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extern crate libc;
use std::marker::PhantomData;
use std::ops::Deref;
use std::slice;
use libc::c_void;
struct MallocPtr(*mut c_void);
impl Drop for MallocPtr {
fn drop(&mut self) {
unsafe {
libc::free(self.0);
}
}
}
/// A type that represents a `malloc`'d chunk of memory.
pub struct MallocBuffer<T> {
ptr: MallocPtr,
len: usize,
items: PhantomData<[T]>,
}
impl<T: Copy> MallocBuffer<T> {
/// Constructs a new `MallocBuffer` for a `malloc`'d buffer
/// with the given length at the given pointer.
/// Returns `None` if the given pointer is null and the length is not 0.
///
/// When this `MallocBuffer` drops, the buffer will be `free`'d.
///
/// Unsafe because there must be `len` contiguous, valid instances of `T`
/// at `ptr`.
pub unsafe fn new(ptr: *mut T, len: usize) -> Option<MallocBuffer<T>> {
if len > 0 && ptr.is_null() {
None
} else {
Some(MallocBuffer {
ptr: MallocPtr(ptr as *mut c_void),
len: len,
items: PhantomData,
})
}
}
}
impl<T> Deref for MallocBuffer<T> {
type Target = [T];
fn deref(&self) -> &[T] {
let ptr = if self.len == 0 && self.ptr.0.is_null() {
// Even a 0-size slice cannot be null, so just use another pointer
0x1 as *const T
} else {
self.ptr.0 as *const T
};
unsafe {
slice::from_raw_parts(ptr, self.len)
}
}
}
#[cfg(test)]
mod tests {
use std::ptr;
use libc;
use super::MallocBuffer;
#[test]
fn test_null_buf() {
let buf = unsafe {
MallocBuffer::<u32>::new(ptr::null_mut(), 0).unwrap()
};
assert!(&*buf == []);
assert!(Some(&*buf) == Some(&[]));
let buf = unsafe {
MallocBuffer::<u32>::new(ptr::null_mut(), 7)
};
assert!(buf.is_none());
}
#[test]
fn test_buf() {
let buf = unsafe {
let ptr = libc::malloc(12) as *mut u32;
*ptr = 1;
*ptr.offset(1) = 2;
*ptr.offset(2) = 3;
MallocBuffer::new(ptr, 3).unwrap()
};
assert!(&*buf == [1, 2, 3]);
}
}