Typechecking Java Protocols with [St]Mungo

Abstract

This is a tutorial paper on [St]Mungo, a toolchain based on multiparty session types and their connection to typestates for safe distributed programming in Java language. The StMungo ("Scribble-to-Mungo") tool is a bridge between multiparty session types and typestates. StMungo translates a communication protocol, namely a sequence of sends and receives of messages, given as a multiparty session type in the Scribble language, into a typestate specification and a Java API skeleton. The generated API skeleton is then further extended with the necessary logic, and finally typechecked by Mungo. The Mungo tool extends Java with (optional) typestate specifications. A typestate is a state machine specifying a Java object protocol, namely the permitted sequence of method calls of that object. Mungo statically typechecks that method calls follow the object's protocol, as defined by its typestate specification. Finally, if no errors are reported, the code is compiled with javac and run as standard Java code. In this tutorial paper we give an overview of the stages of the [St]Mungo toolchain, starting from Scribble communication protocols, translating to Java classes with typestates, and finally to typechecking method calls with Mungo. We illustrate the [St]Mungo toolchain via a real-world case study, the HTTP client-server request-response protocol over TCP. During the tutorial session, we will apply [St]Mungo to a range of examples having increasing complexity, with HTTP being one of them.

Papaya: Global Typestate Analysis of Aliased Objects

“…This is different from the previous implementations of the Mungo tool. In the original implementation [6,21,22,37] the tool infers the typestate of objects in the program and then checks that this respects the typestate defined for the classes. Since that version of the Mungo tool requires a linear treatment of references, the tool works similar to a classic type system for object-oriented language where each class is checked in isolation.…”

“…We introduce an object-oriented calculus with classes and enumeration types, similar to previous work on Mungo [3,6,21,22,37].…”

Retrofitting Typestates into Rust

“…We use the enumeration to represent the non-deterministic nature of the transition [12], as well as force the user to match against both cases. This enumeration has a few rules; all variants must be of Unit type 13 , and they must also share their identifier with an existing state.…”

“…The Mungo project [8,13], comprises several pieces which work towards a common and bigger goal, allowing developers to make use of typestates in languages such as Java.…”

“…The toolchain consists of a Java annotation and a typestate description language along with its checker. The compilation process starts by typechecking the code according to regular Java and then using the Mungo toolchain, which reads the typestate protocol declared by the annotation (@Typestate("ProtocolName")), extracts the method call behavior and checks the extracted information against the typestate [13].…”