PyLink/protocols/unreal.py

"""
unreal.py: UnrealIRCd 4.0 protocol module for PyLink.
"""

import time
import sys
import os
import codecs
import socket
import re

# Import hacks to access utils and classes...
curdir = os.path.dirname(__file__)
sys.path += [curdir, os.path.dirname(curdir)]

import utils
from log import log
from classes import *
from ts6_common import TS6BaseProtocol

class UnrealProtocol(TS6BaseProtocol):
    def __init__(self, irc):
        super(UnrealProtocol, self).__init__(irc)
        # Set our case mapping (rfc1459 maps "\" and "|" together, for example".
        self.casemapping = 'ascii'
        self.proto_ver = 3999
        self.min_proto_ver = 3999
        self.hook_map = {'UMODE2': 'MODE', 'SVSKILL': 'KILL', 'SVSMODE': 'MODE',
                         'SVS2MODE': 'MODE', 'SJOIN': 'JOIN', 'SETHOST': 'CHGHOST',
                         'SETIDENT': 'CHGIDENT', 'SETNAME': 'CHGNAME',
                         'EOS': 'ENDBURST'}
        self.uidgen = {}
        self.sidgen = utils.TS6SIDGenerator(self.irc)

        self.caps = {}
        self.irc.prefixmodes = {'q': '~', 'a': '&', 'o': '@', 'h': '%', 'v': '+'}
        self._unrealCmodes = {'l': 'limit', 'c': 'blockcolor', 'G': 'censor',
                         'D': 'delayjoin', 'n': 'noextmsg', 's': 'secret',
                         'T': 'nonotice', 'z': 'sslonly', 'b': 'ban', 'V': 'noinvite',
                         'Z': 'issecure', 'r': 'registered', 'N': 'nonick',
                         'e': 'banexception', 'R': 'regonly', 'M': 'regmoderated',
                         'p': 'private', 'Q': 'nokick', 'P': 'permanent', 'k': 'key',
                         'C': 'noctcp', 'O': 'operonly', 'S': 'stripcolor',
                         'm': 'moderated', 'K': 'noknock', 'o': 'op', 'v': 'voice',
                         'I': 'invex', 't': 'topiclock', 'f': 'flood_unreal'}

        self._neededCaps = ["VL", "SID", "CHANMODES", "NOQUIT", "SJ3"]

        # Some command aliases
        self.handle_svskill = self.handle_kill

    ### OUTGOING COMMAND FUNCTIONS
    def spawnClient(self, nick, ident='null', host='null', realhost=None, modes=set(),
            server=None, ip='0.0.0.0', realname=None, ts=None, opertype=None,
            manipulatable=False):
        """Spawns a client with nick <nick> on the given IRC connection.

        Note: No nick collision / valid nickname checks are done here; it is
        up to plugins to make sure they don't introduce anything invalid."""
        server = server or self.irc.sid
        if not self.irc.isInternalServer(server):
            raise ValueError('Server %r is not a PyLink internal PseudoServer!' % server)
        # Unreal 3.4 uses TS6-style UIDs. They don't start from AAAAAA like other IRCd's
        # do, but we can do that fine...
        uid = self.uidgen.setdefault(server, utils.TS6UIDGenerator(server)).next_uid()
        ts = ts or int(time.time())
        realname = realname or self.irc.botdata['realname']
        realhost = realhost or host
        raw_modes = utils.joinModes(modes)
        u = self.irc.users[uid] = IrcUser(nick, ts, uid, ident=ident, host=host, realname=realname,
            realhost=realhost, ip=ip, manipulatable=manipulatable)
        utils.applyModes(self.irc, uid, modes)
        self.irc.servers[server].users.add(uid)

        # UnrealIRCd requires encoding the IP by first packing it into a binary format,
        # and then encoding the binary with Base64.
        if ip == '0.0.0.0':  # Dummy IP (for services, etc.) use a single *.
            encoded_ip = '*'
        else:
            try:  # Try encoding as IPv4 first.
                binary_ip = socket.inet_pton(socket.AF_INET, ip)
            except OSError:
                try:  # That failed, try IPv6 next.
                    binary_ip = socket.inet_pton(socket.AF_INET6, ip)
                except OSError:
                    raise ValueError("Invalid IPv4 or IPv6 address %r." % ip)

            # Encode in Base64.
            encoded_ip = codecs.encode(binary_ip, "base64")
            # Now, strip the trailing \n and decode into a string again.
            encoded_ip = encoded_ip.strip().decode()

        # <- :001 UID GL 0 1441306929 gl localhost 0018S7901 0 +iowx * midnight-1C620195 fwAAAQ== :realname
        self._send(server, "UID {nick} 0 {ts} {ident} {realhost} {uid} 0 {modes} "
                           "{host} * {ip} :{realname}".format(ts=ts, host=host,
                                nick=nick, ident=ident, uid=uid,
                                modes=raw_modes, realname=realname,
                                realhost=realhost, ip=encoded_ip))

        # Force the virtual hostname to show correctly by running SETHOST on
        # the user. Otherwise, Unreal will show the real host of the person
        # instead, which is probably not what we want.
        self.updateClient(uid, 'HOST', host)

        return u

    def joinClient(self, client, channel):
        """Joins a PyLink client to a channel."""
        channel = utils.toLower(self.irc, channel)
        if not self.irc.isInternalClient(client):
            raise LookupError('No such PyLink client exists.')
        self._send(client, "JOIN %s" % channel)
        self.irc.channels[channel].users.add(client)
        self.irc.users[client].channels.add(channel)

    def sjoinServer(self, server, channel, users, ts=None):
        """Sends an SJOIN for a group of users to a channel.

        The sender should always be a server (SID). TS is optional, and defaults
        to the one we've stored in the channel state if not given.
        <users> is a list of (prefix mode, UID) pairs:

        Example uses:
            sjoinServer('100', '#test', [('', '100AAABBC'), ('o', 100AAABBB'), ('v', '100AAADDD')])
            sjoinServer(self.irc.sid, '#test', [('o', self.irc.pseudoclient.uid)])

        Note that for UnrealIRCd, no mode data is sent in an SJOIN command, only
        The channel name, TS, and user list.
        """
        # <- :001 SJOIN 1444361345 #endlessvoid :001DJ1O02
        # The nicklist consists of users joining the channel, with status prefixes for
        # their status ('@+', '@', '+' or ''), for example:
        # '@+1JJAAAAAB +2JJAAAA4C 1JJAAAADS'.
        channel = utils.toLower(self.irc, channel)
        server = server or self.irc.sid
        assert users, "sjoinServer: No users sent?"
        if not server:
            raise LookupError('No such PyLink server exists.')

        orig_ts = self.irc.channels[channel].ts
        ts = ts or orig_ts
        self.updateTS(channel, ts)

        changedmodes = []
        uids = []
        namelist = []
        for userpair in users:
            assert len(userpair) == 2, "Incorrect format of userpair: %r" % userpair
            prefixes, user = userpair
            # Unreal uses slightly different prefixes in SJOIN. +q is * instead of ~,
            # and +a is ~ instead of &.
            # &, ", and ' are used for bursting bans.
            sjoin_prefixes = {'q': '*', 'a': '~', 'o': '@', 'h': '%', 'v': '+'}
            prefixchars = ''.join([sjoin_prefixes.get(prefix, '') for prefix in prefixes])
            if prefixchars:
                changedmodes + [('+%s' % prefix, user) for prefix in prefixes]
            namelist.append(prefixchars+user)
            uids.append(user)
            try:
                self.irc.users[user].channels.add(channel)
            except KeyError:  # Not initialized yet?
                log.debug("(%s) sjoinServer: KeyError trying to add %r to %r's channel list?", self.irc.name, channel, user)
        namelist = ' '.join(namelist)
        self._send(server, "SJOIN {ts} {channel} :{users}".format(
                   ts=ts, users=namelist, channel=channel))
        self.irc.channels[channel].users.update(uids)
        if ts <= orig_ts:
           # Only save our prefix modes in the channel state if our TS is lower than or equal to theirs.
            utils.applyModes(self.irc, channel, changedmodes)

    def pingServer(self, source=None, target=None):
        """Sends a PING to a target server. Periodic PINGs are sent to our uplink
        automatically by the Irc() internals; plugins shouldn't have to use this."""
        source = source or self.irc.sid
        target = target or self.irc.uplink
        if not (target is None or source is None):
            self._send(source, 'PING %s %s' % (self.irc.servers[source].name, self.irc.servers[target].name))

    def killServer(self, numeric, target, reason):
        """Sends a kill from a PyLink server."""
        # <- :GL KILL 38QAAAAAA :hidden-1C620195!GL (test)
        if not self.irc.isInternalServer(numeric):
            raise LookupError('No such PyLink server exists.')

        assert target in self.irc.users, "Unknown target %r for killServer!" % target
        # The killpath doesn't really matter here...
        self._send(numeric, 'KILL %s :%s!PyLink (%s)' % (target, self.irc.serverdata['hostname'], reason))
        self.removeClient(target)

    def killClient(self, numeric, target, reason):
        """Sends a kill from a PyLink client."""
        if not self.irc.isInternalClient(numeric):
            raise LookupError('No such PyLink client exists.')
        assert target in self.irc.users, "Unknown target %r for killClient!" % target
        self._send(numeric, 'KILL %s :%s!PyLink (%s)' % (target, self.irc.serverdata['hostname'], reason))
        self.removeClient(target)

    def _sendModes(self, numeric, target, modes, ts=None):
        """Internal function to send mode changes from a PyLink client/server."""
        # <- :unreal.midnight.vpn MODE #endlessvoid +ntCo GL 1444361345
        utils.applyModes(self.irc, target, modes)
        joinedmodes = utils.joinModes(modes)
        if utils.isChannel(target):
            # The MODE command is used for channel mode changes only
            ts = ts or self.irc.channels[utils.toLower(self.irc, target)].ts
            self._send(numeric, 'MODE %s %s %s' % (target, joinedmodes, ts))
        else:
            # For user modes, the only way to set modes (for non-U:Lined servers)
            # is through UMODE2, which sets the modes on the caller.
            # U:Lines can use SVSMODE/SVS2MODE, but I won't expect people to
            # U:Line a PyLink daemon...
            if not self.irc.isInternalClient(target):
                raise ProtocolError('Cannot force mode change on external clients!')
            self._send(target, 'UMODE2 %s' % joinedmodes)

    def modeClient(self, numeric, target, modes, ts=None):
        """
        Sends mode changes from a PyLink client. The mode list should be
        a list of (mode, arg) tuples, i.e. the format of utils.parseModes() output.
        """
        if not self.irc.isInternalClient(numeric):
            raise LookupError('No such PyLink client exists.')
        self._sendModes(numeric, target, modes, ts=ts)

    def modeServer(self, numeric, target, modes, ts=None):
        """
        Sends mode changes from a PyLink server. The mode list should be
        a list of (mode, arg) tuples, i.e. the format of utils.parseModes() output.
        """
        if not self.irc.isInternalServer(numeric):
            raise LookupError('No such PyLink server exists.')
        self._sendModes(numeric, target, modes, ts=ts)

    def topicServer(self, numeric, target, text):
        """Sends a TOPIC change from a PyLink server."""
        if not self.irc.isInternalServer(numeric):
            raise LookupError('No such PyLink server exists.')
        self._send(numeric, 'TOPIC %s :%s' % (target, text))
        self.irc.channels[target].topic = text
        self.irc.channels[target].topicset = True

    def updateClient(self, target, field, text):
        """Updates the ident, host, or realname of any connected client."""
        field = field.upper()

        if field not in ('IDENT', 'HOST', 'REALNAME', 'GECOS'):
            raise NotImplementedError("Changing field %r of a client is "
                                      "unsupported by this protocol." % field)

        if self.irc.isInternalClient(target):
            # It is one of our clients, use SETIDENT/HOST/NAME.
            if field == 'IDENT':
                self.irc.users[target].ident = text
                self._send(target, 'SETIDENT %s' % text)
            elif field == 'HOST':
                self.irc.users[target].host = text
                self._send(target, 'SETHOST %s' % text)
            elif field in ('REALNAME', 'GECOS'):
                self.irc.users[target].realname = text
                self._send(target, 'SETNAME :%s' % text)
        else:
            # It is a client on another server, use CHGIDENT/HOST/NAME.
            if field == 'IDENT':
                self.irc.users[target].ident = text
                self._send(self.irc.sid, 'CHGIDENT %s %s' % (target, text))

                # Send hook payloads for other plugins to listen to.
                self.irc.callHooks([self.irc.sid, 'CHGIDENT',
                                   {'target': target, 'newident': text}])

            elif field == 'HOST':
                self.irc.users[target].host = text
                self._send(self.irc.sid, 'CHGHOST %s %s' % (target, text))

                self.irc.callHooks([self.irc.sid, 'CHGHOST',
                                   {'target': target, 'newhost': text}])

            elif field in ('REALNAME', 'GECOS'):
                self.irc.users[target].realname = text
                self._send(self.irc.sid, 'CHGNAME %s :%s' % (target, text))

                self.irc.callHooks([self.irc.sid, 'CHGNAME',
                                   {'target': target, 'newgecos': text}])

    def inviteClient(self, numeric, target, channel):
        """Sends an INVITE from a PyLink client.."""
        if not self.irc.isInternalClient(numeric):
            raise LookupError('No such PyLink client exists.')
        self._send(numeric, 'INVITE %s %s' % (target, channel))

    def knockClient(self, numeric, target, text):
        """Sends a KNOCK from a PyLink client."""
        # KNOCKs in UnrealIRCd are actually just specially formatted NOTICEs,
        # sent to all ops in a channel.
        # <- :unreal.midnight.vpn NOTICE @#test :[Knock] by GL|!gl@hidden-1C620195 (test)
        assert utils.isChannel(target), "Can only knock on channels!"
        sender = self.irc.getServer(numeric)
        s = '[Knock] by %s (%s)' % (utils.getHostmask(self.irc, numeric), text)
        self._send(sender, 'NOTICE @%s :%s' % (target, s))

    ### HANDLERS

    def connect(self):
        """Initializes a connection to a server."""
        ts = self.irc.start_ts
        self.irc.prefixmodes = {'q': '~', 'a': '&', 'o': '@', 'h': '%', 'v': '+'}

        self.irc.umodes.update({'deaf': 'd', 'invisible': 'i', 'hidechans': 'p',
                                'protected': 'q', 'registered': 'r',
                                'snomask': 's', 'vhost': 't', 'wallops': 'w',
                                'bot': 'B', 'cloak': 'x', 'ssl': 'z',
                                'filter': 'G', 'hideoper': 'H', 'hideidle': 'I',
                                'regdeaf': 'R', 'servprotect': 'S',
                                'u_noctcp': 'T', 'showwhois': 'W',
                                '*A': '', '*B': '', '*C': '', '*D': 'dipqrstwBxzGHIRSTW'})

        f = self.irc.send
        host = self.irc.serverdata["hostname"]

        f('PASS :%s' % self.irc.serverdata["sendpass"])
        # https://github.com/unrealself.ircd/unrealself.ircd/blob/2f8cb55e/doc/technical/protoctl.txt
        # We support the following protocol features:
        # SJ3 - extended SJOIN
        # NOQUIT - QUIT messages aren't sent for all users in a netsplit
        # NICKv2 - Extended NICK command, sending MODE and CHGHOST info with it
        # SID - Use UIDs and SIDs (unreal 3.4)
        # VL - Sends version string in below SERVER message
        # UMODE2 - used for users setting modes on themselves (one less argument needed)
        # EAUTH - Early auth? (Unreal 3.4 linking protocol)
        f('PROTOCTL SJ3 NOQUIT NICKv2 VL UMODE2 PROTOCTL EAUTH=%s SID=%s' % (self.irc.serverdata["hostname"], self.irc.sid))
        sdesc = self.irc.serverdata.get('serverdesc') or self.irc.botdata['serverdesc']
        f('SERVER %s 1 U%s-h6e-%s :%s' % (host, self.proto_ver, self.irc.sid, sdesc))
        f('NETINFO 1 %s %s * 0 0 0 :%s' % (self.irc.start_ts, self.proto_ver, self.irc.serverdata.get("netname", self.irc.name)))
        self._send(self.irc.sid, 'EOS')

    def handle_eos(self, numeric, command, args):
        """EOS is used to denote end of burst."""
        return {}

    def handle_uid(self, numeric, command, args):
        # <- :001 UID GL 0 1441306929 gl localhost 0018S7901 0 +iowx * midnight-1C620195 fwAAAQ== :realname
        # <- :001 UID GL| 0 1441389007 gl 10.120.0.6 001ZO8F03 0 +iwx * 391A9CB9.26A16454.D9847B69.IP CngABg== :realname
        # arguments: nick, hopcount???, ts, ident, real-host, UID, number???, modes,
        #            displayed host, cloaked (+x) host, base64-encoded IP, and realname
        # TODO: find out what all the "???" fields mean.
        nick = args[0]
        ts, ident, realhost, uid = args[2:6]
        modestring = args[7]
        host = args[8]
        if host == '*':
            # A single * means that there is no displayed/virtual host, and
            # that it's the same as the real host
            host = args[9]
        raw_ip = args[10].encode()  # codecs.decode only takes bytes, not str
        if raw_ip == b'*':  # Dummy IP (for services, etc.)
            ip = '0.0.0.0'
        else:
            # First, decode the Base64 string into a packed binary IP address.
            ip = codecs.decode(raw_ip, "base64")

            try:  # IPv4 address.
                ip = socket.inet_ntop(socket.AF_INET, ip)
            except ValueError:  # IPv6 address.
                ip = socket.inet_ntop(socket.AF_INET6, ip)
                # HACK: make sure a leading ":" in the IPv6 address (e.g. ::1)
                # doesn't cause it to be misinterpreted as the last argument
                # in a line, should it be mirrored to other networks.
                if ip.startswith(':'):
                    ip = '0' + ip
            else:
                raise ProtocolError("Invalid number of bits in IP address field (got %s, expected 4 or 16)." % len(ipbits))
        realname = args[-1]

        self.irc.users[uid] = IrcUser(nick, ts, uid, ident, host, realname, realhost, ip)
        self.irc.servers[numeric].users.add(uid)

        parsedmodes = utils.parseModes(self.irc, uid, [modestring])
        utils.applyModes(self.irc, uid, parsedmodes)

        # The cloaked (+x) host is completely separate from the displayed host
        # and real host in that it is ONLY shown if the user is +x (cloak mode
        # enabled) but NOT +t (vHost set). We'll store this separately for now,
        # but more handling is needed so that plugins can update the cloak host
        # appropriately.
        self.irc.users[uid].cloaked_host = args[9]

        if ('+o', None) in parsedmodes:
            # If +o being set, call the CLIENT_OPERED internal hook.
            self.irc.callHooks([uid, 'CLIENT_OPERED', {'text': 'IRC_Operator'}])

        if ('+x', None) not in parsedmodes:
            # If +x is not set, update to use the person's real host.
            self.updateClient(uid, 'HOST', realhost)

        return {'uid': uid, 'ts': ts, 'nick': nick, 'realhost': realhost, 'host': host, 'ident': ident, 'ip': ip}

    def handle_pass(self, numeric, command, args):
        # <- PASS :abcdefg
        if args[0] != self.irc.serverdata['recvpass']:
            raise ProtocolError("Error: RECVPASS from uplink does not match configuration!")

    def handle_ping(self, numeric, command, args):
        if numeric == self.irc.uplink:
            self.irc.send('PONG %s :%s' % (self.irc.serverdata['hostname'], args[-1]))

    def handle_pong(self, source, command, args):
        log.debug('(%s) Ping received from %s for %s.', self.irc.name, source, args[-1])
        if source in (self.irc.uplink, self.irc.servers[self.irc.uplink].name) and args[-1] == self.irc.serverdata['hostname']:
            log.debug('(%s) Set self.irc.lastping.', self.irc.name)
            self.irc.lastping = time.time()

    def handle_server(self, numeric, command, args):
        """Handles the SERVER command, which is used for both authentication and
        introducing legacy (non-SID) servers."""
        # <- SERVER unreal.midnight.vpn 1 :U3999-Fhin6OoEM UnrealIRCd test server
        sname = args[0]
        if numeric == self.irc.uplink:  # We're doing authentication
            for cap in self._neededCaps:
                if cap not in self.caps:
                    raise ProtocolError("Not all required capabilities were met "
                                        "by the remote server. Your version of UnrealIRCd "
                                        "is probably too old! (Got: %s, needed: %s)" %
                                        (sorted(self.caps.keys()),
                                         sorted(_neededCaps)))
            sdesc = args[-1].split(" ")
            # Get our protocol version :)
            vline = sdesc[0].split('-', 1)
            try:
                protover = int(vline[0].strip('U'))
            except ValueError:
                raise ProtocolError("Protocol version too old! (needs at least %s "
                                    "(Unreal 4.0.0-rc1), got something invalid; "
                                    "is VL being sent?)" % self.min_proto_ver)
            sdesc = args[-1][1:]
            if protover < self.min_proto_ver:
                raise ProtocolError("Protocol version too old! (needs at least %s "
                                    "(Unreal 4.0.0-rc1), got %s)" % (self.min_proto_ver, protover))
            self.irc.servers[numeric] = IrcServer(None, sname)
        else:
            # Legacy (non-SID) servers can still be introduced using the SERVER command.
            # <- :services.int SERVER a.bc 2 :(H) [GL] a
            servername = args[0].lower()
            sdesc = args[-1]
            self.irc.servers[servername] = IrcServer(numeric, servername, desc=sdesc)
            return {'name': servername, 'sid': None, 'text': sdesc}

    def handle_sid(self, numeric, command, args):
        """Handles the SID command, used for introducing remote servers by our uplink."""
        # <- SID services.int 2 00A :Shaltúre IRC Services
        sname = args[0].lower()
        sid = args[2]
        sdesc = args[-1]
        self.irc.servers[sid] = IrcServer(numeric, sname, desc=sdesc)
        return {'name': sname, 'sid': sid, 'text': sdesc}

    def handle_squit(self, numeric, command, args):
        """Handles the SQUIT command."""
        # <- SQUIT services.int :Read error
        # Convert the server name to a SID...
        args[0] = self._getSid(args[0])
        # Then, use the SQUIT handler in TS6BaseProtocol as usual.
        return super(UnrealProtocol, self).handle_squit(numeric, 'SQUIT', args)

    def handle_protoctl(self, numeric, command, args):
        # <- PROTOCTL NOQUIT NICKv2 SJOIN SJOIN2 UMODE2 VL SJ3 TKLEXT TKLEXT2 NICKIP ESVID
        # <- PROTOCTL CHANMODES=beI,k,l,psmntirzMQNRTOVKDdGPZSCc NICKCHARS= SID=001 MLOCK TS=1441314501 EXTSWHOIS
        for cap in args:
            if cap.startswith('SID'):
                self.irc.uplink = cap.split('=', 1)[1]
                self.caps['SID'] = True
            elif cap.startswith('CHANMODES'):
                cmodes = cap.split('=', 1)[1]
                self.irc.cmodes['*A'], self.irc.cmodes['*B'], self.irc.cmodes['*C'], self.irc.cmodes['*D'] = cmodes.split(',')
                for m in cmodes:
                    if m in self._unrealCmodes:
                        self.irc.cmodes[self._unrealCmodes[m]] = m
                self.caps['CHANMODES'] = True
                self.irc.cmodes['*B'] += 'f'  # Add +f to the list too, dunno why it isn't there.
            # Because more than one PROTOCTL line is sent, we have to delay the
            # check to see whether our needed capabilities are all there...
            # That's done by handle_server(), which comes right after PROTOCTL.
            elif cap == 'VL':
                self.caps['VL'] = True
            elif cap == 'NOQUIT':
                self.caps['NOQUIT'] = True
            elif cap == 'SJ3':
                self.caps['SJ3'] = True
        self.irc.cmodes.update({'halfop': 'h', 'admin': 'a', 'owner': 'q',
                                'op': 'o', 'voice': 'v'})

        # Set irc.connected to True, meaning that protocol negotiation passed.
        log.debug('(%s) self.irc.connected set!', self.irc.name)
        self.irc.connected.set()

    def _getNick(self, target):
        """Converts a nick argument to its matching UID. This differs from irc.nickToUid()
        in that it returns the original text instead of None, if no matching nick is found."""
        target = self.irc.nickToUid(target) or target
        if target not in self.irc.users and not utils.isChannel(target):
            log.debug("(%s) Possible desync? Got command target %s, who "
                        "isn't in our user list!", self.irc.name, target)
        return target

    def handle_events(self, data):
        """Event handler for the UnrealIRCd 3.4+ protocol.

        This passes most commands to the various handle_ABCD() functions
        elsewhere in this module, coersing various sender prefixes from nicks
        to UIDs wherever possible.

        Unreal 3.4's protocol operates similarly to TS6, where lines can have :
        indicating a long argument lasting to the end of the line. Not all commands
        send an explicit sender prefix, in which case, it will be set to the SID
        of the uplink server.
        """
        data = data.split(" ")
        try:  # Message starts with a SID/UID prefix.
            args = self.parseTS6Args(data)
            sender = args[0]
            command = args[1]
            args = args[2:]
            # If the sender isn't in UID format, try to convert it automatically.
            # Unreal's protocol isn't quite consistent with this yet!
            sender_server = self._getSid(sender)
            if sender_server in self.irc.servers:
                # Sender is a server when converted from name to SID.
                numeric = sender_server
            else:
                # Sender is a user.
                numeric = self._getNick(sender)
        # parseTS6Args() will raise IndexError if the TS6 sender prefix is missing.
        except IndexError:
            # Raw command without an explicit sender; assume it's being sent by our uplink.
            args = self.parseArgs(data)
            numeric = self.irc.uplink
            command = args[0]
            args = args[1:]
        try:
            func = getattr(self, 'handle_'+command.lower())
        except AttributeError:  # unhandled command
            pass
        else:
            parsed_args = func(numeric, command, args)
            if parsed_args is not None:
                return [numeric, command, parsed_args]

    def handle_privmsg(self, source, command, args):
        # Convert nicks to UIDs, where they exist.
        target = self._getNick(args[0])
        # We use lowercase channels internally, but uppercase UIDs.
        if utils.isChannel(target):
            target = utils.toLower(self.irc, target)
        return {'target': target, 'text': args[1]}
    handle_notice = handle_privmsg

    def handle_join(self, numeric, command, args):
        """Handles the UnrealIRCd JOIN command."""
        # <- :GL JOIN #pylink,#test
        for channel in args[0].split(','):
            c = self.irc.channels[channel]
            if args[0] == '0':
                # /join 0; part the user from all channels
                oldchans = self.irc.users[numeric].channels.copy()
                log.debug('(%s) Got /join 0 from %r, channel list is %r',
                          self.irc.name, numeric, oldchans)
                for ch in oldchans:
                    self.irc.channels[ch].users.discard(numeric)
                    self.irc.users[numeric].channels.discard(ch)
                return {'channels': oldchans, 'text': 'Left all channels.', 'parse_as': 'PART'}

            self.irc.users[numeric].channels.add(channel)
            self.irc.channels[channel].users.add(numeric)
            # Call hooks manually, because one JOIN command in UnrealIRCd can
            # have multiple channels...
            self.irc.callHooks([numeric, command, {'channel': channel, 'users': [numeric], 'modes':
                                                   c.modes, 'ts': c.ts}])

    def handle_sjoin(self, numeric, command, args):
        """Handles the UnrealIRCd SJOIN command."""
        # <- :001 SJOIN 1444361345 #endlessvoid :001DJ1O02
        # memberlist should be a list of UIDs with their channel status prefixes, as
        # in ":001AAAAAA @001AAAAAB +001AAAAAC".
        # Interestingly, no modes are ever sent in this command as far as I've seen.
        channel = utils.toLower(self.irc, args[1])
        userlist = args[-1].split()

        our_ts = self.irc.channels[channel].ts
        their_ts = int(args[0])
        self.updateTS(channel, their_ts)

        namelist = []
        log.debug('(%s) handle_sjoin: got userlist %r for %r', self.irc.name, userlist, channel)
        for userpair in userlist:
            if userpair.startswith("&\"'"):  # TODO: handle ban bursts too
                # &, ", and ' entries are used for bursting bans:
                # https://www.unrealircd.org/files/docs/technical/serverprotocol.html#S5_1
                break
            r = re.search(r'([^\d]*)(.*)', userpair)
            user = r.group(2)
            # Unreal uses slightly different prefixes in SJOIN. +q is * instead of ~,
            # and +a is ~ instead of &.
            modeprefix = (r.group(1) or '').replace("~", "&").replace("*", "~")
            finalprefix = ''
            assert user, 'Failed to get the UID from %r; our regex needs updating?' % userpair
            log.debug('(%s) handle_sjoin: got modeprefix %r for user %r', self.irc.name, modeprefix, user)
            for m in modeprefix:
                # Iterate over the mapping of prefix chars to prefixes, and
                # find the characters that match.
                for char, prefix in self.irc.prefixmodes.items():
                    if m == prefix:
                        finalprefix += char
            namelist.append(user)
            self.irc.users[user].channels.add(channel)
            # Only merge the remote's prefix modes if their TS is smaller or equal to ours.
            if their_ts <= our_ts:
                utils.applyModes(self.irc, channel, [('+%s' % mode, user) for mode in finalprefix])
            self.irc.channels[channel].users.add(user)
        return {'channel': channel, 'users': namelist, 'modes': self.irc.channels[channel].modes, 'ts': their_ts}

    def handle_mode(self, numeric, command, args):
        # <- :unreal.midnight.vpn MODE #endlessvoid +bb test!*@* *!*@bad.net
        # <- :unreal.midnight.vpn MODE #endlessvoid +q GL 1444361345
        # <- :unreal.midnight.vpn MODE #endlessvoid +ntCo GL 1444361345
        # <- :unreal.midnight.vpn MODE #endlessvoid +mntClfo 5 [10t]:5  GL 1444361345
        # <- :GL MODE #services +v GL

        # This seems pretty relatively inconsistent - why do some commands have a TS at the end while others don't?
        # Answer: the first syntax (MODE sent by SERVER) is used for channel bursts - according to Unreal 3.2 docs,
        # the last argument should be interpreted as a timestamp ONLY if it is a number and the sender is a server.
        # Ban bursting does not give any TS, nor do normal users setting modes. SAMODE is special though, it will
        # send 0 as a TS argument (which should be ignored unless breaking the internal channel TS is desired).

        # Also, we need to get rid of that extra space following the +f argument. :|
        if utils.isChannel(args[0]):
            channel = utils.toLower(self.irc, args[0])
            oldobj = self.irc.channels[channel].deepcopy()
            modes = list(filter(None, args[1:]))  # normalize whitespace
            parsedmodes = utils.parseModes(self.irc, channel, modes)
            if parsedmodes:
                utils.applyModes(self.irc, channel, parsedmodes)
            if numeric in self.irc.servers and args[-1].isdigit():
                # Sender is a server AND last arg is number. Perform TS updates.
                their_ts = int(args[-1])
                if their_ts > 0:
                    self.updateTS(channel, their_ts)
            return {'target': channel, 'modes': parsedmodes, 'oldchan': oldobj}
        else:
            log.warning("(%s) received MODE for non-channel target: %r",
                        self.irc.name, args)
            raise NotImplementedError

    def checkCloakChange(self, uid, parsedmodes):
        """
        Checks whether +x/-x was set in the mode query, and changes the
        hostname of the user given to or from their cloaked host if True.
        """

        userobj = self.irc.users[uid]
        final_modes = userobj.modes
        oldhost = userobj.host

        if (('+x', None) in parsedmodes and ('t', None) not in final_modes) \
                or (('-t', None) in parsedmodes and ('x', None) in final_modes):
            # If either:
            #    1) +x is being set, and the user does NOT have +t.
            #    2) -t is being set, but the user has +x set already.
            # We should update the user's host to their cloaked host and send
            # out a hook payload saying that the host has changed.
            newhost = userobj.host = userobj.cloaked_host
        elif ('-x', None) in parsedmodes or ('-t', None) in parsedmodes:
            # Otherwise, if either:
            #    1) -x is being set.
            #    2) -t is being set, but the person doesn't have +x set already.
            #       (the case where the person DOES have +x is handled above)
            # Restore the person's host to the uncloaked real host.
            newhost = userobj.host = userobj.realhost
        else:
            # Nothing changed, just return.
            return

        if newhost != oldhost:
            # Only send a payload if the old and new hosts are different.
            self.irc.callHooks([uid, 'SETHOST',
                               {'target': uid, 'newhost': newhost}])

    def handle_svsmode(self, numeric, command, args):
        """Handle SVSMODE/SVS2MODE, used for setting user modes on others (services)."""
        # <- :source SVSMODE target +usermodes
        target = self._getNick(args[0])
        modes = args[1:]

        parsedmodes = utils.parseModes(self.irc, target, modes)
        utils.applyModes(self.irc, target, parsedmodes)

        # If +x/-x is being set, update cloaked host info.
        self.checkCloakChange(numeric, parsedmodes)

        return {'target': numeric, 'modes': parsedmodes}
    handle_svs2mode = handle_svsmode

    def handle_umode2(self, numeric, command, args):
        """Handles UMODE2, used to set user modes on oneself."""
        # <- :GL UMODE2 +W
        parsedmodes = utils.parseModes(self.irc, numeric, args)
        utils.applyModes(self.irc, numeric, parsedmodes)

        if ('+o', None) in parsedmodes:
            # If +o being set, call the CLIENT_OPERED internal hook.
            self.irc.callHooks([uid, 'CLIENT_OPERED', {'text': 'IRC_Operator'}])

        self.checkCloakChange(numeric, parsedmodes)

        return {'target': numeric, 'modes': parsedmodes}

    def handle_topic(self, numeric, command, args):
        """Handles the TOPIC command."""
        # <- GL TOPIC #services GL 1444699395 :weeee
        channel = utils.toLower(self.irc, args[0])
        topic = args[-1]
        ts = args[2]
        oldtopic = self.irc.channels[channel].topic
        self.irc.channels[channel].topic = topic
        self.irc.channels[channel].topicset = True
        return {'channel': channel, 'setter': numeric, 'ts': ts, 'text': topic,
                'oldtopic': oldtopic}

    def handle_whois(self, numeric, command, args):
        """Handles WHOIS queries."""
        # <- :GL WHOIS PyLink-devel :pylink-devel
        # In this case, the first argument is actually the server that the
        # WHOIS query is requested from - IRCds should pass these requests on
        # to the server in question. Since we're a services server, we can just
        # process it regardless.
        # The second argument is the ACTUAL nick requested.

        # The actual WHOIS handling is done protocol-independently by coreplugin.
        return {'target': self._getNick(args[-1])}

    def handle_setident(self, numeric, command, args):
        """Handles SETIDENT, used for self ident changes."""
        # <- :70MAAAAAB SETIDENT test
        self.irc.users[numeric].ident = newident = args[0]
        return {'target': numeric, 'newident': newident}

    def handle_sethost(self, numeric, command, args):
        """Handles CHGHOST, used for self hostname changes."""
        # <- :70MAAAAAB SETIDENT some.host
        self.irc.users[numeric].host = newhost = args[0]

        # When SETHOST or CHGHOST is used, modes +xt are implicitly set on the
        # target.
        utils.applyModes(self.irc, numeric, [('+x', None), ('+t', None)])

        return {'target': numeric, 'newhost': newhost}

    def handle_setname(self, numeric, command, args):
        """Handles SETNAME, used for self real name/gecos changes."""
        # <- :70MAAAAAB SETNAME :afdsafasf
        self.irc.users[numeric].realname = newgecos = args[0]
        return {'target': numeric, 'newgecos': newgecos}

    def handle_chgident(self, numeric, command, args):
        """Handles CHGIDENT, used for denoting ident changes."""
        # <- :GL CHGIDENT GL test
        target = self._getNick(args[0])
        self.irc.users[target].ident = newident = args[1]
        return {'target': target, 'newident': newident}

    def handle_chghost(self, numeric, command, args):
        """Handles CHGHOST, used for denoting hostname changes."""
        # <- :GL CHGHOST GL some.host
        target = self._getNick(args[0])
        self.irc.users[target].host = newhost = args[1]

        # When SETHOST or CHGHOST is used, modes +xt are implicitly set on the
        # target.
        utils.applyModes(self.irc, target, [('+x', None), ('+t', None)])

        return {'target': target, 'newhost': newhost}

    def handle_chgname(self, numeric, command, args):
        """Handles CHGNAME, used for denoting real name/gecos changes."""
        # <- :GL CHGNAME GL :afdsafasf
        target = self._getNick(args[0])
        self.irc.users[target].realname = newgecos = args[1]
        return {'target': target, 'newgecos': newgecos}

    def handle_invite(self, numeric, command, args):
        """Handles incoming INVITEs."""
        # <- :GL INVITE PyLink-devel :#a
        target = self._getNick(args[0])
        channel = args[1].lower()
        # We don't actually need to process this; it's just something plugins/hooks can use
        return {'target': target, 'channel': channel}

Class = UnrealProtocol