'This performs an HTTP POST or GET, following redirects along
the way. If a body is specified, then the request will be a
POST. Otherwise, it will be a GET.
@param headers: HTTP headers to include with the request
@type headers: {str:str}
@return: An object representing the server\'s HTTP response. If
there are network or protocol errors, an exception will be
raised. HTTP error responses, like 404 or 500, do not
cause exceptions.
@rtype: L{HTTPResponse}
@raise Exception: Different implementations will raise
different errors based on the underlying HTTP library.'

def fetch(self, url, body=None, headers=None):

    raise NotImplementedError
