aio-libs/aiohttp · error · RuntimeError

Already started

Error message

Already started

What it means

Error "Already started" thrown in aio-libs/aiohttp.

Source

Thrown at aiohttp/web_ws.py:402

        loop = self._loop
        assert loop is not None
        self._reader = WebSocketDataQueue(
            request._protocol, DEFAULT_CHUNK_SIZE, loop=loop
        )
        parser = WebSocketReader(
            self._reader,
            self._max_msg_size,
            compress=bool(self._compress),
            decode_text=self._decode_text,
        )
        cb = None if self._heartbeat is None else self._on_data_received
        request.protocol.set_parser(parser, data_received_cb=cb)
        # disable HTTP keepalive for WebSocket
        request.protocol.keep_alive(False)

    def can_prepare(self, request: BaseRequest) -> WebSocketReady:
        if self._writer is not None:
            raise RuntimeError("Already started")
        try:
            _, protocol, _, _ = self._handshake(request)
        except HTTPException:
            return WebSocketReady(False, None)
        else:
            return WebSocketReady(True, protocol)

    @property
    def prepared(self) -> bool:
        return self._writer is not None

    @property
    def closed(self) -> bool:
        return self._closed

    @property
    def close_code(self) -> int | None:
        return self._close_code

View on GitHub (pinned to c0ef574e29)

When it happens

Trigger: Thrown at aiohttp/web_ws.py:402 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of aio-libs/aiohttp@c0ef574e29 (2026-08-04). Data as JSON: /data/errors/c11a1db9c2a60284.json. Report an issue: GitHub.