1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
//! Owned and borrowed Unix-like file descriptors.

#![stable(feature = "io_safety", since = "1.63.0")]
#![deny(unsafe_op_in_unsafe_fn)]

use super::raw::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
use crate::fmt;
use crate::fs;
use crate::io;
use crate::marker::PhantomData;
use crate::mem::forget;
#[cfg(not(any(target_arch = "wasm32", target_env = "sgx", target_os = "hermit")))]
use crate::sys::cvt;
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. For the duration of that lifetime, it is guaranteed that nobody will close 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`.
///
/// This type's `.to_owned()` implementation returns another `BorrowedFd`
/// rather than an `OwnedFd`. It just makes a trivial copy of the raw file
/// descriptor, which is then borrowed under the same lifetime.
#[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)]
#[rustc_nonnull_optimization_guaranteed]
#[stable(feature = "io_safety", since = "1.63.0")]
pub struct BorrowedFd<'fd> {
    fd: RawFd,
    _phantom: PhantomData<&'fd OwnedFd>,
}

/// An owned file descriptor.
///
/// This closes the file descriptor on drop. It is guaranteed that nobody else will close 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 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)]
#[rustc_nonnull_optimization_guaranteed]
#[stable(feature = "io_safety", since = "1.63.0")]
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]
    #[rustc_const_stable(feature = "io_safety", since = "1.63.0")]
    #[stable(feature = "io_safety", since = "1.63.0")]
    pub const unsafe fn borrow_raw(fd: RawFd) -> Self {
        assert!(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 } }
    }
}

impl OwnedFd {
    /// Creates a new `OwnedFd` instance that shares the same underlying file
    /// description as the existing `OwnedFd` instance.
    #[stable(feature = "io_safety", since = "1.63.0")]
    pub fn try_clone(&self) -> crate::io::Result<Self> {
        self.as_fd().try_clone_to_owned()
    }
}

impl BorrowedFd<'_> {
    /// Creates a new `OwnedFd` instance that shares the same underlying file
    /// description as the existing `BorrowedFd` instance.
    #[cfg(not(any(target_arch = "wasm32", target_os = "hermit")))]
    #[stable(feature = "io_safety", since = "1.63.0")]
    pub fn try_clone_to_owned(&self) -> crate::io::Result<OwnedFd> {
        // We want to atomically duplicate this file descriptor and set the
        // CLOEXEC flag, and currently that's done via F_DUPFD_CLOEXEC. This
        // is a POSIX flag that was added to Linux in 2.6.24.
        #[cfg(not(any(target_os = "espidf", target_os = "vita")))]
        let cmd = libc::F_DUPFD_CLOEXEC;

        // For ESP-IDF, F_DUPFD is used instead, because the CLOEXEC semantics
        // will never be supported, as this is a bare metal framework with
        // no capabilities for multi-process execution. While F_DUPFD is also
        // not supported yet, it might be (currently it returns ENOSYS).
        #[cfg(any(target_os = "espidf", target_os = "vita"))]
        let cmd = libc::F_DUPFD;

        // Avoid using file descriptors below 3 as they are used for stdio
        let fd = cvt(unsafe { libc::fcntl(self.as_raw_fd(), cmd, 3) })?;
        Ok(unsafe { OwnedFd::from_raw_fd(fd) })
    }

    /// Creates a new `OwnedFd` instance that shares the same underlying file
    /// description as the existing `BorrowedFd` instance.
    #[cfg(any(target_arch = "wasm32", target_os = "hermit"))]
    #[stable(feature = "io_safety", since = "1.63.0")]
    pub fn try_clone_to_owned(&self) -> crate::io::Result<OwnedFd> {
        Err(crate::io::Error::UNSUPPORTED_PLATFORM)
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsRawFd for BorrowedFd<'_> {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.fd
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsRawFd for OwnedFd {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.fd
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl IntoRawFd for OwnedFd {
    #[inline]
    fn into_raw_fd(self) -> RawFd {
        let fd = self.fd;
        forget(self);
        fd
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
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][io-safety]. The resource must not require any cleanup other than `close`.
    ///
    /// [io-safety]: io#io-safety
    #[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 } }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
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.
            #[cfg(not(target_os = "hermit"))]
            let _ = libc::close(self.fd);
            #[cfg(target_os = "hermit")]
            let _ = hermit_abi::close(self.fd);
        }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl fmt::Debug for BorrowedFd<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("BorrowedFd").field("fd", &self.fd).finish()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl fmt::Debug for OwnedFd {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("OwnedFd").field("fd", &self.fd).finish()
    }
}

macro_rules! impl_is_terminal {
    ($($t:ty),*$(,)?) => {$(
        #[unstable(feature = "sealed", issue = "none")]
        impl crate::sealed::Sealed for $t {}

        #[stable(feature = "is_terminal", since = "1.70.0")]
        impl crate::io::IsTerminal for $t {
            #[inline]
            fn is_terminal(&self) -> bool {
                crate::sys::io::is_terminal(self)
            }
        }
    )*}
}

impl_is_terminal!(BorrowedFd<'_>, OwnedFd);

/// 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.
#[stable(feature = "io_safety", since = "1.63.0")]
pub trait AsFd {
    /// Borrows the file descriptor.
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// use std::fs::File;
    /// # use std::io;
    /// # #[cfg(any(unix, target_os = "wasi"))]
    /// # use std::os::fd::{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>(())
    /// ```
    #[stable(feature = "io_safety", since = "1.63.0")]
    fn as_fd(&self) -> BorrowedFd<'_>;
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl<T: AsFd + ?Sized> AsFd for &T {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        T::as_fd(self)
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl<T: AsFd + ?Sized> AsFd for &mut T {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        T::as_fd(self)
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for BorrowedFd<'_> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        *self
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for OwnedFd {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        // Safety: `OwnedFd` and `BorrowedFd` have the same validity
        // invariants, and the `BorrowedFd` is bounded by the lifetime
        // of `&self`.
        unsafe { BorrowedFd::borrow_raw(self.as_raw_fd()) }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for fs::File {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().as_fd()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl From<fs::File> for OwnedFd {
    /// Takes ownership of a [`File`](fs::File)'s underlying file descriptor.
    #[inline]
    fn from(file: fs::File) -> OwnedFd {
        file.into_inner().into_inner().into_inner()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl From<OwnedFd> for fs::File {
    /// Returns a [`File`](fs::File) that takes ownership of the given
    /// file descriptor.
    #[inline]
    fn from(owned_fd: OwnedFd) -> Self {
        Self::from_inner(FromInner::from_inner(FromInner::from_inner(owned_fd)))
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for crate::net::TcpStream {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().socket().as_fd()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl From<crate::net::TcpStream> for OwnedFd {
    /// Takes ownership of a [`TcpStream`](crate::net::TcpStream)'s socket file descriptor.
    #[inline]
    fn from(tcp_stream: crate::net::TcpStream) -> OwnedFd {
        tcp_stream.into_inner().into_socket().into_inner().into_inner().into()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
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,
        ))))
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for crate::net::TcpListener {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().socket().as_fd()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl From<crate::net::TcpListener> for OwnedFd {
    /// Takes ownership of a [`TcpListener`](crate::net::TcpListener)'s socket file descriptor.
    #[inline]
    fn from(tcp_listener: crate::net::TcpListener) -> OwnedFd {
        tcp_listener.into_inner().into_socket().into_inner().into_inner().into()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
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,
        ))))
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for crate::net::UdpSocket {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.as_inner().socket().as_fd()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl From<crate::net::UdpSocket> for OwnedFd {
    /// Takes ownership of a [`UdpSocket`](crate::net::UdpSocket)'s file descriptor.
    #[inline]
    fn from(udp_socket: crate::net::UdpSocket) -> OwnedFd {
        udp_socket.into_inner().into_socket().into_inner().into_inner().into()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
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,
        ))))
    }
}

#[stable(feature = "asfd_ptrs", since = "1.64.0")]
/// This impl allows implementing traits that require `AsFd` on Arc.
/// ```
/// # #[cfg(any(unix, target_os = "wasi"))] mod group_cfg {
/// # #[cfg(target_os = "wasi")]
/// # use std::os::wasi::io::AsFd;
/// # #[cfg(unix)]
/// # use std::os::unix::io::AsFd;
/// use std::net::UdpSocket;
/// use std::sync::Arc;
///
/// trait MyTrait: AsFd {}
/// impl MyTrait for Arc<UdpSocket> {}
/// impl MyTrait for Box<UdpSocket> {}
/// # }
/// ```
impl<T: AsFd + ?Sized> AsFd for crate::sync::Arc<T> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        (**self).as_fd()
    }
}

#[stable(feature = "asfd_rc", since = "1.69.0")]
impl<T: AsFd + ?Sized> AsFd for crate::rc::Rc<T> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        (**self).as_fd()
    }
}

#[stable(feature = "asfd_ptrs", since = "1.64.0")]
impl<T: AsFd + ?Sized> AsFd for Box<T> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        (**self).as_fd()
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for io::Stdin {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        unsafe { BorrowedFd::borrow_raw(0) }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl<'a> AsFd for io::StdinLock<'a> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        // SAFETY: user code should not close stdin out from under the standard library
        unsafe { BorrowedFd::borrow_raw(0) }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for io::Stdout {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        unsafe { BorrowedFd::borrow_raw(1) }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl<'a> AsFd for io::StdoutLock<'a> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        // SAFETY: user code should not close stdout out from under the standard library
        unsafe { BorrowedFd::borrow_raw(1) }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl AsFd for io::Stderr {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        unsafe { BorrowedFd::borrow_raw(2) }
    }
}

#[stable(feature = "io_safety", since = "1.63.0")]
impl<'a> AsFd for io::StderrLock<'a> {
    #[inline]
    fn as_fd(&self) -> BorrowedFd<'_> {
        // SAFETY: user code should not close stderr out from under the standard library
        unsafe { BorrowedFd::borrow_raw(2) }
    }
}