gotd: ensure user is member of channels before starting getDifference loop

pkg/gotd/telegram/updates/manager.go

@@ -2,6 +2,7 @@ package updates
 
 import (
 	"context"
+	"fmt"
 	"sync"
 
 	"github.com/go-faster/errors"
@@ -11,6 +12,7 @@ import (
 
 	"go.mau.fi/mautrix-telegram/pkg/gotd/telegram"
 	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tgerr"
 )
 
 var _ telegram.UpdateHandler = (*Manager)(nil)
@@ -74,6 +76,47 @@ type AuthOptions struct {
 	OnStart func(ctx context.Context)
 }
 
+type PtsAccessHashTuple struct {
+	Pts        int
+	AccessHash int64
+}
+
+func (m *Manager) checkParticipant(ctx context.Context, api API, userID, channelID, hash int64) error {
+	lg := m.lg.With(zap.Int64("channel_id", channelID))
+	lg.Info("Ensuring user is still in channel")
+	pcp, err := api.ChannelsGetParticipant(ctx, &tg.ChannelsGetParticipantRequest{
+		Channel: &tg.InputChannel{
+			ChannelID:  channelID,
+			AccessHash: hash,
+		},
+		Participant: &tg.InputPeerSelf{},
+	})
+	if err != nil {
+		if tgerr.Is(err, tg.ErrChannelInvalid, tg.ErrChannelPrivate, tg.ErrUserNotParticipant) {
+			lg.Warn("Removing update state for channel after error", zap.Error(err))
+		} else {
+			lg.Error("channels.getParticipant failed", zap.Error(err))
+			// TODO fatal error?
+			return nil
+		}
+	} else {
+		switch pcp.Participant.(type) {
+		case *tg.ChannelParticipantLeft, *tg.ChannelParticipantBanned:
+			lg.Warn("Removing update state for channel as user is left or banned")
+		default:
+			lg.Debug("Membership confirmed", zap.Any("participant", pcp.Participant))
+			return nil
+		}
+	}
+
+	if err := m.cfg.Storage.SetChannelPts(ctx, userID, channelID, -1); err != nil {
+		return fmt.Errorf("failed to clear pts: %w", err)
+	} else if err = m.cfg.OnNotChannelMember(ctx, channelID); err != nil {
+		return fmt.Errorf("OnNotChannelMember callback failed: %w", err)
+	}
+	return nil
+}
+
 // Run notifies manager about user authentication on the telegram server.
 //
 // If forget is true, local internalState (if exist) will be overwritten
@@ -101,10 +144,7 @@ func (m *Manager) Run(ctx context.Context, api API, userID int64, opt AuthOption
 		if err != nil {
 			return errors.Wrap(err, "load internalState")
 		}
-		channels := make(map[int64]struct {
-			Pts        int
-			AccessHash int64
-		})
+		channels := make(map[int64]PtsAccessHashTuple)
 		if err := m.cfg.Storage.ForEachChannels(ctx, userID, func(ctx context.Context, channelID int64, pts int) error {
 			if pts == -1 {
 				return nil
@@ -112,16 +152,12 @@ func (m *Manager) Run(ctx context.Context, api API, userID int64, opt AuthOption
 			hash, found, err := m.cfg.AccessHasher.GetChannelAccessHash(ctx, userID, channelID)
 			if err != nil {
 				return errors.Wrap(err, "get channel access hash")
-			}
-
-			if !found {
+			} else if !found {
 				return nil
+			} else if err = m.checkParticipant(ctx, api, userID, channelID, hash); err != nil {
+				return fmt.Errorf("failed to check if user is participant of channel %d: %w", channelID, err)
 			}
-
-			channels[channelID] = struct {
-				Pts        int
-				AccessHash int64
-			}{Pts: pts, AccessHash: hash}
+			channels[channelID] = PtsAccessHashTuple{Pts: pts, AccessHash: hash}
 			return nil
 		}); err != nil {
 			return errors.Wrap(err, "iterate channels")