django中间件介绍

1、django.middleware.common.CommonMiddleware

功能：通用中间件，会处理一些URL，比如baidu.com会自动的处理成www.baidu.com。比如/blog/111会处理成/blog/111/自动加上反斜杠，还有能对User-Agent进行限制：限制settings.DISALLOWED_USER_AGENTS中指定的请求头来访问本网站。DISALLOWED_USER_AGENTS是一个正则表达式列表。
实例代码：

import re
DISALLOWED_USER_AGENTS = [
 	re.compile(r'^\s$|^$')			  空白字符或空字符
 	re.compile(r'.*PhantomJS.*')   包含PhantomJS
]

但是，如果请求中不带User-Agent字段，就不能进行检验，因此要自定义中间件。

    def process_request(self, request):
        """
        Check for denied User-Agents and rewrite the URL based on
        settings.APPEND_SLASH and settings.PREPEND_WWW
        """
	
	#检查User-Agents
        # Check for denied User-Agents
        if 'HTTP_USER_AGENT' in request.META:
            for user_agent_regex in settings.DISALLOWED_USER_AGENTS:
                if user_agent_regex.search(request.META['HTTP_USER_AGENT']):
                    raise PermissionDenied('Forbidden user agent')
	#检查WWW，没有就给你添加
        # Check for a redirect based on settings.PREPEND_WWW
        host = request.get_host()
        must_prepend = settings.PREPEND_WWW and host and not host.startswith('www.')
        redirect_url = ('%s://www.%s' % (request.scheme, host)) if must_prepend else ''
   #检查是否应附加斜线  
        # Check if a slash should be appended
        if self.should_redirect_with_slash(request):
            path = self.get_full_path_with_slash(request)
        else:
            path = request.get_full_path()
  #必要时返回重定向
        # Return