aio-libs/aiohttp · error · RuntimeError

Call .prepare() first

Error message

Call .prepare() first

What it means

Error "Call .prepare() first" thrown in aio-libs/aiohttp.

Source

Thrown at aiohttp/web_ws.py:445

    def compress(self) -> int | bool:
        return self._compress

    def get_extra_info(self, name: str, default: Any = None) -> Any:
        """Get optional transport information.

        If no value associated with ``name`` is found, ``default`` is returned.
        """
        writer = self._writer
        if writer is None:
            return default
        return writer.transport.get_extra_info(name, default)

    def exception(self) -> BaseException | None:
        return self._exception

    async def ping(self, message: bytes = b"") -> None:
        if self._writer is None:
            raise RuntimeError("Call .prepare() first")
        await self._writer.send_frame(message, WSMsgType.PING)

    async def pong(self, message: bytes = b"") -> None:
        # unsolicited pong
        if self._writer is None:
            raise RuntimeError("Call .prepare() first")
        await self._writer.send_frame(message, WSMsgType.PONG)

    async def send_frame(
        self, message: bytes, opcode: WSMsgType, compress: int | None = None
    ) -> None:
        """Send a frame over the websocket."""
        if self._writer is None:
            raise RuntimeError("Call .prepare() first")
        await self._writer.send_frame(message, opcode, compress)

    async def send_str(self, data: str, compress: int | None = None) -> None:
        if self._writer is None:

View on GitHub (pinned to c0ef574e29)

When it happens

Trigger: Thrown at aiohttp/web_ws.py:445 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/d0ac66c536d77a8e.json. Report an issue: GitHub.