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EDITING: dbus.py

#
# Copyright (C) 2022 Red Hat, Inc.
# SPDX-License-Identifier: GPL-3.0-or-later

# Missing stuff compared to the C bridge that we should probably add:
#
# - removing matches
# - removing watches
# - emitting of signals
# - publishing of objects
# - failing more gracefully in some cases (during open, etc)
#
# Stuff we might or might not do:
#
# - using non-default service names
#
# Stuff we should probably not do:
#
# - emulation of ObjectManager via recursive introspection
# - automatic detection of ObjectManager below the given path_namespace
# - recursive scraping of properties for new object paths
#   (for path_namespace watches that don't hit an ObjectManager)

import asyncio
import errno
import json
import logging
import traceback
import xml.etree.ElementTree as ET

from cockpit._vendor import systemd_ctypes
from cockpit._vendor.systemd_ctypes import Bus, BusError, introspection

from ..channel import Channel, ChannelError

logger = logging.getLogger(__name__)

# The dbusjson3 payload
#
# This channel payload type translates JSON encoded messages on a
# Cockpit channel to D-Bus messages, in a mostly straightforward way.
# See doc/protocol.md for a description of the basics.
#
# However, dbusjson3 offers some advanced features as well that are
# meant to support the "magic" DBusProxy objects implemented by
# cockpit.js.  Those proxy objects "magically" expose all the methods
# and properties of a D-Bus interface without requiring any explicit
# binding code to be generated for a JavaScript client.  A dbusjson3
# channel does this by doing automatic introspection and property
# retrieval without much direction from the JavaScript client.
#
# The details of what exactly is done is not specified very strictly,
# and the Python bridge will likely differ from the C bridge
# significantly. This will be informed by what existing code actually
# needs, and we might end up with a more concrete description of what
# a client can actually expect.
#
# Here is an example of a more complex scenario:
#
# - The client adds a "watch" for a path namespace.  There is a
#   ObjectManager at the given path and the bridge emits "meta" and
#   "notify" messages to describe all interfaces and objects reported
#   by that ObjectManager.
#
# - The client makes a method call that causes a new object with a new
#   interface to appear at the ObjectManager.  The bridge will send a
#   "meta" and "notify" message to describe this new object.
#
# - Since the InterfacesAdded signal was emitted before the method
#   reply, the bridge must send the "meta" and "notify" messages
#   before the method reply message.
#
# - However, in order to construct the "meta" message, the bridge must
#   perform a Introspect call, and consequently must delay sending the
#   method reply until that call has finished.
#
# The Python bridge implements this delaying of messages with
# coroutines and a fair mutex. Every message coming from D-Bus will
# wait on the mutex for its turn to send its message on the Cockpit
# channel, and will keep that mutex locked until it is done with
# sending.  Since the mutex is fair, everyone will nicely wait in line
# without messages getting re-ordered.
#
# The scenario above will play out like this:
#
# - While adding the initial "watch", the lock is held until the
#   "meta" and "notify" messages have been sent.
#
# - Later, when the InterfacesAdded signal comes in that has been
#   triggered by the method call, the mutex will be locked while the
#   necessary introspection is going on.
#
# - The method reply will likely come while the mutex is locked, and
#   the task for sending that reply on the Cockpit channel will enter
#   the wait queue of the mutex.
#
# - Once the introspection is done and the new "meta" and "notify"
#   messages have been sent, the mutex is unlocked, the method reply
#   task acquires it, and sends its message.

class InterfaceCache:
    def __init__(self):
        self.cache = {}
        self.old = set()  # Interfaces already returned by get_interface_if_new

def inject(self, interfaces) -> None:
        self.cache.update(interfaces)

async def introspect_path(self, bus, destination, object_path):
        xml, = await bus.call_method_async(destination, object_path,
                                           'org.freedesktop.DBus.Introspectable',
                                           'Introspect')

et = ET.fromstring(xml)

interfaces = {tag.attrib['name']: introspection.parse_interface(tag) for tag in et.findall('interface')}

# Add all interfaces we found: we might use them later
        self.inject(interfaces)

return interfaces

async def get_interface(self, interface_name, bus=None, destination=None, object_path=None):
        try:
            return self.cache[interface_name]
        except KeyError:
            pass

if bus and object_path:
            try:
                await self.introspect_path(bus, destination, object_path)
            except BusError:
                pass

return self.cache.get(interface_name)

async def get_interface_if_new(self, interface_name, bus, destination, object_path):
        if interface_name in self.old:
            return None
        self.old.add(interface_name)
        return await self.get_interface(interface_name, bus, destination, object_path)

async def get_signature(self, interface_name, method, bus=None, destination=None, object_path=None):
        interface = await self.get_interface(interface_name, bus, destination, object_path)
        if interface is None:
            raise KeyError(f'Interface {interface_name} is not found')

return ''.join(interface['methods'][method]['in'])

def notify_update(notify, path, interface_name, props):
    notify.setdefault(path, {})[interface_name] = {k: v.value for k, v in props.items()}

class DBusChannel(Channel):
    json_encoder = systemd_ctypes.JSONEncoder(indent=2)
    payload = 'dbus-json3'

matches = None
    name = None
    bus = None
    owner = None

async def setup_name_owner_tracking(self):
        def send_owner(owner):
            # We must be careful not to send duplicate owner
            # notifications. cockpit.js relies on that.
            if self.owner != owner:
                self.owner = owner
                self.send_json(owner=owner)

def handler(message):
            _name, _old, new = message.get_body()
            send_owner(owner=new if new != "" else None)
        self.add_signal_handler(handler,
                                sender='org.freedesktop.DBus',
                                path='/org/freedesktop/DBus',
                                interface='org.freedesktop.DBus',
                                member='NameOwnerChanged',
                                arg0=self.name)
        try:
            unique_name, = await self.bus.call_method_async("org.freedesktop.DBus",
                                                            "/org/freedesktop/DBus",
                                                            "org.freedesktop.DBus",
                                                            "GetNameOwner", "s", self.name)
        except BusError as error:
            if error.name == "org.freedesktop.DBus.Error.NameHasNoOwner":
                # Try to start it.  If it starts successfully, we will
                # get a NameOwnerChanged signal (which will set
                # self.owner) before StartServiceByName returns.
                try:
                    await self.bus.call_method_async("org.freedesktop.DBus",
                                                     "/org/freedesktop/DBus",
                                                     "org.freedesktop.DBus",
                                                     "StartServiceByName", "su", self.name, 0)
                except BusError as start_error:
                    logger.debug("Failed to start service '%s': %s", self.name, start_error.message)
                    self.send_json(owner=None)
            else:
                logger.debug("Failed to get owner of service '%s': %s", self.name, error.message)
        else:
            send_owner(unique_name)

def do_open(self, options):
        self.cache = InterfaceCache()
        self.name = options.get('name')
        self.matches = []

bus = options.get('bus')
        address = options.get('address')

try:
            if address is not None:
                if bus is not None and bus != 'none':
                    raise ChannelError('protocol-error', message='only one of "bus" and "address" can be specified')
                logger.debug('get bus with address %s for %s', address, self.name)
                self.bus = Bus.new(address=address, bus_client=self.name is not None)
            elif bus == 'internal':
                logger.debug('get internal bus for %s', self.name)
                self.bus = self.router.internal_bus.client
            else:
                if bus == 'session':
                    logger.debug('get session bus for %s', self.name)
                    self.bus = Bus.default_user()
                elif bus == 'system' or bus is None:
                    logger.debug('get system bus for %s', self.name)
                    self.bus = Bus.default_system()
                else:
                    raise ChannelError('protocol-error', message=f'invalid bus "{bus}"')
        except OSError as exc:
            raise ChannelError('protocol-error', message=f'failed to connect to {bus} bus: {exc}') from exc

try:
            self.bus.attach_event(None, 0)
        except OSError as err:
            if err.errno != errno.EBUSY:
                raise

# This needs to be a fair mutex so that outgoing messages don't
        # get re-ordered.  asyncio.Lock is fair.
        self.watch_processing_lock = asyncio.Lock()

if self.name is not None:
            async def get_ready() -> None:
                async with self.watch_processing_lock:
                    await self.setup_name_owner_tracking()
                    if self.owner:
                        self.ready(unique_name=self.owner)
                    else:
                        self.close({'problem': 'not-found'})
            self.create_task(get_ready())
        else:
            self.ready()

def add_signal_handler(self, handler, **kwargs):
        r = dict(**kwargs)
        r['type'] = 'signal'
        if 'sender' not in r and self.name is not None:
            r['sender'] = self.name
        # HACK - https://github.com/bus1/dbus-broker/issues/309
        # path_namespace='/' in a rule does not work.
        if r.get('path_namespace') == "/":
            del r['path_namespace']

def filter_owner(message):
            if self.owner is not None and self.owner == message.get_sender():
                handler(message)

if self.name is not None and 'sender' in r and r['sender'] == self.name:
            func = filter_owner
        else:
            func = handler
        r_string = ','.join(f"{key}='{value}'" for key, value in r.items())
        if not self.is_closing():
            # this gets an EINTR very often especially on RHEL 8
            while True:
                try:
                    match = self.bus.add_match(r_string, func)
                    break
                except InterruptedError:
                    pass

self.matches.append(match)

def add_async_signal_handler(self, handler, **kwargs):
        def sync_handler(message):
            self.create_task(handler(message))
        self.add_signal_handler(sync_handler, **kwargs)

async def do_call(self, message):
        path, iface, method, args = message['call']
        cookie = message.get('id')
        flags = message.get('flags')

timeout = message.get('timeout')
        if timeout is not None:
            # sd_bus timeout is μs, cockpit API timeout is ms
            timeout *= 1000
        else:
            # sd_bus has no "indefinite" timeout, so use MAX_UINT64
            timeout = 2 ** 64 - 1

# We have to figure out the signature of the call.  Either we got told it:
        signature = message.get('type')

# ... or there aren't any arguments
        if signature is None and len(args) == 0:
            signature = ''

# ... or we need to introspect
        if signature is None:
            try:
                logger.debug('Doing introspection request for %s %s', iface, method)
                signature = await self.cache.get_signature(iface, method, self.bus, self.name, path)
            except BusError as error:
                self.send_json(error=[error.name, [f'Introspection: {error.message}']], id=cookie)
                return
            except KeyError:
                self.send_json(
                    error=[
                        "org.freedesktop.DBus.Error.UnknownMethod",
                        [f"Introspection data for method {iface} {method} not available"]],
                    id=cookie)
                return
            except Exception as exc:
                self.send_json(error=['python.error', [f'Introspection: {exc!s}']], id=cookie)
                return

try:
            method_call = self.bus.message_new_method_call(self.name, path, iface, method, signature, *args)
            reply = await self.bus.call_async(method_call, timeout=timeout)
            # If the method call has kicked off any signals related to
            # watch processing, wait for that to be done.
            async with self.watch_processing_lock:
                # TODO: stop hard-coding the endian flag here.
                self.send_json(
                    reply=[reply.get_body()], id=cookie,
                    flags="<" if flags is not None else None,
                    type=reply.get_signature(True))  # noqa: FBT003
        except BusError as error:
            # actually, should send the fields from the message body
            self.send_json(error=[error.name, [error.message]], id=cookie)
        except Exception:
            logger.exception("do_call(%s): generic exception", message)
            self.send_json(error=['python.error', [traceback.format_exc()]], id=cookie)

async def do_add_match(self, message):
        add_match = message['add-match']
        logger.debug('adding match %s', add_match)

async def match_hit(message):
            logger.debug('got match')
            async with self.watch_processing_lock:
                self.send_json(signal=[
                    message.get_path(),
                    message.get_interface(),
                    message.get_member(),
                    list(message.get_body())
                ])

self.add_async_signal_handler(match_hit, **add_match)

async def setup_objectmanager_watch(self, path, interface_name, meta, notify):
        # Watch the objects managed by the ObjectManager at "path".
        # Properties are not watched, that is done by setup_path_watch
        # below via recursive_props == True.

async def handler(message):
            member = message.get_member()
            if member == "InterfacesAdded":
                (path, interface_props) = message.get_body()
                logger.debug('interfaces added %s %s', path, interface_props)
                meta = {}
                notify = {}
                async with self.watch_processing_lock:
                    for name, props in interface_props.items():
                        if interface_name is None or name == interface_name:
                            mm = await self.cache.get_interface_if_new(name, self.bus, self.name, path)
                            if mm:
                                meta.update({name: mm})
                            notify_update(notify, path, name, props)
                    self.send_json(meta=meta)
                    self.send_json(notify=notify)
            elif member == "InterfacesRemoved":
                (path, interfaces) = message.get_body()
                logger.debug('interfaces removed %s %s', path, interfaces)
                async with self.watch_processing_lock:
                    notify = {path: dict.fromkeys(interfaces)}
                    self.send_json(notify=notify)

self.add_async_signal_handler(handler,
                                      path=path,
                                      interface="org.freedesktop.DBus.ObjectManager")
        objects, = await self.bus.call_method_async(self.name, path,
                                                    'org.freedesktop.DBus.ObjectManager',
                                                    'GetManagedObjects')
        for p, ifaces in objects.items():
            for iface, props in ifaces.items():
                if interface_name is None or iface == interface_name:
                    mm = await self.cache.get_interface_if_new(iface, self.bus, self.name, p)
                    if mm:
                        meta.update({iface: mm})
                    notify_update(notify, p, iface, props)

async def setup_path_watch(self, path, interface_name, recursive_props, meta, notify):
        # Watch a single object at "path", but maybe also watch for
        # property changes for all objects below "path".

async def handler(message):
            async with self.watch_processing_lock:
                path = message.get_path()
                name, props, invalids = message.get_body()
                logger.debug('NOTIFY: %s %s %s %s', path, name, props, invalids)
                for inv in invalids:
                    try:
                        reply, = await self.bus.call_method_async(self.name, path,
                                                                  'org.freedesktop.DBus.Properties', 'Get',
                                                                  'ss', name, inv)
                    except BusError as exc:
                        logger.debug('failed to fetch property %s.%s on %s %s: %s',
                                     name, inv, self.name, path, exc)
                        continue
                    props[inv] = reply
                notify = {}
                notify_update(notify, path, name, props)
                self.send_json(notify=notify)

this_meta = await self.cache.introspect_path(self.bus, self.name, path)
        if interface_name is not None:
            interface = this_meta.get(interface_name)
            this_meta = {interface_name: interface}
        meta.update(this_meta)
        if recursive_props:
            self.add_async_signal_handler(handler,
                                          interface="org.freedesktop.DBus.Properties",
                                          path_namespace=path)
        else:
            self.add_async_signal_handler(handler,
                                          interface="org.freedesktop.DBus.Properties",
                                          path=path)

for name in meta:
            if name.startswith("org.freedesktop.DBus."):
                continue
            try:
                props, = await self.bus.call_method_async(self.name, path,
                                                          'org.freedesktop.DBus.Properties',
                                                          'GetAll', 's', name)
                notify_update(notify, path, name, props)
            except BusError:
                pass

async def do_watch(self, message):
        watch = message['watch']
        path = watch.get('path')
        path_namespace = watch.get('path_namespace')
        interface_name = watch.get('interface')
        cookie = message.get('id')

path = path or path_namespace
        recursive = path == path_namespace

if path is None or cookie is None:
            logger.debug('ignored incomplete watch request %s', message)
            self.send_json(error=['x.y.z', ['Not Implemented']], id=cookie)
            self.send_json(reply=[], id=cookie)
            return

try:
            async with self.watch_processing_lock:
                meta = {}
                notify = {}
                await self.setup_path_watch(path, interface_name, recursive, meta, notify)
                if recursive:
                    await self.setup_objectmanager_watch(path, interface_name, meta, notify)
                self.send_json(meta=meta)
                self.send_json(notify=notify)
                self.send_json(reply=[], id=message['id'])
        except BusError as error:
            logger.debug("do_watch(%s) caught D-Bus error: %s", message, error.message)
            self.send_json(error=[error.name, [error.message]], id=cookie)

async def do_meta(self, message):
        self.cache.inject(message['meta'])

def do_data(self, data):
        message = json.loads(data)
        logger.debug('receive dbus request %s %s', self.name, message)

if 'call' in message:
            self.create_task(self.do_call(message))
        elif 'add-match' in message:
            self.create_task(self.do_add_match(message))
        elif 'watch' in message:
            self.create_task(self.do_watch(message))
        elif 'meta' in message:
            self.create_task(self.do_meta(message))
        else:
            logger.debug('ignored dbus request %s', message)
            return

def do_close(self):
        for slot in self.matches:
            slot.cancel()
        self.matches = []
        self.close()

CANCEL

Name	Type	Size	Modified	Actions
↩ ..	DIR	—	—
📁 __pycache__/	DIR	—	2026-10-22 22:32
📄 __init__.py	PY	858 B	2026-09-15 22:10	EDIT
📄 dbus.py	PY	21.1 KB	2026-09-15 22:10	EDIT
📄 filesystem.py	PY	24.4 KB	2026-09-15 22:10	EDIT
📄 http_channel.py	PY	5.5 KB	2026-09-15 22:10	EDIT
📄 info.py	PY	377 B	2026-09-15 22:10	EDIT
📄 metrics.py	PY	6.1 KB	2026-09-15 22:10	EDIT
📄 packages.py	PY	3.3 KB	2026-09-15 22:10	EDIT
📄 pcp.py	PY	27.3 KB	2026-09-15 22:10	EDIT
📄 stream.py	PY	4.3 KB	2026-09-15 22:10	EDIT
📄 trivial.py	PY	660 B	2026-09-15 22:10	EDIT