在Python的Tornado框架中实现简单的在线代理的教程

实现代理的方式很多种，流行的web服务器也大都有代理的功能。

最近，我在开发一个移动运用(以下简称APP)的后台程序(Server)，该运用需要调用到另一平台产品(Platform)的API。对于这个系统来说，可选的一种实现方式方式是APP同时跟Server&Platform两者交互；另一种则在Server端封装掉Platform的API，APP只和Server交互。显然后一种方式的系统架构会清晰些，APP编程时也就相对简单。那么如何在Server端封装Platform的API呢，我首先考虑到的就是用代理的方式来实现。碰巧最近Tornado邮件群组里有人在讨论using Tornado as a proxy，贴主提到的运用场景跟我这碰到的场景非常的相似，我把原帖的代码做了些整理和简化，源代码如下：

# -*- coding: utf-8 -*-

#

# Copyright(c) 2011 Felinx Lee & http://feilong.me/

#

# Licensed under the Apache License, Version 2.0 (the "License"); you may

# not use this file except in compliance with the License. You may obtain

# a copy of the License at

#

# http://www.apache.org/licenses/LICENSE-2.0

#

# Unless required by applicable law or agreed to in writing, software

# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT

# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the

# License for the specific language governing permissions and limitations

# under the License.

import logging

import tornado.httpserver

import tornado.ioloop

import tornado.options

import tornado.web

import tornado.httpclient

from tornado.web import HTTPError, asynchronous

from tornado.httpclient import HTTPRequest

from tornado.options import define, options

try:

from tornado.curl_httpclient import CurlAsyncHTTPClient as AsyncHTTPClient

except ImportError:

from tornado.simple_httpclient import SimpleAsyncHTTPClient as AsyncHTTPClient

define("port", default=8888, help="run on the given port", type=int)

define("api_protocol", default="http")

define("api_host", default="feilong.me")

define("api_port", default="80")

define("debug", default=True, type=bool)

class ProxyHandler(tornado.web.RequestHandler):

@asynchronous

def get(self):

# enable API GET request when debugging

if options.debug:

return self.post()

else:

raise HTTPError(405)

@asynchronous

def post(self):

protocol = options.api_protocol

host = options.api_host

port = options.api_port

# port suffix

port = "" if port == "80" else ":%s" % port

uri = self.request.uri

url = "%s://%s%s%s" % (protocol, host, port, uri)

# update host to destination host

headers = dict(self.request.headers)

headers["Host"] = host

try:

AsyncHTTPClient().fetch(

HTTPRequest(url=url,

method="POST",

body=self.request.body,

headers=headers,

follow_redirects=False),

self._on_proxy)

except tornado.httpclient.HTTPError, x:

if hasattr(x, "response") and x.response:

self._on_proxy(x.response)

else:

logging.error("Tornado signalled HTTPError %s", x)

def _on_proxy(self, response):

if response.error and not isinstance(response.error,

tornado.httpclient.HTTPError):

raise HTTPError(500)

else:

self.set_status(response.code)

for header in ("Date", "Cache-Control", "Server", "Content-Type", "Location"):

v = response.headers.get(header)

if v:

self.set_header(header, v)

if response.body:

self.write(response.body)

self.finish()

def main():

tornado.options.parse_command_line()

application = tornado.web.Application([

(r"/.*", ProxyHandler),

])

http_server = tornado.httpserver.HTTPServer(application)

http_server.listen(options.port)

tornado.ioloop.IOLoop.instance().start()

if __name__ == "__main__":

main()

运行上面的代码后，访问 http://localhost:8888/ 将会完整显示博客的首页，即代理访问了http://down.amdin5.com/的内容。

我考虑用程序的方式来做代理而不是直接用Nginx来做代理，其中一点是考虑到用程序可以很容易的控制Platform的哪些API是需要代理的，而哪些是要屏蔽掉的，还有哪些可能是要重写的(比如Server的login可能不能直接代理Platform的login，但却要调用到Platform的login API)。

以上这段代码只是做了简单的页面内容代理，并没有对页面进行进一步的解析处理，比如链接替换等，这些就交个有兴趣的朋友去开发了。基于以上这段代码，将其扩展一下，是完全可以实现一个完整的在线代理程序的。