Awesome! That helped a lot. Thanks! On Wed, Mar 21, 2012 at 6:28 PM, Jay McCarthy <jay.mccar...@gmail.com>wrote:
> Since you did not tell us what error you had, I assume the error was: > > serve/servlet: contract violation, expected: can-be-response?, given: > #<promise> > > When I tried your code, I also had the error: > > current-directory: `exists' access denied for /home/jay/Downloads/ > > because you need to give the sandbox permission to read, like: > > #:allow-read (list "/") > > But I assume that you know that error doesn't have to do with the Web > server. > > Returning to the serve/servlet error... > > If you change your 'start' to: > > (define (start request) > (define prm ((lazy-eval 'lazy-handler) request)) > (printf "~a ~a\n" prm (promise? prm)) > (define ans (force prm)) > (printf "~a\n" ans (promise-forced? prm)) > ans) > > You will see the output: > > #<promise> #f > Servlet (@ /main) exception: > promise-forced?: expected argument of type <promise>; given: #<promise> > > This indicates the thing returned by your handler is not a promise and > therefore cannot be forced. > > This is called structure generativity: every instantiation of a module > has different structures, and sandboxes lead to multiple > instantiations of the same module---racket/promise in this case. Thus, > different 'promise' data structures. > > Fixing this is what 'sandbox-namespace-specs' is for. > > If you wrap your call to 'make-evaluator' in: > > (parameterize ([sandbox-namespace-specs > (list sandbox-make-namespace > 'racket/promise > 'web-server/http)]) > .....) > > Then it will work. This shares the modules 'racket/promise' (to get > the right promise data structure) and 'web-server/http' (to get the > right request and response structures) between the evaluator and the > host Racket program. > > In case you don't realize, using an evaluator is totally unnecessary. > You can just write another module in the lazy language and require it > in the strict program and call force normally. For example: > > #lang racket/load > > (module lazy-handler lazy > (require web-server/http/bindings > web-server/http/response-structs > web-server/http/xexpr) > (define (lazy-handler request) > (let ((bindings (request-bindings request))) > (if (exists-binding? 'hi bindings) > (response/xexpr "Hi!") > (response/xexpr "")))) > (provide lazy-handler)) > > (module the-server racket > (require web-server/servlet-env > web-server/http/bindings > web-server/http/response-structs > web-server/http/xexpr > 'lazy-handler) > > (define (start request) > (define prm (lazy-handler request)) > (printf "~a ~a\n" prm (promise? prm)) > (define ans (force prm)) > (printf "~a ~a\n" ans (promise-forced? prm)) > ans) > > (serve/servlet start > #:launch-browser? #t > #:quit? #f > #:listen-ip #f > #:servlet-path "/main" > #:port 8080 > #:servlet-regexp #rx"main.*" > #:extra-files-paths > (list (build-path (current-directory))))) > > (require 'the-server) > > Hope this helps, > > Jay > > > > On Wed, Mar 21, 2012 at 11:44 AM, Nathan Breit <nabr...@gmail.com> wrote: > > I'm trying to write a servlet that plugs into the existing server. > Here's an > > example: > > > > #lang racket > > (require web-server/servlet-env) > > (require web-server/http/bindings) > > (require web-server/http/response-structs) > > (require web-server/http/xexpr) > > > > (require racket/sandbox) > > (define lazy-eval (make-evaluator 'lazy)) > > > > (map lazy-eval > > '( > > (require web-server/http/bindings) > > (require web-server/http/response-structs) > > (require web-server/http/xexpr) > > (require racket/promise) > > (define (lazy-handler request) > > (let ((bindings (request-bindings request))) > > (if (exists-binding? 'hi bindings) > > (response/xexpr "Hi!") > > ""))) > > )) > > > > (define (start request) > > (force ((lazy-eval 'lazy-handler) > > request))) > > > > (serve/servlet start > > #:launch-browser? #f > > #:quit? #f > > #:listen-ip #f > > #:servlet-path "" > > #:port 8080 > > #:servlet-regexp #rx"main.*" > > #:extra-files-paths > > (list (build-path (current-directory) "extraFiles"))) > > > > On Wed, Mar 21, 2012 at 6:22 AM, Matthias Felleisen < > matth...@ccs.neu.edu> > > wrote: > >> > >> > >> > >> On Mar 21, 2012, at 5:18 AM, Nathan Breit wrote: > >> > >> > Hi, > >> > I'm trying to implement a Racket web-server handler that does lazy > >> > evaluation. My approach so far as been to try making a > evaluator/namespace > >> > that uses the lazy racket, then evaluate a function in it that > returns a > >> > lazy request handler. However, I'm running into problems getting the > handler > >> > to read the request object. My last resort will be to make a request > >> > serializer and pass serialized requests into the handler, but is > there a > >> > better way? > >> > Thanks, > >> > -Nathan > >> > ____________________ > >> > Racket Users list: > >> > http://lists.racket-lang.org/users > >> > >> > >> > >> Are you trying to write a web server in Lazy or are you trying to write > a > >> servlet in Lazy and plug it into the existing strict server? Perhaps you > >> want to post a code snippet that shows where things fail. -- Matthias > >> > > > > > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > > > > > > -- > Jay McCarthy <j...@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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