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    //! Typed views using temporary objects.
    //!
    //! This module defines the return types for [`AsFilelike::as_filelike_view`]
    //! and [`AsSocketlike::as_socketlike_view`].
    //!
    //! [`AsSocketlike::as_socketlike_view`]: crate::AsSocketlike::as_socketlike_view

    use crate::raw::{
        AsRawFilelike, AsRawSocketlike, FromRawFilelike, FromRawSocketlike, IntoRawFilelike,
        IntoRawSocketlike, RawFilelike, RawSocketlike,
    };
    #[cfg(any(unix, target_os = "wasi"))]
    use crate::OwnedFd;
    use crate::{
        AsFilelike, AsSocketlike, FromFilelike, FromSocketlike, IntoFilelike, IntoSocketlike,
        OwnedFilelike, OwnedSocketlike,
    };
    #[cfg(windows)]
    use crate::{OwnedHandle, OwnedSocket};
    use std::fmt;
    use std::marker::PhantomData;
    use std::mem::ManuallyDrop;
    use std::ops::Deref;

    /// Declare that a type is safe to use in a [`FilelikeView`].
    ///
    /// # Safety
    ///
    /// Types implementing this trait declare that if they are constructed with
    /// [`FromFilelike`] and consumed with [`IntoFilelike`], their `IntoFilelike`
    /// will return the same `OwnedFd` value that was passed to their
    /// `FromFilelike`.
    pub unsafe trait FilelikeViewType: FromFilelike + IntoFilelike {}

    /// Declare that a type is safe to use in a [`SocketlikeView`].
    ///
    /// # Safety
    ///
    /// Types implementing this trait declare that if they are constructed with
    /// [`FromSocketlike`] and consumed with [`IntoSocketlike`], their
    /// `IntoSocketlike` will return the same `OwnedFd` value that was passed to
    /// their `FromSocketlike`.
    pub unsafe trait SocketlikeViewType: FromSocketlike + IntoSocketlike {}

    /// A non-owning view of a resource which dereferences to a `&Target` or
    /// `&mut Target`. These are returned by [`AsFilelike::as_filelike_view`].
    pub struct FilelikeView<'filelike, Target: FilelikeViewType> {
        /// The value to dereference to. This is a `ManuallyDrop` so that we can
        /// consume it in our `Drop` impl.
        target: ManuallyDrop<Target>,

        /// `FilelikeViewType` implementors guarantee that their `Into<OwnedFd>`
        /// returns the same fd as their `From<OwnedFd>` gave them. This field
        /// allows us to verify this.
        #[cfg(debug_assertions)]
        orig: RawFilelike,

        /// This field exists because we don't otherwise explicitly use
        /// `'filelike`.
        _phantom: PhantomData<&'filelike OwnedFilelike>,
    }

    /// A non-owning view of a resource which dereferences to a `&Target` or
    /// `&mut Target`. These are returned by [`AsSocketlike::as_socketlike_view`].
    pub struct SocketlikeView<'socketlike, Target: SocketlikeViewType> {
        /// The value to dereference to. This is a `ManuallyDrop` so that we can
        /// consume it in our `Drop` impl.
        target: ManuallyDrop<Target>,

        /// `SocketlikeViewType` implementors guarantee that their `Into<OwnedFd>`
        /// returns the same fd as their `From<OwnedFd>` gave them. This field
        /// allows us to verify this.
        #[cfg(debug_assertions)]
        orig: RawSocketlike,

        /// This field exists because we don't otherwise explicitly use
        /// `'socketlike`.
        _phantom: PhantomData<&'socketlike OwnedSocketlike>,
    }

    impl<Target: FilelikeViewType> FilelikeView<'_, Target> {
        /// Construct a temporary `Target` and wrap it in a `FilelikeView` object.
        #[inline]
        pub(crate) fn new<T: AsFilelike>(filelike: &T) -> Self {
            // Safety: The returned `FilelikeView` is scoped to the lifetime of
            // `filelike`, which we've borrowed here, so the view won't outlive
            // the object it's borrowed from.
            unsafe { Self::view_raw(filelike.as_filelike().as_raw_filelike()) }
        }

        /// Construct a temporary `Target` from raw and wrap it in a `FilelikeView`
        /// object.
        ///
        /// # Safety
        ///
        /// `raw` must be a valid raw filelike referencing a resource that outlives
        /// the resulting view.
        #[inline]
        pub unsafe fn view_raw(raw: RawFilelike) -> Self {
            let owned = OwnedFilelike::from_raw_filelike(raw);
            Self {
                target: ManuallyDrop::new(Target::from_filelike(owned)),
                #[cfg(debug_assertions)]
                orig: raw,
                _phantom: PhantomData,
            }
        }
    }

    impl<Target: SocketlikeViewType> SocketlikeView<'_, Target> {
        /// Construct a temporary `Target` and wrap it in a `SocketlikeView`
        /// object.
        #[inline]
        pub(crate) fn new<T: AsSocketlike>(socketlike: &T) -> Self {
            // Safety: The returned `SocketlikeView` is scoped to the lifetime of
            // `socketlike`, which we've borrowed here, so the view won't outlive
            // the object it's borrowed from.
            unsafe { Self::view_raw(socketlike.as_socketlike().as_raw_socketlike()) }
        }

        /// Construct a temporary `Target` from raw and wrap it in a
        /// `SocketlikeView` object.
        ///
        /// # Safety
        ///
        /// `raw` must be a valid raw socketlike referencing a resource that
        /// outlives the resulting view.
        #[inline]
        pub unsafe fn view_raw(raw: RawSocketlike) -> Self {
            let owned = OwnedSocketlike::from_raw_socketlike(raw);
            Self {
                target: ManuallyDrop::new(Target::from_socketlike(owned)),
                #[cfg(debug_assertions)]
                orig: raw,
                _phantom: PhantomData,
            }
        }
    }

    impl<Target: FilelikeViewType> Deref for FilelikeView<'_, Target> {
        type Target = Target;

        #[inline]
        fn deref(&self) -> &Self::Target {
            &self.target
        }
    }

    impl<Target: SocketlikeViewType> Deref for SocketlikeView<'_, Target> {
        type Target = Target;

        #[inline]
        fn deref(&self) -> &Self::Target {
            &self.target
        }
    }

    impl<Target: FilelikeViewType> Drop for FilelikeView<'_, Target> {
        #[inline]
        fn drop(&mut self) {
            // Use `Into*` to consume `self.target` without freeing its resource.
            //
            // Safety: Using `ManuallyDrop::take` requires us to ensure that
            // `self.target` is not used again. We don't use it again here, and
            // this is the `drop` function, so we know it's not used afterward.
            let _raw = unsafe { ManuallyDrop::take(&mut self.target) }
                .into_filelike()
                .into_raw_filelike();

            #[cfg(debug_assertions)]
            debug_assert_eq!(self.orig, _raw);
        }
    }

    impl<Target: SocketlikeViewType> Drop for SocketlikeView<'_, Target> {
        #[inline]
        fn drop(&mut self) {
            // Use `Into*` to consume `self.target` without freeing its resource.
            //
            // Safety: Using `ManuallyDrop::take` requires us to ensure that
            // `self.target` is not used again. We don't use it again here, and
            // this is the `drop` function, so we know it's not used afterward.
            let _raw = unsafe { ManuallyDrop::take(&mut self.target) }
                .into_socketlike()
                .into_raw_socketlike();

            #[cfg(debug_assertions)]
            debug_assert_eq!(self.orig, _raw);
        }
    }

    impl<Target: FilelikeViewType> fmt::Debug for FilelikeView<'_, Target> {
        #[allow(clippy::missing_inline_in_public_items)]
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("FilelikeView")
                .field("target", &*self)
                .finish()
        }
    }

    impl<Target: SocketlikeViewType> fmt::Debug for SocketlikeView<'_, Target> {
        #[allow(clippy::missing_inline_in_public_items)]
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("SocketlikeView")
                .field("target", &*self)
                .finish()
        }
    }

    #[cfg(any(unix, target_os = "wasi"))]
    unsafe impl FilelikeViewType for OwnedFd {}
    #[cfg(windows)]
    unsafe impl FilelikeViewType for OwnedHandle {}
    #[cfg(windows)]
    unsafe impl SocketlikeViewType for OwnedSocket {}
    unsafe impl FilelikeViewType for std::fs::File {}
    unsafe impl SocketlikeViewType for std::net::TcpStream {}
    unsafe impl SocketlikeViewType for std::net::TcpListener {}
    unsafe impl SocketlikeViewType for std::net::UdpSocket {}
    #[cfg(unix)]
    unsafe impl SocketlikeViewType for std::os::unix::net::UnixStream {}
    #[cfg(unix)]
    unsafe impl SocketlikeViewType for std::os::unix::net::UnixListener {}

    #[cfg(unix)]
    unsafe impl SocketlikeViewType for std::os::unix::net::UnixDatagram {}
    #[cfg(not(target_os = "wasi"))]
    #[cfg(feature = "os_pipe")]
    unsafe impl FilelikeViewType for os_pipe::PipeWriter {}
    #[cfg(not(target_os = "wasi"))]
    #[cfg(feature = "os_pipe")]
    unsafe impl FilelikeViewType for os_pipe::PipeReader {}

    #[cfg(not(target_os = "wasi"))]
    #[cfg(feature = "socket2")]
    unsafe impl SocketlikeViewType for socket2::Socket {}

    #[cfg(not(target_os = "wasi"))]
    #[cfg(feature = "async_std")]
    unsafe impl SocketlikeViewType for async_std::net::TcpStream {}
    #[cfg(not(target_os = "wasi"))]
    #[cfg(feature = "async_std")]
    unsafe impl SocketlikeViewType for async_std::net::TcpListener {}
    #[cfg(not(target_os = "wasi"))]
    #[cfg(feature = "async_std")]
    unsafe impl SocketlikeViewType for async_std::net::UdpSocket {}
    #[cfg(unix)]
    #[cfg(feature = "async_std")]
    unsafe impl SocketlikeViewType for async_std::os::unix::net::UnixStream {}
    #[cfg(unix)]
    #[cfg(feature = "async_std")]
    unsafe impl SocketlikeViewType for async_std::os::unix::net::UnixListener {}
    #[cfg(unix)]
    #[cfg(feature = "async_std")]
    unsafe impl SocketlikeViewType for async_std::os::unix::net::UnixDatagram {}

    #[cfg(feature = "mio")]
    unsafe impl SocketlikeViewType for mio::net::TcpStream {}
    #[cfg(feature = "mio")]
    unsafe impl SocketlikeViewType for mio::net::TcpListener {}
    #[cfg(feature = "mio")]
    unsafe impl SocketlikeViewType for mio::net::UdpSocket {}
    #[cfg(unix)]
    #[cfg(feature = "mio")]
    unsafe impl SocketlikeViewType for mio::net::UnixDatagram {}
    #[cfg(unix)]
    #[cfg(feature = "mio")]
    unsafe impl SocketlikeViewType for mio::net::UnixListener {}
    #[cfg(unix)]
    #[cfg(feature = "mio")]
    unsafe impl SocketlikeViewType for mio::net::UnixStream {}
    #[cfg(unix)]
    #[cfg(feature = "mio")]
    unsafe impl FilelikeViewType for mio::unix::pipe::Receiver {}
    #[cfg(unix)]
    #[cfg(feature = "mio")]
    unsafe impl FilelikeViewType for mio::unix::pipe::Sender {}