Pydantic Validation

fastsio can validate event payloads into Pydantic models, similar to FastAPI.

Rules

• Only non-reserved events (not connect/disconnect) are parsed into models.

• The client must send a single payload argument (e.g. a dict). If multiple arguments are sent, validation will error.

• The handler must annotate a parameter with a Pydantic BaseModel subclass.

Example

from pydantic import BaseModel
from fastsio import RouterSIO

router = RouterSIO()

class Message(BaseModel):
    text: str
    room: str

@router.on("message")
async def on_message(data: Message):
    # data is a validated Pydantic model
    ...

Error cases

• If the payload cannot be validated, an error is raised and the handler is not invoked.

• If more than one payload argument is sent while a model is expected, an error is raised.