WebSocketException Class — fastapi Architecture

Source Code

fastapi/exceptions.py lines 86–154

class WebSocketException(StarletteWebSocketException):
    """
    A WebSocket exception you can raise in your own code to show errors to the client.

    This is for client errors, invalid authentication, invalid data, etc. Not for server
    errors in your code.

    Read more about it in the
    [FastAPI docs for WebSockets](https://fastapi.tiangolo.com/advanced/websockets/).

    ## Example

    ```python
    from typing import Annotated

    from fastapi import (
        Cookie,
        FastAPI,
        WebSocket,
        WebSocketException,
        status,
    )

    app = FastAPI()

    @app.websocket("/items/{item_id}/ws")
    async def websocket_endpoint(
        *,
        websocket: WebSocket,
        session: Annotated[str | None, Cookie()] = None,
        item_id: str,
    ):
        if session is None:
            raise WebSocketException(code=status.WS_1008_POLICY_VIOLATION)
        await websocket.accept()
        while True:
            data = await websocket.receive_text()
            await websocket.send_text(f"Session cookie is: {session}")
            await websocket.send_text(f"Message text was: {data}, for item ID: {item_id}")
    ```
    """

    def __init__(
        self,
        code: Annotated[
            int,
            Doc(
                """
                A closing code from the
                [valid codes defined in the specification](https://datatracker.ietf.org/doc/html/rfc6455#section-7.4.1).
                """
            ),
        ],
        reason: Annotated[
            Union[str, None],
            Doc(
                """
                The reason to close the WebSocket connection.

                It is UTF-8-encoded data. The interpretation of the reason is up to the
                application, it is not specified by the WebSocket specification.

                It could contain text that could be human-readable or interpretable
                by the client code, etc.
                """
            ),
        ] = None,
    ) -> None:
        super().__init__(code=code, reason=reason)