racket/sandbox: add sandbox-propagate-exceptions

collects/racket/sandbox.rkt

@@ -32,6 +32,7 @@
          sandbox-memory-limit
          sandbox-eval-limits
          sandbox-eval-handlers
+         sandbox-propagate-exceptions
          call-with-trusted-sandbox-configuration
          evaluator-alive?
          kill-evaluator
@@ -78,6 +79,7 @@
 (define sandbox-eval-limits  (make-parameter '(30 20))) ; 30sec, 20mb
 (define sandbox-propagate-breaks (make-parameter #t))
 (define sandbox-coverage-enabled (make-parameter #f))
+(define sandbox-propagate-exceptions (make-parameter #t))
 
 (define (call-with-trusted-sandbox-configuration thunk)
   (parameterize ([sandbox-propagate-breaks    #t]
@@ -679,6 +681,7 @@
   (define user-cust     (make-custodian memory-cust))
   (define user-cust-box (make-custodian-box user-cust #t))
   (define coverage?     (sandbox-coverage-enabled))
+  (define propagate-exceptions? (sandbox-propagate-exceptions))
   (define uncovered     #f)
   (define default-coverage-source-filter #f)
   (define input-ch      (make-channel))
@@ -759,7 +762,13 @@
        (when (eof-object? expr)
          (terminated! 'eof) (channel-put result-ch expr) (user-kill))
        (with-handlers ([void (lambda (exn)
-                               (channel-put result-ch (cons 'exn exn)))])
+                               (if propagate-exceptions?
+                                   (channel-put result-ch (cons 'exn exn))
+                                   (begin
+                                     (call-with-continuation-prompt
+                                      (lambda ()
+                                        (raise exn)))
+                                     (channel-put result-ch (cons 'vals (list (void)))))))])
          (define run
            (if (evaluator-message? expr)
              (case (evaluator-message-msg expr)

collects/scribblings/reference/sandbox.scrbl

@@ -232,13 +232,14 @@ sandboxed code, for example:
 ]
 An error will be signaled in such cases.
 
-Evaluation can also be instrumented to track coverage information when
-@racket[sandbox-coverage-enabled] is set. Exceptions (both syntax and
+If the value of @racket[sandbox-propagate-exceptions] is true (the
+default) when the sandbox is created, then exceptions (both syntax and
 run-time) are propagated as usual to the caller of the evaluation
-function (i.e., catch it with @racket[with-handlers]).  However, note
-that a sandboxed evaluator is convenient for testing, since all
-exceptions happen in the same way, so you don't need special code to
-catch syntax errors.
+function (i.e., catch them with @racket[with-handlers]).  If the value
+of @racket[sandbox-propagate-exceptions] is @racket[#f] when the
+sandbox is created, then uncaught exceptions in a sandbox evaluation
+cause the error to be printed to the sandbox's error port, and the
+caller of the evaluation receives @|void-const|.
 
 Finally, the fact that a sandboxed evaluator accept syntax objects
 makes it usable as the value for @racket[current-eval], which means
@@ -456,6 +457,17 @@ the evaluator (or the break is lost if the evaluator is not used
 further). The default is @racket[#t].}
 
 
+@defboolparam[sandbox-propagate-exceptions propagate?]{
+
+A parameter that controls how uncaught exceptions during a sandbox
+evaluation are treated. When the parameter value is @racket[#t], 
+then the exception is propagated to the caller of sandbox.
+When the parameter value is @racket[#f], the exception message
+is printed to the sandbox's error port, and the caller of the
+sandbox receives @|void-const| for the evaluation. The default
+is @racket[#t].}
+
+
 @defparam[sandbox-namespace-specs spec (cons/c (-> namespace?) 
                                                (listof module-path?))]{
 

collects/tests/racket/sandbox.rktl

@@ -172,6 +172,15 @@
                                              (make-bytes 500000)))))
         =err> "out of memor(?:y)"))
 
+   ;; check non-propagation of errors
+   --top--
+   (parameterize ([sandbox-propagate-exceptions #f]
+                  [sandbox-error-output 'string])
+     (make-base-evaluator! '(void)))
+   --eval--
+   (/ 0) => (void)
+   --top--
+   (regexp-match #rx"^.*?\n" (get-error-output ev)) => '("/: division by zero\n")
    ;; i/o
    --top--
    (parameterize ([sandbox-input "3\n"]

doc/release-notes/racket/HISTORY.txt

@@ -3,6 +3,7 @@ Changed the format of error messages
 Added raise-argument-error, raise-result-error,
  raise-arguments-error, raise-range-error
 racket/contract: added procedure-arity-includes/c
+racket/sandbox: added sandbox-propagate-exceptions
 
 Version 5.3.0.8
 Required modules are instantiated in the order that they are required