Stop fetching new blocks while app is not active

Saves some traffic (blocks with transactions are heavy) and infura
requests.

api/geth_backend.go

@@ -783,6 +783,37 @@ func (b *GethStatusBackend) AppStateChange(state string) {
 	b.log.Info("App State changed", "new-state", s)
 	b.appState = s
 
+	if s == appStateForeground {
+		wallet, err := b.statusNode.WalletService()
+		if err != nil {
+			b.log.Error("Retrieving of wallet service failed on app state change to active", "error", err)
+			return
+		}
+		if !wallet.IsStarted() {
+			err = wallet.Start(b.statusNode.Server())
+			if err != nil {
+				b.log.Error("Wallet service start failed on app state change to active", "error", err)
+				return
+			}
+
+			err = b.startWallet()
+			if err != nil {
+				b.log.Error("Wallet reactor start failed on app state change to active", "error", err)
+				return
+			}
+		}
+	} else if s == appStateBackground {
+		wallet, err := b.statusNode.WalletService()
+		if err != nil {
+			b.log.Error("Retrieving of wallet service failed on app state change to background", "error", err)
+			return
+		}
+		err = wallet.Stop()
+		if err != nil {
+			b.log.Error("Wallet service stop failed on app state change to background", "error", err)
+			return
+		}
+	}
 	// TODO: put node in low-power mode if the app is in background (or inactive)
 	// and normal mode if the app is in foreground.
 }

services/wallet/service.go

@@ -149,3 +149,7 @@ func mapToList(m map[common.Address]struct{}) []common.Address {
 	}
 	return rst
 }
+
+func (s *Service) IsStarted() bool {
+	return s.group != nil
+}

services/wallet/service_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/require"
 	"github.com/stretchr/testify/suite"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -108,3 +109,27 @@ func (s *ReactorChangesSuite) TestWatchNewAccounts() {
 		return nil
 	}, 5*time.Second, 500*time.Millisecond))
 }
+
+func TestServiceStartStop(t *testing.T) {
+	db, stop := setupTestDB(t)
+	defer stop()
+
+	backend, err := testchain.NewBackend()
+	require.NoError(t, err)
+
+	s := NewService(db, &event.Feed{})
+	require.NoError(t, s.Start(nil))
+
+	account, err := crypto.GenerateKey()
+	require.NoError(t, err)
+
+	err = s.StartReactor(backend.Client, []common.Address{crypto.PubkeyToAddress(account.PublicKey)}, big.NewInt(1337))
+	require.NoError(t, err)
+
+	require.NoError(t, s.Stop())
+	require.NoError(t, s.Start(nil))
+
+	err = s.StartReactor(backend.Client, []common.Address{crypto.PubkeyToAddress(account.PublicKey)}, big.NewInt(1337))
+	require.NoError(t, err)
+	require.NoError(t, s.Stop())
+}