安全 FFI 封装容器

Rust 为通过 外部函数接口 (FFI) 调用函数提供了出色的支持。我们将使用它为 libc 函数构建一个安全封装容器，用于从 C 代码中读取目录中的文件名称。

建议您参考以下手册页面：

您还需要浏览“std::ffi”模块。在下方，您会发现完成这个练习所需的多种字符串类型：

类型编码使用
“str”和“String”UTF-8用 Rust 进行文本处理
“CStr”和“CString”以空字符结尾与 C 函数通信
“OsStr”和“OsString”特定于操作系统与操作系统通信

您将在以下所有类型之间进行转换：

  • 将 &str 转换为 CString：您需要为尾随 \0 字符分配空格，
  • 将 CString 转换为 \*const i8 ：您需要一个指针来调用 C 函数，
  • 将 \*const i8 转换为 &CStr ：您需要一些能够找到尾随 \0 字符的内容，
  • &CStr to &[u8]: a slice of bytes is the universal interface for “some unknown data”,
  • 将 &\[u8\] 转换为 &OsStr ：&OsStr 是向 OsString 迈进的一步，请使用OsStrExt来创建它，
  • 将“&OsStr”转换为“OsString”：您需要克隆“&OsStr”中的数据，以便能够返回它并再次调用“readdir”。

秘典 中也有一个关于 FFI 的非常实用的章节。

将以下代码复制到 https://play.rust-lang.org/，并填入缺少的函数和方法：

  1. // TODO: remove this when you're done with your implementation.
  2. #![allow(unused_imports, unused_variables, dead_code)]
  4. mod ffi {
  5.     use std::os::raw::{c_char, c_int};
  6.     #[cfg(not(target_os = "macos"))]
  7.     use std::os::raw::{c_long, c_uchar, c_ulong, c_ushort};
  9.     // Opaque type. See https://doc.rust-lang.org/nomicon/ffi.html.
  10.     #[repr(C)]
  11.     pub struct DIR {
  12.         _data: [u8; 0],
  13.         _marker: core::marker::PhantomData<(*mut u8, core::marker::PhantomPinned)>,
  14.     }
  16.     // Layout according to the Linux man page for readdir(3), where ino_t and
  17.     // off_t are resolved according to the definitions in
  18.     // /usr/include/x86_64-linux-gnu/{sys/types.h, bits/typesizes.h}.
  19.     #[cfg(not(target_os = "macos"))]
  20.     #[repr(C)]
  21.     pub struct dirent {
  22.         pub d_ino: c_ulong,
  23.         pub d_off: c_long,
  24.         pub d_reclen: c_ushort,
  25.         pub d_type: c_uchar,
  26.         pub d_name: [c_char; 256],
  27.     }
  29.     // Layout according to the macOS man page for dir(5).
  30.     #[cfg(all(target_os = "macos"))]
  31.     #[repr(C)]
  32.     pub struct dirent {
  33.         pub d_fileno: u64,
  34.         pub d_seekoff: u64,
  35.         pub d_reclen: u16,
  36.         pub d_namlen: u16,
  37.         pub d_type: u8,
  38.         pub d_name: [c_char; 1024],
  39.     }
  41.     extern "C" {
  42.         pub fn opendir(s: *const c_char) -> *mut DIR;
  44.         #[cfg(not(all(target_os = "macos", target_arch = "x86_64")))]
  45.         pub fn readdir(s: *mut DIR) -> *const dirent;
  47.         // See https://github.com/rust-lang/libc/issues/414 and the section on
  48.         // _DARWIN_FEATURE_64_BIT_INODE in the macOS man page for stat(2).
  49.         //
  50.         // "Platforms that existed before these updates were available" refers
  51.         // to macOS (as opposed to iOS / wearOS / etc.) on Intel and PowerPC.
  52.         #[cfg(all(target_os = "macos", target_arch = "x86_64"))]
  53.         #[link_name = "readdir$INODE64"]
  54.         pub fn readdir(s: *mut DIR) -> *const dirent;
  56.         pub fn closedir(s: *mut DIR) -> c_int;
  57.     }
  58. }
  60. use std::ffi::{CStr, CString, OsStr, OsString};
  61. use std::os::unix::ffi::OsStrExt;
  63. #[derive(Debug)]
  64. struct DirectoryIterator {
  65.     path: CString,
  66.     dir: *mut ffi::DIR,
  67. }
  69. impl DirectoryIterator {
  70.     fn new(path: &str) -> Result<DirectoryIterator, String> {
  71.         // Call opendir and return a Ok value if that worked,
  72.         // otherwise return Err with a message.
  73.         unimplemented!()
  74.     }
  75. }
  77. impl Iterator for DirectoryIterator {
  78.     type Item = OsString;
  79.     fn next(&mut self) -> Option<OsString> {
  80.         // Keep calling readdir until we get a NULL pointer back.
  81.         unimplemented!()
  82.     }
  83. }
  85. impl Drop for DirectoryIterator {
  86.     fn drop(&mut self) {
  87.         // Call closedir as needed.
  88.         unimplemented!()
  89.     }
  90. }
  92. fn main() -> Result<(), String> {
  93.     let iter = DirectoryIterator::new(".")?;
  94.     println!("files: {:#?}", iter.collect::<Vec<_>>());
  95.     Ok(())
  96. }