fast-fastapi-json.py

# SPDX-License-Identifier: 0BSD

from collections.abc import Callable
from functools import wraps
from fastapi.datastructures import DefaultPlaceholder
from fastapi.dependencies.utils import get_dependant
from fastapi.routing import APIRoute
from starlette.responses import JSONResponse
from starlette.routing import request_response

...

def fast_response_serialization(app: FastAPI) -> None:
    """
    Setup FastAPI application to use optimized JSON serialization.
    Default serialization behavior is slow and redundant.
    This is quite hacky as FastAPI does not expose an easy way to override it.
    """

    def wrap_endpoint(endpoint: Callable, cls: type[Response]):
        @wraps(endpoint)
        async def wrapper(*args, **kwargs):
            content = await endpoint(*args, **kwargs)
            return content if isinstance(content, Response) else cls(content)

        return wrapper

    for route in app.routes:
        if not isinstance(route, APIRoute):
            continue

        response_class = route.response_class
        if isinstance(response_class, DefaultPlaceholder):
            response_class = response_class.value
        if issubclass(response_class, JSONResponse):
            route.endpoint = wrap_endpoint(route.endpoint, response_class)
            route.dependant = get_dependant(path=route.path_format, call=route.endpoint)
            route.app = request_response(route.get_route_handler())