A Language-Agnostic Logical Relation for Message-Passing Protocols

Abstract: Today's computing landscape has been gradually shifting to applications targeting distributed and heterogeneous systems, such as cloud computing and Internet of Things (IoT) applications. These applications are predominantly concurrent, employ message-passing, and interface with foreign objects, ranging from externally implemented code to actual physical devices such as sensors. Verifying that the resulting systems adhere to the intended protocol of interaction is challenging -- the usual assumption of a common implementation language, let alone a type system, no longer applies, ruling out any verification method based on them. This paper develops a framework for certifying protocol compliance of heterogeneous message-passing systems. It contributes the first mechanization of a language-agnostic logical relation, asserting that its inhabitants comply with the protocol specified. This definition relies entirely on a labelled transition-based semantics, accommodating arbitrary inhabitants, typed and untyped alike, including foreign objects. As a case study, the paper considers two scenarios: (1) per-instance verification of a specific application or hardware device, and (2) once-and-for-all verification of well-typed applications for a given type system. The logical relation and both scenarios are mechanized in the Coq theorem prover.