service

Documentation

Overview

Package service defines a pluggable service for the Flow system.

Services are low-level constructs which run for the lifetime of the Flow controller, and are given deeper levels of access to the overall system compared to components, such as the individual instances of running components.

Index

• type Consumer
• type ConsumerType
  • func (ct ConsumerType) String() string
• type Controller
• type Definition
• type Host
• type Service

Types

type Consumer

type Consumer struct {
	Type ConsumerType // Type of consumer.
	ID   string       // Unique identifier for the consumer.

	// Value of the consumer. When Type is ConsumerTypeComponent, this is an
	// instance of [component.Component]. When Type is ConsumerTypeServcice, this
	// is an instance of [Service].
	Value any
}

type ConsumerType

type ConsumerType int

ConsumerType represents the type of consumer who is consuming a service.

const (
	// ConsumerTypeInvalid is the default value for ConsumerType.
	ConsumerTypeInvalid ConsumerType = iota

	ConsumerTypeService // ConsumerTypeService represents a service which uses another service.
)

func (ConsumerType) String

func (ct ConsumerType) String() string

String returns a string representation of the ConsumerType.

type Controller

type Controller interface {
	Run(ctx context.Context)
	LoadSource(source []byte, args map[string]any) error
	Ready() bool
}

Controller is implemented by flow.Flow.

type Definition

type Definition struct {
	// Name uniquely defines a service.
	Name string

	// ConfigType is an optional config type to configure a
	// service at runtime. The Name of the service is used
	// as the River block name to configure the service.
	// If nil, the service has no runtime configuration.
	//
	// When non-nil, ConfigType must be a struct type with River
	// tags for decoding as a config block.
	ConfigType any

	// DependsOn defines a set of dependencies for a
	// specific service by name. If DependsOn includes an invalid
	// reference to a service (either because of a cyclic dependency,
	// or a named service doesn't exist), it is treated as a fatal
	// error and the root Flow module will exit.
	DependsOn []string
}

Definition describes an individual Flow service. Services have unique names and optional ConfigTypes where they can be configured within the root Flow module.

type Host

type Host interface {
	// GetComponent gets a running component by ID.
	//
	// GetComponent returns [component.ErrComponentNotFound] if a component is
	// not found.
	GetComponent(id component.ID, opts component.InfoOptions) (*component.Info, error)

	// ListComponents lists all running components within a given module.
	//
	// Returns [component.ErrModuleNotFound] if the provided moduleID doesn't
	// exist.
	ListComponents(moduleID string, opts component.InfoOptions) ([]*component.Info, error)

	// GetService gets a running service using its name.
	GetService(name string) (Service, bool)

	// GetServiceConsumers gets the list of services which depend on a service by
	// name.
	GetServiceConsumers(serviceName string) []Consumer

	// NewController returns an unstarted, isolated Controller that a Service
	// can use to instantiate its own components.
	NewController(id string) Controller
}

Host is a controller for services and Flow components.

type Service

type Service interface {
	// Definition returns the Definition of the Service.
	// Definition must always return the same value across all
	// calls.
	Definition() Definition

	// Run starts a Service. Run must block until the provided
	// context is canceled. Returning an error should be treated
	// as a fatal error for the Service.
	Run(ctx context.Context, host Host) error

	// Update updates a Service at runtime. Update is never
	// called if [Definition.ConfigType] is nil. newConfig will
	// be the same type as ConfigType; if ConfigType is a
	// pointer to a type, newConfig will be a pointer to the
	// same type.
	//
	// Update will be called once before Run, and may be called
	// while Run is active.
	Update(newConfig any) error

	// Data returns the Data associated with a Service. Data must always return
	// the same value across multiple calls, as callers are expected to be able
	// to cache the result.
	//
	// The return result of Data must not rely on the runtime config of the
	// service.
	//
	// Data may be invoked before Run.
	Data() any
}

Service is an individual service to run.