Multiparty Session Type-safe Web Development with Static Linearity

Jonathan King
(Imperial College London & Habito)
Nicholas Ng
(Imperial College London)
Nobuko Yoshida
(Imperial College London)

Modern web applications can now offer desktop-like experiences from within the browser, thanks to technologies such as WebSockets, which enable low-latency duplex communication between the browser and the server. While these advances are great for the user experience, they represent a new responsibility for web developers who now need to manage and verify the correctness of more complex and potentially stateful interactions in their application.

In this paper, we present a technique for developing interactive web applications that are statically guaranteed to communicate following a given protocol. First, the global interaction protocol is described in the Scribble protocol language – based on multiparty session types. Scribble protocols are checked for well-formedness, and then each role is projected to a Finite State Machine representing the structure of communication from the perspective of the role. We use source code generation and a novel type-level encoding of FSMs using multi-parameter type classes to leverage the type system of the target language and guarantee only programs that communicate following the protocol will type check.

Our work targets PureScript – a functional language that compiles to JavaScript – which crucially has an expressive enough type system to provide static linearity guarantees. We demonstrate the effectiveness of our approach through a web-based Battleship game where communication is performed through WebSocket connections.

In Francisco Martins and Dominic Orchard: Proceedings Programming Language Approaches to Concurrency- and Communication-cEntric Software (PLACES 2019), Prague, Czech Republic, 7th April 2019, Electronic Proceedings in Theoretical Computer Science 291, pp. 35–46.
Published: 2nd April 2019.

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