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Graph/async-boundary-contract-drift

AntiPattern

Async Boundary Contract Drift

async-boundary-contract-drift

Async boundaries silently break when mocks/handlers return the wrong type (coroutine vs async context manager) or block the event loop with synchronous completion, causing route/streaming/websocket behavior to fail under ASGI.

Node Details

Public graph metadata

Updated7/16/2026

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30 linked nodes

MATCHESSolution

Handle server→client synchronization inside the socket event handler (or a centralized layer like middleware) to keep updates consistent and avoid lifecycle coupling. Use component-level listeners only for client→server events where it’s appropriate, ensuring callbacks are registered/unregistered correctly.

MATCHESSolution

I'm playing around with NextJS app router, and Suspense — In my App router page. Tension: this suspense boundary won't do anything.

MATCHESSolution

Manage the refreshing state more robustly — ensuring it only turns off after all async operations are complete. Tension: remove the arbitrary timeout. Outcome: ensure no state updates occur after the component begins to unmount.

MATCHESSolution

And HTTP Client errors (if you're using `HttpClient` or `HttpClientFactory`) — On ASP.NET Core. Tension: you just need to opt-in. Outcome: options.CaptureFailedRequests = true;.

MATCHESSolution

delete the async from `fake_execute` — your `AsyncContextMock` needs to handle both use cases in your endpoint `await conn.execute()` and `async with conn.execute()`. Outcome: just make it a regular function so it returns your context manager directly, no coroutine wrapper.

MATCHESSolution

single worker running async loop. Outcome: So you have a single worker running async loop and you block that loop.

MATCHESSolution

Pass `BackgroundTasks` from the route into your dependency. — when declared inside an async dependency. Tension: the background job never runs. Outcome: async def test_route(bg: BackgroundTasks, data=Depends(dependency)):.

MATCHESSolution

If you convert all operations to perform asynchronously (using `aiosqlite`) , the issue will be mitigated. — When a route in FastAPI is listed as asynchronous (`async def`). Tension: that doesn't fully solve the inherent single writer problem of Sqlite. Outcome: Here's a fully operational update of the FastAPI server logic:.

MATCHESSolution

Removing `async` before the function definition solved it. — class LoggingAPIRoute(APIRoute):. Outcome: def get_route_handler(self) -> Callable:.

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Change the engine async fixture from session scope to function scope (remove scope="session") so all async fixtures/tests run on the same event loop, preventing the cross-loop Future/Task error.

MATCHESSolution

using `magicmock` to mock it could lead to unusual or unexpected behavior when checking for call counts — Since `get_item` might be an asynchronous function in your middleware. Tension: using `magicmock` to mock it could lead to unusual or unexpected behavior. Outcome: which is designed to work with async functions.

MATCHESSolution

the reason for the various threads appearing in the logs — when you pass a synchronous generator to `EventSourceResponse`. Tension: a normal `def` function instead of `async def`. Outcome: please take a look at the implementation of the `EventSourceResponse` class.

MATCHESSolution

use `pytest_asyncio` and the async fixture — If you don't want to utilize an `AsyncClient` like the one by `httpx`. Tension: ensuring that the FastAPI app's lifespan context correctly works.

MATCHESSolution

Ensure the server yields to the asyncio event loop while processing (e.g., add an `await asyncio.sleep(0)` / periodic yielding) so WebSocket messages are dispatched immediately. Optionally add client/server `onopen/onerror/onclose` logging to confirm connection state.

MATCHESSolution

ASGIMiddleware. Tension: Currently i add ASGIMiddleware to fastapi app, it catches both websocket and http.

MATCHESSolution

any time you have an I/O bound process with lots of idle time — waiting for user input, waiting for a TLS handshake. Tension: wrapping it in an async task can let other code run.

MATCHESSolution

bound it with a "progress ceiling" — a process emitting bytes but making NO semantic progress. Tension: a process emitting bytes but making NO semantic progress (livelock) would be shielded forever. Outcome: re-arms recovery after a long no-progress window even while bytes flow.

MATCHESSolution

Try this: — api/example/route.ts. Tension: Client. Outcome: return new NextResponse(stream, { headers: { 'Content-Type': 'text/event-stream', 'Connection': 'keep-alive', 'Cache-Control': 'no-cache, no-transform', }, });.

MATCHESSolution

An async function was passed to useActionState.

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Async-iterate the Result instead of awaiting `.records` — The driver's Result is async-iterable. Tension: Combined with a streaming HTTP response, records flow end-to-end without any single buffer. Outcome: records flow end-to-end without any single buffer.

MATCHESSolution

case "CallbackRouteError": return { error: "Invalid credentials!" } — in my `login.ts` server action in the switch case clause. Tension: to return the correct errors. Outcome: bypass this error.

MATCHESSolution

Rewrite the test as an async test and run it with an async test runner (e.g., pytest.mark.asyncio), using await on the async ORM methods (acreate/acount) instead of asyncio.run().

MATCHESSolution

the goroutine blocks forever on the channel send because nobody is reading — When the parent context is cancelled, the goroutine blocks forever on the channel send because nobody is reading. Tension: if the result is ready at the exact moment the context cancels, which case fires?

MATCHESSolution

Use Component.Task (TaskSource) for all async work inside components — inside components. Tension: it auto-cancels when the component is destroyed.

MATCHESSolution

anonymous REST adapters and lazy registration — TypeScript/Hono agent platform. Tension: non-MCP agents and anonymous write attempts hit avoidable friction.

MATCHESSolution

Avoid relying on the pure SSE push write path for server-initiated notifications; use a different delivery mechanism per client (e.g., webhook/polling/channel-specific adapter) with capability negotiation and graceful degradation. Alternatively, patch/upgrade the Hono dependency or change the transport implementation so SSE writes never attempt res.writeHead() after headers are sent, and ensure failures propagate to the notifier.

MATCHESSolution

Don't build per-client adapters. — client capabilities change with updates. Tension: They become a maintenance nightmare — every new feature needs N implementations. Outcome: one delivery function that degrades.

MATCHESSolution

Facepunch Sandbox demonstrates a clean dual-scope event architecture using `Local` and `Global` static classes. Tension: Difficulty implementing cancellable events.

MATCHESSolution

Kept the protocol mismatch as a classified close cause — Added [REDACTED] and scoped device-auth invalidation for auth-state migrations, but did not clear unrelated browser storage. Tension: The real remediation for the observed loop is closing or hard-refreshing the stale tab so it loads the current SPA bundle. Outcome: Browser harness evidence classified the failure as protocol mismatch with high confidence, while fresh navigation connected normally.

MATCHESSolution

Gate activity-page RPCs on the host app's post-handshake connected state instead of the raw WebSocket-open flag, while still checking `ws.readyState === 1` — activity-page RPCs. Tension: The page checked the gateway browser client for an open WebSocket and then immediately sent RPCs such as session subscribe/list/history. Outcome: Gate activity-page RPCs on the host app's post-handshake connected state instead of the raw WebSocket-open flag, while still checking `ws.readyState === 1`.

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