pythongetp2pbittorrent

BitTorrent Client : Getting Peer List From Trackers [Python]


I am trying to get the peer list from the trackers using https://wiki.theory.org/BitTorrent_Tracker_Protocol

But most of the torrent files available on the net use a udp tracker. The above website is for HTTP trackers. The torrent files with HTTP based trackers give an error.(Passkey error , or hash error or user error or 404 not found response)

Right now my request code for all HTTP trackers look like :

payload = urllib.urlencode(payload)
        for ann in self.torrent.announce_list:
            if("udp" not in ann[0]):
                url = ann[0]
                print "Encoded Request URL :",(url + "?" + payload)
                print "Requesting Tracker for Peer List"
                try:
                    response = urllib.urlopen(url + "?" + payload).read()
                    print "RESPONSE :",response
                except Exception, e:
                    print e

I have crosschecked my request URL against the requests being made by uTorrent using wireshark. They all match. The info-hash is being generated correctly.

How do I retrieve the peer list from UDP as well as HTTP trackers ? I am trying not to use any external library like lib-torrent. Some guidance would be really helpful.


Solution

  • The following code worked for me. Calling announce_udp() with the tracker URL and the payload dictionary with all the URL parameeters.

    import binascii, urllib, socket, random, struct
    from bcode import bdecode
    from urlparse import urlparse, urlunsplit
    
    def announce_udp(tracker,payload):
        tracker = tracker.lower()
        parsed = urlparse(tracker)
    
        # Teporarly Change udp:// to http:// to get hostname and portnumbe
        url = parsed.geturl()[3:]
        url = "http" + url
        hostname = urlparse(url).hostname
        port = urlparse(url).port
    
    
        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        sock.settimeout(8)
        conn = (socket.gethostbyname(hostname), port)
        #sock.bind((socket.gethostname(),s_port))
    
        #Get connection ID
        req, transaction_id = udp_create_connection_request()
        sock.sendto(req, conn);
        buf = sock.recvfrom(2048)[0]
        connection_id = udp_parse_connection_response(buf, transaction_id)
    
        #Annoucing
        s_port = sock.getsockname()[1] #get port number to which socket is connected
        req, transaction_id = udp_create_announce_request(connection_id, payload,s_port)
        sock.sendto(req, conn)
        print "Announce Request Sent"
        buf = sock.recvfrom(2048)[0]
        print "Response received"
        return udp_parse_announce_response(buf, transaction_id)
    
    def udp_create_announce_request(connection_id, payload, s_port):
        action = 0x1 #action (1 = announce)
        transaction_id = udp_get_transaction_id()
        # print "2.Transaction ID :", transaction_id
        buf = struct.pack("!q", connection_id)                                  #first 8 bytes is connection id
        buf += struct.pack("!i", action)                                        #next 4 bytes is action 
        buf += struct.pack("!i", transaction_id)                                #followed by 4 byte transaction id
        buf += struct.pack("!20s", urllib.unquote(payload['info_hash']))        #the info hash of the torrent we announce ourselves in
        buf += struct.pack("!20s", urllib.unquote(payload['peer_id']))          #the peer_id we announce
        buf += struct.pack("!q", int(urllib.unquote(payload['downloaded'])))    #number of bytes downloaded
        buf += struct.pack("!q", int(urllib.unquote(payload['left'])))          #number of bytes left
        buf += struct.pack("!q", int(urllib.unquote(payload['uploaded'])))      #number of bytes uploaded
        buf += struct.pack("!i", 0x2)                                           #event 2 denotes start of downloading
        buf += struct.pack("!i", 0x0)                                           #IP address set to 0. Response received to the sender of this packet
        key = udp_get_transaction_id()                                          #Unique key randomized by client
        buf += struct.pack("!i", key)
        buf += struct.pack("!i", -1)                                            #Number of peers required. Set to -1 for default
        buf += struct.pack("!i", s_port)                                        #port on which response will be sent
        return (buf, transaction_id)
    
    def udp_parse_announce_response(buf, sent_transaction_id):
        #print "Response is:"+str(buf)  
        if len(buf) < 20:
            raise RuntimeError("Wrong response length while announcing: %s" % len(buf)) 
        action = struct.unpack_from("!i", buf)[0] #first 4 bytes is action
        res_transaction_id = struct.unpack_from("!i", buf, 4)[0] #next 4 bytes is transaction id    
        if res_transaction_id != sent_transaction_id:
            raise RuntimeError("Transaction ID doesnt match in announce response! Expected %s, got %s"
                % (sent_transaction_id, res_transaction_id))
        print "Reading Response"
        if action == 0x1:
            print "Action is 3"
            ret = dict()
            offset = 8; #next 4 bytes after action is transaction_id, so data doesnt start till byte 8      
            ret['interval'] = struct.unpack_from("!i", buf, offset)[0]
            print "Interval:"+str(ret['interval'])
            offset += 4
            ret['leeches'] = struct.unpack_from("!i", buf, offset)[0]
            print "Leeches:"+str(ret['leeches'])
            offset += 4
            ret['seeds'] = struct.unpack_from("!i", buf, offset)[0]
            print "Seeds:"+str(ret['seeds'])
            offset += 4
            peers = list()
            x = 0
            while offset != len(buf):
                peers.append(dict())
                peers[x]['IP'] = struct.unpack_from("!i",buf,offset)[0]
                print "IP: "+socket.inet_ntoa(struct.pack("!i",peers[x]['IP']))
                offset += 4
                if offset >= len(buf):
                    raise RuntimeError("Error while reading peer port")
                peers[x]['port'] = struct.unpack_from("!H",buf,offset)[0]
                print "Port: "+str(peers[x]['port'])
                offset += 2
                x += 1
            return ret,peers
        else:
            #an error occured, try and extract the error string
            error = struct.unpack_from("!s", buf, 8)
            print "Action="+str(action)
            raise RuntimeError("Error while annoucing: %s" % error)
    
    def udp_create_connection_request():
        connection_id = 0x41727101980                   #default connection id
        action = 0x0                                    #action (0 = give me a new connection id)   
        transaction_id = udp_get_transaction_id()
        print "1.Transaction ID :", transaction_id
        buf = struct.pack("!q", connection_id)          #first 8 bytes is connection id
        buf += struct.pack("!i", action)                #next 4 bytes is action
        buf += struct.pack("!i", transaction_id)        #next 4 bytes is transaction id
        return (buf, transaction_id)
    
    def udp_parse_connection_response(buf, sent_transaction_id):
        if len(buf) < 16:
            raise RuntimeError("Wrong response length getting connection id: %s" % len(buf))            
        action = struct.unpack_from("!i", buf)[0] #first 4 bytes is action
    
        res_transaction_id = struct.unpack_from("!i", buf, 4)[0] #next 4 bytes is transaction id
        if res_transaction_id != sent_transaction_id:
            raise RuntimeError("Transaction ID doesnt match in connection response! Expected %s, got %s"
                % (sent_transaction_id, res_transaction_id))
    
        if action == 0x0:
            connection_id = struct.unpack_from("!q", buf, 8)[0] #unpack 8 bytes from byte 8, should be the connection_id
            return connection_id
        elif action == 0x3:     
            error = struct.unpack_from("!s", buf, 8)
            raise RuntimeError("Error while trying to get a connection response: %s" % error)
        pass
    
    def udp_get_transaction_id():
        return int(random.randrange(0, 255))