
 
 /// The protocol identifier this plugin announces.
 /// The protocol id of this plugin.
@@ -795,11 +796,14 @@ impl IpPlugin for WireguardPlugin {
         Box::pin(async move {
             let (reply_tx, reply_rx) = oneshot::channel();
             if self.commands.send(Command::Stop(reply_tx)).await.is_ok() {
-                let _ = reply_rx.await;
+                // Bounded here as well as by the agent's grace: that grace
+                // abandons this future, which would leave the runtime task
+                // running behind it.
+                let _ = tokio::time::timeout(TASK_GRACE, reply_rx).await;
             }
             let task = self.task.lock().ok().and_then(|mut guard| guard.take());
             if let Some(task) = task {
-                let _ = task.await;
+                wind_down(task, TASK_GRACE, "wg-quic runtime").await;
             }
         })
     }

crates/tsunagi/src/agent/mod.rs

@@ -51,6 +51,7 @@ use crate::proto::message::ControlMessage;
 use crate::state::Ipv4Range;
 use crate::storage::{CacheOutcome, Storage};
 
+use crate::task::{TASK_GRACE, wind_down};
 use network::{InboundSession, NetCommand, NetworkHandle, RuntimeParams};
 use shutdown::Shutdown;
 
@@ -750,12 +751,22 @@ impl Agent {
             handle.stop().await;
         }
 
-        self.inner.adapter.close().await;
+        // iroh's own close waits for peers to acknowledge; a peer that has
+        // gone silent must not decide how long that takes.
+        if tokio::time::timeout(TASK_GRACE, self.inner.adapter.close())
+            .await
+            .is_err()
+        {
+            tracing::warn!("the endpoint did not close in time; abandoning it");
+        }
 
-        for handle in [&self.inner.accept_task, &self.inner.plugin_task] {
+        for (what, handle) in [
+            ("inbound connections", &self.inner.accept_task),
+            ("plugin requests", &self.inner.plugin_task),
+        ] {
             let task = handle.lock().ok().and_then(|mut guard| guard.take());
             if let Some(task) = task {
-                let _ = task.await;
+                wind_down(task, TASK_GRACE, what).await;
             }
         }
 

crates/tsunagi/src/agent/network.rs

@@ -105,7 +105,7 @@ impl NetworkHandle {
     /// Stops the runtime and waits for its task to finish.
     pub(crate) async fn stop(self) {
         self.shutdown.trigger();
-        let _ = self.task.await;
+        crate::task::wind_down(self.task, crate::task::TASK_GRACE, "network runtime").await;
     }
 }
 

crates/tsunagi/src/agent/shutdown.rs

@@ -51,3 +51,25 @@ impl Shutdown {
         // The sender is gone, which for our purposes means "stop".
     }
 }
+
+#[cfg(test)]
+mod tests {
+    #![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
+
+    use super::*;
+
+    #[tokio::test]
+    async fn waiting_resolves_once_triggered_and_stays_resolved() {
+        let shutdown = Shutdown::new();
+        assert!(!shutdown.is_triggered());
+        let waiter = shutdown.clone();
+        let waiting = tokio::spawn(async move { waiter.wait().await });
+        shutdown.trigger();
+        waiting.await.unwrap();
+        assert!(shutdown.is_triggered());
+        // Triggering twice is not an error, and a token cloned afterwards
+        // sees the trigger that already happened.
+        shutdown.trigger();
+        shutdown.clone().wait().await;
+    }
+}

crates/tsunagi/src/error.rs

@@ -110,6 +110,16 @@ pub enum Error {
     #[error("agent is stopped")]
     Stopped,
 
+    /// Something that had to answer in bounded time did not.
+    ///
+    /// Reported instead of waited out: an agent that has wedged must not
+    /// leave a command hanging with nothing on screen and no way out.
+    #[error("{what} did not answer in time")]
+    Timeout {
+        /// What was asked, phrased so the message stands on its own.
+        what: String,
+    },
+
     /// Discovery backend failure. Never fatal for the agent.
     #[error("discovery error: {0}")]
     Discovery(String),

crates/tsunagi/src/ipc/unix.rs

@@ -7,6 +7,7 @@
 
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
+use std::time::Duration;
 
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::{UnixListener, UnixStream};
@@ -146,7 +147,19 @@ async fn serve(listener: UnixListener, source: Arc<dyn ReportSource>) {
 }
 
 async fn handle(mut stream: UnixStream, source: Arc<dyn ReportSource>) -> Result<()> {
-    let request: Request = read_message(&mut stream).await?;
+    // Bounded, so a connection that sends nothing cannot hold a task open.
+    // Only the wait for the request: building the report afterwards takes as
+    // long as it takes, and cutting it off would answer a live client with a
+    // closed socket.
+    let request: Request =
+        match tokio::time::timeout(EXCHANGE_TIMEOUT, read_message(&mut stream)).await {
+            Ok(request) => request?,
+            Err(_) => {
+                return Err(Error::Timeout {
+                    what: "a local control connection".to_string(),
+                });
+            }
+        };
     let response = match request {
         Request::Status => Response::Status(Box::new(source.report().await)),
         Request::SetHostname(hostname) => match source.set_hostname(hostname).await {
@@ -157,17 +170,18 @@ async fn handle(mut stream: UnixStream, source: Arc<dyn ReportSource>) -> Result
     write_message(&mut stream, &response).await
 }
 
+/// How long either end waits for the other.
+///
+/// A local answer comes from memory, so anything this slow means the agent is
+/// wedged rather than busy. Saying so beats waiting: unbounded, one wedged
+/// runtime leaves `tsunagi status` hanging with nothing on screen and no way
+/// out but Ctrl-C.
+const EXCHANGE_TIMEOUT: Duration = Duration::from_secs(5);
+
 /// Asks a running agent for its status.
 pub async fn request_status(path: impl AsRef<Path>) -> Result<StatusReport> {
     let path = path.as_ref();
-    let mut stream = UnixStream::connect(path)
-        .await
-        .map_err(|source| Error::Io {
-            path: path.to_path_buf(),
-            source,
-        })?;
-    write_message(&mut stream, &Request::Status).await?;
-    match read_message::<Response>(&mut stream).await? {
+    match exchange(path, &Request::Status, EXCHANGE_TIMEOUT).await? {
         Response::Status(report) => Ok(*report),
         Response::Error(reason) => Err(Error::Storage(reason)),
         other => Err(Error::Storage(format!("unexpected answer: {other:?}"))),
@@ -180,20 +194,38 @@ pub async fn request_status(path: impl AsRef<Path>) -> Result<StatusReport> {
 /// asked for and may differ from it.
 pub async fn set_hostname(path: impl AsRef<Path>, hostname: &str) -> Result<String> {
     let path = path.as_ref();
-    let mut stream = UnixStream::connect(path)
-        .await
-        .map_err(|source| Error::Io {
-            path: path.to_path_buf(),
-            source,
-        })?;
-    write_message(&mut stream, &Request::SetHostname(hostname.to_string())).await?;
-    match read_message::<Response>(&mut stream).await? {
+    let request = Request::SetHostname(hostname.to_string());
+    match exchange(path, &request, EXCHANGE_TIMEOUT).await? {
         Response::Hostname(accepted) => Ok(accepted),
         Response::Error(reason) => Err(Error::Storage(reason)),
         other => Err(Error::Storage(format!("unexpected answer: {other:?}"))),
     }
 }
 
+/// Connects, sends one request and reads the answer, all within `within`.
+///
+/// The bound covers the whole exchange rather than each read: an agent that
+/// answers the header and then stops is as stuck as one that never answers.
+async fn exchange(path: &Path, request: &Request, within: Duration) -> Result<Response> {
+    let attempt = async {
+        let mut stream = UnixStream::connect(path)
+            .await
+            .map_err(|source| Error::Io {
+                path: path.to_path_buf(),
+                source,
+            })?;
+        write_message(&mut stream, request).await?;
+        read_message::<Response>(&mut stream).await
+    };
+
+    match tokio::time::timeout(within, attempt).await {
+        Ok(result) => result,
+        Err(_) => Err(Error::Timeout {
+            what: format!("the agent at {}", path.display()),
+        }),
+    }
+}
+
 /// Marks the wire format of the local control socket.
 ///
 /// `b"TSN"` followed by the version, so a mismatch is recognised as one
@@ -258,3 +290,49 @@ fn io_error(source: std::io::Error) -> Error {
         source,
     }
 }
+
+#[cfg(test)]
+mod tests {
+    #![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
+
+    use super::*;
+
+    #[tokio::test]
+    async fn a_silent_agent_is_reported_rather_than_waited_out() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("control.sock");
+        // A socket that accepts and then says nothing, like a wedged agent:
+        // the connection succeeds, the answer never comes. Unbounded, this
+        // call would never return.
+        let _listener = UnixListener::bind(&path).unwrap();
+
+        let error = exchange(&path, &Request::Status, Duration::from_millis(100))
+            .await
+            .expect_err("a silent agent cannot be reported as healthy");
+
+        match error {
+            Error::Timeout { what } => assert!(
+                what.contains("control.sock"),
+                "the message names what did not answer: {what}"
+            ),
+            other => panic!("expected a timeout, got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn an_answered_request_is_not_affected_by_the_bound() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("control.sock");
+        let source: Arc<dyn ReportSource> = Arc::new(|| -> BoxFuture<'static, StatusReport> {
+            Box::pin(async { StatusReport::default() })
+        });
+        let control = ControlSocket::bind(&path, source).await.unwrap();
+
+        let answer = exchange(&path, &Request::Status, EXCHANGE_TIMEOUT)
+            .await
+            .unwrap();
+        assert!(matches!(answer, Response::Status(_)));
+
+        control.shutdown().await;
+    }
+}

crates/tsunagi/src/lib.rs

@@ -48,6 +48,7 @@ pub mod overlay;
 pub mod proto;
 pub mod state;
 pub mod storage;
+pub mod task;
 #[cfg(feature = "testing")]
 pub mod testing;
 

crates/tsunagi/src/overlay/interface.rs

@@ -238,7 +238,17 @@ impl Interface {
 
     /// Removes the interface from the host.
     pub async fn remove(&self) {
+        // The packet loop holds the device open, and it ends only when the
+        // device reports end of stream — which a real interface never does
+        // while it exists. So it is stopped here, not left to notice.
+        let task = match self.task.lock() {
+            Ok(mut guard) => guard.take(),
+            Err(poisoned) => poisoned.into_inner().take(),
+        };
         self.factory.destroy(self.device.name()).await;
+        if let Some(task) = task {
+            crate::task::wind_down(task, crate::task::TASK_GRACE, "overlay packet loop").await;
+        }
     }
 
     /// The counters as they stand.

crates/tsunagi/src/task.rs

@@ -0,0 +1,74 @@
+//! Stopping the tasks an agent started.
+//!
+//! Shutdown is cooperative first and bounded always: every loop watches a
+//! cancellation token, and anything still running when its grace period ends
+//! is aborted. Nothing an agent owns may outlive the agent, and no peer may
+//! hold shutdown open by refusing to read.
+//!
+//! Public because a protocol crate spawns tasks of its own and is held to
+//! the same rule: the agent gives each plugin a grace period, but abandoning
+//! the future it is awaiting does not stop the task behind it.
+
+use std::time::Duration;
+
+use tokio::task::JoinHandle;
+
+/// How long a task gets to notice cancellation before it is cut off.
+///
+/// Winding down is cooperative first: a task in the middle of a write to a
+/// peer gets a moment to finish it. After that it is aborted, because a peer
+/// that stops reading must not be able to hold shutdown open.
+pub const TASK_GRACE: Duration = Duration::from_secs(5);
+
+/// Waits for `task` to finish, aborting it if it outlasts `grace`.
+///
+/// Returns whether it finished on its own. `what` names it in the warning,
+/// which is the only signal that something was cut off rather than stopped.
+pub async fn wind_down(task: JoinHandle<()>, grace: Duration, what: &str) -> bool {
+    let abort = task.abort_handle();
+    if tokio::time::timeout(grace, task).await.is_err() {
+        tracing::warn!(
+            task = what,
+            grace_secs = grace.as_secs_f32(),
+            "task did not wind down in time; aborting it"
+        );
+        abort.abort();
+        return false;
+    }
+    true
+}
+
+#[cfg(test)]
+mod tests {
+    #![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
+
+    use super::*;
+
+    #[tokio::test]
+    async fn a_task_that_stops_on_its_own_is_not_aborted() {
+        let (tx, mut rx) = tokio::sync::mpsc::channel::<()>(1);
+        let task = tokio::spawn(async move {
+            tx.send(()).await.ok();
+        });
+        assert!(wind_down(task, Duration::from_secs(5), "cooperative").await);
+        assert_eq!(rx.recv().await, Some(()), "it ran to completion");
+    }
+
+    #[tokio::test]
+    async fn a_task_that_ignores_the_grace_is_aborted() {
+        // A stand-in for a task blocked writing to a peer that stopped
+        // reading: it will never finish by itself.
+        let (tx, mut rx) = tokio::sync::mpsc::channel::<()>(1);
+        let task = tokio::spawn(async move {
+            let _held = tx;
+            std::future::pending::<()>().await;
+        });
+
+        let finished = wind_down(task, Duration::from_millis(50), "wedged").await;
+        assert!(!finished, "it had to be cut off");
+
+        // Aborted for real: the task is gone, so what it held is dropped.
+        let closed = tokio::time::timeout(Duration::from_secs(5), rx.recv()).await;
+        assert_eq!(closed, Ok(None), "the aborted task dropped its sender");
+    }
+}

crates/tsunagi/src/testing.rs

@@ -155,14 +155,22 @@ where
 {
     let deadline = Instant::now() + DEADLINE;
     loop {
-        if let Some(value) = probe().await {
-            return value;
-        }
+        let remaining = deadline
+            .checked_duration_since(Instant::now())
+            .unwrap_or_default();
         assert!(
-            Instant::now() < deadline,
+            !remaining.is_zero(),
             "timed out waiting for condition: {what}"
         );
-        tokio::time::sleep(POLL_INTERVAL).await;
+
+        // The probe is bounded too. A deadline checked only between probes is
+        // no deadline at all: one call into a wedged agent that never answers
+        // would hang the test process for ever instead of failing it.
+        match tokio::time::timeout(remaining, probe()).await {
+            Ok(Some(value)) => return value,
+            Ok(None) => tokio::time::sleep(POLL_INTERVAL).await,
+            Err(_) => panic!("timed out waiting for condition: {what}"),
+        }
     }
 }
 
@@ -190,3 +198,20 @@ pub async fn wait_for_peers(
     })
     .await
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test(start_paused = true)]
+    #[should_panic(expected = "timed out waiting for condition")]
+    async fn a_probe_that_never_answers_fails_the_deadline_instead_of_hanging() {
+        // Virtual time, so the deadline arrives at once rather than in thirty
+        // real seconds — and the deadline does arrive, which is the point: a
+        // probe that never returns used to hang the process instead.
+        wait_until::<(), _, _>("an answer that never comes", || async {
+            std::future::pending::<Option<()>>().await
+        })
+        .await;
+    }
+}