#lang racket ;; See "<<<" for two small changes, then jump down ;; to `send/suspend'. (require xml net/url racket/control) ;; <<< new import (define (serve port-no) (define main-cust (make-custodian)) (parameterize ([current-custodian main-cust]) (define listener (tcp-listen port-no 5 #t)) (define (loop) (accept-and-handle listener) (loop)) (thread loop)) (lambda () (custodian-shutdown-all main-cust))) (define (accept-and-handle listener) (define cust (make-custodian)) (custodian-limit-memory cust (* 50 1024 1024)) (parameterize ([current-custodian cust]) (define-values (in out) (tcp-accept listener)) (thread (lambda () (handle in out) (close-input-port in) (close-output-port out)))) ;; Watcher thread: (thread (lambda () (sleep 10) (custodian-shutdown-all cust)))) (define (handle in out) (define req ;; Match the first line to extract the request: (regexp-match #rx"^GET (.+) HTTP/[0-9]+\\.[0-9]+" (read-line in))) (when req ;; Discard the rest of the header (up to blank line): (regexp-match #rx"(\r\n|^)\r\n" in) ;; Dispatch: (let ([xexpr (prompt (dispatch (list-ref req 1)))]) ;; <<< changed ;; Send reply: (display "HTTP/1.0 200 Okay\r\n" out) (display "Server: k\r\nContent-Type: text/html\r\n\r\n" out) (display (xexpr->string xexpr) out)))) (define (dispatch str-path) ;; Parse the request as a URL: (define url (string->url str-path)) ;; Extract the path part: (define path (map path/param-path (url-path url))) ;; Find a handler based on the path's first element: (define h (hash-ref dispatch-table (car path) #f)) (if h ;; Call a handler: (h (url-query url)) ;; No handler found: `(html (head (title "Error")) (body (font ((color "red")) "Unknown page: " ,str-path))))) (define dispatch-table (make-hash)) (hash-set! dispatch-table "hello" (lambda (query) `(html (body "Hello, World!")))) ;; ---------------------------------------- (define (build-request-page label next-url hidden) `(html (head (title "Enter a Number to Add")) (body ([bgcolor "white"]) (form ([action ,next-url] [method "get"]) ,label (input ([type "text"] [name "number"] [value ""])) (input ([type "hidden"] [name "hidden"] [value ,hidden])) (input ([type "submit"] [name "enter"] [value "Enter"])))))) (define (many query) ;; Create a page containing the form: (build-request-page "Number of greetings:" "/reply" "")) (define (reply query) ;; Extract and use the form results: (define n (string->number (cdr (assq 'number query)))) `(html (body ,@(for/list ([i (in-range n)]) " hello")))) (hash-set! dispatch-table "many" many) (hash-set! dispatch-table "reply" reply) ;; ---------------------------------------- ;; Old, awkward version: (define (sum query) (build-request-page "First number:" "/one" "")) (define (one query) (build-request-page "Second number:" "/two" (cdr (assq 'number query)))) (define (two query) (let ([n (string->number (cdr (assq 'hidden query)))] [m (string->number (cdr (assq 'number query)))]) `(html (body "The sum is " ,(number->string (+ m n)))))) (hash-set! dispatch-table "sum" sum) (hash-set! dispatch-table "one" one) (hash-set! dispatch-table "two" two) ;; ---------------------------------------- ;; Helper to grab a computation and generate a handler for it: (define (send/suspend mk-page) (let/cc k (define tag (format "k~a" (current-inexact-milliseconds))) (hash-set! dispatch-table tag k) (abort (mk-page (string-append "/" tag))))) ;; Helper to run the number-getting page via `send/suspend': (define (get-number label) (define query ;; Generate a URL for the current computation: (send/suspend ;; Receive the computation-as-URL here: (lambda (k-url) ;; Generate the query-page result for this connection. ;; Send the query result to the saved-computation URL: (build-request-page label k-url "")))) ;; We arrive here later, in a new connection (string->number (cdr (assq 'number query)))) ;; ---------------------------------------- ;; New direct-style servlet: (define (sum2 query) (define m (get-number "First number:")) (define n (get-number "Second number:")) `(html (body "The sum is " ,(number->string (+ m n))))) (hash-set! dispatch-table "sum2" sum2)