Add /_dendrite/admin/purgeRoom/{roomID} (#2662)

This adds a new admin endpoint `/_dendrite/admin/purgeRoom/{roomID}`. It
completely erases all database entries for a given room ID.

The roomserver will start by clearing all data for that room and then
will generate an output event to notify downstream components (i.e. the
sync API and federation API) to do the same.

It does not currently clear media and it is currently not implemented
for SQLite since it relies on SQL array operations right now.

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>
Co-authored-by: Till Faelligen <2353100+S7evinK@users.noreply.github.com>

syncapi/storage/sqlite3/memberships_table.go

@@ -72,6 +72,9 @@ SELECT event_id FROM
 		 	AND ($4 IS NULL OR t.membership <> $4)
 `
 
+const purgeMembershipsSQL = "" +
+	"DELETE FROM syncapi_memberships WHERE room_id = $1"
+
 type membershipsStatements struct {
 	db                        *sql.DB
 	upsertMembershipStmt      *sql.Stmt
@@ -79,6 +82,7 @@ type membershipsStatements struct {
 	//selectHeroesStmt          *sql.Stmt - prepared at runtime due to variadic
 	selectMembershipForUserStmt *sql.Stmt
 	selectMembersStmt           *sql.Stmt
+	purgeMembershipsStmt        *sql.Stmt
 }
 
 func NewSqliteMembershipsTable(db *sql.DB) (tables.Memberships, error) {
@@ -94,6 +98,7 @@ func NewSqliteMembershipsTable(db *sql.DB) (tables.Memberships, error) {
 		{&s.selectMembershipCountStmt, selectMembershipCountSQL},
 		{&s.selectMembershipForUserStmt, selectMembershipBeforeSQL},
 		{&s.selectMembersStmt, selectMembersSQL},
+		{&s.purgeMembershipsStmt, purgeMembershipsSQL},
 	}.Prepare(db)
 }
 
@@ -142,6 +147,13 @@ func (s *membershipsStatements) SelectMembershipForUser(
 	return membership, topologyPos, nil
 }
 
+func (s *membershipsStatements) PurgeMemberships(
+	ctx context.Context, txn *sql.Tx, roomID string,
+) error {
+	_, err := sqlutil.TxStmt(txn, s.purgeMembershipsStmt).ExecContext(ctx, roomID)
+	return err
+}
+
 func (s *membershipsStatements) SelectMemberships(
 	ctx context.Context, txn *sql.Tx,
 	roomID string, pos types.TopologyToken,