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# -*- test-case-name: twisted.python.test.test_systemd -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Integration with systemd.
Currently only the minimum APIs necessary for using systemd's socket activation
feature are supported.
"""
__all__ = ["ListenFDs"]
from os import getpid
from typing import Iterable, List, Mapping, Optional
class ListenFDs:
"""
L{ListenFDs} provides access to file descriptors inherited from systemd.
Typically L{ListenFDs.fromEnvironment} should be used to construct a new
instance of L{ListenFDs}.
@cvar _START: File descriptors inherited from systemd are always
consecutively numbered, with a fixed lowest "starting" descriptor. This
gives the default starting descriptor. Since this must agree with the
value systemd is using, it typically should not be overridden.
@ivar _descriptors: A C{list} of C{int} giving the descriptors which were
inherited.
"""
_START = 3
def __init__(self, descriptors: List[int]) -> None:
"""
@param descriptors: The descriptors which will be returned from calls to
C{inheritedDescriptors}.
"""
self._descriptors = descriptors
@classmethod
def fromEnvironment(
cls,
environ: Optional[Mapping[str, str]] = None,
start: Optional[int] = None,
) -> "ListenFDs":
"""
@param environ: A dictionary-like object to inspect to discover
inherited descriptors. By default, L{None}, indicating that the
real process environment should be inspected. The default is
suitable for typical usage.
@param start: An integer giving the lowest value of an inherited
descriptor systemd will give us. By default, L{None}, indicating
the known correct (that is, in agreement with systemd) value will be
used. The default is suitable for typical usage.
@return: A new instance of C{cls} which can be used to look up the
descriptors which have been inherited.
"""
if environ is None:
from os import environ as _environ
environ = _environ
if start is None:
start = cls._START
descriptors: List[int] = []
try:
pid = int(environ["LISTEN_PID"])
except (KeyError, ValueError):
pass
else:
if pid == getpid():
try:
count = int(environ["LISTEN_FDS"])
except (KeyError, ValueError):
pass
else:
descriptors = list(range(start, start + count))
del environ["LISTEN_PID"], environ["LISTEN_FDS"]
return cls(descriptors)
def inheritedDescriptors(self) -> Iterable[int]:
"""
@return: The configured descriptors.
"""
return list(self._descriptors)
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