1 files changed, 288 insertions, 0 deletions
diff --git a/library/std/src/os/fd/owned.rs b/library/std/src/os/fd/owned.rs
new file mode 100644
index 00000000000..ecaec8b21d8
--- /dev/null
+++ b/library/std/src/os/fd/owned.rs
@@ -0,0 +1,288 @@
+//! Owned and borrowed Unix-like file descriptors.
+
+#![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};
+
+/// A borrowed file descriptor.
+///
+/// This has a lifetime parameter to tie it to the lifetime of something that
+/// owns the file descriptor.
+///
+/// This uses `repr(transparent)` and has the representation of a host file
+/// descriptor, so it can be used in FFI in places where a file descriptor is
+/// passed as an argument, it is not captured or consumed, and it never has the
+/// value `-1`.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+#[rustc_layout_scalar_valid_range_start(0)]
+// libstd/os/raw/mod.rs assures me that every libstd-supported platform has a
+// 32-bit c_int. Below is -2, in two's complement, but that only works out
+// because c_int is 32 bits.
+#[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>,
+}
+
+/// An owned file descriptor.
+///
+/// This closes the file descriptor on drop.
+///
+/// This uses `repr(transparent)` and has the representation of a host file
+/// descriptor, so it can be used in FFI in places where a file descriptor is
+/// passed as a consumed argument or returned as an owned value, and it never
+/// has the value `-1`.
+#[repr(transparent)]
+#[rustc_layout_scalar_valid_range_start(0)]
+// libstd/os/raw/mod.rs assures me that every libstd-supported platform has a
+// 32-bit c_int. Below is -2, in two's complement, but that only works out
+// because c_int is 32 bits.
+#[rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)]
+#[unstable(feature = "io_safety", issue = "87074")]
+pub struct OwnedFd {
+    fd: RawFd,
+}
+
+impl BorrowedFd<'_> {
+    /// Return a `BorrowedFd` holding the given raw file descriptor.
+    ///
+    /// # Safety
+    ///
+    /// The resource pointed to by `fd` must remain open for the duration of
+    /// the returned `BorrowedFd`, and it must not have the value `-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: we just asserted that the value is in the valid range and isn't `-1` (the only value bigger than `0xFF_FF_FF_FE` unsigned)
+        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 {
+    /// Constructs a new instance of `Self` from the given raw file descriptor.
+    ///
+    /// # Safety
+    ///
+    /// The resource pointed to by `fd` must be open and suitable for assuming
+    /// ownership. The resource must not require any cleanup other than `close`.
+    #[inline]
+    unsafe fn from_raw_fd(fd: RawFd) -> Self {
+        assert_ne!(fd, u32::MAX as RawFd);
+        // SAFETY: we just asserted that the value is in the valid range and isn't `-1` (the only value bigger than `0xFF_FF_FF_FE` unsigned)
+        unsafe { Self { fd } }
+    }
+}
+
+#[unstable(feature = "io_safety", issue = "87074")]
+impl Drop for OwnedFd {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            // Note that errors are ignored when closing a file descriptor. The
+            // reason for this is that if an error occurs we don't actually know if
+            // the file descriptor was closed or not, and if we retried (for
+            // something like EINTR), we might close another valid file descriptor
+            // opened after we closed ours.
+            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()
+    }
+}
+
+/// A trait to borrow the file descriptor from an underlying object.
+///
+/// This is only available on unix platforms and must be imported in order to
+/// call the method. Windows platforms have a corresponding `AsHandle` and
+/// `AsSocket` set of traits.
+#[unstable(feature = "io_safety", issue = "87074")]
+pub trait AsFd {
+    /// Borrows the file descriptor.
+    ///
+    /// # 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")?;
+    /// 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<'_> {
+        // Safety: `OwnedFd` and `BorrowedFd` have the same validity
+        // invariants, and the `BorrowdFd` is bounded by the lifetime
+        // of `&self`.
+        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,
+        ))))
+    }
+}