Persist partition|offset|user_id in the keyserver (#1226)

* Persist partition|offset|user_id in the keyserver

Required for a query API which will be used by the syncapi which
will be called when a `/sync` request comes in which will return
a list of user IDs of people who have changed their device keys
between two tokens.

* Add tests and fix maxOffset bug

* s/offset/log_offset/g because 'offset' is a reserved word in postgres

keyserver/storage/sqlite3/key_changes_table.go

@@ -0,0 +1,98 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// 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"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/keyserver/storage/tables"
+)
+
+var keyChangesSchema = `
+-- Stores key change information about users. Used to determine when to send updated device lists to clients.
+CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+	partition BIGINT NOT NULL,
+	offset BIGINT NOT NULL,
+	-- The key owner
+	user_id TEXT NOT NULL,
+	UNIQUE (partition, offset)
+);
+`
+
+// Replace based on partition|offset - we should never insert duplicates unless the kafka logs are wiped.
+// Rather than falling over, just overwrite (though this will mean clients with an existing sync token will
+// miss out on updates). TODO: Ideally we would detect when kafka logs are purged then purge this table too.
+const upsertKeyChangeSQL = "" +
+	"INSERT INTO keyserver_key_changes (partition, offset, user_id)" +
+	" VALUES ($1, $2, $3)" +
+	" ON CONFLICT (partition, offset)" +
+	" DO UPDATE SET user_id = $3"
+
+// select the highest offset for each user in the range. The grouping by user gives distinct entries and then we just
+// take the max offset value as the latest offset.
+const selectKeyChangesSQL = "" +
+	"SELECT user_id, MAX(offset) FROM keyserver_key_changes WHERE partition = $1 AND offset > $2 GROUP BY user_id"
+
+type keyChangesStatements struct {
+	db                   *sql.DB
+	upsertKeyChangeStmt  *sql.Stmt
+	selectKeyChangesStmt *sql.Stmt
+}
+
+func NewSqliteKeyChangesTable(db *sql.DB) (tables.KeyChanges, error) {
+	s := &keyChangesStatements{
+		db: db,
+	}
+	_, err := db.Exec(keyChangesSchema)
+	if err != nil {
+		return nil, err
+	}
+	if s.upsertKeyChangeStmt, err = db.Prepare(upsertKeyChangeSQL); err != nil {
+		return nil, err
+	}
+	if s.selectKeyChangesStmt, err = db.Prepare(selectKeyChangesSQL); err != nil {
+		return nil, err
+	}
+	return s, nil
+}
+
+func (s *keyChangesStatements) InsertKeyChange(ctx context.Context, partition int32, offset int64, userID string) error {
+	_, err := s.upsertKeyChangeStmt.ExecContext(ctx, partition, offset, userID)
+	return err
+}
+
+func (s *keyChangesStatements) SelectKeyChanges(
+	ctx context.Context, partition int32, fromOffset int64,
+) (userIDs []string, latestOffset int64, err error) {
+	rows, err := s.selectKeyChangesStmt.QueryContext(ctx, partition, fromOffset)
+	if err != nil {
+		return nil, 0, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeyChangesStmt: rows.close() failed")
+	for rows.Next() {
+		var userID string
+		var offset int64
+		if err := rows.Scan(&userID, &offset); err != nil {
+			return nil, 0, err
+		}
+		if offset > latestOffset {
+			latestOffset = offset
+		}
+		userIDs = append(userIDs, userID)
+	}
+	return
+}

keyserver/storage/sqlite3/storage.go

@@ -37,9 +37,14 @@ func NewDatabase(dataSourceName string) (*shared.Database, error) {
 	if err != nil {
 		return nil, err
 	}
+	kc, err := NewSqliteKeyChangesTable(db)
+	if err != nil {
+		return nil, err
+	}
 	return &shared.Database{
 		DB:               db,
 		OneTimeKeysTable: otk,
 		DeviceKeysTable:  dk,
+		KeyChangesTable:  kc,
 	}, nil
 }