Python: How to run a simple P2P network framework

Question

I found a code about Implements the core functionality in a P2P network. Because I just know C and Java, I have very little knowledge about Python. So, can anyone instruct me how to run this code? To be specific, I want to create peers and invoke some functions such as addpeer or removepeer. I try to run it with command "python btpeer.py" but nothing happens. Thanks adv.

#!/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

Answer 1

That code only defines classes and methods, so it won't do anything when you run it with the python command. You'll need to import it as a library, something like this:

import btpeer

peer = BTPeer(...)
peer.addpeer(...)

(You'll need to fill in the parameters to the methods (where I've written ... ) appropriately.)