Fix grantee lookup for Share/Space Created event for groups

'ShareCreated' and 'SpaceCreate' events for group shares have an empty
GranteeUserID attribute. We need to lookup the GranteeGroup to get the Grantee
Name for the notification mail

Partial Fix: #4703

services/notifications/pkg/service/service.go

@@ -10,6 +10,7 @@ import (
 	"syscall"
 
 	gateway "github.com/cs3org/go-cs3apis/cs3/gateway/v1beta1"
+	groupv1beta1 "github.com/cs3org/go-cs3apis/cs3/identity/group/v1beta1"
 	userv1beta1 "github.com/cs3org/go-cs3apis/cs3/identity/user/v1beta1"
 	rpcv1beta1 "github.com/cs3org/go-cs3apis/cs3/rpc/v1beta1"
 	providerv1beta1 "github.com/cs3org/go-cs3apis/cs3/storage/provider/v1beta1"
@@ -85,16 +86,6 @@ func (s eventsNotifier) handleSpaceShared(e events.SpaceShared) {
 		return
 	}
 
-	granteeUserResponse, err := s.gwClient.GetUser(context.Background(), &userv1beta1.GetUserRequest{
-		UserId: e.GranteeUserID,
-	})
-	if err != nil || sharerUserResponse.Status.Code != rpcv1beta1.Code_CODE_OK {
-		s.logger.Error().
-			Err(err).
-			Str("event", "SpaceCreated").
-			Msg("Could not get user response from gatway client")
-		return
-	}
 	// Get auth context
 	ownerCtx := ctxpkg.ContextSetUser(context.Background(), sharerUserResponse.User)
 	authRes, err := s.gwClient.Authenticate(ownerCtx, &gateway.AuthenticateRequest{
@@ -165,10 +156,45 @@ func (s eventsNotifier) handleSpaceShared(e events.SpaceShared) {
 			Msg("could not create link to the share")
 		return
 	}
+	spaceGrantee := ""
+	switch {
+	// Note: We're using the 'ownerCtx' (authenticated as the share owner) here for requesting
+	// the Grantees of the shares. Ideally the notfication service would use some kind of service
+	// user for this.
+	case e.GranteeUserID != nil:
+		granteeUserResponse, err := s.gwClient.GetUser(ownerCtx, &userv1beta1.GetUserRequest{
+			UserId: e.GranteeUserID,
+		})
+		if err != nil || granteeUserResponse.Status.Code != rpcv1beta1.Code_CODE_OK {
+			s.logger.Error().
+				Err(err).
+				Str("event", "ShareCreated").
+				Msg("Could not get user response from gatway client")
+			return
+		}
+		spaceGrantee = granteeUserResponse.GetUser().DisplayName
+	case e.GranteeGroupID != nil:
+		granteeGroupResponse, err := s.gwClient.GetGroup(ownerCtx, &groupv1beta1.GetGroupRequest{
+			GroupId: e.GranteeGroupID,
+		})
+		if err != nil || granteeGroupResponse.Status.Code != rpcv1beta1.Code_CODE_OK {
+			s.logger.Error().
+				Err(err).
+				Str("event", "ShareCreated").
+				Msg("Could not get group response from gatway client")
+			return
+		}
+		spaceGrantee = granteeGroupResponse.GetGroup().DisplayName
+	default:
+		s.logger.Error().
+			Str("event", "ShareCreated").
+			Msg("Event 'ShareCreated' has no grantee")
+		return
+	}
 
 	sharerDisplayName := sharerUserResponse.GetUser().DisplayName
 	msg, err := email.RenderEmailTemplate("sharedSpace.email.tmpl", map[string]string{
-		"SpaceGrantee": granteeUserResponse.GetUser().DisplayName,
+		"SpaceGrantee": spaceGrantee,
 		"SpaceSharer":  sharerDisplayName,
 		"SpaceName":    md.GetInfo().GetSpace().Name,
 		"ShareLink":    shareLink,
@@ -207,17 +233,6 @@ func (s eventsNotifier) handleShareCreated(e events.ShareCreated) {
 		return
 	}
 
-	granteeUserResponse, err := s.gwClient.GetUser(context.Background(), &userv1beta1.GetUserRequest{
-		UserId: e.GranteeUserID,
-	})
-	if err != nil || sharerUserResponse.Status.Code != rpcv1beta1.Code_CODE_OK {
-		s.logger.Error().
-			Err(err).
-			Str("event", "ShareCreated").
-			Msg("Could not get user response from gatway client")
-		return
-	}
-
 	// Get auth context
 	ownerCtx := ctxpkg.ContextSetUser(context.Background(), sharerUserResponse.User)
 	authRes, err := s.gwClient.Authenticate(ownerCtx, &gateway.AuthenticateRequest{
@@ -279,9 +294,45 @@ func (s eventsNotifier) handleShareCreated(e events.ShareCreated) {
 		return
 	}
 
+	shareGrantee := ""
+	switch {
+	// Note: We're using the 'ownerCtx' (authenticated as the share owner) here for requesting
+	// the Grantees of the shares. Ideally the notfication service would use some kind of service
+	// user for this.
+	case e.GranteeUserID != nil:
+		granteeUserResponse, err := s.gwClient.GetUser(ownerCtx, &userv1beta1.GetUserRequest{
+			UserId: e.GranteeUserID,
+		})
+		if err != nil || granteeUserResponse.Status.Code != rpcv1beta1.Code_CODE_OK {
+			s.logger.Error().
+				Err(err).
+				Str("event", "ShareCreated").
+				Msg("Could not get user response from gatway client")
+			return
+		}
+		shareGrantee = granteeUserResponse.GetUser().DisplayName
+	case e.GranteeGroupID != nil:
+		granteeGroupResponse, err := s.gwClient.GetGroup(ownerCtx, &groupv1beta1.GetGroupRequest{
+			GroupId: e.GranteeGroupID,
+		})
+		if err != nil || granteeGroupResponse.Status.Code != rpcv1beta1.Code_CODE_OK {
+			s.logger.Error().
+				Err(err).
+				Str("event", "ShareCreated").
+				Msg("Could not get group response from gatway client")
+			return
+		}
+		shareGrantee = granteeGroupResponse.GetGroup().DisplayName
+	default:
+		s.logger.Error().
+			Str("event", "ShareCreated").
+			Msg("Event 'ShareCreated' has no grantee")
+		return
+	}
+
 	sharerDisplayName := sharerUserResponse.GetUser().DisplayName
 	msg, err := email.RenderEmailTemplate("shareCreated.email.tmpl", map[string]string{
-		"ShareGrantee": granteeUserResponse.GetUser().DisplayName,
+		"ShareGrantee": shareGrantee,
 		"ShareSharer":  sharerDisplayName,
 		"ShareFolder":  md.GetInfo().Name,
 		"ShareLink":    shareLink,