Contract-Oriented Design of Distributed Applications: A Tutorial
Nicola Atzei, Massimo Bartoletti, Maurizio Murgia, Emilio Tuosto, Roberto Zunino · River Publishers eBooks · 2022
Modern distributed applications typically blend new code with legacy (and possibly untrusted) third-party services. Behavioural contracts can be used to discipline the interaction among these services. Contract-oriented design advocates that composition is possible only among services with compliant contracts, and execution is monitored to detect (and possibly sanction) contract breaches. In this tutorial we illustrate a contract-oriented design methodology consisting of five phases: specification writing, specification analysis, code generation, code refinement, and code analysis. Specifications are written in CO 2 , a process calculus whose primitives include contract advertisement, stipulation, and contractual actions. Our analysis verifies a property called honesty: intuitively, a process is honest if it always honors its contracts upon stipulation, so being guaranteed to never be sanctioned at run-time. We automatically translate a given honest specification into a skeletal Java program which renders the contract-oriented interactions, to be completed with the application logic. Then, programmers can refine this skeleton into the actual Java application: however, doing so they could accidentally break its honesty. The last phase is an automated code analysis to verify that honesty has not been compromised by the refinement. 2 All the phases of our methodology are supported by a toolchain, called Diogenes. We guide the reader through Diogenes to design small contract-oriented applications.