# Best way to implement a "front controller" with Racket's web server **URL:** \ **Category:** Questions & Answers\ **Tags:** question, web-server, web\ **Created:** [October 2, 2024, 1:10am UTC](https://racket.discourse.group/t/best-way-to-implement-a-front-controller-with-rackets-web-server/3193 "2024-10-02T01:10:52Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![badkins](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/badkins/32/99_2.png) [@badkins](https://racket.discourse.group/u/badkins)\ **Post date:** [October 2, 2024, 1:10am UTC](https://racket.discourse.group/t/best-way-to-implement-a-front-controller-with-rackets-web-server/3193/1 "2024-10-02T01:10:52Z")
This question is primarily directed to @jeapostrophe , but anyone can feel free to comment 🙂 I think back in 2019, Jay mentioned my use of `web-server/dispatchers/dispatch-lift` in [Axio](https://github.com/lojic/axio-alpha) was less than ideal, and I never bothered to follow up for more detail re: why. I'm not using continuations, and I simply want a straightforward way for the Racket web server to dispatch to my own "front controller", and using `dispatch-lift` seemed like the most straightforward way to dispatch to a function. The relevant code is [`axio-app-init`](https://github.com/lojic/axio-alpha/blob/master/axio-lib/private/axio-app.rkt#L39-L54) and [`front-controller`](https://github.com/lojic/axio-alpha/blob/master/axio-lib/private/axio-app.rkt#L67-L88) If there's a better way to get the web server to call my front controller, I'm all ears 🙂 I'm about to use @bogdan 's [`sentry`](https://docs.racket-lang.org/sentry/index.html) package to send unhandled exceptions to Sentry, so it's a good time to tweak this part of the architecture if necessary. Thanks! ---
**Author:** ![benknoble](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/benknoble/32/16_2.png) [@benknoble](https://racket.discourse.group/u/benknoble)\ **Post date:** [October 2, 2024, 4:03pm UTC](https://racket.discourse.group/t/best-way-to-implement-a-front-controller-with-rackets-web-server/3193/2 "2024-10-02T16:03:08Z")
Replying partly to keep track of this thread. IIRC when I started development on Frosthaven Manager's web server, I looked at `lift:make`, too. I don't recall what for and I don't have any commit records of the experiment (sadly), but I seem to remember the primary issue being that the implementation doesn't handle continuations well: ```racket (define ((make procedure) conn req) (output-response/method conn (procedure req) (request-method req))) ``` Again, I don't remember the specific problem, but I _think_ it had to do with adding "middleware" to the request handling and not having that work correctly in certain cases? Jay and others can probably comment more thoroughly. I know Brian is also interested in how Koyo handles this, and I haven't dived into the code yet to find out 🙂 ---
**Author:** ![bogdan](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/bogdan/32/8_2.png) [@bogdan](https://racket.discourse.group/u/bogdan)\ **Post date:** [October 3, 2024, 5:33am UTC](https://racket.discourse.group/t/best-way-to-implement-a-front-controller-with-rackets-web-server/3193/3 "2024-10-03T05:33:36Z")
If you don't want to use continuations in your application, then I don't think there's anything particularly wrong with avoiding `dispatch/servlet` and using `dispatch-lift`. I like to put my middleware at a level below dispatchers, though, so I typically have middleware defined as procedures from a request handler to a request handler: ```scheme (define-values (app reverse-uri) [("") index-page]) (define (stack handler) (~> handler (wrap-cors) (wrap-auth) (wrap-session) (wrap-sentry)) (dispatch/servlet (stack app)) ``` where `wrap-sentry` might look like: ```scheme (define ((wrap-sentry hdl) req . args) (with-handlers ([exn:fail? (lambda (e) (sentry-capture-exception! e) (raise e))]) (apply hdl req args))) ``` ---
**Author:** ![dstorrs](https://avatars.discourse-cdn.com/v4/letter/d/898d66/32.png) [@dstorrs](https://racket.discourse.group/u/dstorrs)\ **Post date:** [October 8, 2024, 6:11pm UTC](https://racket.discourse.group/t/best-way-to-implement-a-front-controller-with-rackets-web-server/3193/4 "2024-10-08T18:11:23Z")
Bit of thread necromancy here, my apologies. I checked the the [axio link from up above](https://github.com/lojic/axio-alpha/blob/master/axio-lib/private/axio-app.rkt#L67-L88) and noticed this bit of code: ```scheme (dynamic-wind void run void) ``` I was wondering about the purpose of it -- my understanding of `dynamic-wind` is that it ensures the pre and post thunks are always called before/after the value thunk regardless of continuation jumps, but if you use `void` for those thunks then it seems pointless. I went to [the docs on dynamic-wind](https://docs.racket-lang.org/reference/cont.html#%28def._%28%28quote._~23~25kernel%29._dynamic-wind%29%29) and had trouble following it. Can someone walk me through why this would be used? ---
**Author:** ![badkins](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/badkins/32/99_2.png) [@badkins](https://racket.discourse.group/u/badkins)\ **Post date:** [October 9, 2024, 2:24pm UTC](https://racket.discourse.group/t/best-way-to-implement-a-front-controller-with-rackets-web-server/3193/5 "2024-10-09T14:24:02Z")
Ha! When I posted that (very old) code, I noticed the same thing re: `dynamic-wind`, and wondered if I'd get any comments 🙂 I _think_ that the `void`s may have been placeholders that never got replaced, and then maybe I went with `with-handlers` instead. I'm not expecting to use any continuations, so maybe `dynamic-wind` is unnecessary, but the post thunk may be a good place to report exceptions to Sentry.