Fix undefined behavior on some CPUs

src/syntatic/header.rs

@@ -1,11 +1,11 @@
+use std::mem::size_of;
 use super::Data;
 
 pub type HeaderDataSize = u32;
 pub type HeaderDataType = u16;
 pub type HeaderQueue = u8;
 
-#[repr(packed)]  // required for network exchange
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 /// The Header part of the Box.
 ///
 /// It can be copied or cloned cheaply.
@@ -14,14 +14,14 @@ pub type HeaderQueue = u8;
 /// - data_type - unsigned 16 bit value used to inform the reader about the type of incoming Data
 /// - queue - unsigned 8 bit value used to inform the server to which queue use to handle the Box
 pub struct Header {
-    data_size: HeaderDataSize,  // cannot access due to packed representation
+    data_size: HeaderDataSize,
     data_type: HeaderDataType,
     queue: HeaderQueue,
 }
 
 impl Header {
     /// Size of the Header in bytes.
-    pub const SIZE: usize = std::mem::size_of::<Header>();
+    pub const SIZE: usize = size_of::<HeaderDataSize>() + size_of::<HeaderDataType>() + size_of::<HeaderQueue>();
 
     // getters needed due to packed representation of the struct
 
@@ -75,13 +75,114 @@ impl Header {
 /// Same as `Header::into_array`
 impl Into<[u8; Header::SIZE]> for Header {
     fn into(self) -> [u8; Header::SIZE] {
-        unsafe { std::mem::transmute(self) }
+        let mut buffer = [0x00_u8; Header::SIZE];
+        let buffer_ptr = buffer.as_mut_ptr();
+
+        let data_size_ptr = self.data_size.to_le_bytes().as_ptr();
+        let data_type_ptr = self.data_type.to_le_bytes().as_ptr();
+        let queue_ptr = self.queue.to_le_bytes().as_ptr();
+
+        let mut cursor = 0;
+
+        unsafe {
+            copy_bytes_to(
+                data_size_ptr,
+                buffer_ptr,
+                size_of::<HeaderDataSize>(),
+                &mut cursor,
+            );
+
+            copy_bytes_to(
+                data_type_ptr,
+                buffer_ptr,
+                size_of::<HeaderDataType>(),
+                &mut cursor,
+            );
+
+            copy_bytes_to(
+                queue_ptr,
+                buffer_ptr,
+                size_of::<HeaderQueue>(),
+                &mut cursor,
+            );
+        }
+
+        buffer
     }
 }
 
 /// Same as `Header::from_array`
 impl From<[u8; Header::SIZE]> for Header {
     fn from(bytes: [u8; Header::SIZE]) -> Self {
-        unsafe { std::mem::transmute(bytes) }
+        let mut buffer_data_size = [0x00_u8; size_of::<HeaderDataSize>()];
+        let mut buffer_data_type = [0x00_u8; size_of::<HeaderDataType>()];
+        let mut buffer_queue = [0x00_u8; size_of::<HeaderQueue>()];
+
+        let bytes_ptr = bytes.as_ptr();
+
+        let mut cursor = 0;
+
+        unsafe {
+            copy_bytes_from(
+                bytes_ptr,
+                buffer_data_size.as_mut_ptr(),
+                size_of::<HeaderDataSize>(),
+                &mut cursor,
+            );
+
+            copy_bytes_from(
+                bytes_ptr,
+                buffer_data_type.as_mut_ptr(),
+                size_of::<HeaderDataType>(),
+                &mut cursor,
+            );
+
+            copy_bytes_from(
+                bytes_ptr,
+                buffer_queue.as_mut_ptr(),
+                size_of::<HeaderQueue>(),
+                &mut cursor,
+            );
+        }
+
+        Self {
+            data_size: HeaderDataSize::from_le_bytes(buffer_data_size),
+            data_type: HeaderDataType::from_le_bytes(buffer_data_type),
+            queue: HeaderQueue::from_le_bytes(buffer_queue),
+        }
     }
 }
+
+/// Copies bytes into one specific buffer.
+///
+/// # Args
+/// - src - pointer to a byte array from which bytes will be copied
+/// - dst - pointer to a buffer
+/// - count - amount of bytes to copy from src (should be size_of src)
+/// - cursor - cursor over the buffer
+unsafe fn copy_bytes_to(src: *const u8, dst: *mut u8, count: usize, cursor: &mut usize) {
+    std::ptr::copy(
+        src,
+        dst.add(*cursor),
+        count
+    );
+
+    *cursor += count;
+}
+
+/// Copies bytes from one specific array.
+///
+/// # Args
+/// - src - pointer to an array
+/// - dst - pointer to a buffer into which bytes will be copied to
+/// - count - amount of bytes to copy from src (should be size_of dst)
+/// - cursor - cursor over the array
+unsafe fn copy_bytes_from(src: *const u8, dst: *mut u8, count: usize, cursor: &mut usize) {
+    std::ptr::copy(
+        src.add(*cursor),
+        dst,
+        count
+    );
+
+    *cursor += count;
+}