feat(flagd): add Shutdown support for in-process sync (#687)

Signed-off-by: liran2000 <[email protected]>

Author: liran2000

providers/flagd/README.md

@@ -43,7 +43,8 @@ In the above example, in-process handlers attempt to connect to a sync service o
 #### Custom sync provider
 
 In-process resolver can also be configured with a custom sync provider to change how the in-process resolver fetches flags.
-The custom sync provider must implement the [sync.ISync interface](https://github.com/open-feature/flagd/blob/main/core/pkg/sync/isync.go). Optional URI can be provided for the custom sync provider.
+The custom sync provider must implement the [sync.ISync interface](https://github.com/open-feature/flagd/blob/main/core/pkg/sync/isync.go). Optional URI can be provided for the custom sync provider.  
+The custom sync provider can implement the _sync.Shutdowner_ interface from [service](https://github.com/open-feature/go-sdk-contrib/blob/main/providers/flagd/pkg/service/in_process/service.go).
 
 ```go
 var syncProvider sync.ISync = MyAwesomeSyncProvider{}

providers/flagd/pkg/service/in_process/service.go

@@ -7,6 +7,7 @@ import (
 	"regexp"
 	parallel "sync"
 
+	"go.uber.org/zap"
 	googlegrpc "google.golang.org/grpc"
 
 	"github.com/open-feature/flagd/core/pkg/evaluator"
@@ -46,6 +47,10 @@ type Configuration struct {
 	GrpcDialOptionsOverride []googlegrpc.DialOption
 }
 
+type Shutdowner interface {
+	Shutdown() error
+}
+
 func NewInProcessService(cfg Configuration) *InProcess {
 	log := logger.NewLogger(NewRaw(), false)
 
@@ -116,6 +121,12 @@ func (i *InProcess) Init() error {
 					ProviderEventDetails: of.ProviderEventDetails{Message: "New flag sync", FlagChanges: maps.Keys(changes)}}
 			case <-i.listenerShutdown:
 				i.logger.Info("Shutting down data sync listener")
+				if shutdowner, ok := i.sync.(Shutdowner); ok {
+					err := shutdowner.Shutdown()
+					if err != nil {
+						i.logger.Error("Error shutdown sync provider", zap.Error(err))
+					}
+				}
 				return
 			}
 		}