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 Aliases

ActionFuncResult

Result of a function that implements a saga action

ActionResult

Result of a saga action

UndoResult

Result of a saga undo action