Cannot specify Depends for type Response, yet docs imply you can?

[holyoaks]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google "How to X in FastAPI" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from typing import Annotated
import arrow
from fastapi import FastAPI, Response

app = FastAPI()

def set_no_cache_headers(response: Response) -> Response:
    response.headers["Expires"] = arrow.utcnow().format(arrow.FORMAT_RFC1123)
    response.headers["Cache-Control"] = "max-age=0, no-cache, no-store, must-revalidate, private"
    return response


class NoCacheResponse:
    def __init__(self, header_directives: List[str]) -> None:
        self.header_directives = header_directives

    def __call__(self, response: Response) -> None:
        if "no_cache" in self.header_directives:
            set_no_cache_headers(response=response)


NO_CACHE_RESPONSE = NoCacheResponse(["no_cache"])

@app.get("/testing/")
def testing_response(
    response: Annotated[Response, Depends(NO_CACHE_RESPONSE)],
):
    return {}

Description

Previously (up to FastAPI 0.89.1, which is the last version I used before trying to update), the code above worked just fine. I use this to add caching headers to my GET responses (as certain network devices will cache unless specifically told not to). I built this as the docs here specify that You can also declare the Response parameter in dependencies, and set headers (and cookies) in them.. Again, it worked fine until at least 0.89.1.

Now, FastAPI specifically block this functionality. Lines 383-387 of fastapi/dependencies/utils.py:

if lenient_issubclass(
        type_annotation,
        (Request, WebSocket, HTTPConnection, Response, BackgroundTasks, SecurityScopes),
    ):
        assert depends is None, f"Cannot specify `Depends` for type {type_annotation!r}"

checks to see if the parameter is of certain types, and immediately fails indicating AssertionError: Cannot specify Depends for type <class 'starlette.responses.Response'>.

My question is this: Which is correct, the code or the docs? If I'm simply misunderstanding how to declare the Response parameter in dependencies, please help me understand how best to accomplish what I used to be able to. Thanks!

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.100.0

Python Version

3.11

Additional Context

No response

[Kludex]

Can you reproduce with fastapi 0.99.0?

[holyoaks]

I can. Exact same behavior, in the exact same lenient_issubclass method

[holyoaks]

@Kludex Should I create an issue from this discussion? Don't want to see this fall through the cracks

[Kludex]

#10127

[Kludex]

This is a bug.

For the time being, you can do the following as a workaround:

from typing import Annotated
from fastapi import FastAPI, Response, Depends

app = FastAPI()

def set_no_cache_headers(response: Response) -> Response:
    response.headers["Potato"] = "potato"
    return response

@app.get("/")
def testing_response(response = Depends(set_no_cache_headers)):
    return {}