[racket] Help needed in writing Macro to transform (lambda (req) ....) to be used in web-server/servlet using auth cookies

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