Issue #4409 has been updated by Cory Banks.


Nicolas, thank you for reporting this issue - http://roofracksforvan.com
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Bug #4409: DRb: discrepency between DRb.here? and DRb.uri leads to failure to dereference a DrbObject
http://redmine.ruby-lang.org/issues/4409

Author: Nicolas Bondoux
Status: Closed
Priority: Normal
Assignee: Masatoshi Seki
Category: lib
Target version: 1.9.3
ruby -v: ruby 1.9.2p0 (2010-08-18 revision 29036) [i486-linux]


=begin
 When a reference on a local object is sent back by a client to a server, it may not be recognised as a local object during marshalling:
 An object instance being sent as a reference is wrapped in a DRbObject built by make_proxy with DRbObject.new(obj); the DRbObject's uri will be the uri returned by DRb::uri.
 When this reference is sent back, DRbObject::_load checks if it matches uri of current server with DRb::here? method.
 
 The problem is that DRb.here? checks that a DRbObject uri is the same as the uri which was used by current DRbServer at his creation, while DRb.uri will return an uri created from the local socket from current thread's connection.
 
 So, when a DRbObject it sent back, it may not be recognized as referencing a local object
 
 Fixing DRb.here? so that it compares with the uri returned by DRb.uri should be enough to quick fix this problem, and seems safe to me.
 (I call it a quick fix because I am sure that even with this change, it is possible to build some less realistics cases with the same kind of problem, due to the fact that a same reference may be valid or not depending which client sent it back ...)
 
 
 Here is a very simple proof of concept:
 The server:
 
 #!/usr/bin/ruby
 require 'drb'
 class A
   include DRb::DRbUndumped
 end
 
 class TheServer
   include DRb::DRbUndumped
   def initialize
     @a = A.new
   end
 
   def get_a
     @a
   end
 
   def is_a(iA)
     puts "inside is_a: current DRb.uri:#{DRb.uri}; iA.class = #{iA.class} #{iA.__drburi if DRb::DRbObject === iA}"
     @a.eql? iA
   end
   
   def getToken
     retVal = @@token.clone
     @@token.inc
     return retVal
   end
   
 end
 
 theServer = TheServer.new
 DRb.start_service(nil,theServer)
 puts "DRb.uri just after start_service: #{DRb.uri}"
 DRb.thread.join
 
 
 #############
 The client:
 
 #!/usr/bin/ruby
 require 'drb'
 
 
 theServer = DRb::DRbObject.new(nil,ARGV.shift)
 
 a = theServer.get_a
 puts "a.__drburi == #{a.__drburi}"
 puts "theServer.is_a(a) == #{theServer.is_a(a)}"
 
 
 #############
 the outputs:
 server side:
 DRb.uri just after start_service: druby://Venus:60106
 inside is_a: current DRb.uri:druby://127.0.0.1:60106; iA.class = DRb::DRbObject druby://127.0.0.1:60106
 
 
 client side:
 a.__drburi == druby://127.0.0.1:60106
 theServer.is_a(a) == false
 
 
 Cheers,
 
 Nicolas
=end



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