ServerDisconnectedError if view don't read POST body

[Cykooz]

Long story short

If I use ClientSession with persistent connection (keep-alive) and sends two POST-requests with form-data that contains a file represented as io.BytesIO(), and web.Application() don't reads body of request, then second client's request fails with exception ServerDisconnectedError.

Steps to reproduce

Shot example to reproduce the problem:

import asyncio
from io import BytesIO

from aiohttp import FormData, web
from aiohttp.test_utils import TestServer, TestClient


async def view(request):
    return web.Response(body=b'')


async def test_example():
    app = web.Application()
    app.router.add_post('/', view)
    async with TestClient(TestServer(app)) as client:
        for i in range(3):
            print(f'Send request {i + 1}')
            form_data = FormData([('file', BytesIO(b'*'))])
            res = await client.post('/', data=form_data)
            assert res.status == 200
        print('Done')


asyncio.run(test_example())

$ python3.7 example.py
Send request 1
Send request 2
Traceback (most recent call last):
  File "example.py", line 28, in <module>
    asyncio.run(test_example())
  File "/usr/lib/python3.7/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.7/asyncio/base_events.py", line 573, in run_until_complete
    return future.result()
  File "test_example.py", line 23, in test_example
    res = await client.post('/', data=form_data)
  File "/home/cykooz/buildout-eggs/cp37m/aiohttp-3.5.4-py3.7-linux-x86_64.egg/aiohttp/test_utils.py", line 295, in request
    method, self.make_url(path), **kwargs
  File "/home/cykooz/buildout-eggs/cp37m/aiohttp-3.5.4-py3.7-linux-x86_64.egg/aiohttp/client.py", line 497, in _request
    await resp.start(conn)
  File "/home/cykooz/buildout-eggs/cp37m/aiohttp-3.5.4-py3.7-linux-x86_64.egg/aiohttp/client_reqrep.py", line 844, in start
    message, payload = await self._protocol.read()  # type: ignore  # noqa
  File "/home/cykooz/buildout-eggs/cp37m/aiohttp-3.5.4-py3.7-linux-x86_64.egg/aiohttp/streams.py", line 588, in read
    await self._waiter
aiohttp.client_exceptions.ServerDisconnectedError: None

Your environment

Ubuntu 18.04
Python 3.7.1
aiohttp 3.5.4

[aio-libs-bot]

GitMate.io thinks the contributor most likely able to help you is @asvetlov.

Possibly related issues are #3087 (request.post() should raise HTTPRequestEntityTooLarge same as request.read()), #2895 (Raise an exception on request body reading after sending response), #2908 (How to use make_mocked_request to make a post request with body?), #394 (ServerDisconnectedError is trigger happy), and #96 (Close connection if response body is not consumed.).

[asvetlov]

Thanks for the report!
Perhaps FormData in the example can be replaced with sending raw data bytes.

[Cykooz]

Perhaps FormData in the example can be replaced with sending raw data bytes.

No, the error does not occur if change code to this:

res = await client.post('/', data=BytesIO(b'*'))

or to this

res = await client.post('/', data=b'*')

Also the error does not occur if change code to this:

form_data = FormData([('file', b'*')])
res = await client.post('/', data=form_data)

or to this:

form_data = FormData([('file', BytesIO(b'*'))])
res = await client.post('/', data=form_data, headers={'Connection': 'close'})

[Cykooz]

I have found case then error is occur with raw data bytes:

size = 128 * 1024 + 1
res = await client.post('/', data=BytesIO(b'*' * size))
# and without BytesIO too
res = await client.post('/', data=b'*' * size)

[asvetlov]

Related to #5220