langchain-ai/langgraph · error · RuntimeError

Protocol transport is closed.

Error message

Protocol transport is closed.

What it means

Error "Protocol transport is closed." thrown in langchain-ai/langgraph.

Source

Thrown at libs/sdk-py/langgraph_sdk/stream/transport/http.py:73

        )
        self._stream_url = (
            stream_path or f"/threads/{_quote_path_param(thread_id)}/stream/events"
        )
        self._default_headers: dict[str, str] = dict(headers or {})
        self._max_queue_size = max_queue_size
        self._closed = False
        self._event_streams: set[asyncio.Task[None]] = set()

    async def send_command(self, command: dict[str, Any]) -> dict[str, Any] | None:
        """POST a command. Returns the response JSON, or `None` for 202/204.

        Raises:
            httpx.HTTPStatusError: server returned >= 400.
            RuntimeError: the transport has been closed via `close()`.
            RuntimeError: server returned a response missing the protocol envelope.
        """
        if self._closed:
            raise RuntimeError("Protocol transport is closed.")
        # Merge default headers first so content-type always wins.
        merged_headers = {**self._default_headers, "content-type": "application/json"}
        response = await self._client.post(
            self._commands_url,
            content=orjson.dumps(command),
            headers=merged_headers,
        )
        response.raise_for_status()
        if response.status_code in (202, 204):
            return None
        if not response.content:
            raise RuntimeError("Protocol command did not return a valid response.")
        try:
            payload = orjson.loads(response.content)
        except orjson.JSONDecodeError as err:
            raise RuntimeError(
                "Protocol command did not return a valid response."
            ) from err

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/sdk-py/langgraph_sdk/stream/transport/http.py:73 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/95480f05febce7ff. Report an issue: GitHub.