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python/aqmp: add socket bind step to legacy.py
The synchronous QMP library would bind to the server address during __init__(). The new library delays this to the accept() call, because binding occurs inside of the call to start_[unix_]server(), which is an async method -- so it cannot happen during __init__ anymore. Python 3.7+ adds the ability to create the server (and thus the bind() call) and begin the active listening in separate steps, but we don't have that functionality in 3.6, our current minimum. Therefore ... Add a temporary workaround that allows the synchronous version of the client to bind the socket in advance, guaranteeing that there will be a UNIX socket in the filesystem ready for the QEMU client to connect to without a race condition. (Yes, it's a bit ugly. Fixing it more nicely will have to wait until our minimum Python version is 3.7+.) Signed-off-by: John Snow <jsnow@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Message-id: 20220201041134.1237016-5-jsnow@redhat.com Signed-off-by: John Snow <jsnow@redhat.com>
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@ -56,6 +56,9 @@ def __init__(self, address: SocketAddrT,
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self._address = address
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self._timeout: Optional[float] = None
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if server:
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self._aqmp._bind_hack(address) # pylint: disable=protected-access
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_T = TypeVar('_T')
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def _sync(
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@ -15,6 +15,7 @@
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from enum import Enum
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from functools import wraps
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import logging
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import socket
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from ssl import SSLContext
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from typing import (
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Any,
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@ -238,6 +239,9 @@ def __init__(self, name: Optional[str] = None) -> None:
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self._runstate = Runstate.IDLE
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self._runstate_changed: Optional[asyncio.Event] = None
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# Workaround for bind()
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self._sock: Optional[socket.socket] = None
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def __repr__(self) -> str:
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cls_name = type(self).__name__
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tokens = []
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@ -427,6 +431,34 @@ async def _establish_connection(
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else:
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await self._do_connect(address, ssl)
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def _bind_hack(self, address: Union[str, Tuple[str, int]]) -> None:
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"""
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Used to create a socket in advance of accept().
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This is a workaround to ensure that we can guarantee timing of
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precisely when a socket exists to avoid a connection attempt
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bouncing off of nothing.
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Python 3.7+ adds a feature to separate the server creation and
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listening phases instead, and should be used instead of this
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hack.
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"""
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if isinstance(address, tuple):
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family = socket.AF_INET
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else:
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family = socket.AF_UNIX
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sock = socket.socket(family, socket.SOCK_STREAM)
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sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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try:
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sock.bind(address)
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except:
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sock.close()
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raise
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self._sock = sock
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@upper_half
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async def _do_accept(self, address: SocketAddrT,
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ssl: Optional[SSLContext] = None) -> None:
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@ -464,24 +496,27 @@ async def _client_connected_cb(reader: asyncio.StreamReader,
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if isinstance(address, tuple):
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coro = asyncio.start_server(
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_client_connected_cb,
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host=address[0],
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port=address[1],
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host=None if self._sock else address[0],
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port=None if self._sock else address[1],
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ssl=ssl,
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backlog=1,
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limit=self._limit,
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sock=self._sock,
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)
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else:
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coro = asyncio.start_unix_server(
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_client_connected_cb,
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path=address,
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path=None if self._sock else address,
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ssl=ssl,
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backlog=1,
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limit=self._limit,
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sock=self._sock,
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)
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server = await coro # Starts listening
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await connected.wait() # Waits for the callback to fire (and finish)
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assert server is None
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self._sock = None
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self.logger.debug("Connection accepted.")
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