What is the correct way to inspect/modify the return value of a route function *before* it becomes a response

[rbhalla]

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Example Code

def custom_decorator(func: Callable) -> Callable:
    async def wrapper(*args: Any, **kwargs: Any) -> Any:
        result = await func(*args, **kwargs)
        # Inspect/modify the result here as needed
        return result

    return wrapper

Description

Problem
I would like to apply the above custom_decorator to every route in my application. While, possible, it's cumbersome, and introduces an opportunity for errors later (by missing it).

What I've tried
Unfortunately, when I do try and apply a global decorator to routes (using approaches I've found here and through online searching), instead of getting the result of the route function itself (e.g. a pydantic model), I instead get a Response or some serialized view of the response.

What I have tried:

1. Modifying app.router.route_class (only have access to response)
   a) modifying the endpoint in __init__
   b) overriding get_route_handler
2. Middleware applied to the app (only have access to response)
3. Specifying a custom response (only have access to serialized response)

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.95.1

Python Version

3.10.3

Additional Context

The extra context here is that I want to ensure pydantic models exclude fields from being serialised only when being returned by the API. In my internal logic, I want the fields to be present. I am therefore hoping to add a decorator to each route that excludes appropriate fields depending on what is returned.