code: def describe_error(failure):
      
      if failure.check(ResponseFailed):
          if any(f.check(InfiniteRedirection)
                 for f in failure.value.reasons):
              return u'Encountered too many redirects.'
          return u'Received incomplete response from server.'
      if failure.check(ConnectError, DNSLookupError, BlacklistedHost):
          return u'Could not connect to server.'
      return failure
docs: If *failure* is a common connection error, return a Unicode
      string describing it.  Otherwise, return *failure*.