Add API to listen to app state changes.

geth/api/api.go

@@ -234,3 +234,14 @@ func (api *StatusAPI) ConnectionChange(typ string, expensive bool) {
 	}
 	api.b.ConnectionChange(state)
 }
+
+// AppStateChange handles app state changes (background/foreground).
+// state values: see https://facebook.github.io/react-native/docs/appstate.html
+func (api *StatusAPI) AppStateChange(state string) {
+	appState, err := ParseAppState(state)
+	if err != nil {
+		log.Error("AppStateChange failed, ignoring it:", err)
+		return // and do nothing
+	}
+	api.b.AppStateChange(appState)
+}

geth/api/app_state.go

@@ -0,0 +1,42 @@
+package api
+
+import (
+	"fmt"
+	"strings"
+)
+
+// AppState represents if the app is in foreground, background or some other state
+type AppState string
+
+func (a AppState) String() string {
+	return string(a)
+}
+
+// Specific app states
+// see https://facebook.github.io/react-native/docs/appstate.html
+const (
+	AppStateForeground = AppState("foreground")
+	AppStateBackground = AppState("background")
+	AppStateInactive   = AppState("inactive")
+
+	AppStateInvalid = AppState("")
+)
+
+// validAppStates returns an immutable set of valid states.
+func validAppStates() []AppState {
+	return []AppState{AppStateInactive, AppStateBackground, AppStateForeground}
+}
+
+// ParseAppState creates AppState from a string
+func ParseAppState(stateString string) (AppState, error) {
+	// a bit of cleaning up
+	stateString = strings.ToLower(strings.TrimSpace(stateString))
+
+	for _, state := range validAppStates() {
+		if stateString == state.String() {
+			return state, nil
+		}
+	}
+
+	return AppStateInvalid, fmt.Errorf("could not parse app state: %s", stateString)
+}

geth/api/app_state_test.go

@@ -0,0 +1,28 @@
+package api
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseAppType(t *testing.T) {
+	check := func(input string, expectedState AppState, expectError bool) {
+		actualState, err := ParseAppState(input)
+		assert.Equalf(t, expectedState, actualState, "unexpected result from ParseAppState")
+		if expectError {
+			assert.NotNil(t, err, "error should not be nil")
+		}
+	}
+
+	check("foreground", AppStateForeground, false)
+	check("background", AppStateBackground, false)
+	check("inactive", AppStateInactive, false)
+	check(" forEGROUnd ", AppStateForeground, false)
+	check("    backGROUND  ", AppStateBackground, false)
+	check("   INACTIVE   ", AppStateInactive, false)
+	check("", AppStateInvalid, true)
+	check("back ground", AppStateInvalid, true)
+	check(" back ground ", AppStateInvalid, true)
+	check("      ", AppStateInvalid, true)
+}

geth/api/backend.go

@@ -236,3 +236,11 @@ func (b *StatusBackend) ConnectionChange(state ConnectionState) {
 	// logic of handling state changes here
 	// restart node? force peers reconnect? etc
 }
+
+// AppStateChange handles app state changes (background/foreground).
+func (b *StatusBackend) AppStateChange(state AppState) {
+	log.Info("App State changed: %s", state)
+
+	// TODO: put node in low-power mode if the app is in background (or inactive)
+	// and normal mode if the app is in foreground.
+}

lib/library.go

@@ -456,3 +456,9 @@ func AddPeer(enode *C.char) *C.char {
 func ConnectionChange(typ *C.char, expensive C.int) {
 	statusAPI.ConnectionChange(C.GoString(typ), expensive == 1)
 }
+
+// AppStateChange handles app state changes (background/foreground).
+//export AppStateChange
+func AppStateChange(state *C.char) {
+	statusAPI.AppStateChange(C.GoString(state))
+}