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http 204 causes gunicorn shutdown on appengine [BUG]

See original GitHub issue

Describe the bug

I’ve found that a simple endpoint with status_code=204 is causing gunicorn to shutdown when running on Google appengine.

I suspect the bug is probably outside of FastAPI (eg maybe in uvicorn?), but I haven’t yet managed to reproduce it with a simpler stack, and maybe this will help others with the same issue.

To Reproduce

Create the following:

main.py:

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.delete("/", status_code=204)
def delete_root():
    print("deleted a thing...")
    return ""

requirements.txt:

fastapi
gunicorn
uvicorn

app.yaml:

runtime: python37

instance_class: F1

entrypoint: gunicorn --bind :$PORT --workers 1 --worker-class uvicorn.workers.UvicornWorker main:app

handlers:
    - url: /.*
      secure: always
      script: auto

Install gcloud cli, login to gcloud and then deploy to appengine with:

gcloud app deploy

Call the delete endpoint

curl -XDELETE https://YOURPROJECT.appspot.com

It hangs for a couple of seconds and then returns an error like this:

<html><head>
<meta http-equiv="content-type" content="text/html;charset=utf-8">
<title>500 Server Error</title>
</head>
<body text=#000000 bgcolor=#ffffff>
<h1>Error: Server Error</h1>
<h2>The server encountered an error and could not complete your request.<p>Please try again in 30 seconds.</h2>
<h2></h2>
</body></html>

And logs as follows:

2020-05-23 15:08:11.658 NZST deleted a thing...
2020-05-23 15:08:13.193 NZST [start] 2020/05/23 03:08:13.192900 Quitting on terminated signal
2020-05-23 15:08:13.198 NZST [2020-05-23 03:08:13 +0000] [7] [INFO] Handling signal: term
2020-05-23 15:08:13.259 NZST [2020-05-23 03:08:13 +0000] [15] [INFO] Shutting down
2020-05-23 15:08:13.259 NZST [2020-05-23 03:08:13 +0000] [15] [INFO] Error while closing socket [Errno 9] Bad file descriptor
2020-05-23 15:08:13.360 NZST [2020-05-23 03:08:13 +0000] [15] [INFO] Waiting for application shutdown.
2020-05-23 15:08:13.360 NZST [2020-05-23 03:08:13 +0000] [15] [INFO] Application shutdown complete.
2020-05-23 15:08:13.360 NZST [2020-05-23 03:08:13 +0000] [15] [INFO] Finished server process 
2020-05-23 15:08:13.361 NZST [2020-05-23 03:08:13 +0000] [15] [INFO] Worker exiting (pid: 15)
2020-05-23 15:08:13.502 NZST [2020-05-23 03:08:13 +0000] [7] [INFO] Shutting down: Master
2020-05-23 15:08:13.556 NZST [start] 2020/05/23 03:08:13.555603 Start program failed: termination triggered by nginx exit

But I expected it to return an empty body with http status 204.

Note - changing status code to something else, eg 200 resolves the issue.

Expected behavior

I expected an empty 204 response to be returned.

Environment

OS: Linux (appengine)
FastAPI Version

0.54.2

Python version

3.7 (whatever as used by appengine)

Issue Analytics

State:
Created 3 years ago
Reactions:3
Comments:6 (1 by maintainers)

Top GitHub Comments

1reaction

jwmngcommented, Aug 24, 2020

Can confirm this happens on standalone uvicorn 0.11.8 as well. The 204 response indicates that no content will follow. However, return "" sends a response body that is two characters long for some reason. This causes an ASGI exception, the related uvicorn traceback shows:

[31mERROR[0m:    Exception in ASGI application
Traceback (most recent call last):
  File "<snip>\env\lib\site-packages\uvicorn\protocols\http\h11_impl.py", line 388, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "<snip>\env\lib\site-packages\uvicorn\middleware\proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "<snip>\env\lib\site-packages\fastapi\applications.py", line 179, in __call__
    await super().__call__(scope, receive, send)
  File "<snip>\env\lib\site-packages\starlette\applications.py", line 111, in __call__
    await self.middleware_stack(scope, receive, send)
  File "<snip>\env\lib\site-packages\starlette\middleware\errors.py", line 181, in __call__
    raise exc from None
  File "<snip>\env\lib\site-packages\starlette\middleware\errors.py", line 159, in __call__
    await self.app(scope, receive, _send)
  File "<snip>\env\lib\site-packages\starlette\exceptions.py", line 82, in __call__
    raise exc from None
  File "<snip>\env\lib\site-packages\starlette\exceptions.py", line 71, in __call__
    await self.app(scope, receive, sender)
  File "<snip>\env\lib\site-packages\starlette\routing.py", line 566, in __call__
    await route.handle(scope, receive, send)
  File "<snip>\env\lib\site-packages\starlette\routing.py", line 227, in handle
    await self.app(scope, receive, send)
  File "<snip>\env\lib\site-packages\starlette\routing.py", line 44, in app
    await response(scope, receive, send)
  File "<snip>\env\lib\site-packages\starlette\responses.py", line 139, in __call__
    await send({"type": "http.response.body", "body": self.body})
  File "<snip>\env\lib\site-packages\starlette\exceptions.py", line 68, in sender
    await send(message)
  File "<snip>\env\lib\site-packages\starlette\middleware\errors.py", line 156, in _send
    await send(message)
  File "<snip>\env\lib\site-packages\uvicorn\protocols\http\h11_impl.py", line 482, in send
    output = self.conn.send(event)
  File "<snip>\env\lib\site-packages\h11\_connection.py", line 469, in send
    data_list = self.send_with_data_passthrough(event)
  File "<snip>\env\lib\site-packages\h11\_connection.py", line 502, in send_with_data_passthrough
    writer(event, data_list.append)
  File "<snip>\env\lib\site-packages\h11\_writers.py", line 77, in __call__
    self.send_data(event.data, write)
  File "<snip>\env\lib\site-packages\h11\_writers.py", line 97, in send_data
    raise LocalProtocolError("Too much data for declared Content-Length")
h11._util.LocalProtocolError: Too much data for declared Content-Length

If you return None the response body will remain empty and the 204 response works.

I’m not sure if this is a bug in FastAPI, Starlette or h11, or which of them interprets the empty string as a literal '' response

0reactions

therefromherecommented, Sep 4, 2022

Thanks @tiangolo , yes confirming this is fixed now