sunet/seval.scm

;;; 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

;;; 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)
  (let ((request-method (request:method req)))
    (cond 
     ((string=? request-method "POST")	; Could do others also.

      (let ((modern-protocol? (not (v0.9-request? req))))
	(if modern-protocol?
	    (begin
	      (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)
  (cond 
   ((get-header (request:headers req) 'content-length) =>
    (lambda (cl-str)		 ; Take the first Content-length: header,
      (let* ((cl-start (string-skip cl-str char-set:whitespace))	   ; 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 (cond ((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."))))