django middware only “process_response” when miss trailing slash

Question

i've write a middware like this:

class LogMiddleware( object ):

    def process_request( self, request ):
        logging.debug("start")

    def process_response( self, request, response ):
        logging.debug("end")
        return response

and I put it in the bottom of MIDDLEWARE_CLASSES

most time it works fine.

and when I test with url /admin without an trailing "/" and I could only see the "end" logged, why?

Answer 1

The documentation explains this.

Middleware classes are processed in the order they appear. The CommonMiddleware class is higher up than your LogMiddleware class, so is processed first. It performs a redirect because your URL doesn't end with a slash, so returns an HttpResponseRedirect.

If a request middleware returns a response, as in this case, no further request middleware classes are processed, so 'start' is not logged. However, response middleware classes are always processed, so 'end' is logged.