MM-34002: Improve AddUserToChannel (#17174)

* MM-34002: Improve AddUserToChannel When we would add a user to a channel, we would check whether the user is removed from that team or not. During LDAP sync, this check is not required because the team member would have just been created. Hence, we pass a boolean flag to bypass the check. And with that done, we can freely query the replica. https://mattermost.atlassian.net/browse/MM-34002 ```release-note NONE ``` * Refactor code * Rename a struct field * fix double negative
2021-04-02 14:33:23 +05:30
--- a/app/app_iface.go
+++ b/app/app_iface.go
@@ -42,12 +42,16 @@ type AppIface interface {
 	ListAutocompleteCommands(teamID string, T i18n.TranslateFunc) ([]*model.Command, *model.AppError)
 	// @openTracingParams teamID, skipSlackParsing
 	CreateCommandPost(post *model.Post, teamID string, response *model.CommandResponse, skipSlackParsing bool) (*model.Post, *model.AppError)
+	// AddChannelMember adds a user to a channel. It is a wrapper over AddUserToChannel.
+	AddChannelMember(userID string, channel *model.Channel, opts ChannelMemberOpts) (*model.ChannelMember, *model.AppError)
 	// AddCursorIdsForPostList adds NextPostId and PrevPostId as cursor to the PostList.
 	// The conditional blocks ensure that it sets those cursor IDs immediately as afterPost, beforePost or empty,
 	// and only query to database whenever necessary.
 	AddCursorIdsForPostList(originalList *model.PostList, afterPost, beforePost string, since int64, page, perPage int, collapsedThreads bool)
 	// AddPublicKey will add plugin public key to the config. Overwrites the previous file
 	AddPublicKey(name string, key io.Reader) *model.AppError
+	// AddUserToChannel adds a user to a given channel.
+	AddUserToChannel(user *model.User, channel *model.Channel, skipTeamMemberIntegrityCheck bool) (*model.ChannelMember, *model.AppError)
 	// Caller must close the first return value
 	FileReader(path string) (filestore.ReadCloseSeeker, *model.AppError)
 	// ChannelMembersMinusGroupMembers returns the set of users in the given channel minus the set of users in the given
@@ -359,7 +363,6 @@ type AppIface interface {
 	AcceptLanguage() string
 	AccountMigration() einterfaces.AccountMigrationInterface
 	ActivateMfa(userID, token string) *model.AppError
-	AddChannelMember(userID string, channel *model.Channel, userRequestorId string, postRootId string) (*model.ChannelMember, *model.AppError)
 	AddConfigListener(listener func(*model.Config, *model.Config)) string
 	AddDirectChannels(teamID string, user *model.User) *model.AppError
 	AddLdapPrivateCertificate(fileData *multipart.FileHeader) *model.AppError
@@ -375,7 +378,6 @@ type AppIface interface {
 	AddTeamMemberByInviteId(inviteId, userID string) (*model.TeamMember, *model.AppError)
 	AddTeamMemberByToken(userID, tokenID string) (*model.TeamMember, *model.AppError)
 	AddTeamMembers(teamID string, userIDs []string, userRequestorId string, graceful bool) ([]*model.TeamMemberWithError, *model.AppError)
-	AddUserToChannel(user *model.User, channel *model.Channel) (*model.ChannelMember, *model.AppError)
 	AddUserToTeam(teamID string, userID string, userRequestorId string) (*model.Team, *model.TeamMember, *model.AppError)
 	AddUserToTeamByInviteId(inviteId string, userID string) (*model.Team, *model.TeamMember, *model.AppError)
 	AddUserToTeamByTeamId(teamID string, user *model.User) *model.AppError
--- a/app/channel.go
+++ b/app/channel.go
@@ -15,7 +15,6 @@ import (
 	"github.com/mattermost/mattermost-server/v5/shared/i18n"
 	"github.com/mattermost/mattermost-server/v5/shared/mlog"
 	"github.com/mattermost/mattermost-server/v5/store"
-	"github.com/mattermost/mattermost-server/v5/store/sqlstore"
 	"github.com/mattermost/mattermost-server/v5/utils"
 )

@@ -1372,24 +1371,23 @@ func (a *App) addUserToChannel(user *model.User, channel *model.Channel) (*model
 	return newMember, nil
 }

-func (a *App) AddUserToChannel(user *model.User, channel *model.Channel) (*model.ChannelMember, *model.AppError) {
-	// We have to query master here because this is called during LDAP sync from:
-	// a.createDefaultChannelMemberships -> a.AddTeamMember -> a.AddChannelMember
-	// So we get a teamMember right after adding a team member which leads to a failure.
-	// TODO: pass the team member to this method.
-	teamMember, nErr := a.Srv().Store.Team().GetMember(sqlstore.WithMaster(context.Background()), channel.TeamId, user.Id)
-	if nErr != nil {
-		var nfErr *store.ErrNotFound
-		switch {
-		case errors.As(nErr, &nfErr):
-			return nil, model.NewAppError("AddUserToChannel", "app.team.get_member.missing.app_error", nil, nfErr.Error(), http.StatusNotFound)
-		default:
-			return nil, model.NewAppError("AddUserToChannel", "app.team.get_member.app_error", nil, nErr.Error(), http.StatusInternalServerError)
+// AddUserToChannel adds a user to a given channel.
+func (a *App) AddUserToChannel(user *model.User, channel *model.Channel, skipTeamMemberIntegrityCheck bool) (*model.ChannelMember, *model.AppError) {
+	if !skipTeamMemberIntegrityCheck {
+		teamMember, nErr := a.Srv().Store.Team().GetMember(context.Background(), channel.TeamId, user.Id)
+		if nErr != nil {
+			var nfErr *store.ErrNotFound
+			switch {
+			case errors.As(nErr, &nfErr):
+				return nil, model.NewAppError("AddUserToChannel", "app.team.get_member.missing.app_error", nil, nfErr.Error(), http.StatusNotFound)
+			default:
+				return nil, model.NewAppError("AddUserToChannel", "app.team.get_member.app_error", nil, nErr.Error(), http.StatusInternalServerError)
+			}
 		}
-	}

-	if teamMember.DeleteAt > 0 {
-		return nil, model.NewAppError("AddUserToChannel", "api.channel.add_user.to.channel.failed.deleted.app_error", nil, "", http.StatusBadRequest)
+		if teamMember.DeleteAt > 0 {
+			return nil, model.NewAppError("AddUserToChannel", "api.channel.add_user.to.channel.failed.deleted.app_error", nil, "", http.StatusBadRequest)
+		}
 	}

 	newMember, err := a.addUserToChannel(user, channel)
@@ -1405,7 +1403,18 @@ func (a *App) AddUserToChannel(user *model.User, channel *model.Channel) (*model
 	return newMember, nil
 }

-func (a *App) AddChannelMember(userID string, channel *model.Channel, userRequestorId string, postRootId string) (*model.ChannelMember, *model.AppError) {
+type ChannelMemberOpts struct {
+	UserRequestorID string
+	PostRootID      string
+	// SkipTeamMemberIntegrityCheck is used to indicate whether it should be checked
+	// that a user has already been removed from that team or not.
+	// This is useful to avoid in scenarios when we just added the team member,
+	// and thereby know that there is no need to check this.
+	SkipTeamMemberIntegrityCheck bool
+}
+
+// AddChannelMember adds a user to a channel. It is a wrapper over AddUserToChannel.
+func (a *App) AddChannelMember(userID string, channel *model.Channel, opts ChannelMemberOpts) (*model.ChannelMember, *model.AppError) {
 	if member, err := a.Srv().Store.Channel().GetMember(context.Background(), channel.Id, userID); err != nil {
 		var nfErr *store.ErrNotFound
 		if !errors.As(err, &nfErr) {
@@ -1423,13 +1432,13 @@ func (a *App) AddChannelMember(userID string, channel *model.Channel, userReques
 	}

 	var userRequestor *model.User
-	if userRequestorId != "" {
-		if userRequestor, err = a.GetUser(userRequestorId); err != nil {
+	if opts.UserRequestorID != "" {
+		if userRequestor, err = a.GetUser(opts.UserRequestorID); err != nil {
 			return nil, err
 		}
 	}

-	cm, err := a.AddUserToChannel(user, channel)
+	cm, err := a.AddUserToChannel(user, channel, opts.SkipTeamMemberIntegrityCheck)
 	if err != nil {
 		return nil, err
 	}
@@ -1444,11 +1453,11 @@ func (a *App) AddChannelMember(userID string, channel *model.Channel, userReques
 		})
 	}

-	if userRequestorId == "" || userID == userRequestorId {
+	if opts.UserRequestorID == "" || userID == opts.UserRequestorID {
 		a.postJoinChannelMessage(user, channel)
 	} else {
 		a.Srv().Go(func() {
-			a.PostAddToChannelMessage(userRequestor, user, channel, postRootId)
+			a.PostAddToChannelMessage(userRequestor, user, channel, opts.PostRootID)
 		})
 	}

@@ -1938,7 +1947,7 @@ func (a *App) JoinChannel(channel *model.Channel, userID string) *model.AppError
 		return model.NewAppError("JoinChannel", "api.channel.join_channel.permissions.app_error", nil, "", http.StatusBadRequest)
 	}

-	cm, err := a.AddUserToChannel(user, channel)
+	cm, err := a.AddUserToChannel(user, channel, false)
 	if err != nil {
 		return err
 	}
--- a/app/channel_test.go
+++ b/app/channel_test.go
@@ -87,7 +87,7 @@ func TestRemoveAllDeactivatedMembersFromChannel(t *testing.T) {
 	deacivatedUser := th.CreateUser()
 	_, _, err = th.App.AddUserToTeam(team.Id, deacivatedUser.Id, "")
 	require.Nil(t, err)
-	_, err = th.App.AddUserToChannel(deacivatedUser, channel)
+	_, err = th.App.AddUserToChannel(deacivatedUser, channel, false)
 	require.Nil(t, err)
 	channelMembers, err := th.App.GetChannelMembersPage(channel.Id, 0, 10000000)
 	require.Nil(t, err)
@@ -127,10 +127,10 @@ func TestMoveChannel(t *testing.T) {
 		_, _, err = th.App.AddUserToTeam(targetTeam.Id, th.BasicUser.Id, "")
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(th.BasicUser, channel1)
+		_, err = th.App.AddUserToChannel(th.BasicUser, channel1, false)
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(th.BasicUser2, channel1)
+		_, err = th.App.AddUserToChannel(th.BasicUser2, channel1, false)
 		require.Nil(t, err)

 		err = th.App.MoveChannel(targetTeam, channel1, th.BasicUser)
@@ -150,10 +150,10 @@ func TestMoveChannel(t *testing.T) {

 		_, _, err = th.App.AddUserToTeam(sourceTeam.Id, deacivatedUser.Id, "")
 		require.Nil(t, err)
-		_, err = th.App.AddUserToChannel(th.BasicUser, channel2)
+		_, err = th.App.AddUserToChannel(th.BasicUser, channel2, false)
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(deacivatedUser, channel2)
+		_, err = th.App.AddUserToChannel(deacivatedUser, channel2, false)
 		require.Nil(t, err)

 		_, err = th.App.UpdateActive(deacivatedUser, false)
@@ -241,9 +241,9 @@ func TestRemoveUsersFromChannelNotMemberOfTeam(t *testing.T) {
 	_, _, err = th.App.AddUserToTeam(team.Id, th.BasicUser2.Id, "")
 	require.Nil(t, err)

-	_, err = th.App.AddUserToChannel(th.BasicUser, channel1)
+	_, err = th.App.AddUserToChannel(th.BasicUser, channel1, false)
 	require.Nil(t, err)
-	_, err = th.App.AddUserToChannel(th.BasicUser2, channel1)
+	_, err = th.App.AddUserToChannel(th.BasicUser2, channel1, false)
 	require.Nil(t, err)

 	err = th.App.RemoveUsersFromChannelNotMemberOfTeam(th.SystemAdminUser, channel1, team2)
@@ -495,7 +495,7 @@ func TestAddUserToChannelCreatesChannelMemberHistoryRecord(t *testing.T) {

 	channel := th.createChannel(th.BasicTeam, model.CHANNEL_OPEN)

-	_, err = th.App.AddUserToChannel(user, channel)
+	_, err = th.App.AddUserToChannel(user, channel, false)
 	require.Nil(t, err, "Failed to add user to channel.")

 	// there should be a ChannelMemberHistory record for the user
@@ -581,9 +581,8 @@ func TestAddChannelMemberNoUserRequestor(t *testing.T) {
 	groupUserIds = append(groupUserIds, user.Id)

 	channel := th.createChannel(th.BasicTeam, model.CHANNEL_OPEN)
-	userRequestorId := ""
-	postRootId := ""
-	_, err = th.App.AddChannelMember(user.Id, channel, userRequestorId, postRootId)
+
+	_, err = th.App.AddChannelMember(user.Id, channel, ChannelMemberOpts{})
 	require.Nil(t, err, "Failed to add user to channel.")

 	// there should be a ChannelMemberHistory record for the user
@@ -952,9 +951,7 @@ func TestGetChannelMembersTimezones(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()

-	userRequestorId := ""
-	postRootId := ""
-	_, err := th.App.AddChannelMember(th.BasicUser2.Id, th.BasicChannel, userRequestorId, postRootId)
+	_, err := th.App.AddChannelMember(th.BasicUser2.Id, th.BasicChannel, ChannelMemberOpts{})
 	require.Nil(t, err, "Failed to add user to channel.")

 	user := th.BasicUser
@@ -968,14 +965,14 @@ func TestGetChannelMembersTimezones(t *testing.T) {

 	user3 := model.User{Email: strings.ToLower(model.NewId()) + "success+test@example.com", Nickname: "Darth Vader", Username: "vader" + model.NewId(), Password: "passwd1", AuthService: ""}
 	ruser, _ := th.App.CreateUser(&user3)
-	th.App.AddUserToChannel(ruser, th.BasicChannel)
+	th.App.AddUserToChannel(ruser, th.BasicChannel, false)

 	ruser.Timezone["automaticTimezone"] = "NoWhere/Island"
 	th.App.UpdateUser(ruser, false)

 	user4 := model.User{Email: strings.ToLower(model.NewId()) + "success+test@example.com", Nickname: "Darth Vader", Username: "vader" + model.NewId(), Password: "passwd1", AuthService: ""}
 	ruser, _ = th.App.CreateUser(&user4)
-	th.App.AddUserToChannel(ruser, th.BasicChannel)
+	th.App.AddUserToChannel(ruser, th.BasicChannel, false)

 	timezones, err := th.App.GetChannelMembersTimezones(th.BasicChannel.Id)
 	require.Nil(t, err, "Failed to get the timezones for a channel.")
@@ -1101,7 +1098,7 @@ func TestUpdateChannelMemberRolesChangingGuest(t *testing.T) {
 		_, _, err := th.App.AddUserToTeam(th.BasicTeam.Id, ruser.Id, "")
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel)
+		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel, false)
 		require.Nil(t, err)

 		_, err = th.App.UpdateChannelMemberRoles(th.BasicChannel.Id, ruser.Id, "channel_user")
@@ -1115,7 +1112,7 @@ func TestUpdateChannelMemberRolesChangingGuest(t *testing.T) {
 		_, _, err := th.App.AddUserToTeam(th.BasicTeam.Id, ruser.Id, "")
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel)
+		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel, false)
 		require.Nil(t, err)

 		_, err = th.App.UpdateChannelMemberRoles(th.BasicChannel.Id, ruser.Id, "channel_guest")
@@ -1129,7 +1126,7 @@ func TestUpdateChannelMemberRolesChangingGuest(t *testing.T) {
 		_, _, err := th.App.AddUserToTeam(th.BasicTeam.Id, ruser.Id, "")
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel)
+		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel, false)
 		require.Nil(t, err)

 		_, err = th.App.UpdateChannelMemberRoles(th.BasicChannel.Id, ruser.Id, "channel_user channel_admin")
@@ -1143,7 +1140,7 @@ func TestUpdateChannelMemberRolesChangingGuest(t *testing.T) {
 		_, _, err := th.App.AddUserToTeam(th.BasicTeam.Id, ruser.Id, "")
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel)
+		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel, false)
 		require.Nil(t, err)

 		_, err = th.App.CreateRole(&model.Role{Name: "custom", DisplayName: "custom", Description: "custom"})
@@ -1160,7 +1157,7 @@ func TestUpdateChannelMemberRolesChangingGuest(t *testing.T) {
 		_, _, err := th.App.AddUserToTeam(th.BasicTeam.Id, ruser.Id, "")
 		require.Nil(t, err)

-		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel)
+		_, err = th.App.AddUserToChannel(ruser, th.BasicChannel, false)
 		require.Nil(t, err)

 		_, err = th.App.UpdateChannelMemberRoles(th.BasicChannel.Id, ruser.Id, "channel_guest channel_user")
@@ -1205,9 +1202,9 @@ func TestSearchChannelsForUser(t *testing.T) {
 	}()

 	// add user to test-dev-1 and dev3
-	_, err = th.App.AddUserToChannel(th.BasicUser, c1)
+	_, err = th.App.AddUserToChannel(th.BasicUser, c1, false)
 	require.Nil(t, err)
-	_, err = th.App.AddUserToChannel(th.BasicUser, c3)
+	_, err = th.App.AddUserToChannel(th.BasicUser, c3, false)
 	require.Nil(t, err)

 	searchAndCheck := func(t *testing.T, term string, expectedDisplayNames []string) {
@@ -1231,7 +1228,7 @@ func TestSearchChannelsForUser(t *testing.T) {
 	})

 	t.Run("After adding user to test-dev-2, search for dev, the three channels should be returned", func(t *testing.T) {
-		_, err = th.App.AddUserToChannel(th.BasicUser, c2)
+		_, err = th.App.AddUserToChannel(th.BasicUser, c2, false)
 		require.Nil(t, err)

 		searchAndCheck(t, "dev", []string{"test-dev-1", "test-dev-2", "dev-3"})
@@ -1332,7 +1329,7 @@ func TestMarkChannelAsUnreadFromPost(t *testing.T) {

 	t.Run("Unread with mentions", func(t *testing.T) {
 		c2 := th.CreateChannel(th.BasicTeam)
-		_, err := th.App.AddUserToChannel(u2, c2)
+		_, err := th.App.AddUserToChannel(u2, c2, false)
 		require.Nil(t, err)

 		p4, err := th.App.CreatePost(&model.Post{
@@ -1445,7 +1442,7 @@ func TestAddUserToChannel(t *testing.T) {
 	require.Nil(t, err)

 	// Should allow a bot to be added to a public group synced channel
-	_, err = th.App.AddUserToChannel(botUser, th.BasicChannel)
+	_, err = th.App.AddUserToChannel(botUser, th.BasicChannel, false)
 	require.Nil(t, err)

 	// verify user was added as an admin
@@ -1466,11 +1463,11 @@ func TestAddUserToChannel(t *testing.T) {
 	require.Nil(t, err)

 	// Should allow a group synced user to be added to a group synced private channel
-	_, err = th.App.AddUserToChannel(ruser1, privateChannel)
+	_, err = th.App.AddUserToChannel(ruser1, privateChannel, false)
 	require.Nil(t, err)

 	// Should allow a bot to be added to a private group synced channel
-	_, err = th.App.AddUserToChannel(botUser, privateChannel)
+	_, err = th.App.AddUserToChannel(botUser, privateChannel, false)
 	require.Nil(t, err)
 }

@@ -1491,9 +1488,9 @@ func TestRemoveUserFromChannel(t *testing.T) {

 	privateChannel := th.CreatePrivateChannel(th.BasicTeam)

-	_, err := th.App.AddUserToChannel(ruser, privateChannel)
+	_, err := th.App.AddUserToChannel(ruser, privateChannel, false)
 	require.Nil(t, err)
-	_, err = th.App.AddUserToChannel(botUser, privateChannel)
+	_, err = th.App.AddUserToChannel(botUser, privateChannel, false)
 	require.Nil(t, err)

 	group := th.CreateGroup()
--- a/app/helper_test.go
+++ b/app/helper_test.go
@@ -422,7 +422,7 @@ func (th *TestHelper) RemoveUserFromTeam(user *model.User, team *model.Team) {
 func (th *TestHelper) AddUserToChannel(user *model.User, channel *model.Channel) *model.ChannelMember {
 	utils.DisableDebugLogForTest()

-	member, err := th.App.AddUserToChannel(user, channel)
+	member, err := th.App.AddUserToChannel(user, channel, false)
 	if err != nil {
 		panic(err)
 	}
--- a/app/notification_test.go
+++ b/app/notification_test.go
@@ -19,7 +19,7 @@ func TestSendNotifications(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()

-	th.App.AddUserToChannel(th.BasicUser2, th.BasicChannel)
+	th.App.AddUserToChannel(th.BasicUser2, th.BasicChannel, false)

 	post1, appErr := th.App.CreatePostMissingChannel(&model.Post{
 		UserId:    th.BasicUser.Id,
@@ -126,7 +126,7 @@ func TestSendNotificationsWithManyUsers(t *testing.T) {
 	for i := 0; i < 10; i++ {
 		user := th.CreateUser()
 		th.LinkUserToTeam(user, th.BasicTeam)
-		th.App.AddUserToChannel(user, th.BasicChannel)
+		th.App.AddUserToChannel(user, th.BasicChannel, false)
 		users = append(users, user)
 	}

@@ -217,9 +217,9 @@ func TestFilterOutOfChannelMentions(t *testing.T) {
 	th.LinkUserToTeam(user3, th.BasicTeam)
 	th.LinkUserToTeam(user4, th.BasicTeam)
 	th.LinkUserToTeam(guest, th.BasicTeam)
-	th.App.AddUserToChannel(guest, channel)
-	th.App.AddUserToChannel(user4, guestAndUser4Channel)
-	th.App.AddUserToChannel(guest, guestAndUser4Channel)
+	th.App.AddUserToChannel(guest, channel, false)
+	th.App.AddUserToChannel(user4, guestAndUser4Channel, false)
+	th.App.AddUserToChannel(guest, guestAndUser4Channel, false)

 	t.Run("should return users not in the channel", func(t *testing.T) {
 		post := &model.Post{}
@@ -2420,13 +2420,13 @@ func TestInsertGroupMentions(t *testing.T) {

 	groupChannelMember := th.CreateUser()
 	th.LinkUserToTeam(groupChannelMember, team)
-	th.App.AddUserToChannel(groupChannelMember, channel)
+	th.App.AddUserToChannel(groupChannelMember, channel, false)
 	_, err = th.App.UpsertGroupMember(group.Id, groupChannelMember.Id)
 	require.Nil(t, err)

 	nonGroupChannelMember := th.CreateUser()
 	th.LinkUserToTeam(nonGroupChannelMember, team)
-	th.App.AddUserToChannel(nonGroupChannelMember, channel)
+	th.App.AddUserToChannel(nonGroupChannelMember, channel, false)

 	nonChannelGroupMember := th.CreateUser()
 	th.LinkUserToTeam(nonChannelGroupMember, team)
--- a/app/opentracing/opentracing_layer.go
+++ b/app/opentracing/opentracing_layer.go
@@ -94,7 +94,7 @@ func (a *OpenTracingAppLayer) ActivateMfa(userID string, token string) *model.Ap
 	return resultVar0
 }

-func (a *OpenTracingAppLayer) AddChannelMember(userID string, channel *model.Channel, userRequestorId string, postRootId string) (*model.ChannelMember, *model.AppError) {
+func (a *OpenTracingAppLayer) AddChannelMember(userID string, channel *model.Channel, opts app.ChannelMemberOpts) (*model.ChannelMember, *model.AppError) {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.AddChannelMember")

@@ -106,7 +106,7 @@ func (a *OpenTracingAppLayer) AddChannelMember(userID string, channel *model.Cha
 	}()

 	defer span.Finish()
-	resultVar0, resultVar1 := a.app.AddChannelMember(userID, channel, userRequestorId, postRootId)
+	resultVar0, resultVar1 := a.app.AddChannelMember(userID, channel, opts)

 	if resultVar1 != nil {
 		span.LogFields(spanlog.Error(resultVar1))
@@ -457,7 +457,7 @@ func (a *OpenTracingAppLayer) AddTeamMembers(teamID string, userIDs []string, us
 	return resultVar0, resultVar1
 }

-func (a *OpenTracingAppLayer) AddUserToChannel(user *model.User, channel *model.Channel) (*model.ChannelMember, *model.AppError) {
+func (a *OpenTracingAppLayer) AddUserToChannel(user *model.User, channel *model.Channel, skipTeamMemberIntegrityCheck bool) (*model.ChannelMember, *model.AppError) {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.AddUserToChannel")

@@ -469,7 +469,7 @@ func (a *OpenTracingAppLayer) AddUserToChannel(user *model.User, channel *model.
 	}()

 	defer span.Finish()
-	resultVar0, resultVar1 := a.app.AddUserToChannel(user, channel)
+	resultVar0, resultVar1 := a.app.AddUserToChannel(user, channel, skipTeamMemberIntegrityCheck)

 	if resultVar1 != nil {
 		span.LogFields(spanlog.Error(resultVar1))
--- a/app/plugin_api.go
+++ b/app/plugin_api.go
@@ -478,27 +478,27 @@ func (api *PluginAPI) SearchPostsInTeamForUser(teamID string, userID string, sea
 }

 func (api *PluginAPI) AddChannelMember(channelID, userID string) (*model.ChannelMember, *model.AppError) {
-	// For now, don't allow overriding these via the plugin API.
-	userRequestorId := ""
-	postRootId := ""
-
 	channel, err := api.GetChannel(channelID)
 	if err != nil {
 		return nil, err
 	}

-	return api.app.AddChannelMember(userID, channel, userRequestorId, postRootId)
+	return api.app.AddChannelMember(userID, channel, ChannelMemberOpts{
+		// For now, don't allow overriding these via the plugin API.
+		UserRequestorID: "",
+		PostRootID:      "",
+	})
 }

-func (api *PluginAPI) AddUserToChannel(channelID, userID, asUserId string) (*model.ChannelMember, *model.AppError) {
-	postRootId := ""
-
+func (api *PluginAPI) AddUserToChannel(channelID, userID, asUserID string) (*model.ChannelMember, *model.AppError) {
 	channel, err := api.GetChannel(channelID)
 	if err != nil {
 		return nil, err
 	}

-	return api.app.AddChannelMember(userID, channel, asUserId, postRootId)
+	return api.app.AddChannelMember(userID, channel, ChannelMemberOpts{
+		UserRequestorID: asUserID,
+	})
 }

 func (api *PluginAPI) GetChannelMember(channelID, userID string) (*model.ChannelMember, *model.AppError) {
--- a/app/post_test.go
+++ b/app/post_test.go
@@ -338,7 +338,7 @@ func TestPostReplyToPostWhereRootPosterLeftChannel(t *testing.T) {
 	userNotInChannel := th.BasicUser
 	rootPost := th.BasicPost

-	_, err := th.App.AddUserToChannel(userInChannel, channel)
+	_, err := th.App.AddUserToChannel(userInChannel, channel, false)
 	require.Nil(t, err)

 	err = th.App.RemoveUserFromChannel(userNotInChannel.Id, "", channel)
@@ -421,7 +421,7 @@ func TestPostChannelMentions(t *testing.T) {
 	require.Nil(t, err)
 	defer th.App.PermanentDeleteChannel(channelToMention)

-	_, err = th.App.AddUserToChannel(user, channel)
+	_, err = th.App.AddUserToChannel(user, channel, false)
 	require.Nil(t, err)

 	post := &model.Post{
--- a/app/slashcommands/command_invite.go
+++ b/app/slashcommands/command_invite.go
@@ -140,7 +140,9 @@ func (*InviteProvider) DoCommand(a *app.App, args *model.CommandArgs, message st
 		}
 	}

-	if _, err := a.AddChannelMember(userProfile.Id, channelToJoin, args.UserId, ""); err != nil {
+	if _, err := a.AddChannelMember(userProfile.Id, channelToJoin, app.ChannelMemberOpts{
+		UserRequestorID: args.UserId,
+	}); err != nil {
 		var text string
 		if err.Id == "api.channel.add_members.user_denied" {
 			text = args.T("api.command_invite.group_constrained_user_denied")
--- a/app/slashcommands/command_invite_test.go
+++ b/app/slashcommands/command_invite_test.go
@@ -9,6 +9,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"

+	"github.com/mattermost/mattermost-server/v5/app"
 	"github.com/mattermost/mattermost-server/v5/model"
 )

@@ -72,7 +73,7 @@ func TestInviteProvider(t *testing.T) {
 	deactivatedUserPublicChannel := "@" + deactivatedUser.Username + " ~" + channel.Name

 	groupChannel := th.createChannel(th.BasicTeam, model.CHANNEL_PRIVATE)
-	_, err = th.App.AddChannelMember(th.BasicUser.Id, groupChannel, "", "")
+	_, err = th.App.AddChannelMember(th.BasicUser.Id, groupChannel, app.ChannelMemberOpts{})
 	require.Nil(t, err)
 	groupChannel.GroupConstrained = model.NewBool(true)
 	groupChannel, _ = th.App.UpdateChannel(groupChannel)
--- a/app/slashcommands/command_leave_test.go
+++ b/app/slashcommands/command_leave_test.go
@@ -41,11 +41,11 @@ func TestLeaveProviderDoCommand(t *testing.T) {
 	guest := th.createGuest()

 	th.App.AddUserToTeam(th.BasicTeam.Id, th.BasicUser.Id, th.BasicUser.Id)
-	th.App.AddUserToChannel(th.BasicUser, publicChannel)
-	th.App.AddUserToChannel(th.BasicUser, privateChannel)
+	th.App.AddUserToChannel(th.BasicUser, publicChannel, false)
+	th.App.AddUserToChannel(th.BasicUser, privateChannel, false)
 	th.App.AddUserToTeam(th.BasicTeam.Id, guest.Id, guest.Id)
-	th.App.AddUserToChannel(guest, publicChannel)
-	th.App.AddUserToChannel(guest, defaultChannel)
+	th.App.AddUserToChannel(guest, publicChannel, false)
+	th.App.AddUserToChannel(guest, defaultChannel, false)

 	t.Run("Should error when no Channel ID in args", func(t *testing.T) {
 		args := &model.CommandArgs{
--- a/app/slashcommands/command_remove_test.go
+++ b/app/slashcommands/command_remove_test.go
@@ -35,8 +35,8 @@ func TestRemoveProviderDoCommand(t *testing.T) {

 	targetUser := th.createUser()
 	th.App.AddUserToTeam(th.BasicTeam.Id, targetUser.Id, targetUser.Id)
-	th.App.AddUserToChannel(targetUser, publicChannel)
-	th.App.AddUserToChannel(targetUser, privateChannel)
+	th.App.AddUserToChannel(targetUser, publicChannel, false)
+	th.App.AddUserToChannel(targetUser, privateChannel, false)

 	// Try a public channel *without* permission.
 	args := &model.CommandArgs{
@@ -49,7 +49,7 @@ func TestRemoveProviderDoCommand(t *testing.T) {
 	assert.Equal(t, "api.command_remove.permission.app_error", actual)

 	// Try a public channel *with* permission.
-	th.App.AddUserToChannel(th.BasicUser, publicChannel)
+	th.App.AddUserToChannel(th.BasicUser, publicChannel, false)
 	args = &model.CommandArgs{
 		T:         func(s string, args ...interface{}) string { return s },
 		ChannelId: publicChannel.Id,
@@ -70,7 +70,7 @@ func TestRemoveProviderDoCommand(t *testing.T) {
 	assert.Equal(t, "api.command_remove.permission.app_error", actual)

 	// Try a private channel *with* permission.
-	th.App.AddUserToChannel(th.BasicUser, privateChannel)
+	th.App.AddUserToChannel(th.BasicUser, privateChannel, false)
 	args = &model.CommandArgs{
 		T:         func(s string, args ...interface{}) string { return s },
 		ChannelId: privateChannel.Id,
@@ -110,7 +110,7 @@ func TestRemoveProviderDoCommand(t *testing.T) {
 	// Try a public channel with a deactivated user.
 	deactivatedUser := th.createUser()
 	th.App.AddUserToTeam(th.BasicTeam.Id, deactivatedUser.Id, deactivatedUser.Id)
-	th.App.AddUserToChannel(deactivatedUser, publicChannel)
+	th.App.AddUserToChannel(deactivatedUser, publicChannel, false)
 	th.App.UpdateActive(deactivatedUser, false)

 	args = &model.CommandArgs{
--- a/app/slashcommands/helper_test.go
+++ b/app/slashcommands/helper_test.go
@@ -358,7 +358,7 @@ func (th *TestHelper) linkUserToTeam(user *model.User, team *model.Team) {
 func (th *TestHelper) addUserToChannel(user *model.User, channel *model.Channel) *model.ChannelMember {
 	utils.DisableDebugLogForTest()

-	member, err := th.App.AddUserToChannel(user, channel)
+	member, err := th.App.AddUserToChannel(user, channel, false)
 	if err != nil {
 		panic(err)
 	}
--- a/app/syncables.go
+++ b/app/syncables.go
@@ -52,7 +52,9 @@ func (a *App) createDefaultChannelMemberships(since int64, channelID *string) er
 			)
 		}

-		_, err = a.AddChannelMember(userChannel.UserID, channel, "", "")
+		_, err = a.AddChannelMember(userChannel.UserID, channel, ChannelMemberOpts{
+			SkipTeamMemberIntegrityCheck: true,
+		})
 		if err != nil {
 			if err.Id == "api.channel.add_user.to.channel.failed.deleted.app_error" {
 				a.Log().Info("Not adding user to channel because they have already left the team",
--- a/app/syncables_test.go
+++ b/app/syncables_test.go
@@ -262,7 +262,7 @@ func TestCreateDefaultMemberships(t *testing.T) {
 	}

 	// Ensure members are in channel
-	_, err = th.App.AddChannelMember(scientist1.Id, experimentsChannel, "", "")
+	_, err = th.App.AddChannelMember(scientist1.Id, experimentsChannel, ChannelMemberOpts{})
 	if err != nil {
 		t.Errorf("unable to add user to channel: %s", err.Error())
 	}
@@ -272,7 +272,7 @@ func TestCreateDefaultMemberships(t *testing.T) {
 	if err != nil {
 		t.Errorf("unable to add user to team: %s", err.Error())
 	}
-	_, err = th.App.AddChannelMember(singer1.Id, experimentsChannel, "", "")
+	_, err = th.App.AddChannelMember(singer1.Id, experimentsChannel, ChannelMemberOpts{})
 	if err != nil {
 		t.Errorf("unable to add user to channel: %s", err.Error())
 	}
@@ -388,7 +388,7 @@ func TestDeleteGroupMemberships(t *testing.T) {
 		_, err = th.App.AddTeamMember(th.BasicTeam.Id, userID)
 		require.Nil(t, err)

-		_, err = th.App.AddChannelMember(userID, th.BasicChannel, "", "")
+		_, err = th.App.AddChannelMember(userID, th.BasicChannel, ChannelMemberOpts{})
 		require.Nil(t, err)
 	}

--- a/app/team.go
+++ b/app/team.go
@@ -623,7 +623,7 @@ func (a *App) AddUserToTeamByToken(userID string, tokenID string) (*model.Team,
 		}

 		for _, channel := range channels {
-			_, err := a.AddUserToChannel(user, channel)
+			_, err := a.AddUserToChannel(user, channel, false)
 			if err != nil {
 				mlog.Warn("Error adding user to channel", mlog.Err(err))
 			}
--- a/app/user.go
+++ b/app/user.go
@@ -104,7 +104,7 @@ func (a *App) CreateUserWithToken(user *model.User, token *model.Token) (*model.

 	if token.Type == TokenTypeGuestInvitation {
 		for _, channel := range channels {
-			_, err := a.AddChannelMember(ruser.Id, channel, "", "")
+			_, err := a.AddChannelMember(ruser.Id, channel, ChannelMemberOpts{})
 			if err != nil {
 				mlog.Warn("Failed to add channel member", mlog.Err(err))
 			}
--- a/app/user_test.go
+++ b/app/user_test.go
@@ -993,9 +993,9 @@ func TestGetViewUsersRestrictions(t *testing.T) {
 	team2townsquare, err := th.App.GetChannelByName("town-square", team2.Id, false)
 	require.Nil(t, err)

-	th.App.AddUserToChannel(user1, team1channel1)
-	th.App.AddUserToChannel(user1, team1channel2)
-	th.App.AddUserToChannel(user1, team2channel1)
+	th.App.AddUserToChannel(user1, team1channel1, false)
+	th.App.AddUserToChannel(user1, team1channel2, false)
+	th.App.AddUserToChannel(user1, team2channel1, false)

 	addPermission := func(role *model.Role, permission string) *model.AppError {
 		newPermissions := append(role.Permissions, permission)