学步园

gevent是一个非常棒的python异步IO库，一般的示例都是用他来做高并发的tcp server，其实它也能很好的工作在udp上，而且超时，并发数都能很好的控制。

#!/usr/bin/env python
#-*- coding:utf8 -*-

import DNS #http://pydns.sourceforge.net/
from gevent import spawn, joinall,socket,sleep
from gevent.coros import BoundedSemaphore
from datetime import datetime
import random

DNS.ParseResolvConf()
SERVER = (DNS.defaults['server'][0],53)
SERVER = ('8.8.8.8',53) #临时使用google的dns
TIMEOUT = 10 
lock = BoundedSemaphore(50) #并发数限制，防止同时pending的请求太多

statis = {} #统计信息
def log(domain,status,responsetime):
    statis.setdefault(status, 0)
    statis[status] += 1
print '%s %s %s' % (domain, status, responsetime)

def getreq(domain, qtype):
'根据域名和查询类型得到dns请求的字节流'
    m = DNS.Lib.Mpacker()
    m.addHeader(id=random.randint(0,65535),
        qr=0,
        opcode=0,
        aa=0,
        tc=0,
        rd=1,
        ra=0,
        z=0,
        rcode=0,
        qdcount=1,
        ancount=0,
        nscount=0,
        arcount=0)
    m.addQuestion(domain, qtype, DNS.Class.IN)
return m.getbuf()

def monitorone(domain): 
try:
        lock.acquire()

        start = datetime.now()
        client = socket.socket(
                family=socket.AF_INET, 
                type=socket.SOCK_DGRAM,
                proto=socket.IPPROTO_UDP)
        client.settimeout(TIMEOUT)

        req = getreq(domain, DNS.Type.MX) #封包
        client.sendto(req, SERVER) #发包
        (rsp, (ip, port)) = client.recvfrom(512) #收包
        u = DNS.Lib.Munpacker(rsp) #解包
        rsp = DNS.Lib.DnsResult(u, {})

        end = datetime.now()
        responsetime = (end - start).microseconds
        log(domain, rsp.header['status'], responsetime)
except Exception, ex:
        log(domain, ex.message, 0)
finally:
        lock.release()

#加载域名列表并解析
list = [spawn(monitorone, domain.strip()) 
for domain in open('./domains.txt')]
joinall(list) 
global statis
print statis

以上代码是从一个文本里加载一个域名列表，然后以50并发的速度去google dns查询DNS应答，记录应答状态码和响应时间。