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Filename : fpm_utils.py
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# -*- coding: utf-8 -*-

# Copyright © Cloud Linux GmbH & Cloud Linux Software, Inc 2010-2021 All Rights Reserved
#
# Licensed under CLOUD LINUX LICENSE AGREEMENT
# http://cloudlinux.com/docs/LICENSE.TXT

import logging
import os
from dataclasses import dataclass
from typing import Optional

from xray import gettext as _
from .constants import fpm_stat_storage, fpm_reload_timeout
from .exceptions import XRayError
from .utils import dbm_storage, filelock, timestamp

logger = logging.getLogger('fpm_utils')


@dataclass
class FPMReloadController:
    """
    Class to control the frequency of FPM service reloading
    """

    fpm_service: str

    @property
    def latest_reload(self) -> Optional[int]:
        """
        Get the timestamp of latest reload of FPM service
        """
        try:
            with dbm_storage(fpm_stat_storage) as _fpm_reload_stat:
                try:
                    return int(_fpm_reload_stat[self.fpm_service].decode())
                except KeyError:
                    return None
        except RuntimeError as e:
            raise XRayError(_('Failed to get the timestamp of latest FPM reload: %s') % str(e), flag='warning')

    def save_latest_reload(self):
        """
        Save the timestamp of latest reload of FPM service
        """
        try:
            # save timestamp of latest reload of corresponding service
            with dbm_storage(fpm_stat_storage) as _fpm_reload_stat:
                _fpm_reload_stat[self.fpm_service] = str(timestamp())
        except RuntimeError as e:
            raise XRayError(
                _('Failed to save the timestamp of latest FPM reload %s, but main operation executed') % str(e),
                flag='warning',
            )

    def delta(self) -> float:
        """
        Get the time delta between current time and saved timestamp
        """
        try:
            # we store timestamp in seconds,
            # but timeout -- fpm_reload_timeout -- in minutes
            return (timestamp() - self.latest_reload) / 60
        except (TypeError, XRayError):
            # 1 hour,
            # big enough for non-blocking flow in case of unexpected errors
            return 60.0

    def restrict(self) -> bool:
        """
        Check if FPM reload should be blocked
        """
        return self.delta() <= fpm_reload_timeout

    def reserve_reload_slot(self) -> bool:
        """
        Atomically decide whether THIS caller may perform the throttled reload
        and, if so, reserve the slot before returning.

        ``restrict`` (the check) and ``save_latest_reload`` (the reserve) must
        run as a single critical section shared across processes. Otherwise
        several concurrent user-mode user-agent processes can each observe an
        expired window, all pass the check, and each run the service reload --
        preserving the server-wide DoS this throttle is meant to close (a tenant
        who owns a mod_php DirectAdmin domain firing N parallel start/stop
        requests triggers N global `service httpd restart`s). A cross-process
        exclusive flock makes check-and-reserve atomic: at most one caller per
        window records the timestamp and returns True; the losers re-read the
        just-saved timestamp under the same lock and return False.

        Reserve-before-act (the timestamp is saved BEFORE the reload runs, not
        after) is deliberate: the reservation must be visible to concurrent
        callers immediately, and a reload that later fails should still consume
        the window (the throttle errs toward FEWER restarts). Root/operator
        callers do not use this method -- they are never throttled.

        Returns True if the slot was reserved (caller must proceed with the
        reload); False if throttled (caller must skip). Any lock/storage failure
        fails safe (returns False) rather than risk an unthrottled restart.
        """
        lock_path = '%s.%s.lock' % (fpm_stat_storage, self.fpm_service)
        try:
            lock_fd = os.open(lock_path, os.O_CREAT | os.O_RDWR | os.O_CLOEXEC, 0o600)
        except OSError as e:
            logger.warning('Failed to open reload lock %s: %s', lock_path, e)
            return False
        try:
            with filelock(lock_fd):
                if self.restrict():
                    return False
                self.save_latest_reload()
                return True
        except XRayError as e:
            # filelock exhausted its retries, or save_latest_reload failed.
            logger.warning('Failed to reserve reload slot for %s: %s', self.fpm_service, e)
            return False
        finally:
            os.close(lock_fd)