flake8 plugin that checks FastAPI code against opiniated style rules 🤓
Project description
flake8-fastapi
A flake8 plugin that helps you avoid simple FastAPI mistakes.
Installation
First, install the package:
pip install flake8-fastapi
Then, check if the plugin is installed using flake8
:
$ flake8 --version
3.9.2 (flake8-fastapi: 0.2.0, mccabe: 0.6.1, pycodestyle: 2.7.0, pyflakes: 2.3.1) CPython 3.8.11 on Linux
Rules
- CF001 - Route Decorator Error
- CF002 - Router Prefix Error
- CF008 - CORSMiddleware Order
- CF009 - Undocumented HTTPException
- CF011 - No Content Response
CF001 - Route Decorator Error
Developers that were used to flask can be persuaded or want to use the same pattern in FastAPI:
from fastapi import FastAPI
app = FastAPI()
@app.route("/", methods=["GET"])
def home():
return "Hello world!"
But on FastAPI, we have a simpler way to define this (and is the most known way to create endpoints):
from fastapi import FastAPI
app = FastAPI()
@app.get("/")
def home():
return "Hello world!"
CF002 - Router Prefix Error
On old FastAPI versions, we were able to add a prefix only on the include_router
method:
from fastapi import APIRouter, FastAPI
router = APIRouter()
@router.get("/")
def home():
...
app = FastAPI()
app.include_router(router, prefix="/prefix")
Now, it's possible to add in the Router
initialization:
from fastapi import APIRouter, FastAPI
router = APIRouter(prefix="/prefix")
@router.get("/")
def home():
...
app = FastAPI()
app.include_router(router)
CF008 - CORSMiddleware Order
There's a tricky issue about CORSMiddleware that people are usually unaware. Which is that this middleware should be the last one on the middleware stack. You can read more about it here.
Let's see an example of what doesn't work:
from fastapi import FastAPI
app = FastAPI()
app.add_middleware(
CORSMiddleware,
allow_origins=['*'],
allow_credentials=True,
allow_methods=['*'],
allow_headers=['*']
)
app.add_middleware(GZipMiddleware)
As you see, the last middleware added is not CORSMiddleware
, so it will not work as expected. On the other hand, if you change the order, it will:
from fastapi import FastAPI
app = FastAPI()
app.add_middleware(GZipMiddleware)
app.add_middleware(
CORSMiddleware,
allow_origins=['*'],
allow_credentials=True,
allow_methods=['*'],
allow_headers=['*']
)
CF009 - Undocumented HTTPException
Currently, there's no automatic solution to document the HTTPException
s, besides the experimental package fastapi-responses
.
For that reason, it's easy to forget the documentation, and have a lot of undocumented endpoints. Let's see an example:
from fastapi import FastAPI, HTTPException
app = FastAPI()
@app.get("/")
def home():
raise HTTPException(status_code=400, detail="Bad Request")
The above endpoint doesn't have a responses
field, even if it's clear that the response will have a 400
status code.
CF011 - No Content Response
Currently, if you try to send a response with no content (204), FastAPI will send a 204 status with a non-empty body. It will send a body content-length being 4 bytes.
You can verify this statement running the following code:
# main.py
from fastapi import FastAPI
app = FastAPI()
@app.get("/", status_code=204)
def home():
...
Now feel free to run with your favorite server implementation:
uvicorn main:app
Then use curl or any other tool to send a request:
$ curl localhost:8000
* Trying 127.0.0.1:8000...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8000 (#0)
> GET / HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.68.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 204 No Content
< date: Sat, 24 Jul 2021 19:21:24 GMT
< server: uvicorn
< content-length: 4
< content-type: application/json
<
* Connection #0 to host localhost left intact
This goes against the RFC, which specifies that a 204 response should have no body.
License
This project is licensed under the terms of the MIT license.
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