让 Python 在下载的时候使用 IPv4 域名解析 - Jacky Liu's Blog

让 Python 在下载的时候使用 IPv4 域名解析

Jacky Liu posted @ 2011年7月16日 03:30 in Python with tags python DNS IPv4 地址解析域名解析 , 3789 阅读

---- 这个话题由来于我想从深交所的网站扒些信息下来，发现用 Python 下载时，每次都要 30 秒才能连上，浏览器访问却正常。于是查找原因，最后用抓包分析，发现问题出在域名解析阶段。浏览器访问时，向 DNS 服务器发送的是 A 型查询，要求做 IPv4 地址解析; 而 Python 的 urllib.request 模块发送的却是 AAAA 型查询，要求做 IPv6 地址解析，对深交所网址进行 IPv6 解析居然要花 30 秒，不知道为什么。

---- 然后就是各种 Google + 查看代码，追根溯源。不细说了，只贴结果:

def Resolver_IPv4(hostname):
	return socket.gethostbyname(hostname)    # 此函数返回 IPv4 地址
													
class HTTPConnection_IPv4(http.client.HTTPConnection):
	def connect(self):
		self.sock= socket.create_connection((Resolver_IPv4(self.host), self.port), self.timeout)

class HTTPHandler_IPv4(urllib.request.HTTPHandler):
	def http_open(self, req):
		return self.do_open(HTTPConnection_IPv4, req)
													
urlopen_IPv4= urllib.request.build_opener(HTTPHandler_IPv4).open

如此以后，用这个 urlopen_IPv4() 函数来取代平常用的 urllib.request.urlopen() 函数，就可以用 IPv4 地址解析的方式来下载:

webfile= urlopen_IPv4(fullurl='http://www.szse.cn/', timeout=3)

---- 最后说一下，抓包感觉就跟作弊一样，爽！

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