From: ptkwt@...2.teleport.com (Phil Tomson)
Date: 2001-01-07T00:40:02+09:00
Subject: [ruby-talk:8741] Druby and `backquotes (bug or just me?)


I've got the following code running on a PC (running windows):
#drb_srvr.rb
#this is the server, let's say the machine name is elmer
require 'drb'
require 'socket'
include Process
class TestServer

   def initialize(hostname)
      @hostname = hostname
      @threads = 0
      p "starting TestServer on #{@hostname}"
   end
   #status commands:
   #check the OS version of the PC:
   def osver
      puts "got osver command"
      `uname -r` #of course this is bogus on Windows!
   end
   #get the current working directory of the PC:   
   def pwd
     Dir.pwd 
   end
end
host = Socket.gethostname
aServerObj = TestServer.new(host)
DRb.start_service('druby://localhost:9000', aServerObj)
DRb.thread.join 

(Actually, there's more, but this is the important part)


And I have the following (or close to it, I've cut out a lot) client
running on a linux box:

#this is the client
require 'drb'
DRb.start_service()
drbObj = DRbObject.new(nil, "druby://elmer:9000")
#later:
drbObj.osver
drbObj.pwd
##################################################

Now what happens is that on the Windows PC side I get:

starting TestServer on elmer
got osver command
drb_srver.rb:10: command not found uname -r 

And then it just stops (on the client side as well).  The drbObj.pwd
command never gets executed on the client side (the linux box).

Now, of course, there is no such command as uname on Windows, hence the
error.  The problem is that because of this error, the client just hangs.

I think that perhaps this has something to do with the fact that the
output of the `uname -r` on the Windows machine just gets sent to STDERR
and so there is nothing to be sent back as a result from the osver method.
If this is the case, how might I get around this?  I tried something like:
`uname -r 2>&1` but no help (of course this kind of redirection may not
do anything on Windows 98).

As an experiment, I also tried redefining the backquote method as shown on
pg 75 of the Programming Ruby book:

   #change to drb_srvr (the Windows side)
   alias oldBackquote ` #`#just to make all the colorization workout
   #the following is to make sure that if an illegal command was
   #executed it doesn't stop the whole server!
   def `(cmd)
      puts "In new backquote!"
      result = oldBackquote(cmd)
      if $? != 0
         puts "$? is: #{$?}"
         return "fail"
      end
      puts "result is: #{result}"
      return result
   end
 
It doesn't work either - I get to where it puts "In new backquote!", but
it never goes on from there.  From this it would seem that my theory about
the output of an erroneous `(cmd) only going to STDERR isn't what the
problem is.

Of course, I know that the real solution here is to change the `uname -r`
in the osver method to `ver` for windows, but if I want to have something
like:

  def run_some_command(cmd)
     `cmd`
  end

and the user specifies a bogus command, then the thing will just hang...
of course I know about the obvious security holes here...

Phil