Borx

DISCLAIMER: if you think this plugin is about rock-hard security, you are wrong

This plugin parses a piece of ruby code with ripper, rewrites it a bit and converts it back to ruby code. This lets a central object decide what the code is actually doing.

Usage

Completly trivial:

env = Borx::Environment.new
env.eval("1 + 1") # => 2

Gets tricky:

env = Borx::Environment.new
def env.call_method(binding, receiver, method,*args, &block)
  if method == "+"
    super(binding, receiver, "-", *args, &block)
  else
    super
  end
end
env.eval("1 + 1") # => 0

When to use

Please use your brain before using this. Make sure the following points apply to your situation:

• You have to solve your problem by evaluting ruby code which interacts with the rest of your application e.g. because it's specified by a third party.
• Completly integrating the ruby code is not an option e.g. because it must be user defined.
• Completly jailing the ruby code is not an option either e.g. because it must interact with some of your code.
• The code you evaluate is rather small and simple.
• Performance is not an issue.
• You generally trust the people sending you code (again, this is not about security!).
• You think this solution is ugly as hell. If you don't think like this, you've probably not understood what this library does.

How to use

The most interesting class for you is Borx::Environment. By overriding its methods you can control the behavior of evaled code.

To simplify things you can either you Borx::Environment or Borx::Environment::Base as superclass. The difference is that Borx::Environment contains useful default implementation for all methods mentioned below while Borx::Environemnt::Base does not. So use the earlier if you want the code to behave normally except for some cases and the later if you want to redefine the behavior from scratch.

Example

Calling my_method instead of your_method:

class MyEnv < Borx::Environment
  def call_method( binding, receiver, name, *args, &block )
    name = "my_method" if name == "your_method"
    super( binding, receiver, name, *args, &block)
  end
  def call_private_method( binding, receiver, name, *args, &block)
    name = "my_method" if name == "your_method"
    super( binding, receiver, name, *args, &block)
  end
end

MyEnv.new.eval("your_method") #=> calls my_method

Overrideable methods

These methods are currently overrideable to control behaviour of evaled code:

• get_variable( binding, variable )
• set_variable( binding, variable, value )
• call_method( binding, receiver, method, *args, &block)
• call_private_method( binding, receiver, method, *args, &block) - same as above, but called in a private context
• get_constant( binding, name, namespace = Object)
• set_constant( binding, name, namespace = Object, value)
• get_magic( binding, name, real_value ) - used to get several "magic" values e.g. self, __FILE__, __LINE__
• execute( binding, code ) - handles backtick execution

More will follow.

Helper Module

You don't have to reimplement all the above methods in order to get a working environment. If you want the local variable system to behave as usual you can simply include Borx::Environment::GetSetVariable in you environment. Helper modules so far are:

• Borx::Environment::GetVariable - supplies get_variable
• Borx::Environment::SetVariable - supplies set_variable
• Borx::Environment::GetSetVariable - same as the two above together
• Borx::Environment::CallMethod - supplies call_method and call_private_method
• Borx::Environment::GetMagic - supplies get_magic

License

Copyright (C) 2013 Hannes Georg

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.