Mathewson: Mid-2016 Tor bug retrospective, with lessons for future coding

On the Tor blog, Nick Mathewson reports on an informal survey he did for "severe" bugs in Tor over the last few years. It breaks down the 70 bugs he found into different categories that are correlated with some recommendations for ways to try to avoid them in the future. For example: "Recommendation 5.1: all backward compatibility code should have a timeout date.On several occasions we added backward compatibility code to keep an old version of Tor working, but left it enabled for longer than we needed to. This code has tended not to get the same regular attention it deserves, and has also tended to hold surprising deviations from the specification. We should audit the code that's there today and see what we can remove, and we should never add new code of this kind without adding a ticket and a comment planning to remove it." Many of the recommendations are likely applicable to other projects.