StreamingResponse with async generator get stuck indefinitely #1776
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import asyncio
from starlette.applications import Starlette
from starlette.responses import StreamingResponse
from starlette.routing import Route
def sync_streamer():
try:
while True:
yield b"--boundary\r\nContent-Type: text/plain\r\nContent-Length: 1\r\n\r\n1\r\n"
except asyncio.CancelledError:
print("caught cancelled error")
raise GeneratorExit
async def async_streamer():
try:
while True:
yield b"--boundary\r\nContent-Type: text/plain\r\nContent-Length: 1\r\n\r\n1\r\n"
except asyncio.CancelledError:
print("caught cancelled error")
raise GeneratorExit
async def sync_endpoint(request):
try:
return StreamingResponse(
sync_streamer(),
media_type="multipart/x-mixed-replace; boundary=boundary",
)
except asyncio.CancelledError:
print("caught cancelled error")
raise GeneratorExit
async def async_endpoint(request):
try:
return StreamingResponse(
async_streamer(),
media_type="multipart/x-mixed-replace; boundary=boundary",
)
except KeyboardInterrupt:
exit()
routes = [
Route('/sync', sync_endpoint),
Route('/async', async_endpoint),
]
app = Starlette(routes=routes)CASE 1: When >uvicorn stream:app
INFO: Started server process [23288]
INFO: Waiting for application startup.
INFO: Application startup complete.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: 127.0.0.1:65107 - "GET /async HTTP/1.1" 200 OK
# stuck indefinitely after client cancels the request.CASE 2: When >uvicorn stream:app
INFO: Started server process [24968]
INFO: Waiting for application startup.
INFO: Application startup complete.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: 127.0.0.1:55582 - "GET /sync HTTP/1.1" 200 OK
Exception in callback _ProactorBasePipeTransport._call_connection_lost(None)
handle: <Handle _ProactorBasePipeTransport._call_connection_lost(None)>
Traceback (most recent call last):
File "...\lib\asyncio\events.py", line 80, in _run
self._context.run(self._callback, *self._args)
File "...\lib\asyncio\proactor_events.py", line 162, in _call_connection_lost
self._sock.shutdown(socket.SHUT_RDWR)
ConnectionResetError: [WinError 10054] An existing connection was forcibly closed by the remote hostWhen CASE 1, even `Keyboard Interrupts are ignored. I had to kill Python process forcefully. |
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Replies: 3 comments 4 replies
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Did some quick debugging, seems like its not reaching this part of the code when Cancelled, when Async generator is used. |
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If you add an async def async_streamer():
try:
while True:
yield b"--boundary\r\nContent-Type: text/plain\r\nContent-Length: 1\r\n\r\n1\r\n"
await asyncio.sleep(0) # <--
except asyncio.CancelledError:
print("caught cancelled error")
raise GeneratorExit |
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Yes, it does! Now exceptions are caught, we get What's happening here? |
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Other tasks are not able to run, as it's stuck on the |
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Oh! Is it something the developer is expected to handle (not much aware of async generators yet) or, it'd be a good scenario starlette can handle? |
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Yes. Nothing we can do about it. |
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How to solve this issue. |
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If you add an
await asyncio.sleep(0), does it solve the problem?