[racket] Stateless Web Server: Generating a response on a stuffer error

Wow. Thank you very much.


On Tue, Apr 24, 2012 at 4:31 PM, Jay McCarthy wrote:

> There was no way to do this, but I just added the 92nd keyword to
> serve/servlet to do it:
>
>                #:servlet-responder
>                (λ (url exn)
>                  (response/xexpr
>                   `(html (body "Some other message"))))
>
> allows you to inspect the exception and return a different thing.
>
> (The push will happen shortly.)
>
> Jay
>
> On Mon, Apr 23, 2012 at 3:35 PM, Galler <lzgaller at optonline.net> 
> wrote:
>> Description:
>>
>> the stateless webserver allows a user to generate a stuffer to 
>> manipulate
>> the encoding of the ANF sent to the client in the URL
>>
>> For example
>>
>> (stuffer-chain serialize-stuffer (stuffer-compose base64-stuffer
>> (HMAC-SHA1-stuffer #"mysupersecretkey")))
>>
>> will prepend a digest to the base64-encoded ANF, and recompute and
>> authenticate the digest on receipt.
>>
>> If either the encoded ANF, or the digest has been altered (i.e. 
>> forged) by
>> the client, the stuffer correctly throws an error, which is caught by 
>> the
>> webserver, which sends the following response back to the client:
>>
>> <some html>
>> Exception
>>
>> The application raised an exception with the message:
>>
>> HMAC-SHA1-stuffer: Signature does not match!
>>
>> </some html>
>>
>> Question:
>>
>> While the behavior is absolutely correct, is there someplace to set a
>> response if an error occurs with the stuffer? Is the error caught at 
>> the
>> top-level of the dispatching server and not available for 
>> customization?
>>
>> If the answer is the latter, its ***not*** critical and probably not
>> important to implement.
>>
>> Example code: Once running, alter the url in your browser in any 
>> manner
>> (character addition, deletion, substitution) to generate the expected 
>> error.
>>
>> #lang web-server
>>
>>
>> (require web-server/stuffers)
>> (provide/contract (start (request? . -> . response?)))
>>
>> (define (start request)
>>  (phase-1 request))
>>
>> ; phase-1: request -> response
>> (define (phase-1 request)
>>  (local [(define (response-generator embed/url)
>>            (response/xexpr
>>             `(html
>>               (body (h1 "Phase 1")
>>                     (a ((href ,(embed/url phase-2)))
>>                        "click me!")))))]
>>    (send/suspend/dispatch response-generator)))
>>
>> ; phase-2: request -> response
>> (define (phase-2 request)
>>  (display (request-bindings/raw request))
>>  (local [(define (response-generator embed/url)
>>            (response/xexpr
>>             `(html
>>               (body (h1 "Phase 2")
>>                     (a ((href ,(embed/url phase-1)))
>>                        "click me!")))))]
>>    (send/suspend/dispatch response-generator)))
>>
>>
>> (require web-server/servlet-env)
>> (serve/servlet start
>>              #:stateless? #t
>>              #:launch-browser? #t
>>              #:connection-close? #t
>>              #:stuffer (stuffer-chain serialize-stuffer 
>> (stuffer-compose
>> base64-stuffer (HMAC-SHA1-stuffer #"mysupersecretkey")))
>>              #:quit? #f
>>              #:listen-ip #f
>>               #:servlet-path "/")
>> ____________________
>>  Racket Users list:
>>  http://lists.racket-lang.org/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