What causes "should never drop oneshot tx" in libnyanpasu/clash-nyanpasu?

Replace `.expect` with graceful handling: `rx.await.unwrap_or_else(|_| Err(...))` returning a JS error.

should never drop oneshot tx

Error message

should never drop oneshot tx

What it means

`load_imported_module` fetches module content over an internal oneshot channel spawned on an async runtime and does `rx.await.expect("should never drop oneshot tx")`. If the spawned task panics or the runtime is shut down before sending, the sender drops and the expect panics with this message.

Source

Thrown at backend/boa_utils/src/module/http.rs:177

                    let mime = response
                        .headers()
                        .get(reqwest::header::CONTENT_TYPE)
                        .and_then(|v| v.to_str().ok())
                        .map(|v| v.to_string())
                        .unwrap_or(mime::TEXT_PLAIN.to_string());
                    let body = response.text().await?;

                    log::debug!("finished fetching `{fetcher_url}`");
                    Ok(CachedItem {
                        mime,
                        content: body,
                    })
                }
                .await;
                let _ = tx.send(result);
            });
            rx.await.expect("should never drop oneshot tx")
        };

        if let Ok(item) = &item {
            match postcard::to_stdvec(&item) {
                Ok(item) => {
                    if let Err(err) = async_fs::write(&cache_path, &item).await {
                        log::error!(
                            "failed to write cache for `{url}`; path: `{}`. error: `{}`",
                            cache_path.display(),
                            err
                        );
                    }
                }
                Err(err) => {
                    log::error!("failed to serialize content: {err}");
                }
            }
        }

View on GitHub (pinned to f7dbce2997)

Solutions

Replace `.expect` with graceful handling: `rx.await.unwrap_or_else(|_| Err(...))` returning a JS error.
Ensure the async runtime outlives all module-loading operations.
Fix the root panic in the spawned task (often the invalid-url panic) so the sender always sends.
Wrap module loading so runtime shutdown doesn't race pending imports.

Example fix

// before
rx.await.expect("should never drop oneshot tx")
// after
rx.await.map_err(|_| JsNativeError::typ().with_message("module loader task dropped"))?

Defensive patterns

Strategy: try-catch

Validate before calling

// cannot pre-validate; ensure runtime is alive before loading modules
if (!runtimeAlive()) throw new Error('async runtime unavailable; cannot load modules');

Try / catch

// Rust side: replace expect with graceful JS error
rx.await.map_err(|_| JsNativeError::typ().with_message("module loader task dropped"))?

Prevention

Keep the async runtime alive for the duration of module loading
Fix panics inside the spawned fetch task so the oneshot sender always sends
Avoid runtime shutdown racing in-flight module imports

When it happens

Trigger: Calling `load_imported_module` when the spawned fetch task panics (e.g. the invalid-url panic in the same flow), the async runtime has been dropped, or the task is cancelled before `tx.send` runs.

Common situations: Runtime shutdown during app exit while a module import is in flight; a panic inside the spawned task (like error 238) dropping the oneshot sender; blocking the runtime so the task is aborted.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of libnyanpasu/clash-nyanpasu@f7dbce2997 (2026-09-08). Data as JSON: /api/errors/87308071719af4d0. Report an issue: GitHub.