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关于DHT协议
DHT协议作为BT协议的一个辅助，是非常好玩的。它主要是为了在BT正式下载时得到种子或者BT资源。传统的网络，需要一台中央服务器存放种子或者BT资源，不仅浪费服务器资源，还容易出现单点的各种问题，而DHT网络则是为了去中心化，也就是说任意时刻，这个网络总有节点是亮的，你可以去询问问这些亮的节点，从而将自己加入DHT网络。
要实现DHT协议的网络爬虫，主要分3步，第一步是得到资源信息(infohash，160bit，20字节，可以编码为40字节的十六进制字符串)，第二步是确认这些infohash是有效的，第三步是通过有效的infohash下载到BT的种子文件，从而得到对这个资源的完整描述。
其中第一步是其他节点用DHT协议中的get_peers方法向爬虫发送请求得到的，第二步是其他节点用DHT协议中的announce_peer向爬虫发送请求得到的，第三步可以有几种方式得到，比如可以去一些保存种子的网站根据infohash直接下载到，或者通过announce_peer的节点来下载到，具体如何实现，可以取决于你自己的爬虫。
DHT协议中的主要几个操作：
主要负责通过UDP与外部节点交互，封装4种基本操作的请求以及相应。
ping：检查一个节点是否“存活”
在一个爬虫里主要有两个地方用到ping，第一是初始路由表时，第二是验证节点是否存活时
find_node：向一个节点发送查找节点的请求
在一个爬虫中主要也是两个地方用到find_node，第一是初始路由表时，第二是验证桶是否存活时
get_peers：向一个节点发送查找资源的请求
在爬虫中有节点向自己请求时不仅像个正常节点一样做出回应，还需要以此资源的info_hash为机会尽可能多的去认识更多的节点。如图，get_peers实际上最后一步是announce_peer，但是因为爬虫不能announce_peer，所以实际上get_peers退化成了find_node操作。
announce_peer：向一个节点发送自己已经开始下载某个资源的通知
爬虫中不能用announce_peer，因为这就相当于通报虚假资源，对方很容易从上下文中判断你是否通报了虚假资源从而把你禁掉。
基于Python的DHT爬虫
修改自github开源爬虫，原作者名字有些。。，这里直接将项目地址列出：https://github.com/Fuck-You-GFW/simDHT，有github帐号的请给原作者star，后续我将结果放入db，外加用tornado做一个简单的查询界面出来放在github上，先备份一下代码
#!/usr/bin/env python
# encoding: utf-8
import socket
from hashlib import sha1
from random import randint
from struct import unpack
from socket import inet_ntoa
from threading import Timer, Thread
from time import sleep
from collections import deque
from bencode import bencode, bdecode
BOOTSTRAP_NODES = (
("router.bittorrent.com", 6881),
("dht.transmissionbt.com", 6881),
("router.utorrent.com", 6881)
)
TID_LENGTH = 2
RE_JOIN_DHT_INTERVAL = 3
TOKEN_LENGTH = 2
def entropy(length):
return "".join(chr(randint(0, 255)) for _ in xrange(length))
def random_id():
h = sha1()
h.update(entropy(20))
return h.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()
def get_neighbor(target, nid, end=10):
return target[:end]+nid[end:]
class KNode(object):
def __init__(self, nid, ip, port):
self.nid = nid
self.ip = ip
self.port = port
class DHTClient(Thread):
def __init__(self, max_node_qsize):
Thread.__init__(self)
self.setDaemon(True)
self.max_node_qsize = max_node_qsize
self.nid = random_id()
self.nodes = deque(maxlen=max_node_qsize)
def send_krpc(self, msg, address):
try:
self.ufd.sendto(bencode(msg), address)
except Exception:
pass
def send_find_node(self, address, nid=None):
nid = get_neighbor(nid, self.nid) if nid else self.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.send_find_node(address)
def re_join_DHT(self):
if len(self.nodes) == 0:
self.join_DHT()
timer(RE_JOIN_DHT_INTERVAL, self.re_join_DHT)
def auto_send_find_node(self):
wait = 1.0 / self.max_node_qsize
while True:
try:
node = self.nodes.popleft()
self.send_find_node((node.ip, node.port), node.nid)
except IndexError:
pass
sleep(wait)
def process_find_node_response(self, msg, address):
nodes = decode_nodes(msg["r"]["nodes"])
for node in nodes:
(nid, ip, port) = node
if len(nid) != 20: continue
if ip == self.bind_ip: continue
if port < 1 or port > 65535: continue
n = KNode(nid, ip, port)
self.nodes.append(n)
class DHTServer(DHTClient):
def __init__(self, master, bind_ip, bind_port, max_node_qsize):
DHTClient.__init__(self, max_node_qsize)
self.master = master
self.bind_ip = bind_ip
self.bind_port = bind_port
self.process_request_actions = {
"get_peers": self.on_get_peers_request,
"announce_peer": self.on_announce_peer_request,
}
self.ufd = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
self.ufd.bind((self.bind_ip, self.bind_port))
timer(RE_JOIN_DHT_INTERVAL, self.re_join_DHT)
def run(self):
self.re_join_DHT()
while True:
try:
(data, address) = self.ufd.recvfrom(65536)
msg = bdecode(data)
self.on_message(msg, address)
except Exception:
pass
def on_message(self, msg, address):
try:
if msg["y"] == "r":
if msg["r"].has_key("nodes"):
self.process_find_node_response(msg, address)
elif msg["y"] == "q":
try:
self.process_request_actions[msg["q"]](msg, address)
except KeyError:
self.play_dead(msg, address)
except KeyError:
pass
def on_get_peers_request(self, msg, address):
try:
infohash = msg["a"]["info_hash"]
tid = msg["t"]
nid = msg["a"]["id"]
token = infohash[:TOKEN_LENGTH]
msg = {
"t": tid,
"y": "r",
"r": {
"id": get_neighbor(infohash, self.nid),
"nodes": "",
"token": token
}
}
self.send_krpc(msg, address)
except KeyError:
pass
def on_announce_peer_request(self, msg, address):
try:
infohash = msg["a"]["info_hash"]
#print msg["a"]
tname = msg["a"]["name"]
token = msg["a"]["token"]
nid = msg["a"]["id"]
tid = msg["t"]
if infohash[:TOKEN_LENGTH] == token:
if msg["a"].has_key("implied_port") and msg["a"]["implied_port"] != 0:
port = address[1]
else:
port = msg["a"]["port"]
if port < 1 or port > 65535: return
self.master.log(infohash, (address[0], port),tname)
except Exception:
pass
finally:
self.ok(msg, address)
def play_dead(self, msg, address):
try:
tid = msg["t"]
msg = {
"t": tid,
"y": "e",
"e": [202, "Server Error"]
}
self.send_krpc(msg, address)
except KeyError:
pass
def ok(self, msg, address):
try:
tid = msg["t"]
nid = msg["a"]["id"]
msg = {
"t": tid,
"y": "r",
"r": {
"id": get_neighbor(nid, self.nid)
}
}
self.send_krpc(msg, address)
except KeyError:
pass
class Master(object):
def log(self, infohash,address=None,tname=None):
hexinfohash = infohash.encode("hex")
print "info_hash is: %s,name is: %s from %s:%s" % (
hexinfohash,tname, address[0], address[1]
)
prin