MM-52600: [Shared Channels] Shared channels do not sync channel membership (#30976)

server/channels/app/channel.go

@@ -1711,6 +1711,13 @@ func (a *App) addUserToChannel(c request.CTX, user *model.User, channel *model.C
 	a.Srv().Platform().InvalidateChannelCacheForUser(user.Id)
 	a.invalidateCacheForChannelMembers(channel.Id)
 
+	// Synchronize membership change for shared channels
+	if channel.IsShared() {
+		if scs := a.Srv().Platform().GetSharedChannelService(); scs != nil {
+			scs.HandleMembershipChange(channel.Id, user.Id, true, user.GetRemoteID())
+		}
+	}
+
 	return newMember, nil
 }
 
@@ -2236,7 +2243,12 @@ func (s *Server) getChannelMemberLastViewedAt(c request.CTX, channelID string, u
 }
 
 func (a *App) GetChannelMembersPage(c request.CTX, channelID string, page, perPage int) (model.ChannelMembers, *model.AppError) {
-	channelMembers, err := a.Srv().Store().Channel().GetMembers(channelID, page*perPage, perPage)
+	opts := model.ChannelMembersGetOptions{
+		ChannelID: channelID,
+		Offset:    page * perPage,
+		Limit:     perPage,
+	}
+	channelMembers, err := a.Srv().Store().Channel().GetMembers(opts)
 	if err != nil {
 		return nil, model.NewAppError("GetChannelMembersPage", "app.channel.get_members.app_error", nil, "", http.StatusInternalServerError).Wrap(err)
 	}
@@ -2740,6 +2752,14 @@ func (a *App) removeUserFromChannel(c request.CTX, userIDToRemove string, remove
 	userMsg.Add("remover_id", removerUserId)
 	a.Publish(userMsg)
 
+	// Synchronize membership change for shared channels
+	if channel.IsShared() {
+		// isAdd=false, empty remoteId means locally initiated
+		if scs := a.Srv().Platform().GetSharedChannelService(); scs != nil {
+			scs.HandleMembershipChange(channel.Id, userIDToRemove, false, "")
+		}
+	}
+
 	return nil
 }
 
@@ -3639,7 +3659,12 @@ func (a *App) forEachChannelMember(c request.CTX, channelID string, f func(model
 	page := 0
 
 	for {
-		channelMembers, err := a.Srv().Store().Channel().GetMembers(channelID, page*perPage, perPage)
+		opts := model.ChannelMembersGetOptions{
+			ChannelID: channelID,
+			Offset:    page * perPage,
+			Limit:     perPage,
+		}
+		channelMembers, err := a.Srv().Store().Channel().GetMembers(opts)
 		if err != nil {
 			return err
 		}

server/channels/app/channel_test.go

@@ -2513,8 +2513,16 @@ func TestClearChannelMembersCache(t *testing.T) {
 			ChannelId: "1",
 		})
 	}
-	mockChannelStore.On("GetMembers", "channelID", 0, 100).Return(cms, nil)
-	mockChannelStore.On("GetMembers", "channelID", 100, 100).Return(model.ChannelMembers{
+	mockChannelStore.On("GetMembers", model.ChannelMembersGetOptions{
+		ChannelID: "channelID",
+		Offset:    0,
+		Limit:     100,
+	}).Return(cms, nil)
+	mockChannelStore.On("GetMembers", model.ChannelMembersGetOptions{
+		ChannelID: "channelID",
+		Offset:    100,
+		Limit:     100,
+	}).Return(model.ChannelMembers{
 		model.ChannelMember{
 			ChannelId: "1",
 		},

server/channels/app/platform/shared_channel_service_iface.go

@@ -23,6 +23,7 @@ type SharedChannelServiceIFace interface {
 	CheckChannelNotShared(channelID string) error
 	CheckChannelIsShared(channelID string) error
 	CheckCanInviteToSharedChannel(channelId string) error
+	HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string)
 }
 
 type MockOptionSharedChannelService func(service *mockSharedChannelService)
@@ -77,3 +78,7 @@ func (mrcs *mockSharedChannelService) SendChannelInvite(channel *model.Channel,
 func (mrcs *mockSharedChannelService) NumInvitations() int {
 	return mrcs.numInvitations
 }
+
+func (mrcs *mockSharedChannelService) HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string) {
+	// This is a mock implementation - it doesn't need to do anything
+}

server/channels/app/shared_channel_service_iface.go

@@ -26,6 +26,7 @@ type SharedChannelServiceIFace interface {
 	CheckChannelNotShared(channelID string) error
 	CheckChannelIsShared(channelID string) error
 	CheckCanInviteToSharedChannel(channelId string) error
+	HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string)
 }
 
 func NewMockSharedChannelService(service SharedChannelServiceIFace) *mockSharedChannelService {
@@ -91,3 +92,9 @@ func (mrcs *mockSharedChannelService) SendChannelInvite(channel *model.Channel,
 func (mrcs *mockSharedChannelService) NumInvitations() int {
 	return mrcs.numInvitations
 }
+
+func (mrcs *mockSharedChannelService) HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string) {
+	if mrcs.SharedChannelServiceIFace != nil {
+		mrcs.SharedChannelServiceIFace.HandleMembershipChange(channelID, userID, isAdd, remoteID)
+	}
+}

server/channels/app/shared_channel_sync_self_referential_utils_test.go

@@ -105,6 +105,27 @@ func (h *SelfReferentialSyncHandler) HandleRequest(w http.ResponseWriter, r *htt
 						}
 					}
 
+					// Handle membership sync using unified field
+					if len(syncMsg.MembershipChanges) > 0 {
+						batch := make([]string, 0)
+						for _, change := range syncMsg.MembershipChanges {
+							if change.IsAdd {
+								syncResp.UsersSyncd = append(syncResp.UsersSyncd, change.UserId)
+								batch = append(batch, change.UserId)
+							}
+						}
+
+						// Call appropriate callback
+						if len(batch) > 0 {
+							if h.OnBatchSync != nil {
+								h.OnBatchSync(batch, currentCall)
+							}
+							if len(batch) == 1 && h.OnIndividualSync != nil {
+								h.OnIndividualSync(batch[0], currentCall)
+							}
+						}
+					}
+
 					_ = response.SetPayload(syncResp)
 				}
 			}
@@ -135,28 +156,36 @@ func (h *SelfReferentialSyncHandler) GetSyncMessageCount() int32 {
 	return atomic.LoadInt32(h.syncMessageCount)
 }
 
-// GetUsersFromSyncMsg extracts user IDs from a sync message
-func GetUsersFromSyncMsg(msg model.SyncMsg) []string {
-	var userIds []string
-
-	// Extract from users field
-	for userId := range msg.Users {
-		userIds = append(userIds, userId)
-	}
-
-	return userIds
-}
-
 // EnsureCleanState ensures a clean test state by removing all shared channels, remote clusters,
 // and extra team/channel members. This helps prevent state pollution between tests.
 func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 	t.Helper()
 
+	// First, wait for any pending async tasks to complete, then shutdown services
+	scsInterface := th.App.Srv().GetSharedChannelSyncService()
+	if scsInterface != nil && scsInterface.Active() {
+		// Cast to concrete type to access testing methods
+		if service, ok := scsInterface.(*sharedchannel.Service); ok {
+			// Wait for any pending tasks from previous tests to complete
+			require.Eventually(t, func() bool {
+				return !service.HasPendingTasksForTesting()
+			}, 10*time.Second, 100*time.Millisecond, "All pending sync tasks should complete before cleanup")
+		}
+
+		// Shutdown the shared channel service to stop any async operations
+		_ = scsInterface.Shutdown()
+
+		// Wait for shutdown to complete with more time
+		require.Eventually(t, func() bool {
+			return !scsInterface.Active()
+		}, 5*time.Second, 100*time.Millisecond, "Shared channel service should be inactive after shutdown")
+	}
+
 	// Clear all shared channels and remotes from previous tests
 	allSharedChannels, _ := ss.SharedChannel().GetAll(0, 1000, model.SharedChannelFilterOpts{})
 	for _, sc := range allSharedChannels {
 		// Delete all remotes for this channel
-		remotes, _ := ss.SharedChannel().GetRemotes(0, 100, model.SharedChannelRemoteFilterOpts{ChannelId: sc.ChannelId})
+		remotes, _ := ss.SharedChannel().GetRemotes(0, 999999, model.SharedChannelRemoteFilterOpts{ChannelId: sc.ChannelId})
 		for _, remote := range remotes {
 			_, _ = ss.SharedChannel().DeleteRemote(remote.Id)
 		}
@@ -170,13 +199,32 @@ func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 		_, _ = ss.RemoteCluster().Delete(rc.RemoteId)
 	}
 
+	// Clear all SharedChannelUsers sync state - this is critical for test isolation
+	// The SharedChannelUsers table tracks per-user sync timestamps that can interfere between tests
+	_, _ = th.SQLStore.GetMaster().Exec("DELETE FROM SharedChannelUsers WHERE 1=1")
+
+	// Clear all SharedChannelAttachments sync state
+	_, _ = th.SQLStore.GetMaster().Exec("DELETE FROM SharedChannelAttachments WHERE 1=1")
+
+	// Reset sync cursors in any remaining SharedChannelRemotes (before they get deleted)
+	// This ensures cursors don't persist if deletion fails
+	_, _ = th.SQLStore.GetMaster().Exec(`UPDATE SharedChannelRemotes SET 
+		LastPostCreateAt = 0, 
+		LastPostCreateId = '', 
+		LastPostUpdateAt = 0, 
+		LastPostId = '', 
+		LastMembersSyncAt = 0 
+		WHERE 1=1`)
+
 	// Remove all channel members from test channels (except the basic team/channel setup)
 	channels, _ := ss.Channel().GetAll(th.BasicTeam.Id)
 	for _, channel := range channels {
 		// Skip direct message and group channels, and skip the default channels
 		if channel.Type != model.ChannelTypeDirect && channel.Type != model.ChannelTypeGroup &&
 			channel.Id != th.BasicChannel.Id {
-			members, _ := ss.Channel().GetMembers(channel.Id, 0, 10000)
+			members, _ := ss.Channel().GetMembers(model.ChannelMembersGetOptions{
+				ChannelID: channel.Id,
+			})
 			for _, member := range members {
 				_ = ss.Channel().RemoveMember(th.Context, channel.Id, member.UserId)
 			}
@@ -228,12 +276,16 @@ func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 		cfg.ConnectedWorkspacesSettings.GlobalUserSyncBatchSize = &defaultBatchSize
 	})
 
-	// Ensure services are running and ready
-	scsInterface := th.App.Srv().GetSharedChannelSyncService()
-	if scs, ok := scsInterface.(*sharedchannel.Service); ok {
-		require.Eventually(t, func() bool {
-			return scs.Active()
-		}, 2*time.Second, 100*time.Millisecond, "Shared channel service should be active")
+	// Restart services and ensure they are running and ready
+	if scsInterface != nil {
+		// Restart the shared channel service
+		_ = scsInterface.Start()
+
+		if scs, ok := scsInterface.(*sharedchannel.Service); ok {
+			require.Eventually(t, func() bool {
+				return scs.Active()
+			}, 5*time.Second, 100*time.Millisecond, "Shared channel service should be active after restart")
+		}
 	}
 
 	rcService := th.App.Srv().GetRemoteClusterService()
@@ -243,6 +295,6 @@ func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 		}
 		require.Eventually(t, func() bool {
 			return rcService.Active()
-		}, 2*time.Second, 100*time.Millisecond, "Remote cluster service should be active")
+		}, 5*time.Second, 100*time.Millisecond, "Remote cluster service should be active")
 	}
 }

server/channels/app/shared_channel_test.go

@@ -16,6 +16,7 @@ func setupSharedChannels(tb testing.TB) *TestHelper {
 	return SetupConfig(tb, func(cfg *model.Config) {
 		*cfg.ConnectedWorkspacesSettings.EnableRemoteClusterService = true
 		*cfg.ConnectedWorkspacesSettings.EnableSharedChannels = true
+		cfg.FeatureFlags.EnableSharedChannelsMemberSync = true
 	})
 }
 

server/channels/db/migrations/migrations.list

@@ -275,6 +275,8 @@ channels/db/migrations/mysql/000138_add_default_category_name_to_channel.down.sq
 channels/db/migrations/mysql/000138_add_default_category_name_to_channel.up.sql
 channels/db/migrations/mysql/000139_remoteclusters_add_last_global_user_sync_at.down.sql
 channels/db/migrations/mysql/000139_remoteclusters_add_last_global_user_sync_at.up.sql
+channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql
+channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql
 channels/db/migrations/postgres/000001_create_teams.down.sql
 channels/db/migrations/postgres/000001_create_teams.up.sql
 channels/db/migrations/postgres/000002_create_team_members.down.sql
@@ -551,3 +553,5 @@ channels/db/migrations/postgres/000138_add_default_category_name_to_channel.down
 channels/db/migrations/postgres/000138_add_default_category_name_to_channel.up.sql
 channels/db/migrations/postgres/000139_remoteclusters_add_last_global_user_sync_at.down.sql
 channels/db/migrations/postgres/000139_remoteclusters_add_last_global_user_sync_at.up.sql
+channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql
+channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql

server/channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql

@@ -0,0 +1,29 @@
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelRemotes'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembersSyncAt'
+    ) > 0,
+    'ALTER TABLE SharedChannelRemotes DROP COLUMN LastMembersSyncAt;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists FROM @preparedStatement;
+EXECUTE alterIfExists;
+DEALLOCATE PREPARE alterIfExists;
+
+SET @preparedStatement2 = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelUsers'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembershipSyncAt'
+    ) > 0,
+    'ALTER TABLE SharedChannelUsers DROP COLUMN LastMembershipSyncAt;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists2 FROM @preparedStatement2;
+EXECUTE alterIfExists2;
+DEALLOCATE PREPARE alterIfExists2;

server/channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql

@@ -0,0 +1,29 @@
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelRemotes'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembersSyncAt'
+    ) > 0,
+    'SELECT 1',
+    'ALTER TABLE SharedChannelRemotes ADD LastMembersSyncAt bigint DEFAULT 0;'
+));
+
+PREPARE alterIfNotExists FROM @preparedStatement;
+EXECUTE alterIfNotExists;
+DEALLOCATE PREPARE alterIfNotExists;
+
+SET @preparedStatement2 = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelUsers'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembershipSyncAt'
+    ) > 0,
+    'SELECT 1',
+    'ALTER TABLE SharedChannelUsers ADD LastMembershipSyncAt bigint DEFAULT 0;'
+));
+
+PREPARE alterIfNotExists2 FROM @preparedStatement2;
+EXECUTE alterIfNotExists2;
+DEALLOCATE PREPARE alterIfNotExists2;

server/channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE sharedchannelremotes DROP COLUMN IF EXISTS lastmemberssyncat;
+ALTER TABLE sharedchannelusers DROP COLUMN IF EXISTS lastmembershipsyncat;

server/channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE sharedchannelremotes ADD COLUMN IF NOT EXISTS lastmemberssyncat bigint DEFAULT 0;
+ALTER TABLE sharedchannelusers ADD COLUMN IF NOT EXISTS lastmembershipsyncat bigint DEFAULT 0;

server/channels/store/retrylayer/retrylayer.go

@@ -2081,11 +2081,11 @@ func (s *RetryLayerChannelStore) GetMemberLastViewedAt(ctx context.Context, chan
 
 }
 
-func (s *RetryLayerChannelStore) GetMembers(channelID string, offset int, limit int) (model.ChannelMembers, error) {
+func (s *RetryLayerChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
 
 	tries := 0
 	for {
-		result, err := s.ChannelStore.GetMembers(channelID, offset, limit)
+		result, err := s.ChannelStore.GetMembers(opts)
 		if err == nil {
 			return result, nil
 		}
@@ -11642,6 +11642,27 @@ func (s *RetryLayerSharedChannelStore) GetSingleUser(userID string, channelID st
 
 }
 
+func (s *RetryLayerSharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+
+	tries := 0
+	for {
+		result, err := s.SharedChannelStore.GetUserChanges(userID, channelID, afterTime)
+		if err == nil {
+			return result, nil
+		}
+		if !isRepeatableError(err) {
+			return result, err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return result, err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
 func (s *RetryLayerSharedChannelStore) GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error) {
 
 	tries := 0
@@ -11894,6 +11915,48 @@ func (s *RetryLayerSharedChannelStore) UpdateRemoteCursor(id string, cursor mode
 
 }
 
+func (s *RetryLayerSharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+
+	tries := 0
+	for {
+		err := s.SharedChannelStore.UpdateRemoteMembershipCursor(id, syncTime)
+		if err == nil {
+			return nil
+		}
+		if !isRepeatableError(err) {
+			return err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
+func (s *RetryLayerSharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+
+	tries := 0
+	for {
+		err := s.SharedChannelStore.UpdateUserLastMembershipSyncAt(userID, channelID, remoteID, syncTime)
+		if err == nil {
+			return nil
+		}
+		if !isRepeatableError(err) {
+			return err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
 func (s *RetryLayerSharedChannelStore) UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error {
 
 	tries := 0

server/channels/store/sqlstore/channel_store.go

@@ -2070,22 +2070,34 @@ func (s SqlChannelStore) PatchMultipleMembersNotifyProps(members []*model.Channe
 	return updated, nil
 }
 
-func (s SqlChannelStore) GetMembers(channelID string, offset, limit int) (model.ChannelMembers, error) {
-	sql, args, err := s.channelMembersForTeamWithSchemeSelectQuery.
+func (s SqlChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
+	query := s.channelMembersForTeamWithSchemeSelectQuery.
 		Where(sq.Eq{
-			"ChannelId": channelID,
-		}).
-		Limit(uint64(limit)).
-		Offset(uint64(offset)).
-		ToSql()
+			"ChannelId": opts.ChannelID,
+		})
+
+	if opts.UpdatedAfter > 0 {
+		query = query.Where(sq.Gt{"ChannelMembers.LastUpdateAt": opts.UpdatedAfter})
+		query = query.OrderBy("ChannelMembers.LastUpdateAt")
+	}
+
+	if opts.Limit > 0 {
+		query = query.Limit(uint64(opts.Limit))
+	}
+
+	if opts.Offset > 0 {
+		query = query.Offset(uint64(opts.Offset))
+	}
+
+	sql, args, err := query.ToSql()
 	if err != nil {
-		return nil, errors.Wrapf(err, "GetMember_ToSql ChannelID=%s", channelID)
+		return nil, errors.Wrapf(err, "GetMember_ToSql ChannelID=%s", opts.ChannelID)
 	}
 
 	dbMembers := channelMemberWithSchemeRolesList{}
 	err = s.GetReplica().Select(&dbMembers, sql, args...)
 	if err != nil {
-		return nil, errors.Wrapf(err, "failed to get ChannelMembers with channelId=%s", channelID)
+		return nil, errors.Wrapf(err, "failed to get ChannelMembers with channelId=%s", opts.ChannelID)
 	}
 
 	return dbMembers.ToModel(), nil

server/channels/store/sqlstore/shared_channel_store.go

@@ -417,6 +417,7 @@ func sharedChannelRemoteFields(prefix string) []string {
 		"COALESCE(" + prefix + "LastPostCreateID,'') AS LastPostCreateID",
 		prefix + "LastPostUpdateAt",
 		"COALESCE(" + prefix + "LastPostId,'') AS LastPostUpdateID",
+		prefix + "LastMembersSyncAt",
 	}
 }
 
@@ -708,6 +709,7 @@ func sharedChannelUserFields(prefix string) []string {
 		prefix + "RemoteId",
 		prefix + "CreateAt",
 		prefix + "LastSyncAt",
+		prefix + "LastMembershipSyncAt",
 	}
 }
 
@@ -720,7 +722,7 @@ func (s SqlSharedChannelStore) SaveUser(scUser *model.SharedChannelUser) (*model
 
 	query, args, err := s.getQueryBuilder().Insert("SharedChannelUsers").
 		Columns(sharedChannelUserFields("")...).
-		Values(scUser.Id, scUser.UserId, scUser.ChannelId, scUser.RemoteId, scUser.CreateAt, scUser.LastSyncAt).
+		Values(scUser.Id, scUser.UserId, scUser.ChannelId, scUser.RemoteId, scUser.CreateAt, scUser.LastSyncAt, scUser.LastMembershipSyncAt).
 		ToSql()
 	if err != nil {
 		return nil, errors.Wrapf(err, "savesharedchanneluser_tosql")
@@ -853,6 +855,25 @@ func (s SqlSharedChannelStore) UpdateUserLastSyncAt(userID string, channelID str
 	return nil
 }
 
+// UpdateUserLastMembershipSyncAt updates the LastMembershipSyncAt timestamp for the specified SharedChannelUser using the provided sync time.
+func (s SqlSharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+	query := s.getQueryBuilder().
+		Update("SharedChannelUsers AS scu").
+		Set("LastMembershipSyncAt", sq.Expr("GREATEST(scu.LastMembershipSyncAt, ?)", syncTime)).
+		Where(sq.Eq{
+			"scu.UserId":    userID,
+			"scu.ChannelId": channelID,
+			"scu.RemoteId":  remoteID,
+		})
+
+	_, err := s.GetMaster().ExecBuilder(query)
+	if err != nil {
+		return fmt.Errorf("failed to update LastMembershipSyncAt for SharedChannelUser with userId=%s, channelId=%s, remoteId=%s: %w",
+			userID, channelID, remoteID, err)
+	}
+	return nil
+}
+
 func sharedChannelAttachementFields(prefix string) []string {
 	if prefix != "" && !strings.HasSuffix(prefix, ".") {
 		prefix = prefix + "."

server/channels/store/sqlstore/shared_channel_store_membership.go

@@ -0,0 +1,66 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package sqlstore
+
+import (
+	"database/sql"
+	"fmt"
+
+	"github.com/mattermost/mattermost/server/public/model"
+	sq "github.com/mattermost/squirrel"
+	"github.com/pkg/errors"
+)
+
+// UpdateRemoteMembershipCursor updates the LastMembersSyncAt timestamp for the specified SharedChannelRemote,
+// but only if the new timestamp is greater than the current value.
+func (s SqlSharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+	query := s.getQueryBuilder().
+		Update("SharedChannelRemotes")
+
+	query = query.Set("LastMembersSyncAt", sq.Expr("GREATEST(LastMembersSyncAt, ?)", syncTime))
+
+	query = query.Where(sq.Eq{"Id": id})
+
+	result, err := s.GetMaster().ExecBuilder(query)
+	if err != nil {
+		return errors.Wrap(err, "failed to update membership cursor for SharedChannelRemote")
+	}
+
+	count, err := result.RowsAffected()
+	if err != nil {
+		return errors.Wrap(err, "failed to determine rows affected")
+	}
+
+	if count == 0 {
+		return fmt.Errorf("id not found: %s", id)
+	}
+
+	return nil
+}
+
+// GetUserChanges gets all SharedChannelUser changes for a given user, channel after a specific time.
+// This is used to detect if there are conflicting membership changes.
+func (s SqlSharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+	squery, args, err := s.getQueryBuilder().
+		Select(sharedChannelUserFields("")...).
+		From("SharedChannelUsers").
+		Where(sq.Eq{"SharedChannelUsers.UserId": userID}).
+		Where(sq.Eq{"SharedChannelUsers.ChannelId": channelID}).
+		Where(sq.Gt{"SharedChannelUsers.LastSyncAt": afterTime}).
+		ToSql()
+
+	if err != nil {
+		return nil, errors.Wrapf(err, "getsharedchanneluserchanges_tosql")
+	}
+
+	users := []*model.SharedChannelUser{}
+	if err := s.GetReplica().Select(&users, squery, args...); err != nil {
+		if err == sql.ErrNoRows {
+			return make([]*model.SharedChannelUser, 0), nil
+		}
+		return nil, errors.Wrapf(err, "failed to find shared channel user changes with UserId=%s, ChannelId=%s, afterTime=%d",
+			userID, channelID, afterTime)
+	}
+	return users, nil
+}

server/channels/store/store.go

@@ -232,7 +232,7 @@ type ChannelStore interface {
 	// It replaces existing fields and creates new ones which don't exist.
 	UpdateMemberNotifyProps(channelID, userID string, props map[string]string) (*model.ChannelMember, error)
 	PatchMultipleMembersNotifyProps(members []*model.ChannelMemberIdentifier, notifyProps map[string]string) ([]*model.ChannelMember, error)
-	GetMembers(channelID string, offset, limit int) (model.ChannelMembers, error)
+	GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error)
 	GetMember(ctx context.Context, channelID string, userID string) (*model.ChannelMember, error)
 	GetMemberLastViewedAt(ctx context.Context, channelID string, userID string) (int64, error)
 	GetChannelMembersTimezones(channelID string) ([]model.StringMap, error)
@@ -1014,6 +1014,7 @@ type SharedChannelStore interface {
 	GetRemoteByIds(channelID string, remoteID string) (*model.SharedChannelRemote, error)
 	GetRemotes(offset, limit int, opts model.SharedChannelRemoteFilterOpts) ([]*model.SharedChannelRemote, error)
 	UpdateRemoteCursor(id string, cursor model.GetPostsSinceForSyncCursor) error
+	UpdateRemoteMembershipCursor(id string, syncTime int64) error
 	DeleteRemote(remoteID string) (bool, error)
 	GetRemotesStatus(channelID string) ([]*model.SharedChannelRemoteStatus, error)
 
@@ -1021,7 +1022,9 @@ type SharedChannelStore interface {
 	GetSingleUser(userID string, channelID string, remoteID string) (*model.SharedChannelUser, error)
 	GetUsersForUser(userID string) ([]*model.SharedChannelUser, error)
 	GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error)
+	GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error)
 	UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error
+	UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error
 
 	SaveAttachment(remote *model.SharedChannelAttachment) (*model.SharedChannelAttachment, error)
 	UpsertAttachment(remote *model.SharedChannelAttachment) (string, error)

server/channels/store/storetest/channel_store.go

@@ -73,6 +73,7 @@ func TestChannelStore(t *testing.T, rctx request.CTX, ss store.Store, s SqlStore
 	t.Run("Save", func(t *testing.T) { testChannelStoreSave(t, rctx, ss) })
 	t.Run("SaveDirectChannel", func(t *testing.T) { testChannelStoreSaveDirectChannel(t, rctx, ss, s) })
 	t.Run("CreateDirectChannel", func(t *testing.T) { testChannelStoreCreateDirectChannel(t, rctx, ss) })
+	t.Run("GetMembersWithCursorPagination", func(t *testing.T) { testChannelStoreGetMembersWithCursorPagination(t, rctx, ss) })
 	t.Run("Update", func(t *testing.T) { testChannelStoreUpdate(t, rctx, ss) })
 	t.Run("GetChannelUnread", func(t *testing.T) { testGetChannelUnread(t, rctx, ss) })
 	t.Run("Get", func(t *testing.T) { testChannelStoreGet(t, rctx, ss, s) })
@@ -265,7 +266,7 @@ func testChannelStoreSaveDirectChannel(t *testing.T, rctx request.CTX, ss store.
 	_, nErr = ss.Channel().SaveDirectChannel(rctx, &o1, &m1, &m2)
 	require.NoError(t, nErr, "couldn't save direct channel", nErr)
 
-	members, nErr := ss.Channel().GetMembers(o1.Id, 0, 100)
+	members, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: o1.Id, Offset: 0, Limit: 100})
 	require.NoError(t, nErr)
 	require.Len(t, members, 2, "should have saved 2 members")
 
@@ -305,7 +306,7 @@ func testChannelStoreSaveDirectChannel(t *testing.T, rctx request.CTX, ss store.
 	_, nErr = ss.Channel().SaveDirectChannel(rctx, &o1, &m1, &m1)
 	require.NoError(t, nErr, "couldn't save direct channel", nErr)
 
-	members, nErr = ss.Channel().GetMembers(o1.Id, 0, 100)
+	members, nErr = ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: o1.Id, Offset: 0, Limit: 100})
 	require.NoError(t, nErr)
 	require.Len(t, members, 1, "should have saved just 1 member")
 
@@ -341,11 +342,72 @@ func testChannelStoreCreateDirectChannel(t *testing.T, rctx request.CTX, ss stor
 		ss.Channel().PermanentDelete(rctx, c1.Id)
 	}()
 
-	members, nErr := ss.Channel().GetMembers(c1.Id, 0, 100)
+	members, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 100})
 	require.NoError(t, nErr)
 	require.Len(t, members, 2, "should have saved 2 members")
 }
 
+// testChannelStoreGetMembersWithCursorPagination tests the cursor-based pagination functionality
+// of the GetMembers method, using the UpdatedAfter parameter to return only members that were
+// updated after a specific timestamp.
+func testChannelStoreGetMembersWithCursorPagination(t *testing.T, rctx request.CTX, ss store.Store) {
+	// Create two users
+	u1 := &model.User{}
+	u1.Email = MakeEmail()
+	u1.Nickname = model.NewId()
+	_, err := ss.User().Save(rctx, u1)
+	require.NoError(t, err)
+	_, nErr := ss.Team().SaveMember(rctx, &model.TeamMember{TeamId: model.NewId(), UserId: u1.Id}, -1)
+	require.NoError(t, nErr)
+
+	u2 := &model.User{}
+	u2.Email = MakeEmail()
+	u2.Nickname = model.NewId()
+	_, err = ss.User().Save(rctx, u2)
+	require.NoError(t, err)
+	_, nErr = ss.Team().SaveMember(rctx, &model.TeamMember{TeamId: model.NewId(), UserId: u2.Id}, -1)
+	require.NoError(t, nErr)
+
+	// Create direct channel between the users
+	c1, nErr := ss.Channel().CreateDirectChannel(rctx, u1, u2)
+	require.NoError(t, nErr, "couldn't create direct channel", nErr)
+	defer func() {
+		ss.Channel().PermanentDeleteMembersByChannel(rctx, c1.Id)
+		ss.Channel().PermanentDelete(rctx, c1.Id)
+	}()
+
+	// First get all members
+	members, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 100})
+	require.NoError(t, nErr)
+	require.Len(t, members, 2, "should have saved 2 members")
+
+	// Ensure members have different LastUpdateAt values by updating one of them after a short delay
+	time.Sleep(1 * time.Millisecond)
+	member := members[0]
+	_, err = ss.Channel().UpdateMember(rctx, &member)
+	require.NoError(t, err)
+
+	// Get members again after the update
+	members, nErr = ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 100})
+	require.NoError(t, nErr)
+	require.Len(t, members, 2, "should have 2 members")
+
+	// Find member with smaller LastUpdateAt
+	sort.Slice(members, func(i, j int) bool {
+		return members[i].LastUpdateAt < members[j].LastUpdateAt
+	})
+	updateTime := members[0].LastUpdateAt
+
+	// Test cursor-based pagination by querying for members updated after that timestamp
+	membersAfter, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{
+		ChannelID:    c1.Id,
+		UpdatedAfter: updateTime,
+		Limit:        100,
+	})
+	require.NoError(t, nErr)
+	require.Len(t, membersAfter, 1, "should have found only 1 member created after the timestamp")
+}
+
 func testChannelStoreUpdate(t *testing.T, rctx request.CTX, ss store.Store) {
 	o1 := model.Channel{}
 	o1.TeamId = model.NewId()
@@ -7867,7 +7929,7 @@ func testChannelStoreRemoveAllDeactivatedMembers(t *testing.T, rctx request.CTX,
 	require.NoError(t, err)
 
 	// Get all the channel members. Check there are 3.
-	d1, err := ss.Channel().GetMembers(c1.Id, 0, 1000)
+	d1, err := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 1000})
 	assert.NoError(t, err)
 	assert.Len(t, d1, 3)
 
@@ -7887,7 +7949,7 @@ func testChannelStoreRemoveAllDeactivatedMembers(t *testing.T, rctx request.CTX,
 	assert.NoError(t, ss.Channel().RemoveAllDeactivatedMembers(rctx, c1.Id))
 
 	// Get all the channel members. Check there is now only 1: m3.
-	d2, err := ss.Channel().GetMembers(c1.Id, 0, 1000)
+	d2, err := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 1000})
 	assert.NoError(t, err)
 	assert.Len(t, d2, 1)
 	assert.Equal(t, u3.Id, d2[0].UserId)

server/channels/store/storetest/group_store.go

@@ -5340,7 +5340,7 @@ func groupTestpUpdateMembersRoleChannel(t *testing.T, rctx request.CTX, ss store
 			}
 			assert.ElementsMatch(t, tt.expectedUpdatedUsers, updatedUserIDs)
 
-			members, err := ss.Channel().GetMembers(channel.Id, 0, 100)
+			members, err := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: channel.Id, Offset: 0, Limit: 100})
 			require.NoError(t, err)
 			assert.GreaterOrEqual(t, len(members), 4) // sanity check for channel membership
 

server/channels/store/storetest/mocks/ChannelStore.go

@@ -1580,9 +1580,9 @@ func (_m *ChannelStore) GetMemberLastViewedAt(ctx context.Context, channelID str
 	return r0, r1
 }
 
-// GetMembers provides a mock function with given fields: channelID, offset, limit
-func (_m *ChannelStore) GetMembers(channelID string, offset int, limit int) (model.ChannelMembers, error) {
-	ret := _m.Called(channelID, offset, limit)
+// GetMembers provides a mock function with given fields: opts
+func (_m *ChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
+	ret := _m.Called(opts)
 
 	if len(ret) == 0 {
 		panic("no return value specified for GetMembers")
@@ -1590,19 +1590,19 @@ func (_m *ChannelStore) GetMembers(channelID string, offset int, limit int) (mod
 
 	var r0 model.ChannelMembers
 	var r1 error
-	if rf, ok := ret.Get(0).(func(string, int, int) (model.ChannelMembers, error)); ok {
-		return rf(channelID, offset, limit)
+	if rf, ok := ret.Get(0).(func(model.ChannelMembersGetOptions) (model.ChannelMembers, error)); ok {
+		return rf(opts)
 	}
-	if rf, ok := ret.Get(0).(func(string, int, int) model.ChannelMembers); ok {
-		r0 = rf(channelID, offset, limit)
+	if rf, ok := ret.Get(0).(func(model.ChannelMembersGetOptions) model.ChannelMembers); ok {
+		r0 = rf(opts)
 	} else {
 		if ret.Get(0) != nil {
 			r0 = ret.Get(0).(model.ChannelMembers)
 		}
 	}
 
-	if rf, ok := ret.Get(1).(func(string, int, int) error); ok {
-		r1 = rf(channelID, offset, limit)
+	if rf, ok := ret.Get(1).(func(model.ChannelMembersGetOptions) error); ok {
+		r1 = rf(opts)
 	} else {
 		r1 = ret.Error(1)
 	}

server/channels/store/storetest/mocks/SharedChannelStore.go

@@ -368,6 +368,36 @@ func (_m *SharedChannelStore) GetSingleUser(userID string, channelID string, rem
 	return r0, r1
 }
 
+// GetUserChanges provides a mock function with given fields: userID, channelID, afterTime
+func (_m *SharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+	ret := _m.Called(userID, channelID, afterTime)
+
+	if len(ret) == 0 {
+		panic("no return value specified for GetUserChanges")
+	}
+
+	var r0 []*model.SharedChannelUser
+	var r1 error
+	if rf, ok := ret.Get(0).(func(string, string, int64) ([]*model.SharedChannelUser, error)); ok {
+		return rf(userID, channelID, afterTime)
+	}
+	if rf, ok := ret.Get(0).(func(string, string, int64) []*model.SharedChannelUser); ok {
+		r0 = rf(userID, channelID, afterTime)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).([]*model.SharedChannelUser)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(string, string, int64) error); ok {
+		r1 = rf(userID, channelID, afterTime)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
 // GetUsersForSync provides a mock function with given fields: filter
 func (_m *SharedChannelStore) GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error) {
 	ret := _m.Called(filter)
@@ -700,6 +730,42 @@ func (_m *SharedChannelStore) UpdateRemoteCursor(id string, cursor model.GetPost
 	return r0
 }
 
+// UpdateRemoteMembershipCursor provides a mock function with given fields: id, syncTime
+func (_m *SharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+	ret := _m.Called(id, syncTime)
+
+	if len(ret) == 0 {
+		panic("no return value specified for UpdateRemoteMembershipCursor")
+	}
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(string, int64) error); ok {
+		r0 = rf(id, syncTime)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// UpdateUserLastMembershipSyncAt provides a mock function with given fields: userID, channelID, remoteID, syncTime
+func (_m *SharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+	ret := _m.Called(userID, channelID, remoteID, syncTime)
+
+	if len(ret) == 0 {
+		panic("no return value specified for UpdateUserLastMembershipSyncAt")
+	}
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(string, string, string, int64) error); ok {
+		r0 = rf(userID, channelID, remoteID, syncTime)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
 // UpdateUserLastSyncAt provides a mock function with given fields: userID, channelID, remoteID
 func (_m *SharedChannelStore) UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error {
 	ret := _m.Called(userID, channelID, remoteID)

server/channels/store/timerlayer/timerlayer.go

@@ -1729,10 +1729,10 @@ func (s *TimerLayerChannelStore) GetMemberLastViewedAt(ctx context.Context, chan
 	return result, err
 }
 
-func (s *TimerLayerChannelStore) GetMembers(channelID string, offset int, limit int) (model.ChannelMembers, error) {
+func (s *TimerLayerChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
 	start := time.Now()
 
-	result, err := s.ChannelStore.GetMembers(channelID, offset, limit)
+	result, err := s.ChannelStore.GetMembers(opts)
 
 	elapsed := float64(time.Since(start)) / float64(time.Second)
 	if s.Root.Metrics != nil {
@@ -9173,6 +9173,22 @@ func (s *TimerLayerSharedChannelStore) GetSingleUser(userID string, channelID st
 	return result, err
 }
 
+func (s *TimerLayerSharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+	start := time.Now()
+
+	result, err := s.SharedChannelStore.GetUserChanges(userID, channelID, afterTime)
+
+	elapsed := float64(time.Since(start)) / float64(time.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("SharedChannelStore.GetUserChanges", success, elapsed)
+	}
+	return result, err
+}
+
 func (s *TimerLayerSharedChannelStore) GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error) {
 	start := time.Now()
 
@@ -9365,6 +9381,38 @@ func (s *TimerLayerSharedChannelStore) UpdateRemoteCursor(id string, cursor mode
 	return err
 }
 
+func (s *TimerLayerSharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+	start := time.Now()
+
+	err := s.SharedChannelStore.UpdateRemoteMembershipCursor(id, syncTime)
+
+	elapsed := float64(time.Since(start)) / float64(time.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("SharedChannelStore.UpdateRemoteMembershipCursor", success, elapsed)
+	}
+	return err
+}
+
+func (s *TimerLayerSharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+	start := time.Now()
+
+	err := s.SharedChannelStore.UpdateUserLastMembershipSyncAt(userID, channelID, remoteID, syncTime)
+
+	elapsed := float64(time.Since(start)) / float64(time.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("SharedChannelStore.UpdateUserLastMembershipSyncAt", success, elapsed)
+	}
+	return err
+}
+
 func (s *TimerLayerSharedChannelStore) UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error {
 	start := time.Now()