graph/users: small ooptimization for filter by role queries

When filtering by role assignment we now populate the
'appRoleAssignments' property of the returned users when the incoming
request contained and '$expand=appRoleAssignments'. This avoids having
to query the role assignments for all users in the result set a second
time.
The effect of this optimization depends a lot on the actual setup. In
single binary all-in-one installations it is rather small (this it saves
quite a few CPU cycles). In distributed setup it should be larger as it
reduces the number of network round trips to the settings service
significantly.

services/graph/pkg/service/v0/users.go

@@ -298,7 +298,7 @@ func (g Graph) GetUsers(w http.ResponseWriter, r *http.Request) {
 	expandAppRoleAssignments := slices.Contains(exp, "appRoleAssignments")
 	expandMemberOf := slices.Contains(exp, "memberOf")
 	for _, u := range users {
-		if expandAppRoleAssignments {
+		if expandAppRoleAssignments && u.AppRoleAssignments == nil {
 			u.AppRoleAssignments, err = g.fetchAppRoleAssignments(r.Context(), u.GetId())
 			if err != nil {
 				// TODO I think we should not continue here, see http://docs.oasis-open.org/odata/odata/v4.01/odata-v4.01-part1-protocol.html#sec_SystemQueryOptionexpand

services/graph/pkg/service/v0/users_filter.go

@@ -156,7 +156,7 @@ func (g Graph) applyFilterLogicalAnd(ctx context.Context, req *godata.GoDataRequ
 			return []*libregraph.User{}, err
 		}
 		logger.Debug().Str("property", property).Str("value", value).Msg("applying approleAssignments filter on result set")
-		return g.filterUsersByAppRoleID(ctx, value, res2)
+		return g.filterUsersByAppRoleID(ctx, req, value, res2)
 	}
 
 	// 1st part is no appRoleAssignmentFilter, run the filter query
@@ -172,7 +172,7 @@ func (g Graph) applyFilterLogicalAnd(ctx context.Context, req *godata.GoDataRequ
 			return users, unsupportedFilterError()
 		}
 		logger.Debug().Str("property", property).Str("value", value).Msg("applying approleAssignments filter on result set")
-		return g.filterUsersByAppRoleID(ctx, value, res1)
+		return g.filterUsersByAppRoleID(ctx, req, value, res1)
 	}
 
 	// 2nd part is no appRoleAssignmentFilter either
@@ -329,22 +329,40 @@ func (g Graph) applyAppRoleAssignmentEq(ctx context.Context, req *godata.GoDataR
 			return users, err
 		}
 
-		return g.filterUsersByAppRoleID(ctx, filterValue, users)
+		return g.filterUsersByAppRoleID(ctx, req, filterValue, users)
 	}
 	return users, unsupportedFilterError()
 }
 
-func (g Graph) filterUsersByAppRoleID(ctx context.Context, id string, users []*libregraph.User) ([]*libregraph.User, error) {
+func (g Graph) filterUsersByAppRoleID(ctx context.Context, req *godata.GoDataRequest, id string, users []*libregraph.User) ([]*libregraph.User, error) {
 	// We're using a map for the results here, in order to avoid returning
 	// a user twice. The settings API, still has an issue that causes it to
 	// duplicate some assignments on restart:
 	// https://github.com/owncloud/ocis/issues/3432
+
+	var expand bool
+	exp := req.Query.GetExpand()
+	if exp != nil {
+		for _, item := range exp.ExpandItems {
+			if item.Path[0].Value == "appRoleAssignments" {
+				expand = true
+				break
+			}
+		}
+	}
+
 	resultUsersMap := make(map[string]*libregraph.User, len(users))
 	for _, user := range users {
 		assignments, err := g.fetchAppRoleAssignments(ctx, user.GetId())
 		if err != nil {
 			return users, err
 		}
+		// To avoid re-fetching all assignments in the upper layer handler when
+		// the $expand query parameter is set, we're adding the assignments to the
+		// resulting users here already.
+		if expand {
+			user.AppRoleAssignments = assignments
+		}
 		for _, assignment := range assignments {
 			if assignment.GetAppRoleId() == id {
 				if _, ok := resultUsersMap[user.GetId()]; !ok {