irkerd

#!/usr/bin/env python
"""
irkerd - a simple IRC multiplexer daemon

Listens for JSON objects of the form {'to':<irc-url>, 'privmsg':<text>}
and relays messages to IRC channels. Each request must be followed by
a newline.

The <text> must be a string.  The value of the 'to' attribute can be a
string containing an IRC URL (e.g. 'irc://chat.freenet.net/botwar') or
a list of such strings; in the latter case the message is broadcast to
all listed channels.  Note that the channel portion of the URL need
*not* have a leading '#' unless the channel name itself does.

Options: -d sets the debug-message level (probably only of interest to
developers). The -V option prints the program version and exits.

Design and code by Eric S. Raymond <esr@thyrsus.com>. See the project
resource page at <http://www.catb.org/~esr/irker/>.

Requires Python 2.6 and the irc client library at version >= 2.0.2: see

http://pypi.python.org/pypi/irc/
"""
# These things might need tuning

HOST = "localhost"
PORT = 6659

NAMESTYLE = "irker%03d"		# IRC nick template - must contain '%d'
XMIT_TTL = (3 * 60 * 60)	# Time to live, seconds from last transmit
PING_TTL = (15 * 60)		# Time to live, seconds from last PING
DISCONNECT_TTL = (24 * 60 * 60)	# Time to live, seconds from last connect
UNSEEN_TTL = 60			# Time to live, seconds since first request
CHANNEL_MAX = 18		# Max channels open per socket (default)
ANTI_FLOOD_DELAY = 0.5		# Anti-flood delay after transmissions, seconds
ANTI_BUZZ_DELAY = 0.09		# Anti-buzz delay after queue-empty check

# No user-serviceable parts below this line

# This black magic imports support for green threads (coroutines),
# then has kinky sex with the import library internals, replacing
# "threading" with a coroutine-using imposter.  Threads then become
# ultra-light-weight and cooperatively scheduled.
try:
    import eventlet
    eventlet.monkey_patch()
    green_threads = True
    # With greenlets we don't worry about thread exhaustion, only the
    # file descriptor limit (typically 1024 on modern Unixes). Thus we
    # can handle a lot more concurrent sessions and generate less
    # join/leave spam under heavy load.
    CONNECTION_MAX = 1000
except ImportError:
    # Threads are more expensive if we have to use OS-level ones
    # rather than greenlets.  We need to avoid pushing thread limits
    # as well as fd limits.  See security.txt for discussion.
    CONNECTION_MAX = 200
    green_threads = False

import sys, json, getopt, urlparse, time, random
import threading, Queue, SocketServer
import irc.client, logging

version = "1.4"

# Sketch of implementation:
#
# One Irker object manages multiple IRC sessions.  It holds a map of
# Dispatcher objects, one per (server, port) combination, which are
# responsible for routing messages to one of any number of Connection
# objects that do the actual socket conversations.  The reason for the
# Dispatcher layer is that IRC daemons limit the number of channels a
# client (that is, from the daemon's point of view, a socket) can be
# joined to, so each session to a server needs a flock of Connection
# instances each with its own socket.
#
# Connections are timed out and removed when either they haven't seen a
# PING for a while (indicating that the server may be stalled or down)
# or there has been no message traffic to them for a while, or
# even if the queue is nonempty but efforts to connect have failed for
# a long time.
#
# There are multiple threads. One accepts incoming traffic from all servers.
# Each Connection also has a consumer thread and a thread-safe message queue.
# The program main appends messages to queues as JSON requests are received;
# the consumer threads try to ship them to servers.  When a socket write
# stalls, it only blocks an individual consumer thread; if it stalls long
# enough, the session will be timed out.
#
# Message delivery is thus not reliable in the face of network stalls,
# but this was considered acceptable because IRC (notoriously) has the
# same problem - there is little point in reliable delivery to a relay
# that is down or unreliable.
#
# This code uses only NICK, JOIN, MODE, and PRIVMSG. It is strictly
# compliant to RFC1459, except for the interpretation and use of the
# DEAF and CHANLIMIT and (obsolete) MAXCHANNELS features.  CHANLIMIT
# is as described in the Internet RFC draft
# draft-brocklesby-irc-isupport-03 at <http://www.mirc.com/isupport.html>.

class Connection:
    def __init__(self, irkerd, servername, port):
        self.irker = irkerd
        self.servername = servername
        self.port = port
        self.nick_trial = None
        self.connection = None
        self.status = "unseen"
        self.last_xmit = time.time()
        self.last_ping = time.time()
        self.channels_joined = []
        self.channel_limits = {}
        # The consumer thread
        self.queue = Queue.Queue()
        self.thread = threading.Thread(target=self.dequeue)
        self.thread.daemon = True
        self.thread.start()
    def nickname(self, n=None):
        "Return a name for the nth server connection."
        if n is None:
            n = self.nick_trial
        return (NAMESTYLE % n)
    def handle_ping(self):
        "Register the fact that the server has pinged this connection."
        self.last_ping = time.time()
    def handle_welcome(self):
        "The server says we're OK, with a non-conflicting nick."
        self.status = "ready"
        self.irker.debug(1, "nick %s accepted" % self.nickname())
    def handle_badnick(self):
        "The server says our nick has a conflict."
        self.irker.debug(1, "nick %s rejected" % self.nickname())
        # Randomness prevents a malicious user or bot from antcipating the
        # next trial name in order to block us from completing the handshake.
        self.nick_trial += random.randint(1, 3)
        self.connection.nick(self.nickname())
    def handle_disconnect(self):
        "Server disconnected us for flooding or some other reason."
        self.connection = None
    def handle_kick(self, outof):
        "We've been kicked."
        self.status = "handshaking"
        try:
            self.channels_joined.remove(outof)
        except ValueError:
            self.irker.logerr("kicked by %s from %s that's not joined" \
                              % (self.servername, outof))
        qcopy = []
        while not self.queue.empty():
            (channel, message) = self.queue.get()
            if channel != outof:
                qcopy.append((channel, message))
        for (channel, message) in qcopy:
            self.queue.put((channel, message))
        self.status = "ready"
    def enqueue(self, channel, message):
        "Enque a message for transmission."
        self.queue.put((channel, message))
    def dequeue(self):
        "Try to ship pending messages from the queue."
        while True:
            # We want to be kind to the IRC servers and not hold unused
            # sockets open forever, so they have a time-to-live.  The
            # loop is coded this particular way so that we can drop
            # the actual server connection when its time-to-live
            # expires, then reconnect and resume transmission if the
            # queue fills up again.
            if not self.connection:
                self.connection = self.irker.irc.server()
                self.connection.context = self
                # Try to avoid colliding with other instances
                self.nick_trial = random.randint(1, 990)
                self.channels_joined = []
                # This will throw irc.client.ServerConnectionError on failure
                try:
                    self.connection.connect(self.servername,
                                        self.port,
                                        nickname=self.nickname(),
                                        username="irker",
                                        ircname="irker relaying client")
                    self.status = "handshaking"
                    self.irker.debug(1, "XMIT_TTL bump (%s connection) at %s" % (self.servername, time.asctime()))
                    self.last_xmit = time.time()
                except irc.client.ServerConnectionError:
                    self.status = "disconnected"
            elif self.status == "handshaking":
                # Don't buzz on the empty-queue test while we're handshaking 
                time.sleep(ANTI_BUZZ_DELAY)
            elif self.queue.empty():
                # Queue is empty, at some point we want to time out
                # the connection rather than holding a socket open in
                # the server forever.
                now = time.time()
                if now > self.last_xmit + XMIT_TTL \
                       or now > self.last_ping + PING_TTL:
                    self.irker.debug(1, "timing out inactive connection to %s at %s" % (self.servername, time.asctime()))
                    self.connection.context = None
                    self.connection.close()
                    self.connection = None
                    self.status = "disconnected"
                else:
                    # Prevent this thread from hogging the CPU by pausing
                    # for just a little bit after the queue-empty check.
                    # As long as this is less that the duration of a human
                    # reflex arc it is highly unlikely any human will ever
                    # notice.
                    time.sleep(ANTI_BUZZ_DELAY)
            elif self.status == "disconnected" \
                     and time.time() > self.last_xmit + DISCONNECT_TTL:
                # Queue is nonempty, but the IRC server might be down. Letting
                # failed connections retain queue space forever would be a
                # memory leak.  
                self.status = "expired"
                break
            elif self.status == "unseen" \
                     and time.time() > self.last_xmit + UNSEEN_TTL:
                # Nasty people could attempt a denial-of-service
                # attack by flooding us with requests with invalid
                # servernames. We guard against this by rapidly
                # expiring connections that have a nonempty queue but
                # have never had a successful open.
                self.status = "expired"
                break
            elif self.status == "ready":
                (channel, message) = self.queue.get()
                if channel not in self.channels_joined:
                    self.channels_joined.append(channel)
                    self.connection.join(channel)
                    self.irker.debug(1, "joining %s on %s." % (channel, self.servername))
                for segment in message.split("\n"):
                    self.connection.privmsg(channel, segment)
                    time.sleep(ANTI_FLOOD_DELAY)
                self.last_xmit = time.time()
                self.irker.debug(1, "XMIT_TTL bump (%s transmission) at %s" % (self.servername, time.asctime()))
                self.queue.task_done()
    def live(self):
        "Should this connection not be scavenged?"
        return self.status != "expired"
    def joined_to(self, channel):
        "Is this connection joined to the specified channel?"
        return channel in self.channels_joined
    def accepting(self, channel):
        "Can this connection accept a join of this channel?"
        if self.channel_limits:
            match_count = 0
            for already in self.channels_joined:
                if already[0] == channel[0]:
                    match_count += 1
            return match_count < self.channel_limits.get(channel[0], CHANNEL_MAX)
        else:
            return len(self.channels_joined) < CHANNEL_MAX

class Target():
    "Represent a transmission target."
    def __init__(self, url):
        parsed = urlparse.urlparse(url)
        irchost, _, ircport = parsed.netloc.partition(':')
        if not ircport:
            ircport = 6667
        self.servername = irchost
        # IRC channel names are case-insensitive.  If we don't smash
        # case here we may run into problems later. There was a bug
        # observed on irc.rizon.net where an irkerd user specified #Channel,
        # got kicked, and irkerd crashed because the server returned
        # "#channel" in the notification that our kick handler saw.
        self.channel = parsed.path.lstrip('/').lower()
        if self.channel and self.channel[0] not in "#&+":
            self.channel = "#" + self.channel
        self.port = int(ircport)
    def valid(self):
        "Both components must be present for a valid target."
        return self.servername and self.channel
    def server(self):
        "Return a hashable tuple representing the destination server."
        return (self.servername, self.port)

class Dispatcher:
    "Manage connections to a particular server-port combination."
    def __init__(self, irkerd, servername, port):
        self.irker = irkerd
        self.servername = servername
        self.port = port
        self.connections = []
    def dispatch(self, channel, message):
        "Dispatch messages for our server-port combination."
        connections = [x for x in self.connections if x.live()]
        eligibles = [x for x in connections if x.joined_to(channel)] \
                    or [x for x in connections if x.accepting(channel)]
        if not eligibles:
            newconn = Connection(self.irker,
                                 self.servername,
                                 self.port)
            self.connections.append(newconn)
            eligibles = [newconn]
        eligibles[0].enqueue(channel, message)
    def live(self):
        "Does this server-port combination have any live connections?"
        self.connections = [x for x in self.connections if x.live()]
        return len(self.connections) > 0

class Irker:
    "Persistent IRC multiplexer."
    def __init__(self, debuglevel=0):
        self.debuglevel = debuglevel
        self.irc = irc.client.IRC()
        self.irc.add_global_handler("ping", self._handle_ping)
        self.irc.add_global_handler("welcome", self._handle_welcome)
        self.irc.add_global_handler("erroneusnickname", self._handle_badnick)
        self.irc.add_global_handler("nicknameinuse", self._handle_badnick)
        self.irc.add_global_handler("nickcollision", self._handle_badnick)
        self.irc.add_global_handler("unavailresource", self._handle_badnick)
        self.irc.add_global_handler("featurelist", self._handle_features)
        self.irc.add_global_handler("disconnect", self._handle_disconnect)
        self.irc.add_global_handler("kick", self._handle_kick)
        thread = threading.Thread(target=self.irc.process_forever)
        thread.daemon = True
        self.irc._thread = thread
        thread.start()
        self.servers = {}
    def logerr(self, errmsg):
        "Log a processing error."
        sys.stderr.write("irkerd: " + errmsg + "\n")
    def debug(self, level, errmsg):
        "Debugging information."
        if self.debuglevel >= level:
            sys.stderr.write("irkerd: %s\n" % errmsg)
    def _handle_ping(self, connection, _event):
        "PING arrived, bump the last-received time for the connection."
        if connection.context:
            connection.context.handle_ping()
    def _handle_welcome(self, connection, _event):
        "Welcome arrived, nick accepted for this connection."
        if connection.context:
            connection.context.handle_welcome()
    def _handle_badnick(self, connection, _event):
        "Nick not accepted for this connection."
        if connection.context:
            connection.context.handle_badnick()
    def _handle_features(self, connection, event):
        "Determine if and how we can set deaf mode."
        if connection.context:
            cxt = connection.context
            for lump in event.arguments():
                if lump.startswith("DEAF="):
                    connection.mode(cxt.nickname(), "+"+lump[5:])
                elif lump.startswith("MAXCHANNELS="):
                    m = int(lump[12:])
                    for pref in "#&+":
                        cxt.channel_limits[pref] = m
                    self.debug(1, "%s maxchannels is %d" \
                               % (connection.server, m))
                elif lump.startswith("CHANLIMIT=#:"):
                    limits = lump[10:].split(",")
                    try:
                        for token in limits:
                            (prefixes, limit) = token.split(":")
                            limit = int(limit)
                            for c in prefixes:
                                cxt.channel_limits[c] = limit
                        self.debug(1, "%s channel limit map is %s" \
                                   % (connection.server, cxt.channel_limits))
                    except ValueError:
                        self.logerr("ill-formed CHANLIMIT property")
    def _handle_disconnect(self, connection, _event):
        "Server hung up the connection."
        self.debug(1, "server %s disconnected" % connection.server)
        if connection.context:
            connection.context.handle_disconnect()
    def _handle_kick(self, connection, event):
        "Server hung up the connection."
        self.debug(1, "irker has been kicked from %s on %s" % (event.target(), connection.server))
        if connection.context:
            connection.context.handle_kick(event.target())
    def handle(self, line):
        "Perform a JSON relay request."
        try:
            request = json.loads(line.strip())
            if type(request) != type({}):
                self.logerr("request in tot a JSON dictionary: %s" % repr(request))
            elif "to" not in request or "privmsg" not in request:
                self.logerr("malformed reqest - 'to' or 'privmsg' missing: %s" % repr(request))
            else:
                channels = request['to']
                message = request['privmsg']
                if type(channels) not in (type([]), type(u"")) \
                       or type(message) != type(u""):
                    self.logerr("malformed request - unexpected types: %s" % repr(request))
                else:
                    if type(channels) == type(u""):
                        channels = [channels]
                    for url in channels:
                        if type(url) != type(u""):
                            self.logerr("malformed request - unexpected type: %s" % repr(request))
                        else:
                            target = Target(url)
                            if not target.valid():
                                return
                            if target.server() not in self.servers:
                                self.servers[target.server()] = Dispatcher(self, target.servername, target.port)
                            self.servers[target.server()].dispatch(target.channel, message)
                            # GC dispatchers with no active connections
                            servernames = self.servers.keys()
                            for servername in servernames:
                                if not self.servers[servername].live():
                                    del self.servers[servername]
                            # If we might be pushing a resource limit
                            # even after garbage collection, remove a
                            # session.  The goal here is to head off
                            # DoS attacks that aim at exhausting
                            # thread space or file descriptors.  The
                            # cost is that attempts to DoS this
                            # service will cause lots of join/leave
                            # spam as we scavenge old channels after
                            # connecting to new ones. The particular
                            # method used for selecting a session to
                            # be terminated doesn't matter much; we
                            # choose the one longest idle on the
                            # assumption that message activity is likely
                            # to be clumpy.
                            oldest = None
                            if len(self.servers) >= CONNECTION_MAX:
                                for (name, server) in self.servers.items():
                                    if not oldest or server.last_xmit < self.servers[oldest].last_xmit:
                                        oldest = name
                                del self.servers[oldest]
        except ValueError:
            self.logerr("can't recognize JSON on input: %s" % repr(line))
        except RuntimeError:
            self.logerr("wildly malformed JSON blew the parser stack.")

class IrkerTCPHandler(SocketServer.StreamRequestHandler):
    def handle(self):
        while True:
            line = self.rfile.readline()
            if not line:
                break
            irker.handle(line.strip())

class IrkerUDPHandler(SocketServer.BaseRequestHandler):
    def handle(self):
        data = self.request[0].strip()
        #socket = self.request[1]
        irker.handle(data)

if __name__ == '__main__':
    debuglvl = 0
    (options, arguments) = getopt.getopt(sys.argv[1:], "d:V")
    for (opt, val) in options:
        if opt == '-d':		# Enable debug/progress messages
            debuglvl = int(val)
            if debuglvl > 1:
                logging.basicConfig(level=logging.DEBUG)
        elif opt == '-V':	# Emit version and exit
            sys.stdout.write("irkerd version %s\n" % version)
            sys.exit(0)
    irker = Irker(debuglevel=debuglvl)
    tcpserver = SocketServer.TCPServer((HOST, PORT), IrkerTCPHandler)
    tcpserver = threading.Thread(target=tcpserver.serve_forever)
    tcpserver.daemon = True
    tcpserver.start()
    udpserver = SocketServer.UDPServer((HOST, PORT), IrkerUDPHandler)
    udpserver = threading.Thread(target=udpserver.serve_forever)
    udpserver.daemon = True
    udpserver.start()
    try:
        while True:
            time.sleep(10)
    except KeyboardInterrupt:
        raise SystemExit, 1

# end