You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.rs
    path of file: ./repos/cnosdb/query_server/sqllogicaltests/src
    
    the code of the file until where you have to start completion: use std::error::Error;
use std::path::{Path, PathBuf};

use crate::instance::SqlClientOptions;

mod db_request;
mod error;
mod instance;
mod os;
mod utils;

const TEST_DIRECTORY: &str = "query_server/sqllogicaltests/cases";

const CNOSDB_FLIGHT_HOST_ENV: &str = "CNOSDB_FLIGHT_HOST";
const CNOSDB_FLIGHT_PORT_ENV: &str = "CNOSDB_FLIGHT_PORT";
const CNOSDB_HT
    
pub(crate) fn read_dir_recursive<P: AsRef<Path>>(path: P) -> Box<dyn Iterator<Item = PathBuf>> {
    Box::new(
        std::fs::read_dir(path)
            .expect("Readable directory")
            .map(|path| path.expect("Readable entry").path())
            .flat_map(|path| {
                if path.is_dir() {
                    read_dir_recursive(path)
                } else {
                    Box::new(std::iter::once(path))
                }
            }),
    )
}