sunet/seval.scm

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2000-09-26 10:35:26 -04:00
;;; Path handler for uploading Scheme code to the SU web server -*- Scheme -*-
;;; This is really just an handler example demonstrating how to upload code
;;; into the server.
;;; Copyright (c) 1995 by Olin Shivers.
;;; Imports and non-R4RS'isms
;;; \r and \n in string for cr and lf.
;;; SWITCH conditional, ? for COND
;;; HTTP request record stucture
;;; HTTP-ERROR & reply codes
;;; Basic path handler support
;;; scsh syscalls
;;; Pretty-printing P proc.
;;; htmlout stuff
;;; SAFE-EVAL
;;; ERROR
;;; INDEX
;;; URI decoding
;;; string hacks (SKIP-WHITESPACE)
;;; HTML forms
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; This path handler is suitable for receiving code entered into an
;;; HTML text form. The Scheme code being uploaded is being POST'd to us
;;; (from a form). See http-forms.scm for info on the format of this kind
;;; of request. After parsing the request into the submitted string, we
;;; parse *that* into a Scheme sexp with READ, and eval it.
;;; (do/timeout secs thunk)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Run THUNK, and gun it down if it hasn't finished in SECS seconds.
;;; Returns nothing useful, and THUNK gets executed in a subprocess,
;;; so its side-effects are invisible, as well. This is a clever kludge --
;;; it uses three subprocesses -- but I don't have interrupts, so I'm hosed.
(define (do/timeout* secs thunk)
(run (begin (let ((timer (fork (lambda () (sleep secs))))
(worker (fork thunk)))
(receive (process status) (wait-any)
(ignore-errors
(lambda ()
(signal-process (proc:pid (if (eq? worker process)
timer
worker))
signal/kill))))))))
(define-syntax do/timeout
(syntax-rules ()
((do/timeout secs body ...) (do/timeout* secs (lambda () body ...)))))
;;; The path handler for seval ops.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (seval-handler path req)
(switch string=? (request:method req)
(("POST") ; Could do others also.
(let ((modern-protocol? (not (v0.9-request? req))))
(when modern-protocol?
(begin-http-header #t 200)
(write-string "Content-type: text/html\r\n\r\n"))
(with-tag #t HEAD ()
(newline)
(emit-title #t "Scheme program output"))
(newline))
(with-tag #t BODY ()
(newline)
(let ((sexp (read-request-sexp req)))
(do/timeout 10
(receive vals
;; Do the computation.
(begin (emit-header #t 2 "Output from execution")
(newline)
(with-tag #t PRE ()
(newline)
(force-output) ; In case we're gunned down.
(eval-safely sexp)))
;; Pretty-print the returned value(s).
(emit-header #t 2 "Return value(s)")
(with-tag #t PRE ()
(for-each p vals)))))))
(else (http-error http-reply/method-not-allowed #f req))))
;;; Read an HTTP request entity body from stdin. The Content-length:
;;; element of request REQ's header tells how many bytes to this entity
;;; is. The entity should be a URI-encoded form body. Pull out the
;;; program=<stuff>
;;; string, extract <stuff>, uri-decode it, parse that into an s-expression,
;;; and return it.
(define (read-request-sexp req)
(? ((get-header (request:headers req) 'content-length) =>
(lambda (cl-str) ; Take the first Content-length: header,
(let* ((cl-start (skip-whitespace cl-str)) ; skip whitespace,
(cl (if cl-start ; & convert to
(string->number (substring cl-str ; a number.
cl-start
(string-length cl-str)))
0)) ; All whitespace?? -- WTF.
(qs (read-string cl)) ; Read in CL chars,
(q (parse-html-form-query qs)) ; and parse them up.
(s (? ((assoc "program" q) => cdr)
(else (error "No program in entity body.")))))
(http-log "Seval sexp:~%~s~%" s)
(read (make-string-input-port s)))))
(else (http-error http-reply/bad-request req
"No Content-length: field in POST request."))))