path: root/python/src/tcf/services/local/LocatorService.py

# *******************************************************************************
# * Copyright (c) 2011 Wind River Systems, Inc. and others.
# * All rights reserved. This program and the accompanying materials
# * are made available under the terms of the Eclipse Public License v1.0
# * which accompanies this distribution, and is available at
# * http://www.eclipse.org/legal/epl-v10.html
# *
# * Contributors:
# *     Wind River Systems - initial API and implementation
# *******************************************************************************

"""
Locator service uses transport layer to search
for peers and to collect and maintain up-to-date
data about peer's attributes.
"""

import threading, time, socket, cStringIO
from tcf.services import locator
from tcf.util import logging
from tcf.channel import fromJSONSequence, toJSONSequence
from tcf.channel.ChannelProxy import ChannelProxy
from tcf import protocol, services, channel, peer, errors

# Flag indicating whether tracing of the the discovery activity is enabled.
__TRACE_DISCOVERY__ = False

class SubNet(object):
    def __init__(self, prefix_length, address, broadcast):
        self.prefix_length = prefix_length
        self.address = address
        self.broadcast = broadcast
        self.last_slaves_req_time = 0
    def contains(self, addr):
        if addr is None or self.address is None: return False
        a1 = addr.getAddress()
        a2 = self.address.getAddress()
        if len(a1) != len(a2): return False
        i = 0
        if self.prefix_length <= len(a1) * 8:
            l = self.prefix_length
        else:
            l = len(a1) * 8
        while i + 8 <= l:
            n = i / 8
            if a1[n] != a2[n]: return False
            i += 8
        while i < l:
            n = i / 8
            m = 1 << (7 - i % 8)
            if (a1[n] & m) != (a2[n] & m): return False
            i += 1
        return True
    def __eq__(self, o):
        if not isinstance(o, SubNet): return False
        return self.prefix_length == o.prefix_length and \
            self.broadcast == o.broadcast and \
            self.address == o.address
    def __hash__(self):
        return hash(self.address)
    def __str__(self):
        return "%s/%d" % (self.address.getHostAddress(), self.prefix_length)

class Slave(object):
    # Time of last packet receiver from self slave
    last_packet_time = 0
    #Time of last REQ_SLAVES packet received from self slave
    last_req_slaves_time = 0

    def __init__(self, address, port):
        self.address = address
        self.port = port
    def __str__(self):
        return "%s/%d" % (self.address.getHostAddress(), self.port)

class AddressCacheItem(object):
    address = None
    time_stamp = 0
    used = False
    def __init__(self, host):
        self.host = host

class InetAddress(object):
    "Mimicking Java InetAddress class"
    def __init__(self, host, addr):
        self.host = host
        self.addr = addr
    def getAddress(self):
        return socket.inet_aton(self.addr)
    def getHostAddress(self):
        return self.addr
    def __eq__(self, other):
        if not isinstance(other, InetAddress): return False
        return self.addr == other.addr
    def __str__(self):
        return "%s/%s" % (self.host or "", self.addr)

class InputPacket(object):
    "Wrapper for UDP packet data."
    def __init__(self, data, addr, port):
        self.data = data
        self.addr = addr
        self.port = port
    def getLength(self):
        return len(self.data)
    def getData(self):
        return self.data
    def getPort(self):
        return self.port
    def getAddress(self):
        return self.addr
    def __str__(self):
        return "[address=%s,port=%d,data=\"%s\"]" % (self.getAddress(), self.getPort(), self.data)

DISCOVEY_PORT = 1534
MAX_PACKET_SIZE = 9000 - 40 - 8
PREF_PACKET_SIZE = 1500 - 40 - 8

# TODO: research usage of DNS-SD (DNS Service Discovery) to discover TCF peers
class LocatorService(locator.LocatorService):
    locator = None
    peers = {} # str->Peer
    listeners = [] # list of LocatorListener
    error_log = set() # set of str

    addr_cache = {} # str->AddressCacheItem
    addr_request = False
    local_peer = None
    last_master_packet_time = 0

    @classmethod
    def getLocalPeer(cls):
        return cls.local_peer

    @classmethod
    def getListeners(cls):
        return cls.listeners[:]

    @classmethod
    def startup(cls):
        if cls.locator:
            cls.locator._startup()
    
    @classmethod
    def shutdown(cls):
        if cls.locator:
            cls.locator._shutdown()

    def __init__(self):
        self._error_log_lock = threading.RLock()
        self._alive = False
        LocatorService.locator = self
        LocatorService.local_peer = peer.LocalPeer()
    
    def _startup(self):
        if self._alive: return
        self._alive = True
        self._addr_cache_lock = threading.Condition()
        self.subnets = set()
        self.slaves = []
        self.inp_buf = bytearray(MAX_PACKET_SIZE)
        self.out_buf = bytearray(MAX_PACKET_SIZE)
        service = self
        class TimerThread(threading.Thread):
            def __init__(self, callable):
                self._callable = callable
                super(TimerThread, self).__init__()
            def run(self):
                while service._alive:
                    try:
                        time.sleep(locator.DATA_RETENTION_PERIOD / 4 / 1000.)
                        protocol.invokeAndWait(self._callable)
                    except RuntimeError:
                        # TCF event dispatch is shut down
                        return
                    except Exception as x:
                        service._log("Unhandled exception in TCF discovery timer thread", x)
        self.timer_thread = TimerThread(self.__refresh_timer)
        class DNSLookupThread(threading.Thread):
            def run(self):
                while service._alive:
                    try:
                        itemSet = None
                        with service._addr_cache_lock:
                            if not LocatorService.addr_request:
                                service._addr_cache_lock.wait(locator.DATA_RETENTION_PERIOD)
                            msec = int(time.time() * 1000)
                            for a in LocatorService.addr_cache.values():
                                if a.time_stamp + locator.DATA_RETENTION_PERIOD * 10 < msec:
                                    if a.used:
                                        if itemSet is None: itemSet = set()
                                        itemSet.add(a)
                                    else:
                                        LocatorService.addr_cache.remove(a)
                            LocatorService.addr_request = False
                        if itemSet is not None:
                            for a in itemSet:
                                addr = None
                                try:
                                    addr = socket.gethostbyname(a.host)
                                except socket.gaierror:
                                    pass
                                with service._addr_cache_lock:
                                    if addr is None:
                                        a.address = None
                                    else:
                                        a.address = InetAddress(a.host, addr)
                                    a.time_stamp = time
                                    a.used = False
                    except Exception as x:
                        service._log("Unhandled exception in TCF discovery DNS lookup thread", x)
        self.dns_lookup_thread = DNSLookupThread()
        class InputThread(threading.Thread):
            def __init__(self, callable):
                self._callable = callable
                super(InputThread, self).__init__()
            def run(self):
                try:
                    while service._alive:
                        sock = service.socket
                        try:
                            data, addr = sock.recvfrom(MAX_PACKET_SIZE)
                            p = InputPacket(data, InetAddress(None, addr[0]), addr[1])
                            protocol.invokeAndWait(self._callable, p)
                        except RuntimeError:
                            # TCF event dispatch is shutdown
                            return
                        except socket.error as x:
                            if sock != service.socket: continue
                            # frequent  error on windows, unknown reason
                            if x.errno == 10054: continue
                            port = sock.getsockname()[1]
                            service._log("Cannot read from datagram socket at port %d" % port, x)
                            time.sleep(2)
                except Exception as x:
                    service._log("Unhandled exception in socket reading thread", x)
        self.input_thread = InputThread(self.__handleDatagramPacket)
        try:
            self.loopback_addr = InetAddress(None, "127.0.0.1")
            self.out_buf[0:8] = 'TCF%s\0\0\0\0' % locator.CONF_VERSION
            self.socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
            try:
                self.socket.bind(('', DISCOVEY_PORT))
                if __TRACE_DISCOVERY__:
                    logging.trace("Became the master agent (bound to port %d)" % self.socket.getsockname()[1])
            except socket.error as x:
                self.socket.bind(('', 0))
                if __TRACE_DISCOVERY__:
                    logging.trace("Became a slave agent (bound to port %d)" % self.socket.getsockname()[1])
            self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
            self.input_thread.setName("TCF Locator Receiver")
            self.timer_thread.setName("TCF Locator Timer")
            self.dns_lookup_thread.setName("TCF Locator DNS Lookup")
            self.input_thread.setDaemon(True)
            self.timer_thread.setDaemon(True)
            self.dns_lookup_thread.setDaemon(True)
            self.input_thread.start()
            self.timer_thread.start()
            self.dns_lookup_thread.start()
            class LocatorListener(locator.LocatorListener):
                def peerAdded(self, peer):
                    service._sendPeerInfo(peer, None, 0)
                def peerChanged(self, peer):
                    service._sendPeerInfo(peer, None, 0)
            self.listeners.append(LocatorListener())
            self.__refreshSubNetList()
            self.__sendPeersRequest(None, 0)
            self.__sendAll(None, 0, None, int(time.time() * 1000))
        except Exception as x:
            self._log("Cannot open UDP socket for TCF discovery protocol", x)

    def _shutdown(self):
        if self._alive:
            self._alive = False

    def __makeErrorReport(self, code, msg):
        err = {}
        err[errors.ERROR_TIME] = int(time.time() * 1000)
        err[errors.ERROR_CODE] = code
        err[errors.ERROR_FORMAT] = msg
        return err

    def __command(self, channel, token, name, data):
        try:
            if name == "redirect":
                peer_id = fromJSONSequence(data)[0]
                _peer = self.peers.get(peer_id)
                if _peer is None:
                    error = self.__makeErrorReport(errors.TCF_ERROR_UNKNOWN_PEER, "Unknown peer ID")
                    channel.sendResult(token, toJSONSequence((error,)))
                    return
                channel.sendResult(token, toJSONSequence((None,)))
                if isinstance(_peer, peer.LocalPeer):
                    channel.sendEvent(protocol.getLocator(), "Hello", toJSONSequence((channel.getLocalServices(),)))
                    return
                ChannelProxy(channel, _peer.openChannel())
            elif name == "sync":
                channel.sendResult(token, None)
            elif name == "getPeers":
                arr = []
                for p in self.peers.values():
                    arr.append(p.getAttributes())
                channel.sendResult(token, toJSONSequence((None, arr)))
            else:
                channel.rejectCommand(token)
        except Exception as x:
            channel.terminate(x)

    def _log(self, msg, x):
        if not self._alive: return
        # Don't report same error multiple times to avoid filling up the log file.
        with self._error_log_lock:
            if msg in self.error_log: return
            self.error_log.add(msg)
        protocol.log(msg, x)

    def __getInetAddress(self, host):
        if not host: return None
        with self._addr_cache_lock:
            i = self.addr_cache.get(host)
            if i is None:
                i = AddressCacheItem(host)
                ch = host[0]
                if ch == '[' or ch == ':' or ch >= '0' and ch <= '9':
                    try:
                        addr = socket.gethostbyname(host)
                        i.address = InetAddress(host, addr)
                    except socket.gaierror:
                        pass
                    i.time_stamp = int(time.time() * 1000)
                else:
                    # socket.gethostbyname() can cause long delay - delegate to background thread
                    LocatorService.addr_request = True
                    self._addr_cache_lock.notify()
                self.addr_cache[host] = i
            i.used = True
            return i.address

    def __refresh_timer(self):
        tm = int(time.time() * 1000)
        # Cleanup slave table
        if self.slaves:
            i = 0
            while i < len(self.slaves):
                s = self.slaves[i]
                if s.last_packet_time + locator.DATA_RETENTION_PERIOD < tm:
                    del self.slaves[i]
                else:
                    i += 1

        # Cleanup peers table
        stale_peers = None
        for p in self.peers.values():
            if isinstance(p, peer.RemotePeer):
                if p.getLastUpdateTime() + locator.DATA_RETENTION_PERIOD < time:
                    if stale_peers == None: stale_peers = []
                    stale_peers.append(p)
        if stale_peers is not None:
            for p in stale_peers: p.dispose()

        # Try to become a master
        port = self.socket.getsockname()[1]
        if port != DISCOVEY_PORT and \
                self.last_master_packet_time + locator.DATA_RETENTION_PERIOD / 2 <= tm:
            s0 = self.socket
            s1 = None
            try:
                s1 = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
                s1.bind(DISCOVEY_PORT)
                s1.setsockopt(socket.SOL_UDP, socket.SO_BROADCAST, 1)
                self.socket = s1
                s0.close()
            except:
                pass
        self.__refreshSubNetList()
        if port != DISCOVEY_PORT:
            for subnet in self.subnets:
                self.__addSlave(subnet.address, port, tm, tm)
        self.__sendAll(None, 0, None, tm)

    def __addSlave(self, addr, port, timestamp, time_now):
        for s in self.slaves:
            if s.port == port and s.address == addr:
                if s.last_packet_time < timestamp: s.last_packet_time = timestamp
                return s
        s = Slave(addr, port)
        s.last_packet_time = timestamp
        self.slaves.append(s)
        self.__sendPeersRequest(addr, port)
        self.__sendAll(addr, port, s, time_now)
        self.__sendSlaveInfo(s, time_now)
        return s

    def __refreshSubNetList(self):
        subNetSet = set()
        try:
            self.__getSubNetList(subNetSet)
        except Exception as x:
            self._log("Cannot get list of network interfaces", x)
        for s in tuple(self.subnets):
            if s in subNetSet: continue
            self.subnets.remove(s)
        for s in subNetSet:
            if s in self.subnets: continue
            self.subnets.add(s)
        if __TRACE_DISCOVERY__:
            str = cStringIO.StringIO()
            str.write("Refreshed subnet list:")
            for subnet in self.subnets:
                str.write("\n\t* address=%s, broadcast=%s" % (subnet.address, subnet.broadcast))
            logging.trace(str.getvalue())

    def __getSubNetList(self, set):
        # TODO iterate over network interfaces to get proper broadcast addresses
        hostname = socket.gethostname()
        _, _, addresses = socket.gethostbyname_ex(hostname)
        if not "127.0.0.1" in addresses:
            addresses.append("127.0.0.1")
        for address in addresses:
            rawaddr = socket.inet_aton(address)
            if len(rawaddr) != 4: continue
            rawaddr = rawaddr[:3] + '\xFF'
            broadcast = socket.inet_ntoa(rawaddr)
            set.add(SubNet(24, InetAddress(hostname, address), InetAddress(None, broadcast)))

    def __getUTF8Bytes(self, s):
        return s.encode("UTF-8")

    # Used for tracing
    packetTypes = [
        None,
        "CONF_REQ_INFO",
        "CONF_PEER_INFO",
        "CONF_REQ_SLAVES",
        "CONF_SLAVES_INFO"
    ]

    def __sendDatagramPacket(self, subnet, size, addr, port):
        try:
            if addr is None:
                addr = subnet.broadcast
                port = DISCOVEY_PORT
                for slave in self.slaves:
                    self.__sendDatagramPacket(subnet, size, slave.address, slave.port)
            if not subnet.contains(addr): return False
            if port == self.socket.getsockname()[1] and addr == subnet.address: return False
            self.socket.sendto(str(self.out_buf[:size]), (addr.getHostAddress(), port))

            if __TRACE_DISCOVERY__:
                map = None
                if self.out_buf[4] == locator.CONF_PEER_INFO:
                    map = self.__parsePeerAttributes(self.out_buf, 8)
                self.__traceDiscoveryPacket(False, self.packetTypes[self.out_buf[4]], map, addr, port)
        except Exception as x:
            self._log("Cannot send datagram packet to %s" % addr, x)
            return False
        return True

    def __parsePeerAttributes(self, data, size):
        """
        Parse peer attributes in CONF_INFO_PEER packet data

        @param data
                   the packet section that contain the peer attributes
        @param size
                   the number of bytes in [data] that contain peer attributes
        @return a map containing the attributes
        """
        map = {}
        s = data[8:size - 8].decode("UTF-8")
        l = len(s)
        i = 0
        while i < l:
            i0 = i
            while i < l and s[i] != '=' and s[i] != '\0': i += 1
            i1 = i
            if i < l and s[i] == '=': i += 1
            i2 = i
            while i < l and s[i] != '\0': i += 1
            i3 = i
            if i < l and s[i] == '\0': i += 1
            key = s[i0:i1]
            val = s[i2:i3]
            map[key] = val
        return map

    def __sendPeersRequest(self, addr, port):
        self.out_buf[4] = locator.CONF_REQ_INFO
        for subnet in self.subnets:
            self.__sendDatagramPacket(subnet, 8, addr, port)

    def _sendPeerInfo(self, _peer, addr, port):
        attrs = _peer.getAttributes()
        peer_addr = self.__getInetAddress(attrs.get(peer.ATTR_IP_HOST))
        if peer_addr is None: return
        if attrs.get(peer.ATTR_IP_PORT) is None: return
        self.out_buf[4] = locator.CONF_PEER_INFO
        i = 8

        for subnet in self.subnets:
            if isinstance(_peer, peer.RemotePeer):
                if self.socket.getsockname()[1] != DISCOVEY_PORT: return
                if not subnet.address == self.loopback_addr and not subnet.address == peer_addr: continue
            if not subnet.address == self.loopback_addr:
                if not subnet.contains(peer_addr): continue
            if i == 8:
                sb = cStringIO.StringIO()
                for key in attrs.keys():
                    sb.write(key)
                    sb.write('=')
                    sb.write(attrs.get(key))
                    sb.write('\0')
                bt = self.__getUTF8Bytes(sb.getvalue())
                if i + len(bt) > len(self.out_buf): return
                self.out_buf[i:i+len(bt)] = bt
                i += len(bt)
            if self.__sendDatagramPacket(subnet, i, addr, port): subnet.send_all_ok = True

    def __sendEmptyPacket(self, addr, port):
        self.out_buf[4] = locator.CONF_SLAVES_INFO
        for subnet in self.subnets:
            if subnet.send_all_ok: continue
            self.__sendDatagramPacket(subnet, 8, addr, port)

    def __sendAll(self, addr, port, sl, tm):
        for subnet in self.subnets: subnet.send_all_ok = False
        for peer in self.peers.values(): self._sendPeerInfo(peer, addr, port)
        if addr is not None and sl is not None and sl.last_req_slaves_time + locator.DATA_RETENTION_PERIOD >= tm:
            self.__sendSlavesInfo(addr, port, tm)
        self.__sendEmptyPacket(addr, port)

    def __sendSlavesRequest(self, subnet, addr, port):
        self.out_buf[4] = locator.CONF_REQ_SLAVES
        self.__sendDatagramPacket(subnet, 8, addr, port)

    def __sendSlaveInfo(self, x, tm):
        ttl = x.last_packet_time + locator.DATA_RETENTION_PERIOD - tm
        if ttl <= 0: return
        self.out_buf[4] = locator.CONF_SLAVES_INFO
        for subnet in self.subnets:
            if not subnet.contains(x.address): continue
            i = 8
            s = "%d:%s:%s" % (ttl, x.port, x.address.getHostAddress())
            bt = self.__getUTF8Bytes(s)
            self.out_buf[i:i+len(bt)] = bt
            i += len(bt)
            self.out_buf[i] = 0
            i += 1
            for y in self.slaves:
                if not subnet.contains(y.address): continue
                if y.last_req_slaves_time + locator.DATA_RETENTION_PERIOD < tm: continue
                self.__sendDatagramPacket(subnet, i, y.address, y.port)

    def __sendSlavesInfo(self, addr, port, tm):
        self.out_buf[4] = locator.CONF_SLAVES_INFO
        for subnet in self.subnets:
            if not subnet.contains(addr): continue
            i = 8
            for x in self.slaves:
                ttl = x.last_packet_time + locator.DATA_RETENTION_PERIOD - tm
                if ttl <= 0: return
                if x.port == port and x.address == addr: continue
                if not subnet.address == self.loopback_addr:
                    if not subnet.contains(x.address): continue
                subnet.send_all_ok = True
                s = "%d:%s:%s" % (x.last_packet_time, x.port, x.address.getHostAddress())
                bt = self.__getUTF8Bytes(s)
                if i > 8 and i + len(bt) >= PREF_PACKET_SIZE:
                    self.__sendDatagramPacket(subnet, i, addr, port)
                    i = 8
                self.out_buf[i:len(bt)] = bt
                i += len(bt)
                self.out_buf[i] = 0
                i += 1
            if i > 8: self.__sendDatagramPacket(subnet, i, addr, port)

    def __isRemote(self, address, port):
        if port != self.socket.getsockname()[1]: return True
        for s in self.subnets:
            if s.address == address: return False
        return True

    def __handleDatagramPacket(self, p):
        try:
            tm = int(time.time() * 1000)
            buf = p.getData()
            len = p.getLength()
            if len < 8: return
            if buf[0] != 'T': return
            if buf[1] != 'C': return
            if buf[2] != 'F': return
            if buf[3] != locator.CONF_VERSION: return
            remote_port = p.getPort()
            remote_address = p.getAddress()
            if self.__isRemote(remote_address, remote_port):
                sl = None
                if remote_port != DISCOVEY_PORT:
                    sl = self.__addSlave(remote_address, remote_port, tm, tm)
                code = ord(buf[4])
                if code == locator.CONF_PEER_INFO:
                    self.__handlePeerInfoPacket(p)
                elif code == locator.CONF_REQ_INFO:
                    self.__handleReqInfoPacket(p, sl, tm)
                elif code == locator.CONF_SLAVES_INFO:
                    self.__handleSlavesInfoPacket(p, tm)
                elif code == locator.CONF_REQ_SLAVES:
                    self.__handleReqSlavesPacket(p, sl, tm)
                for subnet in self.subnets:
                    if not subnet.contains(remote_address): continue
                    delay = locator.DATA_RETENTION_PERIOD / 3
                    if remote_port != DISCOVEY_PORT: delay = locator.DATA_RETENTION_PERIOD / 32
                    elif subnet.address != remote_address: delay = locator.DATA_RETENTION_PERIOD / 2
                    if subnet.last_slaves_req_time + delay <= tm:
                        self.__sendSlavesRequest(subnet, remote_address, remote_port)
                        subnet.last_slaves_req_time = tm
                    if subnet.address == remote_address and remote_port == DISCOVEY_PORT:
                        self.last_master_packet_time = tm
        except Exception as x:
            self._log("Invalid datagram packet received from %s/%s" % (p.getAddress(), p.getPort()), x)

    def __handlePeerInfoPacket(self, p):
        try:
            map = self.__parsePeerAttributes(p.getData(), p.getLength())
            if __TRACE_DISCOVERY__: self.__traceDiscoveryPacket(True, "CONF_PEER_INFO", map, p)
            id = map.get(peer.ATTR_ID)
            if id is None: raise RuntimeError("Invalid peer info: no ID")
            ok = True
            host = map.get(peer.ATTR_IP_HOST)
            if host is not None:
                ok = False
                peer_addr = self.__getInetAddress(host)
                if peer_addr is not None:
                    for subnet in self.subnets:
                        if subnet.contains(peer_addr):
                            ok = True
                            break
            if ok:
                _peer = self.peers.get(id)
                if isinstance(_peer, peer.RemotePeer):
                    _peer.updateAttributes(map)
                elif _peer is None:
                    peer.RemotePeer(map)
        except Exception as x:
            self._log("Invalid datagram packet received from %s/%s" % (p.getAddress(), p.getPort()), x)

    def __handleReqInfoPacket(self, p, sl, tm):
        if __TRACE_DISCOVERY__:
            self.__traceDiscoveryPacket(True, "CONF_REQ_INFO", None, p)
        self.__sendAll(p.getAddress(), p.getPort(), sl, tm)

    def __handleSlavesInfoPacket(self, p, time_now):
        try:
            trace_map = None # used for tracing only
            slave_index = 0  # used for tracing only
            if __TRACE_DISCOVERY__:
                trace_map = {}

            s = p.getData()[8:p.getLength() - 8].decode("UTF-8")
            l = len(s)
            i = 0
            while i < l:
                time0 = i
                while i < l and s[i] != ':' and s[i] != '\0': i += 1
                time1 = i
                if i < l and s[i] == ':': i += 1
                port0 = i
                while i < l and s[i] != ':' and s[i] != '\0': i += 1
                port1 = i
                if i < l and s[i] == ':': i += 1
                host0 = i
                while i < l and s[i] != '\0': i += 1
                host1 = i
                if i < l and s[i] == '\0': i += 1
                port = int(s[port0:port1])
                timestamp = s[time0:time1]
                host = s[host0:host1]
                if __TRACE_DISCOVERY__:
                    trace_map["slave[%d]" % slave_index] = "%s:%d:%s" % (timestamp, port, host)
                    slave_index += 1
                if port != DISCOVEY_PORT:
                    addr = self.__getInetAddress(host)
                    if addr is not None:
                        delta = 10006030 # 30 minutes
                        if len(timestamp) > 0:
                            time_val =  int(timestamp)
                        else:
                            time_val = time_now
                        if time_val < 3600000:
                            # Time stamp is "time to live" in milliseconds
                            time_val = time_now + time_val / 1000 - locator.DATA_RETENTION_PERIOD
                        elif time_val < time_now / 1000 + 50000000:
                            # Time stamp is in seconds
                            time_val= 1000
                        else:
                            # Time stamp is in milliseconds
                            pass
                        if time_val < time_now - delta or time_val > time_now + delta:
                            msg = "Invalid slave info timestamp: %s -> %s" % (
                                    timestamp, time.strftime("%Y-%m-%d %H:%M:%S", time.localtime(time_val/1000.)))
                            self._log("Invalid datagram packet received from %s/%s" % (p.getAddress(), p.getPort()), Exception(msg))
                            time_val = time_now - locator.DATA_RETENTION_PERIOD / 2
                        self.__addSlave(addr, port, time_val, time_now)
            if __TRACE_DISCOVERY__:
                self.__traceDiscoveryPacket(True, "CONF_SLAVES_INFO", trace_map, p)
        except Exception as x:
            self._log("Invalid datagram packet received from %s/%s" % (p.getAddress(), p.getPort()), x)

    def __handleReqSlavesPacket(self, p, sl, tm):
        if __TRACE_DISCOVERY__:
            self.__traceDiscoveryPacket(True, "CONF_REQ_SLAVES", None, p)
        if sl is not None: sl.last_req_slaves_time = tm
        self.__sendSlavesInfo(p.getAddress(), p.getPort(), tm)

    @classmethod
    def getLocator(cls):
        return cls.locator

    def getPeers(self):
        assert protocol.isDispatchThread()
        return self.peers

    def redirect(self, peer, done):
        raise RuntimeError("Channel redirect cannot be done on local peer")

    def sync(self, done):
        raise RuntimeError("Channel sync cannot be done on local peer")

    def addListener(self, listener):
        assert listener is not None
        assert protocol.isDispatchThread()
        self.listeners.add(listener)

    def removeListener(self, listener):
        assert protocol.isDispatchThread()
        self.listeners.remove(listener)

    @classmethod
    def __traceDiscoveryPacket(cls, received, type, attrs, addr, port=None):
        """
        Log that a TCF Discovery packet has be sent or received. The trace is
        sent to stdout. This should be called only if the tracing has been turned
        on.

        @param received
                   True if the packet was sent, otherwise it was received
        @param type
                   a string specifying the type of packet, e.g., "CONF_PEER_INFO"
        @param attrs
                   a set of attributes relevant to the type of packet (typically
                   a peer's attributes)
        @param addr
                   the network address the packet is being sent to
        @param port
                   the port the packet is being sent to
        """
        assert __TRACE_DISCOVERY__
        if port is None:
            # addr is a InputPacket
            port = addr.getPort()
            addr = addr.getAddress()
        str = cStringIO.StringIO()
        str.write(type)
        str.write((" sent to ", " received from ")[received])
        str.write("%s/%s" % (addr, port))
        if attrs is not None:
            for key, value in attrs.items():
                str.write("\n\t%s=%s" % (key, value))
        logging.trace(str.getvalue())

class LocatorServiceProvider(services.ServiceProvider):
    def getLocalService(self, _channel):
        class CommandServer(channel.CommandServer):
            def command(self, token, name, data):
                LocatorService.locator.command(channel, token, name, data)
        _channel.addCommandServer(LocatorService.locator, CommandServer())
        return (LocatorService.locator,)

services.addServiceProvider(LocatorServiceProvider())