PyLink/plugins/relay.py

# relay.py: PyLink Relay plugin
import sys
import os
sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))

import pickle
import time
import threading
import string
from collections import defaultdict

import utils
from log import log
import world

### GLOBAL (statekeeping) VARIABLES
relayusers = defaultdict(dict)
relayservers = defaultdict(dict)
spawnlocks = defaultdict(threading.RLock)
spawnlocks_servers = defaultdict(threading.RLock)

exportdb_timer = None

dbname = utils.getDatabaseName('pylinkrelay')

### INTERNAL FUNCTIONS

def initializeAll(irc):
    """Initializes all relay channels for the given IRC object."""

    # Wait for all IRC objects to be created first. This prevents
    # relay servers from being spawned too early (before server authentication),
    # which would break connections.
    world.started.wait(2)

    for chanpair, entrydata in db.items():
        # Iterate over all the channels stored in our relay links DB.
        network, channel = chanpair

        # Initialize each relay channel on their home network, and on every linked one too.
        initializeChannel(irc, channel)
        for link in entrydata['links']:
            network, channel = link
            initializeChannel(irc, channel)

def main(irc=None):
    """Main function, called during plugin loading at start."""

    # Load the relay links database.
    loadDB()

    # Schedule periodic exports of the links database.
    scheduleExport(starting=True)

    if irc is not None:
        # irc is defined when the plugin is reloaded. Otherweise,
        # it means that we've just started the server.
        # Iterate over all known networks and initialize them.
        for ircobj in world.networkobjects.values():
            initializeAll(ircobj)

def die(sourceirc):
    """Deinitialize PyLink Relay by quitting all relay clients and saving the
    relay DB."""

    # For every connected network:
    for irc in world.networkobjects.values():
        # 1) Find all the relay clients and quit them.
        for user in irc.users.copy():
            if isRelayClient(irc, user):
                irc.proto.quit(user, "Relay plugin unloaded.")

        # 2) SQUIT every relay subserver.
        for server, sobj in irc.servers.copy().items():
            if hasattr(sobj, 'remote'):
                irc.proto.squit(irc.sid, server, text="Relay plugin unloaded.")

    # 3) Clear our internal servers and users caches.
    relayservers.clear()
    relayusers.clear()

    # 4) Export the relay links database.
    exportDB()

    # 5) Kill the scheduling for any other exports.
    global exportdb_timer
    if exportdb_timer:
        log.debug("Relay: cancelling exportDB timer thread %s due to die()", threading.get_ident())
        exportdb_timer.cancel()

def normalizeNick(irc, netname, nick, separator=None, uid=''):
    """Creates a normalized nickname for the given nick suitable for
    introduction to a remote network (as a relay client)."""
    separator = separator or irc.serverdata.get('separator') or "/"
    log.debug('(%s) relay.normalizeNick: using %r as separator.', irc.name, separator)
    orig_nick = nick
    protoname = irc.protoname
    maxnicklen = irc.maxnicklen
    if '/' not in separator or not protoname.startswith(('insp', 'unreal')):
        # Charybdis doesn't allow / in usernames, and will SQUIT with
        # a protocol violation if it sees one.
        separator = separator.replace('/', '|')
        nick = nick.replace('/', '|')
    if nick.startswith(tuple(string.digits)):
        # On TS6 IRCds, nicks that start with 0-9 are only allowed if
        # they match the UID of the originating server. Otherwise, you'll
        # get nasty protocol violation SQUITs!
        nick = '_' + nick
    tagnicks = True

    suffix = separator + netname
    nick = nick[:maxnicklen]
    # Maximum allowed length of a nickname, minus the obligatory /network tag.
    allowedlength = maxnicklen - len(suffix)

    # If a nick is too long, the real nick portion will be cut off, but the
    # /network suffix MUST remain the same.
    nick = nick[:allowedlength]
    nick += suffix

    # The nick we want exists? Darn, create another one then.
    # Increase the separator length by 1 if the user was already tagged,
    # but couldn't be created due to a nick conflict.
    # This can happen when someone steals a relay user's nick.

    # However, if the user is changing from, say, a long, cut-off nick to another long,
    # cut-off nick, we don't need to check for duplicates and tag the nick twice.

    # somecutoffnick/net would otherwise be erroneous NICK'ed to somecutoffnic//net,
    # even though there would be no collision because the old and new nicks are from
    # the same client.
    while irc.nickToUid(nick) and irc.nickToUid(nick) != uid:
        new_sep = separator + separator[-1]
        log.debug('(%s) relay.normalizeNick: nick %r is in use; using %r as new_sep.', irc.name, nick, new_sep)
        nick = normalizeNick(irc, netname, orig_nick, separator=new_sep)
    finalLength = len(nick)
    assert finalLength <= maxnicklen, "Normalized nick %r went over max " \
        "nick length (got: %s, allowed: %s!)" % (nick, finalLength, maxnicklen)

    return nick

def normalizeHost(irc, host):
    """Creates a normalized hostname for the given host suitable for
    introduction to a remote network (as a relay client)."""
    if irc.protoname == 'unreal':
        # UnrealIRCd doesn't allow slashes in hostnames
        host = host.replace('/', '.')
    return host[:64]  # Limited to 64 chars

def loadDB():
    """Loads the relay database, creating a new one if this fails."""
    global db
    try:
        with open(dbname, "rb") as f:
            db = pickle.load(f)
    except (ValueError, IOError, OSError):
        log.info("Relay: failed to load links database %s"
                 ", creating a new one in memory...", dbname)
        db = {}

def exportDB():
    """Exports the relay database."""

    log.debug("Relay: exporting links database to %s", dbname)
    with open(dbname, 'wb') as f:
        pickle.dump(db, f, protocol=4)

def scheduleExport(starting=False):
    """
    Schedules exporting of the relay database in a repeated loop.
    """
    global exportdb_timer

    if not starting:
        # Export the database, unless this is being called the first
        # thing after start (i.e. DB has just been loaded).
        exportDB()

    # TODO: possibly make delay between exports configurable
    exportdb_timer = threading.Timer(30, scheduleExport)
    exportdb_timer.name = 'PyLink Relay exportDB Loop'
    exportdb_timer.start()

def getPrefixModes(irc, remoteirc, channel, user, mlist=None):
    """
    Fetches all prefix modes for a user in a channel that are supported by the
    remote IRC network given.

    Optionally, an mlist argument can be given to look at an earlier state of
    the channel, e.g. for checking the op status of a mode setter before their
    modes are processed and added to the channel state.
    """
    modes = ''

    if user in irc.channels[channel].users:
        # Iterate over the the prefix modes for relay supported by IRCd
        for pmode in irc.channels[channel].getPrefixModes(user, prefixmodes=mlist):
            if pmode in remoteirc.cmodes:
                modes += remoteirc.cmodes[pmode]
    return modes

def getRemoteSid(irc, remoteirc):
    """Gets the remote server SID representing remoteirc on irc, spawning
    it if it doesn't exist."""
    # Don't spawn servers too early.
    irc.connected.wait(2)

    try:
        spawnservers = irc.conf['relay']['spawn_servers']
    except KeyError:
        spawnservers = True
    if not spawnservers:
        return irc.sid
    with spawnlocks_servers[irc.name]:
        try:
            sid = relayservers[irc.name][remoteirc.name]
        except KeyError:
            try:
                # ENDBURST is delayed by 3 secs on supported IRCds to prevent
                # triggering join-flood protection and the like.
                sid = irc.proto.spawnServer('%s.relay' % remoteirc.name,
                                            desc="PyLink Relay network - %s" %
                                            (remoteirc.serverdata.get('netname')\
                                            or remoteirc.name), endburst_delay=3)
            except ValueError:  # Network not initialized yet, or a server name conflict.
                log.exception('(%s) Failed to spawn server for %r:',
                              irc.name, remoteirc.name)
                # We will just bail here. Disconnect the bad network.
                handle_disconnect(irc, None, 'PYLINK_DISCONNECT_RELAY_FORCED', {})
                irc.disconnect()
                raise
            else:
                irc.servers[sid].remote = remoteirc.name
            relayservers[irc.name][remoteirc.name] = sid
        return sid

def getRemoteUser(irc, remoteirc, user, spawnIfMissing=True):
    """Gets the UID of the relay client for the given IRC network/user pair,
    spawning one if it doesn't exist and spawnIfMissing is True."""
    # If the user (stored here as {('netname', 'UID'):
    # {'network1': 'UID1', 'network2': 'UID2'}}) exists, don't spawn it
    # again!
    try:
        if user == irc.pseudoclient.uid:
            return remoteirc.pseudoclient.uid
    except AttributeError:  # Network hasn't been initialized yet?
        pass
    with spawnlocks[irc.name]:
        try:
            u = relayusers[(irc.name, user)][remoteirc.name]
        except KeyError:
            userobj = irc.users.get(user)
            if userobj is None or (not spawnIfMissing) or (not remoteirc.connected.is_set()):
                # The query wasn't actually a valid user, or the network hasn't
                # been connected yet... Oh well!
                return
            nick = normalizeNick(remoteirc, irc.name, userobj.nick)
            # Truncate idents at 10 characters, because TS6 won't like them otherwise!
            ident = userobj.ident[:10]
            # Normalize hostnames
            host = normalizeHost(remoteirc, userobj.host)
            realname = userobj.realname
            modes = set(getSupportedUmodes(irc, remoteirc, userobj.modes))
            opertype = ''
            if ('o', None) in userobj.modes:
                if hasattr(userobj, 'opertype'):
                    # InspIRCd's special OPERTYPE command; this is mandatory
                    # and setting of umode +/-o will fail unless this
                    # is used instead. This also sets an oper type for
                    # the user, which is used in WHOIS, etc.

                    # If an opertype exists for the user, add " (remote)"
                    # for the relayed clone, so that it shows in whois.
                    # Janus does this too. :)
                    log.debug('(%s) relay.getRemoteUser: setting OPERTYPE of client for %r to %s',
                              irc.name, user, userobj.opertype)
                    opertype = userobj.opertype + ' (remote)'
                else:
                    opertype = 'IRC Operator (remote)'
                # Set hideoper on remote opers, to prevent inflating
                # /lusers and various /stats
                hideoper_mode = remoteirc.umodes.get('hideoper')
                try:
                    use_hideoper = irc.conf['relay']['hideoper']
                except KeyError:
                    use_hideoper = True
                if hideoper_mode and use_hideoper:
                    modes.add((hideoper_mode, None))

            rsid = getRemoteSid(remoteirc, irc)
            try:
                showRealIP = irc.conf['relay']['show_ips'] and not \
                             irc.serverdata.get('relay_no_ips') and not \
                             remoteirc.serverdata.get('relay_no_ips')
            except KeyError:
                showRealIP = False
            if showRealIP:
                ip = userobj.ip
                realhost = userobj.realhost
            else:
                realhost = None
                ip = '0.0.0.0'
            u = remoteirc.proto.spawnClient(nick, ident=ident,
                                                host=host, realname=realname,
                                                modes=modes, ts=userobj.ts,
                                                opertype=opertype, server=rsid,
                                                ip=ip, realhost=realhost).uid
            remoteirc.users[u].remote = (irc.name, user)
            remoteirc.users[u].opertype = opertype
            away = userobj.away
            if away:
                remoteirc.proto.away(u, away)
        relayusers[(irc.name, user)][remoteirc.name] = u
        return u

def getOrigUser(irc, user, targetirc=None):
    """
    Given the UID of a relay client, returns a tuple of the home network name
    and original UID of the user it was spawned for.

    If targetirc is given, getRemoteUser() is called to get the relay client
    representing the original user on that target network."""
    # First, iterate over everyone!
    try:
        remoteuser = irc.users[user].remote
    except (AttributeError, KeyError):
        remoteuser = None
    log.debug('(%s) relay.getOrigUser: remoteuser set to %r (looking up %s/%s).',
              irc.name, remoteuser, user, irc.name)
    if remoteuser:
        # If targetirc is given, we'll return simply the UID of the user on the
        # target network, if it exists. Otherwise, we'll return a tuple
        # with the home network name and the original user's UID.
        sourceobj = world.networkobjects.get(remoteuser[0])
        if targetirc and sourceobj:
            if remoteuser[0] == targetirc.name:
                # The user we found's home network happens to be the one being
                # requested; just return the UID then.
                return remoteuser[1]
            # Otherwise, use getRemoteUser to find our UID.
            res = getRemoteUser(sourceobj, targetirc, remoteuser[1],
                                spawnIfMissing=False)
            log.debug('(%s) relay.getOrigUser: targetirc found, getting %r as '
                      'remoteuser for %r (looking up %s/%s).', irc.name, res,
                      remoteuser[1], user, irc.name)
            return res
        else:
            return remoteuser

def getRelay(chanpair):
    """Finds the matching relay entry name for the given (network name, channel)
    pair, if one exists."""
    if chanpair in db:  # This chanpair is a shared channel; others link to it
        return chanpair
    # This chanpair is linked *to* a remote channel
    for name, dbentry in db.items():
        if chanpair in dbentry['links']:
            return name

def getRemoteChan(irc, remoteirc, channel):
    """Returns the linked channel name for the given channel on remoteirc,
    if one exists."""
    query = (irc.name, channel)
    remotenetname = remoteirc.name
    chanpair = getRelay(query)
    if chanpair is None:
        return
    if chanpair[0] == remotenetname:
        return chanpair[1]
    else:
        for link in db[chanpair]['links']:
            if link[0] == remotenetname:
                return link[1]

def initializeChannel(irc, channel):
    """Initializes a relay channel (merge local/remote users, set modes, etc.)."""
    # We're initializing a relay that already exists. This can be done at
    # ENDBURST, or on the LINK command.
    relay = getRelay((irc.name, channel))
    log.debug('(%s) relay.initializeChannel being called on %s', irc.name, channel)
    log.debug('(%s) relay.initializeChannel: relay pair found to be %s', irc.name, relay)
    queued_users = []
    if relay:
        all_links = db[relay]['links'].copy()
        all_links.update((relay,))
        log.debug('(%s) relay.initializeChannel: all_links: %s', irc.name, all_links)

        # Iterate over all the remote channels linked in this relay.
        for link in all_links:
            remotenet, remotechan = link
            if remotenet == irc.name:  # If the network is us, skip.
                continue
            remoteirc = world.networkobjects.get(remotenet)

            if remoteirc is None:
                # Remote network doesn't have an IRC object; e.g. it was removed
                # from the config. Skip this.
                continue
            rc = remoteirc.channels[remotechan]

            if not (remoteirc.connected.is_set() and getRemoteChan(remoteirc, irc, remotechan)):
                continue  # Remote network isn't connected.

            # Join their (remote) users and set their modes.
            relayJoins(remoteirc, remotechan, rc.users, rc.ts)
            topic = remoteirc.channels[remotechan].topic

            # Only update the topic if it's different from what we already have,
            # and topic bursting is complete.
            if remoteirc.channels[remotechan].topicset and topic != irc.channels[channel].topic:
                irc.proto.topicBurst(getRemoteSid(irc, remoteirc), channel, topic)

        # Send our users and channel modes to the other nets
        log.debug('(%s) relay.initializeChannel: joining our (%s) users: %s', irc.name, remotenet, irc.channels[channel].users)
        relayJoins(irc, channel, irc.channels[channel].users, irc.channels[channel].ts)
        if irc.pseudoclient and irc.pseudoclient.uid not in irc.channels[channel].users:
            irc.proto.join(irc.pseudoclient.uid, channel)

def removeChannel(irc, channel):
    """Destroys a relay channel by parting all of its users."""
    if irc is None:
        return

    if channel not in map(str.lower, irc.serverdata['channels']):
        irc.proto.part(irc.pseudoclient.uid, channel, 'Channel delinked.')

    relay = getRelay((irc.name, channel))
    if relay:
        for user in irc.channels[channel].users.copy():
            if not isRelayClient(irc, user):
                relayPart(irc, channel, user)
            # Don't ever part the main client from any of its autojoin channels.
            else:
                if user == irc.pseudoclient.uid and channel in \
                        irc.serverdata['channels']:
                    continue
                irc.proto.part(user, channel, 'Channel delinked.')
                # Don't ever quit it either...
                if user != irc.pseudoclient.uid and not irc.users[user].channels:
                    remoteuser = getOrigUser(irc, user)
                    del relayusers[remoteuser][irc.name]
                    irc.proto.quit(user, 'Left all shared channels.')

def checkClaim(irc, channel, sender, chanobj=None):
    """
    Checks whether the sender of a kick/mode change passes CLAIM checks for
    a given channel. This returns True if any of the following criteria are met:

    1) No relay exists for the channel in question.
    2) The originating network is the one that created the relay.
    3) The CLAIM list for the relay in question is empty.
    4) The originating network is in the CLAIM list for the relay in question.
    5) The sender is halfop or above in the channel.
    6) The sender is a PyLink client/server (checks are suppressed in this case).
    """
    relay = getRelay((irc.name, channel))
    try:
        mlist = chanobj.prefixmodes
    except AttributeError:
        mlist = None

    sender_modes = getPrefixModes(irc, irc, channel, sender, mlist=mlist)
    log.debug('(%s) relay.checkClaim: sender modes (%s/%s) are %s (mlist=%s)', irc.name,
              sender, channel, sender_modes, mlist)
    # XXX: stop hardcoding modes to check for and support mlist in isHalfopPlus and friends
    return (not relay) or irc.name == relay[0] or not db[relay]['claim'] or \
        irc.name in db[relay]['claim'] or \
        any([mode in sender_modes for mode in ('y', 'q', 'a', 'o', 'h')]) \
        or irc.isInternalClient(sender) or \
        irc.isInternalServer(sender)

def getSupportedUmodes(irc, remoteirc, modes):
    """Given a list of user modes, filters out all of those not supported by the
    remote network."""
    supported_modes = []

    # Iterate over all mode pairs.
    for modepair in modes:
        try:
            # Get the prefix and the actual mode character (the prefix being + or -, or
            # whether we're setting or unsetting a mode)
            prefix, modechar = modepair[0]
        except ValueError:
            # If the prefix is missing, assume we're adding a mode.
            modechar = modepair[0]
            prefix = '+'

        # Get the mode argument.
        arg = modepair[1]

        # Iterate over all supported user modes for the current network.
        for name, m in irc.umodes.items():
            supported_char = None

            # Mode character matches one in our list, so set that named mode
            # as the one we're trying to set. Then, look up that named mode
            # in the supported modes list for the TARGET network, and set that
            # mode character as the one we're setting, if it exists.
            if modechar == m:
                if name not in whitelisted_umodes:
                    log.debug("(%s) relay.getSupportedUmodes: skipping mode (%r, %r) because "
                              "it isn't a whitelisted (safe) mode for relay.",
                              irc.name, modechar, arg)
                    break
                supported_char = remoteirc.umodes.get(name)

            if supported_char:
                supported_modes.append((prefix+supported_char, arg))
                break
        else:
            log.debug("(%s) relay.getSupportedUmodes: skipping mode (%r, %r) because "
                      "the remote network (%s)'s IRCd (%s) doesn't support it.",
                      irc.name, modechar, arg, remoteirc.name,
                      remoteirc.protoname)
    return supported_modes

def isRelayClient(irc, user):
    """Returns whether the given user is a relay client."""
    try:
        if irc.users[user].remote:
            # Is the .remote attribute set? If so, don't relay already
            # relayed clients; that'll trigger an endless loop!
            return True
    except AttributeError:  # Nope, it isn't.
        pass
    except KeyError:  # The user doesn't exist?!?
        return True
    return False

### EVENT HANDLER INTERNALS

def relayJoins(irc, channel, users, ts, burst=True):
    """
    Relays one or more users' joins from a channel to its relay links.
    """
    for name, remoteirc in world.networkobjects.copy().items():
        queued_users = []
        if name == irc.name or not remoteirc.connected.is_set():
            # Don't relay things to their source network...
            continue

        remotechan = getRemoteChan(irc, remoteirc, channel)
        if remotechan is None:
            # If there is no link on the current network for the channel in question,
            # just skip it
            continue

        log.debug('(%s) relay.relayJoins: got %r for users', irc.name, users)

        for user in users.copy():
            if isRelayClient(irc, user):
                # Don't clone relay clients; that'll cause bad infinite loops.
                continue

            assert user in irc.users, "(%s) relay.relayJoins: How is this possible? %r isn't in our user database." % (irc.name, user)
            u = getRemoteUser(irc, remoteirc, user)


            if u not in remoteirc.channels[remotechan].users:
                # Note: only join users if they aren't already joined. This prevents op floods
                # on charybdis from repeated SJOINs sent for one user.

                # Fetch the known channel TS and all the prefix modes for each user. This ensures
                # the different sides of the relay are merged properly.
                ts = irc.channels[channel].ts
                prefixes = getPrefixModes(irc, remoteirc, channel, user)

                # proto.sjoin() takes its users as a list of (prefix mode characters, UID) pairs.
                userpair = (prefixes, u)
                queued_users.append(userpair)

        if queued_users:
            # Look at whether we should relay this join as a regular JOIN, or a SJOIN.
            # SJOIN will be used if either the amount of users to join is > 1, or there are modes
            # to be set on the joining user.
            if burst or len(queued_users) > 1 or queued_users[0][0]:
                # Send the SJOIN from the relay subserver on the target network.
                rsid = getRemoteSid(remoteirc, irc)
                remoteirc.proto.sjoin(rsid, remotechan, queued_users, ts=ts)
                relayModes(irc, remoteirc, getRemoteSid(irc, remoteirc), channel, irc.channels[channel].modes)
            else:
                # A regular JOIN only needs the user and the channel. TS, source SID, etc., can all be omitted.
                remoteirc.proto.join(queued_users[0][1], remotechan)

def relayPart(irc, channel, user):
    """
    Relays a user part from a channel to its relay links, as part of a channel delink.
    """
    for name, remoteirc in world.networkobjects.copy().items():
        if name == irc.name or not remoteirc.connected.is_set():
            # Don't relay things to their source network...
            continue

        remotechan = getRemoteChan(irc, remoteirc, channel)
        log.debug('(%s) relay.relayPart: looking for %s/%s on %s', irc.name, user, irc.name, remoteirc.name)
        log.debug('(%s) relay.relayPart: remotechan found as %s', irc.name, remotechan)

        remoteuser = getRemoteUser(irc, remoteirc, user, spawnIfMissing=False)
        log.debug('(%s) relay.relayPart: remoteuser for %s/%s found as %s', irc.name, user, irc.name, remoteuser)

        if remotechan is None or remoteuser is None:
            # If there is no relay channel on the target network, or the relay
            # user doesn't exist, just do nothing.
            continue

        # Part the relay client with the channel delinked message.
        remoteirc.proto.part(remoteuser, remotechan, 'Channel delinked.')

        # If the relay client no longer has any channels, quit them to prevent inflating /lusers.
        if isRelayClient(remoteirc, remoteuser) and not remoteirc.users[remoteuser].channels:
            remoteirc.proto.quit(remoteuser, 'Left all shared channels.')
            del relayusers[(irc.name, user)][remoteirc.name]


whitelisted_cmodes = {'admin', 'allowinvite', 'autoop', 'ban', 'banexception',
                      'blockcolor', 'halfop', 'invex', 'inviteonly', 'key',
                      'limit', 'moderated', 'noctcp', 'noextmsg', 'nokick',
                      'noknock', 'nonick', 'nonotice', 'op', 'operonly',
                      'opmoderated', 'owner', 'private', 'regonly',
                      'regmoderated', 'secret', 'sslonly', 'adminonly',
                      'stripcolor', 'topiclock', 'voice'}
whitelisted_umodes = {'bot', 'hidechans', 'hideoper', 'invisible', 'oper',
                      'regdeaf', 'u_stripcolor', 'u_noctcp', 'wallops',
                      'hideidle'}
def relayModes(irc, remoteirc, sender, channel, modes=None):
    """
    Relays a mode change on a channel to its relay links.
    """
    remotechan = getRemoteChan(irc, remoteirc, channel)
    log.debug('(%s) relay.relayModes: remotechan for %s on %s is %s', irc.name, channel, irc.name, remotechan)

    if remotechan is None:
        return

    if modes is None:
        modes = irc.channels[channel].modes
        log.debug('(%s) relay.relayModes: channel data for %s%s: %s', irc.name, remoteirc.name, remotechan, remoteirc.channels[remotechan])
    supported_modes = []
    log.debug('(%s) relay.relayModes: initial modelist for %s is %s', irc.name, channel, modes)

    for modepair in modes:
        try:
            prefix, modechar = modepair[0]
        except ValueError:
            modechar = modepair[0]
            prefix = '+'
        arg = modepair[1]

        # Iterate over every mode see whether the remote IRCd supports
        # this mode, and what its mode char for it is (if it is different).
        for name, m in irc.cmodes.items():
            supported_char = None
            if modechar == m:
                supported_char = remoteirc.cmodes.get(name)

                if supported_char is None:
                    break

                if name not in whitelisted_cmodes:
                    log.debug("(%s) relay.relayModes: skipping mode (%r, %r) because "
                              "it isn't a whitelisted (safe) mode for relay.",
                              irc.name, modechar, arg)
                    break

                if modechar in irc.prefixmodes:
                    # This is a prefix mode (e.g. +o). We must coerse the argument
                    # so that the target exists on the remote relay network.
                    log.debug("(%s) relay.relayModes: coersing argument of (%r, %r) "
                              "for network %r.",
                              irc.name, modechar, arg, remoteirc.name)

                    # If the target is a remote user, get the real target
                    # (original user).
                    arg = getOrigUser(irc, arg, targetirc=remoteirc) or \
                        getRemoteUser(irc, remoteirc, arg, spawnIfMissing=False)

                    log.debug("(%s) relay.relayModes: argument found as (%r, %r) "
                              "for network %r.",
                              irc.name, modechar, arg, remoteirc.name)
                    oplist = remoteirc.channels[remotechan].prefixmodes[name]

                    log.debug("(%s) relay.relayModes: list of %ss on %r is: %s",
                              irc.name, name, remotechan, oplist)

                    if prefix == '+' and arg in oplist:

                        # Don't set prefix modes that are already set.
                        log.debug("(%s) relay.relayModes: skipping setting %s on %s/%s because it appears to be already set.",
                                  irc.name, name, arg, remoteirc.name)
                        break

                supported_char = remoteirc.cmodes.get(name)

            if supported_char:
                final_modepair = (prefix+supported_char, arg)
                if name in ('ban', 'banexception', 'invex') and not utils.isHostmask(arg):

                    # Don't add bans that don't match n!u@h syntax!
                    log.debug("(%s) relay.relayModes: skipping mode (%r, %r) because it doesn't match nick!user@host syntax.",
                              irc.name, modechar, arg)
                    break

                # Don't set modes that are already set, to prevent floods on TS6
                # where the same mode can be set infinite times.
                if prefix == '+' and final_modepair in remoteirc.channels[remotechan].modes:
                    log.debug("(%s) relay.relayModes: skipping setting mode (%r, %r) on %s%s because it appears to be already set.",
                              irc.name, supported_char, arg, remoteirc.name, remotechan)
                    break

                supported_modes.append(final_modepair)

    log.debug('(%s) relay.relayModes: final modelist (sending to %s%s) is %s', irc.name, remoteirc.name, remotechan, supported_modes)

    # Don't send anything if there are no supported modes left after filtering.
    if supported_modes:
        # Check if the sender is a user; remember servers are allowed to set modes too.
        u = getRemoteUser(irc, remoteirc, sender, spawnIfMissing=False)
        if u:
            remoteirc.proto.mode(u, remotechan, supported_modes)
        else:
            rsid = getRemoteSid(remoteirc, irc)
            remoteirc.proto.mode(rsid, remotechan, supported_modes)

def relayWhoisHandler(irc, target):
    """
    WHOIS handler for the relay plugin.
    """
    user = irc.users[target]
    orig = getOrigUser(irc, target)
    if orig:
        network, remoteuid = orig
        remotenick = world.networkobjects[network].users[remoteuid].nick
        return [320, "%s :is a remote user connected via PyLink Relay. Home "
                     "network: %s; Home nick: %s" % (user.nick, network,
                                                     remotenick)]
world.whois_handlers.append(relayWhoisHandler)

### GENERIC EVENT HOOK HANDLERS

def handle_operup(irc, numeric, command, args):
    newtype = args['text'] + '_(remote)'
    for netname, user in relayusers[(irc.name, numeric)].items():
        log.debug('(%s) relay.handle_opertype: setting OPERTYPE of %s/%s to %s',
                  irc.name, user, netname, newtype)
        remoteirc = world.networkobjects[netname]
        remoteirc.users[user].opertype = newtype
utils.add_hook(handle_operup, 'CLIENT_OPERED')

def handle_join(irc, numeric, command, args):
    channel = args['channel']
    if not getRelay((irc.name, channel)):
        # No relay here, return.
        return
    ts = args['ts']
    users = set(args['users'])
    relayJoins(irc, channel, users, ts, burst=False)
utils.add_hook(handle_join, 'JOIN')

def handle_quit(irc, numeric, command, args):
    for netname, user in relayusers[(irc.name, numeric)].copy().items():
        remoteirc = world.networkobjects[netname]
        remoteirc.proto.quit(user, args['text'])
    del relayusers[(irc.name, numeric)]
utils.add_hook(handle_quit, 'QUIT')

def handle_squit(irc, numeric, command, args):
    users = args['users']
    target = args['target']
    # Someone /SQUIT one of our relay subservers. Bad! Rejoin them!
    if target in relayservers[irc.name].values():
        sname = args['name']
        remotenet = sname.split('.', 1)[0]
        del relayservers[irc.name][remotenet]
        for userpair in relayusers:
            if userpair[0] == remotenet and irc.name in relayusers[userpair]:
                del relayusers[userpair][irc.name]
        remoteirc = world.networkobjects[remotenet]
        initializeAll(remoteirc)
    else:
        # Some other netsplit happened on the network, we'll have to fake
        # some *.net *.split quits for that.
        for user in users:
            log.debug('(%s) relay.handle_squit: sending handle_quit on %s', irc.name, user)
            handle_quit(irc, user, command, {'text': '*.net *.split'})
utils.add_hook(handle_squit, 'SQUIT')

def handle_nick(irc, numeric, command, args):
    for netname, user in relayusers[(irc.name, numeric)].items():
        remoteirc = world.networkobjects[netname]
        newnick = normalizeNick(remoteirc, irc.name, args['newnick'], uid=user)
        if remoteirc.users[user].nick != newnick:
            remoteirc.proto.nick(user, newnick)
utils.add_hook(handle_nick, 'NICK')

def handle_part(irc, numeric, command, args):
    channels = args['channels']
    text = args['text']
    # Don't allow the PyLink client PARTing to be relayed.
    if numeric == irc.pseudoclient.uid:
        return
    for channel in channels:
        for netname, user in relayusers[(irc.name, numeric)].copy().items():
            remoteirc = world.networkobjects[netname]
            remotechan = getRemoteChan(irc, remoteirc, channel)
            if remotechan is None:
                continue
            remoteirc.proto.part(user, remotechan, text)
            if not remoteirc.users[user].channels:
                remoteirc.proto.quit(user, 'Left all shared channels.')
                del relayusers[(irc.name, numeric)][remoteirc.name]
utils.add_hook(handle_part, 'PART')

def handle_messages(irc, numeric, command, args):
    notice = (command in ('NOTICE', 'PYLINK_SELF_NOTICE'))
    target = args['target']
    text = args['text']
    if irc.isInternalClient(numeric) and irc.isInternalClient(target):
        # Drop attempted PMs between internal clients (this shouldn't happen,
        # but whatever).
        return

    elif numeric in irc.servers:
        # Sender is a server? This shouldn't be allowed, except for some truly
        # special cases... We'll route these through the main PyLink client,
        # tagging the message with the sender name.
        text = '[from %s] %s' % (irc.servers[numeric].name, text)
        numeric = irc.pseudoclient.uid

    elif numeric not in irc.users:
        # Sender didn't pass the check above, AND isn't a user.
        log.debug('(%s) relay.handle_messages: Unknown message sender %s.', irc.name, numeric)
        return

    relay = getRelay((irc.name, target))
    remoteusers = relayusers[(irc.name, numeric)]

    # HACK: Don't break on sending to @#channel or similar.
    try:
        prefix, target = target.split('#', 1)
    except ValueError:
        prefix = ''
    else:
        target = '#' + target

    log.debug('(%s) relay.handle_messages: prefix is %r, target is %r', irc.name, prefix, target)
    if utils.isChannel(target) and relay and numeric not in irc.channels[target].users:
        # The sender must be in the target channel to send messages over the relay;
        # it's the only way we can make sure they have a spawned client on ALL
        # of the linked networks. This affects -n channels too; see
        # https://github.com/GLolol/PyLink/issues/91 for an explanation of why.
        irc.msg(numeric, 'Error: You must be in %r in order to send '
                  'messages over the relay.' % target, notice=True)
        return

    if utils.isChannel(target):
        for name, remoteirc in world.networkobjects.copy().items():
            real_target = getRemoteChan(irc, remoteirc, target)

            # Don't relay anything back to the source net, or to disconnected networks
            # and networks without a relay for this channel
            if irc.name == name or (not remoteirc.connected.is_set()) or (not real_target) \
                    or (not irc.connected.is_set()):
                continue

            user = getRemoteUser(irc, remoteirc, numeric, spawnIfMissing=False)
            real_target = prefix + real_target
            log.debug('(%s) relay.handle_messages: sending message to %s from %s on behalf of %s',
                      irc.name, real_target, user, numeric)
            if notice:
                remoteirc.proto.notice(user, real_target, text)
            else:
                remoteirc.proto.message(user, real_target, text)

    else:
        # Get the real user that the PM was meant for
        origuser = getOrigUser(irc, target)
        if origuser is None:  # Not a relay client, return
            return
        homenet, real_target = origuser

        # For PMs, we must be on a common channel with the target.
        # Otherwise, the sender doesn't have a client representing them
        # on the remote network, and we won't have anything to send our
        # messages from.
        if homenet not in remoteusers.keys():
            irc.msg(numeric, 'Error: You must be in a common channel '
                      'with %r in order to send messages.' % \
                      irc.users[target].nick, notice=True)
            return
        remoteirc = world.networkobjects[homenet]
        user = getRemoteUser(irc, remoteirc, numeric, spawnIfMissing=False)

        if notice:
            remoteirc.proto.notice(user, real_target, text)
        else:
            remoteirc.proto.message(user, real_target, text)

for cmd in ('PRIVMSG', 'NOTICE', 'PYLINK_SELF_NOTICE', 'PYLINK_SELF_PRIVMSG'):
    utils.add_hook(handle_messages, cmd)

def handle_kick(irc, source, command, args):
    channel = args['channel']
    target = args['target']
    text = args['text']
    kicker = source
    relay = getRelay((irc.name, channel))
    # Don't allow kicks to the PyLink client to be relayed.
    if relay is None or target == irc.pseudoclient.uid:
        return
    origuser = getOrigUser(irc, target)
    for name, remoteirc in world.networkobjects.copy().items():
        if irc.name == name or not remoteirc.connected.is_set():
            continue
        remotechan = getRemoteChan(irc, remoteirc, channel)
        log.debug('(%s) relay.handle_kick: remotechan for %s on %s is %s', irc.name, channel, name, remotechan)
        if remotechan is None:
            continue
        real_kicker = getRemoteUser(irc, remoteirc, kicker, spawnIfMissing=False)
        log.debug('(%s) relay.handle_kick: real kicker for %s on %s is %s', irc.name, kicker, name, real_kicker)
        if not isRelayClient(irc, target):
            log.debug('(%s) relay.handle_kick: target %s is NOT an internal client', irc.name, target)
            # Both the target and kicker are external clients; i.e.
            # they originate from the same network. We won't have
            # to filter this; the uplink IRCd will handle it appropriately,
            # and we'll just follow.
            real_target = getRemoteUser(irc, remoteirc, target, spawnIfMissing=False)
            log.debug('(%s) relay.handle_kick: real target for %s is %s', irc.name, target, real_target)
        else:
            log.debug('(%s) relay.handle_kick: target %s is an internal client, going to look up the real user', irc.name, target)
            real_target = getOrigUser(irc, target, targetirc=remoteirc)
            if not checkClaim(irc, channel, kicker):
                log.debug('(%s) relay.handle_kick: kicker %s is not opped... We should rejoin the target user %s', irc.name, kicker, real_target)
                # Home network is not in the channel's claim AND the kicker is not
                # opped. We won't propograte the kick then.
                # TODO: make the check slightly more advanced: i.e. halfops can't
                # kick ops, admins can't kick owners, etc.
                modes = getPrefixModes(remoteirc, irc, remotechan, real_target)
                # Join the kicked client back with its respective modes.
                irc.proto.sjoin(irc.sid, channel, [(modes, target)])
                if kicker in irc.users:
                    log.info('(%s) relay: Blocked KICK (reason %r) from %s/%s to relay client %s/%s on %s.',
                             irc.name, args['text'], irc.users[source].nick, irc.name,
                             remoteirc.users[real_target].nick, remoteirc.name, channel)
                    irc.msg(kicker, "This channel is claimed; your kick to "
                                    "%s has been blocked because you are not "
                                    "(half)opped." % channel, notice=True)
                else:
                    log.info('(%s) relay: Blocked KICK (reason %r) from server %s to relay client %s/%s on %s.',
                             irc.name, args['text'], irc.servers[source].name,
                             remoteirc.users[real_target].nick, remoteirc.name, channel)
                return

        if not real_target:
            continue
        # Propogate the kick!
        if real_kicker:
            log.debug('(%s) relay.handle_kick: Kicking %s from channel %s via %s on behalf of %s/%s', irc.name, real_target, remotechan,real_kicker, kicker, irc.name)
            remoteirc.proto.kick(real_kicker, remotechan, real_target, args['text'])
        else:
            # Kick originated from a server, or the kicker isn't in any
            # common channels with the target relay network.
            rsid = getRemoteSid(remoteirc, irc)
            log.debug('(%s) relay.handle_kick: Kicking %s from channel %s via %s on behalf of %s/%s', irc.name, real_target, remotechan, rsid, kicker, irc.name)
            try:
                if kicker in irc.servers:
                    kname = irc.servers[kicker].name
                else:
                    kname = irc.users.get(kicker).nick
                text = "(%s/%s) %s" % (kname, irc.name, args['text'])
            except AttributeError:
                text = "(<unknown kicker>@%s) %s" % (irc.name, args['text'])
            remoteirc.proto.kick(rsid, remotechan, real_target, text)

        # If the target isn't on any channels, quit them.
        if remoteirc != irc and (not remoteirc.users[real_target].channels) and not origuser:
            del relayusers[(irc.name, target)][remoteirc.name]
            remoteirc.proto.quit(real_target, 'Left all shared channels.')

    if origuser and not irc.users[target].channels:
        del relayusers[origuser][irc.name]
        irc.proto.quit(target, 'Left all shared channels.')

utils.add_hook(handle_kick, 'KICK')

def handle_chgclient(irc, source, command, args):
    target = args['target']
    if args.get('newhost'):
        field = 'HOST'
        text = args['newhost']
    elif args.get('newident'):
        field = 'IDENT'
        text = args['newident']
    elif args.get('newgecos'):
        field = 'GECOS'
        text = args['newgecos']
    if field:
        for netname, user in relayusers[(irc.name, target)].items():
            remoteirc = world.networkobjects[netname]
            try:
                if field == 'HOST':
                    text = normalizeHost(remoteirc, text)
                remoteirc.proto.updateClient(user, field, text)
            except NotImplementedError:  # IRCd doesn't support changing the field we want
                log.debug('(%s) relay.handle_chgclient: Ignoring changing field %r of %s on %s (for %s/%s);'
                          ' remote IRCd doesn\'t support it', irc.name, field,
                          user, netname, target, irc.name)
                continue

for c in ('CHGHOST', 'CHGNAME', 'CHGIDENT'):
    utils.add_hook(handle_chgclient, c)

def handle_mode(irc, numeric, command, args):
    target = args['target']
    modes = args['modes']
    for name, remoteirc in world.networkobjects.copy().items():
        if irc.name == name or not remoteirc.connected.is_set():
            continue

        if utils.isChannel(target):
            oldchan = args.get('oldchan')

            if checkClaim(irc, target, numeric, chanobj=oldchan):
                relayModes(irc, remoteirc, numeric, target, modes)
            else:  # Mode change blocked by CLAIM.
                reversed_modes = irc.reverseModes(target, modes, oldobj=oldchan)
                log.debug('(%s) relay.handle_mode: Reversing mode changes of %r with %r (CLAIM).',
                          irc.name, modes, reversed_modes)
                irc.proto.mode(irc.pseudoclient.uid, target, reversed_modes)
                break

        else:
            # Set hideoper on remote opers, to prevent inflating
            # /lusers and various /stats
            hideoper_mode = remoteirc.umodes.get('hideoper')
            modes = getSupportedUmodes(irc, remoteirc, modes)

            if hideoper_mode:
                if ('+o', None) in modes:
                    modes.append(('+%s' % hideoper_mode, None))
                elif ('-o', None) in modes:
                    modes.append(('-%s' % hideoper_mode, None))

            remoteuser = getRemoteUser(irc, remoteirc, target, spawnIfMissing=False)

            if remoteuser and modes:
                remoteirc.proto.mode(remoteuser, remoteuser, modes)

utils.add_hook(handle_mode, 'MODE')

def handle_topic(irc, numeric, command, args):
    channel = args['channel']
    oldtopic = args.get('oldtopic')
    topic = args['text']
    if checkClaim(irc, channel, numeric):
        for name, remoteirc in world.networkobjects.copy().items():
            if irc.name == name or not remoteirc.connected.is_set():
                continue

            remotechan = getRemoteChan(irc, remoteirc, channel)
            # Don't send if the remote topic is the same as ours.
            if remotechan is None or topic == remoteirc.channels[remotechan].topic:
                continue
            # This might originate from a server too.
            remoteuser = getRemoteUser(irc, remoteirc, numeric, spawnIfMissing=False)
            if remoteuser:
                remoteirc.proto.topic(remoteuser, remotechan, topic)
            else:
                rsid = getRemoteSid(remoteirc, irc)
                remoteirc.proto.topicBurst(rsid, remotechan, topic)
    elif oldtopic:  # Topic change blocked by claim.
        irc.proto.topic(irc.pseudoclient.uid, channel, oldtopic)

utils.add_hook(handle_topic, 'TOPIC')

def handle_kill(irc, numeric, command, args):
    target = args['target']
    userdata = args['userdata']

    # Try to find the original client of the target being killed
    if userdata and hasattr(userdata, 'remote'):
        realuser = userdata.remote
    else:
        realuser = getOrigUser(irc, target)

    log.debug('(%s) relay.handle_kill: realuser is %r', irc.name, realuser)

    # Target user was remote:
    if realuser and realuser[0] != irc.name:
        # We don't allow killing over the relay, so we must respawn the affected
        # client and rejoin it to its channels.
        del relayusers[realuser][irc.name]
        remoteirc = world.networkobjects[realuser[0]]
        for remotechan in remoteirc.users[realuser[1]].channels:
            localchan = getRemoteChan(remoteirc, irc, remotechan)
            if localchan:
                modes = getPrefixModes(remoteirc, irc, remotechan, realuser[1])
                log.debug('(%s) relay.handle_kill: userpair: %s, %s', irc.name, modes, realuser)
                client = getRemoteUser(remoteirc, irc, realuser[1])
                irc.proto.sjoin(getRemoteSid(irc, remoteirc), localchan, [(modes, client)])

        if userdata and numeric in irc.users:
            log.info('(%s) relay.handle_kill: Blocked KILL (reason %r) from %s to relay client %s/%s.',
                     irc.name, args['text'], irc.users[numeric].nick,
                     remoteirc.users[realuser[1]].nick, realuser[0])
            irc.msg(numeric, "Your kill to %s has been blocked "
                             "because PyLink does not allow killing"
                             " users over the relay at this time." % \
                             userdata.nick, notice=True)
        else:
            log.info('(%s) relay.handle_kill: Blocked KILL (reason %r) from server %s to relay client %s/%s.',
                     irc.name, args['text'], irc.servers[numeric].name,
                     remoteirc.users[realuser[1]].nick, realuser[0])

    # Target user was local.
    else:
        # IMPORTANT: some IRCds (charybdis) don't send explicit QUIT messages
        # for locally killed clients, while others (inspircd) do!
        # If we receive a user object in 'userdata' instead of None, it means
        # that the KILL hasn't been handled by a preceding QUIT message.
        if userdata:
            handle_quit(irc, target, 'KILL', {'text': args['text']})

utils.add_hook(handle_kill, 'KILL')

def handle_away(irc, numeric, command, args):
    for netname, user in relayusers[(irc.name, numeric)].items():
        remoteirc = world.networkobjects[netname]
        remoteirc.proto.away(user, args['text'])
utils.add_hook(handle_away, 'AWAY')

def handle_invite(irc, source, command, args):
    target = args['target']
    channel = args['channel']
    if isRelayClient(irc, target):
        remotenet, remoteuser = getOrigUser(irc, target)
        remoteirc = world.networkobjects[remotenet]
        remotechan = getRemoteChan(irc, remoteirc, channel)
        remotesource = getRemoteUser(irc, remoteirc, source, spawnIfMissing=False)
        if remotesource is None:
            irc.msg(source, 'Error: You must be in a common channel '
                                   'with %s to invite them to channels.' % \
                                   irc.users[target].nick,
                                   notice=True)
        elif remotechan is None:
            irc.msg(source, 'Error: You cannot invite someone to a '
                                   'channel not on their network!',
                                   notice=True)
        else:
            remoteirc.proto.invite(remotesource, remoteuser,
                                         remotechan)
utils.add_hook(handle_invite, 'INVITE')

def handle_endburst(irc, numeric, command, args):
    if numeric == irc.uplink:
        initializeAll(irc)
utils.add_hook(handle_endburst, "ENDBURST")

def handle_disconnect(irc, numeric, command, args):
    """Handles IRC network disconnections (internal hook)."""
    # Quit all of our users' representations on other nets, and remove
    # them from our relay clients index.
    with spawnlocks[irc.name]:
        for k, v in relayusers.copy().items():
            if irc.name in v:
                del relayusers[k][irc.name]
            if k[0] == irc.name:
                try:
                    handle_quit(irc, k[1], 'PYLINK_DISCONNECT', {'text': 'Relay network lost connection.'})
                    del relayusers[k]
                except KeyError:
                    pass
    # SQUIT all relay pseudoservers spawned for us, and remove them
    # from our relay subservers index.
    with spawnlocks_servers[irc.name]:
        for name, ircobj in world.networkobjects.copy().items():
            if name != irc.name and ircobj.connected.is_set():
                try:
                    rsid = relayservers[name][irc.name]
                except KeyError:
                    continue
                else:
                    ircobj.proto.squit(ircobj.sid, rsid, text='Relay network lost connection.')

            try:
                del relayservers[name][irc.name]
            except KeyError:
                pass

        try:
            del relayservers[irc.name]
        except KeyError:
            pass

utils.add_hook(handle_disconnect, "PYLINK_DISCONNECT")

def handle_save(irc, numeric, command, args):
    target = args['target']
    realuser = getOrigUser(irc, target)
    log.debug('(%s) relay.handle_save: %r got in a nick collision! Real user: %r',
                  irc.name, target, realuser)
    if isRelayClient(irc, target) and realuser:
        # Nick collision!
        # It's one of our relay clients; try to fix our nick to the next
        # available normalized nick.
        remotenet, remoteuser = realuser
        remoteirc = world.networkobjects[remotenet]
        nick = remoteirc.users[remoteuser].nick

        newnick = normalizeNick(irc, remotenet, nick)
        log.info('(%s) relay.handle_save: SAVE received for relay client %r (%s), fixing nick to %s',
                 irc.name, target, nick, newnick)
        irc.proto.nick(target, newnick)
    else:
        # Somebody else on the network (not a PyLink client) had a nick collision;
        # relay this as a nick change appropriately.
        handle_nick(irc, target, 'SAVE', {'oldnick': None, 'newnick': target})

utils.add_hook(handle_save, "SAVE")

### PUBLIC COMMANDS

@utils.add_cmd
def create(irc, source, args):
    """<channel>

    Creates the channel <channel> over the relay."""
    try:
        channel = utils.toLower(irc, args[0])
    except IndexError:
        irc.reply("Error: Not enough arguments. Needs 1: channel.")
        return
    if not utils.isChannel(channel):
        irc.reply('Error: Invalid channel %r.' % channel)
        return
    if source not in irc.channels[channel].users:
        irc.reply('Error: You must be in %r to complete this operation.' % channel)
        return
    irc.checkAuthenticated(source)

    # Check to see whether the channel requested is already part of a different
    # relay.
    localentry = getRelay((irc.name, channel))
    if localentry:
        irc.reply('Error: Channel %r is already part of a relay.' % channel)
        return

    creator = irc.getHostmask(source)
    # Create the relay database entry with the (network name, channel name)
    # pair - this is just a dict with various keys.
    db[(irc.name, channel)] = {'claim': [irc.name], 'links': set(),
                               'blocked_nets': set(), 'creator': creator,
                               'ts': time.time()}
    log.info('(%s) relay: Channel %s created by %s.', irc.name, channel, creator)
    initializeChannel(irc, channel)
    irc.reply('Done.')

@utils.add_cmd
def destroy(irc, source, args):
    """[<home network>] <channel>

    Removes <channel> from the relay, delinking all networks linked to it. If <home network> is given and you are logged in as admin, this can also remove relay channels from other networks."""
    try:  # Two args were given: first one is network name, second is channel.
        channel = utils.toLower(irc, args[1])
        network = args[0]
    except IndexError:
        try:  # One argument was given; assume it's just the channel.
            channel = utils.toLower(irc, args[0])
            network = irc.name
        except IndexError:
            irc.reply("Error: Not enough arguments. Needs 1-2: channel, network (optional).")
            return

    if not utils.isChannel(channel):
        irc.reply('Error: Invalid channel %r.' % channel)
        return

    if network == irc.name:
        # If we're destroying a channel on the current network, only oper is needed.
        irc.checkAuthenticated(source)
    else:
        # Otherwise, we'll need to be logged in as admin.
        irc.checkAuthenticated(source, allowOper=False)

    entry = (network, channel)

    if entry in db:
        # Iterate over all the channel links and deinitialize them.
        for link in db[entry]['links']:
            removeChannel(world.networkobjects.get(link[0]), link[1])
        removeChannel(world.networkobjects.get(network), channel)

        del db[entry]
        log.info('(%s) relay: Channel %s destroyed by %s.', irc.name,
                 channel, irc.getHostmask(source))
        irc.reply('Done.')
    else:
        irc.reply('Error: No such relay %r exists.' % channel)
        return

@utils.add_cmd
def link(irc, source, args):
    """<remotenet> <channel> <local channel>

    Links channel <channel> on <remotenet> over the relay to <local channel>.
    If <local channel> is not specified, it defaults to the same name as <channel>."""
    try:
        channel = utils.toLower(irc, args[1])
        remotenet = args[0]
    except IndexError:
        irc.reply("Error: Not enough arguments. Needs 2-3: remote netname, channel, local channel name (optional).")
        return
    try:
        localchan = utils.toLower(irc, args[2])
    except IndexError:
        localchan = channel
    for c in (channel, localchan):
        if not utils.isChannel(c):
            irc.reply('Error: Invalid channel %r.' % c)
            return
    if source not in irc.channels[localchan].users:
        irc.reply('Error: You must be in %r to complete this operation.' % localchan)
        return
    irc.checkAuthenticated(source)
    if remotenet not in world.networkobjects:
        irc.reply('Error: No network named %r exists.' % remotenet)
        return
    localentry = getRelay((irc.name, localchan))
    if localentry:
        irc.reply('Error: Channel %r is already part of a relay.' % localchan)
        return
    try:
        entry = db[(remotenet, channel)]
    except KeyError:
        irc.reply('Error: No such relay %r exists.' % channel)
        return
    else:
        if irc.name in entry['blocked_nets']:
            irc.reply('Error: Access denied (network is banned from linking to this channel).')
            return
        for link in entry['links']:
            if link[0] == irc.name:
                irc.reply("Error: Remote channel '%s%s' is already linked here "
                          "as %r." % (remotenet, channel, link[1]))
                return
        entry['links'].add((irc.name, localchan))
        log.info('(%s) relay: Channel %s linked to %s%s by %s.', irc.name,
                 localchan, remotenet, channel, irc.getHostmask(source))
        initializeChannel(irc, localchan)
        irc.reply('Done.')

@utils.add_cmd
def delink(irc, source, args):
    """<local channel> [<network>]

    Delinks channel <local channel>. <network> must and can only be specified if you are on the host network for <local channel>, and allows you to pick which network to delink.
    To remove a relay entirely, use the 'destroy' command instead."""
    try:
        channel = utils.toLower(irc, args[0])
    except IndexError:
        irc.reply("Error: Not enough arguments. Needs 1-2: channel, remote netname (optional).")
        return
    try:
        remotenet = args[1]
    except IndexError:
        remotenet = None
    irc.checkAuthenticated(source)
    if not utils.isChannel(channel):
        irc.reply('Error: Invalid channel %r.' % channel)
        return
    entry = getRelay((irc.name, channel))
    if entry:
        if entry[0] == irc.name:  # We own this channel.
            if not remotenet:
                irc.reply("Error: You must select a network to "
                          "delink, or use the 'destroy' command to remove "
                          "this relay entirely (it was created on the current "
                          "network).")
                return
            else:
               for link in db[entry]['links'].copy():
                    if link[0] == remotenet:
                        removeChannel(world.networkobjects.get(remotenet), link[1])
                        db[entry]['links'].remove(link)
        else:
            removeChannel(irc, channel)
            db[entry]['links'].remove((irc.name, channel))
        irc.reply('Done.')
        log.info('(%s) relay: Channel %s delinked from %s%s by %s.', irc.name,
                 channel, entry[0], entry[1], irc.getHostmask(source))
    else:
        irc.reply('Error: No such relay %r.' % channel)

@utils.add_cmd
def linked(irc, source, args):
    """takes no arguments.

    Returns a list of channels shared across the relay."""

    # Only show remote networks that are marked as connected.
    remote_networks = [netname for netname, ircobj in world.networkobjects.copy().items()
                       if ircobj.connected.is_set()]

    # But remove the current network from the list, so that it isn't shown twice.
    remote_networks.remove(irc.name)

    remote_networks.sort()

    s = 'Connected networks: \x02%s\x02 %s' % (irc.name, ' '.join(remote_networks))
    irc.msg(source, s)

    # Sort the list of shared channels when displaying
    for k, v in sorted(db.items()):

        # Bold each network/channel name pair
        s = '\x02%s%s\x02 ' % k
        remoteirc = world.networkobjects.get(k[0])
        channel = k[1]  # Get the channel name from the network/channel pair

        if remoteirc and channel in remoteirc.channels:
            c = remoteirc.channels[channel]
            if ('s', None) in c.modes or ('p', None) in c.modes:
                # Only show secret channels to opers, and tag them with
                # [secret].
                if irc.isOper(source):
                    s += '\x02[secret]\x02 '
                else:
                    continue

        if v['links']:  # Join up and output all the linked channel names.
            s += ' '.join([''.join(link) for link in sorted(v['links'])])

        else:  # Unless it's empty; then, well... just say no relays yet.
            s += '(no relays yet)'

        irc.msg(source, s)

        if irc.isOper(source):
            s = ''

            # If the caller is an oper, we can show the hostmasks of people
            # that created all the available channels (Janus does this too!!)
            creator = v.get('creator')
            if creator:
                # But only if the value actually exists (old DBs will have it
                # missing).
                s += ' by \x02%s\x02' % creator

            # Ditto for creation date
            ts = v.get('ts')
            if ts:
                s += ' on %s' % time.ctime(ts)

            if s:  # Indent to make the list look nicer
                irc.msg(source, '    Channel created%s.' % s)

@utils.add_cmd
def linkacl(irc, source, args):
    """ALLOW|DENY|LIST <channel> <remotenet>

    Allows blocking / unblocking certain networks from linking to a relay, based on a blacklist.
    LINKACL LIST returns a list of blocked networks for a channel, while the ALLOW and DENY subcommands allow manipulating this blacklist."""
    missingargs = "Error: Not enough arguments. Needs 2-3: subcommand (ALLOW/DENY/LIST), channel, remote network (for ALLOW/DENY)."
    irc.checkAuthenticated(source)
    try:
        cmd = args[0].lower()
        channel = utils.toLower(irc, args[1])
    except IndexError:
        irc.reply(missingargs)
        return
    if not utils.isChannel(channel):
        irc.reply('Error: Invalid channel %r.' % channel)
        return
    relay = getRelay((irc.name, channel))
    if not relay:
        irc.reply('Error: No such relay %r exists.' % channel)
        return
    if cmd == 'list':
        s = 'Blocked networks for \x02%s\x02: \x02%s\x02' % (channel, ', '.join(db[relay]['blocked_nets']) or '(empty)')
        irc.reply(s)
        return

    try:
        remotenet = args[2]
    except IndexError:
        irc.reply(missingargs)
        return
    if cmd == 'deny':
        db[relay]['blocked_nets'].add(remotenet)
        irc.reply('Done.')
    elif cmd == 'allow':
        try:
            db[relay]['blocked_nets'].remove(remotenet)
        except KeyError:
            irc.reply('Error: Network %r is not on the blacklist for %r.' % (remotenet, channel))
        else:
            irc.reply('Done.')
    else:
        irc.reply('Error: Unknown subcommand %r: valid ones are ALLOW, DENY, and LIST.' % cmd)

@utils.add_cmd
def showuser(irc, source, args):
    """<user>

    Shows relay data about user <user>. This supplements the 'showuser' command in the 'commands' plugin, which provides more general information."""
    try:
        target = args[0]
    except IndexError:
        # No errors here; showuser from the commands plugin already does this
        # for us.
        return
    u = irc.nickToUid(target)
    if u:
        try:
            userpair = getOrigUser(irc, u) or (irc.name, u)
            remoteusers = relayusers[userpair].items()
        except KeyError:
            pass
        else:
            nicks = []
            if remoteusers:
                nicks.append('%s:\x02%s\x02' % (userpair[0],
                             world.networkobjects[userpair[0]].users[userpair[1]].nick))
                for r in remoteusers:
                    remotenet, remoteuser = r
                    remoteirc = world.networkobjects[remotenet]
                    nicks.append('%s:\x02%s\x02' % (remotenet, remoteirc.users[remoteuser].nick))
                irc.msg(source, "\x02Relay nicks\x02: %s" % ', '.join(nicks))
        relaychannels = []
        for ch in irc.users[u].channels:
            relay = getRelay((irc.name, ch))
            if relay:
                relaychannels.append(''.join(relay))
        if relaychannels and (irc.isOper(source) or u == source):
            irc.msg(source, "\x02Relay channels\x02: %s" % ' '.join(relaychannels))

@utils.add_cmd
def save(irc, source, args):
    """takes no arguments.

    Saves the relay database to disk."""
    irc.checkAuthenticated(source)
    exportDB()
    irc.reply('Done.')

@utils.add_cmd
def claim(irc, source, args):
    """<channel> [<comma separated list of networks>]

    Sets the CLAIM for a channel to a case-sensitive list of networks. If no list of networks is given, shows which networks have claim over the channel. A single hyphen (-) can also be given as a list of networks to remove claim from the channel entirely.

    CLAIM is a way of enforcing network ownership for a channel, similarly to Janus. Unless the list is empty, only networks on the CLAIM list for a channel (plus the creating network) are allowed to override kicks, mode changes, and topic changes in it - attempts from other networks' opers to do this are simply blocked or reverted."""
    irc.checkAuthenticated(source)
    try:
        channel = utils.toLower(irc, args[0])
    except IndexError:
        irc.reply("Error: Not enough arguments. Needs 1-2: channel, list of networks (optional).")
        return

    # We override getRelay() here to limit the search to the current network.
    relay = (irc.name, channel)
    if relay not in db:
        irc.reply('Error: No such relay %r exists.' % channel)
        return
    claimed = db[relay]["claim"]
    try:
        nets = args[1].strip()
    except IndexError:  # No networks given.
        irc.reply('Channel \x02%s\x02 is claimed by: %s' %
                (channel, ', '.join(claimed) or '\x1D(none)\x1D'))
    else:
        if nets == '-' or not nets:
            claimed = set()
        else:
            claimed = set(nets.split(','))
        db[relay]["claim"] = claimed
        irc.reply('CLAIM for channel \x02%s\x02 set to: %s' %
                (channel, ', '.join(claimed) or '\x1D(none)\x1D'))