Safe FFI Wrapper

러스트는 _외부 기능 호출(FFI)_을 지원합니다. 이를 이용하여 C에서 사용할 폴더 내 파일이름을 읽어오는 glibc함수를 만들 것입니다.

아래 리눅스 메뉴얼 문서들을 참조하시기 바랍니다:

• opendir(3)
• readdir(3)
• closedir(3)

아래 코드를 https://play.rust-lang.org/에 복사하고 빠진 함수와 메서드를 채워봅니다.

Rust has great support for calling functions through a foreign function interface (FFI). We will use this to build a safe wrapper the glibc functions you would use from C to read the filenames of a directory.

You will want to consult the manual pages:

• opendir(3)
• readdir(3)
• closedir(3)

You will also want to browse the std::ffi module, particular for CStr and CString types which are used to hold NUL-terminated strings coming from C. The Nomicon also has a very useful chapter about FFI.

Copy the code below to https://play.rust-lang.org/ and fill in the missing functions and methods:

// TODO: remove this when you're done with your implementation.
#![allow(unused_imports, unused_variables, dead_code)]

mod ffi {
    use std::os::raw::{c_char, c_int, c_long, c_ulong, c_ushort};

    // Opaque type. See https://doc.rust-lang.org/nomicon/ffi.html.
    #[repr(C)]
    pub struct DIR {
        _data: [u8; 0],
        _marker: core::marker::PhantomData<(*mut u8, core::marker::PhantomPinned)>,
    }

    // Layout as per readdir(3) and definitions in /usr/include/x86_64-linux-gnu.
    #[repr(C)]
    pub struct dirent {
        pub d_ino: c_long,
        pub d_off: c_ulong,
        pub d_reclen: c_ushort,
        pub d_type: c_char,
        pub d_name: [c_char; 256],
    }

    extern "C" {
        pub fn opendir(s: *const c_char) -> *mut DIR;
        pub fn readdir(s: *mut DIR) -> *const dirent;
        pub fn closedir(s: *mut DIR) -> c_int;
    }
}

use std::ffi::{CStr, CString, OsStr, OsString};
use std::os::unix::ffi::OsStrExt;

#[derive(Debug)]
struct DirectoryIterator {
    path: CString,
    dir: *mut ffi::DIR,
}

impl DirectoryIterator {
    fn new(path: &str) -> Result<DirectoryIterator, String> {
        // Call opendir and return a Ok value if that worked,
        // otherwise return Err with a message.
        unimplemented!()
    }
}

impl Iterator for DirectoryIterator {
    type Item = OsString;
    fn next(&mut self) -> Option<OsString> {
        // Keep calling readdir until we get a NULL pointer back.
        unimplemented!()
    }
}

impl Drop for DirectoryIterator {
    fn drop(&mut self) {
        // Call closedir as needed.
        unimplemented!()
    }
}

fn main() -> Result<(), String> {
    let iter = DirectoryIterator::new(".")?;
    println!("files: {:#?}", iter.collect::<Vec<_>>());
    Ok(())
}

역주

• DirectoryIterator, Iterator, Drop impl 블록을 채우면 됩니다.
• 참조문서를 싹 훝어도 어려운데(…)