code: def check_connection (self):
          
          # proxy support (we support only http)
          self.set_proxy(self.aggregate.config["proxy"].get(self.scheme))
          if self.proxy:
              # using a (HTTP) proxy
              http = httpurl.HttpUrl(self.base_url,
                    self.recursion_level,
                    self.aggregate,
                    parent_url=self.parent_url,
                    base_ref=self.base_ref,
                    line=self.line,
                    column=self.column,
                    name=self.name)
              http.build_url()
              return http.check()
          self.login()
          self.negotiate_encoding()
          self.filename = self.cwd()
          self.listfile()
          self.files = []
          return None
docs: In case of proxy, delegate to HttpUrl. Else check in this
          order: login, changing directory, list the file.