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File Content: `web_server.py`

import asyncio
import inspect
import io
import logging
import os
import re
import shlex
import shutil
import string
import xml.etree.ElementTree as ET
from contextlib import suppress
from contextvars import ContextVar
from datetime import timedelta
from packaging.version import Version
from pathlib import Path
from subprocess import check_call, DEVNULL
from typing import Any, Callable, List, Optional, Set, Tuple, Iterable

import psutil

from defence360agent.api.integration_conf import IntegrationConfig
from defence360agent.application.determine_hosting_panel import (
    is_generic_panel_installed,
    is_plesk_installed,
)
from defence360agent.internals.global_scope import g
from defence360agent.utils import (
    async_lru_cache,
    atomic_rewrite,
    check_run,
    get_system_user_names,
    OsReleaseInfo,
    CheckRunError,
    TimedCache,
    BACKUP_EXTENSION,
)
from defence360agent.utils.common import webserver_gracefull_restart

GRACEFUL_RESTART_MIN_PERIOD = int(
    os.environ.get("IM360_GRACEFUL_RESTART_MIN_PERIOD", 5 * 60)
)  # seconds
"""
how many seconds should pass minimum between web server restarts.
"""
CPANEL_RESTART_APACHE_SCRIPT = "/usr/local/cpanel/scripts/restartsrv_httpd"
# according to LS docs https://www.litespeedtech.com/docs/webserver/admin
LITESPEED_PID_FILE_PATH = Path("/tmp/lshttpd/lshttpd.pid")
LITESPEED_RESTART_CMD = ("/usr/local/lsws/bin/lswsctrl", "condrestart")
LITESPEED_CONF_PATH = "/usr/local/lsws/conf/httpd_config.xml"
APACHE2_BIN_PATH = "/usr/sbin/apache2"
HTTPD_BIN_PATH = "/usr/sbin/httpd"
apache_version_regexp = re.compile(r"Server version:.*(\d+\.\d+\.\d+)")
BYTE_SPACES = tuple(x.encode() for x in list(string.whitespace))
APACHE = "apache"

logger = logging.getLogger(__name__)


class NotRunningError(RuntimeError):
    """
    Error for cases when the web server is expected to be running but it
    is not.

    """


class ConfigInvalidError(RuntimeError):
    """
    Error used to indicate that the web server config is having error(s).
    """


class LiteSpeedConfig:
    CLIENT_IP_IN_HEADER_TAG = "useIpInProxyHeader"
    SECURITY_TAG = "security"
    ACCESS_CONTROL_TAG = "accessControl"
    ACCESS_CONTROL_ALLOWED_TAG = "allow"
    ACCESS_CONTROL_DENIED_TAG = "deny"
    CLIENT_IP_IN_HEADER_DISABLED = 0
    CLIENT_IP_IN_HEADER_ENABLED = 1
    CLIENT_IP_IN_HEADER_TRUSTED_IP_ONLY = 2

    def __init__(self, content):
        self.config = ET.fromstring(content)

    def client_ip_in_header(self) -> int:
        element = self.config.find(self.CLIENT_IP_IN_HEADER_TAG)
        if element is None or not element.text:
            return self.CLIENT_IP_IN_HEADER_DISABLED
        return int(element.text)

    def set_client_ip_in_header(self, value: int):
        element = self.config.find(self.CLIENT_IP_IN_HEADER_TAG)
        if element is None:
            element = ET.Element(self.CLIENT_IP_IN_HEADER_TAG)
            self.config.append(element)
        element.text = str(value)

    def access_control_allowed_list(self) -> Set[Tuple[str, bool]]:
        element = self.config.find(
            "/".join(
                [
                    ".",
                    self.SECURITY_TAG,
                    self.ACCESS_CONTROL_TAG,
                    self.ACCESS_CONTROL_ALLOWED_TAG,
                ]
            )
        )
        if element is not None and element.text:
            return {
                (item[:-1] if item.endswith("T") else item, item.endswith("T"))
                for s in element.text.split()
                for item in s.split(",")
                if item
            }
        return set()

    def set_access_control_allowed_list(self, allowed):
        items = [item[0] + "T" if item[1] else item[0] for item in allowed]
        value = ",".join(items)
        element = self.config.find(
            "/".join(
                [
                    ".",
                    self.SECURITY_TAG,
                    self.ACCESS_CONTROL_TAG,
                    self.ACCESS_CONTROL_ALLOWED_TAG,
                ]
            )
        )
        if element is None:
            element = ET.Element(self.ACCESS_CONTROL_ALLOWED_TAG)
            access_control = self.config.find(
                "/".join(
                    [
                        ".",
                        self.SECURITY_TAG,
                        self.ACCESS_CONTROL_TAG,
                    ]
                )
            )
            if access_control is None:
                access_control = ET.Element(self.ACCESS_CONTROL_TAG)
                security = self.config.find(self.SECURITY_TAG)
                if security is None:
                    security = ET.Element(self.SECURITY_TAG)
                    self.config.append(security)
                security.append(access_control)
            access_control.append(element)
        element.text = value

    def tostring(self) -> bytes:
        buf = io.BytesIO()
        tree = ET.ElementTree(self.config)
        tree.write(buf, encoding="utf-8", xml_declaration=True)
        return buf.getvalue()


def _get_litespeed_pid():
    """Return LiteSpeed's pid or None if it can't be read."""
    with suppress(OSError, ValueError):
        return int(LITESPEED_PID_FILE_PATH.read_bytes())


def litespeed_running():
    """
    Litespeed use constant PID file path, so using it to determinate status
    :return bool
    """
    pid = _get_litespeed_pid()
    try:
        return bool(pid and psutil.pid_exists(pid))
    except OverflowError:
        return False


def apache_running() -> Optional[str]:
    """
    Finding process with name 'httpd' which belongs to system user.
    :return str: path to the apache binary if it is running
    :return None: if apache is not running
    """
    info = _apache_running_process()
    return info["httpd_bin"] if info else None


async def apache_binary_call(*args) -> bytes:
    httpd_bin = apache_running()
    if not httpd_bin:
        raise NotRunningError("Apache is not running")
    try:
        if (
            OsReleaseInfo.id_like() & OsReleaseInfo.DEBIAN
            and Path("/etc/apache2/envvars").exists()
        ):
            # on Debian OS apache requires some env variables
            # that are set in /etc/apache2/envvars (see DEF-6844)
            stdout = await check_run(
                ". /etc/apache2/envvars && {} {}".format(
                    shlex.quote(httpd_bin), shlex.join(args)
                ),
                shell=True,
            )
        else:
            stdout = await check_run([httpd_bin, *args])
    except CheckRunError:
        logger.warning("Apache doesn't work properly")
        return b""
    return stdout


def _apache_running_process(*, exclude_users=frozenset()):
    """
    Finding process with name 'httpd' which belongs to system user.

    Return process info for the apache binary if it is running.
    Return None if apache is not running
    """
    # Cpanel works on rpm based os and uses packages
    # according documentation https://documentation.cpanel.net/display/EA4/Apache   # noqa
    # httpd binary is /usr/sbin/httpd

    # Plesk/Generic uses pkgs from os
    # so it has /usr/sbin/httpd on rpm based os and /usr/sbin/apache2 on debian

    # DirectAdmin uses custombuild
    # It's httpd binary is /usr/sbib/httpd

    def is_generic_panel_on_apache():
        if is_generic_panel_installed():
            return IntegrationConfig.get("web_server", "server_type") == APACHE
        return False

    if (OsReleaseInfo.id_like() & OsReleaseInfo.DEBIAN) and (
        is_plesk_installed() or is_generic_panel_on_apache()
    ):
        httpd_bin = APACHE2_BIN_PATH
    else:
        httpd_bin = HTTPD_BIN_PATH
    sys_users = set(get_system_user_names()) - exclude_users
    info = _apache_running_process_info(sys_users)
    if info:
        assert info["exe"] is not None
        info["httpd_bin"] = httpd_bin
        try:
            httpd_process_exe = info["exe"]
            if os.path.samefile(httpd_bin, httpd_process_exe):
                return info
        except OSError as exc:
            logger.info("Can't determine apache bin path: %s", exc)
    return None


def _apache_running_process_info(sys_users):
    """Retry process_iter() on IndexError."""
    for _ in range(2):  # retry
        with suppress(IndexError):
            return next(
                (
                    p.info
                    for p in psutil.process_iter(
                        attrs=["name", "username", "exe", "uids", "gids"]
                    )
                    if (
                        p.info["exe"] is not None  # non ad_value
                        and p.info["exe"].endswith(("/httpd", "/apache2"))
                        and p.info["username"] in sys_users
                    )
                ),
                None,
            )


def chown(path):
    """Make web server user/group own *path*."""
    info = _apache_running_process(exclude_users={"root"})
    if not info:
        raise NotRunningError(
            "Can't find running apache process without root owner."
        )
    os.chown(path, info["uids"][0], info["gids"][0])


def find_running_nginx():
    """Return path to a running nginx binary or None if not found."""
    return next(
        (
            p.info["exe"]
            for p in psutil.process_iter(attrs=["name", "username", "exe"])
            if (
                p.info["name"] is not None  # non ad_value
                and p.info["name"].endswith("nginx")
                and p.info["exe"] is not None  # non ad_value
                and "nginx" in p.info["exe"]
                and p.info["username"] in ("nginx", "www-data")
            )
        ),
        None,
    )


async def check_with_timeout(
    webserver_running_cb: Callable[[], Any],
    timeout_sec=10,
    granularity: int = 10,
):
    assert granularity > 0

    for _ in range(granularity):
        result = webserver_running_cb()
        if result:
            return result
        await asyncio.sleep(timeout_sec / granularity)
    else:
        return result


def is_EA4_available():
    """
    though, available != running
    :return bool:
    """
    return os.path.isfile("/etc/cpanel/ea4/is_ea4")


def _apache_graceful_restart_cmd(apachectl) -> List[str]:
    """
    :return list: command which can be passed to check_call(..., shell=False)

    'apache2 -k graceful' will not work for Ubuntu
    and will produce
    'Invalid Mutex directory in argument file:${APACHE_LOCK_DIR}' error.
    https://serverfault.com/questions/558283/apache2-config-variable-is-not-defined

    That is why this specialization for Ubuntu graceful restart.
    """  # noqa
    restartsrv_httpd = shutil.which(CPANEL_RESTART_APACHE_SCRIPT)
    if restartsrv_httpd:  # use cpanel specific script if found
        return [restartsrv_httpd]
    if OsReleaseInfo.id_like() & OsReleaseInfo.DEBIAN:
        # see DEF-16795 for details
        return [
            "systemctl",
            "reload",
            "--job-mode=replace-irreversibly",
            os.path.basename(apachectl),
        ]
    else:
        return [apachectl, "-k", "graceful"]


def _graceful_restart_cmd_from_integration_conf() -> Optional[Iterable[str]]:
    if IntegrationConfig.exists():
        # Fallback on regular restart techniques
        # in case of missing restart script.
        try:
            restart_script = IntegrationConfig.to_dict()["web_server"][
                "graceful_restart_script"
            ]
        except KeyError:
            logger.warning(
                "Integration config is missing graceful_restart_script field"
            )
        else:
            if not restart_script:
                logger.warning(
                    "graceful_restart_script option is empty",
                )
                return None
            cmd = restart_script.split()
            if os.path.exists(cmd[0]):
                return cmd
            logger.warning(
                "Web server restart script does not exist: %s",
                restart_script,
            )
    return None


def _graceful_restart_cmd() -> Iterable[str]:
    """Gracefully restart a web server."""
    # Do not restart web server in the agent cgroup
    # (to avoid attaching its processes to it, see DEF-20577)
    prefix = []
    if systemd_run := shutil.which("systemd-run"):
        prefix += [
            systemd_run,
            "-p",
            "SendSIGKILL=no",
            "--slice=graceful_restart",
            "--",
        ]

    cmd = _graceful_restart_cmd_from_integration_conf()
    if cmd is not None:
        return prefix + list(cmd)

    if litespeed_running():
        return prefix + list(LITESPEED_RESTART_CMD)

    if apachectl := apache_running():
        return prefix + _apache_graceful_restart_cmd(apachectl)

    raise RuntimeError("Could not detect a web server")


def _configtest_cmd() -> Iterable[str]:
    if is_generic_panel_installed():
        try:
            cmd = IntegrationConfig.get("web_server", "config_test_script")
            if cmd:
                return cmd.split()
        except KeyError:
            # if setting is not present, fall back to default detection
            pass
    if apache_bin := apache_running():
        if OsReleaseInfo.id_like() & OsReleaseInfo.DEBIAN:
            return ["apachectl", "configtest"]
        return [apache_bin, "-t"]
    elif litespeed_running():
        return ["lightspeed", "-t"]
    elif nginx_bin := find_running_nginx():
        return [nginx_bin, "-t"]
    raise RuntimeError("Could not detect a web server")


_graceful_restart_caller = ContextVar("graceful_restart_caller")


async def safe_update_config(config_path, new_config: str) -> bool:
    """
    Update Web-server config with fallback in case of an error happens.
    It tries to do all the best but because of graceful_restart() the
    faulty config might still be applied but in practice it is barely
    probable (because of premature config check).

    1. The new config is checked before to be applied.
    2. The new config (if checked valid) is atomically applied.
    3. The graceful Web-server restart is scheduled. It may hold the actual
        restart for some time, but it is a required workaround
        of a litespeed issue.
    4. If the Web-server failed to restart the config is reverted.

    Return value: True if no errors (at least up to the server restart),
    False if There was an error and config was reverted.
    Note: It is possible that the config may be reverted even when return
    value is True. It is because the graceful_restart may delay the actual
    restart and config may be reverted on that (delayed) stage.
    """

    config_backup_path = os.fspath(config_path) + BACKUP_EXTENSION

    def remove_backup():
        with suppress(FileNotFoundError):
            os.unlink(config_backup_path)

    make_backup = os.path.exists(config_path)
    if not atomic_rewrite(config_path, new_config, backup=make_backup):
        # nothing has changed => no need to restart
        return True

    def revert():
        try:
            os.rename(config_backup_path, config_path)
        except FileNotFoundError:
            # truncate file if backup does not exist
            open(config_path, "w").close()

    try:
        await configtest(raise_exception=True)
    except ConfigInvalidError as e:
        logger.error("Web server config is invalid: %s", e)
        revert()
    else:
        try:
            restart_cmd = _graceful_restart_cmd()
        except RuntimeError as e:
            logger.error("Failed to get graceful restart command: %s", e)
            revert()
            return False

        loop = asyncio.get_running_loop()

        def restart_callback(task):
            def log_config_error(fut):
                if not fut.cancelled() and fut.exception() is not None:
                    logger.critical(
                        "The reverted config seems to be invalid",
                        exc_info=fut.exception(),
                    )

            def log_uncaught_exception(fut):
                if not fut.cancelled() and fut.exception() is not None:
                    logger.critical(
                        "uncaught exception", exc_info=fut.exception()
                    )

            if not task.cancelled() and task.exception() is not None:
                logger.error(
                    "Web server failed to start... Revert changes back. (%s)",
                    task.exception(),
                )
                revert()
                task = loop.create_task(configtest(raise_exception=True))
                task.add_done_callback(log_config_error)
                # the least we can do is to try to restart
                task = loop.create_task(_graceful_restart(restart_cmd))
                task.add_done_callback(log_uncaught_exception)
            else:
                remove_backup()

        graceful_restart = webserver_gracefull_restart.coalesce_calls(
            GRACEFUL_RESTART_MIN_PERIOD, done_callback=restart_callback
        )(_graceful_restart)

        caller_frame = inspect.stack()[1]
        context_token = _graceful_restart_caller.set(caller_frame.function)
        try:
            await graceful_restart(restart_cmd)
        finally:
            _graceful_restart_caller.reset(context_token)
        logger.info("Successfully scheduled web server restart")
        return True
    return False


async def _graceful_restart(restart_cmd=None):
    """
    Gracefully restart a web server.

    If web server cannot be detected, do nothing.
    """
    _log_graceful_restart_start()
    try:
        await check_run(restart_cmd or _graceful_restart_cmd())
    except RuntimeError as err:
        logger.warning("Could not restart a Web server: %s", err)
    else:
        logger.info("Successfully restarted web server")


@webserver_gracefull_restart.coalesce_calls(GRACEFUL_RESTART_MIN_PERIOD)
async def _graceful_restart_coalesced(restart_cmd=None):
    task = _graceful_restart(restart_cmd)
    g.web_server_restart_task = task
    try:
        return await task
    finally:
        g.pop("web_server_restart_task")


async def graceful_restart(restart_cmd=None):
    """
    Gracefully restart a web server.

    If web server cannot be detected, do nothing.
    """

    caller_frame = inspect.stack()[1]
    context_token = _graceful_restart_caller.set(caller_frame.function)
    try:
        result = await _graceful_restart_coalesced(restart_cmd)
    finally:
        _graceful_restart_caller.reset(context_token)
    return result


def _log_graceful_restart_start():
    caller = _graceful_restart_caller.get("unknown")
    logger.info("Performing web server graceful restart, from %s", caller)


def graceful_restart_sync():
    """
    Gracefully restart a web server synchronously.

    If web server cannot be detected, do nothing.
    """
    caller_frame = inspect.stack()[1]
    context_token = _graceful_restart_caller.set(caller_frame.function)
    try:
        _log_graceful_restart_start()
    finally:
        _graceful_restart_caller.reset(context_token)

    try:
        check_call(_graceful_restart_cmd(), stdout=DEVNULL, stderr=DEVNULL)
    except RuntimeError as err:
        logger.warning("Could not restart a Web server: %s", err)
    else:
        logger.info("Successfully restarted web server")


async def configtest(raise_exception=False):
    """
    Check web server's config file.

    If web server cannot be detected, do nothing.
    """
    logger.info("Performing web server config test")
    try:
        await check_run(_configtest_cmd(), raise_exc=ConfigInvalidError)
    except RuntimeError as err:
        logger.warning("Could not run configtest: %s", err)
        if raise_exception:
            raise ConfigInvalidError("Failed to check config") from err


def _parse_apache_version_output(output):
    match = apache_version_regexp.search(output)
    if match is not None:
        return Version(match.group(1))
    else:
        raise ValueError(
            "Failed to parse apache version string: {}".format(output)
        )


def _parse_apache_module_list(output: bytes) -> List[bytes]:
    """
        Parse response of httpd -M
        :param output: stdout of httpd -M (with spaces before module name)
        Output example:
    Loaded Modules:
     core_module (static)
     so_module (static)
     http_module (static)
     mpm_prefork_module (shared)
         :return: list with installed modules
    """
    return [
        line.strip().split()[0]
        for line in output.splitlines()
        if line.startswith(BYTE_SPACES)
    ]


def _parse_includes(dump):
    includes = []
    for line in dump.decode().split("\n"):
        index = line.find("/")
        if index > 0:
            includes.append(line[index:].strip())
    return includes


async def dump_includes():
    try:
        return _parse_includes(
            await check_run(["apachectl", "-t", "-D", "DUMP_INCLUDES"])
        )
    except FileNotFoundError:
        return []


@async_lru_cache(maxsize=1)
async def apache_version():
    apache_bin = apache_running()
    if apache_bin is None:
        raise NotRunningError("Apache is not running")
    out = await check_run([apache_bin, "-v"])
    version = _parse_apache_version_output(out.decode())
    logger.info("Apache %s version detected", version)
    return version


@TimedCache(
    expiration=timedelta(
        seconds=int(
            os.environ.get("IMUNIFY360_APACHE_MODULES_CACHE_TIMEOUT", 600)
        )
    )
)
async def apache_modules():
    stdout = await apache_binary_call("-M")
    return _parse_apache_module_list(stdout)
Name	Size	Permission
__pycache__	---	0755
features	---	0755
panels	---	0755
__init__.py	0 bytes	0644
backup_systems.py	11457 bytes	0644
clcagefs.py	7975 bytes	0644
notifier.py	1865 bytes	0644
persistent_state.py	1925 bytes	0644
svcctl.py	8582 bytes	0644
sysctl.py	379 bytes	0644
systemd_notifier.py	1615 bytes	0644
web_server.py	21725 bytes	0644
File Content: web_server.py

File Content: `web_server.py`
