Aspectual Session Types

International audienceMultiparty session types allow the definition of distributed processes with strong communication safety properties. A global type is a choreographic specification of the interactions between peers, which is then projected locally in each peer. Well-typed processes behave accordingly to the global protocol specification. Multiparty session types are however monolithic entities that are not amenable to modular extensions. Also, session types impose conservative requirements to prevent any race condition, which prohibit the uni- form application of extensions at different points in a protocol. In this paper, we describe a means to support modular extensions with aspectual session types, a static pointcut/advice mechanism at the session type level. To support the modular definition of crosscut- ting concerns, we augment the expressivity of session types to al- low harmless race conditions. We formally prove that well-formed aspectual session types entail communication safety. As a result, aspectual session types make multiparty session types more flexible, modular, and extensible

A theory of composing protocols

In programming, protocols are everywhere. Protocols describe the pattern of interaction (or communication) between software systems, for example, between a user-space program and the kernel or between a local application and an online service. Ensuring conformance to protocols avoids a significant class of software errors. Subsequently, there has been a lot of work on verifying code against formal protocol specifications. The pervading approaches focus on distributed settings involving parallel composition of processes within a single monolithic protocol description. However we observe that, at the level of a single thread/process, modern software must often implement a number of clearly delineated protocols at the same time which become dependent on each other, e.g., a banking API and one or more authentication protocols. Rather than plugging together modular protocol-following components, the code must re-integrate multiple protocols into a single component. We address this concern of combining protocols via a novel notion of ‘interleaving’ composition for protocols described via a process algebra. User-specified, domain-specific constraints can be inserted into the individual protocols to serve as ‘contact points’ to guide this composition procedure, which outputs a single combined protocol that can be programmed against. Our approach allows an engineer to then program against a number of protocols that have been composed (re-integrated), reflecting the true nature of applications that must handle multiple protocols at once. We prove various desirable properties of the composition, including behaviour preservation: that the composed protocol implements the behaviour of both component protocols. We demonstrate our approach in the practical setting of Erlang, with a tool implementing protocol composition that both generates Erlang code from a protocol and generates a protocol from Erlang code. This tool shows that, for a range of sample protocols (including real-world examples), a modest set of constraints can be inserted to produce a small number of candidate compositions to choose from. As we increasingly build software interacting with many programs and subsystems, this new perspective gives a foundation for improving software quality via protocol conformance in a multi-protocol setting

A Theory of Composing Protocols

In programming, protocols are everywhere. Protocols describe the pattern of interaction (or communication) between software systems, for example, between a user-space program and the kernel or between a local application and an online service. Ensuring conformance to protocols avoids a significant class of software errors. Subsequently, there has been a lot of work on verifying code against formal protocol specifications. The pervading approaches focus on distributed settings involving parallel composition of processes within a single monolithic protocol description. However we observe that, at the level of a single thread/process, modern software must often implement a number of clearly delineated protocols at the same time which become dependent on each other, e.g., a banking API and one or more authentication protocols. Rather than plugging together modular protocol-following components, the code must re-integrate multiple protocols into a single component. We address this concern of combining protocols via a novel notion of ‘interleaving’ composition for protocols described via a process algebra. User-specified, domain-specific constraints can be inserted into the individual protocols to serve as ‘contact points’ to guide this composition procedure, which outputs a single combined protocol that can be programmed against. Our approach allows an engineer to then program against a number of protocols that have been composed (re-integrated), reflecting the true nature of applications that must handle multiple protocols at once. We prove various desirable properties of the composition, including behaviour preservation: that the composed protocol implements the behaviour of both component protocols. We demonstrate our approach in the practical setting of Erlang, with a tool implementing protocol composition that both generates Erlang code from a protocol and generates a protocol from Erlang code. This tool shows that, for a range of sample protocols (including real-world examples), a modest set of constraints can be inserted to produce a small number of candidate compositions to choose from. As we increasingly build software interacting with many programs and subsystems, this new perspective gives a foundation for improving software quality via protocol conformance in a multi-protocol setting

A theory of protocol composition

Real-world communication protocols are often built out of a number of simpler protocols that cater for some specific functionality (e.g., banking, authentication). However much of the formal definitions of protocols used for program verification treat protocols as monolithic units. Composition is considered for implementations of a protocol, but not for the protocols themselves as engineering components. We propose primitives and techniques for the modular composition of protocols. Our notion of composition defines an interleaving of two or more protocols in a way that satisfies user-specified context-dependent constraints which serve to explain “contact points” between the protocols. The resulting approach gives a theoretical basis for protocol (re-)engineering based on a process calculus with constraint annotations. We have implemented our approach as a tool for Erlang that supports generation of protocol compositions with formal guarantees, and code generation/extraction