Implement /sync limited and read timeline limit from stored filters (#1168)

* Move filter table to syncapi where it is used

* Implement /sync `limited` and read timeline limit from stored filters

We now fully handle `room.timeline.limit` filters (in-line + stored) and
return the right value for `limited` syncs.

* Update whitelist

* Default to the default timeline limit if it's unset, also strip the extra event correctly

* Update whitelist

syncapi/routing/filter.go

@@ -0,0 +1,128 @@
+// Copyright 2017 Jan Christian Grünhage
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package routing
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/sync"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	"github.com/tidwall/gjson"
+)
+
+// GetFilter implements GET /_matrix/client/r0/user/{userId}/filter/{filterId}
+func GetFilter(
+	req *http.Request, device *api.Device, syncDB storage.Database, userID string, filterID string,
+) util.JSONResponse {
+	if userID != device.UserID {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: jsonerror.Forbidden("Cannot get filters for other users"),
+		}
+	}
+	localpart, _, err := gomatrixserverlib.SplitID('@', userID)
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
+		return jsonerror.InternalServerError()
+	}
+
+	filter, err := syncDB.GetFilter(req.Context(), localpart, filterID)
+	if err != nil {
+		//TODO better error handling. This error message is *probably* right,
+		// but if there are obscure db errors, this will also be returned,
+		// even though it is not correct.
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.NotFound("No such filter"),
+		}
+	}
+
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: filter,
+	}
+}
+
+type filterResponse struct {
+	FilterID string `json:"filter_id"`
+}
+
+//PutFilter implements POST /_matrix/client/r0/user/{userId}/filter
+func PutFilter(
+	req *http.Request, device *api.Device, syncDB storage.Database, userID string,
+) util.JSONResponse {
+	if userID != device.UserID {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: jsonerror.Forbidden("Cannot create filters for other users"),
+		}
+	}
+
+	localpart, _, err := gomatrixserverlib.SplitID('@', userID)
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
+		return jsonerror.InternalServerError()
+	}
+
+	var filter gomatrixserverlib.Filter
+
+	defer req.Body.Close() // nolint:errcheck
+	body, err := ioutil.ReadAll(req.Body)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON("The request body could not be read. " + err.Error()),
+		}
+	}
+
+	if err = json.Unmarshal(body, &filter); err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON("The request body could not be decoded into valid JSON. " + err.Error()),
+		}
+	}
+	// the filter `limit` is `int` which defaults to 0 if not set which is not what we want. We want to use the default
+	// limit if it is unset, which is what this does.
+	limitRes := gjson.GetBytes(body, "room.timeline.limit")
+	if !limitRes.Exists() {
+		util.GetLogger(req.Context()).Infof("missing timeline limit, using default")
+		filter.Room.Timeline.Limit = sync.DefaultTimelineLimit
+	}
+
+	// Validate generates a user-friendly error
+	if err = filter.Validate(); err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON("Invalid filter: " + err.Error()),
+		}
+	}
+
+	filterID, err := syncDB.PutFilter(req.Context(), localpart, &filter)
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).Error("syncDB.PutFilter failed")
+		return jsonerror.InternalServerError()
+	}
+
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: filterResponse{FilterID: filterID},
+	}
+}

syncapi/routing/routing.go

@@ -55,4 +55,24 @@ func Setup(
 		}
 		return OnIncomingMessagesRequest(req, syncDB, vars["roomID"], federation, rsAPI, cfg)
 	})).Methods(http.MethodGet, http.MethodOptions)
+
+	r0mux.Handle("/user/{userId}/filter",
+		httputil.MakeAuthAPI("put_filter", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+			if err != nil {
+				return util.ErrorResponse(err)
+			}
+			return PutFilter(req, device, syncDB, vars["userId"])
+		}),
+	).Methods(http.MethodPost, http.MethodOptions)
+
+	r0mux.Handle("/user/{userId}/filter/{filterId}",
+		httputil.MakeAuthAPI("get_filter", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+			if err != nil {
+				return util.ErrorResponse(err)
+			}
+			return GetFilter(req, device, syncDB, vars["userId"], vars["filterId"])
+		}),
+	).Methods(http.MethodGet, http.MethodOptions)
 }

syncapi/storage/interface.go

@@ -128,4 +128,12 @@ type Database interface {
 	CleanSendToDeviceUpdates(ctx context.Context, toUpdate, toDelete []types.SendToDeviceNID, token types.StreamingToken) (err error)
 	// SendToDeviceUpdatesWaiting returns true if there are send-to-device updates waiting to be sent.
 	SendToDeviceUpdatesWaiting(ctx context.Context, userID, deviceID string) (bool, error)
+	// GetFilter looks up the filter associated with a given local user and filter ID.
+	// Returns a filter structure. Otherwise returns an error if no such filter exists
+	// or if there was an error talking to the database.
+	GetFilter(ctx context.Context, localpart string, filterID string) (*gomatrixserverlib.Filter, error)
+	// PutFilter puts the passed filter into the database.
+	// Returns the filterID as a string. Otherwise returns an error if something
+	// goes wrong.
+	PutFilter(ctx context.Context, localpart string, filter *gomatrixserverlib.Filter) (string, error)
 }

syncapi/storage/postgres/filter_table.go

@@ -0,0 +1,129 @@
+// Copyright 2017 Jan Christian Grünhage
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+
+	"github.com/matrix-org/dendrite/syncapi/storage/tables"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const filterSchema = `
+-- Stores data about filters
+CREATE TABLE IF NOT EXISTS syncapi_filter (
+	-- The filter
+	filter TEXT NOT NULL,
+	-- The ID
+	id SERIAL UNIQUE,
+	-- The localpart of the Matrix user ID associated to this filter
+	localpart TEXT NOT NULL,
+
+	PRIMARY KEY(id, localpart)
+);
+
+CREATE INDEX IF NOT EXISTS syncapi_filter_localpart ON syncapi_filter(localpart);
+`
+
+const selectFilterSQL = "" +
+	"SELECT filter FROM syncapi_filter WHERE localpart = $1 AND id = $2"
+
+const selectFilterIDByContentSQL = "" +
+	"SELECT id FROM syncapi_filter WHERE localpart = $1 AND filter = $2"
+
+const insertFilterSQL = "" +
+	"INSERT INTO syncapi_filter (filter, id, localpart) VALUES ($1, DEFAULT, $2) RETURNING id"
+
+type filterStatements struct {
+	selectFilterStmt            *sql.Stmt
+	selectFilterIDByContentStmt *sql.Stmt
+	insertFilterStmt            *sql.Stmt
+}
+
+func NewPostgresFilterTable(db *sql.DB) (tables.Filter, error) {
+	_, err := db.Exec(filterSchema)
+	if err != nil {
+		return nil, err
+	}
+	s := &filterStatements{}
+	if s.selectFilterStmt, err = db.Prepare(selectFilterSQL); err != nil {
+		return nil, err
+	}
+	if s.selectFilterIDByContentStmt, err = db.Prepare(selectFilterIDByContentSQL); err != nil {
+		return nil, err
+	}
+	if s.insertFilterStmt, err = db.Prepare(insertFilterSQL); err != nil {
+		return nil, err
+	}
+	return s, nil
+}
+
+func (s *filterStatements) SelectFilter(
+	ctx context.Context, localpart string, filterID string,
+) (*gomatrixserverlib.Filter, error) {
+	// Retrieve filter from database (stored as canonical JSON)
+	var filterData []byte
+	err := s.selectFilterStmt.QueryRowContext(ctx, localpart, filterID).Scan(&filterData)
+	if err != nil {
+		return nil, err
+	}
+
+	// Unmarshal JSON into Filter struct
+	var filter gomatrixserverlib.Filter
+	if err = json.Unmarshal(filterData, &filter); err != nil {
+		return nil, err
+	}
+	return &filter, nil
+}
+
+func (s *filterStatements) InsertFilter(
+	ctx context.Context, filter *gomatrixserverlib.Filter, localpart string,
+) (filterID string, err error) {
+	var existingFilterID string
+
+	// Serialise json
+	filterJSON, err := json.Marshal(filter)
+	if err != nil {
+		return "", err
+	}
+	// Remove whitespaces and sort JSON data
+	// needed to prevent from inserting the same filter multiple times
+	filterJSON, err = gomatrixserverlib.CanonicalJSON(filterJSON)
+	if err != nil {
+		return "", err
+	}
+
+	// Check if filter already exists in the database using its localpart and content
+	//
+	// This can result in a race condition when two clients try to insert the
+	// same filter and localpart at the same time, however this is not a
+	// problem as both calls will result in the same filterID
+	err = s.selectFilterIDByContentStmt.QueryRowContext(ctx,
+		localpart, filterJSON).Scan(&existingFilterID)
+	if err != nil && err != sql.ErrNoRows {
+		return "", err
+	}
+	// If it does, return the existing ID
+	if existingFilterID != "" {
+		return existingFilterID, err
+	}
+
+	// Otherwise insert the filter and return the new ID
+	err = s.insertFilterStmt.QueryRowContext(ctx, filterJSON, localpart).
+		Scan(&filterID)
+	return
+}

syncapi/storage/postgres/output_room_events_table.go

@@ -301,21 +301,21 @@ func (s *outputRoomEventsStatements) SelectRecentEvents(
 	ctx context.Context, txn *sql.Tx,
 	roomID string, r types.Range, limit int,
 	chronologicalOrder bool, onlySyncEvents bool,
-) ([]types.StreamEvent, error) {
+) ([]types.StreamEvent, bool, error) {
 	var stmt *sql.Stmt
 	if onlySyncEvents {
 		stmt = sqlutil.TxStmt(txn, s.selectRecentEventsForSyncStmt)
 	} else {
 		stmt = sqlutil.TxStmt(txn, s.selectRecentEventsStmt)
 	}
-	rows, err := stmt.QueryContext(ctx, roomID, r.Low(), r.High(), limit)
+	rows, err := stmt.QueryContext(ctx, roomID, r.Low(), r.High(), limit+1)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 	defer internal.CloseAndLogIfError(ctx, rows, "selectRecentEvents: rows.close() failed")
 	events, err := rowsToStreamEvents(rows)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 	if chronologicalOrder {
 		// The events need to be returned from oldest to latest, which isn't
@@ -325,7 +325,19 @@ func (s *outputRoomEventsStatements) SelectRecentEvents(
 			return events[i].StreamPosition < events[j].StreamPosition
 		})
 	}
-	return events, nil
+	// we queried for 1 more than the limit, so if we returned one more mark limited=true
+	limited := false
+	if len(events) > limit {
+		limited = true
+		// re-slice the extra (oldest) event out: in chronological order this is the first entry, else the last.
+		if chronologicalOrder {
+			events = events[1:]
+		} else {
+			events = events[:len(events)-1]
+		}
+	}
+
+	return events, limited, nil
 }
 
 // selectEarlyEvents returns the earliest events in the given room, starting

syncapi/storage/postgres/syncserver.go

@@ -71,6 +71,10 @@ func NewDatabase(dbDataSourceName string, dbProperties sqlutil.DbProperties) (*S
 	if err != nil {
 		return nil, err
 	}
+	filter, err := NewPostgresFilterTable(d.db)
+	if err != nil {
+		return nil, err
+	}
 	d.Database = shared.Database{
 		DB:                  d.db,
 		Invites:             invites,
@@ -79,6 +83,7 @@ func NewDatabase(dbDataSourceName string, dbProperties sqlutil.DbProperties) (*S
 		Topology:            topology,
 		CurrentRoomState:    currState,
 		BackwardExtremities: backwardExtremities,
+		Filter:              filter,
 		SendToDevice:        sendToDevice,
 		SendToDeviceWriter:  sqlutil.NewTransactionWriter(),
 		EDUCache:            cache.New(),

syncapi/storage/shared/syncserver.go

@@ -43,6 +43,7 @@ type Database struct {
 	CurrentRoomState    tables.CurrentRoomState
 	BackwardExtremities tables.BackwardsExtremities
 	SendToDevice        tables.SendToDevice
+	Filter              tables.Filter
 	SendToDeviceWriter  *sqlutil.TransactionWriter
 	EDUCache            *cache.EDUCache
 }
@@ -78,7 +79,7 @@ func (d *Database) GetEventsInStreamingRange(
 	}
 	if backwardOrdering {
 		// When using backward ordering, we want the most recent events first.
-		if events, err = d.OutputEvents.SelectRecentEvents(
+		if events, _, err = d.OutputEvents.SelectRecentEvents(
 			ctx, nil, roomID, r, limit, false, false,
 		); err != nil {
 			return
@@ -545,6 +546,18 @@ func (d *Database) addEDUDeltaToResponse(
 	return
 }
 
+func (d *Database) GetFilter(
+	ctx context.Context, localpart string, filterID string,
+) (*gomatrixserverlib.Filter, error) {
+	return d.Filter.SelectFilter(ctx, localpart, filterID)
+}
+
+func (d *Database) PutFilter(
+	ctx context.Context, localpart string, filter *gomatrixserverlib.Filter,
+) (string, error) {
+	return d.Filter.InsertFilter(ctx, filter, localpart)
+}
+
 func (d *Database) IncrementalSync(
 	ctx context.Context, res *types.Response,
 	device userapi.Device,
@@ -642,7 +655,8 @@ func (d *Database) getResponseWithPDUsForCompleteSync(
 		// TODO: When filters are added, we may need to call this multiple times to get enough events.
 		//       See: https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L316
 		var recentStreamEvents []types.StreamEvent
-		recentStreamEvents, err = d.OutputEvents.SelectRecentEvents(
+		var limited bool
+		recentStreamEvents, limited, err = d.OutputEvents.SelectRecentEvents(
 			ctx, txn, roomID, r, numRecentEventsPerRoom, true, true,
 		)
 		if err != nil {
@@ -670,7 +684,7 @@ func (d *Database) getResponseWithPDUsForCompleteSync(
 		jr := types.NewJoinResponse()
 		jr.Timeline.PrevBatch = prevBatchStr
 		jr.Timeline.Events = gomatrixserverlib.HeaderedToClientEvents(recentEvents, gomatrixserverlib.FormatSync)
-		jr.Timeline.Limited = true
+		jr.Timeline.Limited = limited
 		jr.State.Events = gomatrixserverlib.HeaderedToClientEvents(stateEvents, gomatrixserverlib.FormatSync)
 		res.Rooms.Join[roomID] = *jr
 	}
@@ -776,7 +790,7 @@ func (d *Database) addRoomDeltaToResponse(
 		// This is all "okay" assuming history_visibility == "shared" which it is by default.
 		r.To = delta.membershipPos
 	}
-	recentStreamEvents, err := d.OutputEvents.SelectRecentEvents(
+	recentStreamEvents, limited, err := d.OutputEvents.SelectRecentEvents(
 		ctx, txn, delta.roomID, r,
 		numRecentEventsPerRoom, true, true,
 	)
@@ -796,7 +810,7 @@ func (d *Database) addRoomDeltaToResponse(
 
 		jr.Timeline.PrevBatch = prevBatch.String()
 		jr.Timeline.Events = gomatrixserverlib.HeaderedToClientEvents(recentEvents, gomatrixserverlib.FormatSync)
-		jr.Timeline.Limited = false // TODO: if len(events) >= numRecents + 1 and then set limited:true
+		jr.Timeline.Limited = limited
 		jr.State.Events = gomatrixserverlib.HeaderedToClientEvents(delta.stateEvents, gomatrixserverlib.FormatSync)
 		res.Rooms.Join[delta.roomID] = *jr
 	case gomatrixserverlib.Leave:

syncapi/storage/sqlite3/filter_table.go

@@ -0,0 +1,137 @@
+// Copyright 2017 Jan Christian Grünhage
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/syncapi/storage/tables"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const filterSchema = `
+-- Stores data about filters
+CREATE TABLE IF NOT EXISTS syncapi_filter (
+	-- The filter
+	filter TEXT NOT NULL,
+	-- The ID
+	id INTEGER PRIMARY KEY AUTOINCREMENT,
+	-- The localpart of the Matrix user ID associated to this filter
+	localpart TEXT NOT NULL,
+
+	UNIQUE (id, localpart)
+);
+
+CREATE INDEX IF NOT EXISTS syncapi_filter_localpart ON syncapi_filter(localpart);
+`
+
+const selectFilterSQL = "" +
+	"SELECT filter FROM syncapi_filter WHERE localpart = $1 AND id = $2"
+
+const selectFilterIDByContentSQL = "" +
+	"SELECT id FROM syncapi_filter WHERE localpart = $1 AND filter = $2"
+
+const insertFilterSQL = "" +
+	"INSERT INTO syncapi_filter (filter, localpart) VALUES ($1, $2)"
+
+type filterStatements struct {
+	selectFilterStmt            *sql.Stmt
+	selectFilterIDByContentStmt *sql.Stmt
+	insertFilterStmt            *sql.Stmt
+}
+
+func NewSqliteFilterTable(db *sql.DB) (tables.Filter, error) {
+	_, err := db.Exec(filterSchema)
+	if err != nil {
+		return nil, err
+	}
+	s := &filterStatements{}
+	if s.selectFilterStmt, err = db.Prepare(selectFilterSQL); err != nil {
+		return nil, err
+	}
+	if s.selectFilterIDByContentStmt, err = db.Prepare(selectFilterIDByContentSQL); err != nil {
+		return nil, err
+	}
+	if s.insertFilterStmt, err = db.Prepare(insertFilterSQL); err != nil {
+		return nil, err
+	}
+	return s, nil
+}
+
+func (s *filterStatements) SelectFilter(
+	ctx context.Context, localpart string, filterID string,
+) (*gomatrixserverlib.Filter, error) {
+	// Retrieve filter from database (stored as canonical JSON)
+	var filterData []byte
+	err := s.selectFilterStmt.QueryRowContext(ctx, localpart, filterID).Scan(&filterData)
+	if err != nil {
+		return nil, err
+	}
+
+	// Unmarshal JSON into Filter struct
+	var filter gomatrixserverlib.Filter
+	if err = json.Unmarshal(filterData, &filter); err != nil {
+		return nil, err
+	}
+	return &filter, nil
+}
+
+func (s *filterStatements) InsertFilter(
+	ctx context.Context, filter *gomatrixserverlib.Filter, localpart string,
+) (filterID string, err error) {
+	var existingFilterID string
+
+	// Serialise json
+	filterJSON, err := json.Marshal(filter)
+	if err != nil {
+		return "", err
+	}
+	// Remove whitespaces and sort JSON data
+	// needed to prevent from inserting the same filter multiple times
+	filterJSON, err = gomatrixserverlib.CanonicalJSON(filterJSON)
+	if err != nil {
+		return "", err
+	}
+
+	// Check if filter already exists in the database using its localpart and content
+	//
+	// This can result in a race condition when two clients try to insert the
+	// same filter and localpart at the same time, however this is not a
+	// problem as both calls will result in the same filterID
+	err = s.selectFilterIDByContentStmt.QueryRowContext(ctx,
+		localpart, filterJSON).Scan(&existingFilterID)
+	if err != nil && err != sql.ErrNoRows {
+		return "", err
+	}
+	// If it does, return the existing ID
+	if existingFilterID != "" {
+		return existingFilterID, err
+	}
+
+	// Otherwise insert the filter and return the new ID
+	res, err := s.insertFilterStmt.ExecContext(ctx, filterJSON, localpart)
+	if err != nil {
+		return "", err
+	}
+	rowid, err := res.LastInsertId()
+	if err != nil {
+		return "", err
+	}
+	filterID = fmt.Sprintf("%d", rowid)
+	return
+}

syncapi/storage/sqlite3/output_room_events_table.go

@@ -311,7 +311,7 @@ func (s *outputRoomEventsStatements) SelectRecentEvents(
 	ctx context.Context, txn *sql.Tx,
 	roomID string, r types.Range, limit int,
 	chronologicalOrder bool, onlySyncEvents bool,
-) ([]types.StreamEvent, error) {
+) ([]types.StreamEvent, bool, error) {
 	var stmt *sql.Stmt
 	if onlySyncEvents {
 		stmt = sqlutil.TxStmt(txn, s.selectRecentEventsForSyncStmt)
@@ -319,14 +319,14 @@ func (s *outputRoomEventsStatements) SelectRecentEvents(
 		stmt = sqlutil.TxStmt(txn, s.selectRecentEventsStmt)
 	}
 
-	rows, err := stmt.QueryContext(ctx, roomID, r.Low(), r.High(), limit)
+	rows, err := stmt.QueryContext(ctx, roomID, r.Low(), r.High(), limit+1)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 	defer internal.CloseAndLogIfError(ctx, rows, "selectRecentEvents: rows.close() failed")
 	events, err := rowsToStreamEvents(rows)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 	if chronologicalOrder {
 		// The events need to be returned from oldest to latest, which isn't
@@ -336,7 +336,18 @@ func (s *outputRoomEventsStatements) SelectRecentEvents(
 			return events[i].StreamPosition < events[j].StreamPosition
 		})
 	}
-	return events, nil
+	// we queried for 1 more than the limit, so if we returned one more mark limited=true
+	limited := false
+	if len(events) > limit {
+		limited = true
+		// re-slice the extra (oldest) event out: in chronological order this is the first entry, else the last.
+		if chronologicalOrder {
+			events = events[1:]
+		} else {
+			events = events[:len(events)-1]
+		}
+	}
+	return events, limited, nil
 }
 
 func (s *outputRoomEventsStatements) SelectEarlyEvents(

syncapi/storage/sqlite3/syncserver.go

@@ -87,6 +87,10 @@ func (d *SyncServerDatasource) prepare() (err error) {
 	if err != nil {
 		return err
 	}
+	filter, err := NewSqliteFilterTable(d.db)
+	if err != nil {
+		return err
+	}
 	d.Database = shared.Database{
 		DB:                  d.db,
 		Invites:             invites,
@@ -95,6 +99,7 @@ func (d *SyncServerDatasource) prepare() (err error) {
 		BackwardExtremities: bwExtrem,
 		CurrentRoomState:    roomState,
 		Topology:            topology,
+		Filter:              filter,
 		SendToDevice:        sendToDevice,
 		SendToDeviceWriter:  sqlutil.NewTransactionWriter(),
 		EDUCache:            cache.New(),

syncapi/storage/tables/interface.go

@@ -44,8 +44,8 @@ type Events interface {
 	InsertEvent(ctx context.Context, txn *sql.Tx, event *gomatrixserverlib.HeaderedEvent, addState, removeState []string, transactionID *api.TransactionID, excludeFromSync bool) (streamPos types.StreamPosition, err error)
 	// SelectRecentEvents returns events between the two stream positions: exclusive of low and inclusive of high.
 	// If onlySyncEvents has a value of true, only returns the events that aren't marked as to exclude from sync.
-	// Returns up to `limit` events.
-	SelectRecentEvents(ctx context.Context, txn *sql.Tx, roomID string, r types.Range, limit int, chronologicalOrder bool, onlySyncEvents bool) ([]types.StreamEvent, error)
+	// Returns up to `limit` events. Returns `limited=true` if there are more events in this range but we hit the `limit`.
+	SelectRecentEvents(ctx context.Context, txn *sql.Tx, roomID string, r types.Range, limit int, chronologicalOrder bool, onlySyncEvents bool) ([]types.StreamEvent, bool, error)
 	// SelectEarlyEvents returns the earliest events in the given room.
 	SelectEarlyEvents(ctx context.Context, txn *sql.Tx, roomID string, r types.Range, limit int) ([]types.StreamEvent, error)
 	SelectEvents(ctx context.Context, txn *sql.Tx, eventIDs []string) ([]types.StreamEvent, error)
@@ -133,3 +133,8 @@ type SendToDevice interface {
 	DeleteSendToDeviceMessages(ctx context.Context, txn *sql.Tx, nids []types.SendToDeviceNID) (err error)
 	CountSendToDeviceMessages(ctx context.Context, txn *sql.Tx, userID, deviceID string) (count int, err error)
 }
+
+type Filter interface {
+	SelectFilter(ctx context.Context, localpart string, filterID string) (*gomatrixserverlib.Filter, error)
+	InsertFilter(ctx context.Context, filter *gomatrixserverlib.Filter, localpart string) (filterID string, err error)
+}

syncapi/sync/notifier_test.go

@@ -363,7 +363,7 @@ func newTestSyncRequest(userID, deviceID string, since types.StreamingToken) syn
 		timeout:       1 * time.Minute,
 		since:         &since,
 		wantFullState: false,
-		limit:         defaultTimelineLimit,
+		limit:         DefaultTimelineLimit,
 		log:           util.GetLogger(context.TODO()),
 		ctx:           context.TODO(),
 	}

syncapi/sync/request.go

@@ -21,14 +21,16 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	log "github.com/sirupsen/logrus"
 )
 
 const defaultSyncTimeout = time.Duration(0)
-const defaultTimelineLimit = 20
+const DefaultTimelineLimit = 20
 
 type filter struct {
 	Room struct {
@@ -49,7 +51,7 @@ type syncRequest struct {
 	log           *log.Entry
 }
 
-func newSyncRequest(req *http.Request, device userapi.Device) (*syncRequest, error) {
+func newSyncRequest(req *http.Request, device userapi.Device, syncDB storage.Database) (*syncRequest, error) {
 	timeout := getTimeout(req.URL.Query().Get("timeout"))
 	fullState := req.URL.Query().Get("full_state")
 	wantFullState := fullState != "" && fullState != "false"
@@ -66,15 +68,28 @@ func newSyncRequest(req *http.Request, device userapi.Device) (*syncRequest, err
 		tok := types.NewStreamToken(0, 0)
 		since = &tok
 	}
-	timelineLimit := defaultTimelineLimit
+	timelineLimit := DefaultTimelineLimit
 	// TODO: read from stored filters too
 	filterQuery := req.URL.Query().Get("filter")
-	if filterQuery != "" && filterQuery[0] == '{' {
-		// attempt to parse the timeline limit at least
-		var f filter
-		err := json.Unmarshal([]byte(filterQuery), &f)
-		if err == nil && f.Room.Timeline.Limit != nil {
-			timelineLimit = *f.Room.Timeline.Limit
+	if filterQuery != "" {
+		if filterQuery[0] == '{' {
+			// attempt to parse the timeline limit at least
+			var f filter
+			err := json.Unmarshal([]byte(filterQuery), &f)
+			if err == nil && f.Room.Timeline.Limit != nil {
+				timelineLimit = *f.Room.Timeline.Limit
+			}
+		} else {
+			// attempt to load the filter ID
+			localpart, _, err := gomatrixserverlib.SplitID('@', device.UserID)
+			if err != nil {
+				util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
+				return nil, err
+			}
+			f, err := syncDB.GetFilter(req.Context(), localpart, filterQuery)
+			if err == nil {
+				timelineLimit = f.Room.Timeline.Limit
+			}
 		}
 	}
 	// TODO: Additional query params: set_presence, filter

syncapi/sync/requestpool.go

@@ -49,7 +49,7 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request, device *userapi.
 	var syncData *types.Response
 
 	// Extract values from request
-	syncReq, err := newSyncRequest(req, *device)
+	syncReq, err := newSyncRequest(req, *device, rp.db)
 	if err != nil {
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,