From: ahoward <ahoward@...>
Date: 2003-05-14T05:35:56+09:00
Subject: Re: RCR for child execution

On Tue, 13 May 2003, Simon Strandgaard wrote:

> On Tue, 13 May 2003 23:44:53 +0900, Brian Candler wrote:
>
> > On Tue, May 13, 2003 at 06:50:54PM +0900, Simon Strandgaard wrote:
> >> > In the general case, your Ruby program could do lots of things which force
> >> > a direct output to stdout/stderr. Here is one small valid Ruby program:
> >> >
> >> >         pid = fork do
> >> >           exec("ls /nonexistent")
> >> >         end
> >> >         Process.waitpid(pid)
> >> >
> >> > How are you going to modify Ruby so that the output of those four lines are
> >> > captured in the sandbox?
> >>
> >> All "child-process" routines should parse rb_stdout to the children, in
> >> this case fork.  I know I have only mentioned system&backquote before.
> >> Well all routines in Rubys Core which spawns children should do this.
> >
> > Not acceptable... this time I must insist that you answer the question :-)

why must this be done in ruby simon?  this can all be done from within c or c--:

i think this does exactly what you want - it captures all output, including
output from any child, from a ruby script run from within c.

----CODE----
  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  #include <assert.h>
  #include "ruby.h"

  /*
  gcc redirect2.c -I /usr/local/ruby-1.6.6/ /usr/local/ruby-1.6.6/libruby.a -lm -ldl -lcrypt
  */

  char *script =
    "system 'ls'\n"
    "`ls non-existent-file`\n"
    "system 'ls non-existent-file'\n"
    "STDOUT.puts 42\n"
    "STDERR.puts 42\n"
    "$defout.puts 42\n"
    "$stdout.puts 42\n"
    "$stderr.puts 42\n"
    "puts 42\n"
   "pid = fork {exec('ls /nonexistent')}\n"
   "Process.waitpid(pid)\n"
  ;

  int
  main (argc, argv)
       int argc;
       char **argv;
  {
    int fd[2];
    int f;
    int __out, __err;
    int c;

    /* save */
    assert ((__out = dup (STDOUT_FILENO)) != -1);
    assert ((__err = dup (STDERR_FILENO)) != -1);

    /* redirect */
    assert (pipe (fd) == 0);
    assert (dup2 (fd[1], STDOUT_FILENO) != -1);
    assert (dup2 (fd[1], STDERR_FILENO) != -1);

    /* sandboxed */
    ruby_init ();
    ruby_init_loadpath ();
    rb_eval_string (script);

    /* restore */
    dup2 (__out, STDOUT_FILENO);
    dup2 (__err, STDERR_FILENO);

    /* display */
    write (STDOUT_FILENO, "REDIRECTED:\n", 12);
    assert (close (fd[1]) != -1);
    while (read (fd[0], &c, 1) && write (STDOUT_FILENO, &c, 1));
    assert (close (fd[0]) != -1);

    return (EXIT_SUCCESS);
  }
----CODE----


> Kernel#fork  does spawn a child.. changes to Rubys Core is necessary.
> unix-fork inherit stdin/stdout/stderr from parent to the child process.  I
> want Rubys Kernel#fork to inherit rb_stdin/rb_stdout/rb_stderr from the
> parent to the child process.  But hey.. unix-fork() does not take any
> arguments.  Is this possible?  My guess - Yes this should be possible. Here
> is some pseudo code.
>
> void Kernel#fork() {
>     backup_stdout = stdout;      /* what i want */
>     stdout = rb_stdout;          /* what i want */
>     pid = fork();
>     if(pid == 0)
>         stdout = backup_stdout;  /* what i want */
> }
<snip>

it is possible, but requires no changes to ruby's core, the above accomplishes
this in c.

> Again assignment to stdout is illegal.. freopen should be used. I just use
> assignment in this pseudo-code in order to keep it simple. Further more
> stderr/stdin is left out.. they should of cause also be redirected.

if this is done using dup(2) - all is well in the world.

> This way stdout/stderr/stdin should be untouched and remain usable in the
> C/C++ application.

this cannot be the case - but they are restored to their previous values.

-a

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