uvicorn's "Response content longer than Content-Length" RuntimeError for DELETE endpoints #1635
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When dealing with DELETE endpoints that have an empty JSONResponse content and 204 status, e.g.: from starlette.applications import Starlette
from starlette.responses import JSONResponse, PlainTextResponse
from starlette.routing import Route
async def homepage(request):
return JSONResponse(None, status_code=204)
# return PlainTextResponse(None, status_code=204)
routes = [
Route("/", endpoint=homepage, methods=["DELETE"])
]
starapp = Starlette(routes=routes)and run it with uvicorn, like this: we get this error from uvicorn: This happens since starlette Note that this doesn't happen with I'm also not sure how to debug uvicorn server per se, {'body': b'null',
'message': {'body': b'null', 'type': 'http.response.body'},
'message_type': 'http.response.body',
'more_body': False,
'num_bytes': 4,
'self': <uvicorn.protocols.http.httptools_impl.RequestResponseCycle object at 0x1105809a0>}If instead of with the same error from uvicorn. Also, note that I originally noticed that when using FastAPI v0.76. |
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Replies: 4 comments 10 replies
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Hey slafs I tried to reproduce it and a similar error raised: Also I've found that is not related to DELETE verb and when you replace it with different verbs like GET, POST, ... nothing changes. Then, I tried to reproduce it with other ASGI workers like daphne and hypercorn and I noticed that everything works well. So, It's probably an issue with Thanks for reporting. |
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This is not a uvicorn issue. Uvicorn does what is right here. Starlette could document better the |
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That issue doesn't happen with FastAPI on the latest version anymore... It only happens if you explicitly add You'll only have this issue if you manually add the |
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I need to update flake8-fastapi. |
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the value "" (empty string) also encodes to '""' (two double quotes) and produces same issue. also a b"" (a zero-byte binary) is not allowed because binary values aren't json serializable. |
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Well... Then... You shouldn't use As I said below, we don't remove the content body, and we remove the content length according to the status code. This was a decision, is not a bug. We can discuss about that decision if wanted tho, but it's not a bug... |
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I understand, thanks @Kludex, I learned more. |
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I think It's better to put the problem in an issue. |
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It was a decision to not remove the content body of any response. Even if we remove the headers, we don't remove the body. |
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Shouldn't we raise an exception about it? any usage of JSONResponse (and any other response which renders a non-zero-byte value) with 204 status would produce an error in uvicorn. |
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Maybe... I don't know. 👍 Or maybe we could remove the body... It's something to think about. |
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Another, maybe simpler example, that reproduces the problem: from starlette.applications import Starlette
from starlette.routing import Route
from starlette.responses import Response
from starlette.requests import Request
def endpoint(request: Request):
return Response("null", status_code=204)
app = Starlette(
routes=[Route("/", endpoint=endpoint)],
)The problem is even more notorious when using FastAPI, as the same response from above is generated automatically because a function implicitly always returns with from fastapi import FastAPI
app = FastAPI()
@app.get("/", status_code=204)
def endpoint():
print("Oh, hi mark")I created an issue here with a lot more details: #1764, I'm gonna work on it. |
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This is not a uvicorn issue. Uvicorn does what is right here.
Starlette could document better the
JSONResponseinteraction with status codes that should not have any content. In this case what is happening is that Starlette'sJSONResponseis sending 4 bytes (null), but there's noContent-Lengthheader, and the status code is 204.