simDHT.py

#encoding: utf-8
import socket
from hashlib import sha1
from random import randint
from struct import unpack, pack
from socket import inet_aton, inet_ntoa
from threading import Timer, Thread
from time import sleep

from bencode import bencode, bdecode

BOOTSTRAP_NODES = [
    ("router.bittorrent.com", 6881),
    ("dht.transmissionbt.com", 6881),
    ("router.utorrent.com", 6881)
] 
TID_LENGTH = 4
KRPC_TIMEOUT = 10

def entropy(bytes):
    s = ""
    for i in range(bytes):
        s += chr(randint(0, 255))
    return s

def random_id():
    hash = sha1()
    hash.update(entropy(20))
    return hash.digest()

def decode_nodes(nodes):
    n = []
    length = len(nodes)
    if (length % 26) != 0: 
        return n

    for i in range(0, length, 26):
        nid = nodes[i:i+20]
        ip = inet_ntoa(nodes[i+20:i+24])
        port = unpack("!H", nodes[i+24:i+26])[0]
        n.append((nid, ip, port))

    return n

def timer(t, f):
    Timer(t, f).start()


class KRPC(Thread):
    def __init__(self):
        Thread.__init__(self)
        self.setDaemon(True)
        self.types = {
            "r": self.response_received,
            "q": self.query_received
        }
        self.actions = {
            "get_peers": self.get_peers_received,
        }

        self.ufd = socket.socket(socket.AF_INET, 
            socket.SOCK_DGRAM, socket.IPPROTO_UDP)
        self.ufd.bind((self.ip, self.port))

    def response_received(self, msg, address):
        try:
            nodes = decode_nodes(msg["r"]["nodes"])
            for node in nodes:
                (nid, ip, port) = node
                if len(nid) != 20: continue
                if ip == self.ip: continue
                self.table.put(KNode(nid, ip, port))
        except KeyError:
            pass

    def query_received(self, msg, address):
        try:
            self.actions[msg["q"]](msg, address)
        except KeyError:
            pass

    def send_krpc(self, msg, address):
        try:
            self.ufd.sendto(bencode(msg), address)
        except:
            pass

    def get_neighbor(self, target):
        return target[:10]+random_id()[10:]


class Client(KRPC):
    def __init__(self, table):
        self.table = table

        timer(KRPC_TIMEOUT, self.timeout)
        KRPC.__init__(self)

    def find_node(self, address, nid=None):
        nid = self.get_neighbor(nid) if nid else self.table.nid
        tid = entropy(TID_LENGTH)
        msg = {
            "t": tid,
            "y": "q",
            "q": "find_node",
            "a": {"id": nid, "target": random_id()}
        }
        self.send_krpc(msg, address)

    def join_DHT(self):
        for address in BOOTSTRAP_NODES: 
            self.find_node(address)

    def timeout(self):
        if not self.table.nodes:
            self.join_DHT()
        timer(KRPC_TIMEOUT, self.timeout)

    def run(self):
        self.join_DHT()
        while True:
            try:
                (data, address) = self.ufd.recvfrom(65536)
                msg = bdecode(data)
                self.types[msg["y"]](msg, address)
            except Exception:
                pass

    def wander(self):
        while True:
            for node in list(set(self.table.nodes))[:self.max_node_qsize]:
                self.find_node((node.ip, node.port), node.nid)
            self.table.nodes = []
            sleep(1)


class Server(Client):
    def __init__(self, master, ip, port, max_node_qsize):
        self.max_node_qsize = max_node_qsize
        self.table = KTable()
        self.master = master
        self.ip = ip
        self.port = port
        Client.__init__(self, self.table)

    def get_peers_received(self, msg, address):
        try:
            infohash = msg["a"]["info_hash"]
            self.master.log(infohash)
        except Exception, e:
            pass


class KTable():
    def __init__(self):
        self.nid = random_id()
        self.nodes = []

    def put(self, node):
        self.nodes.append(node)


class KNode(object):
    def __init__(self, nid, ip=None, port=None):
        self.nid = nid
        self.ip = ip
        self.port = port

    def __eq__(self, node):
        return node.nid == self.nid

    def __hash__(self):
        return hash(self.nid)


#using example
class Master(object):
    def log(self, infohash):
        print infohash.encode("hex")


if __name__ == "__main__":
    #max_node_qsize bigger, bandwith bigger.
    s = Server(Master(), "0.0.0.0", 3881, max_node_qsize=200)
    s.start()
    s.wander()