Requires

Ruby MRI or Ruby 1.9.

Will not work with Rubinius! It does not support $SAFE.

I do not know JRuby.

Install

gem install Safebox

Usage

First load the safebox:

#! ruby
require 'safebox'

The most things in your Safebox are possible:

value = Safebox.eval "1+2**9"  # => 513
value = Safebox.eval {|| 1+2**8 }  # => 257

You can use a String or a Proc, also as argument:

value = Safebox.eval lambda {|| 1+2**7 }

More complex code with classes and everything else...

value = Safebox.eval do
	class Mail
		attr_accessor :subject, :body, :to, :from
		def generate
			[ "To: #{@to}", "From: #{@from}",
				"Subject: #{@subject}", '', @body ].join "\n"
		end
	end
	mail = Mail.new
	mail.from, mail.to, mail.subject = "me", "root", "Plz install Ruby :)"
	mail.subject = "..."
	mail.generate
end

Only some good things are not possible:

Safebox.eval "$stdout.puts 'I am OK!'"  # not possible :(

But, very bad code will not damage your system.

Safebox.eval "class Unsecure;def self.code() system 'rm *' ; end end; Unsecure.code"  # will fail :)

This will raise a SecurityError.

What is with raised exceptions, like SecurityError or others?

Safebox.eval "raise Exception"

This will print the Exception to Console.

You want to get the Exception?

ret = Safebox.run "raise Exception"
ret # => [:exception, #<Exception>]

What is Safebox.run?

ret = Safebox.run "1+2**9"
ret # => [:value, 513]

It returns the value or the raised exception. -- Nothing else.

You should know, Ruby is not stupid. I am very surprised, because this is not possible:

aA = Safebox.eval do
	class A
		def to_s
			'Owned!'
		end
	end
	A.new
end
aA.to_s  # => SecurityError: calling insecure method: to_s

A#to_s is defined in our Safebox, so every call outside can be a security hole.

But you can use #to_s in an other Safebox, withour any risk:

Safebox.eval aA.method( :to_s)  # => "Owned!"  # Not really :)

Behind Safebox

It uses only a Thread, $SAFE=4 and some code for automatism.

The real magic is Ruby itself.