August 12, 2011

Summer of Code Progress: Tor configuration

Filed under: Blog — krkhan @ 4:52 am
Summer of Code Archive Inspirated Code
Original Proposal Google Docs
Repository Tor Project Git
Mentor Blog arm Development Log

“O Marvelous! what new configuration will come next? I am bewildered with multiplicity.” — William Carlos Williams

Up until now my GSoC development was dealing with the “monitoring” aspects of arm. In addition to being a monitor a Tor controller is also supposed to, well, control the Tor client. Tor offers a detailed specification which can be used to interact with a running client and control it in a myriad of ways. This specification is then used by controllers like arm and Vidalia to fetch and/or update the client configuration.

The CLI configuration panel for arm already understood the control specification quite well. The first step towards reusing those portions for the GUI was to rewrite the inheritance code so that underlying data structures of the CLI were automagically connected to the Gtk+ models. That made the actual implementation of GUI configuration panel a whole lot cleaner. As things are, the panel detects the data types of configuration options and opens pertinent dialogs for user input:

Configuration panel for garm
(Click on the thumbnail for larger version.)

Next item in to-do list was implementing a path selection panel in arm. After a thorough discussion on IRC with the core Tor developers it was decided that giving end-users complete access to the PathSupport component of TorCtl would ultimately hurt their anonymity with little (if any) pay-off. Letting them choose the country of their exit relay was still seen as a useful feature which is what I’m working on right now.

Meanwhile, while setting the configuration options needed to choose an exit country I figured that arm should be notified of any changes made by other controllers to the options in question. Damian pointed me to ticket #1692 which proposed an enhancement for this very purpose. He had already created a patch for the job but few quirks needed to be addressed before the patch was ready for being merged. Thanks to help from Nick Mathewson and Robert Ransom I was able to fix the code and get it inside the tor and tor-spec repositories.

To make use of the new CONF_CHANGED event I also wrote patches for TorCtl and Vidalia. The TorCtl patch shall help me in making arm aware of configuration changes. While the Vidalia one is a proof-of-concept which created a signal and connected it to a debug function which for the time being just logs the options changed for the running Tor instance.

I hope to be done with exit node selection within a couple of days after which I’ll port the feature to CLI version of arm. It’ll be a good little exercise to start decoupling the arm interfaces from its backend so that future development is more streamlined and fun.

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