BUG, EASY, PY38: web_protocol.RequestHandler mismatch _keepalive field with __slots__

[cjrh]

Long story short

In RequestHandler, the spelling in __slots__ is _keep_alive but in the default assignment in __init__(), the name of the field is _keepalive. The latter is what actually gets used in the module, not the slots name.

In Python 3.7, this appears to be ok because instances are getting a __dict__ from somewhere (presumably from an ancestor in the MRO chain). However, in Python 3.8 it seems that instances of RequestHandler are not getting a __dict__ attached to them, which is why an AttributeError gets raised.

The slots declaration in aiohttp/web_protocol.py:

class RequestHandler(BaseProtocol):
    KEEPALIVE_RESCHEDULE_DELAY = 1

    __slots__ = ('_request_count', '_keep_alive', '_manager',
                 '_request_handler', '_request_factory', '_tcp_keepalive',
                 '_keepalive_time', '_keepalive_handle', '_keepalive_timeout',
                 '_lingering_time', '_messages', '_message_tail',
                 '_waiter', '_error_handler', '_task_handler',
                 '_upgrade', '_payload_parser', '_request_parser',
                 '_reading_paused', 'logger', 'debug', 'access_log',
                 'access_logger', '_close', '_force_close')

    def __init__(self, manager: 'Server', *,
                 loop: asyncio.AbstractEventLoop,
                 keepalive_timeout: float=75.,  # NGINX default is 75 secs
                 tcp_keepalive: bool=True,
                 logger: Logger=server_logger,
                 access_log_class: Type[AbstractAccessLogger]=AccessLogger,
                 access_log: Logger=access_logger,
                 access_log_format: str=AccessLogger.LOG_FORMAT,
                 debug: bool=False,
                 max_line_size: int=8190,
                 max_headers: int=32768,
                 max_field_size: int=8190,
                 lingering_time: float=10.0):

        super().__init__(loop)

        self._request_count = 0

        self._keepalive = False      # <----- NAME DIFFERS TO _keep_alive IN SLOTS

        self._manager = manager  # type: Optional[Server]
        self._request_handler = manager.request_handler  # type: Optional[_RequestHandler]  # noqa
        self._request_factory = manager.request_factory  # type: Optional[_RequestFactory]  # noqa

This code was added in #3095.

Expected behaviour

In Python 3.8 requests to the aiohttp web server should succeed.

Actual behaviour

In Python 3.8, requests fail with this traceback:

Exception in callback BaseProactorEventLoop._start_serving.<locals>.loop(<_OverlappedF...0.1', 64284))>) at G:\Programs\Python38\lib\asyncio\proactor_events.py:651
handle: <Handle BaseProactorEventLoop._start_serving.<locals>.loop(<_OverlappedF...0.1', 64284))>) at G:\Programs\Python38\lib\asyncio\proactor_events.py:651>
Traceback (most recent call last):
  File "G:\Programs\Python38\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "G:\Programs\Python38\lib\asyncio\proactor_events.py", line 658, in loop
    protocol = protocol_factory()
  File "G:\Documents\repos\blah\venv\lib\site-packages\aiohttp\web_server.py", line 57, in __call__
    return RequestHandler(self, loop=self._loop, **self._kwargs)
  File "G:\Documents\repos\blah\venv\lib\site-packages\aiohttp\web_protocol.py", line 136, in __init__
    self._keepalive = False
AttributeError: 'RequestHandler' object has no attribute '_keepalive'

Immediately at the offending line (in a debugger), the __mro__ for the RequestHandler instance appears to be the same when running under Python 3.7 and Python 3.8:

[
    <class 'tuple'>: (<class 'aiohttp.web_protocol.RequestHandler'>, 
    <class 'aiohttp.base_protocol.BaseProtocol'>, 
    <class 'asyncio.protocols.Protocol'>, 
    <class 'asyncio.protocols.BaseProtocol'>, 
    <class 'object'>)
]

This leads me to suspect that something might have changed with either Protocol or BaseProtocol in upstream asyncio (i.e. declaring slots so as to prevent __dict__ appearing on the instance), but I've not confirmed this.

Regardless, the name mismatch of the field must still be fixed.

Steps to reproduce

Server code with:

import sys
from aiohttp import web
routes = web.RouteTableDef()
FILENAME = 'reveal/reveal.js-3.6.0/index.html'  # Or whatever

@routes.get('/')
async def handle(request):
    return web.FileResponse(FILENAME)

app = web.Application()
app.router.add_static('/js', 'reveal/reveal.js-3.6.0/js')
app.router.add_static('/css', 'reveal/reveal.js-3.6.0/css')
app.router.add_static('/img', 'reveal/reveal.js-3.6.0/img')
app.router.add_static('/lib', 'reveal/reveal.js-3.6.0/lib')
app.router.add_static('/plugin', 'reveal/reveal.js-3.6.0/plugin')
app.router.add_routes(routes)
web.run_app(app)

Then open localhost:8080 in a browser.

Your environment

• Windows 10 x64
• Python 3.8.0a2 (downloaded installer from python.org), with requirements.txt:

aiohttp==3.5.4
async-timeout==3.0.1
attrs==19.1.0
chardet==3.0.4
Cython==0.29.6
dominate==2.3.5
idna==2.8
multidict==4.5.2
numpy==1.16.2
yarl==1.3.0

[aio-libs-bot]

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

Possibly related issues are #2752 (IndexError in RequestHandler), #103 (BasicAuth bugged ?), and #2620 (DNSCache BUG).