From b0b662bb2b340d63529672b5bdae596a6243c4d0 Mon Sep 17 00:00:00 2001 From: John Snow Date: Mon, 31 Jan 2022 23:11:34 -0500 Subject: [PATCH] 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 Reviewed-by: Kevin Wolf Message-id: 20220201041134.1237016-5-jsnow@redhat.com Signed-off-by: John Snow --- python/qemu/aqmp/legacy.py | 3 +++ python/qemu/aqmp/protocol.py | 41 +++++++++++++++++++++++++++++++++--- 2 files changed, 41 insertions(+), 3 deletions(-) diff --git a/python/qemu/aqmp/legacy.py b/python/qemu/aqmp/legacy.py index 0890f95b16..6baa5f3409 100644 --- a/python/qemu/aqmp/legacy.py +++ b/python/qemu/aqmp/legacy.py @@ -56,6 +56,9 @@ class QEMUMonitorProtocol(qemu.qmp.QEMUMonitorProtocol): self._address = address self._timeout: Optional[float] = None + if server: + self._aqmp._bind_hack(address) # pylint: disable=protected-access + _T = TypeVar('_T') def _sync( diff --git a/python/qemu/aqmp/protocol.py b/python/qemu/aqmp/protocol.py index 50e973c2f2..33358f5cd7 100644 --- a/python/qemu/aqmp/protocol.py +++ b/python/qemu/aqmp/protocol.py @@ -15,6 +15,7 @@ from asyncio import StreamReader, StreamWriter from enum import Enum from functools import wraps import logging +import socket from ssl import SSLContext from typing import ( Any, @@ -238,6 +239,9 @@ class AsyncProtocol(Generic[T]): self._runstate = Runstate.IDLE self._runstate_changed: Optional[asyncio.Event] = None + # Workaround for bind() + self._sock: Optional[socket.socket] = None + def __repr__(self) -> str: cls_name = type(self).__name__ tokens = [] @@ -427,6 +431,34 @@ class AsyncProtocol(Generic[T]): else: await self._do_connect(address, ssl) + def _bind_hack(self, address: Union[str, Tuple[str, int]]) -> None: + """ + Used to create a socket in advance of accept(). + + This is a workaround to ensure that we can guarantee timing of + precisely when a socket exists to avoid a connection attempt + bouncing off of nothing. + + Python 3.7+ adds a feature to separate the server creation and + listening phases instead, and should be used instead of this + hack. + """ + if isinstance(address, tuple): + family = socket.AF_INET + else: + family = socket.AF_UNIX + + sock = socket.socket(family, socket.SOCK_STREAM) + sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) + + try: + sock.bind(address) + except: + sock.close() + raise + + self._sock = sock + @upper_half async def _do_accept(self, address: SocketAddrT, ssl: Optional[SSLContext] = None) -> None: @@ -464,24 +496,27 @@ class AsyncProtocol(Generic[T]): if isinstance(address, tuple): coro = asyncio.start_server( _client_connected_cb, - host=address[0], - port=address[1], + host=None if self._sock else address[0], + port=None if self._sock else address[1], ssl=ssl, backlog=1, limit=self._limit, + sock=self._sock, ) else: coro = asyncio.start_unix_server( _client_connected_cb, - path=address, + path=None if self._sock else address, ssl=ssl, backlog=1, limit=self._limit, + sock=self._sock, ) server = await coro # Starts listening await connected.wait() # Waits for the callback to fire (and finish) assert server is None + self._sock = None self.logger.debug("Connection accepted.")