sunet/scheme/httpd/handlers.scm

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;; Request-handlers for scheme web server
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;; general request-handler-combinator:
;; predicate: path x request --> boolean
;; if #t, handler is called
;; if #f, default-handler is called
(define (make-request-handler predicate handler default-handler)
(lambda (path req)
(if (predicate path req)
(handler path req)
(default-handler path req))))
;; same as make-request-handler except that the predicate is only
;; called with the path:
;; predicate: path --> boolean
(define (make-path-handler predicate handler default-handler)
(make-request-handler
(lambda (path req) (predicate path)) handler default-handler))
;; selects handler according to host-field of http-request
(define (make-hostname-handler hostname handler default-handler)
(make-request-handler
(lambda (path req)
;; we expect only one host-header-field
(string=? hostname (string-trim (get-header (request:headers req) 'host))))
handler default-handler))
;; selects handler according to path-prefix
;; if path-prefix matches, handler is called without the path-prefix
(define (make-path-prefix-handler path-prefix handler default-handler)
(lambda (path req)
(if (string=? path-prefix (car path))
(handler (cdr path) req)
(default-handler path req))))
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;;; (alist-path-dispatcher handler-alist default-handler) -> handler
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; This function creates a table-driven path-handler that dispatches off
;;; of the car of the request path. The handler uses the car to index into
;;; a path-handler alist. If it finds a hit, it recurses using the table's
;;; path-handler. If no hits, it handles the path with a default handler.
;;; An alist handler is passed the tail of the original path; the
;;; default handler gets the entire original path.
;;;
;;; This procedure is how you say: "If the first element of the URL's
;;; path is 'foo', do X; if it's 'bar', do Y; otherwise, do Z."
(define (alist-path-dispatcher handler-alist default-handler)
(fold-right
(lambda (handler-pair default-handler)
(make-path-prefix-handler
(car handler-pair)
(cdr handler-pair)
default-handler))
default-handler
handler-alist))