Various netlink-proto Encoder impl fixes

netlink-proto/src/codecs.rs

@@ -1,4 +1,4 @@
-use std::{fmt::Debug, io, marker::PhantomData, slice};
+use std::{fmt::Debug, io, marker::PhantomData};
 
 use bytes::{BufMut, BytesMut};
 use netlink_packet_core::{
@@ -147,43 +147,25 @@ where
 
     fn encode(&mut self, msg: NetlinkMessage<T>, buf: &mut BytesMut) -> Result<(), Self::Error> {
         let msg_len = msg.buffer_len();
-        // FIXME: we should have a max length for the buffer
-        while buf.remaining_mut() < msg_len {
-            let new_len = buf.len() + 2048;
-            buf.resize(new_len, 0);
-        }
-        let size = msg.buffer_len();
-        if buf.remaining_mut() < size {
+        if buf.remaining_mut() < msg_len {
+            // BytesMut can expand till usize::MAX... unlikely to hit this one.
             return Err(io::Error::new(
                 io::ErrorKind::Other,
                 format!(
                     "message is {} bytes, but only {} bytes left in the buffer",
-                    size,
+                    msg_len,
                     buf.remaining_mut()
                 ),
             ));
         }
 
-        // Safety: we initialize the buffer we're passing to
-        // NetlinkMessage::serialize(). In theory, `serialize()`
-        // should be safe because it's not supposed to _read_ from
-        // the buffer, which is potentially
-        // un-initialized. However, since we delegate the actual
-        // implementation to users, we cannot guarantee
-        // anything. Therefore we have to initialize the buffer
-        // here.
-        let bytes = &mut buf.chunk_mut()[..size];
-        for i in 0..bytes.len() {
-            bytes.write_byte(i, 0);
-        }
-
-        unsafe {
-            let initialized_bytes = slice::from_raw_parts_mut(bytes.as_mut_ptr(), bytes.len());
-
-            msg.serialize(initialized_bytes);
-            trace!(">>> {:?}", msg);
-            buf.advance_mut(size);
-        }
+        // As NetlinkMessage::serialize needs an initialized buffer anyway
+        // no need for any `unsafe` magic.
+        let old_len = buf.len();
+        let new_len = old_len + msg_len;
+        buf.resize(new_len, 0);
+        msg.serialize(&mut buf[old_len..][..msg_len]);
+        trace!(">>> {:?}", msg);
         Ok(())
     }
 }