Hi Marc,
send/suspend generates a unique URL. You can use the context to ensure
it is only useful once.
Essentially you want something like this...
(define (get-url-for-user user)
(let/ec return
(define submitted-once-already? #f)
(define user-clicked-req
(send/suspend
(λ (k-url)
(return k-url))))
(cond
[submitted-once-already?
(send/back (generate-already-done-page))]
[else
(set! submitted-once-already? #t)
(send/back (generate-survey-page))])))
(define (send-email-to-users user->email)
(for ([(u e) (in-hash user->email)])
(send-email e (get-url-for-user u)))
(send/back `(html "Done!")))
Jay
On Mon, Jan 4, 2016 at 7:10 AM, Marc Kaufmann <marc.kaufman...@gmail.com> wrote:
> Hi,
>
> I want to generate links, which will be sent via email to survey
> participants, that depend on the participant, and so that if the form has
> been submitted once, it cannot be resubmitted. Obviously
>
> mysurvey.com/marc
>
> would work, if there is only one form for user marc, but is totally insecure.
> I could use SHA1-encoded identifiers, say if a user's identifier is 1234,
> encode it which gives encoded-1234, store both of those values in the
> database and when the server sees encoded-1234, return the form appropriate
> for user 1234. (They will be different, sometimes only on the submit button,
> but usually also the forms.) This also means that I can ensure that the link
> only works as long as the form hasn't yet been submitted.
>
> I am wondering whether there are some functions in the web server that would
> make the creation of such links easier, since when I went through the
> tutorial on blogs, it seemed like Racket created random-looking URLs with
> continuations already.
>
> Thanks,
> Marc
>
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--
Jay McCarthy
Associate Professor
PLT @ CS @ UMass Lowell
http://jeapostrophe.github.io
"Wherefore, be not weary in well-doing,
for ye are laying the foundation of a great work.
And out of small things proceedeth that which is great."
- D&C 64:33
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