//! 拥有和借用类 Unix 文件描述符。

#![unstable(feature = "io_safety", issue = "87074")]
#![deny(unsafe_op_in_unsafe_fn)]

use super::raw::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
use crate::fmt;
use crate::fs;
use crate::marker::PhantomData;
use crate::mem::forget;
use crate::sys_common::{AsInner, FromInner, IntoInner};

/// 借用的文件描述符。
///
/// 它有一个生命周期参数，将它与拥有文件描述符的事物的生命周期联系起来。
///
/// 这使用 `repr(transparent)` 并具有主机文件描述符的表示，因此它可以在 FFI 中使用文件描述符作为参数传递的地方，它不会被捕获或消耗，它永远不会有值 `-1`。
///
///
///
///
#[derive(Copy, Clone)]
#[repr(transparent)]
#[rustc_layout_scalar_valid_range_start(0)]
// libstd/os/raw/mod.rs 向我保证，每个支持 libstd 的平台都有一个
// 32 位 c_int。
// 下面是 -2，以 2 的补码形式出现，但这仅适用于 c_int 为 32 位的情况。
#[rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)]
#[unstable(feature = "io_safety", issue = "87074")]
pub struct BorrowedFd<'fd> {
    fd: RawFd,
    _phantom: PhantomData<&'fd OwnedFd>,
}

/// 拥有所有权的文件描述符。
///
/// 这将在关闭文件描述符时丢弃。
///
/// 这使用 `repr(transparent)` 并具有主机文件描述符的表示，因此它可以在 FFI 中的文件描述符作为消耗参数传递或作为拥有值返回的地方使用，并且它永远不会有值 `-1`。
///
///
///
#[repr(transparent)]
#[rustc_layout_scalar_valid_range_start(0)]
// libstd/os/raw/mod.rs 向我保证，每个支持 libstd 的平台都有一个
// 32 位 c_int。
// 下面是 -2，以 2 的补码形式出现，但这仅适用于 c_int 为 32 位的情况。
#[rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)]
#[unstable(feature = "io_safety", issue = "87074")]
pub struct OwnedFd {
    fd: RawFd,
}

impl BorrowedFd<'_> {
    /// 返回包含给定原始文件描述符的 `BorrowedFd`。
    ///
    /// # Safety
    ///
    /// `fd` 指向的资源在返回的 `BorrowedFd` 期间必须保持打开状态，并且它不能具有值 `-1`。
    ///
    #[inline]
    #[unstable(feature = "io_safety", issue = "87074")]
    pub unsafe fn borrow_raw_fd(fd: RawFd) -> Self {
        assert_ne!(fd, u32::MAX as RawFd);
        // SAFETY: 我们只是断言该值在有效范围内，并且不是 `-1` (唯一大于 `0xFF_FF_FF_FE` 无符号的值)
        unsafe { Self { fd, _phantom: PhantomData } }
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsRawFd for BorrowedFd<'_> {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.fd
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsRawFd for OwnedFd {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.fd
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl IntoRawFd for OwnedFd {
    #[inline]
    fn into_raw_fd(self) -> RawFd {
        let fd = self.fd;
        forget(self);
        fd
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl FromRawFd for OwnedFd {
    /// 根据给定的原始文件描述符构造 `Self` 的新实例。
    ///
    /// # Safety
    ///
    /// `fd` 指向的资源必须是开放的并且适合承担所有权。
    /// 除了 `close` 之外，资源不得需要任何清理。
    #[inline]
    unsafe fn from_raw_fd(fd: RawFd) -> Self {
        assert_ne!(fd, u32::MAX as RawFd);
        // SAFETY: 我们只是断言该值在有效范围内，并且不是 `-1` (唯一大于 `0xFF_FF_FF_FE` 无符号的值)
        unsafe { Self { fd } }
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl Drop for OwnedFd {
    #[inline]
    fn drop(&mut self) {
        unsafe {
            // 请注意，关闭文件描述符时将忽略错误。
            // 这样做的原因是，如果发生错误，我们实际上不知道文件描述符是否已关闭，并且如果我们重试 (针对 EINTR 之类的东西)，则可能会关闭另一个在关闭文件描述符后打开的有效文件描述符。
            //
            //
            //
            let _ = libc::close(self.fd);
        }
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl fmt::Debug for BorrowedFd<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("BorrowedFd").field("fd", &self.fd).finish()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl fmt::Debug for OwnedFd {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("OwnedFd").field("fd", &self.fd).finish()
    }
}

/// 一个 trait 来借用来自底层对象的文件描述符。
///
/// 这仅在 unix 平台上可用，并且必须导入才能调用该方法。
/// Windows 平台有相应的 `AsHandle` 和 `AsSocket` 的 traits 集合。
///
#[unstable(feature = "io_safety", issue = "87074")]
pub trait AsFd {
    /// 借用文件描述符。
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # #![feature(io_safety)]
    /// use std::fs::File;
    /// # use std::io;
    /// # #[cfg(target_os = "wasi")]
    /// # use std::os::wasi::io::{AsFd, BorrowedFd};
    /// # #[cfg(unix)]
    /// # use std::os::unix::io::{AsFd, BorrowedFd};
    ///
    /// let mut f = File::open("foo.txt")?;
    /// # #[cfg(any(unix, target_os = "wasi"))]
    /// let borrowed_fd: BorrowedFd<'_> = f.as_fd();
    /// # Ok::<(), io::Error>(())
    /// ```
    #[unstable(feature = "io_safety", issue = "87074")]
    fn as_fd(&self) -> BorrowedFd<'_>;
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsFd for BorrowedFd<'_> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        *self
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsFd for OwnedFd {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        // 安全性: `OwnedFd` 和 `BorrowedFd` 具有相同的有效性不变量，`BorrowdFd` 受 `&self` 的生命周期限制。
        //
        //
        unsafe { BorrowedFd::borrow_raw_fd(self.as_raw_fd()) }
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsFd for fs::File {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().as_fd()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<fs::File> for OwnedFd {
    #[inline]
    fn from(file: fs::File) -> OwnedFd {
        file.into_inner().into_inner().into_inner()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<OwnedFd> for fs::File {
    #[inline]
    fn from(owned_fd: OwnedFd) -> Self {
        Self::from_inner(FromInner::from_inner(FromInner::from_inner(owned_fd)))
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsFd for crate::net::TcpStream {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().socket().as_fd()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<crate::net::TcpStream> for OwnedFd {
    #[inline]
    fn from(tcp_stream: crate::net::TcpStream) -> OwnedFd {
        tcp_stream.into_inner().into_socket().into_inner().into_inner().into()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<OwnedFd> for crate::net::TcpStream {
    #[inline]
    fn from(owned_fd: OwnedFd) -> Self {
        Self::from_inner(FromInner::from_inner(FromInner::from_inner(FromInner::from_inner(
            owned_fd,
        ))))
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsFd for crate::net::TcpListener {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().socket().as_fd()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<crate::net::TcpListener> for OwnedFd {
    #[inline]
    fn from(tcp_listener: crate::net::TcpListener) -> OwnedFd {
        tcp_listener.into_inner().into_socket().into_inner().into_inner().into()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<OwnedFd> for crate::net::TcpListener {
    #[inline]
    fn from(owned_fd: OwnedFd) -> Self {
        Self::from_inner(FromInner::from_inner(FromInner::from_inner(FromInner::from_inner(
            owned_fd,
        ))))
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl AsFd for crate::net::UdpSocket {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().socket().as_fd()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<crate::net::UdpSocket> for OwnedFd {
    #[inline]
    fn from(udp_socket: crate::net::UdpSocket) -> OwnedFd {
        udp_socket.into_inner().into_socket().into_inner().into_inner().into()
    }
}

#[unstable(feature = "io_safety", issue = "87074")]
impl From<OwnedFd> for crate::net::UdpSocket {
    #[inline]
    fn from(owned_fd: OwnedFd) -> Self {
        Self::from_inner(FromInner::from_inner(FromInner::from_inner(FromInner::from_inner(
            owned_fd,
        ))))
    }
}