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    //! Unix-specific extensions to general I/O primitives.

    #![stable(feature = "rust1", since = "1.0.0")]

    use crate::fs;
    use crate::io;
    use crate::os::raw;
    use crate::sys;
    use crate::sys_common::{AsInner, FromInner, IntoInner};

    /// Raw file descriptors.
    #[stable(feature = "rust1", since = "1.0.0")]
    pub type RawFd = raw::c_int;

    /// A trait to extract the raw unix 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 `AsRawHandle`
    /// and `AsRawSocket` set of traits.
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait AsRawFd {
        /// Extracts the raw file descriptor.
        ///
        /// This method does **not** pass ownership of the raw file descriptor
        /// to the caller. The descriptor is only guaranteed to be valid while
        /// the original object has not yet been destroyed.
        ///
        /// # Example
        ///
        /// ```no_run
        /// use std::fs::File;
        /// # use std::io;
        /// use std::os::unix::io::{AsRawFd, RawFd};
        ///
        /// let mut f = File::open("foo.txt")?;
        /// // Note that `raw_fd` is only valid as long as `f` exists.
        /// let raw_fd: RawFd = f.as_raw_fd();
        /// # Ok::<(), io::Error>(())
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        fn as_raw_fd(&self) -> RawFd;
    }

    /// A trait to express the ability to construct an object from a raw file
    /// descriptor.
    #[stable(feature = "from_raw_os", since = "1.1.0")]
    pub trait FromRawFd {
        /// Constructs a new instance of `Self` from the given raw file
        /// descriptor.
        ///
        /// This function **consumes ownership** of the specified file
        /// descriptor. The returned object will take responsibility for closing
        /// it when the object goes out of scope.
        ///
        /// This function is also unsafe as the primitives currently returned
        /// have the contract that they are the sole owner of the file
        /// descriptor they are wrapping. Usage of this function could
        /// accidentally allow violating this contract which can cause memory
        /// unsafety in code that relies on it being true.
        ///
        /// # Example
        ///
        /// ```no_run
        /// use std::fs::File;
        /// # use std::io;
        /// use std::os::unix::io::{FromRawFd, IntoRawFd, RawFd};
        ///
        /// let f = File::open("foo.txt")?;
        /// let raw_fd: RawFd = f.into_raw_fd();
        /// // SAFETY: no other functions should call `from_raw_fd`, so there
        /// // is only one owner for the file descriptor.
        /// let f = unsafe { File::from_raw_fd(raw_fd) };
        /// # Ok::<(), io::Error>(())
        /// ```
        #[stable(feature = "from_raw_os", since = "1.1.0")]
        unsafe fn from_raw_fd(fd: RawFd) -> Self;
    }

    /// A trait to express the ability to consume an object and acquire ownership of
    /// its raw file descriptor.
    #[stable(feature = "into_raw_os", since = "1.4.0")]
    pub trait IntoRawFd {
        /// Consumes this object, returning the raw underlying file descriptor.
        ///
        /// This function **transfers ownership** of the underlying file descriptor
        /// to the caller. Callers are then the unique owners of the file descriptor
        /// and must close the descriptor once it's no longer needed.
        ///
        /// # Example
        ///
        /// ```no_run
        /// use std::fs::File;
        /// # use std::io;
        /// use std::os::unix::io::{IntoRawFd, RawFd};
        ///
        /// let f = File::open("foo.txt")?;
        /// let raw_fd: RawFd = f.into_raw_fd();
        /// # Ok::<(), io::Error>(())
        /// ```
        #[stable(feature = "into_raw_os", since = "1.4.0")]
        fn into_raw_fd(self) -> RawFd;
    }

    #[stable(feature = "raw_fd_reflexive_traits", since = "1.48.0")]
    impl AsRawFd for RawFd {
        fn as_raw_fd(&self) -> RawFd {
            *self
        }
    }
    #[stable(feature = "raw_fd_reflexive_traits", since = "1.48.0")]
    impl IntoRawFd for RawFd {
        fn into_raw_fd(self) -> RawFd {
            self
        }
    }
    #[stable(feature = "raw_fd_reflexive_traits", since = "1.48.0")]
    impl FromRawFd for RawFd {
        unsafe fn from_raw_fd(fd: RawFd) -> RawFd {
            fd
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl AsRawFd for fs::File {
        fn as_raw_fd(&self) -> RawFd {
            self.as_inner().fd().raw()
        }
    }
    #[stable(feature = "from_raw_os", since = "1.1.0")]
    impl FromRawFd for fs::File {
        unsafe fn from_raw_fd(fd: RawFd) -> fs::File {
            fs::File::from_inner(sys::fs::File::from_inner(fd))
        }
    }
    #[stable(feature = "into_raw_os", since = "1.4.0")]
    impl IntoRawFd for fs::File {
        fn into_raw_fd(self) -> RawFd {
            self.into_inner().into_fd().into_raw()
        }
    }

    #[stable(feature = "asraw_stdio", since = "1.21.0")]
    impl AsRawFd for io::Stdin {
        fn as_raw_fd(&self) -> RawFd {
            libc::STDIN_FILENO
        }
    }

    #[stable(feature = "asraw_stdio", since = "1.21.0")]
    impl AsRawFd for io::Stdout {
        fn as_raw_fd(&self) -> RawFd {
            libc::STDOUT_FILENO
        }
    }

    #[stable(feature = "asraw_stdio", since = "1.21.0")]
    impl AsRawFd for io::Stderr {
        fn as_raw_fd(&self) -> RawFd {
            libc::STDERR_FILENO
        }
    }

    #[stable(feature = "asraw_stdio_locks", since = "1.35.0")]
    impl<'a> AsRawFd for io::StdinLock<'a> {
        fn as_raw_fd(&self) -> RawFd {
            libc::STDIN_FILENO
        }
    }

    #[stable(feature = "asraw_stdio_locks", since = "1.35.0")]
    impl<'a> AsRawFd for io::StdoutLock<'a> {
        fn as_raw_fd(&self) -> RawFd {
            libc::STDOUT_FILENO
        }
    }

    #[stable(feature = "asraw_stdio_locks", since = "1.35.0")]
    impl<'a> AsRawFd for io::StderrLock<'a> {
        fn as_raw_fd(&self) -> RawFd {
            libc::STDERR_FILENO
        }
    }