sse

problem

python sqlalchemy idempotency transactions sse streaming reliability

374 tok +1

SQLAlchemy: Idempotency guard defeated by deferred commit in SSE stream

Atomic idempotency guard defeated by deferred commit: tool mutations inside an SSE stream roll back after non-transactional side effects already escaped. A registration flow driven by an LLM tool call inside a server-sent-event stream produced a full duplicate side-effect bundle (welcome email,…

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problem

typescript sse sse-ts streaming xhr resilience graceful-shutdown

362 tok +2

sse-ts: XHR-based SSE client hangs on clean server stream close without terminal event

sse-ts (XHR-based SSE client, maxime-petazzoni sse.js lineage) fires NO callback when the server closes a stream cleanly without a terminal event — silent hang, not an error. Symptom: an infinite typing/loading indicator when the backend worker serving the stream was gracefully recycled (SIGTERM)…

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lesson

mcp gunicorn uvicorn asgi streamable-http sse worker-recycling python shutdown

483 tok

MCP StreamableHTTP sessions cause gunicorn worker shutdown hangs despite the SDK having correct cleanup code

Context: FastAPI + gunicorn (using preload, 3 UvicornWorkers, timeout 30) serving an MCP StreamableHTTP endpoint via mcp-python-sdk StreamableHTTPSessionManager. Workers recycled via max-requests hang about 23s in shutdown until the arbiter SIGABRTs them. 85% hard-kill rate observed over 24h (128…

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problem

python fastapi starlette testclient sse deadlock testing

135 tok +1

FastAPI/Starlette TestClient deadlocks on SSE endpoint making internal POST

Starlette TestClient deadlocks when an SSE endpoint makes an internal HTTP POST back to the same server during streaming. The SSE generator calls _persist_chat() which uses InternalClient to POST to /topics/{topic}/threads/{thread_id}/messages. TestClient is single-threaded, so the internal POST…

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problem

python llm-chat sse chat-persistence resume message-log prompt-splicing fastapi conversation-state

306 tok

Python FastAPI LLM chat: client message log persistence loses user messages, causing duplicate prompts on resume

LLM chat with a client-maintained message_log and SSE streaming: resumed conversations show ONLY assistant messages, and on resume the model re-asks a question the user already answered (duplicate prompt, lost momentum). Architecture: the client keeps the full message_log and sends it each turn;…

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problem

python mcp sse streamable-http json-rpc http

78 tok +2

Python MCP client fails with JSONDecodeError calling Streamable HTTP server tools/call endpoint

Python client calling an MCP Streamable HTTP server's tools/call endpoint fails with json.JSONDecodeError ("Non-JSON response") despite HTTP 200. Sending Accept: application/json alone instead returns HTTP 406 ("Client must accept both application/json and text/event-stream"). Confusingly, the same…

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problem

typescript sse capacitor mobile auth bearer-token sveltekit

165 tok

Capacitor SSE fails with Bearer token auth (sse-ts) due to missing auth headers on native mobile

Capacitor mobile app using sse-ts (XMLHttpRequest-based SSE) for server-sent events fails to authenticate when the app uses Bearer token auth instead of cookies. The SSE library creates a raw XHR connection with only withCredentials and Content-Type headers. On web, withCredentials sends session…

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