Fix broken Message::from(Box<[u8]>)

The size information was not preserved when handing the memory back to
the Rust allocator for deallocation.

Author: kalcutter

src/message.rs

@@ -37,8 +37,8 @@ impl fmt::Debug for Message {
     }
 }
 
-unsafe extern "C" fn drop_msg_content_box(data: *mut c_void, _hint: *mut c_void) {
-    let _ = Box::from_raw(data as *mut u8);
+unsafe extern "C" fn drop_msg_data_box(data: *mut c_void, hint: *mut c_void) {
+    let _ = Box::from_raw(slice::from_raw_parts_mut(data as *mut u8, hint as usize));
 }
 
 impl Message {
@@ -204,8 +204,8 @@ impl From<Vec<u8>> for Message {
 impl From<Box<[u8]>> for Message {
     /// Construct a message from a boxed slice without copying the data.
     fn from(data: Box<[u8]>) -> Self {
-        let n = data.len();
-        if n == 0 {
+        let len = data.len();
+        if len == 0 {
             return Message::new();
         }
         let raw = Box::into_raw(data);
@@ -214,9 +214,9 @@ impl From<Box<[u8]>> for Message {
                 zmq_sys::zmq_msg_init_data(
                     msg,
                     raw as *mut c_void,
-                    n,
-                    Some(drop_msg_content_box),
-                    ptr::null_mut(),
+                    len,
+                    Some(drop_msg_data_box),
+                    len as *mut c_void,
                 )
             })
         }

tests/message_from_boxed_slice.rs

@@ -0,0 +1,31 @@
+use std::alloc::{GlobalAlloc, Layout, System};
+use std::ptr;
+use std::sync::atomic::{AtomicPtr, Ordering};
+
+struct Allocator;
+
+static CHECK_PTR: AtomicPtr<u8> = AtomicPtr::new(ptr::null_mut());
+
+unsafe impl GlobalAlloc for Allocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        System.alloc(layout)
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        if ptr == CHECK_PTR.load(Ordering::SeqCst) {
+            assert_eq!(layout, Layout::new::<[u8; 42]>());
+            CHECK_PTR.store(ptr::null_mut(), Ordering::SeqCst);
+        }
+        System.dealloc(ptr, layout);
+    }
+}
+
+#[global_allocator]
+static A: Allocator = Allocator;
+
+#[test]
+fn message_from_boxed_slice() {
+    let mut b: Box<[u8]> = Box::new([0u8; 42]);
+    CHECK_PTR.store(b.as_mut_ptr() as *mut u8, Ordering::SeqCst);
+    let _ = zmq::Message::from(b);
+}