Mysteries of Dropbox: Property-based Testing of a Distributed Synchronization Service

Paper in proceeding, 2016

File synchronization services such as Dropbox are used by hundreds of millions of people to replicate vital data. Yet rigorous models of their behavior are lacking. We present the first formal---and testable---model of the core behavior of a modern file synchronizer, and we use it to discover surprising behavior in two widely deployed synchronizers. Our model is based on a technique for testing nondeterministic systems that avoids requiring that the system's internal choices be made visible to the testing framework.