1 files changed, 95 insertions, 0 deletions
diff --git a/third_party/rust/malloc_buf/src/lib.rs b/third_party/rust/malloc_buf/src/lib.rs
new file mode 100644
index 0000000000..24066b69d4
--- /dev/null
+++ b/third_party/rust/malloc_buf/src/lib.rs
@@ -0,0 +1,95 @@
+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]);
+    }
+}