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service.go
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service.go
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// 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.
package service
import (
"context"
"fmt"
"github.com/grafana/agent/component"
)
// Definition describes an individual Flow service. Services have unique names
// and optional ConfigTypes where they can be configured within the root Flow
// module.
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
}
// Host is a controller for services and Flow components.
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)
// GetServiceConsumers gets the list of components and services which depend
// on a service by name.
GetServiceConsumers(serviceName string) []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
}
// ConsumerType represents the type of consumer who is consuming a service.
type ConsumerType int
const (
// ConsumerTypeInvalid is the default value for ConsumerType.
ConsumerTypeInvalid ConsumerType = iota
ConsumerTypeComponent // ConsumerTypeComponent represents a component which uses a service.
ConsumerTypeService // ConsumerTypeService represents a serviec which uses another service.
)
// String returns a string representation of the ConsumerType.
func (ct ConsumerType) String() string {
switch ct {
case ConsumerTypeInvalid:
return "invalid"
case ConsumerTypeComponent:
return "component"
case ConsumerTypeService:
return "service"
}
return fmt.Sprintf("ConsumerType(%d)", ct)
}
// Service is an individual service to run.
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.
//
// Data may be invoked before Run.
Data() any
}