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|
#! /usr/local/bin/guile -s
!#
;;; examples/safe/safe -- Example for safe (sand-boxed) evaluation.
;;; Commentary:
;;; This is a demo program for evaluating arbitrary (untrusted) Scheme
;;; code in a controlled, safe environment. Evaluation in safe
;;; environments restricts the evaluated code's access to some given
;;; primitives, which are considered `safe', that means which cannot
;;; do any harm to the world outside of Guile (creating/deleting files
;;; etc.)
;;;
;;; *Note* that the files in this directory are only suitable for
;;; demonstration purposes, if you have to implement safe evaluation
;;; mechanisms in important environments, you will have to do more
;;; than shown here -- for example disabling input/output operations.
;;; Author: Martin Grabmueller
;;; Date: 2001-05-30
;;; Code:
;; Safe module creation is implemented in this module:
;;
(use-modules (ice-9 safe))
;; This is the main program. It expects one parameter in the format
;; returned by (command-line) and expects that exactly one file name
;; is passed in this list (after the script name, which is passed as
;; the 0th parameter.)
;;
;; The given file is opened for reading, one expression after the
;; other is read and evaluated in a safe environment. All exceptions
;; caused by this evaluation are caught and printed out.
;;
(define (main cmd-line)
;; Internal definition of the procedure which prints usage
;; information.
;;
(define (display-help)
(display "Usage: safe FILENAME")
(newline)
(quit 1))
;; Check that we received exactly one command line argument after
;; the script name
;;
(if (not (= (length cmd-line) 2))
(display-help)
(let ((port (open-input-file (cadr cmd-line)))
;; Create the safe module.
(safe-module (make-safe-module)))
;; Read one expression a time.
(let lp ((expr (read port)))
;; End of file? -> Return.
(if (eof-object? expr)
#t
(catch #t
(lambda ()
;; Evaluate the expression in the safe environment.
(eval expr safe-module)
;; ... and read the next expression if no error occured.
(lp (read port)))
;; Handle exceptions. This procedure will be called when an
;; error occurs while evaluating the expression. It just
;; prints out a message telling so and returns from the
;; evaluation loop, thus terminating the program.
;;
(lambda args
(display "** Exception: ")
(write args)
(newline))))))))
;; Start the main program.
;;
(main (command-line))
;; Local variables:
;; mode: scheme
;; End:
|
