Multiparty Session Type-safe Web Development with Static Linearity

Abstract

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.

Communication-safe web programming in TypeScript with routed multiparty session types

“…When the server receives a move, it notifies the game logic to update the game state asynchronously and return the game result caused by that move. The expressiveness of STScript enable the developer to define the handlers as async functions to use the game logic API correctly -this is prevalent in modern web programming, but not directly addressed in [13,20].…”

“…Whereas session type programming is well-studied [1], its application on web programming, in particular, interactive web applications, remains relatively unexplored. Integrating session types with web programming has been piloted by recent work [13,20,24], yet none are able to seamlessly implement the previous application scenario: Fowler [13] uses binary (2-party) session types; and King et al [20] require each non-server role to only communicate to the server, hence preventing interactions between non-server roles (cf. talking to a friend in the scenario).…”

“…3). The local type of an endpoint can be then used in the code generation process, to generate APIs that are correct by construction [17,20,35].…”

“…Our work encodes multiparty session types for web applications, subsuming binary sessions. King et al [20] extend the Scribble toolchain for web applications targeting PureScript [28], a functional web programming language. In their work, a client may only communicate with one designated server role, whereas our work addresses this limitation via routing through a designated role.…”

Generating Interactive WebSocket Applications in TypeScript

“…Session Types in Web Development King et al [13] targeted web development in PureScript using the Concur UI framework and proposed a type-level encoding of EFSMs as multi-parameter type classes. However, it presents a trade-off between achieving static linearity guarantees from the type-level EFSM encoding under the expressive type system and providing an intuitive development experience to developers, especially given the prevalence of JavaScript and TypeScript applications in industry.…”