std/os/fd/
owned.rs

1//! Owned and borrowed Unix-like file descriptors.
2
3#![stable(feature = "io_safety", since = "1.63.0")]
4#![deny(unsafe_op_in_unsafe_fn)]
5
6use super::raw::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
7#[cfg(not(target_os = "trusty"))]
8use crate::fs;
9use crate::marker::PhantomData;
10use crate::mem::ManuallyDrop;
11#[cfg(not(any(
12    target_arch = "wasm32",
13    target_env = "sgx",
14    target_os = "hermit",
15    target_os = "trusty"
16)))]
17use crate::sys::cvt;
18#[cfg(not(target_os = "trusty"))]
19use crate::sys_common::{AsInner, FromInner, IntoInner};
20use crate::{fmt, io};
21
22type ValidRawFd = core::num::niche_types::NotAllOnes<RawFd>;
23
24/// A borrowed file descriptor.
25///
26/// This has a lifetime parameter to tie it to the lifetime of something that owns the file
27/// descriptor. For the duration of that lifetime, it is guaranteed that nobody will close the file
28/// descriptor.
29///
30/// This uses `repr(transparent)` and has the representation of a host file
31/// descriptor, so it can be used in FFI in places where a file descriptor is
32/// passed as an argument, it is not captured or consumed, and it never has the
33/// value `-1`.
34///
35/// This type does not have a [`ToOwned`][crate::borrow::ToOwned]
36/// implementation. Calling `.to_owned()` on a variable of this type will call
37/// it on `&BorrowedFd` and use `Clone::clone()` like `ToOwned` does for all
38/// types implementing `Clone`. The result will be descriptor borrowed under
39/// the same lifetime.
40///
41/// To obtain an [`OwnedFd`], you can use [`BorrowedFd::try_clone_to_owned`]
42/// instead, but this is not supported on all platforms.
43#[derive(Copy, Clone)]
44#[repr(transparent)]
45#[rustc_nonnull_optimization_guaranteed]
46#[stable(feature = "io_safety", since = "1.63.0")]
47pub struct BorrowedFd<'fd> {
48    fd: ValidRawFd,
49    _phantom: PhantomData<&'fd OwnedFd>,
50}
51
52/// An owned file descriptor.
53///
54/// This closes the file descriptor on drop. It is guaranteed that nobody else will close the file
55/// descriptor.
56///
57/// This uses `repr(transparent)` and has the representation of a host file
58/// descriptor, so it can be used in FFI in places where a file descriptor is
59/// passed as a consumed argument or returned as an owned value, and it never
60/// has the value `-1`.
61///
62/// You can use [`AsFd::as_fd`] to obtain a [`BorrowedFd`].
63#[repr(transparent)]
64#[rustc_nonnull_optimization_guaranteed]
65#[stable(feature = "io_safety", since = "1.63.0")]
66pub struct OwnedFd {
67    fd: ValidRawFd,
68}
69
70impl BorrowedFd<'_> {
71    /// Returns a `BorrowedFd` holding the given raw file descriptor.
72    ///
73    /// # Safety
74    ///
75    /// The resource pointed to by `fd` must remain open for the duration of
76    /// the returned `BorrowedFd`, and it must not have the value `-1`.
77    #[inline]
78    #[track_caller]
79    #[rustc_const_stable(feature = "io_safety", since = "1.63.0")]
80    #[stable(feature = "io_safety", since = "1.63.0")]
81    pub const unsafe fn borrow_raw(fd: RawFd) -> Self {
82        Self { fd: ValidRawFd::new(fd).expect("fd != -1"), _phantom: PhantomData }
83    }
84}
85
86impl OwnedFd {
87    /// Creates a new `OwnedFd` instance that shares the same underlying file
88    /// description as the existing `OwnedFd` instance.
89    #[stable(feature = "io_safety", since = "1.63.0")]
90    pub fn try_clone(&self) -> crate::io::Result<Self> {
91        self.as_fd().try_clone_to_owned()
92    }
93}
94
95impl BorrowedFd<'_> {
96    /// Creates a new `OwnedFd` instance that shares the same underlying file
97    /// description as the existing `BorrowedFd` instance.
98    #[cfg(not(any(target_arch = "wasm32", target_os = "hermit", target_os = "trusty")))]
99    #[stable(feature = "io_safety", since = "1.63.0")]
100    pub fn try_clone_to_owned(&self) -> crate::io::Result<OwnedFd> {
101        // We want to atomically duplicate this file descriptor and set the
102        // CLOEXEC flag, and currently that's done via F_DUPFD_CLOEXEC. This
103        // is a POSIX flag that was added to Linux in 2.6.24.
104        #[cfg(not(any(target_os = "espidf", target_os = "vita")))]
105        let cmd = libc::F_DUPFD_CLOEXEC;
106
107        // For ESP-IDF, F_DUPFD is used instead, because the CLOEXEC semantics
108        // will never be supported, as this is a bare metal framework with
109        // no capabilities for multi-process execution. While F_DUPFD is also
110        // not supported yet, it might be (currently it returns ENOSYS).
111        #[cfg(any(target_os = "espidf", target_os = "vita"))]
112        let cmd = libc::F_DUPFD;
113
114        // Avoid using file descriptors below 3 as they are used for stdio
115        let fd = cvt(unsafe { libc::fcntl(self.as_raw_fd(), cmd, 3) })?;
116        Ok(unsafe { OwnedFd::from_raw_fd(fd) })
117    }
118
119    /// Creates a new `OwnedFd` instance that shares the same underlying file
120    /// description as the existing `BorrowedFd` instance.
121    #[cfg(any(target_arch = "wasm32", target_os = "hermit", target_os = "trusty"))]
122    #[stable(feature = "io_safety", since = "1.63.0")]
123    pub fn try_clone_to_owned(&self) -> crate::io::Result<OwnedFd> {
124        Err(crate::io::Error::UNSUPPORTED_PLATFORM)
125    }
126}
127
128#[stable(feature = "io_safety", since = "1.63.0")]
129impl AsRawFd for BorrowedFd<'_> {
130    #[inline]
131    fn as_raw_fd(&self) -> RawFd {
132        self.fd.as_inner()
133    }
134}
135
136#[stable(feature = "io_safety", since = "1.63.0")]
137impl AsRawFd for OwnedFd {
138    #[inline]
139    fn as_raw_fd(&self) -> RawFd {
140        self.fd.as_inner()
141    }
142}
143
144#[stable(feature = "io_safety", since = "1.63.0")]
145impl IntoRawFd for OwnedFd {
146    #[inline]
147    fn into_raw_fd(self) -> RawFd {
148        ManuallyDrop::new(self).fd.as_inner()
149    }
150}
151
152#[stable(feature = "io_safety", since = "1.63.0")]
153impl FromRawFd for OwnedFd {
154    /// Constructs a new instance of `Self` from the given raw file descriptor.
155    ///
156    /// # Safety
157    ///
158    /// The resource pointed to by `fd` must be open and suitable for assuming
159    /// [ownership][io-safety]. The resource must not require any cleanup other than `close`.
160    ///
161    /// [io-safety]: io#io-safety
162    #[inline]
163    #[track_caller]
164    unsafe fn from_raw_fd(fd: RawFd) -> Self {
165        Self { fd: ValidRawFd::new(fd).expect("fd != -1") }
166    }
167}
168
169#[stable(feature = "io_safety", since = "1.63.0")]
170impl Drop for OwnedFd {
171    #[inline]
172    fn drop(&mut self) {
173        unsafe {
174            // Note that errors are ignored when closing a file descriptor. According to POSIX 2024,
175            // we can and indeed should retry `close` on `EINTR`
176            // (https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/functions/close.html),
177            // but it is not clear yet how well widely-used implementations are conforming with this
178            // mandate since older versions of POSIX left the state of the FD after an `EINTR`
179            // unspecified. Ignoring errors is "fine" because some of the major Unices (in
180            // particular, Linux) do make sure to always close the FD, even when `close()` is
181            // interrupted, and the scenario is rare to begin with. If we retried on a
182            // not-POSIX-compliant implementation, the consequences could be really bad since we may
183            // close the wrong FD. Helpful link to an epic discussion by POSIX workgroup that led to
184            // the latest POSIX wording: http://austingroupbugs.net/view.php?id=529
185            #[cfg(not(target_os = "hermit"))]
186            {
187                #[cfg(unix)]
188                crate::sys::fs::debug_assert_fd_is_open(self.fd.as_inner());
189
190                let _ = libc::close(self.fd.as_inner());
191            }
192            #[cfg(target_os = "hermit")]
193            let _ = hermit_abi::close(self.fd.as_inner());
194        }
195    }
196}
197
198#[stable(feature = "io_safety", since = "1.63.0")]
199impl fmt::Debug for BorrowedFd<'_> {
200    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
201        f.debug_struct("BorrowedFd").field("fd", &self.fd).finish()
202    }
203}
204
205#[stable(feature = "io_safety", since = "1.63.0")]
206impl fmt::Debug for OwnedFd {
207    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
208        f.debug_struct("OwnedFd").field("fd", &self.fd).finish()
209    }
210}
211
212macro_rules! impl_is_terminal {
213    ($($t:ty),*$(,)?) => {$(
214        #[unstable(feature = "sealed", issue = "none")]
215        impl crate::sealed::Sealed for $t {}
216
217        #[stable(feature = "is_terminal", since = "1.70.0")]
218        impl crate::io::IsTerminal for $t {
219            #[inline]
220            fn is_terminal(&self) -> bool {
221                crate::sys::io::is_terminal(self)
222            }
223        }
224    )*}
225}
226
227impl_is_terminal!(BorrowedFd<'_>, OwnedFd);
228
229/// A trait to borrow the file descriptor from an underlying object.
230///
231/// This is only available on unix platforms and must be imported in order to
232/// call the method. Windows platforms have a corresponding `AsHandle` and
233/// `AsSocket` set of traits.
234#[stable(feature = "io_safety", since = "1.63.0")]
235pub trait AsFd {
236    /// Borrows the file descriptor.
237    ///
238    /// # Example
239    ///
240    /// ```rust,no_run
241    /// use std::fs::File;
242    /// # use std::io;
243    /// # #[cfg(any(unix, target_os = "wasi"))]
244    /// # use std::os::fd::{AsFd, BorrowedFd};
245    ///
246    /// let mut f = File::open("foo.txt")?;
247    /// # #[cfg(any(unix, target_os = "wasi"))]
248    /// let borrowed_fd: BorrowedFd<'_> = f.as_fd();
249    /// # Ok::<(), io::Error>(())
250    /// ```
251    #[stable(feature = "io_safety", since = "1.63.0")]
252    fn as_fd(&self) -> BorrowedFd<'_>;
253}
254
255#[stable(feature = "io_safety", since = "1.63.0")]
256impl<T: AsFd + ?Sized> AsFd for &T {
257    #[inline]
258    fn as_fd(&self) -> BorrowedFd<'_> {
259        T::as_fd(self)
260    }
261}
262
263#[stable(feature = "io_safety", since = "1.63.0")]
264impl<T: AsFd + ?Sized> AsFd for &mut T {
265    #[inline]
266    fn as_fd(&self) -> BorrowedFd<'_> {
267        T::as_fd(self)
268    }
269}
270
271#[stable(feature = "io_safety", since = "1.63.0")]
272impl AsFd for BorrowedFd<'_> {
273    #[inline]
274    fn as_fd(&self) -> BorrowedFd<'_> {
275        *self
276    }
277}
278
279#[stable(feature = "io_safety", since = "1.63.0")]
280impl AsFd for OwnedFd {
281    #[inline]
282    fn as_fd(&self) -> BorrowedFd<'_> {
283        // Safety: `OwnedFd` and `BorrowedFd` have the same validity
284        // invariants, and the `BorrowedFd` is bounded by the lifetime
285        // of `&self`.
286        unsafe { BorrowedFd::borrow_raw(self.as_raw_fd()) }
287    }
288}
289
290#[stable(feature = "io_safety", since = "1.63.0")]
291#[cfg(not(target_os = "trusty"))]
292impl AsFd for fs::File {
293    #[inline]
294    fn as_fd(&self) -> BorrowedFd<'_> {
295        self.as_inner().as_fd()
296    }
297}
298
299#[stable(feature = "io_safety", since = "1.63.0")]
300#[cfg(not(target_os = "trusty"))]
301impl From<fs::File> for OwnedFd {
302    /// Takes ownership of a [`File`](fs::File)'s underlying file descriptor.
303    #[inline]
304    fn from(file: fs::File) -> OwnedFd {
305        file.into_inner().into_inner().into_inner()
306    }
307}
308
309#[stable(feature = "io_safety", since = "1.63.0")]
310#[cfg(not(target_os = "trusty"))]
311impl From<OwnedFd> for fs::File {
312    /// Returns a [`File`](fs::File) that takes ownership of the given
313    /// file descriptor.
314    #[inline]
315    fn from(owned_fd: OwnedFd) -> Self {
316        Self::from_inner(FromInner::from_inner(FromInner::from_inner(owned_fd)))
317    }
318}
319
320#[stable(feature = "io_safety", since = "1.63.0")]
321#[cfg(not(target_os = "trusty"))]
322impl AsFd for crate::net::TcpStream {
323    #[inline]
324    fn as_fd(&self) -> BorrowedFd<'_> {
325        self.as_inner().socket().as_fd()
326    }
327}
328
329#[stable(feature = "io_safety", since = "1.63.0")]
330#[cfg(not(target_os = "trusty"))]
331impl From<crate::net::TcpStream> for OwnedFd {
332    /// Takes ownership of a [`TcpStream`](crate::net::TcpStream)'s socket file descriptor.
333    #[inline]
334    fn from(tcp_stream: crate::net::TcpStream) -> OwnedFd {
335        tcp_stream.into_inner().into_socket().into_inner().into_inner().into()
336    }
337}
338
339#[stable(feature = "io_safety", since = "1.63.0")]
340#[cfg(not(target_os = "trusty"))]
341impl From<OwnedFd> for crate::net::TcpStream {
342    #[inline]
343    fn from(owned_fd: OwnedFd) -> Self {
344        Self::from_inner(FromInner::from_inner(FromInner::from_inner(FromInner::from_inner(
345            owned_fd,
346        ))))
347    }
348}
349
350#[stable(feature = "io_safety", since = "1.63.0")]
351#[cfg(not(target_os = "trusty"))]
352impl AsFd for crate::net::TcpListener {
353    #[inline]
354    fn as_fd(&self) -> BorrowedFd<'_> {
355        self.as_inner().socket().as_fd()
356    }
357}
358
359#[stable(feature = "io_safety", since = "1.63.0")]
360#[cfg(not(target_os = "trusty"))]
361impl From<crate::net::TcpListener> for OwnedFd {
362    /// Takes ownership of a [`TcpListener`](crate::net::TcpListener)'s socket file descriptor.
363    #[inline]
364    fn from(tcp_listener: crate::net::TcpListener) -> OwnedFd {
365        tcp_listener.into_inner().into_socket().into_inner().into_inner().into()
366    }
367}
368
369#[stable(feature = "io_safety", since = "1.63.0")]
370#[cfg(not(target_os = "trusty"))]
371impl From<OwnedFd> for crate::net::TcpListener {
372    #[inline]
373    fn from(owned_fd: OwnedFd) -> Self {
374        Self::from_inner(FromInner::from_inner(FromInner::from_inner(FromInner::from_inner(
375            owned_fd,
376        ))))
377    }
378}
379
380#[stable(feature = "io_safety", since = "1.63.0")]
381#[cfg(not(target_os = "trusty"))]
382impl AsFd for crate::net::UdpSocket {
383    #[inline]
384    fn as_fd(&self) -> BorrowedFd<'_> {
385        self.as_inner().socket().as_fd()
386    }
387}
388
389#[stable(feature = "io_safety", since = "1.63.0")]
390#[cfg(not(target_os = "trusty"))]
391impl From<crate::net::UdpSocket> for OwnedFd {
392    /// Takes ownership of a [`UdpSocket`](crate::net::UdpSocket)'s file descriptor.
393    #[inline]
394    fn from(udp_socket: crate::net::UdpSocket) -> OwnedFd {
395        udp_socket.into_inner().into_socket().into_inner().into_inner().into()
396    }
397}
398
399#[stable(feature = "io_safety", since = "1.63.0")]
400#[cfg(not(target_os = "trusty"))]
401impl From<OwnedFd> for crate::net::UdpSocket {
402    #[inline]
403    fn from(owned_fd: OwnedFd) -> Self {
404        Self::from_inner(FromInner::from_inner(FromInner::from_inner(FromInner::from_inner(
405            owned_fd,
406        ))))
407    }
408}
409
410#[stable(feature = "asfd_ptrs", since = "1.64.0")]
411/// This impl allows implementing traits that require `AsFd` on Arc.
412/// ```
413/// # #[cfg(any(unix, target_os = "wasi"))] mod group_cfg {
414/// # #[cfg(target_os = "wasi")]
415/// # use std::os::wasi::io::AsFd;
416/// # #[cfg(unix)]
417/// # use std::os::unix::io::AsFd;
418/// use std::net::UdpSocket;
419/// use std::sync::Arc;
420///
421/// trait MyTrait: AsFd {}
422/// impl MyTrait for Arc<UdpSocket> {}
423/// impl MyTrait for Box<UdpSocket> {}
424/// # }
425/// ```
426impl<T: AsFd + ?Sized> AsFd for crate::sync::Arc<T> {
427    #[inline]
428    fn as_fd(&self) -> BorrowedFd<'_> {
429        (**self).as_fd()
430    }
431}
432
433#[stable(feature = "asfd_rc", since = "1.69.0")]
434impl<T: AsFd + ?Sized> AsFd for crate::rc::Rc<T> {
435    #[inline]
436    fn as_fd(&self) -> BorrowedFd<'_> {
437        (**self).as_fd()
438    }
439}
440
441#[unstable(feature = "unique_rc_arc", issue = "112566")]
442impl<T: AsFd + ?Sized> AsFd for crate::rc::UniqueRc<T> {
443    #[inline]
444    fn as_fd(&self) -> BorrowedFd<'_> {
445        (**self).as_fd()
446    }
447}
448
449#[stable(feature = "asfd_ptrs", since = "1.64.0")]
450impl<T: AsFd + ?Sized> AsFd for Box<T> {
451    #[inline]
452    fn as_fd(&self) -> BorrowedFd<'_> {
453        (**self).as_fd()
454    }
455}
456
457#[stable(feature = "io_safety", since = "1.63.0")]
458impl AsFd for io::Stdin {
459    #[inline]
460    fn as_fd(&self) -> BorrowedFd<'_> {
461        unsafe { BorrowedFd::borrow_raw(0) }
462    }
463}
464
465#[stable(feature = "io_safety", since = "1.63.0")]
466impl<'a> AsFd for io::StdinLock<'a> {
467    #[inline]
468    fn as_fd(&self) -> BorrowedFd<'_> {
469        // SAFETY: user code should not close stdin out from under the standard library
470        unsafe { BorrowedFd::borrow_raw(0) }
471    }
472}
473
474#[stable(feature = "io_safety", since = "1.63.0")]
475impl AsFd for io::Stdout {
476    #[inline]
477    fn as_fd(&self) -> BorrowedFd<'_> {
478        unsafe { BorrowedFd::borrow_raw(1) }
479    }
480}
481
482#[stable(feature = "io_safety", since = "1.63.0")]
483impl<'a> AsFd for io::StdoutLock<'a> {
484    #[inline]
485    fn as_fd(&self) -> BorrowedFd<'_> {
486        // SAFETY: user code should not close stdout out from under the standard library
487        unsafe { BorrowedFd::borrow_raw(1) }
488    }
489}
490
491#[stable(feature = "io_safety", since = "1.63.0")]
492impl AsFd for io::Stderr {
493    #[inline]
494    fn as_fd(&self) -> BorrowedFd<'_> {
495        unsafe { BorrowedFd::borrow_raw(2) }
496    }
497}
498
499#[stable(feature = "io_safety", since = "1.63.0")]
500impl<'a> AsFd for io::StderrLock<'a> {
501    #[inline]
502    fn as_fd(&self) -> BorrowedFd<'_> {
503        // SAFETY: user code should not close stderr out from under the standard library
504        unsafe { BorrowedFd::borrow_raw(2) }
505    }
506}
507
508#[stable(feature = "anonymous_pipe", since = "1.87.0")]
509#[cfg(not(target_os = "trusty"))]
510impl AsFd for io::PipeReader {
511    fn as_fd(&self) -> BorrowedFd<'_> {
512        self.0.as_fd()
513    }
514}
515
516#[stable(feature = "anonymous_pipe", since = "1.87.0")]
517#[cfg(not(target_os = "trusty"))]
518impl From<io::PipeReader> for OwnedFd {
519    fn from(pipe: io::PipeReader) -> Self {
520        pipe.0.into_inner()
521    }
522}
523
524#[stable(feature = "anonymous_pipe", since = "1.87.0")]
525#[cfg(not(target_os = "trusty"))]
526impl AsFd for io::PipeWriter {
527    fn as_fd(&self) -> BorrowedFd<'_> {
528        self.0.as_fd()
529    }
530}
531
532#[stable(feature = "anonymous_pipe", since = "1.87.0")]
533#[cfg(not(target_os = "trusty"))]
534impl From<io::PipeWriter> for OwnedFd {
535    fn from(pipe: io::PipeWriter) -> Self {
536        pipe.0.into_inner()
537    }
538}
539
540#[stable(feature = "anonymous_pipe", since = "1.87.0")]
541#[cfg(not(target_os = "trusty"))]
542impl From<OwnedFd> for io::PipeReader {
543    fn from(owned_fd: OwnedFd) -> Self {
544        Self(FromInner::from_inner(owned_fd))
545    }
546}
547
548#[stable(feature = "anonymous_pipe", since = "1.87.0")]
549#[cfg(not(target_os = "trusty"))]
550impl From<OwnedFd> for io::PipeWriter {
551    fn from(owned_fd: OwnedFd) -> Self {
552        Self(FromInner::from_inner(owned_fd))
553    }
554}
std/os/fd/owned.rs

std/os/fd/
owned.rs
