Towards QUIC Debuggability

Abstract

QUIC has been called the mother of all web protocols, as it deeply integrates aspects of TCP (reliability, flow control, congestion control, loss recovery), TLS (handshake, encryption keys) and HTTP/2 (streams, prioritization) together into one cross-layer implementation over UDP. However, such ambition comes at the cost of high complexity, which in turn leads to misinterpretations, bugs and unwanted behaviour in implementations. This was also witnessed in the recently standardized HTTP/2 protocol. We posit that QUIC should thus take a proactive approach in ensuring its testability and debuggability. To that end, this work introduces the first version of a common logging format for QUIC endpoints, called qlog. This format allows the capture of internal QUIC state that is not visible on the network. It is easily deployable and empowers the creation of reusable (visual) tools to aid in interpreting QUIC’s behaviour. We implement and evaluate three such tools (a timeline, sequence diagram and congestion/flow control graph) in the proposed QUICvis toolset and show their usefulness in comparing behaviours across three competing QUIC implementations, as well as in performing root cause analysis on bugs and issues. We hope this work will foster the discussion on QUIC debuggability and that it will raise community awareness.