Support graceful agent interruption (#5287)

codex-rs/async-utils/src/lib.rs

@@ -0,0 +1,86 @@
+use async_trait::async_trait;
+use std::future::Future;
+use tokio_util::sync::CancellationToken;
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum CancelErr {
+    Cancelled,
+}
+
+#[async_trait]
+pub trait OrCancelExt: Sized {
+    type Output;
+
+    async fn or_cancel(self, token: &CancellationToken) -> Result<Self::Output, CancelErr>;
+}
+
+#[async_trait]
+impl<F> OrCancelExt for F
+where
+    F: Future + Send,
+    F::Output: Send,
+{
+    type Output = F::Output;
+
+    async fn or_cancel(self, token: &CancellationToken) -> Result<Self::Output, CancelErr> {
+        tokio::select! {
+            _ = token.cancelled() => Err(CancelErr::Cancelled),
+            res = self => Ok(res),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+    use std::time::Duration;
+    use tokio::task;
+    use tokio::time::sleep;
+
+    #[tokio::test]
+    async fn returns_ok_when_future_completes_first() {
+        let token = CancellationToken::new();
+        let value = async { 42 };
+
+        let result = value.or_cancel(&token).await;
+
+        assert_eq!(Ok(42), result);
+    }
+
+    #[tokio::test]
+    async fn returns_err_when_token_cancelled_first() {
+        let token = CancellationToken::new();
+        let token_clone = token.clone();
+
+        let cancel_handle = task::spawn(async move {
+            sleep(Duration::from_millis(10)).await;
+            token_clone.cancel();
+        });
+
+        let result = async {
+            sleep(Duration::from_millis(100)).await;
+            7
+        }
+        .or_cancel(&token)
+        .await;
+
+        cancel_handle.await.expect("cancel task panicked");
+        assert_eq!(Err(CancelErr::Cancelled), result);
+    }
+
+    #[tokio::test]
+    async fn returns_err_when_token_already_cancelled() {
+        let token = CancellationToken::new();
+        token.cancel();
+
+        let result = async {
+            sleep(Duration::from_millis(50)).await;
+            5
+        }
+        .or_cancel(&token)
+        .await;
+
+        assert_eq!(Err(CancelErr::Cancelled), result);
+    }
+}