A session type provider: compile-time API generation of distributed protocols with refinements in F#

Abstract

We present a library for the specification and implementation of distributed protocols in native F# (and other .NET languages) based on multiparty session types (MPST). There are two main contributions. Our library is the first practical development of MPST to support what we refer to as interaction refinements: a collection of features related to the refinement of protocols, such as message-type refinements (value constraints) and message-value dependent control flow. A well-typed endpoint program using our library is guaranteed to perform only compliant session I/O actions w.r.t. to the refined protocol, up to premature termination. Second, our library is developed as a session type provider, that performs on-demand compile-time protocol validation and generation of protocol-specific .NET types for users writing the distributed endpoint programs. It is implemented by extending and integrating Scribble (a toolchain for MPST) with an SMT solver into the type providers framework. The safety guarantees are achieved by a combination of static type checking of the generated types for messages and I/O operations, correctness by construction from code generation, and automated inlining of assertions. CCS Concepts • Software and its engineering → Source code generation; • Computing methodologies → Distributed programming languages; • Networks → Peerto-peer protocols;

Value-Dependent Session Design in a Dependently Typed Language

“…Sessions achieves value-dependent session descriptions by maintaining a knowledge index. This compliments existing work [37,27] in which the authors define knowledge in much the same way. However, we have embedded the knowledge index directly within the type-system of the global session description ensuring that our EDSL instances are correct-by-construction with respect to value dependencies.…”

“…Scribble-Refined Recent work [27] has extended Scribble specifically for F# to leverage the language's support for refinement types [17] and type providers [31]. The authors present an expressive refinement language to specify boolean refinements related to messages being sent.…”

“…Session designers cannot specify value dependencies between sent messages, or reason about message contents. Recent work has extended the theory of MPST to incorporate value based reasoning on messages [37,38,5,27].…”

Verifying Asynchronous Interactions via Communicating Session Automata

“…Communicating automata and asynchronous multiparty session types [29] are closely related: the latter can be seen as a syntactical representation of the former [17] where a sending state corresponds to an internal choice and a receiving state to an external choice. This correspondence between communicating automata and multiparty session types has become the foundation of many tools centred on session types, e.g., for generating communication API from multiparty session (global) types [31,32,48,62], for detecting deadlocks in message-passing programs [51,68], and for monitoring session-enabled programs [5,16,47,49,50]. These tools rely on a property called multiparty compatibility [6,18,40], which guarantees that communicating automata representing session types interact correctly, hence enabling the identification of correct protocols or the detection of errors in endpoint programs.…”

Multiparty Session Type-safe Web Development with Static Linearity

“…The implementation uses the Akka actor framework and supports all transport abstractions provided by Akka. Neykova et al [25] implemented in F# a session type provider to support on-demand compile-time protocol by generating protocol-specific .NET types from Scribble. Pabble [26] generates C/MPI skeleton code from parameterised Scribble for correct-by-construction role-parameterised MPI parallel programming but do not use types to check for conformance.…”