aio-libs/aiohttp · error · ConnectionResetError

Connection lost

Error message

Connection lost

What it means

Error "Connection lost" thrown in aio-libs/aiohttp.

Source

Thrown at aiohttp/web_ws.py:365

        return (
            response_headers,
            protocol,
            compress,
            notakeover,
        )

    def _pre_start(self, request: BaseRequest) -> tuple[str | None, WebSocketWriter]:
        self._loop = request._loop

        headers, protocol, compress, notakeover = self._handshake(request)

        self.set_status(101)
        self.headers.update(headers)
        self.force_close()
        self._compress = compress
        transport = request._protocol.transport
        if transport is None:
            raise ConnectionResetError("Connection lost")
        writer = WebSocketWriter(
            request._protocol,
            transport,
            compress=compress,
            notakeover=notakeover,
            limit=self._writer_limit,
        )

        return protocol, writer

    def _post_start(
        self, request: BaseRequest, protocol: str | None, writer: WebSocketWriter
    ) -> None:
        self._ws_protocol = protocol
        self._writer = writer

        self._reset_heartbeat()

View on GitHub (pinned to c0ef574e29)

When it happens

Trigger: Thrown at aiohttp/web_ws.py:365 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/58c61ec4847764c2.json. Report an issue: GitHub.