Stuck with: WARNING: Invalid HTTP request received.

Hi there,

I’m using FastAPI with uvicorn and I’m running into an issue which I’m not sure how to debug/solve. I wasn’t sure where to post this, but since the error message comes from uvicorn I decided to post it here.

There is no issue if I send a single GET request:

DEBUG: ('10.144.0.115', 48348) - Connected
DEBUG: ('10.144.0.115', 48348) - ASGI [48] Started
DEBUG: ('10.144.0.115', 48348) - ASGI [48] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('10.144.0.115', 48348) - "GET /charts HTTP/1.1" 200
DEBUG: ('10.144.0.115', 48348) - ASGI [48] Received {'type': 'http.response.body', 'body': '<41112 bytes>'}
DEBUG: ('10.144.0.115', 48348) - ASGI [48] Completed
DEBUG: ('10.144.0.115', 48348) - Disconnected

But if I send a second GET request while the connection from the first request is still open I get WARNING: Invalid HTTP request received.. Here is the complete log for the two requests:

DEBUG: ('10.144.0.115', 49422) - Connected
DEBUG: ('10.144.0.115', 49422) - ASGI [51] Started
DEBUG: ('10.144.0.115', 49422) - ASGI [51] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('10.144.0.115', 49422) - "GET /charts HTTP/1.1" 200
DEBUG: ('10.144.0.115', 49422) - ASGI [51] Received {'type': 'http.response.body', 'body': '<41112 bytes>'}
DEBUG: ('10.144.0.115', 49422) - ASGI [51] Completed
WARNING: Invalid HTTP request received.
DEBUG: ('10.144.0.115', 49422) - Disconnected
DEBUG: ('10.144.0.115', 49430) - Connected
DEBUG: ('10.144.0.115', 49430) - ASGI [52] Started
DEBUG: ('10.144.0.115', 49430) - ASGI [52] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('10.144.0.115', 49430) - "GET /charts HTTP/1.1" 200
DEBUG: ('10.144.0.115', 49430) - ASGI [52] Received {'type': 'http.response.body', 'body': '<41112 bytes>'}
DEBUG: ('10.144.0.115', 49430) - ASGI [52] Completed
DEBUG: ('10.144.0.115', 49430) - Disconnected

This isn’t too bad, because I still receive the responses for each request, even with the warning.

But if I try to send a POST request from a react-frontend it gets worse. The POST request from the frontend comes with a Preflight OPTIONS request. That means if I hit the send-button in the frontend the browser sends an OPTIONS request immediately followed by a POST request.

The server log looks like this:

DEBUG: ('10.144.0.115', 44982) - Connected
DEBUG: ('10.144.0.115', 44982) - ASGI [14] Started
DEBUG: ('10.144.0.115', 44982) - ASGI [14] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('10.144.0.115', 44982) - "OPTIONS /colors HTTP/1.1" 200
DEBUG: ('10.144.0.115', 44982) - ASGI [14] Received {'type': 'http.response.body', 'body': '<2 bytes>'}
DEBUG: ('10.144.0.115', 44982) - ASGI [14] Completed
WARNING: Invalid HTTP request received.
DEBUG: ('10.144.0.115', 44982) - Disconnected

The OPTIONS request gets through, but the POST request doesn’t. The payload from the frontend doesn’t reach the backend.

Now the strangest thing: If I hammer the send-button multiple times a second, the POST request will get through eventually.

Does anyone know what’s going on or how this could be solved?