Modeling and Testing Implementations of Protocols with Complex Messages

TL;DR

This paper introduces APSL, a formal language for describing complex communication protocols with nested and variable message formats, enabling automated testing of implementation correctness and robustness.

Contribution

It presents a new expressive language, APSL, capable of modeling complex message structures for protocol testing, demonstrated through a practical email server case study.

Findings

APSL effectively models complex message formats.

Automated testing with APSL improves protocol implementation validation.

Case study confirms APSL's practical applicability.

Abstract

This paper presents a new language called APSL for formally describing protocols to facilitate automated testing. Many real world communication protocols exchange messages whose structures are not trivial, e.g. they may consist of multiple and nested fields, some could be optional, and some may have values that depend on other fields. To properly test implementations of such a protocol, it is not sufficient to only explore different orders of sending and receiving messages. We also need to investigate if the implementation indeed produces correctly formatted messages, and if it responds correctly when it receives different variations of every message type. APSL's main contribution is its sublanguage that is expressive enough to describe complex message formats, both text-based and binary. As an example, this paper also presents a case study where APSL is used to model and test a subset of Courier IMAP email server.