relaylist.py

from stem.descriptor.router_status_entry import RouterStatusEntryV3
from stem.descriptor.server_descriptor import ServerDescriptor
from stem import Flag, DescriptorUnavailable, ControllerError
from stem.util.connection import is_valid_ipv4_address
from stem.util.connection import is_valid_ipv6_address
import random
import time
import logging
from sbws.globals import resolve
from threading import Lock

log = logging.getLogger(__name__)


class Relay:
    def __init__(self, fp, cont, ns=None, desc=None):
        '''
        Given a relay fingerprint, fetch all the information about a relay that
        sbws currently needs and store it in this class. Acts as an abstraction
        to hide the confusion that is Tor consensus/descriptor stuff.

        :param str fp: fingerprint of the relay.
        :param cont: active and valid stem Tor controller connection
        '''
        assert isinstance(fp, str)
        assert len(fp) == 40
        if ns is not None:
            assert isinstance(ns, RouterStatusEntryV3)
            self._ns = ns
        else:
            try:
                self._ns = cont.get_network_status(fp, default=None)
            except (DescriptorUnavailable, ControllerError) as e:
                log.exception("Exception trying to get ns %s", e)
                self._ns = None
        if desc is not None:
            assert isinstance(desc, ServerDescriptor)
            self._desc = desc
        else:
            try:
                self._desc = cont.get_server_descriptor(fp, default=None)
            except (DescriptorUnavailable, ControllerError) as e:
                log.exception("Exception trying to get desc %s", e)

    def _from_desc(self, attr):
        if not self._desc:
            return None
        assert hasattr(self._desc, attr)
        return getattr(self._desc, attr)

    def _from_ns(self, attr):
        if not self._ns:
            return None
        assert hasattr(self._ns, attr)
        return getattr(self._ns, attr)

    @property
    def nickname(self):
        return self._from_ns('nickname')

    @property
    def fingerprint(self):
        return self._from_ns('fingerprint')

    @property
    def flags(self):
        return self._from_ns('flags')

    @property
    def exit_policy(self):
        return self._from_desc('exit_policy')

    @property
    def average_bandwidth(self):
        return self._from_desc('average_bandwidth')

    @property
    def bandwidth(self):
        return self._from_ns('bandwidth')

    @property
    def address(self):
        return self._from_ns('address')

    @property
    def master_key_ed25519(self):
        """Obtain ed25519 master key of the relay in server descriptors.

        :returns: str, the ed25519 master key base 64 encoded without
        trailing '='s.
        """
        # Even if this key is called master-key-ed25519 in dir-spec.txt,
        # it seems that stem parses it as ed25519_master_key
        key = self._from_desc('ed25519_master_key')
        if key is None:
            return None
        return key.rstrip('=')

    def can_exit_to(self, host, port):
        '''
        Returns if this relay can MOST LIKELY exit to the given host:port.
        **host** can be a hostname, but be warned that we will resolve it
        locally and use the first (arbitrary/unknown order) result when
        checking exit policies, which is different than what other parts of the
        code may do (leaving it up to the exit to resolve the name).
        '''
        if not self.exit_policy:
            return False
        assert isinstance(host, str)
        assert isinstance(port, int)
        if not is_valid_ipv4_address(host) and not is_valid_ipv6_address(host):
            # It certainly isn't perfect trying to guess if an exit can connect
            # to an ipv4/6 address based on the DNS result we got locally. But
            # it's the best we can do.
            #
            # Also, only use the first ipv4/6 we get even if there is more than
            # one.
            host = resolve(host)[0]
        assert is_valid_ipv4_address(host) or is_valid_ipv6_address(host)
        return self.exit_policy.can_exit_to(host, port)


class RelayList:
    ''' Keeps a list of all relays in the current Tor network and updates it
    transparently in the background. Provides useful interfaces for getting
    only relays of a certain type.
    '''
    REFRESH_INTERVAL = 300  # seconds

    def __init__(self, args, conf, controller):
        self._controller = controller
        self.rng = random.SystemRandom()
        self._refresh_lock = Lock()
        self._refresh()

    def _need_refresh(self):
        return time.time() >= self._last_refresh + self.REFRESH_INTERVAL

    @property
    def relays(self):
        # See if we can get the list of relays without having to do a refresh,
        # which is expensive and blocks other threads
        if self._need_refresh():
            log.debug('We need to refresh our list of relays. '
                      'Going to wait for lock.')
            # Whelp we couldn't just get the list of relays because the list is
            # stale. Wait for the lock so we can refresh it.
            with self._refresh_lock:
                log.debug('We got the lock. Now to see if we still '
                          'need to refresh.')
                # Now we have the lock ... but wait! Maybe someone else already
                # did the refreshing. So check if it still needs refreshing. If
                # not, we can do nothing.
                if self._need_refresh():
                    log.debug('Yup we need to refresh our relays. Doing so.')
                    self._refresh()
                else:
                    log.debug('No we don\'t need to refresh our relays. '
                              'It was done by someone else.')
            log.debug('Giving back the lock for refreshing relays.')
        return self._relays

    @property
    def fast(self):
        return self._relays_with_flag(Flag.FAST)

    @property
    def exits(self):
        return self._relays_with_flag(Flag.EXIT)

    @property
    def bad_exits(self):
        return self._relays_with_flag(Flag.BADEXIT)

    @property
    def non_exits(self):
        return self._relays_without_flag(Flag.EXIT)

    @property
    def guards(self):
        return self._relays_with_flag(Flag.GUARD)

    @property
    def authorities(self):
        return self._relays_with_flag(Flag.AUTHORITY)

    def random_relay(self):
        return self.rng.choice(self.relays)

    def _relays_with_flag(self, flag):
        return [r for r in self.relays if flag in r.flags]

    def _relays_without_flag(self, flag):
        return [r for r in self.relays if flag not in r.flags]

    def _init_relays(self):
        c = self._controller
        try:
            relays = [Relay(ns.fingerprint, c, ns=ns)
                      for ns in c.get_network_statuses()]
        except ControllerError as e:
            log.exception("Exception trying to init relays %s", e)
            return []
        return relays

    def _refresh(self):
        self._relays = self._init_relays()
        self._last_refresh = time.time()