Send device list updates to servers (outbound only) (#1237)

* Add QueryDeviceMessages to serve up device keys and stream IDs

* Consume key change events in fedsender

Don't yet send them to destinations as we haven't worked them out yet

* Send device list updates to all required servers

* Glue it all together

federationsender/storage/postgres/joined_hosts_table.go

@@ -60,12 +60,16 @@ const selectJoinedHostsSQL = "" +
 const selectAllJoinedHostsSQL = "" +
 	"SELECT DISTINCT server_name FROM federationsender_joined_hosts"
 
+const selectJoinedHostsForRoomsSQL = "" +
+	"SELECT DISTINCT server_name FROM federationsender_joined_hosts WHERE room_id = ANY($1)"
+
 type joinedHostsStatements struct {
-	db                       *sql.DB
-	insertJoinedHostsStmt    *sql.Stmt
-	deleteJoinedHostsStmt    *sql.Stmt
-	selectJoinedHostsStmt    *sql.Stmt
-	selectAllJoinedHostsStmt *sql.Stmt
+	db                            *sql.DB
+	insertJoinedHostsStmt         *sql.Stmt
+	deleteJoinedHostsStmt         *sql.Stmt
+	selectJoinedHostsStmt         *sql.Stmt
+	selectAllJoinedHostsStmt      *sql.Stmt
+	selectJoinedHostsForRoomsStmt *sql.Stmt
 }
 
 func NewPostgresJoinedHostsTable(db *sql.DB) (s *joinedHostsStatements, err error) {
@@ -88,6 +92,9 @@ func NewPostgresJoinedHostsTable(db *sql.DB) (s *joinedHostsStatements, err erro
 	if s.selectAllJoinedHostsStmt, err = s.db.Prepare(selectAllJoinedHostsSQL); err != nil {
 		return
 	}
+	if s.selectJoinedHostsForRoomsStmt, err = s.db.Prepare(selectJoinedHostsForRoomsSQL); err != nil {
+		return
+	}
 	return
 }
 
@@ -144,6 +151,27 @@ func (s *joinedHostsStatements) SelectAllJoinedHosts(
 	return result, rows.Err()
 }
 
+func (s *joinedHostsStatements) SelectJoinedHostsForRooms(
+	ctx context.Context, roomIDs []string,
+) ([]gomatrixserverlib.ServerName, error) {
+	rows, err := s.selectJoinedHostsForRoomsStmt.QueryContext(ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectJoinedHostsForRoomsStmt: rows.close() failed")
+
+	var result []gomatrixserverlib.ServerName
+	for rows.Next() {
+		var serverName string
+		if err = rows.Scan(&serverName); err != nil {
+			return nil, err
+		}
+		result = append(result, gomatrixserverlib.ServerName(serverName))
+	}
+
+	return result, rows.Err()
+}
+
 func joinedHostsFromStmt(
 	ctx context.Context, stmt *sql.Stmt, roomID string,
 ) ([]types.JoinedHost, error) {