From: Guido De Rosa <guidoderosa@...>
Date: 2010-10-19T07:18:01+09:00
Subject: Re: su {block of code.}

Tony Arcieri wrote in post #955183:
> I'd suggest spawning a new Ruby instance which runs under sudo and
> talking
> to it with DRb

My big concern comes directly from DRb doc:

"As blocks (or rather the Proc objects that represent them) are not 
marshallable, the block executes in the local, not the remote, context."

Following your suggestion, I thought about a solution based on a DRb 
server run as root:


  require 'drb/drb'

  URI="druby://localhost:8787"

  class Executor
    def execute(&blk)
      blk.call
    end
  end

  DRb.start_service(URI, Executor.new)

  DRb.thread.join


The client code being executed as a non-privileged user:


  require 'drb/drb'

  SERVER_URI="druby://localhost:8787"

  DRb.start_service

  executor = DRbObject.new_with_uri(SERVER_URI)

  executor.execute do
    # a file writable only by root
    File.open('/TEST', 'w'){|f| f.puts 'hello!'}
  end


BUT I get a permission denied!

On the other if I don't use Procs, everything works fine:

server.rb:


  # ...
  class FileWriter
    def write(file, str)
      File.open(file, 'w'){|f| f.puts str}
    end
  end
  #
  DRb.start_service(URI, FileWriter.new)


client.rb:


  # ...
  writer = DRbObject.new_with_uri(SERVER_URI)

  writer.write '/TEST', 'hello!'

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