#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
#
"""
*New in pywbem 0.9 as experimental and finalized in 0.10.*
The :class:`~pywbem.WBEMListener` class provides a thread-based WBEM listener
service that can receive CIM indications from multiple WBEM servers and that
calls registered callback functions to deliver the received indications.
The listener receives indications from an indication sender, validates the
formatting of the indication and queues each received indication into an
interprocess queue (`indication queue`). A seperate thread monitors this
queue and calls registered callback functions for each indication in the queue.
This insures that timing in the callback functions does not interfere with the
reception of indications from the indication sender.
Examples
--------
The following example creates and runs a listener::
import logging
from pywbem import WBEMListener
def process_indication(indication, host):
'''This function gets called when an indication is received.'''
print(f"Received CIM indication from {host}: {indication!r}")
def main():
# Configure logging of the listener via the Python root logger
logging.basicConfig(
filename='listener.log', level=logging.WARNING,
format='%(asctime)s - %(levelname)s - %(message)s')
certkeyfile = 'listener.pem'
# Set host name to wildcard host address to recieve indications on
# any network address defined for this system.
listener = WBEMListener(host="",
http_port=5990,
https_port=5991,
certfile=certkeyfile,
keyfile=certkeyfile)
listener.add_callback(process_indication)
try:
listener.start()
# process_indication() will be called for each received indication
. . . # wait for some condition to end listening
finally:
listener.stop()
Alternative code using the class as a context manager::
with WBEMListener(...) as listener:
listener.add_callback(process_indication)
listener.start()
# process_indication() will be called for each received indication
... # wait for some condition to end listening
# listener.stop() has been called automatically
See the example in section :ref:`WBEMSubscriptionManager` for an example of
using a listener in combination with a subscription manager.
Another listener example is in the script ``examples/listen.py`` (when you
clone the GitHub pywbem/pywbem project). It is an interactive Python shell that
creates a listener and displays any indications it receives, in MOF format.
.. _`Logging in the listener`:
Logging in the listener
-----------------------
Each :class:`~pywbem.WBEMListener` object has its own separate Python logger
object with the name:
`'pywbem.listener.{id}'`
where `{id}` is a string that is unique for each :class:`~pywbem.WBEMListener`
object within the Python process.
The :attr:`~pywbem.WBEMListener.logger` property of a
:class:`~pywbem.WBEMListener` object provides access to that Python logger
object, if needed.
The listener will log any indications it receives and any responses it sends
back to the indication sender, at the ``INFO`` logging level
(see :ref:`py:levels`).
In addition, it will log errors at the ``ERROR`` logging level.
The Python root logger will by default (i.e. when not being configured) print
log records of logging level ``WARNING`` or greater to `sys.stderr`. So the
indication and response interactions will not be printed by default, but any
errors logged at the ``ERROR`` logging level will be printed by default.
Listener indication flood
-------------------------
The pywbem listener processes indications through an interprocess queue
(`indication queue`) between the listener thread that receives the
indication over the network and the callback thread in which the user-provided
callback function runs.
If the callback processing takes longer, indications can pile up in the
indication queue. While this is not normally an issue, a flood of indications
from the sender could result in more indications in the queue than the memory
of the listener can support.
The handling of this situation in pywbem has improved over time:
* Before pywbem 1.8.0, the indication queue had no size limit, and grew
larger until memory limits were reached.
* Starting with pywbem 1.8.0, the :class:`pywbem.WBEMListener` class added
an optional init parameter ``max_ind_queue_size`` to specify a size limit
for the indication queue. When the size limit was reached, the listener and
callback threads terminated and the :meth:`pywbem.WBEMListener.start` method
raised :exc:`pywbem.ListenerQueueFullError`. No CIM-XML error response was
sent back to the sender for the indication that caused the queue to become
full.
This approach was meant to protect from memory full conditions but had the
drawback that the listener stopped and the sender got no information as to
why that happened.
* Starting with pywbem 1.9.0, the behavior has been improved: When the size
limit of the indication queue is reached, the indication is not put into the
queue, a CIM-XML error response with status
:data:`~pywbem._cim_constants.CIM_ERR_FAILED` is sent back to the sender and
the listener and callback threads continue to run. As a result, no exception
indicating that the queue is full is raised anymore from the
:meth:`pywbem.WBEMListener.start` method. For backwards compatibility
reasons, the :exc:`pywbem.ListenerQueueFullError` exception is still defined
(but is no longer raised). In addition, the default for the
``max_ind_queue_size`` input parameter has been changed from 0 (unlimited) to
a reasonable limit.
The following example creates and runs a listener::
import logging
from pywbem import WBEMListener
def process_indication(indication, host):
'''This function gets called when an indication is received.'''
print(f"Received CIM indication from {host}: {indication!r}")
def main():
# Configure logging of the listener via the Python root logger
logging.basicConfig(
filename='listener.log', level=logging.WARNING,
format='%(asctime)s - %(levelname)s - %(message)s')
certkeyfile = 'listener.pem'
# Set host name to wildcard host address to recieve indications on
# any network address defined for this system.
listener = WBEMListener(host="",
http_port=5990,
https_port=5991,
certfile=certkeyfile,
keyfile=certkeyfile)
listener.add_callback(process_indication)
listener.start()
# process_indication() will be called for each received indication
. . . # wait for some condition to end listening
listener.stop()
.. _`WBEMListener class`:
WBEMListener class
------------------
"""
import sys
import os
import errno
from contextlib import contextmanager
import re
import logging
import ssl
import threading
import atexit
import getpass
import queue
try:
import termios
except ImportError:
# termios is only supported on some operating systems
termios = None
import socketserver
import socket
import http.client
from http.server import HTTPStatus, HTTPServer, BaseHTTPRequestHandler
from time import sleep
from . import _cim_xml
from ._version import __version__
from ._cim_obj import CIMInstance
from ._cim_constants import CIM_ERR_NOT_SUPPORTED, CIM_ERR_INVALID_PARAMETER, \
CIM_ERR_FAILED, _statuscode2name
from ._tupleparse import TupleParser
from ._tupletree import xml_to_tupletree_sax
from ._exceptions import CIMXMLParseError, XMLParseError, CIMVersionError, \
DTDVersionError, ProtocolVersionError, ListenerCertificateError, \
ListenerPortError, ListenerPromptError, ListenerStartError
from ._utils import _format
# CIM-XML protocol related versions implemented by the WBEM listener.
# These are returned in export message responses.
IMPLEMENTED_CIM_VERSION = '2.0'
IMPLEMENTED_DTD_VERSION = '2.4'
IMPLEMENTED_PROTOCOL_VERSION = '1.4'
# CIM-XML protocol related versions supported by the WBEM listener
# These are checked in export message requests.
SUPPORTED_DTD_VERSION_PATTERN = r'2\.\d+'
SUPPORTED_DTD_VERSION_STR = '2.x'
SUPPORTED_PROTOCOL_VERSION_PATTERN = r'1\.\d+'
SUPPORTED_PROTOCOL_VERSION_STR = '1.x'
# Pattern for findall() for header values that are a list of tokens with
# quality values (see RFC2616). The pattern does not verify conformance
# to the valid characters for tokens, but does its job in parsing tokens
# and q values.
TOKEN_QUALITY_FINDALL_PATTERN = re.compile(
r'([^;, ]+)'
r'(?:; *q=([01](?:\.[0-9]*)?))?'
r'(?:, *)?')
TOKEN_CHARSET_FINDALL_PATTERN = re.compile(
r'([^;, ]+)'
r'(?:; *charset="?([^";, ]*)"?)?'
r'(?:, *)?')
# Default maximum size of the indication queue.
DEFAULT_MAX_IND_QUEUE_SIZE = 5000
__all__ = ['WBEMListener', 'callback_interface']
@contextmanager
def saved_term_attrs():
"""
Context manager that saves and restores the attributes of the terminal that
is used by getpass().
getpass() on Linux and macOS modifies the terminal attributes to disable
the echoing of the typed password, and restores the terminal attributes
before it returns. However, when the process calling getpass() gets
terminated with a SIGTERM signal while it waits for getpass() to return,
then getpass() itself will not restore the terminal settings.
This context manager improves that behavior by restoring the settings in
its exit part, and by additionally registering an Python atexit handler
that restores the settings. There is a check so that the settings are
restored only once. This performs the restore in some more cases compared
to the standard getpass() behavior, particularly when the process calling
getpass() is terminated with a SIGTERM signal.
For details on cases where the finally block and thus also the exit part
of a context manager do *not* get control, see
https://stackoverflow.com/a/49262664/1424462.
The logic to obtain the file descriptor of the terminal must be kept
consistent with how it is done in getpass(), see
https://github.com/python/cpython/blob/main/Lib/getpass.py#L46
"""
if termios:
try:
# On Windows, os.O_NOCTTY does not exist.
# pylint: disable=no-member
term_fd = os.open('/dev/tty', os.O_RDWR | os.O_NOCTTY)
except (OSError, AttributeError):
try:
term_fd = sys.stdin.fileno()
except (AttributeError, ValueError):
term_fd = None
else:
term_fd = None
if term_fd is not None:
count_dict = {'count': 0} # must be mutable
saved_attrs = termios.tcgetattr(term_fd)
atexit.register(restore_term_attrs, term_fd, saved_attrs, count_dict)
yield
if term_fd is not None:
restore_term_attrs(term_fd, saved_attrs, count_dict)
def restore_term_attrs(term_fd, saved_attrs, count_dict):
"""
Restore the attributes of the terminal that is used by getpass().
count_dict is used to ensure the restoration is performed only once. This
is necessary because the function is called once directly after the
password prompt, and once at exit.
"""
if count_dict['count'] == 0:
termios.tcsetattr(term_fd, termios.TCSAFLUSH, saved_attrs)
count_dict['count'] += 1
def keyfile_password_prompt(keyfile):
"""
Prompt for the password of a private key file.
This method is only called if the key file has a password set.
Parameters:
keyfile (str): Path name of private key file.
Returns:
str: The password
Raises:
ListenerPromptError: Password prompt was interrupted or ended
"""
prompt = f"Enter password for key file {keyfile}: "
with saved_term_attrs():
try:
pw = getpass.getpass(prompt=prompt)
except KeyboardInterrupt:
new_exc = ListenerPromptError("Password prompt was interrupted")
new_exc.__cause__ = None
raise new_exc # ListenerPromptError
except EOFError:
new_exc = ListenerPromptError("Password prompt was ended")
new_exc.__cause__ = None
raise new_exc # ListenerPromptError
return pw
class ThreadedHTTPServer(socketserver.ThreadingMixIn, HTTPServer):
"""
Defines an HTTPServer class for indication reception.
"""
# Enable the SO_REUSEADDR flag, to reuse the IP address if it still happens
# to be known by the OS from a previous run.
allow_reuse_address = True
def make_server(logger, host, port, handler):
"""
Create and return a ThreadedHTTPServer with the correct addressing family.
Raises:
socket.gaierror: Error resolving host and port.
"""
# The following attempts to handle a bad IPv6 setup, which has happened in
# GitHub Actions on macOS. The straight forward way to get the address
# info would be to use socket.AF_UNSPEC. For host=None, a DNS resolution
# is not actually needed. However, on macOS the underlying OS-level
# getaddrinfo() investigates the IPv6 setup for socket.AF_UNSPEC even when
# host=None, and it does that in a blocking way without the possibility to
# specify a timeout. When the Ipv6 setup is incorrect, this causes the
# OS-level getaddrinfo() to block indefinitely.
# By first trying IPv4 and then IPv6 in the code below (instead of
# AF_UNSPEC), this problem is circumvented.
logger.debug(f"Resolving address of host {host} using AF_INET (IPv4)")
try:
infos = socket.getaddrinfo(
host, port, socket.AF_INET, socket.SOCK_STREAM, 0,
socket.AI_PASSIVE)
except socket.gaierror as exc:
logger.debug(f"Resolving address of host {host} using AF_INET "
f"failed: {exc}")
logger.debug(f"Resolving address of host {host} using AF_INET6 (IPv6)")
infos = socket.getaddrinfo(
host, port, socket.AF_INET6, socket.SOCK_STREAM, 0,
socket.AI_PASSIVE)
logger.debug(f"Successfully resolved address of host {host} to: {infos!r}")
# Pick the first result (usually fine for binding)
info = infos[0]
family = info[0]
sockaddr = info[4] # (host, port) for IPv4, more for IPv6
logger.debug(f"Creating HTTPServer for family {family} and sockaddr "
f"{sockaddr}")
class AFServer(ThreadedHTTPServer):
"""
Class for setting address_family - it must be a class attribute
"""
address_family = family
def server_bind(self):
"""
This overrides the server_bind() from superclass HTTPServer,
in order to avoid the hang when it tries to perform reverse DNS
lookup via socket.getfqdn(host).
"""
# Overriding server_bind() must reapply socket options
if self.allow_reuse_address:
self.socket.setsockopt(
socket.SOL_SOCKET, socket.SO_REUSEADDR, 1
)
if getattr(self, "allow_reuse_port", False):
try:
self.socket.setsockopt(
socket.SOL_SOCKET, socket.SO_REUSEPORT, 1
)
except (AttributeError, OSError):
pass
# Perform the actual bind
self.socket.bind(self.server_address)
# Synchronize the server object with what the actual server address
# the OS decided to use during bind()
self.server_address = self.socket.getsockname()
host, port = self.server_address[:2]
# Set hostname without using reverse DNS lookup
if host in ("0.0.0.0", "::", ""):
self.server_name = "localhost"
else:
self.server_name = host
self.server_port = port
server = AFServer(sockaddr, handler)
logger.debug(f"Successfully created HTTPServer for family {family}")
return server
class ListenerRequestHandler(BaseHTTPRequestHandler):
"""
A request handler for the standard Python HTTP server, with a handler
method for the HTTP POST method, that acts as a WBEM listener.
"""
@property
def logger(self):
"""
:class:`py:logging.Logger`: Logger object for the listener using this
request handler.
Each listener object has its own separate logger object with the name:
`'pywbem.listener.{id}'`
where `{id}` is a unique string for each listener object.
Users of the listener should not look up the logger object by name, but
should use this property to get to it.
"""
return self.server.listener.logger
def invalid_method(self):
"""
Handle invalid HTTP methods by sending HTTP status 405 "Method Not
Allowed" back to the server. See DSP0200 for details on this.
"""
self.send_http_error(405, headers=[('Allow', 'POST')])
# pylint: disable=invalid-name
def do_OPTIONS(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_HEAD(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_GET(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_PUT(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_PATCH(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_DELETE(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_TRACE(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_CONNECT(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_M_POST(self):
"""Invalid method for listener"""
self.invalid_method()
# pylint: disable=invalid-name
def do_POST(self):
"""
This method will be called for each POST request to one of the
listener ports.
It parses the CIM-XML export message and delivers the contained
CIM indication to the stored listener object.
"""
self.logger.debug("Received POST request")
# Accept header check described in DSP0200
accept = self.headers.get('Accept', 'text/xml')
if accept not in ('text/xml', 'application/xml', '*/*'):
self.send_http_error(
406, 'header-mismatch',
_format("Invalid Accept header value: {0} (need text/xml, "
"application/xml or */*)", accept))
return
# Accept-Charset header check described in DSP0200
accept_charset = self.headers.get('Accept-Charset', 'UTF-8')
tq_list = re.findall(TOKEN_QUALITY_FINDALL_PATTERN, accept_charset)
found = False
if tq_list is not None:
for token, _ in tq_list:
if token.lower() in ('utf-8', '*'):
found = True
break
if not found:
self.send_http_error(
406, 'header-mismatch',
_format("Invalid Accept-Charset header value: {0} "
"(need UTF-8 or *)", accept_charset))
return
# Accept-Encoding header check described in DSP0200.
# The WBEM listener needs to support any Accept-Encoding header, so
# no check is performed.
# Note that the requests package adds the Accept-Encoding header with
# values such as "gzip, deflate" if not provided by the requester.
# Accept-Language header check described in DSP0200.
# Ignored, because this WBEM listener does not support multiple
# languages, and hence any language is allowed to be returned.
# Accept-Range header check described in DSP0200
accept_range = self.headers.get('Accept-Range', None)
if accept_range is not None:
self.send_http_error(
406, 'header-mismatch',
_format("Accept-Range header is not permitted {0}",
accept_range))
return
# Content-Type header check described in DSP0200
content_type = self.headers.get('Content-Type', None)
if content_type is None:
self.send_http_error(
406, 'header-mismatch',
"Content-Type header is required")
return
tc_list = re.findall(TOKEN_CHARSET_FINDALL_PATTERN, content_type)
found = False
if tc_list is not None:
for token, charset in tc_list:
if token.lower() in ('text/xml', 'application/xml') and \
(charset == '' or charset.lower() == 'utf-8'):
found = True
break
if not found:
self.send_http_error(
406, 'header-mismatch',
_format("Invalid Content-Type header value: {0} "
"(need text/xml or application/xml with "
"charset=utf-8 or empty)",
content_type))
return
# Content-Encoding header check described in DSP0200
content_encoding = self.headers.get('Content-Encoding', 'identity')
if content_encoding.lower() != 'identity':
self.send_http_error(
406, 'header-mismatch',
_format("Invalid Content-Encoding header value: {0}"
"(listener supports only identity)",
content_encoding))
return
# Content-Language header check described in DSP0200.
# Ignored, because this WBEM listener does not support multiple
# languages, and hence any language is allowed in the request.
# The following headers are ignored. They are not allowed to be used
# by servers, but listeners are not required to reject them:
# Content-Range, Expires, If-Range, Range.
# Start processing the request
content_len = int(self.headers.get('Content-Length', 0))
body = self.rfile.read(content_len)
try:
msgid, methodname, params = self.parse_export_request(body)
except (CIMXMLParseError, XMLParseError) as exc:
self.send_http_error(400, "request-not-well-formed", str(exc))
return
except DTDVersionError as exc:
self.send_http_error(400, "unsupported-dtd-version", str(exc))
return
except ProtocolVersionError as exc:
self.send_http_error(400, "unsupported-protocol-version", str(exc))
return
except CIMVersionError as exc:
self.send_http_error(400, "unsupported-version", str(exc))
return
if methodname == 'ExportIndication':
if len(params) != 1 or 'NewIndication' not in params:
self.send_error_response(
msgid, methodname, CIM_ERR_INVALID_PARAMETER,
_format("Expecting one parameter NewIndication, got {0!A}",
params.keys()))
return
indication_inst = params['NewIndication']
if not isinstance(indication_inst, CIMInstance):
self.send_error_response(
msgid, methodname, CIM_ERR_INVALID_PARAMETER,
_format("NewIndication parameter is not a CIM instance, "
"but {0!A}", indication_inst))
return
# server.listener created in WBEMListener.start function
listener = self.server.listener
try:
# pylint: disable=protected-access
listener._handle_indication(
indication_inst, self.client_address[0], msgid)
except queue.Full:
self.send_error_response(
msgid, methodname, CIM_ERR_FAILED,
_format("Indication queue is full (size {0})",
listener.max_ind_queue_size))
return
self.send_success_response(msgid, methodname, indication_inst)
else:
self.send_error_response(
msgid, methodname, CIM_ERR_NOT_SUPPORTED,
_format("Unknown export method: {0!A}", methodname))
def send_http_error(self, http_code, cim_error=None,
cim_error_details=None, headers=None):
"""
Send an HTTP response back to the WBEM server that indicates
an error at the HTTP level.
"""
self.logger.warning(
"Sending HTTP error response with HTTP status %s and headers: "
"CIMError: %r, CIMErrorDetails: %r",
http_code, cim_error, cim_error_details)
self.send_response(http_code, http.client.responses.get(http_code, ''))
self.send_header("CIMExport", "MethodResponse")
if cim_error is not None:
self.send_header("CIMError", cim_error)
if cim_error_details is not None:
self.send_header("CIMErrorDetails", cim_error_details)
if headers is not None:
for header, value in headers:
self.send_header(header, value)
self.end_headers()
def send_error_response(self, msgid, methodname, status_code, status_desc,
error_insts=None):
"""
Send a CIM-XML response message back to the WBEM server that indicates
an error at the CIM-XML level.
"""
self.logger.warning(
"Sending CIM-XML error response with CIM status %s: %s",
_statuscode2name(status_code), status_desc)
resp_xml = _cim_xml.CIM(
_cim_xml.MESSAGE(
_cim_xml.SIMPLEEXPRSP(
_cim_xml.EXPMETHODRESPONSE(
methodname,
_cim_xml.ERROR(
str(status_code),
status_desc,
error_insts),
), # noqa: E123
), # noqa: E123
msgid, IMPLEMENTED_PROTOCOL_VERSION),
IMPLEMENTED_CIM_VERSION, IMPLEMENTED_DTD_VERSION)
resp_body = '<?xml version="1.0" encoding="utf-8" ?>\n' + \
resp_xml.toxml()
if isinstance(resp_body, str):
resp_body = resp_body.encode("utf-8")
http_code = 200
self.send_response(http_code, http.client.responses.get(http_code, ''))
self.send_header("Content-Type", "text/xml")
self.send_header("Content-Length", str(len(resp_body)))
self.send_header("CIMExport", "MethodResponse")
self.end_headers()
self.wfile.write(resp_body)
def send_success_response(self, msgid, methodname, instance):
"""
Send a CIM-XML response message back to the WBEM server that
indicates success.
"""
self.logger.debug(
"Sending CIM-XML success response for %s with msgid %s",
instance.classname, msgid)
resp_xml = _cim_xml.CIM(
_cim_xml.MESSAGE(
_cim_xml.SIMPLEEXPRSP(
_cim_xml.EXPMETHODRESPONSE(
methodname),
), # noqa: E123
msgid, IMPLEMENTED_PROTOCOL_VERSION),
IMPLEMENTED_CIM_VERSION, IMPLEMENTED_DTD_VERSION)
resp_body = '<?xml version="1.0" encoding="utf-8" ?>\n' + \
resp_xml.toxml()
if isinstance(resp_body, str):
resp_body = resp_body.encode("utf-8")
http_code = 200
self.send_response(http_code, http.client.responses.get(http_code, ''))
self.send_header("Content-Type", "text/xml")
self.send_header("Content-Length", str(len(resp_body)))
self.send_header("CIMExport", "MethodResponse")
self.end_headers()
self.wfile.write(resp_body)
@staticmethod
def parse_export_request(request_str):
"""
Parse a CIM-XML export request message, and return
a tuple(msgid, methodname, params).
"""
# Parse the XML into a tuple tree (may raise CIMXMLParseError or
# XMLParseError):
tt_ = xml_to_tupletree_sax(request_str, "CIM-XML export request")
tp = TupleParser()
tup_tree = tp.parse_cim(tt_)
# Check the tuple tree
if tup_tree[0] != 'CIM':
raise CIMXMLParseError(
_format("Expecting CIM element, got {0}", tup_tree[0]))
tup_tree = tup_tree[2]
if tup_tree[0] != 'MESSAGE':
raise CIMXMLParseError(
_format("Expecting MESSAGE element, got {0}", tup_tree[0]))
msgid = tup_tree[1]['ID']
tup_tree = tup_tree[2]
if tup_tree[0] != 'SIMPLEEXPREQ':
raise CIMXMLParseError(
_format("Expecting SIMPLEEXPREQ element, got {0}",
tup_tree[0]))
tup_tree = tup_tree[2]
if tup_tree[0] != 'EXPMETHODCALL':
raise CIMXMLParseError(
_format("Expecting EXPMETHODCALL element, got {0}",
tup_tree[0]))
methodname = tup_tree[1]['NAME']
params = {}
for name, obj in tup_tree[2]:
params[name] = obj
return (msgid, methodname, params)
def log_request(self, code='-', size='-'):
# pylint: disable=unused-argument
"""
This function is called in
:meth:`~py:http.server.BaseHTTPRequestHandler.send_response`.
We override it to get a little more information logged in a somewhat
better format at the DEBUG level.
"""
if isinstance(code, HTTPStatus):
# On Python 3, it can be an HTTPStatus object
code = code.value
self.logger.debug(
"Sending %s response with HTTP status %s", self.command, code)
def log_error(self, format, *args):
# pylint: disable=redefined-builtin
"""
The :class:`~py:http.server.BaseHTTPRequestHandler` methods call this
method for anything that needs to get logged as an error.
We override it in order to direct that to our own logger at the ERROR
level.
"""
self.logger.error(format, *args)
def log_message(self, format, *args):
# pylint: disable=redefined-builtin
"""
The :class:`~py:http.server.BaseHTTPRequestHandler` methods call this
method for anything that needs to get logged.
We override it in order to direct that to our own logger at the INFO
level.
"""
self.logger.info(format, *args)
def version_string(self):
"""
Overrides the inherited method to add the pywbem listener version.
"""
return _format("pywbem-listener/{0} {1} {2} ",
__version__, self.server_version, self.sys_version)
class StoppableThread(threading.Thread):
"""
Thread subclass with a stop() method.
The thread itself must check regularly for the stopped() event ( i.e. if
stop_event.is_set()) exit the thread code.
This subclass does not pass exceptions to the parent.
"""
def __init__(self, *args, **kwargs):
"""
Init with arguments for the thread
"""
super().__init__(*args, **kwargs)
self.stop_event = threading.Event()
def stop(self):
"""
Set the thread stop_event. To tell thread to stop
"""
self.stop_event.set()
def stopped(self):
"""
Test for thread stop event set
"""
return self.stop_event.is_set()
class ExceptionHandlingThread(threading.Thread):
"""
Thread subclass that passes exceptions from the thread back to the calling
thread to be raised during join().
"""
def __init__(self, *args, **kwargs):
"""
Init with arguments for the thread
"""
super().__init__(*args, **kwargs)
# Store a possible exception.
self.exception = None
def run(self):
"""
Catch any exception raised in the thread function and store it.
"""
try:
super().run()
except Exception as e: # pylint: disable=broad-exception-caught
self.exception = e
def join(self, *args, **kwargs):
"""
Raise any exception that may have been stored.
"""
super().join(*args, **kwargs)
if self.exception:
raise self.exception
class ServerThread(ExceptionHandlingThread):
"""
Thread class to be used for the WBEM listener thread.
"""
pass
class CallbackThread(StoppableThread, ExceptionHandlingThread):
"""
Thread class to be used for the indication callback thread.
"""
pass
# pylint: disable=too-many-instance-attributes
[docs]
class WBEMListener:
"""
*New in pywbem 0.9 as experimental and finalized in 0.10.*
A WBEM listener.
The listener supports starting and stopping threads that listen for
CIM-XML ExportIndication messages using HTTP and/or HTTPS, and that pass
any received indications on to registered callback functions.
The listener must be stopped in order to free the TCP/IP port it listens
on. Using this class as a context manager ensures that the listener is
stopped when leaving the context manager scope.
The listener validates the syntax of the received CIM instance but does not
validate the values of received the MESSAGE_ID or SEQUENCE_NUMBER of
incoming indications. Therefore, it does not know if any indications are
missing from a sequence. The callback function must do any such
processing., etc. that confirms if indications are in the proper sequence
and none were lost.
"""
def __init__(self, host, http_port=None, https_port=None,
certfile=None, keyfile=None,
max_ind_queue_size=DEFAULT_MAX_IND_QUEUE_SIZE):
"""
Parameters:
host (str):
IP address or host name to which this listener is bound (i.e. at
which this listener can be reached). If a listener is bound to a
particular IP address it will only receive indications addressed to
that IP address (or to any IP address on the network interface
containing that address) depending on the OS.
Network wildcard addressing enables receiving indications from
all IP addresses on the system by binding the listener to certain
special addresses. The IPV4 wildcard IP address is "0.0.0.0"
and the IPV6 wildcard IP address is "::".
Setting the host parameter to an empty string (i.e. "") is
equivalent to using the wildcard address with the default
IP addressing family.
http_port (:class:`py:str` or :class:`py:int`):
HTTP port at which this listener can be reached. At
least one port (HTTP or HTTPS) must be set. Both the http and
https ports can be set.
`None` means not to set up a port for HTTP.
https_port (:class:`py:str` or :class:`py:int`):
HTTPS port at which this listener can be reached.
`None` means not to set up a port for HTTPS.
certfile (str):
File path of certificate file to be used as server certificate
during SSL/TLS handshake when creating the secure HTTPS connection.
It is valid for the certificate file to contain a private key; the
server certificate sent during SSL/TLS handshake is sent without
the private key.
`None` means not to use a server certificate file. Setting up a port
for HTTPS requires specifying a certificate file.
keyfile (str):
File path of private key file to be used by the server during
SSL/TLS handshake when creating the secure HTTPS connection.
It is valid to specify a certificate file that contains a private
key.
`None` means not to use a private key file. Setting up a port
for HTTPS requires specifying a private key file.
max_ind_queue_size (int):
A positive integer which defines the maximum size of the indication
queue. If an indication is received and the queue is full, the
indication is not put into the queue and a CIM-XML response
with status :data:`~pywbem._cim_constants.CIM_ERR_FAILED` is sent
back to the sender, indicating that the indication could not be
accepted. The listener and callback threads continue to run.
A value of 0 indicates that the queue has no maximum size. In this
case, the queue size will grow as needed (until the listener
process is out of memory), and all indications will be accepted.
For a reliable operation of the listener, it is recommended to
define a maximum queue size.
Raises:
TypeError: port, max_ind_queue_size arguments invalid type.
ValueError: No connection port specified, max_ind_queue_size
invalid integer.
"""
self._host = host
if isinstance(http_port, int):
self._http_port = int(http_port) # Convert Python 2 long to int
elif isinstance(http_port, str):
self._http_port = int(http_port)
elif http_port is None:
self._http_port = http_port
else:
raise TypeError(
_format("Invalid type for http_port: {0}", type(http_port)))
if isinstance(https_port, int):
self._https_port = int(https_port) # Convert Python 2 long to int
elif isinstance(https_port, str):
self._https_port = int(https_port)
elif https_port is None:
self._https_port = https_port
else:
raise TypeError(
_format("Invalid type for https_port: {0}", type(https_port)))
if self._https_port is not None:
if certfile is None:
raise ValueError("https_port requires certfile")
self._certfile = certfile
if keyfile is None:
raise ValueError("https_port requires keyfile")
self._keyfile = keyfile
else:
self._certfile = None
self._keyfile = None
if self._http_port is None and self._https_port is None:
raise ValueError("Listener requires at least one active port")
self._http_server = None # ThreadedHTTPServer for HTTP
self._http_thread = None # Thread for HTTP
self._https_server = None # ThreadedHTTPServer for HTTPS
self._https_thread = None # Thread for HTTPS
self._logger = logging.getLogger(
_format("pywbem.listener.{0}", id(self)))
self._callbacks = [] # Registered callback functions
if not isinstance(max_ind_queue_size, int):
raise TypeError("max_ind_queue_size argument must be integer.")
if max_ind_queue_size < 0:
raise ValueError(
"max__ind_queue_size argument must be positive integer.")
self._max_ind_queue_size = max_ind_queue_size
# Define timeout in seconds for gets on ind_delivery_queue object.
# Causes wait after indication queue get if queue is empty.
# Choice of 2 seconds was arbitrary.
#
self.queue_get_timeout = 2
self._ind_queue = None
self._callback_thread = None
# State of the indication queue, as detected after the last
# attempt to put an indication into it.
self._queue_full = False
[docs]
def __str__(self):
"""
Return a representation of the :class:`~pywbem.WBEMListener` object
with a subset of its attributes.
"""
return _format(
"WBEMListener("
"_host={s._host!A}, "
"_http_port={s._http_port!A}, "
"_https_port={s._https_port!A}, "
"...)",
s=self)
[docs]
def __repr__(self):
"""
Return a representation of the :class:`~pywbem.WBEMListener` object
with all attributes, that is suitable for debugging.
"""
return _format(
"WBEMListener("
"_host={s._host!A}, "
"_http_port={s._http_port!A}, "
"_https_port={s._https_port!A}, "
"_certfile={s._certfile!A}, "
"_keyfile={s._keyfile!A}, "
"_logger={s._logger!A}, "
"_callbacks={s._callbacks!A}, "
"_max_ind_queue_size={s._max_ind_queue_size!A})",
s=self)
[docs]
def __enter__(self):
"""
Enter method when the class is used as a context manager.
*New in pywbem 0.12.*
Returns the listener object.
Note that the enter method does not start the listener.
"""
return self
[docs]
def __exit__(self, exc_type, exc_value, traceback):
"""
Exit method when the class is used as a context manager.
*New in pywbem 0.12.*
Stops the listener by calling :meth:`~pywbem.WBEMListener.stop`.
"""
self.stop()
return False # re-raise any exceptions
@property
def host(self):
"""
str: IP address or host name to which this listener is
bound. If IP adress 0.0.0.0, this listener is not bound to a particular
IP address and accepts requests from any host on any network.
"""
return self._host
@property
def http_port(self):
"""
int: HTTP port at which this listener can be reached.
`None` means there is no port set up for HTTP.
"""
return self._http_port
@property
def https_port(self):
"""
int: HTTPS port at which this listener can be reached.
`None` means there is no port set up for HTTPS.
"""
return self._https_port
@property
def http_started(self):
"""
bool: Boolean indicating whether the listener is started for the HTTP
port.
If no port is set up for HTTP, `False` is returned.
*New in pywbem 0.12.*
"""
return self._http_server is not None
@property
def https_started(self):
"""
bool: Boolean indicating whether the listener is started for the HTTPS
port.
If no port is set up for HTTPS, `False` is returned.
*New in pywbem 0.12.*
"""
return self._https_server is not None
@property
def certfile(self):
"""
str: File path of the certificate file used as server
certificate during SSL/TLS handshake when creating the secure HTTPS
connection.
`None` means there is no certificate file being used (that is, no port
is set up for HTTPS).
"""
return self._certfile
@property
def keyfile(self):
"""
str: File path of the private key file used by the server
during SSL/TLS handshake when creating the secure HTTPS connection.
`None` means there is no certificate file being used (that is, no port
is set up for HTTPS).
"""
return self._keyfile
@property
def logger(self):
"""
:class:`py:logging.Logger`: Logger object for this listener.
Each listener object has its own separate logger object with the name:
`'pywbem.listener.{id}'`
where `{id}` is a unique string for each listener object.
Users of the listener should not look up the logger object by name, but
should use this property to get to it.
"""
return self._logger
@property
def max_ind_queue_size(self):
"""
int: The maximum size of the indication queue.
A value of 0 means that the indication queue will grow as needed,
limited only by the available memory in the listener process.
"""
return self._max_ind_queue_size
[docs]
def ind_queue_exists(self):
"""
Returns whether the indication queue exists.
Returns:
bool: `True` if the indication queue exists; otherwise
`False`.
"""
return self._ind_queue is not None
[docs]
def ind_queue_empty(self):
"""
Returns whether the indication queue is empty.
Returns:
bool: `True` if the indication queue is empty;
otherwise `False`.
If the indication queue does not exist, `None` is returned.
"""
if self._ind_queue is None:
return None
return self._ind_queue.empty()
[docs]
def ind_queue_size(self):
"""
Returns the number of indications currently in the indication queue.
Note that the number of indications in the queue can vary quickly
as indications flow.
Returns:
int: Number of indications currently in the indication
queue. If the indication queue does not exist, `None` is returned.
"""
if self._ind_queue is None:
return None
return self._ind_queue.qsize()
[docs]
def start(self):
"""
Start the WBEM listener.
The WBEM listener must not already be running.
When the WBEM listener is started, first the callback thread is started
that will lateron call the registered callback functions for each
indication that is received. Then, the listener threads for HTTP and
HTTPS are started (depending on which ports have been specified) to
enable the receiving of indications from a sender.
The listener threads will handle the CIM-XML ExportIndication export
message described in :term:`DSP0200` and they will put each indication
received into the indication queue of the WBEM listener. The callback
thread will get the indications from the queue and will pass them to
registered callback functions.
The listener must be stopped by the user in order to free the TCP/IP
ports it listens on. The listener can be stopped explicitly using the
:meth:`~pywbem.WBEMListener.stop` method. The listener will be
automatically stopped when the main thread terminates (i.e. when the
Python process terminates), or when :class:`~pywbem.WBEMListener`
is used as a context manager when leaving its scope.
In case of HTTPS, the private key file and certificate file are used.
If the private key file is protected with a password, the password
will be prompted for using :func:`py:getpass.getpass`. If the password
is invalid, or if the private key file or certificate file are invalid,
:exc:`pywbem.ListenerCertificateError` is raised.
If this method raises an exception, the callback thread and listener
threads are cleaned up again.
Starting with pywbem 1.9.0, this method no longer raises the
:exc:`pywbem.ListenerQueueFullError` exception.
Raises:
:exc:`pywbem.ListenerCertificateError`: Error with the certificate
file or its private key file when using HTTPS.
:exc:`pywbem.ListenerPortError`: WBEM listener port is already
in use.
:exc:`pywbem.ListenerPromptError`: Error when prompting for the
password of the private key file when using HTTPS.
:exc:`py:OSError`: Other error
:exc:`py:IOError`: Other error (Python 2.7 only)
"""
assert not self._callback_thread
assert not self._ind_queue
# Create indication queue and set its maximum size.
# Note: The value 0 creates the queue without a maximum size.
# Uses Queue and not SimpleQueue because SimpleQueue does not support
# a maximum queue size.
self.logger.info(
"Creating indication queue with max size: %d",
self._max_ind_queue_size)
self._ind_queue = queue.Queue(
maxsize=self._max_ind_queue_size)
# Start callback thread
self.logger.info("Starting callback thread")
self._callback_thread = CallbackThread(
target=self._callback_run,
args=(),
name='CallbackThread',
daemon=False)
self._callback_thread.start()
try:
if self._http_port:
if not self._http_server:
self.logger.info(
"Creating threaded HTTP server for host %r on port %s",
self._host, self._http_port)
try:
server = make_server(
self.logger, self._host, self._http_port,
ListenerRequestHandler)
except OSError as exc:
# Note: socket.gaierror is derived from OSError
self._stop_indication_delivery()
if getattr(exc, 'errno', None) == errno.EADDRINUSE:
# Windows does not raise exception if port is used
msg = (f"WBEM listener port {self._http_port} is "
"already in use")
self.logger.error(msg)
raise ListenerPortError(msg) from exc
msg = ("Creation of threaded HTTP server for host "
f"{self._host!r} on port {self._http_port} "
f"failed: {exc.__class__.__name__}: {exc}")
self.logger.error(msg)
raise ListenerStartError(msg) from exc
# pylint: disable=attribute-defined-outside-init
self.logger.info(
"Starting HTTP listener thread to run threaded "
"HTTP server")
server.listener = self
thread = ServerThread(target=server.serve_forever,
name='http',
daemon=False)
self._http_server = server
self._http_thread = thread
thread.start()
else:
# Just in case someone changed self._http_port after init...
self._http_server = None
self._http_thread = None
if self._https_port:
if not self._https_server:
self.logger.info(
"Creating threaded HTTPS server for host %r on port %s",
self._host, self._https_port)
try:
server = make_server(
self.logger, self._host, self._https_port,
ListenerRequestHandler)
except OSError as exc:
# Note: socket.gaierror is derived from OSError
self._stop_indication_delivery()
if getattr(exc, 'errno', None) == errno.EADDRINUSE:
# Windows does not raise exception if port is used
msg = (f"WBEM listener port {self._https_port} is "
"already in use")
self.logger.error(msg)
raise ListenerPortError(msg) from exc
msg = ("Creation of threaded HTTPS server for host "
f"{self._host!r} on port {self._https_port} "
f"failed: {exc.__class__.__name__}: {exc}")
self.logger.error(msg)
raise ListenerStartError(msg) from exc
# pylint: disable=attribute-defined-outside-init
server.listener = self
try:
try:
# PROTOCOL_TLS was introduced in Py 2.7.13
ssl_protocol = ssl.PROTOCOL_TLS
except AttributeError:
# Alias for PROTOCOL_TLS and deprecated in Py 2.7.13
ssl_protocol = ssl.PROTOCOL_SSLv23
# SSLContext was introduced in Python 2.7.9
ctx = ssl.SSLContext(ssl_protocol)
ctx.options |= ssl.OP_NO_SSLv2
ctx.options |= ssl.OP_NO_SSLv3
def password_prompt():
return keyfile_password_prompt(self._keyfile)
try:
ctx.load_cert_chain(
certfile=self._certfile,
keyfile=self._keyfile,
password=password_prompt)
except ssl.SSLError as exc:
# On Python 3, exc.errno is EBADF, but on Python 2
# it is a number 336265225 that seems to occur for
# other people too but is not understood. Therefore,
# we do not check for errno here.
if exc.library == 'SSL' and 'PEM lib' in str(exc):
new_exc = ListenerCertificateError(
"Invalid password for key file, bad key "
"file, or bad certificate file. Original "
f"error: {exc}")
new_exc.__cause__ = None
raise new_exc # ListenerCertificateError
new_exc = ListenerCertificateError(
"SSL error when loading the certificate chain: "
f"errno={exc.errno}, library={exc.library}: "
f"{exc}")
new_exc.__cause__ = None
raise new_exc # ListenerCertificateError
except OSError as exc:
fn = _cert_key_file(self._certfile, self._keyfile)
new_exc = ListenerCertificateError(
f"Issue opening {fn}: {exc}")
new_exc.__cause__ = None
raise new_exc # ListenerCertificateError
server.socket = ctx.wrap_socket(
server.socket,
server_side=True)
except AttributeError:
# Fall back to deprecated ssl.wrap_socket() before
# Py 2.7.9
# pylint: disable=deprecated-method
server.socket = ssl.wrap_socket(
server.socket,
certfile=self._certfile,
keyfile=self._keyfile,
server_side=True)
self.logger.info(
"Starting HTTPS listener thread to run threaded "
"HTTPS server")
thread = ServerThread(target=server.serve_forever,
name="https",
daemon=False)
self._https_server = server
self._https_thread = thread
thread.start()
else:
# Just in case someone changed self._https_port after init...
self._https_server = None
self._https_thread = None
except Exception as exc: # pylint: disable=broad-exception-caught
self.logger.error("Cleaning up callback thread due to exception "
"%s: %s", exc.__class__.__name__, exc)
self._stop_indication_delivery(immediate=True)
raise
[docs]
def stop(self):
"""
Stop the WBEM listener gracefully.
This method can also be called when the WBEM listener was already
stopped.
When stopping the WBENM listener, the listener threads are first
stopped to make sure that no new indications can be received. Then, the
callback thread completes its delivery of indications that are in the
indication queue, and when the queue is empty, the callback thread is
stopped.
"""
self._stop_listener_threads()
self._stop_indication_delivery()
def _stop_indication_delivery(self, immediate=False):
"""
Stop the callback thread and clear the indication queue.
If immediate is True, indications are cleared from the queue without
waiting for the callback thread to get them.
If immediate is False (default), indications are forwarded to the
callback until the queue is empty before stopping delivery.
"""
if self._ind_queue:
if not immediate:
# Wait for queue to empty through callbacks
qsize = self._ind_queue.qsize()
self.logger.info(
"Waiting for indication queue to be empty "
"(currently %d items)", qsize)
while not self._ind_queue.empty():
sleep(0.1)
self.logger.info(
"Indication queue is now empty")
else:
# Clear the queue immediately
self.logger.info(
"Discarding indications from indication queue")
clr_count = 0
while not self._ind_queue.empty():
self._ind_queue.get(block=False, timeout=0)
clr_count += 1
self._ind_queue.task_done()
self.logger.info(
"%s indications discarded from indication queue",
clr_count)
self._ind_queue = None
# Tolerate that callback thread has already stopped, just in case.
if self._callback_thread:
self.logger.info("Stopping callback thread")
self._callback_thread.stop()
self._callback_thread.join()
self.logger.info("Stopped callback thread")
self._callback_thread = None
def _stop_listener_threads(self):
"""
Stop the listener threads.
"""
if self._http_server:
self.logger.info(
"Stopping threaded HTTP server and its listener thread")
self._http_server.shutdown()
self._http_server.server_close()
self._http_thread.join()
self._http_server = None
self._http_thread = None
self.logger.info(
"Stopped threaded HTTP server and its listener thread")
if self._https_server:
self.logger.info(
"Stopping threaded HTTPS server and its listener thread")
self._https_server.shutdown()
self._https_server.server_close()
self._https_thread.join()
self._https_server = None
self._https_thread = None
self.logger.info(
"Stopped threaded HTTPS server and its listener thread")
def _callback_run(self):
"""
Thread runner function for the callback thread that delivers indications
to the registered callback functions.
This function runs a loop and only returns when the queue is emtpy and
the callback thread's stop() method had been called.
"""
self.logger.info("Entering callback processing loop")
while True:
try:
# This raises queue.Empty when the timeout expires
queue_item = self._ind_queue.get(
block=True,
timeout=self.queue_get_timeout)
indication, host, msgid = queue_item
self._deliver_indication_to_callbacks(indication, host, msgid)
# Marks this item done in queue.
# Really for delivering to multiple workers rather than
# this simple case of a single worker. However this
# keeps the queue clean.
self._ind_queue.task_done()
# If queue empty and stop event set break out of loop
except queue.Empty:
if self._callback_thread.stopped():
break
self.logger.info("Leaving callback processing loop")
def _handle_indication(self, indication, host, msgid):
"""
Method that is called from the listener threads when receiving an
indication.
Puts the indication into the indication queue.
If the listener was defined with a maximum queue size
(max_ind_queue_size > 0), the :exc:`queue.Full` exception will be
raised if the queue is full.
Raises:
queue.Full: Indication queue is full
"""
if self._ind_queue is None:
self.logger.error(
"Indication queue not set up - ignoring indication")
return
try:
# Non-blocking put is required to raise queue.Full exception if full
queue_item = (indication, host, msgid)
self._ind_queue.put(queue_item, block=False)
# If we get here, the put worked so the queue was not full.
# We log a state change if it was previously full.
if self._queue_full is True:
self.logger.warning(
"Indication queue is no longer full "
"(current size: %d, max size: %d)",
self.ind_queue_size(), self.max_ind_queue_size)
self._queue_full = False
except queue.Full:
# If we get here, the put queue was full.
# We log a state change if it was previously not full.
if self._queue_full is False:
self.logger.warning(
"Indication queue is now full (max size: %d)",
self.max_ind_queue_size)
self._queue_full = True
raise
def _deliver_indication_to_callbacks(self, indication, host, msgid):
"""
This function is called in the callback thread to deliver a single
indication to all registered callback functions.
If a callback function raises any exception, this is logged as an error
using the listener logger and the next registered callback function is
called.
Parameters:
indication (:class:`~pywbem.CIMInstance`):
Representation of the CIM indication to be delivered.
host (str):
Host name or IP address of WBEM server sending the indication.
msgid (str):
Message ID of the indication from the export request.
"""
for callback in self._callbacks:
self.logger.debug(
"Calling callback function %r to deliver %s with msgid %s",
callback.__name__, indication.classname, msgid)
try:
callback(indication, host)
except Exception as exc: # pylint: disable=broad-except
self.logger.error(
"Callback function %r raised %s: %s",
callback.__name__, exc.__class__.__name__, exc)
self.logger.debug(
"Returned from callback function %r", callback.__name__)
[docs]
def add_callback(self, callback):
"""
Add a callback function to the listener.
The callback function will be called for each indication this listener
receives from any WBEM server.
If the callback function is already known to the listener, it will not
be added.
Multiple callback functions may be defined by repeating this function
with each callback function required.
All of the defined callbacks will be executed for each indication.
They will be executed serially in the order that they were added and
on the same thread.
The callback interface is defined in the callback_interface function.
Parameters:
callback (:func:`~pywbem.callback_interface`):
Callable that is being called for each CIM indication that is
received while the listener threads are running.
"""
if callback not in self._callbacks:
self.logger.info(
"Adding callback function %r", callback.__name__)
self._callbacks.append(callback)
[docs]
def callback_interface(indication, host):
# pylint: disable=unused-argument
"""
*New in pywbem 0.9 as experimental and finalized in 0.10.*
Interface of a callback function that is provided by the user of the API
and that will be called by the listener for each received CIM indication.
Parameters:
indication (:class:`~pywbem.CIMInstance`):
Representation of the CIM indication that has been received.
Its `path` attribute is `None`.
host (str):
Host name or IP address of WBEM server sending the indication.
Raises:
Exception: If a callback function raises any exception this is logged
as an error using the listener logger and the next registered
callback function is called. The exception is not passed back from
the callback thread.
"""
raise NotImplementedError
def _cert_key_file(certfile, keyfile):
"Return a string for use in messages for the certificate or key files"
if certfile == keyfile or keyfile is None:
return f"certificate/key file {certfile}"
return f"certificate file {certfile} or key file {keyfile}"