Function maybeClearPinnedConnection

src/sessions.ts:983–1022

(
  session: ClientSession,
  options?: EndSessionOptions
)

}

export function maybeClearPinnedConnection(
  session: ClientSession,
  options?: EndSessionOptions
): void {
  // unpin a connection if it has been pinned
  const conn = session.pinnedConnection;
  const error = options?.error;

  if (
    session.inTransaction() &&
    error &&
    error instanceof MongoError &&
    error.hasErrorLabel(MongoErrorLabel.TransientTransactionError)
  ) {
    return;
  }

  const topology = session.client.topology;
  // NOTE: the spec talks about what to do on a network error only, but the tests seem to
  //       to validate that we don't unpin on _all_ errors?
  if (conn && topology != null) {
    const servers = Array.from(topology.s.servers.values());
    const loadBalancer = servers[0];

    if (options?.error == null || options?.force) {
      loadBalancer.pool.checkIn(conn);
      session.pinnedConnection = undefined;
      conn.emit(
        UNPINNED,
        session.transaction.state !== TxnState.NO_TRANSACTION
          ? ConnectionPoolMetrics.TXN
          : ConnectionPoolMetrics.CURSOR
      );

      if (options?.forceClear) {
        loadBalancer.pool.clear({ serviceId: conn.serviceId });
      }
    }
  }
}

function isMaxTimeMSExpiredError(err: MongoError): boolean {
  if (err == null || !(err instanceof MongoServerError)) {