rpc: add pub/sub support

eth/downloader/api.go

@@ -17,18 +17,55 @@
 package downloader
 
 import (
+	"sync"
+
+	"golang.org/x/net/context"
+
+	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/rpc"
 )
 
 // PublicDownloaderAPI provides an API which gives information about the current synchronisation status.
 // It offers only methods that operates on data that can be available to anyone without security risks.
 type PublicDownloaderAPI struct {
-	d *Downloader
+	d                   *Downloader
+	mux                 *event.TypeMux
+	muSyncSubscriptions sync.Mutex
+	syncSubscriptions   map[string]rpc.Subscription
 }
 
 // NewPublicDownloaderAPI create a new PublicDownloaderAPI.
-func NewPublicDownloaderAPI(d *Downloader) *PublicDownloaderAPI {
-	return &PublicDownloaderAPI{d}
+func NewPublicDownloaderAPI(d *Downloader, m *event.TypeMux) *PublicDownloaderAPI {
+	api := &PublicDownloaderAPI{d: d, mux: m, syncSubscriptions: make(map[string]rpc.Subscription)}
+
+	go api.run()
+
+	return api
+}
+
+func (api *PublicDownloaderAPI) run() {
+	sub := api.mux.Subscribe(StartEvent{}, DoneEvent{}, FailedEvent{})
+
+	for event := range sub.Chan() {
+		var notification interface{}
+
+		switch event.Data.(type) {
+		case StartEvent:
+			result := &SyncingResult{Syncing: true}
+			result.Status.Origin, result.Status.Current, result.Status.Height, result.Status.Pulled, result.Status.Known = api.d.Progress()
+			notification = result
+		case DoneEvent, FailedEvent:
+			notification = false
+		}
+
+		api.muSyncSubscriptions.Lock()
+		for id, sub := range api.syncSubscriptions {
+			if sub.Notify(notification) == rpc.ErrNotificationNotFound {
+				delete(api.syncSubscriptions, id)
+			}
+		}
+		api.muSyncSubscriptions.Unlock()
+	}
 }
 
 // Progress gives progress indications when the node is synchronising with the Ethereum network.
@@ -47,19 +84,25 @@ type SyncingResult struct {
 }
 
 // Syncing provides information when this nodes starts synchronising with the Ethereum network and when it's finished.
-func (s *PublicDownloaderAPI) Syncing() (rpc.Subscription, error) {
-	sub := s.d.mux.Subscribe(StartEvent{}, DoneEvent{}, FailedEvent{})
-
-	output := func(event interface{}) interface{} {
-		switch event.(type) {
-		case StartEvent:
-			result := &SyncingResult{Syncing: true}
-			result.Status.Origin, result.Status.Current, result.Status.Height, result.Status.Pulled, result.Status.Known = s.d.Progress()
-			return result
-		case DoneEvent, FailedEvent:
-			return false
-		}
-		return nil
+func (api *PublicDownloaderAPI) Syncing(ctx context.Context) (rpc.Subscription, error) {
+	notifier, supported := ctx.Value(rpc.NotifierContextKey).(rpc.Notifier)
+	if !supported {
+		return nil, rpc.ErrNotificationsUnsupported
 	}
-	return rpc.NewSubscriptionWithOutputFormat(sub, output), nil
+
+	subscription, err := notifier.NewSubscription(func(id string) {
+		api.muSyncSubscriptions.Lock()
+		delete(api.syncSubscriptions, id)
+		api.muSyncSubscriptions.Unlock()
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	api.muSyncSubscriptions.Lock()
+	api.syncSubscriptions[subscription.ID()] = subscription
+	api.muSyncSubscriptions.Unlock()
+
+	return subscription, nil
 }