DHT是什么

• DHT全稱叫分布式哈希表(Distributed Hash Table)，是一種分布式存儲方法。在不需要服務(wù)器的情況下，每個客戶端負(fù)責(zé)一個小范圍的路由，并負(fù)責(zé)存儲一小部分?jǐn)?shù)據(jù)，從而實現(xiàn)整個DHT網(wǎng)絡(luò)的尋址和存儲。
• 各種博客已經(jīng)有很多關(guān)于DHT介紹，這里就不詳細(xì)列舉了

加入DHT網(wǎng)絡(luò)可以做什么

老司機開車(神秘代碼)

P2P資源共享

DHT網(wǎng)絡(luò)的其中一種協(xié)議實現(xiàn)(Kademlia)

• 要加入一個DHT網(wǎng)絡(luò)，需要首先知道這個網(wǎng)絡(luò)中的任意一個節(jié)點。如何獲得這個節(jié)點？在一些開源的P2P軟件中，會提供一些節(jié)點地址
• 主要協(xié)議

ping(用于確定某個節(jié)點是否在線。這個請求主要用于輔助路由表的更新)

find_node(用于查找某個節(jié)點，以獲得其地址信息。)

get_peer(通過資源的infohash獲得資源對應(yīng)的peer列表。)

announce_peer(通知其他節(jié)點自己開始下載某個資源,announce_peer中會攜帶get_peer回應(yīng)消息里的token。)

DHT爬蟲的工作原理

通過其他節(jié)點的announce_peer發(fā)來的infohash確認(rèn)網(wǎng)絡(luò)中有某個資源可被下載

通過從網(wǎng)絡(luò)中獲取這個資源的種子文件，來獲得該資源的描述

不停的認(rèn)識新節(jié)點,讓遠(yuǎn)程節(jié)點保存自身到遠(yuǎn)程的路由表中

爬蟲做的工作

BOOTSTRAP過程,加入DHT網(wǎng)絡(luò)(主動認(rèn)識DHT網(wǎng)絡(luò)的其中一個節(jié)點)

加入進DHT網(wǎng)絡(luò)后。遠(yuǎn)端節(jié)點會主動告訴我們它認(rèn)識哪些節(jié)點

認(rèn)識遠(yuǎn)端節(jié)點認(rèn)識的節(jié)點

當(dāng)遠(yuǎn)端成功保存自身節(jié)點到遠(yuǎn)端路由表中的時候，目的達成

等待遠(yuǎn)端的announce_peer消息

成功獲取遠(yuǎn)端的下載hash

開車！(霧

使用Python實現(xiàn)的爬蟲:

# coding: utf-8import socket from hashlib import sha1 from random import randint from struct import unpack, pack from socket import inet_aton, inet_ntoa from bisect import bisect_left from threading import Timer # 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 REBORN_TIME = 5 * 60 K = 8 def entropy(bytes): s = "" for i in range(bytes): s += chr(randint(0, 255)) return s # """把爬蟲"偽裝"成正常node, 一個正常的node有ip, port, node ID三個屬性, 因為是基于UDP協(xié)議, # 所以向?qū)Ψ桨l(fā)送信息時, 即使沒"明確"說明自己的ip和port時, 對方自然會知道你的ip和port, # 反之亦然. 那么我們自身node就只需要生成一個node ID就行, 協(xié)議里說到node ID用sha1算法生成, # sha1算法生成的值是長度是20 byte, 也就是20 * 8 = 160 bit, 正好如DHT協(xié)議里說的那范圍: 0 至 2的160次方, # 也就是總共能生成1461501637330902918203684832716283019655932542976個獨一無二的node. # ok, 由于sha1總是生成20 byte的值, 所以哪怕你寫SHA1(20)或SHA1(19)或SHA1("I am a 2B")都可以, # 只要保證大大降低與別人重復(fù)幾率就行. 注意, node ID非十六進制, # 也就是說非FF5C85FE1FDB933503999F9EB2EF59E4B0F51ECA這個樣子, 即非hash.hexdigest(). """ 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 encode_nodes(nodes): strings = [] for node in nodes: s = "%s%s%s" % (node.nid, inet_aton(node.ip), pack("!H", node.port)) strings.append(s) return "".join(strings) def intify(hstr): #"""這是一個小工具, 把一個node ID轉(zhuǎn)換為數(shù)字. 后面會頻繁用到.""" return long(hstr.encode('hex'), 16) #先轉(zhuǎn)換成16進制, 再變成數(shù)字 def timer(t, f): Timer(t, f).start() class BucketFull(Exception): pass class KRPC(object): def __init__(self): self.types = { "r": self.response_received, "q": self.query_received } self.actions = { "ping": self.ping_received, "find_node": self.find_node_received, "get_peers": self.get_peers_received, "announce_peer": self.announce_peer_received, } self.socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) self.socket.bind(("0.0.0.0", self.port)) def find_node_handler(self,msg): pass def response_received(self, msg, address): self.find_node_handler(msg) def query_received(self, msg, address): try: self.actions[msg["q"]](msg, address) except KeyError: pass def send_krpc(self, msg, address): try: self.socket.sendto(bencode(msg), address) except: pass class Client(KRPC): def __init__(self, table): self.table = table timer(KRPC_TIMEOUT, self.timeout) timer(REBORN_TIME, self.reborn) KRPC.__init__(self) def find_node(self, address, nid=None): print "find node:",address 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 find_node_handler(self, msg): try: nodes = decode_nodes(msg["r"]["nodes"]) for node in nodes: (nid, ip, port) = node if len(nid) != 20: continue if nid == self.table.nid: continue self.find_node( (ip, port), nid ) except KeyError: pass def joinDHT(self): for address in BOOTSTRAP_NODES: self.find_node(address) def timeout(self): if len( self.table.buckets ) < 2: self.joinDHT() timer(KRPC_TIMEOUT, self.timeout) def reborn(self): self.table.nid = random_id() self.table.buckets = [ KBucket(0, 2**160) ] timer(REBORN_TIME, self.reborn) def start(self): self.joinDHT() while True: try: (data, address) = self.socket.recvfrom(65536) msg = bdecode(data) self.types[msg["y"]](msg, address) except Exception: pass def get_neighbor(self, target): return target[:10]+random_id()[10:] class Server(Client): def __init__(self, master, table, port): self.table = table self.master = master self.port = port Client.__init__(self, table) def ping_received(self, msg, address): try: nid = msg["a"]["id"] msg = { "t": msg["t"], "y": "r", "r": {"id": self.get_neighbor(nid)} } self.send_krpc(msg, address) self.find_node(address, nid) except KeyError: pass def find_node_received(self, msg, address): try: target = msg[

轉(zhuǎn)載于:https://www.cnblogs.com/mamatichong/p/9952255.html

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