kytos.core.controller

Complexity

Total Complexity

163

Size/Duplication

Total Lines	1137
Duplicated Lines	0 %

Importance

Changes

0

"""Kytos SDN Platform main class.

This module contains the main class of Kytos, which is
:class:`~.core.Controller`.

Basic usage:

.. code-block:: python3

    from kytos.core.config import KytosConfig
    from kytos.core import Controller
    config = KytosConfig()
    controller = Controller(config.options)
    controller.start()
"""
import asyncio
import atexit
import importlib
import logging
import os
import re
import sys
import threading
import traceback
from asyncio import AbstractEventLoop
from collections import Counter, defaultdict
from importlib import import_module
from importlib import reload as reload_module
from importlib.util import module_from_spec, spec_from_file_location
from pathlib import Path
from typing import Optional

from pyof.foundation.exceptions import PackException

from kytos.core.api_server import APIServer, JSONResponse, Request
from kytos.core.apm import init_apm
from kytos.core.atcp_server import KytosServer, KytosServerProtocol
from kytos.core.auth import Auth
from kytos.core.buffers import KytosBuffers
from kytos.core.common import EntityStatus
from kytos.core.config import KytosConfig
from kytos.core.connection import Connection, ConnectionState
from kytos.core.db import db_conn_wait
from kytos.core.dead_letter import DeadLetter
from kytos.core.events import KytosEvent
from kytos.core.exceptions import (KytosAPMInitException, KytosDBInitException,
                                   KytosNAppSetupException)
from kytos.core.helpers import executors, now
from kytos.core.interface import Interface
from kytos.core.link import Link
from kytos.core.logs import LogManager
from kytos.core.napps.base import NApp
from kytos.core.napps.manager import NAppsManager
from kytos.core.napps.napp_dir_listener import NAppDirListener
from kytos.core.pacing import Pacer
from kytos.core.queue_monitor import QueueMonitorWindow
from kytos.core.switch import Switch

__all__ = ('Controller',)


def exc_handler(_, exc, __):
    """Log uncaught exceptions.

    Args:
        exc_type (ignored): exception type
        exc: exception instance
        tb (ignored): traceback
    """
    logging.basicConfig(filename='errlog.log',
                        format='%(asctime)s:%(pathname)'
                        's:%(levelname)s:%(message)s')
    logging.exception('Uncaught Exception: %s', exc)


class Controller:
    """Main class of Kytos.

    The main responsibilities of this class are:
        - start a thread with :class:`~.core.tcp_server.KytosServer`;
        - manage KytosNApps (install, load and unload);
        - keep the buffers (instance of :class:`~.core.buffers.KytosBuffers`);
        - manage which event should be sent to NApps methods;
        - manage the buffers handlers, considering one thread per handler.
    """

    # Created issue #568 for the disabled checks.
    # pylint: disable=too-many-instance-attributes,too-many-public-methods,
    # pylint: disable=consider-using-with,unnecessary-dunder-call
    # pylint: disable=too-many-lines
    def __init__(self, options=None, loop: AbstractEventLoop = None):
        """Init method of Controller class takes the parameters below.

        Args:
            options (:attr:`ParseArgs.args`): :attr:`options` attribute from an
                instance of :class:`~kytos.core.config.KytosConfig` class.
            loop asyncio.AbstractEventLoop
        """
        if options is None:
            options = KytosConfig().options['daemon']

        self.loop = loop

        # asyncio tasks
        self._tasks: list[asyncio.Task] = []

        #: KytosBuffers: KytosBuffer object with Controller buffers
        self._buffers: KytosBuffers = None
        #: dict: keep track of the socket connections labeled by ``(ip, port)``
        #:
        #: This dict stores all connections between the controller and the
        #: switches. The key for this dict is a tuple (ip, port). The content
        #: is a Connection
        self.connections: dict[tuple, Connection] = {}
        #: dict: mapping of events and event listeners.
        #:
        #: The key of the dict is a KytosEvent (or a string that represent a
        #: regex to match against KytosEvents) and the value is a list of
        #: methods that will receive the referenced event
        self.events_listeners = {'kytos/core.connection.new':
                                 [self.new_connection]}

        #: dict: Current loaded apps - ``'napp_name'``: ``napp`` (instance)
        #:
        #: The key is the napp name (string), while the value is the napp
        #: instance itself.
        self.napps = {}
        #: Object generated by ParseArgs on config.py file
        self.options = options
        #: KytosServer: Instance of KytosServer that will be listening to TCP
        #: connections.
        self.server = None
        #: dict: Current existing switches.
        #:
        #: The key is the switch dpid, while the value is a Switch object.
        self.switches: dict[str, Switch] = {}
        self.switches_lock = threading.Lock()

        #: datetime.datetime: Time when the controller finished starting.
        self.started_at = None

        #: logging.Logger: Logger instance used by Kytos.
        self.log = None

        #: Observer that handle NApps when they are enabled or disabled.
        self.napp_dir_listener = NAppDirListener(self)

        self.napps_manager = NAppsManager(self)

        #: API Server used to expose rest endpoints.
        self.api_server = APIServer(self.options.listen,
                                    self.options.api_port,
                                    self.napps_manager,
                                    self.options.napps,
                                    self.options.api_traceback_on_500)

        self.auth = None
        self.dead_letter = DeadLetter(self)
        self._alisten_tasks = set()
        self.qmonitors: list[QueueMonitorWindow] = []

        #: APM client in memory to be closed when necessary
        self.apm = None

        self._register_endpoints()
        #: Adding the napps 'enabled' directory into the PATH
        #: Now you can access the enabled napps with:
        #: from napps.<username>.<napp_name> import ?....
        sys.path.append(os.path.join(self.options.napps, os.pardir))
        sys.excepthook = exc_handler

        #: Pacer for controlling the rate which actions can be executed
        self.pacer = Pacer("memory://")

        self.links: dict[str, Link] = {}
        Link.register_status_reason_func("controller_mismatched_reason",
                                         self.detect_mismatched_link)
        Link.register_status_func("controller_mismatched_status",
                                  self.link_status_mismatched)

    def start_auth(self):
        """Initialize Auth() and its services"""
        self.auth = Auth(self)
        self.auth.register_core_auth_services()

    def enable_logs(self):
        """Register kytos log and enable the logs."""
        decorators = self.options.logger_decorators
        try:
            decorators = [self._resolve(deco) for deco in decorators]
        except ModuleNotFoundError as err:
            sys.exit(f'Failed to resolve decorator module: {err.name}')
        except AttributeError:
            sys.exit(f'Failed to resolve decorator name: {decorators}')
        LogManager.decorate_logger_class(*decorators)
        LogManager.load_config_file(self.options.logging, self.options.debug)
        # pylint: disable=fixme
        # TODO issue 371
        # LogManager.enable_websocket(self.api_server.server)
        self.log = logging.getLogger(__name__)
        self._patch_core_loggers()

    @staticmethod
    def _resolve(name):
        """Resolve a dotted name to a global object."""
        mod, _, attr = name.rpartition('.')
        mod = importlib.import_module(mod)
        return getattr(mod, attr)

    @staticmethod
    def _patch_core_loggers():
        """Patch in updated loggers to 'kytos.core.*' modules"""
        match_str = 'kytos.core.'
        str_len = len(match_str)
        reloadable_mods = [module for mod_name, module in sys.modules.items()
                           if mod_name[:str_len] == match_str]
        for module in reloadable_mods:
            new_logger = logging.getLogger(module.__name__)
            if hasattr(module, "LOG"):
                old_logger = module.LOG
                for handler in old_logger.handlers:
                    new_logger.addHandler(handler)
                for log_filter in old_logger.filters:
                    new_logger.addFilter(log_filter)
            module.LOG = new_logger

    @staticmethod
    def loggers():
        """List all logging Loggers.

        Return a list of Logger objects, with name and logging level.
        """
        # pylint: disable=no-member
        return [logging.getLogger(name)
                for name in logging.root.manager.loggerDict
                if "kytos" in name]

    def toggle_debug(self, name=None):
        """Enable/disable logging debug messages to a given logger name.

        If the name parameter is not specified the debug will be
        enabled/disabled following the initial config file. It will decide
        to enable/disable using the 'kytos' name to find the current
        logger level.
        Obs: To disable the debug the logging will be set to NOTSET

        Args:
            name(text): Full hierarchy Logger name. Ex: "kytos.core.controller"
        """
        # pylint: disable=no-member
        if name and name not in logging.root.manager.loggerDict:
            # A Logger name that is not declared in logging will raise an error
            # otherwise logging would create a new Logger.
            raise ValueError(f"Invalid logger name: {name}")

        if not name:
            # Logger name not specified.
            level = logging.getLogger('kytos').getEffectiveLevel()
            enable_debug = level != logging.DEBUG

            # Enable/disable default Loggers
            LogManager.load_config_file(self.options.logging, enable_debug)
            return

        # Get effective logger level for the name
        level = logging.getLogger(name).getEffectiveLevel()
        logger = logging.getLogger(name)

        if level == logging.DEBUG:
            # disable debug
            logger.setLevel(logging.NOTSET)
        else:
            # enable debug
            logger.setLevel(logging.DEBUG)

    async def start(self, restart=False):
        """Create pidfile and call start_controller method."""
        self.enable_logs()
        # pylint: disable=broad-except
        try:
            if self.options.database:
                db_conn_wait(db_backend=self.options.database)
            if self.options.apm:
                self.apm = init_apm(self.options.apm, app=self.api_server.app)
            if not restart:
                self.create_pidfile()
            await self.start_controller()
        except (KytosDBInitException, KytosAPMInitException) as exc:
            message = f"Kytos couldn't start because of {str(exc)}"
            sys.exit(message)
        except Exception as exc:
            exc_fmt = traceback.format_exc(chain=True)
            message = f"Kytos couldn't start because of {str(exc)} {exc_fmt}"
            counter = self._full_queue_counter()
            sys.exit(self._try_to_fmt_traceback_msg(message, counter))

    def start_queue_monitors(self) -> None:
        """Start QueueMonitorWindows."""
        for data in self.options.event_buffer_monitors:
            for qmon in QueueMonitorWindow.from_buffer_config(self, **data):
                self.qmonitors.append(qmon)
        for data in self.options.thread_pool_queue_monitors:
            for qmon in QueueMonitorWindow.from_threadpool_config(**data):
                self.qmonitors.append(qmon)
        for qmonitor in self.qmonitors:
            self.log.info(f"Starting {qmonitor}...")
            qmonitor.start()

    def stop_queue_monitors(self) -> None:
        """Stop QueueMonitorWindows."""
        for qmonitor in self.qmonitors:
            self.log.info(f"Stopping {qmonitor}...")
            qmonitor.stop()

    def create_pidfile(self):
        """Create a pidfile."""
        pid = os.getpid()

        # Creates directory if it doesn't exist
        # System can erase /var/run's content
        pid_folder = Path(self.options.pidfile).parent
        self.log.info(pid_folder)

        # Pylint incorrectly infers Path objects
        # https://github.com/PyCQA/pylint/issues/224
        # pylint: disable=no-member
        if not pid_folder.exists():
            pid_folder.mkdir()
            pid_folder.chmod(0o1777)
        # pylint: enable=no-member

        # Make sure the file is deleted when controller stops
        atexit.register(Path(self.options.pidfile).unlink)

        # Checks if a pidfile exists. Creates a new file.
        try:
            pidfile = open(self.options.pidfile, mode='x', encoding="utf8")
        except OSError:
            # This happens if there is a pidfile already.
            # We shall check if the process that created the pidfile is still
            # running.
            try:
                existing_file = open(self.options.pidfile, mode='r',
                                     encoding="utf8")
                old_pid = int(existing_file.read())
                os.kill(old_pid, 0)
                # If kill() doesn't return an error, there's a process running
                # with the same PID. We assume it is Kytos and quit.
                # Otherwise, overwrite the file and proceed.
                error_msg = ("PID file {} exists. Delete it if Kytos is not "
                             "running. Aborting.")
                sys.exit(error_msg.format(self.options.pidfile))
            except OSError:
                try:
                    pidfile = open(self.options.pidfile, mode='w',
                                   encoding="utf8")
                except OSError as exception:
                    error_msg = "Failed to create pidfile {}: {}."
                    sys.exit(error_msg.format(self.options.pidfile, exception))

        # Identifies the process that created the pidfile.
        pidfile.write(str(pid))
        pidfile.close()

    @property
    def buffers(self) -> KytosBuffers:
        """KytosBuffers exposed through this property to allow lazy
        async initiliation with an event loop running."""
        if not self._buffers:
            self._buffers = KytosBuffers()
        return self._buffers

    async def _wait_api_server_started(self):
        """Use this method to wait for Uvicorn server to start."""
        while not self.api_server.server.started:
            await asyncio.sleep(0.1)

    async def start_controller(self):
        """Start the controller.

        Starts the KytosServer (TCP Server) coroutine.
        Starts a thread for each buffer handler.
        Load the installed apps.
        """
        self.log.info("Starting Kytos - Kytos Controller")
        if not self._buffers:
            self._buffers = KytosBuffers()
        self.server = KytosServer((self.options.listen,
                                   int(self.options.port)),
                                  KytosServerProtocol,
                                  self,
                                  self.options.protocol_name)

        self.log.info("Starting API server")
        task = self.loop.create_task(self.api_server.serve())
        self._tasks.append(task)
        await self._wait_api_server_started()

        self.log.info(f"Starting TCP server: {self.server}")
        self.server.serve_forever()

        # ASYNC TODO: ensure all threads started correctly
        # This is critical, if any of them failed starting we should exit.
        # sys.exit(error_msg.format(thread, exception))

        self.log.info("Starting authorization.")
        self.start_auth()
        self.log.info("Loading Kytos NApps...")
        self.napp_dir_listener.start()
        self.pre_install_napps(self.options.napps_pre_installed)
        self.load_napps()
        self.api_server.start_web_ui()

        # Start task handlers consumers after NApps to potentially
        # avoid discarding an event if a consumer isn't ready yet
        task = self.loop.create_task(self.event_handler("conn"))
        self._tasks.append(task)
        task = self.loop.create_task(self.event_handler("raw"))
        self._tasks.append(task)
        task = self.loop.create_task(self.event_handler("msg_in"))
        self._tasks.append(task)
        task = self.loop.create_task(self.msg_out_event_handler())
        self._tasks.append(task)
        task = self.loop.create_task(self.event_handler("app"))
        self._tasks.append(task)
        task = self.loop.create_task(self.event_handler("meta"))
        self._tasks.append(task)

        self.start_queue_monitors()
        self.started_at = now()

    def _register_endpoints(self):
        """Register all rest endpoint served by kytos.

        -   Register APIServer endpoints
        -   Register WebUI endpoints
        -   Register ``/api/kytos/core/config`` endpoint
        """
        self.api_server.start_api()
        # Register controller endpoints as /api/kytos/core/...
        self.api_server.register_core_endpoint('config/',
                                               self.configuration_endpoint)
        self.api_server.register_core_endpoint('metadata/',
                                               Controller.metadata_endpoint)
        self.api_server.register_core_endpoint(
            'reload/{username}/{napp_name}/',
            self.rest_reload_napp)
        self.api_server.register_core_endpoint('reload/all',
                                               self.rest_reload_all_napps)
        self.dead_letter.register_endpoints()

    def register_rest_endpoint(self, url, function, methods):
        """Deprecate in favor of @rest decorator."""
        self.api_server.register_rest_endpoint(url, function, methods)

    @classmethod
    def metadata_endpoint(cls, _request: Request) -> JSONResponse:
        """Return the Kytos metadata.

        Returns:
            string: Json with current kytos metadata.

        """
        meta_path = f"{os.path.dirname(__file__)}/metadata.py"
        with open(meta_path, encoding="utf8") as file:
            meta_file = file.read()
        metadata = dict(re.findall(r"(__[a-z]+__)\s*=\s*'([^']+)'", meta_file))
        return JSONResponse(metadata)

    def configuration_endpoint(self, _request: Request) -> JSONResponse:
        """Return the configuration options used by Kytos.

        Returns:
            string: Json with current configurations used by kytos.

        """
        return JSONResponse(KytosConfig.options_exposed(self.options.__dict__))

    def restart(self, graceful=True):
        """Restart Kytos SDN Controller.

        Args:
            graceful(bool): Represents the way that Kytos will restart.
        """
        if self.started_at is not None:
            self.stop(graceful)
            self.__init__(self.options)

        self.start(restart=True)

    def stop(self, graceful=True):
        """Shutdown all services used by kytos.

        This method should:
            - stop all Websockets
            - stop the API Server
            - stop the Controller
        """
        if self.started_at:
            self.stop_controller(graceful)

    def stop_controller(self, graceful=True):
        """Stop the controller.

        This method should:
            - announce on the network that the controller will shutdown;
            - stop receiving incoming packages;
            - call the 'shutdown' method of each KytosNApp that is running;
            - finish reading the events on all buffers;
            - stop each running handler;
            - stop all running threads;
            - stop the KytosServer;
        """
        self.log.info("Stopping Kytos")

        self.buffers.send_stop_signal()
        self.napp_dir_listener.stop()

        for pool_name in executors:
            self.log.info("Stopping threadpool: %s", pool_name)

        threads = threading.enumerate()
        self.log.debug("%s threads before threadpool shutdown: %s",
                       len(threads), threads)

        for executor_pool in executors.values():
            executor_pool.shutdown(wait=graceful, cancel_futures=True)

        # self.server.socket.shutdown()
        # self.server.socket.close()

        self.started_at = None
        napps = self.unload_napps()
        self.log.info(
            f"Waiting for {len(napps)} NApps shutdown confirmation..."
        )
        for napp in napps:
            self.log.info(f"Waiting {napp} shutdown confirmation...")
            napp.__dict__['_KytosNApp__event'].wait()
            self.log.info(f"{napp} was shutdown")

        # Cancel all async tasks (event handlers and servers)
        for task in self._tasks:
            task.cancel()

        # ASYNC TODO: close connections
        # self.server.server_close()

        self.stop_queue_monitors()
        if self.apm:
            self.log.info("Stopping APM server...")
            self.apm.close()
            self.log.info("Stopped APM Server")
        self.log.info("Stopping API Server...")
        self.api_server.stop()
        self.log.info("Stopped API Server")
        self.log.info("Stopping TCP Server...")
        self.server.shutdown()
        self.log.info("Stopped TCP Server")
        self.loop.stop()

    def status(self):
        """Return status of Kytos Server.

        If the controller kytos is running this method will be returned
        "Running since 'Started_At'", otherwise "Stopped".

        Returns:
            string: String with kytos status.

        """
        if self.started_at:
            return f"Running since {self.started_at}"
        return "Stopped"

    def uptime(self):
        """Return the uptime of kytos server.

        This method should return:
            - 0 if Kytos Server is stopped.
            - (kytos.start_at - datetime.now) if Kytos Server is running.

        Returns:
           datetime.timedelta: The uptime interval.

        """
        return now() - self.started_at if self.started_at else 0

    def notify_listeners(self, event):
        """Send the event to the specified listeners.

        Loops over self.events_listeners matching (by regexp) the attribute
        name of the event with the keys of events_listeners. If a match occurs,
        then send the event to each registered listener.

        Args:
            event (~kytos.core.KytosEvent): An instance of a KytosEvent.
        """

        self.log.debug("looking for listeners for %s", event)
        for event_regex, listeners in dict(self.events_listeners).items():
            # self.log.debug("listeners found for %s: %r => %s", event,
            #                event_regex, [l.__qualname__ for l in listeners])
            # Do not match if the event has more characters
            # e.g. "shutdown" won't match "shutdown.kytos/of_core"
            if event_regex[-1] != '$' or event_regex[-2] == '\\':
                event_regex += '$'
            if re.match(event_regex, event.name):
                self.log.debug('Calling listeners for %s', event)
                for listener in listeners:
                    if asyncio.iscoroutinefunction(listener):
                        task = asyncio.create_task(listener(event))
                        self._alisten_tasks.add(task)
                        task.add_done_callback(self._alisten_tasks.discard)
                    else:
                        listener(event)

    # pylint: disable=broad-exception-caught
    async def event_handler(self, buffer_name: str):
        """Default event handler that gets from an event buffer."""
        event_buffer = getattr(self.buffers, buffer_name)
        self.log.info(f"Event handler {buffer_name} started")
        while True:
            try:
                # After hitting issues with a large amount of flows being
                # installed (16k which sends 32k events), this task was
                # hogging resources in the MainThread causing disconnections
                # and socket exceptions. With the following sleep, this task
                # yields to other loops mitigating the disconnection issues.
                # Now the cap for flow installation at the same time is 50k.
                await asyncio.sleep(0)
                event = await event_buffer.aget()
                self.notify_listeners(event)

                if event.name == "kytos/core.shutdown":
                    self.log.debug(f"Event handler {buffer_name} stopped")
                    break
            except Exception as exc:
                self.log.exception(f"Unhandled exception on {buffer_name}",
                                   exc_info=exc)

    async def publish_connection_error(self, event):
        """Publish connection error event.

        Args:
            event (KytosEvent): Event that triggered for error propagation.
        """
        event.name = \
            f"kytos/core.{event.destination.protocol.name}.connection.error"
        error_msg = f"Connection state: {event.destination.state}"
        event.content["exception"] = error_msg
        await self.buffers.conn.aput(event)

    # pylint: disable=broad-exception-caught
    async def msg_out_event_handler(self):
        """Handle msg_out events.

        Listen to the msg_out buffer and send all its events to the
        corresponding listeners.
        """
        self.log.info("Event handler msg_out started")
        while True:
            try:
                triggered_event = await self.buffers.msg_out.aget()

                if triggered_event.name == "kytos/core.shutdown":
                    self.log.debug("Message Out Event handler stopped")
                    break

                message = triggered_event.content['message']
                destination = triggered_event.destination
                if (destination and
                        not destination.state == ConnectionState.FINISHED):
                    packet = message.pack()
                    destination.send(packet)
                    self.log.debug('Connection %s: OUT OFP, '
                                   'version: %s, type: %s, xid: %s - %s',
                                   destination.id,
                                   message.header.version,
                                   message.header.message_type,
                                   message.header.xid,
                                   packet.hex())
                    self.notify_listeners(triggered_event)
            except OSError:
                await self.publish_connection_error(triggered_event)
                self.log.info("connection closed. Cannot send message")
            except PackException as err:
                self.log.error(
                    f"Discarding message: {message}, event: {triggered_event} "
                    f"because of PackException {err}"
                )
            except Exception as exc:
                self.log.exception("Unhandled exception on msg_out",
                                   exc_info=exc)

    def get_interface_by_id(self, interface_id):
        """Find a Interface  with interface_id.

        Args:
            interface_id(str): Interface Identifier.

        Returns:
            Interface: Instance of Interface with the id given.

        """
        if interface_id is None:
            return None

        switch_id = ":".join(interface_id.split(":")[:-1])
        interface_number = int(interface_id.split(":")[-1])

        switch = self.switches.get(switch_id)

        if not switch:
            return None

        return switch.interfaces.get(interface_number, None)

    def get_switch_by_dpid(self, dpid):
        """Return a specific switch by dpid.

        Args:
            dpid (|DPID|): dpid object used to identify a switch.

        Returns:
            :class:`~kytos.core.switch.Switch`: Switch with dpid specified.

        """
        return self.switches.get(dpid)

    def get_switch_or_create(self, dpid, connection=None):
        """Return switch or create it if necessary.

        Args:
            dpid (|DPID|): dpid object used to identify a switch.
            connection (:class:`~kytos.core.connection.Connection`):
                connection used by switch. If a switch has a connection that
                will be updated.

        Returns:
            :class:`~kytos.core.switch.Switch`: new or existent switch.

        """
        with self.switches_lock:
            if connection:
                self.create_or_update_connection(connection)

            switch = self.get_switch_by_dpid(dpid)
            event_name = 'kytos/core.switch.'

            if switch is None:
                switch = Switch(dpid=dpid)
                self.add_new_switch(switch)
                event_name += 'new'
            else:
                event_name += 'reconnected'
            event = KytosEvent(name=event_name, content={'switch': switch})

            if connection:
                old_connection = switch.connection
                switch.update_connection(connection)

                if old_connection is not connection:
                    self.remove_connection(old_connection)

            self.buffers.conn.put(event)

            return switch

    def create_or_update_connection(self, connection):
        """Update a connection.

        Args:
            connection (:class:`~kytos.core.connection.Connection`):
                Instance of connection that will be updated.
        """
        self.connections[connection.id] = connection

    def get_connection_by_id(self, conn_id):
        """Return a existent connection by id.

        Args:
            id (int): id from a connection.

        Returns:
            :class:`~kytos.core.connection.Connection`: Instance of connection
                or None Type.

        """
        return self.connections.get(conn_id)

    def remove_connection(self, connection):
        """Close a existent connection and remove it.

        Args:
            connection (:class:`~kytos.core.connection.Connection`):
                Instance of connection that will be removed.
        """
        if connection is None:
            return False

        try:
            connection.close()
            del self.connections[connection.id]
        except KeyError:
            return False
        return True

    def remove_switch(self, switch):
        """Remove an existent switch.

        Args:
            switch (:class:`~kytos.core.switch.Switch`):
                Instance of switch that will be removed.
        """
        try:
            del self.switches[switch.dpid]
        except KeyError:
            return False
        return True

    def new_connection(self, event):
        """Handle a kytos/core.connection.new event.

        This method will read new connection event and store the connection
        (socket) into the connections attribute on the controller.

        It also clear all references to the connection since it is a new
        connection on the same ip:port.

        Args:
            event (~kytos.core.KytosEvent):
                The received event (``kytos/core.connection.new``) with the
                needed info.
        """
        self.log.info("Handling %s...", event)

        connection = event.source
        self.log.debug("Event source: %s", event.source)

        # Remove old connection (aka cleanup) if it exists
        if self.get_connection_by_id(connection.id):
            self.remove_connection(connection.id)

        # Update connections with the new connection
        self.create_or_update_connection(connection)

    def add_new_switch(self, switch):
        """Add a new switch on the controller.

        Args:
            switch (Switch): A Switch object
        """
        self.switches[switch.dpid] = switch

    def _import_napp(self, username, napp_name):
        """Import a NApp module.

        Raises:
            FileNotFoundError: if NApp's main.py is not found.
            ModuleNotFoundError: if any NApp requirement is not installed.

        """
        mod_name = '.'.join(['napps', username, napp_name, 'main'])
        path = os.path.join(self.options.napps, username, napp_name,
                            'main.py')
        napp_spec = spec_from_file_location(mod_name, path)
        napp_module = module_from_spec(napp_spec)
        sys.modules[napp_spec.name] = napp_module
        napp_spec.loader.exec_module(napp_module)
        return napp_module

    def load_napp(self, username, napp_name):
        """Load a single NApp.

        Args:
            username (str): NApp username (makes up NApp's path).
            napp_name (str): Name of the NApp to be loaded.
        """
        if (username, napp_name) in self.napps:
            message = 'NApp %s/%s was already loaded'
            self.log.warning(message, username, napp_name)
            return

        try:
            napp_module = self._import_napp(username, napp_name)
        except ModuleNotFoundError as err:
            self.log.error("Error loading NApp '%s/%s': %s",
                           username, napp_name, err)
            return
        except FileNotFoundError as err:
            msg = "NApp module not found, assuming it's a meta-napp: %s"
            self.log.warning(msg, err.filename)
            return

        try:
            napp = napp_module.Main(controller=self)
        except Exception as exc:  # noqa pylint: disable=bare-except
            msg = f"NApp {username}/{napp_name} exception {str(exc)} "
            raise KytosNAppSetupException(msg) from exc

        self.napps[(username, napp_name)] = napp

        napp.start()
        self.api_server.authenticate_endpoints(napp)
        self.api_server.register_napp_endpoints(napp)

        # pylint: disable=protected-access
        for event, listeners in napp._listeners.items():
            self.events_listeners.setdefault(event, []).extend(listeners)
        # pylint: enable=protected-access

    def pre_install_napps(self, napps, enable=True):
        """Pre install and enable NApps.

        Before installing, it'll check if it's installed yet.

        Args:
            napps ([str]): List of NApps to be pre-installed and enabled.
        """
        all_napps = self.napps_manager.get_installed_napps()
        installed = [str(napp) for napp in all_napps]
        napps_diff = [napp for napp in napps if napp not in installed]
        for napp in napps_diff:
            self.napps_manager.install(napp, enable=enable)

    def load_napps(self):
        """Load all NApps enabled on the NApps dir."""
        for napp in self.napps_manager.get_enabled_napps():
            try:
                self.log.info("Loading NApp %s", napp.id)
                self.load_napp(napp.username, napp.name)
            except FileNotFoundError as exception:
                self.log.error("Could not load NApp %s: %s",
                               napp.id, exception)
                msg = f"NApp {napp.id} exception {str(exception)}"
                raise KytosNAppSetupException(msg) from exception

    def unload_napp(self, username, napp_name):
        """Unload a specific NApp.

        Args:
            username (str): NApp username.
            napp_name (str): Name of the NApp to be unloaded.
        """
        napp = self.napps.pop((username, napp_name), None)

        if napp is None:
            self.log.warning('NApp %s/%s was not loaded', username, napp_name)
        else:
            self.log.info("Shutting down NApp %s/%s...", username, napp_name)
            napp_id = NApp(username, napp_name).id
            event = KytosEvent(name='kytos/core.shutdown.' + napp_id)
            napp_shutdown_fn = self.events_listeners[event.name][0]
            # Call listener before removing it from events_listeners
            napp_shutdown_fn(event)

            # Remove rest endpoints from that napp
            self.api_server.remove_napp_endpoints(napp)

            # Removing listeners from that napp
            # pylint: disable=protected-access
            for event_type, napp_listeners in napp._listeners.items():
                event_listeners = self.events_listeners[event_type]
                for listener in napp_listeners:
                    event_listeners.remove(listener)
                if not event_listeners:
                    del self.events_listeners[event_type]
            # pylint: enable=protected-access

        return napp

    def unload_napps(self):
        """Unload all loaded NApps that are not core NApps

        NApps are unloaded in the reverse order that they are enabled to
        facilitate to shutdown gracefully.
        """
        napps = []
        for napp in reversed(self.napps_manager.get_enabled_napps()):
            if napp := self.unload_napp(napp.username, napp.name):
                napps.append(napp)
        return napps

    def reload_napp_module(self, username, napp_name, napp_file):
        """Reload a NApp Module."""
        mod_name = '.'.join(['napps', username, napp_name, napp_file])
        try:
            napp_module = import_module(mod_name)
        except ModuleNotFoundError:
            self.log.error("Module '%s' not found", mod_name)
            raise
        try:
            napp_module = reload_module(napp_module)
        except ImportError as err:
            self.log.error("Error reloading NApp '%s/%s': %s",
                           username, napp_name, err)
            raise

    def reload_napp(self, username, napp_name):
        """Reload a NApp."""
        self.unload_napp(username, napp_name)
        try:
            self.reload_napp_module(username, napp_name, 'settings')
            self.reload_napp_module(username, napp_name, 'main')
        except (ModuleNotFoundError, ImportError):
            return 400
        self.log.info("NApp '%s/%s' successfully reloaded",
                      username, napp_name)
        self.load_napp(username, napp_name)
        return 200

    def rest_reload_napp(self, request: Request) -> JSONResponse:
        """Request reload a NApp."""
        username = request.path_params["username"]
        napp_name = request.path_params["napp_name"]
        res = self.reload_napp(username, napp_name)
        if res == 200:
            return JSONResponse('reloaded')
        return JSONResponse('fail to reload', status_code=res)

    def rest_reload_all_napps(self, _request: Request) -> JSONResponse:
        """Request reload all NApps."""
        for napp in self.napps:
            self.reload_napp(*napp)
        return JSONResponse('reloaded')

    def _full_queue_counter(self) -> Counter:
        """Generate full queue stats counter."""
        buffer_counter = defaultdict(Counter)
        for buffer in self.buffers.get_all_buffers():
            if not buffer.full():
                continue
            while not buffer.empty():
                event = buffer.get()
                buffer_counter[buffer.name][event.name] += 1
        return buffer_counter

    def _try_to_fmt_traceback_msg(self, message: str, counter: Counter) -> str:
        """Try to fmt traceback message."""
        if counter:
            counter = dict(counter)
            message = (
                f"{message}\nFull KytosEventBuffers counters: {counter}"
            )
        return message

    def get_link_or_create(
        self,
        endpoint_a: Interface,
        endpoint_b: Interface,
        link_dict: Optional[dict] = None,
    ) -> tuple[Link, bool]:
        """Get an existing link or create a new one.

        Returns:
            Tuple(Link, bool): Link and a boolean whether it has been created.
        """
        new_link = Link(endpoint_a, endpoint_b)

        # If new_link is an old link but mismatched,
        # then treat it as a new link
        if (new_link.id in self.links
                and not self.detect_mismatched_link(new_link)):
            return (self.links[new_link.id], False)

        with new_link.lock:
            # Check if any interface already has a link
            # This old_link is a leftover link that needs to be removed
            # The other endpoint of the link is the leftover interface
            if endpoint_a.link and endpoint_a.link != new_link:
                old_link = endpoint_a.link
                leftover_interface = (
                    old_link.endpoint_a
                    if old_link.endpoint_a != endpoint_a
                    else old_link.endpoint_b
                )
                self.log.warning(
                    f"Leftover mismatched link"
                    f" {endpoint_a.link} in interface"
                    f" {leftover_interface}"
                )

            if endpoint_b.link and endpoint_b.link != new_link:
                old_link = endpoint_b.link
                leftover_interface = (
                    old_link.endpoint_b
                    if old_link.endpoint_b != endpoint_b
                    else old_link.endpoint_a
                )
                self.log.warning(
                    f"Leftover mismatched link "
                    f" {endpoint_b.link} in interface"
                    f" {leftover_interface}"
                )

            if new_link.id not in self.links:
                self.links[new_link.id] = new_link

            endpoint_a.update_link(new_link)
            endpoint_b.update_link(new_link)
            new_link.endpoint_a = endpoint_a
            new_link.endpoint_b = endpoint_b
            endpoint_a.nni = True
            endpoint_b.nni = True

            if link_dict:
                if link_dict['enabled']:
                    new_link.enable()
                else:
                    new_link.disable()

                if link_dict.get("metadata"):
                    new_link.extend_metadata(link_dict["metadata"])

        return (self.links[new_link.id], True)

    def get_link(self, link_id: str) -> Optional[Link]:
        """Return a link by its ID.

        Returns:
            Optional[Link]: Link if found, None otherwise.
        """
        return self.links.get(link_id)

    @staticmethod
    def detect_mismatched_link(link: Link) -> frozenset[str]:
        """Check if a link is mismatched."""
        if (link.endpoint_a.link and link.endpoint_b
                and link.endpoint_a.link == link.endpoint_b.link):
            return frozenset()
        return frozenset(["mismatched_link"])

    def link_status_mismatched(self, link: Link) -> Optional[EntityStatus]:
        """Check if a link is mismatched and return a status."""
        if self.detect_mismatched_link(link):
            return EntityStatus.DOWN