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Yesterday, I've showed you how does Clack work. A web app is a function which returns a list with the response or a function which should return create such list pass it to the provided callback.
Now we'll add a logging to our app with the
To do this, we must wrap our app's function into another function like this:
;; Now we'll create a simple app: POFTHEDAY> (defparameter *app* (lambda (env) '(200 (:content-type "text/plain") ("Hello, World")))) ;; And wrap it into the middleware: POFTHEDAY> (defparameter *app-with-access-log* (funcall lack.middleware.accesslog:*lack-middleware-accesslog* *app*)) ;; Now it's time to start our app: POFTHEDAY> (clack:clackup *app-with-access-log* :port 8000) Woo server is started. Listening on 127.0.0.1:8000. ;; And to make a test request: POFTHEDAY> (values (dex:get "http://localhost:8000/")) 127.0.0.1 - [21/Jun/2020:22:50:52 +03:00] "GET / HTTP/1.1" 200 12 "-" "Dexador/0.9.14 (SBCL 2.0.2); Darwin; 19.5.0" "Hello, World"
Look how a log message was printed to the STDOUT.
Now let's see how does this middleware works. Here is its content. It is a little bit complicated because the middleware needs to handle cases when an app returns a function instead of the normal response:
(defparameter *lack-middleware-accesslog* (let ((no-body '#:no-body)) (lambda (app &key (logger (lambda (output) (format t "~&~A~%" output))) (formatter #'default-formatter)) (lambda (env) (funcall-with-cb app env (lambda (res) (funcall logger (funcall formatter env res (now))) res))))) "Middleware for logging requests")
I'll show you a simpler version of this logging middleware:
;; Here is the middleware: POFTHEDAY> (defun simple-logging (app) (lambda (env) (let ((response (funcall app env))) (format t "~A ~A -> ~A~%" (getf env :request-method) (getf env :path-info) (car response)) response))) ;; And this is an example how we can apply it to our app: POFTHEDAY> (defparameter *app-with-simple-log* (simple-logging *app*)) POFTHEDAY> (clack:clackup *app-with-simple-log* :port 8000) Hunchentoot server is started. Listening on 127.0.0.1:8000. POFTHEDAY> (values (dex:get "http://localhost:8000/")) GET / -> 200 "Hello, World" POFTHEDAY> (values (dex:get "http://localhost:8000/foo/bar")) GET /foo/bar -> 200 "Hello, World"
Tomorrow we'll try the better way to apply middlewares to a Clack app.