Crate steno

Steno is an in-progress prototype implementation of distributed sagas. Sagas orchestrate the execution of a set of asynchronous tasks that can fail. The saga pattern provides useful semantics for unwinding the whole operation when any task fails. For more on distributed sagas, see this 2017 JOTB talk by Caitie McCaffrey.

Overview

• Write some functions that will be used as actions and undo actions for your saga. Package these up with ActionFunc::new_action().
• Add these actions to an ActionRegistry
• Use DagBuilder to construct a graph of these actions. Wrap this up in a SagaDag.
• Construct a saga execution coordinator with sec() and use that to run the saga. You can start with an InMemorySecStore or impl your own SecStore.

This crate is necessarily somewhat complex to use. For a detailed, documented example, see examples/trip.rs.

Structs

• ActionContext
  Action’s handle to the saga subsystem
• ActionFunc
  Implementation of Action that uses ordinary functions for the action and undo action
• ActionName
  Unique name for a saga Action
• ActionRegistry
  A registry of saga actions that can be used across multiple sagas.
• Dag
  Describes a directed acyclic graph (DAG) to be used as a saga or subsaga
• DagBuilder
  Used to build a Dag that can then be executed as either a saga or subsaga
• DagBuilderError
• InMemorySecStore
  Implementation of SecStore that doesn’t store any state persistently
• Node
  Describes a node in the saga DAG
• NodeName
  Unique name for a saga Node
• RepeatInjected
  Arguments which can be passed to the SEC instructing it to change the number of times a node is executed.
• SagaCreateParams
  Describes what an impl of SecStore needs to store for a persistent saga record.
• SagaDag
  A Dag plus saga input parameters that together can be used to execute a saga
• SagaExecStatus
  Summarizes in-progress execution state of a saga
• SagaId
  Unique identifier for a Saga (an execution of a saga template)
• SagaLog
  Write to a saga’s log
• SagaName
  Human-readable name for a particular saga
• SagaNodeEvent
  An entry in the saga log
• SagaNodeId
  Unique identifier for a saga node
• SagaResult
  Summarizes the final state of a saga execution
• SagaResultErr
  Provides access to failure details for a saga that failed
• SagaResultOk
  Provides access to outputs from a saga that completed successfully
• SagaSerialized
  Simple file-based serialization and deserialization of a whole saga, intended only for testing and debugging
• SagaView
  External consumer’s view of a saga
• SecClient
  Client handle for a Saga Execution Coordinator (SEC)
• SecExecClient
  Handle used by SagaExecutor for sending messages back to the SEC

Enums

• ActionError
  An error produced by a saga action
• ActionRegistryError
  An error returned from ActionRegistry::get()
• SagaCachedState
  Describes the cacheable state of the saga
• SagaNodeEventType
  Event types that may be found in the log for a particular action
• SagaStateView
  State-specific parts of a consumer’s view of a saga
• UndoActionError
  An error produced by a failed undo action

Traits

• Action
  Building blocks of sagas
• ActionData
  Data produced by the consumer that may need to be serialized to the saga log
• SagaType
  Collection of consumer-provided types, effectively defining the type signature of a saga
• SecStore
  Interfaces implemented by the Steno consumer to storing saga state and saga log state persistently

Functions

• new_action_noop_undo
  Given a function f, return an ActionFunc that uses f as the action and provides a no-op undo function (which does nothing and always succeeds).
• sec
  Creates a new Saga Execution Coordinator

Type Definitions

• ActionFuncResult
  Result of a function that implements a saga action
• ActionResult
  Result of a saga action
• UndoResult
  Result of a saga undo action