#!/usr/bin/python

# btpeer.py

import socket
import struct
import threading
import time
import traceback


def btdebug( msg ):
    """ Prints a messsage to the screen with the name of the current thread """
    print "[%s] %s" % ( str(threading.currentThread().getName()), msg )


#==============================================================================
class BTPeer:
    """ Implements the core functionality that might be used by a peer in a
    P2P network.

    """

    #--------------------------------------------------------------------------
    def __init__( self, maxpeers, serverport, myid=None, serverhost = None ):
    #--------------------------------------------------------------------------
	""" Initializes a peer servent (sic.) with the ability to catalog
	information for up to maxpeers number of peers (maxpeers may
	be set to 0 to allow unlimited number of peers), listening on
	a given server port , with a given canonical peer name (id)
	and host address. If not supplied, the host address
	(serverhost) will be determined by attempting to connect to an
	Internet host like Google.

	"""
	self.debug = 0

	self.maxpeers = int(maxpeers)
	self.serverport = int(serverport)
	if serverhost: self.serverhost = serverhost
	else: self.__initserverhost()

	if myid: self.myid = myid
	else: self.myid = '%s:%d' % (self.serverhost, self.serverport)

	self.peerlock = threading.Lock()  # ensure proper access to
	                            # peers list (maybe better to use
	                            # threading.RLock (reentrant))
	self.peers = {}        # peerid ==> (host, port) mapping
	self.shutdown = False  # used to stop the main loop

	self.handlers = {}
	self.router = None



    #--------------------------------------------------------------------------
    def __initserverhost( self ):
    #--------------------------------------------------------------------------
	""" Attempt to connect to an Internet host in order to determine the
	local machine's IP address.

	"""
	s = socket.socket( socket.AF_INET, socket.SOCK_STREAM )
	s.connect( ( "www.google.com", 80 ) )
	self.serverhost = s.getsockname()[0]
	s.close()



    #--------------------------------------------------------------------------
    def __debug( self, msg ):
    #--------------------------------------------------------------------------
	if self.debug:
	    btdebug( msg )



    #--------------------------------------------------------------------------
    def __handlepeer( self, clientsock ):
    #--------------------------------------------------------------------------
	"""
	handlepeer( new socket connection ) -> ()

	Dispatches messages from the socket connection
	"""

	self.__debug( 'New child ' + str(threading.currentThread().getName()) )
	self.__debug( 'Connected ' + str(clientsock.getpeername()) )

	host, port = clientsock.getpeername()
	peerconn = BTPeerConnection( None, host, port, clientsock, debug=False )
	
	try:
	    msgtype, msgdata = peerconn.recvdata()
	    if msgtype: msgtype = msgtype.upper()
	    if msgtype not in self.handlers:
		self.__debug( 'Not handled: %s: %s' % (msgtype, msgdata) )
	    else:
		self.__debug( 'Handling peer msg: %s: %s' % (msgtype, msgdata) )
		self.handlers[ msgtype ]( peerconn, msgdata )
	except KeyboardInterrupt:
	    raise
	except:
	    if self.debug:
		traceback.print_exc()
	
	self.__debug( 'Disconnecting ' + str(clientsock.getpeername()) )
	peerconn.close()

    # end handlepeer method



    #--------------------------------------------------------------------------
    def __runstabilizer( self, stabilizer, delay ):
    #--------------------------------------------------------------------------
	while not self.shutdown:
	    stabilizer()
	    time.sleep( delay )

	    

    #--------------------------------------------------------------------------
    def setmyid( self, myid ):
    #--------------------------------------------------------------------------
	self.myid = myid



    #--------------------------------------------------------------------------
    def startstabilizer( self, stabilizer, delay ):
    #--------------------------------------------------------------------------
	""" Registers and starts a stabilizer function with this peer. 
	The function will be activated every <delay> seconds. 

	"""
	t = threading.Thread( target = self.__runstabilizer, 
			      args = [ stabilizer, delay ] )
	t.start()

	

    #--------------------------------------------------------------------------
    def addhandler( self, msgtype, handler ):
    #--------------------------------------------------------------------------
	""" Registers the handler for the given message type with this peer """
	assert len(msgtype) == 4
	self.handlers[ msgtype ] = handler



    #--------------------------------------------------------------------------
    def addrouter( self, router ):
    #--------------------------------------------------------------------------
	""" Registers a routing function with this peer. The setup of routing
	is as follows: This peer maintains a list of other known peers
	(in self.peers). The routing function should take the name of
	a peer (which may not necessarily be present in self.peers)
	and decide which of the known peers a message should be routed
	to next in order to (hopefully) reach the desired peer. The router
	function should return a tuple of three values: (next-peer-id, host,
	port). If the message cannot be routed, the next-peer-id should be
	None.

	"""
	self.router = router



    #--------------------------------------------------------------------------
    def addpeer( self, peerid, host, port ):
    #--------------------------------------------------------------------------
	""" Adds a peer name and host:port mapping to the known list of peers.
	
	"""
	if peerid not in self.peers and (self.maxpeers == 0 or
					 len(self.peers) < self.maxpeers):
	    self.peers[ peerid ] = (host, int(port))
	    return True
	else:
	    return False



    #--------------------------------------------------------------------------
    def getpeer( self, peerid ):
    #--------------------------------------------------------------------------
	""" Returns the (host, port) tuple for the given peer name """
	assert peerid in self.peers    # maybe make this just a return NULL?
	return self.peers[ peerid ]



    #--------------------------------------------------------------------------
    def removepeer( self, peerid ):
    #--------------------------------------------------------------------------
	""" Removes peer information from the known list of peers. """
	if peerid in self.peers:
	    del self.peers[ peerid ]



    #--------------------------------------------------------------------------
    def addpeerat( self, loc, peerid, host, port ):
    #--------------------------------------------------------------------------
	""" Inserts a peer's information at a specific position in the 
	list of peers. The functions addpeerat, getpeerat, and removepeerat
	should not be used concurrently with addpeer, getpeer, and/or 
	removepeer. 

	"""
	self.peers[ loc ] = (peerid, host, int(port))



    #--------------------------------------------------------------------------
    def getpeerat( self, loc ):
    #--------------------------------------------------------------------------
	if loc not in self.peers:
	    return None
	return self.peers[ loc ]



    #--------------------------------------------------------------------------
    def removepeerat( self, loc ):
    #--------------------------------------------------------------------------
	removepeer( self, loc ) 



    #--------------------------------------------------------------------------
    def getpeerids( self ):
    #--------------------------------------------------------------------------
	""" Return a list of all known peer id's. """
	return self.peers.keys()



    #--------------------------------------------------------------------------
    def numberofpeers( self ):
    #--------------------------------------------------------------------------
	""" Return the number of known peer's. """
	return len(self.peers)


    
    #--------------------------------------------------------------------------
    def maxpeersreached( self ):
    #--------------------------------------------------------------------------
	""" Returns whether the maximum limit of names has been added to the
	list of known peers. Always returns True if maxpeers is set to
	0.

	"""
	assert self.maxpeers == 0 or len(self.peers) <= self.maxpeers
	return self.maxpeers > 0 and len(self.peers) == self.maxpeers



    #--------------------------------------------------------------------------
    def makeserversocket( self, port, backlog=5 ):
    #--------------------------------------------------------------------------
	""" Constructs and prepares a server socket listening on the given 
	port.

	"""
	s = socket.socket( socket.AF_INET, socket.SOCK_STREAM )
	s.setsockopt( socket.SOL_SOCKET, socket.SO_REUSEADDR, 1 )
	s.bind( ( '', port ) )
	s.listen( backlog )
	return s



    #--------------------------------------------------------------------------
    def sendtopeer( self, peerid, msgtype, msgdata, waitreply=True ):
    #--------------------------------------------------------------------------
	"""
	sendtopeer( peer id, message type, message data, wait for a reply )
	 -> [ ( reply type, reply data ), ... ] 

	Send a message to the identified peer. In order to decide how to
	send the message, the router handler for this peer will be called.
	If no router function has been registered, it will not work. The
	router function should provide the next immediate peer to whom the 
	message should be forwarded. The peer's reply, if it is expected, 
	will be returned.

	Returns None if the message could not be routed.
	"""

	if self.router:
	    nextpid, host, port = self.router( peerid )
	if not self.router or not nextpid:
	    self.__debug( 'Unable to route %s to %s' % (msgtype, peerid) )
	    return None
	#host,port = self.peers[nextpid]
	return self.connectandsend( host, port, msgtype, msgdata,
				    pid=nextpid,
				    waitreply=waitreply )
    


    #--------------------------------------------------------------------------
    def connectandsend( self, host, port, msgtype, msgdata, 
			pid=None, waitreply=True ):
    #--------------------------------------------------------------------------
	"""
	connectandsend( host, port, message type, message data, peer id,
	wait for a reply ) -> [ ( reply type, reply data ), ... ]

	Connects and sends a message to the specified host:port. The host's
	reply, if expected, will be returned as a list of tuples.

	"""
	msgreply = []
	try:
	    peerconn = BTPeerConnection( pid, host, port, debug=self.debug )
	    peerconn.senddata( msgtype, msgdata )
	    self.__debug( 'Sent %s: %s' % (pid, msgtype) )
	    
	    if waitreply:
		onereply = peerconn.recvdata()
		while (onereply != (None,None)):
		    msgreply.append( onereply )
		    self.__debug( 'Got reply %s: %s' 
				  % ( pid, str(msgreply) ) )
		    onereply = peerconn.recvdata()
	    peerconn.close()
	except KeyboardInterrupt:
	    raise
	except:
	    if self.debug:
		traceback.print_exc()
	
	return msgreply

    # end connectsend method



    #--------------------------------------------------------------------------
    def checklivepeers( self ):
    #--------------------------------------------------------------------------
	""" Attempts to ping all currently known peers in order to ensure that
	they are still active. Removes any from the peer list that do
	not reply. This function can be used as a simple stabilizer.

	"""
	todelete = []
	for pid in self.peers:
	    isconnected = False
	    try:
		self.__debug( 'Check live %s' % pid )
		host,port = self.peers[pid]
		peerconn = BTPeerConnection( pid, host, port, debug=self.debug )
		peerconn.senddata( 'PING', '' )
		isconnected = True
	    except:
		todelete.append( pid )
	    if isconnected:
		peerconn.close()

	self.peerlock.acquire()
	try:
	    for pid in todelete: 
		if pid in self.peers: del self.peers[pid]
	finally:
	    self.peerlock.release()
    # end checklivepeers method



    #--------------------------------------------------------------------------
    def mainloop( self ):
    #--------------------------------------------------------------------------
	s = self.makeserversocket( self.serverport )
	s.settimeout(2)
	self.__debug( 'Server started: %s (%s:%d)'
		      % ( self.myid, self.serverhost, self.serverport ) )
	
	while not self.shutdown:
	    try:
		self.__debug( 'Listening for connections...' )
		clientsock, clientaddr = s.accept()
		clientsock.settimeout(None)

		t = threading.Thread( target = self.__handlepeer,
				      args = [ clientsock ] )
		t.start()
	    except KeyboardInterrupt:
		print 'KeyboardInterrupt: stopping mainloop'
		self.shutdown = True
		continue
	    except:
		if self.debug:
		    traceback.print_exc()
		    continue

	# end while loop
	self.__debug( 'Main loop exiting' )

	s.close()

    # end mainloop method

# end BTPeer class




# **********************************************************




class BTPeerConnection:

    #--------------------------------------------------------------------------
    def __init__( self, peerid, host, port, sock=None, debug=False ):
    #--------------------------------------------------------------------------
	# any exceptions thrown upwards

	self.id = peerid
	self.debug = debug

	if not sock:
	    self.s = socket.socket( socket.AF_INET, socket.SOCK_STREAM )
	    self.s.connect( ( host, int(port) ) )
	else:
	    self.s = sock

	self.sd = self.s.makefile( 'rw', 0 )


    #--------------------------------------------------------------------------
    def __makemsg( self, msgtype, msgdata ):
    #--------------------------------------------------------------------------
	msglen = len(msgdata)
	msg = struct.pack( "!4sL%ds" % msglen, msgtype, msglen, msgdata )
	return msg


    #--------------------------------------------------------------------------
    def __debug( self, msg ):
    #--------------------------------------------------------------------------
	if self.debug:
	    btdebug( msg )


    #--------------------------------------------------------------------------
    def senddata( self, msgtype, msgdata ):
    #--------------------------------------------------------------------------
	"""
	senddata( message type, message data ) -> boolean status

	Send a message through a peer connection. Returns True on success
	or False if there was an error.
	"""

	try:
	    msg = self.__makemsg( msgtype, msgdata )
	    self.sd.write( msg )
	    self.sd.flush()
	except KeyboardInterrupt:
	    raise
	except:
	    if self.debug:
		traceback.print_exc()
	    return False
	return True
	    

    #--------------------------------------------------------------------------
    def recvdata( self ):
    #--------------------------------------------------------------------------
	"""
	recvdata() -> (msgtype, msgdata)

	Receive a message from a peer connection. Returns (None, None)
	if there was any error.
	"""

	try:
	    msgtype = self.sd.read( 4 )
	    if not msgtype: return (None, None)
	    
            lenstr = self.sd.read( 4 )
	    msglen = int(struct.unpack( "!L", lenstr )[0])
	    msg = ""

	    while len(msg) != msglen:
		data = self.sd.read( min(2048, msglen - len(msg)) )
		if not len(data):
		    break
		msg += data

	    if len(msg) != msglen:
		return (None, None)

	except KeyboardInterrupt:
	    raise
	except:
	    if self.debug:
		traceback.print_exc()
	    return (None, None)

	return ( msgtype, msg )

    # end recvdata method


    #--------------------------------------------------------------------------
    def close( self ):
    #--------------------------------------------------------------------------
	"""
	close()

	Close the peer connection. The send and recv methods will not work
	after this call.
	"""

	self.s.close()
	self.s = None
	self.sd = None


    #--------------------------------------------------------------------------
    def __str__( self ):
    #--------------------------------------------------------------------------
	return "|%s|" % peerid