Asynchronous distributed monitoring for multiparty session enforcement

Abstract. We propose a formal model of runtime safety enforcement for large-scale, cross-language distributed applications with possibly untrusted endpoints. The underlying theory is based on multiparty session types with logical assertions (MPSA), an expressive protocol specification language that supports runtime val-idation through monitoring. Our method starts from global specifications based on MPSAs which the participants should obey. Distributed monitors use local specifications, projected from global specifications, to detect whether the interac-tions are well-behaved, and take appropriate actions, such as suppressing illegal messages. We illustrate the design of our model with examples from real-world distributed applications. We prove monitor transparency, communication confor-mance, and global session fidelity in the presence of possibly unsafe endpoints.