Add zerocopy push for ByteBuffer

CHANGELOG.md

@@ -6,6 +6,8 @@
 - install `rustfmt` and the Kani verifier automatically via `cargo install`
 - restore Kani proof best practices in `AGENTS.md` and note that proofs run via `verify.sh`
 - limit Kani loop unwind by default and set per-harness bounds
+- `ByteBuffer::push` now accepts any `IntoBytes + Immutable` value when the
+  `zerocopy` feature is enabled
 - increase unwind for prefix/suffix overflow proofs
 - move weak reference and downcasting examples into module docs
 - expand module introduction describing use cases

src/buffer.rs

@@ -102,7 +102,8 @@ impl<const ALIGN: usize> ByteBuffer<ALIGN> {
         self.cap = new_cap;
     }
 
-    /// Push a byte to the end of the buffer.
+    /// Push data to the end of the buffer.
+    #[cfg(not(feature = "zerocopy"))]
     pub fn push(&mut self, byte: u8) {
         self.reserve_more(1);
         unsafe {
@@ -111,6 +112,20 @@ impl<const ALIGN: usize> ByteBuffer<ALIGN> {
         self.len += 1;
     }
 
+    /// Push data to the end of the buffer.
+    #[cfg(feature = "zerocopy")]
+    pub fn push<T>(&mut self, value: T)
+    where
+        T: zerocopy::IntoBytes + zerocopy::Immutable,
+    {
+        let bytes = zerocopy::IntoBytes::as_bytes(&value);
+        self.reserve_more(bytes.len());
+        unsafe {
+            ptr::copy_nonoverlapping(bytes.as_ptr(), self.ptr.as_ptr().add(self.len), bytes.len());
+        }
+        self.len += bytes.len();
+    }
+
     /// Returns a raw pointer to the buffer's memory.
     pub fn as_ptr(&self) -> *const u8 {
         self.ptr.as_ptr()

src/tests.rs

@@ -308,9 +308,9 @@ fn test_bytebuffer_push_and_bytes() {
     use crate::ByteBuffer;
 
     let mut buf: ByteBuffer<8> = ByteBuffer::with_capacity(2);
-    buf.push(1);
-    buf.push(2);
-    buf.push(3);
+    buf.push(1u8);
+    buf.push(2u8);
+    buf.push(3u8);
     assert_eq!(buf.as_ref(), &[1, 2, 3]);
 
     let bytes: Bytes = buf.into();
@@ -322,7 +322,7 @@ fn test_bytebuffer_alignment() {
     use crate::ByteBuffer;
 
     let mut buf: ByteBuffer<64> = ByteBuffer::with_capacity(1);
-    buf.push(1);
+    buf.push(1u8);
     assert_eq!((buf.as_ptr() as usize) % 64, 0);
 }
 
@@ -334,7 +334,7 @@ fn test_bytebuffer_reserve_total() {
     buf.reserve_total(10);
     assert!(buf.capacity() >= 10);
     for _ in 0..10 {
-        buf.push(1);
+        buf.push(1u8);
     }
     assert_eq!(buf.len(), 10);
     assert!(buf.capacity() >= 10);