用python自建一个DNS服务器

class DNSServer(object):
    @staticmethod
    def start():
        # 缓存队列，收到的请求都先放在这里，然后从这里拿数据处理
        DNSServer.deq_cache = Queue(maxsize=deq_size) if deq_size > 0 else Queue()
        # LRU Cache，使用近期最少使用覆盖原则
        DNSServer.dns_cache = pylru.lrucache(lru_size)
 
        # 启动协程，循环处理缓存队列
        gevent.spawn(_init_cache_queue)
 
        # 启动DNS服务器
        print ‘Start DNS server at %s:%d\n‘ % (ip, port)
        dns_server = SocketServer.UDPServer((ip, port), DNSHandler)
        dns_server.serve_forever()

class DNSHandler(SocketServer.BaseRequestHandler):
    def handle(self):
        # 若缓存队列没有存满，把接收到的包放进缓存队列中（存满则直接丢弃包）
        if not DNSServer.deq_cache.full():
            # 缓存队列保存元组：(请求包，请求地址，sock)
            DNSServer.deq_cache.put((self.request[0], self.client_address, self.request[1]))

def _init_cache_queue():
    while True:
        data, addr, sock = DNSServer.deq_cache.get()
        gevent.spawn(handler, data, addr, sock)

dns.header.set_qr(dnslib.QR.RESPONSE)
qname = dns.q.qname
 
try:
    dns = dnslib.DNSRecord.parse(data)
except Exception as e:
    print ‘Not a DNS packet.\n‘, e

response = DNSServer.dns_cache.get(qname)
 
if response:
    # goto 5
else:
    # goto 6

response[:2] = data[:2]
sock.sendto(response, addr)

answers, soa = query(str(qname).rstrip(‘.‘))
answer_dns = pack_dns(dns, answers, soa)
 
DNSServer.dns_cache[qname] = answer_dns.pack()
sock.sendto(answer_dns.pack(), addr)