Asynchronous Timed Session Types

Abstract

We present a behavioural typing system for a higher-order timed calculus using session types to model timed protocols. Behavioural typing ensures that processes in the calculus perform actions in the timewindows prescribed by their protocols. We introduce duality and subtyping for timed asynchronous session types. Our notion of duality allows typing a larger class of processes with respect to previous proposals. Subtyping is critical for the precision of our typing system, especially in the presence of session delegation. The composition of dual (timed asynchronous) types enjoys progress when using an urgent receive semantics, in which receive actions are executed as soon as the expected message is available. Our calculus increases the modelling power of extant calculi on timed sessions, adding a blocking receive primitive with timeout and a primitive that consumes an arbitrary amount of time in a given range.

Session Types for the Transport Layer: Towards an Implementation of TCP

“…The PhantomData-typed field contained within the struct is a zero-sized marker type that simulates a field of the given type to support the Rust type checker. 2 The SelectTwo struct has the same type parameters and is also a zero-sized type. Finally, the nonbranching actions OfferOne and SelectOne have only three type parameters: the peer role, the message type, and the continuation type, but are otherwise analogous.…”

“…As an alternative, to avoid duplication, we chose a nesting approach where a branching of arity N is transformed into a two-way branching between the first case and an N − 1 branching of the other cases. 3 This is recursively expanded until it finally results in a tree of two-way forks, where each left branch represents a single case from the original N. All right branches except the bottom-most one lead to a virtual node which was not present in the original type.…”

“…There are two implementation choices that could be made here: incorporate timeouts into the type system, or leave them out and instead signal session type transitions using external timeouts. The session type theory we are using does not have a notion of timeouts, nor does any session type work containing timeouts [1,2,5] have the ability to model the operations needed for TCP timeouts. Hence, we opt to emulate timeouts by introducing a virtual message type and adding it as another branch to the offer session type.…”

“…Network protocols have been used as examples for various session type theories. The main protocols used as a demonstration in many works are SMTP [3,6,17,18,19,20,21] and POP3 [10,24]. Both of these protocols are application-layer protocols.…”

Comparing Channel Restrictions of Communicating State Machines, High-level Message Sequence Charts, and Multiparty Session Types

“…Multiparty Session Type (MST) frameworks [38,39] provide efficient means to specify and verify such distributed message-passing systems (e.g., see the survey [6]). They have also been applied to various other domains like cyber-physical systems [47], timed systems [10], web services [64], and smart contracts [28]. In MST frameworks, global types are global specifications, which comprise all interactions between roles in a protocol.…”