| From: Jay McCarthy (jay.mccarthy at gmail.com) Date: Sat Jun 25 22:56:05 EDT 2011 |
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2011/6/25 J G Cho <gcho at fundingmatters.com>: > Yikes. I did read those documents before sometime ago when I started > to learn about Racket. Without much comprehension! I really hoped to > stay with WebApps part and stay oblivious to the internals of the > Server. No such luck if I really want to take advantage of all the > neat things it can do. > > Per your reply with links, I read them again trying to make sense of > your sequencing dispatchers code. I think I can sorta get a feel for > sequence:make and lift:make etc but ... > > Right now, I feel very comfortable 'hugging the shore' writing my > little servlets. Stringing together my own custom dispatchers feel > like taking a new sail boat out to uncharted big ocean. > > You see, I am still banging my head making my way around the documents > on Racket HTTP Server, which is not the easiest to digest. > > First, the first sentence I read is "Web Server is just a > configuration of a dispatching server." My reaction is, 'Huh? I've > never heard such statement over the years doing web apps starting with > Perl CGI, PHP, JSP, RoR, GAE to mention a few. The statement might be > true but it's not helping me find my way around. Sounds more like zen > koan or something experts utter that completely makes no sense to a > beginner.' That section then explains what a dispatching server is. > > Second, I am trying out the file server example (from 3. Launching Servers). > > I made a file file-server.rkt by copying the code: > > #lang racket > > (require web-server/webserver You meant (require web-server/web-server) as it says at the top of that page. It's very easy to make typos on this sort of thing. :( Jay > web-server/dispatchers/filesystem-map) > > (define (start-file-server base) > (serve > #:dispatch > (files:make > #:url->path (make->url->path base) > #:path->mime-type (lambda (path) #"application/octet-stream")) > #:indices (list "index.html") > #:port 8080)) > > (start-file-server (current-directory)) > > > I am invoking it with > > path to /Racket5.1/bin/racket -t file-server.rkt > > (the way I start my servlets from command line when not using DrRacket). > > I am greeted with: > > default-load-handler: cannot open input file: "path > to/Racket5.1/collects/web-server/webserver.rkt" (No such file or > directory; errno=2) > > Either the example is wrong or the author has left out a small detail > obvious to him but not so to this beginner. > > It's going to take a bit of blood/sweat/tears/scars... > > But on the other hand, the design seems very promising/exciting if I > can get past the initial learning pains. Taking the auth checking code > out of the procedures is such a huge gain! > > Thank you. > > > On Sat, Jun 25, 2011 at 1:10 PM, Jay McCarthy <jay.mccarthy at gmail.com> wrote: >> The Web server is set up as a pipeline of "dispatchers", which are >> functions that accept the TCP connection and the HTTP request and >> either write a response or refuse to handle the request. This chapter >> of the documentation: >> >> http://docs.racket-lang.org/web-server-internal/dispatchers.html >> >> discusses all the dispatchers that make up the standard server. They >> can be combined very easily to customize the server to do exactly what >> you want. >> >> Launching a server with your custom dispatcher is as easy as using >> serve/servlet or web-server/insta: >> >> http://docs.racket-lang.org/web-server-internal/web-server.html >> >> Jay >> >> 2011/6/25 J G Cho <gcho at fundingmatters.com>: >>> Seems like an elegant approach but.... "dispatcher outside the >>> servlet" goes over my head like an UFO over a crop duster. >>> >>> I guess I will have to dig deeper into how the server is put together. >>> >>> On Sat, Jun 25, 2011 at 1:23 AM, Jay McCarthy <jay.mccarthy at gmail.com> wrote: >>>> I find it more convenient to setup a dispatcher outside the servlet >>>> that checks for the authenticator, that way once it has passed that >>>> part of the dispatch chain, security can be relied upon. Something >>>> like... >>>> >>>> (serve/launch/wait >>>> (sequence:make >>>> (lift:make (lambda (req) (if (or (unsecured-url? req) >>>> (authenticated? req)) (next-dispatcher) (display-error/login-page)))) >>>> (dispatch/servlet ...))) >>>> >>>> Then the servlet code can basically ignore the authenticator. >>>> >>>> Jay >>>> >>>> 2011/6/24 J G Cho <gcho at fundingmatters.com>: >>>>> Hello again, >>>>> >>>>> I am guessing my problem calls for macro (which is "beyond my pay >>>>> scale") and I am hoping this is the right place. >>>>> >>>>> Anyway, after reading this >>>>> http://docs.racket-lang.org/web-server/faq.html#(part._.What_special_considerations_are_there_for_security_with_the_.Web_.Server_) >>>>> >>>>> I am led to believe that I will be writing lots of code like this: >>>>> >>>>> (define (some-sensitive-content req) >>>>> >>>>> (if (user-is-legit req) ;check auth cookie >>>>> (...what have you ...) >>>>> (do-login-and-then-maybe-handle req))) >>>>> >>>>> So here is my first attemp at macro which sorta works: >>>>> >>>>> (define-syntax (guarded-handler stx) >>>>> (syntax-case stx () >>>>> [(_ name body) >>>>> #'(begin (define (name req) >>>>> (if (user-is-legit req) >>>>> body >>>>> (ask-login req))))])) >>>>> >>>>> (guarded-handler gated-content >>>>> (response/xexpr >>>>> `(html (head (title "Gated Content")) >>>>> (body (p "Shhhhhhh") >>>>> (p >>>>> (a ([href "/logout "]) >>>>> "Done")))))) >>>>> >>>>> What I would really like, however, is >>>>> >>>>> (guard (lambda (req) ...)) to transformed to: >>>>> >>>>> (lambda (req) >>>>> (if (user-is-legit req) >>>>> (...what have you ...) >>>>> (do-login-and-then-maybe-handle req))) >>>>> >>>>> such that I can use it like: >>>>> >>>>> (define (count-dot-com i) >>>>> (count-dot-com >>>>> (send/suspend/dispatch >>>>> (λ (embed/url) >>>>> (response/xexpr >>>>> `(html >>>>> (head (title "Count!")) >>>>> (body (h2 (a ([href ,(embed/url >>>>> (guard (λ (req) >>>>> (sub1 i))))]) >>>>> "-")) >>>>> ... >>>>> >>>>> (define (count-dot-com i) >>>>> (send/suspend/dispatch >>>>> (λ (embed/url) >>>>> (response/xexpr >>>>> `(html >>>>> (head (title "Count!")) >>>>> (body (h2 (a ([href ,(embed/url >>>>> >>>>> (guard (λ (req) >>>>> (count-dot-com (sub1 i))))]) >>>>> "-") >>>>> ... >>>>> >>>>> in addition to the first case like this: >>>>> >>>>> (define gated-content >>>>> (guard (lambda (req) ...)) >>>>> >>>>> Seems simple enough but my naive macros (not shown here to protect my >>>>> fragile ego) are failing. >>>>> Any help/suggestion is greatly appreciated. >>>>> >>>>> jGc >>>>> >>>>> _________________________________________________ >>>>> For list-related administrative tasks: >>>>> http://lists.racket-lang.org/listinfo/users >>>> >>>> >>>> >>>> -- >>>> Jay McCarthy <jay at cs.byu.edu> >>>> Assistant Professor / Brigham Young University >>>> http://faculty.cs.byu.edu/~jay >>>> >>>> "The glory of God is Intelligence" - D&C 93 >>>> >>> >> >> >> >> -- >> Jay McCarthy <jay at cs.byu.edu> >> Assistant Professor / Brigham Young University >> http://faculty.cs.byu.edu/~jay >> >> "The glory of God is Intelligence" - D&C 93 >> > -- Jay McCarthy <jay at cs.byu.edu> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93
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