add example helper, translate more examples

update to wip servicepoint lib

src/containers/byte_slice.rs

@@ -1,7 +1,5 @@
 //! FFI slice helper
 
-use std::ptr::NonNull;
-
 /// Represents a span of memory (`&mut [u8]` ) as a struct.
 ///
 /// # Safety
@@ -11,28 +9,39 @@ use std::ptr::NonNull;
 /// - accesses to the memory pointed to with `start` is never accessed outside `length`
 /// - the lifetime of the `CByteSlice` does not outlive the memory it points to, as described in
 ///   the function returning this type.
+/// - if `start` is NULL or `length` is 0, do not dereference `start`.
+/// 
+/// # Examples
+/// 
+/// ```c
+/// ByteSlice empty = {.start: NULL, .length = 0};
+/// ```
 #[repr(C)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct ByteSlice {
     /// The start address of the memory.
-    pub start: NonNull<u8>,
+    pub start: *mut u8,
     /// The amount of memory in bytes.
     pub length: usize,
 }
 
 impl ByteSlice {
+    pub(crate) const INVALID: ByteSlice = ByteSlice {
+        start: std::ptr::null_mut(),
+        length: 0,
+    };
+
     pub(crate) unsafe fn as_slice(&self) -> &[u8] {
-        unsafe { std::slice::from_raw_parts(self.start.as_ptr(), self.length) }
+        unsafe { std::slice::from_raw_parts(self.start, self.length) }
     }
 
     pub(crate) unsafe fn as_slice_mut(&mut self) -> &mut [u8] {
-        unsafe {
-            std::slice::from_raw_parts_mut(self.start.as_ptr(), self.length)
-        }
+        unsafe { std::slice::from_raw_parts_mut(self.start, self.length) }
     }
 
     pub(crate) unsafe fn from_slice(slice: &mut [u8]) -> Self {
         Self {
-            start: NonNull::new(slice.as_mut_ptr()).unwrap(),
+            start: slice.as_mut_ptr(),
             length: slice.len(),
         }
     }