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    //! Buffer management for same-process client<->server communication.

    use std::io::{self, Write};
    use std::mem;
    use std::ops::{Deref, DerefMut};
    use std::slice;

    #[repr(C)]
    struct Slice<'a, T> {
        data: &'a [T; 0],
        len: usize,
    }

    unsafe impl<'a, T: Sync> Sync for Slice<'a, T> {}
    unsafe impl<'a, T: Sync> Send for Slice<'a, T> {}

    impl<T> Copy for Slice<'a, T> {}
    impl<T> Clone for Slice<'a, T> {
        fn clone(&self) -> Self {
            *self
        }
    }

    impl<T> From<&'a [T]> for Slice<'a, T> {
        fn from(xs: &'a [T]) -> Self {
            Slice {
                data: unsafe { &*(xs.as_ptr() as *const [T; 0]) },
                len: xs.len(),
            }
        }
    }

    impl<T> Deref for Slice<'a, T> {
        type Target = [T];
        fn deref(&self) -> &[T] {
            unsafe { slice::from_raw_parts(self.data.as_ptr(), self.len) }
        }
    }

    #[repr(C)]
    pub struct Buffer<T: Copy> {
        data: *mut T,
        len: usize,
        capacity: usize,
        extend_from_slice: extern "C" fn(Buffer<T>, Slice<'_, T>) -> Buffer<T>,
        drop: extern "C" fn(Buffer<T>),
    }

    unsafe impl<T: Copy + Sync> Sync for Buffer<T> {}
    unsafe impl<T: Copy + Send> Send for Buffer<T> {}

    impl<T: Copy> Default for Buffer<T> {
        fn default() -> Self {
            Self::from(vec![])
        }
    }

    impl<T: Copy> Deref for Buffer<T> {
        type Target = [T];
        fn deref(&self) -> &[T] {
            unsafe { slice::from_raw_parts(self.data as *const T, self.len) }
        }
    }

    impl<T: Copy> DerefMut for Buffer<T> {
        fn deref_mut(&mut self) -> &mut [T] {
            unsafe { slice::from_raw_parts_mut(self.data, self.len) }
        }
    }

    impl<T: Copy> Buffer<T> {
        pub(super) fn new() -> Self {
            Self::default()
        }

        pub(super) fn clear(&mut self) {
            self.len = 0;
        }

        pub(super) fn take(&mut self) -> Self {
            mem::take(self)
        }

        pub(super) fn extend_from_slice(&mut self, xs: &[T]) {
            // Fast path to avoid going through an FFI call.
            if let Some(final_len) = self.len.checked_add(xs.len()) {
                if final_len <= self.capacity {
                    let dst = unsafe { slice::from_raw_parts_mut(self.data, self.capacity) };
                    dst[self.len..][..xs.len()].copy_from_slice(xs);
                    self.len = final_len;
                    return;
                }
            }
            let b = self.take();
            *self = (b.extend_from_slice)(b, Slice::from(xs));
        }
    }

    impl Write for Buffer<u8> {
        fn write(&mut self, xs: &[u8]) -> io::Result<usize> {
            self.extend_from_slice(xs);
            Ok(xs.len())
        }

        fn write_all(&mut self, xs: &[u8]) -> io::Result<()> {
            self.extend_from_slice(xs);
            Ok(())
        }

        fn flush(&mut self) -> io::Result<()> {
            Ok(())
        }
    }

    impl<T: Copy> Drop for Buffer<T> {
        fn drop(&mut self) {
            let b = self.take();
            (b.drop)(b);
        }
    }

    impl<T: Copy> From<Vec<T>> for Buffer<T> {
        fn from(mut v: Vec<T>) -> Self {
            let (data, len, capacity) = (v.as_mut_ptr(), v.len(), v.capacity());
            mem::forget(v);

            // This utility function is nested in here because it can *only*
            // be safely called on `Buffer`s created by *this* `proc_macro`.
            fn to_vec<T: Copy>(b: Buffer<T>) -> Vec<T> {
                unsafe {
                    let Buffer {
                        data,
                        len,
                        capacity,
                        ..
                    } = b;
                    mem::forget(b);
                    Vec::from_raw_parts(data, len, capacity)
                }
            }

            extern "C" fn extend_from_slice<T: Copy>(b: Buffer<T>, xs: Slice<'_, T>) -> Buffer<T> {
                let mut v = to_vec(b);
                v.extend_from_slice(&xs);
                Buffer::from(v)
            }

            extern "C" fn drop<T: Copy>(b: Buffer<T>) {
                mem::drop(to_vec(b));
            }

            Buffer {
                data,
                len,
                capacity,
                extend_from_slice,
                drop,
            }
        }
    }