Interoperability by construction: code generation for Arrowhead Clients

This document describes a process to design and develop service-oriented clients to be used within the Arrowhead platform. The approach is centered on the definition of an OpenAPI interface, which is then used to generate the communication code to reach the servers. The paper discusses how to define the interfaces, how to generate a client library using the OpenAPI-generator system, what must be taken into account when configuring the security capabilities of the client to either communicate in cleartext or protect communication by means of Transport Layer Security, and discusses how to use the library to develop a client system. This work then applies the approach to the problem of implementing an Arrowhead-compliant client in the C programming language, which can communicate securely with Arrowhead services. The work highlights peculiarities that emerge from the interaction of programming concepts related to the C programming language, which we used to implement a client, and the Java programming language, which is the main language currently used to implement Arrowhead clients and servers.