go-ethereumを読む(6) 補足 Service

gethではPluggableな実装になっており、serviceという単位でプログラム内では扱われています。
EthServiceがEthereumのコア機能をになっています。
v1.8.15ベースに解説します

具体例 サービスを登録しているプログラム

// cmd/utils/flags.go
// RegisterEthService adds an Ethereum client to the stack.
func RegisterEthService(stack *node.Node, cfg *eth.Config) {
    var err error
    if cfg.SyncMode == downloader.LightSync {
        err = stack.Register(func(ctx *node.ServiceContext) (node.Service, error) {
            return les.New(ctx, cfg)
        })
    } else {
        err = stack.Register(func(ctx *node.ServiceContext) (node.Service, error) {
            fullNode, err := eth.New(ctx, cfg)
            if fullNode != nil && cfg.LightServ > 0 {
                ls, _ := les.NewLesServer(fullNode, cfg)
                fullNode.AddLesServer(ls)
            }
            return fullNode, err
        })
    }
    if err != nil {
        Fatalf("Failed to register the Ethereum service: %v", err)
    }
}

// RegisterDashboardService adds a dashboard to the stack.
func RegisterDashboardService(stack *node.Node, cfg *dashboard.Config, commit string) {
    stack.Register(func(ctx *node.ServiceContext) (node.Service, error) {
        return dashboard.New(cfg, commit, ctx.ResolvePath("logs")), nil
    })
}

// RegisterShhService configures Whisper and adds it to the given node.
func RegisterShhService(stack *node.Node, cfg *whisper.Config) {
    if err := stack.Register(func(n *node.ServiceContext) (node.Service, error) {
        return whisper.New(cfg), nil
    }); err != nil {
        Fatalf("Failed to register the Whisper service: %v", err)
    }
}

ServiceContext

ServiceContextがservicesをmapで保持している

type ServiceContext struct {
    config         *Config
    services       map[reflect.Type]Service // Index of the already constructed services
    EventMux       *event.TypeMux           // Event multiplexer used for decoupled notifications
    AccountManager *accounts.Manager        // Account manager created by the node.
}

func (ctx *ServiceContext) Service(service interface{}) error {
    element := reflect.ValueOf(service).Elem()
    if running, ok := ctx.services[element.Type()]; ok {
        element.Set(reflect.ValueOf(running))
        return nil
    }
    return ErrServiceUnknown
}

type ServiceConstructor func(ctx *ServiceContext) (Service, error)

// Serviceに必要なinterface
type Service interface {
    // Protocols retrieves the P2P protocols the service wishes to start.
    Protocols() []p2p.Protocol

    // APIs retrieves the list of RPC descriptors the service provides
    APIs() []rpc.API

    // Start is called after all services have been constructed and the networking
    // layer was also initialized to spawn any goroutines required by the service.
    Start(server *p2p.Server) error

    // Stop terminates all goroutines belonging to the service, blocking until they
    // are all terminated.
    Stop() error
}