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

3 files changed, 151 insertions, 5 deletions

diff --git a/syncapi/storage/postgres/filter_table.go b/syncapi/storage/postgres/filter_table.go
new file mode 100644
index 00000000..beeb864b
--- /dev/null
+++ b/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
+}
diff --git a/syncapi/storage/postgres/output_room_events_table.go b/syncapi/storage/postgres/output_room_events_table.go
index f01b2eab..c7c4dc63 100644
--- a/syncapi/storage/postgres/output_room_events_table.go
+++ b/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
diff --git a/syncapi/storage/postgres/syncserver.go b/syncapi/storage/postgres/syncserver.go
index 573586cc..10c1b37c 100644
--- a/syncapi/storage/postgres/syncserver.go
+++ b/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(),