feat: Add API to get SDK's App Context

Use the App Context in custom app service to exit long running functions when the context is
canceled due to termination signal.

Signed-off-by: Leonard Goodell <leonard.goodell@intel.com>

app-service-template/main.go

@@ -18,6 +18,7 @@
 package main
 
 import (
+	"context"
 	"os"
 	"reflect"
 
@@ -38,6 +39,7 @@ const (
 type myApp struct {
 	service       interfaces.ApplicationService
 	lc            logger.LoggingClient
+	appCtx        context.Context
 	serviceConfig *config.ServiceConfig
 	configChanged chan bool
 }
@@ -140,6 +142,10 @@ func (app *myApp) CreateAndRunAppService(serviceKey string, newServiceFactory fu
 		return -1
 	}
 
+	// TODO: Use this context in long running function to detect when the context is cancel for function can exit.
+	//       Remove if no long running functions
+	app.appCtx = app.service.AppContext()
+
 	if err := app.service.Run(); err != nil {
 		app.lc.Errorf("Run returned error: %s", err.Error())
 		return -1

app-service-template/main_test.go

@@ -18,6 +18,7 @@
 package main
 
 import (
+	"context"
 	"fmt"
 	"testing"
 
@@ -39,6 +40,7 @@ func TestCreateAndRunService_Success(t *testing.T) {
 
 	mockFactory := func(_ string) (interfaces.ApplicationService, bool) {
 		mockAppService := &mocks.ApplicationService{}
+		mockAppService.On("AppContext").Return(context.Background())
 		mockAppService.On("LoggingClient").Return(logger.NewMockClient())
 		mockAppService.On("GetAppSettingStrings", "DeviceNames").
 			Return([]string{"Random-Boolean-Device, Random-Integer-Device"}, nil)
@@ -81,6 +83,7 @@ func TestCreateAndRunService_GetAppSettingStrings_Failed(t *testing.T) {
 	getAppSettingStringsCalled := false
 	mockFactory := func(_ string) (interfaces.ApplicationService, bool) {
 		mockAppService := &mocks.ApplicationService{}
+		mockAppService.On("AppContext").Return(context.Background())
 		mockAppService.On("LoggingClient").Return(logger.NewMockClient())
 		mockAppService.On("GetAppSettingStrings", "DeviceNames").
 			Return(nil, fmt.Errorf("Failed")).Run(func(args mock.Arguments) {
@@ -104,6 +107,7 @@ func TestCreateAndRunService_SetFunctionsPipeline_Failed(t *testing.T) {
 
 	mockFactory := func(_ string) (interfaces.ApplicationService, bool) {
 		mockAppService := &mocks.ApplicationService{}
+		mockAppService.On("AppContext").Return(context.Background())
 		mockAppService.On("LoggingClient").Return(logger.NewMockClient())
 		mockAppService.On("GetAppSettingStrings", "DeviceNames").
 			Return([]string{"Random-Boolean-Device, Random-Integer-Device"}, nil)
@@ -137,6 +141,7 @@ func TestCreateAndRunService_Run_Failed(t *testing.T) {
 
 	mockFactory := func(_ string) (interfaces.ApplicationService, bool) {
 		mockAppService := &mocks.ApplicationService{}
+		mockAppService.On("AppContext").Return(context.Background())
 		mockAppService.On("LoggingClient").Return(logger.NewMockClient())
 		mockAppService.On("GetAppSettingStrings", "DeviceNames").
 			Return([]string{"Random-Boolean-Device, Random-Integer-Device"}, nil)

internal/app/service.go

@@ -116,6 +116,12 @@ type contextGroup struct {
 	stop                  context.CancelFunc
 }
 
+// AppContext returns the application service context used to detect cancelled context when the service is terminating.
+// Used by custom app service to appropriately exit any long-running functions.
+func (svc *Service) AppContext() context.Context {
+	return svc.ctx.appCtx
+}
+
 // AddRoute allows you to leverage the existing webserver to add routes.
 func (svc *Service) AddRoute(route string, handler func(nethttp.ResponseWriter, *nethttp.Request), methods ...string) error {
 	if route == commonConstants.ApiPingRoute ||

internal/app/service_test.go

@@ -17,6 +17,7 @@
 package app
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"os"
@@ -964,3 +965,15 @@ func TestService_SecretProvider(t *testing.T) {
 	require.NotNil(t, actual)
 	assert.Equal(t, mockSecretProvider, actual)
 }
+
+func TestService_AppContext(t *testing.T) {
+	expected, _ := context.WithCancel(context.Background())
+	sdk := Service{
+		ctx: contextGroup{
+			appCtx: expected,
+		},
+	}
+
+	actual := sdk.AppContext()
+	assert.Equal(t, expected, actual)
+}

pkg/interfaces/service.go

@@ -16,6 +16,7 @@
 package interfaces
 
 import (
+	"context"
 	"net/http"
 	"time"
 
@@ -75,6 +76,9 @@ type UpdatableConfig interface {
 
 // ApplicationService defines the interface for an edgex Application Service
 type ApplicationService interface {
+	// AppContext returns the application service context used to detect cancelled context when the service is terminating.
+	// Used by custom app service to appropriately exit any long-running functions.
+	AppContext() context.Context
 	// AddRoute a custom REST route to the application service's internal webserver
 	// A reference to this ApplicationService is add the the context that is passed to the handler, which
 	// can be retrieved using the `AppService` key