Type-safe distributed programming for OCaml

Abstract

Existing ML-like languages guarantee type-safety, ensuring memory safety and protecting the invariants of abstract types, but only within single executions of single programs. Distributed programming is becoming ever more important, and should benefit even more from such guarantees. In previous work on theoretical calculi and the Acute prototype language we outlined techniques to provide them for simple languages.In this paper we put these ideas into practice, describing the HashCaml extension to the OCaml bytecode compiler, which supports type-safe and abstraction-safe marshalling, together with related naming constructs. Our contribution is threefold: (1) We show how to define globally meaningful runtime type names for key OCaml type constructs that were not covered in our previous work, dealing with the generativity issues involved: user-defined variant and record types, substructures, functors, arbitrary ascription, separate compilation, and external C functions. (2) We support marshalling within polymorphic functions by type-passing, requiring us to build compositional runtime type names and revisit the OCaml relaxed value restriction. We show that with typed marshalling one must fall back to the SML97 value restriction. (3) We show how the above can be implemented with reasonable performance as an unintrusive modification to the existing OCaml language, implementation, and standard libraries. An alpha release of HashCaml, capable of bootstrapping itself, is available, along with an example type-safe distributed communication library written in the language.

Secure Implementations for Typed Session Abstractions

“…Their approach is similar to our treatment of session graphs and roles in Section 2; however, their descriptions are executable programs, not types. More generally, distributed languages such as Acute and HashCaml [26,12,5] also rely on types to provide general functional guarantees for networked programs, in particular type-safe marshalling and dynamic rebinding to local resources.…”

“…Their approach is similar to our treatment of session graphs and roles in Section 2; however, their descriptions are executable programs, not types. More generally, distributed languages such as Acute and HashCaml [26,12,5] also rely on types to provide general functional guarantees for networked programs, in particular type-safe marshalling and dynamic rebinding to local resources.Cryptographic communications protocols have been thoroughly studied, so we focus on related work on their use for securing implementations of programming-language abstractions. They can provide secure implementations for distributed languages with private communication channels [1,2].…”

Practical generic programming in OCaml

“…Appending the time is intended to compensate for the fact that the file name and type name are not alone sufficient to guarantee global uniqueness; there is only limited information about the context available to deriving when the definition is seen. A solution to this problem is given in [1] in the context of a modification to the OCaml compiler, but a solution based on local syntactic transformations remains elusive.…”

“…The HashCaml [1] project extends the OCaml bytecode compiler with type-passing to make the standard Marshal operation type-safe. Cohen and Herrmann [4] discuss the implementation of a staged serialiser in MetaOCaml which bears some similarity to our preprocessor-based approach, with even more reliance on unsafe low-level operations, used by the serialiser to break through abstraction barriers.…”

Typed First-Class Communication Channels and Mobility for Concurrent Scripting Languages

“…Acute extends an ML-like core language to support distributed development, deployment, and execution, allowing type-safe interaction between separately built programs. Some of these ideas were further developed and put into practice in HashCaml language [3], an extension of the OCaml bytecode compiler with support for type-safe marshalling and related naming features.…”